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Battery monitor error?


frahkn

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1 minute ago, Mike the Boilerman said:

 

It's beginning to look as though SoC is a matter of opinion....

 

 

Shirley Soc should be given as a %age not an Ahrs out. Like everyone else SoC is a waste of space and you cant believe any meter that give you a %age. I always just guess my SoC % from the rested voltage (or not so rested) and the Ahrs out.

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1 hour ago, Mike the Boilerman said:

 

But Sir, Sir, most battery SoC charts show 12.7v rested voltage as fully charged....

 

 

 

Quiet correct, disconnect between fingers and brain. Too late to edit now but it should be 12.2 to 12.3

1 hour ago, Mike the Boilerman said:

 

It's beginning to look as though SoC is a matter of opinion....

 

 

As far as rested voltage is you are right. Too much variation between charts and between battery/acid technology to be certain so it can never be 100% accurate.

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5 minutes ago, Tony Brooks said:

Quiet correct, disconnect between fingers and brain. Too late to edit now but it should be 12.2 to 12.3

 

Phew, that's a relief, I was thinking there is something really fundamental I'm failing to understand!!!!!

 

I can edit out my reply if you want to put the right figures into your post....

 

On the other hand, that might just make it a really confusing thread....

 

 

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25 minutes ago, Tony Brooks said:

Thanks Mike - now done. Did not think one can edit so long after posting.

 

Ok, my quotes of the fat finger numbers all edited out now too. 

 

I think the edit window is three hours so prolly just sneaked in the edits at the last possible moment!!

 

 

 

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38 minutes ago, Tony Brooks said:

As far as rested voltage is you are right. Too much variation between charts and between battery/acid technology to be certain so it can never be 100% accurate.

Only way to be 100% accurate is with Relative Density readings, as you’re aware. 1% of capacity as a charge current at 14.4V or above is nearasdammit 100% too. 

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6 hours ago, Dr Bob said:

I am very confused about the facts.

You say it never got below -7Ahr. Did you park up overnight and draw power on the inverter for the night? If so it should have gone below -7Ahr and should have been nearer -100 Ahr.

It sounds like when on shore power you are fully charged. To test the meter I would do the following.

Synchronise the meter to 100%SoC as it sounds like you are full. If you can't do this....chuck it out and buy a Victron BMV.

Disconnect shore power and turn on inverter. Turn on something on the boat to drain the surface charge i.e. the ebersparky for an hour. That will take about 5Ahr if done for an hour. Turn off everything for an hour and then take a voltage reading. It should be around 12.70V. Measure this on the sterling and your multimeter.

Run on the inverter for the night and in the morning turn everything off for an hour and check the voltage and the Ahr meter. If everything is ok then the Ahrs out should show -100Ahr ish (that's what you normally use) and the voltage should show approx the %used (refer to a voltage SoC table). On mine with 660Ahr capacity I would see a voltage of 12.50V with -100Ahr out. Turn shore power on and measure current in against time as it charges to full. That will tell you most of what you need.

This is what I do from time to time but I ignore the 1 hr rest and adjust the voltage up knowing the effect on voltage of a 1.7Ahr draw ...my typical draw with the inverter on with all the gibbons I run, the rasp pi, Alexa, router etc etc. Temperature of batteries does have a effect if you are estimating at rest voltage from a voltage obtained with a current draw.

If you have solar then do the above only when dark as the solar confuses everything.

Thanks for all the help.

 

Sorry for the confusion, I meant that the negative Ah position never returned to nil, in fact it never passed -7, even with 8 hours of charging.

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1 minute ago, Alan de Enfield said:

 

That was my interpretation and I still suggest that there is a calibration fault on the instrument.

 

Everyone has convinced me that it is an instrument fault and a couple of people have suggested that a 17 year old Sterling monitor is not likely to be state of the art.

 

I plan to get a new monitor. Left to my own devices I would get a "smartgauge" but basically I want  just a single item and something easy to fit. Price is not particularly relevant so any advice would be welcome.

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2 minutes ago, frahkn said:

 

Everyone has convinced me that it is an instrument fault and a couple of people have suggested that a 17 year old Sterling monitor is not likely to be state of the art.

 

I plan to get a new monitor. Left to my own devices I would get a "smartgauge" but basically I want  just a single item and something easy to fit. Price is not particularly relevant so any advice would be welcome.

 

I have a BMV on the 'Cat' and happy with it.

 

You could get a BMV 700 or 712

 

https://www.sunshinesolar.co.uk/media/ecom/prodpdf/Datasheet-BMV-712-Smart-EN.pdf

 

- Battery voltage, current, power, ampere-hours consumed and state of charge - Remaining time at the current rate of discharge - Programmable visual and audible alarm - Programmable relay, to turn off non critical loads or to run a generator when needed - 500 Amp quick connect shunt and connection kit - Shunt selection capability up to 10.000 Amps - VE.Direct communication port - Stores a wide range of historical events, which can be used to evaluate usage patterns and battery health - Wide input voltage range: 6,5 – 70V - High current measurement resolution: 10 mA (0,01A) - Additional input to measure voltage (of a second battery), temperature or midpoint voltage, and    corresponding alarm and relay settings 

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1 minute ago, frahkn said:

 

Everyone has convinced me that it is an instrument fault and a couple of people have suggested that a 17 year old Sterling monitor is not likely to be state of the art.

 

I plan to get a new monitor. Left to my own devices I would get a "smartgauge" but basically I want  just a single item and something easy to fit. Price is not particularly relevant so any advice would be welcome.

 

To have the best chance of assessing state of charge an at one tme you need an ammeter to indicate fully charged and a voltmeter for rested voltage. The only meters that provide those in a single instrument are the likes of the BVM and Son of Smartgauge  but I doubt you can afford the later. The Smartguage is fairly good at telling you when you need to start charging (but basically that s every day) or stop using electricity until you can charge. It is less good at giving indication of when fully charged. For a simple instrument that is simple to install the Smartguage is arguably the best there is but the BVM type is likely to be more accurate apart from % charged scales. I got by very well with just an ammeter and voltmeter.

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29 minutes ago, frahkn said:

I plan to get a new monitor.

Save your money. With the batteries fully charged, disconnect the monitor for a while then reconnect it. Hopefully it now shows zero. Now it will reasonably accurately show you how much you pull out of the batteries between charges. Then charge until the current is back down to a few amps at 14.4V and, regardless of what the monitor shows, they’re fully charged. 
 

You can’t go to the pub so open a bottle at your leisure, relax and stop worrying :)

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2 hours ago, frahkn said:

 

Everyone has convinced me that it is an instrument fault and a couple of people have suggested that a 17 year old Sterling monitor is not likely to be state of the art.

 

I plan to get a new monitor. Left to my own devices I would get a "smartgauge" but basically I want  just a single item and something easy to fit. Price is not particularly relevant so any advice would be welcome.

Smartgauge has a good sales pitch, but using it could kill your batteries in short order. When it reaches 100% whilst charging, you would think your batteries would definitely be full. This may be the case, but almost certainly isn’t.

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53 minutes ago, Richard10002 said:

Smartgauge has a good sales pitch, but using it could kill your batteries in short order. When it reaches 100% whilst charging, you would think your batteries would definitely be full. This may be the case, but almost certainly isn’t.

 

But the Smartgauge manual tells you that the reading on charge isnt accurate, so it should only be used to determine  when to start charging (or stop discharging).

 

Once you get used to your boats charging idiosyncrasies you can stop charging ssy 3 hours after the Smartgauge says 100%.

 

 

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56 minutes ago, Richard10002 said:

Smartgauge has a good sales pitch, but using it could kill your batteries in short order. When it reaches 100% whilst charging, you would think your batteries would definitely be full. This may be the case, but almost certainly isn’t.

Smartgauge should be used for what it was designed for - to give you a pretty good indication of SoC whilst discharging. It can only guess the SoC whilst charging so, as I wrote above, use charging current and voltage to reasonably accurately determine ‘full’. 

1 minute ago, cuthound said:

 

But the Smartgauge manual tells you that the reading on charge isnt accurate, so it should only be used to determine  when to start charging (or stop discharging).

 

Once you get used to your boats charging idiosyncrasies you can stop charging ssy 3 hours after the Smartgauge says 100%.

Absolutely :)

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51 minutes ago, WotEver said:

Smartgauge should be used for what it was designed for - to give you a pretty good indication of SoC whilst discharging.

 

But sadly the manual does not make this clear. 

 

Not until you get to page 29, which does not count as 'making it clear' in my book. 

 

 

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1 minute ago, Mike the Boilerman said:

 

But sadly the manual does not make this clear. 

 

Not until you get to page 29, which does not count as 'making it clear' in my book. 

 

 

Depends on your ability to read and attention span, I suppose.

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4 minutes ago, Mike the Boilerman said:

Given what you say is so important, why does the Smartgage display an incorrect value during charging? Surely the display should turn off. 

Because the purpose of the SG was to make people worship its creator. Turning the display off would be an admission of fallibility.

 

I rather prefer the approach taken by the NASA BM1 or BM2, which use voltage (as does the SG) to calculate SoC during discharge, & Ah counting from that figure to calculate SoC while charging. It's not perfect but it's a lot better.

Edited by Keeping Up
To add reference to NASA system
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