SmartGauge v. Mastershunt

[metanoia]

Well all know now what he means just like we did about 6 posts ago. cant we let it go now or is the plan to jar every one off so the dont post

Agreed. Greenie!

[smileypete]

Some good data there Nick, well done!

 

ISTR Gibbo mentioned very heavy current discharges would materially affect the accuracy of the Smartguage reading.

 

Also I noticed the SG charge return characteristic looks rather linear which is interesting... (and I suspect the large alternator means that absorption voltage is reached quite early on in the below chart.)

 

Edited January 27, 2016 by smileypete

[WotEver]

Curses. Lord knows how I will insert the missing posts, though.

 

N

May I suggest re-merging? Or does that throw out the post order?

 

Tony

[ditchcrawler]

Correcting is one thing, going on about it for the next half a dozen posts is something else. It doesnt need rubbing in.

[WotEver]

... surely the database will sort the posts by their creation date automatically (said he not really knowing what he is talking about!)

When I used to sort out threads on AOL in the dim and distant past it was a nightmare involving dummy threads where you could cut-n-paste, then at the end of it making it live and having 20 members all shouting at you for doing it wrong.

 

By contrast, hiding posts was easy-peasy.

 

Tony

[nicknorman]

Correcting is one thing, going on about it for the next half a dozen posts is something else. It doesnt need rubbing in.

It doesn't need rubbing but it may need reinforcing if the poster repeats the mistake. Of course he may be repeating it out of a sense of pride at getting it wrong, but that is a shame. Modern society is becoming increasingly ignorant of science - I just watched Pointless and when a young chap was asked to name an element starting with any of T A B L or E (which gives plenty of choice) he came up with bronze. I don't want to support a society that is that stupid about science!

[WotEver]

I just watched Pointless and when a young chap was asked to name an element starting with any of T A B L or E (which gives plenty of choice) he came up with bronze!

http://www.youtube.com/watch?v=GFIvXVMbII0

Edited January 27, 2016 by WotEver

[Theo]

I have hidden a couple of off topic posts.

 

Please desist from sniping.

 

Theo

 

I just watched Pointless and when a young chap was asked to name an element starting with any of T A B L or E (which gives plenty of choice) he came up with bronze!

That's off topic too but I won't hide it becasue its rather sweet. Bless!

 

(And it's not sniping.)

 

Nick

[Graham.m]

nicknorman, on 24 Jan 2016 - 8:33 PM, said:

I'm doing a monitored comparison discharge between the Smartgauge and the Mastershunt tonight, and was going to post the results on my "smartgauge accuracy" thread but I though I would add a bit about the Mastershunt since it seems to be a relatively rare beast, and this thread about battery monitoring seemed the more relevant one, so I'm going to put it all here.

We started today with around 85% Soc, cruised for a good few hours and tied up with both the Smartgauge (SG) and the Mastershunt (MS) showing 100%. The tail current for our 450AH bank of T105s was 3.7A = 0.8% of capacity at 14.8v, battery temperature 21C.

The batteries are 2 years old and the MS tells me that the total charge taken out is the equivalent of 40 full cycles down to 0%SoC ie 40*450 = 18kAH. As far as I can tell they have the original capacity, in fact better than original since they need 50-100 partial cycles to fully "bed in".

The MS tells me that the average discharge is 121AH ie down to 73% SoC. That would imply around 149 partial cycles (ie 149 days out of the marina) which is probably about right.

Charge Efficiency Factor (ie proportion of charge put in, that can be taken out again, or if you like the reciprocal of the extra charge needed to be put in to replace charge taken out) is calculated by the MS and currently showing 95%

The Smartgauge is configured thus:

Battery type: 1

That's it.

The Mastershunt is configured thus:

Battery capacity: 450AH
Battery type: Wet
Nominal voltage: 12
Amps = full: 1.5% (ie the tail current when the counter will reset to 100%)
Float voltage: 13.24v (voltage must be above this for the counter to reset to 100%)
Absoption voltage: 14.4v (not sure what this is for)

The mastershunt is a shunt + 500A fuse that does all the stuff mentioned above but doesn't have a display. You can connect it to a PC (inconvenient) or a Masterview Easy (ME) touchscreen display, which is what I have, by means of the Masterbus data network. Data is sent from the MS to the ME in digital form, ie all the processing is done in the MS itself. The ME is "plug and play" with other Mastervolt products including our Mastervolt Combi 12/2500-100. When you plug the Combi and the MS into the ME they are both detected and the display looks like this:

Masterview devices.jpg

You can press on any of the 3 items to configure them to your heart's content, eg changing the Combi's charge voltage and max current to whatever you like. You can also see all the parameters output by the devices, eg SoC from the MS and loads more. The MV has a "favourites" page which you can configure, taking data from any connected devices and merging it onto one page. Max 6 items.

Mine is set up like this:

Masterview Favourites.jpg

Top row, SoC, Battery voltage from the MS
Middle row, Current flowing into or out of the Battery, Battery temperature from the MS
Bottom row, current going into or out of the Combi, Inverter output (or throughput) current (ie at 230v)

Later (tomorrow) I'll post the results of the comparison discharge between MS and SG.

Oh and just to mention, I need to put my glasses on to read the ME. I don't need to put my glasses on to read the SG.

 

 

nicknorman, on 25 Jan 2016 - 7:22 PM, said:

So of course one is then stuck with the figures at the end of the discharge, to start the charge process. The Smartgauge was clearly significantly under-reading the SoC at this point. On this graph, note that the current axis is on the right ie it started at around 165A before rapidly falling off.

 

I couldn't quite decide whether to continue the charge until fully charged or not. If I had have done so, I think you can see by the shape of the graphs that the two figures were converging but since the starting point for the SG was bad this didn't seem particularly useful. I therefore decided to terminate the charge prematurely in order to demonstrate one of the SGs major advantages which is that when it does go wrong, it self corrects without any user intervention. More of that in the next post.

 

Recharge.JPG

 

I think one of the things this exercise has demonstrated to me is just how complex battery chemistry is. It is easy to think of a simple model but the reality is complicated. For example, when I started to recharge the current was 165A, rapidly fell off to 125A, but then for some strange reason increased back to 130A. What is going on!

 

 

nicknorman, on 25 Jan 2016 - 7:32 PM, said:

 

What was interesting was the jump the SG took when I bunged on 200A of discharge current for the 2kw kettle and then 100A for the toaster, much more than the drop in the MS, and this was where it went from over-estimate to under-estimate.

 

If you note the point about the final rested voltage, I think it shows that the MS was pretty correct, the SG was under-estimating.

 

 

 

nicknorman, on 25 Jan 2016 - 7:37 PM, said:

Well when the charging finished I had 84 on SG and 93 on MS. Just over 2 hrs later I now have 84 on the SG and 85 on the MS. So it is doing exactly what Gibbo said, it is holding its reading on discharge until the actual SoC passes the indicated SoC when it will become synchronised and track down - hopefully! I'll wait a bit longer and then do another graph.

 

nicknorman, on 25 Jan 2016 - 10:31 PM, said:

Well its all getting a bit weird now. I stopped charging at 90% on the MS and 84% on the SG. 4 hours later the MS is on 77% and accordingly I have taken out 13AH. The SG, however, is still on 84%. Which one is right?

I switched everything off (missed the news on telly!) and quickly the voltage recovered to 12.65 on the Smartgauge, on my DVM and on the Combi's voltage measurement. To 12.56 according to the Mastershunt.

So according to the Voc from the MS and Trojan's table of voltage vs SoC, the SoC is 83%. According to the other devices the SoC is 94%.

And yet I've taken out 13% capacity (aka 58AH).

As I said, what is going on? Anyway at the moment I believe the SG more than I believe the MS - which has obviously suffered from a cycle without reaching 100%.

 

So, which reading is correct?

 

Were any of the readings by a calibrated valid certified device? I suspect not.

 

If not any or all of them could incorrect. The Smartgauge only reads 3 ½ digits so 12.65V could easily be 12.6V or 12.7V. As for the Mastershunt, Voltage accuracy ± 0.6 % ± 1 digit and State of charge accuracy: ± 1% whereas the Smartgauge State of Charge is ± 5%, Voltage Accuracy ± 0.5%

 

So looking at the voltages taking into account accuracy: Which are being put forward as rested battery open circuit voltages after a relatively short rest. The battery industry recommendation being 24 hours. The longer the rested the higher the voltage.

 

The smartgauge voltage assuming a correctly calibrated box could be 12.71V

The Mastershunt assuming a correctly calibrated box could easily be 12.63V

A difference of 0.08V

 

Looking at State of Charge taking into account accuracy:

Smartgauge SoC could be 79.8% but it has not changed since the end of the charge, possibly, it has not re-synced

Mastershunt SoC could be 78%

 

A difference of 1.8%

 

Interestingly the Mastershunt at the end of the charge showed 93% (was this the value at the same time that the smartgauge showed 84% immediately or as the charging was stopped) and at this point 4 hours later, the Mastershunt showed 77%, which is 16%, used and the Smartgauge 84% nil used. Ahs used is declared as being 13Ah, (I am assuming this is a reading from the Mastershunt and not a calculated figure) as a percentage of the declared available battery capacity 90% (at end of charge) of 450Ahs, 13Ahs is (13Ahs/405Ah =) 3.11%. Now is the Mastergauge incorrectly set or is the battery capacity less than originally declared, say down at well that would be 100Ahs.

 

If we use a later figure give for Ahs used, 58Ahs how does that affect the figures. Mastershunt at the end of the charge showed 93% (was this the value at the same time that the smartgauge showed 84% immediately or as the charging was stopped) and at this point 4 hours later, the Mastershunt showed 77%, which is 16%, used and the Smartgauge 84%, nil used. Ahs used is declared as being 58Ah. As a percentage of the declared available battery capacity 93% (at end of charge) of 450Ahs, 58Ahs is (58Ahs/418.2Ah =) 13.86%. Now that would make the Mastershunt to be within 2.14% of the expected reading. Is the battery capacity less than originally declared, say down at 418.47Ahs.

 

Basically this tells us that either of the boxes could be right and does not show either box to be correct or incorrect, the differences are too close to decide. If the charge level had been taken back to the starting level i.e. to “The tail current for our 450AH bank of T105s was 3.7A = 0.8% of capacity at 14.8v” or the battery SoC been check by the Hydrometer that the owner has; we might have got something out of this information. Instead of something where apparently the tests were biased towards the smartgauge.

 

nicknorman, on 26 Jan 2016 - 12:02 AM, said:

HIGNFY was a repeat!

Anyway by 23:30 the SG was on 81%, the MS on 72%. Switching everything off for 5 mins gave 12.55v on the DVM, 12.57 on the Combi, 12.58 or so on the SG, 12.47 on the MS. Even taking the lowest of these gives an SoC of 77%, taking a mean of the values gives over 80% and either of these puts the SG nearer than the MS. The latter is clearly going out of sync after just one cycle of failing to reach 100%.

So in some ways this has become a victory for the SG since its errors are not cumulative. It may bounce around the correct SoC a bit but it never departs too far unlike the MS whose errors are boundless given enough cycles.

But then again what is SoC? From the results tonight I am more convinced than ever that it is very hard to define or measure by any means.

Graph of post-charging SoC showing the SG biding its time until the actual SoC passes the indicated SoC.

Discharge2.JPG

 

Now what does this tell us

 

I note that this time there are no Ahs used readings.

 

The voltages were taken after 5 minutes resting and I would suggest are inaccurate because the battery is still settling and tell us nothing. Again, which of the instruments were calibrated and certified?

What were the State of Charge readings when the voltages were taken?

 

The Smartgauge has an accuracy of +/-5% and that means that the 81% read could be 76.95% and is still re-syncing.

The Mastergauge has an accuracy of +/-1% and that means the 72% reading could be 72.72%

 

Voltage wise the Mastergauge could be 12.395V or 12.54V

Voltage wise the Smartgauge is only readable to 3½ digits so 12.58V must be a guess as it flicks up and down, it was either 12.55 or 12.6V could be 12.49V or 12.66V

 

Whichever way you look at it the voltage readings are both within spec

 

Which is right I do not know, the voltage readings because of the shortness of the resting period tell us little or nothing. I do think these two gauges are very close.

 

I think readings done the next morning when the smartgauge had had a chance to fully re-sync together with specific gravity readings from the batteries would have shown results that were a lot more accurate and interesting.

 

Taking the same voltage reading with four different readings with four different meters does not mean that any of the readings is correct. Just that you have four different meters that read the voltage differently.

 

Think someone quoted a Chinese Proverb something like, “the more meters the more confusion”, and that is so true.

[ditchcrawler]

 

Think someone quoted a Chinese Proverb something like, “the more meters the more confusion”, and that is so true.

 

Me, man with watch knows the time, man with two watches never knows the time.

[nicknorman]

Now what does this tell us

 

I note that this time there are no Ahs used readings.

 

There is no need to quote AHs used when I have given the MS % SoC and the battery capacity set into it. Thus 75% SoC would be 112.5AH taken out etc.

 

The voltages were taken after 5 minutes resting and I would suggest are inaccurate because the battery is still settling and tell us nothing.

5 minutes is a short resting time but we can consider that the reading will be no higher than would have been had the batteries been left for say 1 hr or more, and probably a bit lower (but perhaps not very much, it will depend on the load history up to that point)

 

Again, which of the instruments were calibrated and certified? I suspect they were all calibrated at manufacture, none of them were "certified". However I am not attempting to suggest that this is a rigorous scientific test.

 

What were the State of Charge readings when the voltages were taken? I'm not clear which part of the test you are referring to.

 

The Smartgauge has an accuracy of +/-5% and that means that the 81% read could be 76.95% and is still re-syncing.

The Mastergauge has an accuracy of +/-1% and that means the 72% reading could be 72.72%

 

It's interesting that MS quotes an accuracy for the SoC. And foolish because what it really means is that the current measuring is within 1%. The 1% current accuracy is then integrated into charge and the error of that parameter must empirically be limitless since integration errors increase with time. Even considering a short time, in order for it to claim 1% accuracy in SoC the actual battery capacity must be known, which in reality it is often not. Then there is the CEF which for the MS is a single parameter calculated after reaching an indication of 100% but in reality is a variable amount according to SoC, charging voltage etc. The device cannot map the CEF throughout the charging process and thus intermediate SoC errors due to the CEF approximation is inevitable

 

Therefore as I said, rather foolish of Mastervolt to quote that but I'll leave you to sue them. On the other hand, as we are discovering, it is hard to prove anything to do with SoCs so it would be an uphill struggle to prove in a court that the device wasn't accurate to 1% SoC!

 

Voltage wise the Mastergauge could be 12.395V or 12.54V

Voltage wise the Smartgauge is only readable to 3½ digits so 12.58V must be a guess as it flicks up and down, it was either 12.55 or 12.6V could be 12.49V or 12.66V

 

The Smartgauge "dithers" between readings so for example if the voltage is actually 12.575 it will spend equal time indicating 12.55 and 12.6. The 12.58 was because it was spending slightly more time showing 12.6 than 12.55

 

Whichever way you look at it the voltage readings are both within spec

 

Which is right I do not know, the voltage readings because of the shortness of the resting period tell us little or nothing. I do think these two gauges are very close.

 

I think readings done the next morning when the smartgauge had had a chance to fully re-sync together with specific gravity readings from the batteries would have shown results that were a lot more accurate and interesting.

 

Taking the same voltage reading with four different readings with four different meters does not mean that any of the readings is correct. Just that you have four different meters that read the voltage differently.

 

This is true, I tend to take a majority vote but that is not really very scientific. Especially considering I recalibrated the Smartgauge to match my DVM. So it is not too surprising that they agree!

 

Think someone quoted a Chinese Proverb something like, “the more meters the more confusion”, and that is so true.

 

For me the point was that after a partial cycle the MS was quite a way out, the SG was a little out but it depends on what you consider 100% SoC to be. I appreciate that current was continuing to flow in but my strong feeling is that the MS could not possibly have reached 100% by the time the tail current dropped. 6% would be 27AH and no way was that going to get in. Thus the MS would have jumped from say 95 or 96% straight to 100%, meaning that when it was indicating say 95% it should have been indicating 99%. And that was just after one partial cycle and one (soon to be) full recharge.

 

The key point is that the error in the Smartgauge we saw was the full extent of the error since all the time it is discharging, it has something to go on. It is not in "dead reckoning".

 

Whereas the MS is in dead reckoning, and thus accumulating errors, the whole time that it is not at 100% SoC and with repeated partial cycles this error is going to steadily increase. And that is before we contemplate long term loss of capacity as the batteries age.

 

I intend to log a full charge next time on the boat (using Masteradjust's logging feature) and it will be interesting to see if I can match an equation-generated curve to the charging curve. If so, and by integrating the equation, we will be able to see just how much AH can be put back between say a tail current of 3% and 1%. Of course it will tend to be an over-estimate since some charge is lost to gassing especially right at the end of the charging process.

[Graham.m]

 

For me the point was that after a partial cycle the MS was quite a way out, the SG was a little out but it depends on what you consider 100% SoC to be. I appreciate that current was continuing to flow in but my strong feeling is that the MS could not possibly have reached 100% by the time the tail current dropped. 6% would be 27AH and no way was that going to get in. Thus the MS would have jumped from say 95 or 96% straight to 100%, meaning that when it was indicating say 95% it should have been indicating 99%. And that was just after one partial cycle and one (soon to be) full recharge.

 

The key point is that the error in the Smartgauge we saw was the full extent of the error since all the time it is discharging, it has something to go on. It is not in "dead reckoning".

 

Whereas the MS is in dead reckoning, and thus accumulating errors, the whole time that it is not at 100% SoC and with repeated partial cycles this error is going to steadily increase. And that is before we contemplate long term loss of capacity as the batteries age.

 

I intend to log a full charge next time on the boat (using Masteradjust's logging feature) and it will be interesting to see if I can match an equation-generated curve to the charging curve. If so, and by integrating the equation, we will be able to see just how much AH can be put back between say a tail current of 3% and 1%. Of course it will tend to be an over-estimate since some charge is lost to gassing especially right at the end of the charging process.

 

 

“There is no need to quote AHs used when I have given the MS % SoC and the battery capacity set into it. Thus 75% SoC would be 112.5AH taken out etc.” Sorry that is a load of rot. You are arguing that the Mastershunt’s SoC is inaccurate. Thus, you cannot just quote its SoC and do a simple conversion to Ahs using two unknowns, i.e. the capacities of the batteries used twice and the SoC of the Mastershunt. At least quoting the Ahs used does away with an unknown, unmeasured battery capacity.

 

“5 minutes is a short resting time but we can consider that the reading will be no higher than would have been had the batteries been left for say 1 hr or more, and probably a bit lower (but perhaps not very much, it will depend on the load history up to that point).” That is interesting it does make me wonder why the battery industry knows less than you do and why arising from years of professionally making batteries and testing them do they stupidly come up with the 24 hour resting period. Sorry that is nonsense.

 

“I suspect they were all calibrated at manufacture, none of them were "certified". However I am not attempting to suggest that this is a rigorous scientific test.” I am sorry you are trying to sell the idea that the Smartgauge is better than the Mastershunt. Therefore, the test must be rigorous, accurate, and not inaccurately done.

 

Therefore, you calibrated the Smartgauge to an unknown voltage, and thus the tracking of the smartgauge to your DVM etc is not surprising. Therefore, I would suggest that the accuracy of your Smartgauge is totally unknown. Bearing in mind that the smartgauge relies totally on being able to accurately measure the voltage for its algorithms to be able to accurately calculate its values, if it is not correctly calibrated its readings mean nothing. I wonder why you did that, was it another smartgauge that came out of the factory incorrectly calibrated.

 

I think the manufacturer will tell you that the basic set-up of its voltage calibration is very important to its overall accuracy.

 

Therefore, I am afraid that until your smartgauge is recalibrated, using a voltage source that is accurate to better that 0.0005V, any comparison that you do will be irrelevant. It would also explain the difference between the Mastershunt and the Smartgauge.

 

I would also suggest you need to get yourself a properly certified calibrated DVM accurate to better than 0.005V over the voltage range used for the tests and if you are going to continue doing this sort of test and publishing the results keep its calibration valid.

 

“For me the point was that after a partial cycle the MS was quite a way out, the SG was a little out…” You do not know this, as the Smartgauge is not correctly calibrated. It has a mythical calibration you gave it using an un-calibrated uncertified meter as the reference.

 

"The key point is that the error in the Smartgauge we saw was the full extent of the error since all the time it is discharging, it has something to go on." Sorry that is not correct if its voltage calibration is not correctly calibrated, it is a total unknown.

 

In my opinion you have been playing at pseudo-science to prove what you want others to believe which I find a great shame.

[mickp]

Another interesting thread spoiled

[nicknorman]

 

 

“There is no need to quote AHs used when I have given the MS % SoC and the battery capacity set into it. Thus 75% SoC would be 112.5AH taken out etc.” Sorry that is a load of rot. You are arguing that the Mastershunt’s SoC is inaccurate. Thus, you cannot just quote its SoC and do a simple conversion to Ahs using two unknowns, i.e. the capacities of the batteries used twice and the SoC of the Mastershunt. At least quoting the Ahs used does away with an unknown, unmeasured battery capacity.

 

It is hard to have a serious debate with someone who clearly doesn't understand how an AH-counting gauge works. Let me try to explain. The gauge measures current and time, it integrates the current with respect to time to get charge (AH). The number of AH flowing in or out is then used to modify the SoC value based on the battery's capacity entered into the system by the user. During charge, the CEF is also taken into account. But anyway that means that during discharge, since AH is used to calculate SoC, it follows that there is a direct correlation between SoC and AH. They are effectively one and the same thing, just factored by the entered capacity. In the case of my bank of 450AH, starting from 100% SoC, and therefore zero AH taken out, if 112.5AH is taken out it WILL be the case that the SoC reads 75%, and similarly if the SoC reads 75% it WILL be the case that the gauge will show that 112.5AH has been taken out. Anything else is not possible. Of course both the AH taken out, and therefore the SoC, are subject to the measurement error which is then compounded by the integrating.

 

So please take some time to work out for yourself how an AH counting gauge works before describing my factual post as " a load of rot".

 

 

 

“5 minutes is a short resting time but we can consider that the reading will be no higher than would have been had the batteries been left for say 1 hr or more, and probably a bit lower (but perhaps not very much, it will depend on the load history up to that point).” That is interesting it does make me wonder why the battery industry knows less than you do and why arising from years of professionally making batteries and testing them do they stupidly come up with the 24 hour resting period. Sorry that is nonsense.

 

It is not nonsense. Saying something is "nonsense" without providing an explanation as to why, is plain rude and also demonstrates that you don't actually have a counter argument. For your information a discharging battery has a somewhat depressed voltage. When the load is taken off, the voltage gradually rises following some sort of asymptotic curve. ie it rises more quickly in the first few minutes than it does in the same number of minutes after a few hours resting. The shape of this curve and the time to get very close to the rested voltage will depend on the discharge history. For example if I take a battery and discharge it at 1A for a 1 second, it will reach its rested voltage (within reasonable measurement resolution) very quickly. If I take the same battery and discharge at 200A for an hour, it will take much longer to reach the rested voltage. However the voltage trend is always upwards after the discharge is stopped and so if the voltage is measured prematurely, say after 5 minutes, it can be certain that this voltage is no higher than the final one. In other words we can say that "the final rested voltage is at least x" where x the value measured after 5 minutes. This is what I said so kindly don't refer to it as "nonsense" because in fact it is perfectly correct.

 

“I suspect they were all calibrated at manufacture, none of them were "certified". However I am not attempting to suggest that this is a rigorous scientific test.” I am sorry you are trying to sell the idea that the Smartgauge is better than the Mastershunt. Therefore, the test must be rigorous, accurate, and not inaccurately done.

 

I am not trying to sell anything, I was merely running a discharge whilst comparing readings from 2 different types of gauge each with their own different types of error. If you want a rigorous test, why not do it yourself?

 

Therefore, you calibrated the Smartgauge to an unknown voltage, and thus the tracking of the smartgauge to your DVM etc is not surprising. Therefore, I would suggest that the accuracy of your Smartgauge is totally unknown. Bearing in mind that the smartgauge relies totally on being able to accurately measure the voltage for its algorithms to be able to accurately calculate its values, if it is not correctly calibrated its readings mean nothing. I wonder why you did that, was it another smartgauge that came out of the factory incorrectly calibrated.

 

My smartgauge was on the edge of the calibration limit. I decided to recalibrate it. With hindsight I think I might have overdone it a little the other way, but not much. It is still within the manufacturer's spec of +-0.05v. However this point is largely irrelevant as the gauge performed pretty well except when I discharged the batteries below the normal level and thus took it into a range it was not accustomed to. But of course it soon automatically recovered, as smartgauges do.

 

I think the manufacturer will tell you that the basic set-up of its voltage calibration is very important to its overall accuracy. No, it just has to be with +-0.05v which is not that precise.

 

Therefore, I am afraid that until your smartgauge is recalibrated, using a voltage source that is accurate to better that 0.0005V, any comparison that you do will be irrelevant. It would also explain the difference between the Mastershunt and the Smartgauge. You have added an unnecessary two zeros after the decimal point for some reason. There would be no point in checking a gauge that was calibrated to a higher standard than the manufacture intended.

 

There are a number of differences between the SG and the MS caused by their different types of errors. I have covered the SG's error which of course you are focussing on, but let us not lose focus of the MS's error which is that after only 1 partial cycle and when approaching the end of the second charge, it was clearly around 5% out. I know this not by looking at the Smartgauge but by looking at the tail current and contemplating how much more charge could be accumulated before the tail current fell to insignificant values. It is also behaviour that I have frequently noticed before with the MS. Whilst with a normal cycle of discharge and then full charge it usually smoothly rises to 100%, in the case when we moor up and don't fully charge I often notice that it is slow to reach 100% and consequently has to re-sync, suddenly jumping from perhaps 95 or 96%, straight to 100% when it detects the low tail current.

 

Of course this error is not too bad especially for someone who charges to 100% fairly often. My primary gripe about an AH counting gauge is not this type of error, but rather the massive error that can occur when the actual capacity of the batteries is badly out. I think I mentioned that our previous leisure batteries were down to 50% of their rated capacity after 6 months (hard) leisure use.

 

I would also suggest you need to get yourself a properly certified calibrated DVM accurate to better than 0.005V over the voltage range used for the tests and if you are going to continue doing this sort of test and publishing the results keep its calibration valid. You can suggest whatever you like, I will keep publishing whatever I like.

 

“For me the point was that after a partial cycle the MS was quite a way out, the SG was a little out…” You do not know this, as the Smartgauge is not correctly calibrated. It has a mythical calibration you gave it using an un-calibrated uncertified meter as the reference. The point is that neither gauge is a reference, the test, as per the thread title, was to look at the respective gauge readings. However there is a valid point of reference and that was the final tail current. The SG was a little over-reading, the MS was more under-reading. They were both reasonably close but of course the former is not phased by changing actual battery capacity.

 

"The key point is that the error in the Smartgauge we saw was the full extent of the error since all the time it is discharging, it has something to go on." Sorry that is not correct if its voltage calibration is not correctly calibrated, it is a total unknown. You seem to have latched onto this calibration thing and are making irrational comments about it. The calibration is within limits, it may well not be centred on the optimum value, however the difference is minor. The point is that the SG doesn't accumulate error with time, it self corrects during discharge. Whereas the MS does accumulate error with time, all the time that the actual SoC is not 100%. I do wonder if you grasp this fundamental point and understand what integration error is? It does rather seem not.

 

In my opinion you have been playing at pseudo-science to prove what you want others to believe which I find a great shame.

 

You are entitled to your opinion of course. It was not, nor was it intended to be, a rigorous test. It was, as per the thread title, a comparison of readings. But as I said before, please feel free to do your own absolutely rigorous testing. I think I have proven that both gauges have errors but as I keep saying, one bumbles around the truth and never gets too far away, the other has an error that increases with time until the batteries are fully charged. But that error is not too bad, what is bad is that when the actual capacity of the batteries changes (normally for the worse!) the MS doesn't have a clue, whereas the SG takes it in its stride.

[Graham.m]

 

 

 

“There is no need to quote AHs used when I have given the MS % SoC and the battery capacity set into it. Thus 75% SoC would be 112.5AH taken out etc.” Sorry that is a load of rot. You are arguing that the Mastershunt’s SoC is inaccurate. Thus, you cannot just quote its SoC and do a simple conversion to Ahs using two unknowns, i.e. the capacities of the batteries used twice and the SoC of the Mastershunt. At least quoting the Ahs used does away with an unknown, unmeasured battery capacity.

 

It is hard to have a serious debate with someone who clearly doesn't understand how an AH-counting gauge works. Let me try to explain. The gauge measures current and time, it integrates the current with respect to time to get charge (AH). The number of AH flowing in or out is then used to modify the SoC value based on the battery's capacity entered into the system by the user. During charge, the CEF is also taken into account. But anyway that means that during discharge, since AH is used to calculate SoC, it follows that there is a direct correlation between SoC and AH. They are effectively one and the same thing, just factored by the entered capacity. In the case of my bank of 450AH, starting from 100% SoC, and therefore zero AH taken out, if 112.5AH is taken out it WILL be the case that the SoC reads 75%, and similarly if the SoC reads 75% it WILL be the case that the gauge will show that 112.5AH has been taken out. Anything else is not possible. Of course both the AH taken out, and therefore the SoC, are subject to the measurement error which is then compounded by the integrating.

 

So please take some time to work out for yourself how an AH counting gauge works before describing my factual post as " a load of rot".

 

 

 

“5 minutes is a short resting time but we can consider that the reading will be no higher than would have been had the batteries been left for say 1 hr or more, and probably a bit lower (but perhaps not very much, it will depend on the load history up to that point).” That is interesting it does make me wonder why the battery industry knows less than you do and why arising from years of professionally making batteries and testing them do they stupidly come up with the 24 hour resting period. Sorry that is nonsense.

 

It is not nonsense. Saying something is "nonsense" without providing an explanation as to why, is plain rude and also demonstrates that you don't actually have a counter argument. For your information a discharging battery has a somewhat depressed voltage. When the load is taken off, the voltage gradually rises following some sort of asymptotic curve. ie it rises more quickly in the first few minutes than it does in the same number of minutes after a few hours resting. The shape of this curve and the time to get very close to the rested voltage will depend on the discharge history. For example if I take a battery and discharge it at 1A for a 1 second, it will reach its rested voltage (within reasonable measurement resolution) very quickly. If I take the same battery and discharge at 200A for an hour, it will take much longer to reach the rested voltage. However the voltage trend is always upwards after the discharge is stopped and so if the voltage is measured prematurely, say after 5 minutes, it can be certain that this voltage is no higher than the final one. In other words we can say that "the final rested voltage is at least x" where x the value measured after 5 minutes. This is what I said so kindly don't refer to it as "nonsense" because in fact it is perfectly correct.

 

“I suspect they were all calibrated at manufacture, none of them were "certified". However I am not attempting to suggest that this is a rigorous scientific test.” I am sorry you are trying to sell the idea that the Smartgauge is better than the Mastershunt. Therefore, the test must be rigorous, accurate, and not inaccurately done.

 

I am not trying to sell anything, I was merely running a discharge whilst comparing readings from 2 different types of gauge each with their own different types of error. If you want a rigorous test, why not do it yourself?

 

Therefore, you calibrated the Smartgauge to an unknown voltage, and thus the tracking of the smartgauge to your DVM etc is not surprising. Therefore, I would suggest that the accuracy of your Smartgauge is totally unknown. Bearing in mind that the smartgauge relies totally on being able to accurately measure the voltage for its algorithms to be able to accurately calculate its values, if it is not correctly calibrated its readings mean nothing. I wonder why you did that, was it another smartgauge that came out of the factory incorrectly calibrated.

 

My smartgauge was on the edge of the calibration limit. I decided to recalibrate it. With hindsight I think I might have overdone it a little the other way, but not much. It is still within the manufacturer's spec of +-0.05v. However this point is largely irrelevant as the gauge performed pretty well except when I discharged the batteries below the normal level and thus took it into a range it was not accustomed to. But of course it soon automatically recovered, as smartgauges do.

 

I think the manufacturer will tell you that the basic set-up of its voltage calibration is very important to its overall accuracy. No, it just has to be with +-0.05v which is not that precise.

 

Therefore, I am afraid that until your smartgauge is recalibrated, using a voltage source that is accurate to better that 0.0005V, any comparison that you do will be irrelevant. It would also explain the difference between the Mastershunt and the Smartgauge. You have added an unnecessary two zeros after the decimal point for some reason. There would be no point in checking a gauge that was calibrated to a higher standard than the manufacture intended.

 

There are a number of differences between the SG and the MS caused by their different types of errors. I have covered the SG's error which of course you are focussing on, but let us not lose focus of the MS's error which is that after only 1 partial cycle and when approaching the end of the second charge, it was clearly around 5% out. I know this not by looking at the Smartgauge but by looking at the tail current and contemplating how much more charge could be accumulated before the tail current fell to insignificant values. It is also behaviour that I have frequently noticed before with the MS. Whilst with a normal cycle of discharge and then full charge it usually smoothly rises to 100%, in the case when we moor up and don't fully charge I often notice that it is slow to reach 100% and consequently has to re-sync, suddenly jumping from perhaps 95 or 96%, straight to 100% when it detects the low tail current.

 

Of course this error is not too bad especially for someone who charges to 100% fairly often. My primary gripe about an AH counting gauge is not this type of error, but rather the massive error that can occur when the actual capacity of the batteries is badly out. I think I mentioned that our previous leisure batteries were down to 50% of their rated capacity after 6 months (hard) leisure use.

 

I would also suggest you need to get yourself a properly certified calibrated DVM accurate to better than 0.005V over the voltage range used for the tests and if you are going to continue doing this sort of test and publishing the results keep its calibration valid. You can suggest whatever you like, I will keep publishing whatever I like.

 

“For me the point was that after a partial cycle the MS was quite a way out, the SG was a little out…” You do not know this, as the Smartgauge is not correctly calibrated. It has a mythical calibration you gave it using an un-calibrated uncertified meter as the reference. The point is that neither gauge is a reference, the test, as per the thread title, was to look at the respective gauge readings. However there is a valid point of reference and that was the final tail current. The SG was a little over-reading, the MS was more under-reading. They were both reasonably close but of course the former is not phased by changing actual battery capacity.

 

"The key point is that the error in the Smartgauge we saw was the full extent of the error since all the time it is discharging, it has something to go on." Sorry that is not correct if its voltage calibration is not correctly calibrated, it is a total unknown. You seem to have latched onto this calibration thing and are making irrational comments about it. The calibration is within limits, it may well not be centred on the optimum value, however the difference is minor. The point is that the SG doesn't accumulate error with time, it self corrects during discharge. Whereas the MS does accumulate error with time, all the time that the actual SoC is not 100%. I do wonder if you grasp this fundamental point and understand what integration error is? It does rather seem not.

 

In my opinion you have been playing at pseudo-science to prove what you want others to believe which I find a great shame.

 

You are entitled to your opinion of course. It was not, nor was it intended to be, a rigorous test. It was, as per the thread title, a comparison of readings. But as I said before, please feel free to do your own absolutely rigorous testing. I think I have proven that both gauges have errors but as I keep saying, one bumbles around the truth and never gets too far away, the other has an error that increases with time until the batteries are fully charged. But that error is not too bad, what is bad is that when the actual capacity of the batteries changes (normally for the worse!) the MS doesn't have a clue, whereas the SG takes it in its stride.

 

Putting it simply you did not know that the smartgauge was out of spec or right on the edge of spec when you got it, your means of checking was not calibrated to the standard needed to check it. Thus by adjusting it using an un-calibrated DVM as the reference you do not know what voltage the smartgauge is set to.

 

 

Your batteries are two years old, you do not know the actual capacity of the batteries, they were nominally 450Ah, and what are they today. Unless you specifically do a discharge test, any figure you give them is a guess. I would hope they are up in the 400s.

 

 

The Mastershunt displays calculated Ahs, and then using the battery capacity you have entered gives a SoC. Now as the battery capacity is not really known, and is it only a guessed battery capacity given by you to the Mastershunt, the Mastershunt is only working on guessed capacity that you gave it. Hence, the more accurate of the two figures is Ahs.

 

 

The voltage spec for the smartgauge is 0.5% of the reading. Thus at 12.7V the error can be +/-0.0635V. If the smartgauge were as self-correcting as you seem to believe it would not matter what the voltage it was set at. However, as we are both aware it is important that it is set so the voltage reading is within 0.5% of the reading otherwise it reads inaccurately.

 

 

BTW, if you check a gauge that is supposed to have an accuracy of 0.5% against a voltage source that only has the same accuracy of 0.5% you cannot tweak the gauge into the centre of its band. If the source has an accuracy of 0.005% then the source more accurate than the gauge and you can tweak the gauge to the centre of its accuracy band. I get the impression that you have not done much calibration adjusting.

 

 

As for having a debate I am not having a debate, because the inaccuracies in the instrumentation you are using there is nothing to debate, the inaccuracies make the readings unreliable. You have my opinion

[WotEver]

Another interesting thread spoiled

 

You're not on your own, with generating a huge sigh reading all this again.

 

Tony

[Tony Brooks]

As far as I can see Nick has more or less proved that within the limits of his test BOTH gauges were sufficiently accurate to provide good guidance with one slightly better that the other. But the caveat is "within the limits of his test" and one of the limits is that Nick knows what he is doing and regularly gets his batteries to as fully charged as the Ah counter needs them to be to stay more or less accurate. Another limit is that the test was not of a sufficient duration to see how Ah counter types cope with an ever reducing battery capacity and those two limits are exactly those that render Ah counters more libel to major errors.

 

In real world situations I think most of us know which instrument will be more accurate in the hands of the man on the bus.

[WotEver]

In real world situations I think most of us know which instrument will be more accurate in the hands of the man on the bus.

 

Indeed, Tony. Which is what makes the pointless posturing even more fatiguing.

[nicknorman]

 

As for having a debate I am not having a debate ... You have my opinion

 

 

Jolly good, saves me a lot of typing having to refute your misconceptions.

Edited February 5, 2016 by nicknorman

[George94]

I have to say I sometimes lose the will to live when reading all this, and I may have missed something important - to whit - has Merlin yet tested the allegedly faulty Smartgauge? And if so, what were the findings?

[nicknorman]

I have to say I sometimes lose the will to live when reading all this, and I may have missed something important - to whit - has Merlin yet tested the allegedly faulty Smartgauge? And if so, what were the findings?

 

Only sometimes?

 

Sorry that was a different thread. As far as I know we have had no feedback from Tommy (the owner of said faulty SG) nor any feedback from Merlin so we don't even know if Merlin have received it back. Anyway, I'm sure the findings will be that the gauge was carelessly calibrated and thus significantly out of tolerance. Poor quality control but I guess it happens.

[WotEver]

 

 

... you are trying to sell the idea that the Smartgauge is better than the Mastershunt.

 

For the average lay-person who wants to know when to start charging his batteries it IS better.

 

This simple fact has been pointed out to you numerous times, by a wide range of folk, some of whom use a Smartgauge and some of whom do not. Either accept that fact (you can look up the meaning of 'fact' if you wish) or don't accept it, none of us give a hoot. However we would really love it if you'd stop trying to justify your biased view when everyone here already knows you're wrong.

 

Thank you.

 

Tony

[bottle]

New batteries fitted, they were reading 12.1v on arrival.

 

Smartgauge was not factory reset but it informed that a disconnection had taken place and the SOC was reset to 75% (automatically).

 

BMV set to new batteries capacity. I knew they (batteries) were not capable of that

 

Batteries have now been in one week, difficult to use enough power to get them down below 75% SOC

 

Managed this by running the boat for 24Hrs on the batteries, ( never managed that before) laptops, fridge, freezer, boiling kettle and more.

 

Smartgauge and BMV did not agree at any time until today. Hoorah!!! Well actually they still disagree but only by 1.9% (higher reading on the BMV)

 

What does this suggest... the new batteries were not capable of their maximum capacity (still not) and the Smartgauge has 'learnt'

 

Am I pleased with new batteries, so far so good.

 

Am I pleased with the new BMV, so far so good and it is telling me a lot more about the batteries and my charging or lack of.

 

Am I pleased with the Smartgauge always have been, it does what it says in the manual.

 

It is /was my fault that the last set only lasted 3½ years, lack of charging.

 

For those that do not know,

 

This is a live aboard CCIng with an 'all electric boat', with full size fridge and full size freezer running 24 hrs. (no not continuously, they are thermostatically controlled, just for the pedants )

 

Reason for this post, just to give an insight for the non-technical of us how it is in the real world.

[smileypete]

Am I pleased with the Smartgauge always have been, it does what it says in the manual.

 

It is /was my fault that the last set only lasted 3½ years, lack of charging.

 

....

 

Reason for this post, just to give an insight for the non-technical of us how it is in the real world.

 

So it looks to me that SmG can indeed give a false sense of security?

 

The main determinant of battery life being proper charging, not recharging at some mythical figure?

[WotEver]

The main determinant of battery life being proper charging, not recharging at some mythical figure?

C'mon Pete, you know that it's both. Don't discharge the batteries too far, and recharge them fully (or as full as practical) when they are discharged. The SmartGauge manual explains that very clearly.

 

The SmartGauge is the only reliable tool for the non-technical to achieve the first objective and a cheap Chinese ammeter can achieve the second.

 

Tony