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Another Lithium battery thread


Dr Bob

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7 minutes ago, MoominPapa said:

My 14.0V was under heavy charge, so tells you much more about the charge current than the SOC. and don't forget that this was a 3.5Ah pack, being charged at almost 1C. At the fractional-C charge rates likely with a domestic bank and alternator, I doubt the voltage will reach anywhere near 13.8 until the SOC is pretty high. My next test is a long charge at current limited to  half an amp, which equates to the 0.15C I'll get from a 70A alternator into my 480Ah bank, I need to let the logging subsystem sorted first though: the charge curve will be useful, and I'm not going to sit there for 7 hours manually noting data.

 

I'd expect the difference between doing CV at 13.8 and CV at 14.0 to be that the CV state is reached earlier, and the current fall-off will be more gradual. It will still get  to 100% but take a little longer.

 

MP.

 

 

 

 

 

Very interested in these results. Keep 'em coming!

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49 minutes ago, Dr Bob said:

Ok, this thread is working well to help me map out the way forward. I think I have a reasonable handle on charging and what to do with the alternator now.

Let me ask another question.

If we go back to my original post and look at the diagram suggested by Eric (Eric of the blog on SLA/LiFePo hybrid systems), the hybrid system is designed so the SLA stops any technical issues if the Lithium bank is disconnected in an emergency. I am attracted to this system as all I need to do is put a lithium circuit in place (with auto disconnect on high/low voltage) and a manual disconnect ...and move the BMV712 to the Li circuit. I am wondering how many SLAs to leave in place ...ie I could leave all 6 *110Ahr in place inititally. Under normal operation how would this work.

Let's start in the evening in January with the Li and SLA's with no load and no charge....with the Li's at 75%. Voltage on the Li bank will be 13.0V+ so providing a trickle charge to the SLA which will have some 'internal' discharge (ie the SLA bank is fully charged and would be at 12.7V at rest). I now turn on the inverter and with the fridge and TV on etc, I am taking 10A. I assume from what Eric said that would all come out of the Lithium bank as the voltage drop in the bank is minimal (assume say 360Ahr of LiFePo capacity). I operate overnight like this so by morning the Li's have gone down from 75% SoC to say 40%. At 40% SoC, the lithium voltage is still over 13.0V (????) so the SLA's are still at 100%. Morning comes, I start the engine and the Li's charge back up to a target of 80% . Charge is then switched off and the SLA's are still at 100%.

This sounds like the SLAs will always be full. Yes they will take power out of the Li's to cover their self discharge but in principle, there will be little cycling in the SLA's. The only time the SLA's would go down in SoC is if the Li's drop to a voltage <12.8V but by that time I would have taken action.

Is this thinking correct?

If so I would be tempted into just leaving my SLA's in place and piggy backing the Li system - maybe putting my old BMV501 monitor on the total system and the BMV712 on the Li only circuit

 

Screen Shot 2019-01-06 at 13.21.55.png

This is exactly what JohnV has done and he never sees 12.8 volts, his original batteries wernt that old but he was already starting to see a drop in performance however now he has the LifePo4s in the mix he is never worried about low voltage and he has an all electric boat

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14 hours ago, nicknorman said:

On the subject of making PCBs, whilst I can and do make quite good single sided boards thanks to the joys of modern inkjet printers, double sided boards with vias and solder mask are a bit beyond me! However there is a company called Elecrow in China that will make me 10 double sided boards (100mm x 100mm) with all the trimmings for $5. Yup, five US dollars, or $0.5 each. Of course if you want it quick, there is another $26 for express shipping but if you don't mind waiting a month or so, the shipping is $8 via ordinary airmail. With the expensive shipping, turnaround will be about a week - 10 days. I have yet to try them but they seem to have a good reputation. Been spending tonight finalising the pcb design so should be ready to try soon. It will be mostly surface mount. This is one of the pressure sensors I am using, 8 pads underneath it. But with solder paste and a hot air rework station I had instant success soldering one to a test PCB I'd made. Just need strong glasses and a steady hand to position it! The sensor outputs pressure from 200 to 1200 hPa with a 24bit AtoD, uses a milliamp at 3v, has I2C interface and all for under £3.

IMG_3756.JPG.d11659a707df03c207ebe93d2a77e2b4.JPG

 

Its got no legs ..... and its too small to see. I do think surface mount was a big setback for DIY electronics. Your cheap Chinese PCBs sound very interesting, but I don't have the space on the boat for a soldering oven. I would be quite interested in a company making one off PCBs and sticking the components on.

 

I think with PCB's you have to (try to) get things right first time so this leads on to circuit simulation (probably no bad thing) though I did enjoy building/testing/modifying prototypes on Veroboard.

 

I suspect surface mount is why the Arduino concept uses ready made little PCBs with legs on, it effectively converts surface mount back to legs.

 

I must be old, first big PCB I did (mini computer memory) was all done with that sticky tape stuff.

 

..................Dave

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Thinking about this 14.0 charge cut-off thing.

 

If I'm right that the plan it to charge until the terminal voltage (under charge) reaches 14.0v then cut off, then it may work, but it depends on a lot of things.

 

These cells can take a lot of current. I can push my test cells up to 14.0v when completely flat, at which point they are taking about 1C charge current, which is within spec.

 

On a boat you might sensibly have a 200A alternator and a 200Ah lithium bank. Terminating charge at 14.0 in that situation would be useless: as soon as the alternator started to charge at 200A the terminal voltage would go to 14v and the BMS would shut it all down. On the other hand a big bank and a small alternator would charge at a lower voltage and only rise to 14.0 closer to battery full. 

 

In short, the charge you'd achieve will depend on the ratio of charge current available to bank size. The bigger the alternator, the lower the SOC at cut-off, the larger the bank, the higher the SOC. For some combinations, it would be non-optimal but usable, for others, it's pointless.

 

I really think that it makes sense to use the volts-over-14.x AND current-under-C/20 algorithm, but to do that needs a BMS that measures charge current and can shut down the alternator. This is why Tom and Bex's ardunio alternator controller looks like a winning move.

 

In addition, even that won't necessarily detect a long, slow charge (from solar, for instance). I think you need to use coulomb counting too, and terminate when the charge returned equals the total discharge plus a small margin. Don't  forget that float charging is a no-no.

 

If you don't want to measure current, you could do something like stopping charge periodically, and measuring the off-charge voltage to see if it's rising up the knee. I don't know if LiFePO4 has surface charge like LA, which would mess that up. It doesn't seem worth it to avoid a current sensor, to be honest.

 

MP.

 

 

 

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31 minutes ago, MoominPapa said:

Thinking about this 14.0 charge cut-off thing.

 

If I'm right that the plan it to charge until the terminal voltage (under charge) reaches 14.0v then cut off, then it may work, but it depends on a lot of things.

 

These cells can take a lot of current. I can push my test cells up to 14.0v when completely flat, at which point they are taking about 1C charge current, which is within spec.

 

On a boat you might sensibly have a 200A alternator and a 200Ah lithium bank. Terminating charge at 14.0 in that situation would be useless: as soon as the alternator started to charge at 200A the terminal voltage would go to 14v and the BMS would shut it all down. On the other hand a big bank and a small alternator would charge at a lower voltage and only rise to 14.0 closer to battery full. 

 

In short, the charge you'd achieve will depend on the ratio of charge current available to bank size. The bigger the alternator, the lower the SOC at cut-off, the larger the bank, the higher the SOC. For some combinations, it would be non-optimal but usable, for others, it's pointless.

 

I really think that it makes sense to use the volts-over-14.x AND current-under-C/20 algorithm, but to do that needs a BMS that measures charge current and can shut down the alternator. This is why Tom and Bex's ardunio alternator controller looks like a winning move.

 

In addition, even that won't necessarily detect a long, slow charge (from solar, for instance). I think you need to use coulomb counting too, and terminate when the charge returned equals the total discharge plus a small margin. Don't  forget that float charging is a no-no.

 

If you don't want to measure current, you could do something like stopping charge periodically, and measuring the off-charge voltage to see if it's rising up the knee. I don't know if LiFePO4 has surface charge like LA, which would mess that up. It doesn't seem worth it to avoid a current sensor, to be honest.

 

MP.

 

 

 

Ok, interesting,

The set up I am thinking about is having 300-400Ahr Li capacity with a 90A alternator (that never seems to do more than 60A into my lead acids on initial charging - but I never go under 75% SoC). I guess therefore that it will be up above 80% SoC when the voltage reaches 14.0v. If I go ahead and can find some 2nd hand cells, I will try it and see if the Sterling AtoB will go into float - ie 13.5V soon after it reaches the 14.0V in absorbtion. It always goes into float too soon on the LA's. If it stays in absorption too long then I will have to manually disconnect the Li's. I think by the time I get round to doing all of this, the commercial version of T&B's controller will be available and I can then buy and fit it if necessary.

The question for me then is not so much about the relationship between voltage and SoC on the Li's (the straight line from 20% to 90% with a knee upwards when over 14V...but more about how quickly the tail current drops and what is the tail current to SoC relationship? For example, on my LA's (6*110Ahr) I will have say 30A going in as the votage rises to over 14.0V (ie in absorbtion) which then drops by half in each hour after that...so in 2hrs is down to 7.5A .....and I use that as my 100% SoC.  I guess the Li's tail current will drop more quickly but is 1%, 2%, 4% or 8% tail current 100% SoC?

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6 hours ago, Johny London said:

I have been thinking whether I could add lithiums in addition to the LA's, partly because it's a new thing and I'm 100% dependant on my power, as a liveaboard.

As are we. Never go back now though. Could even be tempted to dispense with our starter battery if/when it fails.

 

6 hours ago, Johny London said:

On another note, all this messing around with extra cabling, switches and fuses - (and protection devices) all adds significant cost, and the resulting "home brew" lithiums only being able to give 50-60% of their capacity

Yes to the cost. Our install cost a little over £1000 - £600 was batteries, and the rest extras. 

 

Not sure where the 50-60% comes from though, we've charged ours to 100% and discharged down to 9% with no issues. 

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10 minutes ago, Tom and Bex said:

As are we. Never go back now though. Could even be tempted to dispense with our starter battery if/when it fails.

 

Yes to the cost. Our install cost a little over £1000 - £600 was batteries, and the rest extras. 

 

Not sure where the 50-60% comes from though, we've charged ours to 100% and discharged down to 9% with no issues. 

Its users like my self that have a 20 -80% regime that means that 60% is available for use, again its to extend the life of the batteries for as long as possible. I have 14 in my system, and new they are 2.5k each! so I have no intention of replacing them any time soon.

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5 hours ago, dmr said:

 

Its got no legs ..... and its too small to see. I do think surface mount was a big setback for DIY electronics. Your cheap Chinese PCBs sound very interesting, but I don't have the space on the boat for a soldering oven. I would be quite interested in a company making one off PCBs and sticking the components on.

 

I think with PCB's you have to (try to) get things right first time so this leads on to circuit simulation (probably no bad thing) though I did enjoy building/testing/modifying prototypes on Veroboard.

 

I suspect surface mount is why the Arduino concept uses ready made little PCBs with legs on, it effectively converts surface mount back to legs.

 

I must be old, first big PCB I did (mini computer memory) was all done with that sticky tape stuff.

 

..................Dave

However I made up a PCB, tin plated but no solder mask, dabbed on some spots of solder paste, heated it up with my £35 ebay hot air rework station and it worked first time. So you don't really need soldering oven for small boards

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10 minutes ago, nicknorman said:

However I made up a PCB, tin plated but no solder mask, dabbed on some spots of solder paste, heated it up with my £35 ebay hot air rework station and it worked first time. So you don't really need soldering oven for small boards

<£29 delivered now...

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F301966004104

 

I fixed a mate’s head torch pcb with a soldering iron last week. Probably more by luck than judgment. Dry joint on an smd diode. 

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3 minutes ago, WotEver said:

<£29 delivered now...

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F301966004104

 

I fixed a mate’s head torch pcb with a soldering iron last week. Probably more by luck than judgment. Dry joint on an smd diode. 

Yes that is the one. One of the most useful gadgets I have bought in a long time. Great for such things as heatshrink as well as repairing / making up PCBs and in fact anything where a precise temperature is required to heat something.

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3 hours ago, WotEver said:

<£29 delivered now...

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F301966004104

 

I fixed a mate’s head torch pcb with a soldering iron last week. Probably more by luck than judgment. Dry joint on an smd diode. 

I soldered some new diodes onto my solar panels late last year and I was surprised that they worked!

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14 hours ago, nicknorman said:

I can't remember what SoC a steady 14v equates to, is it close to 100%?

 

It would be interesting to find out whether, for those people who want to charge only to 80% for reasons of cycle life, charging at 13.8v results in the same initial high current and rapid fall off of current as 80% SoC is reached.

14v will easily reach 100% soc and easily overcharge if left at that. 13.8v will probably also reach 100% as well, just take a bit longer. 

 

13 hours ago, MoominPapa said:

My 14.0V was under heavy charge, so tells you much more about the charge current than the SOC. and don't forget that this was a 3.5Ah pack, being charged at almost 1C. At the fractional-C charge rates likely with a domestic bank and alternator, I doubt the voltage will reach anywhere near 13.8 until the SOC is pretty high

Yes, charge current is important to consider in all this as well. We generally see around 100A or a bit less during bulk charge (depending on engine revs). Batteries tend to spend a lot of the bulk charge at 13.65-13.7v, and are about 80% charged when they hit 14v. We noticed current would tail off too gradually for us if charged at 13.8v. That is on a 320ah bank. 

 

Remember these batteries were designed to be charged at 1c until pretty much full, but that requires a much higher finishing charge voltage than ever likely to be used in a typical narrow boat installation. 

 

13 hours ago, Dr Bob said:

 move the BMV712 to the Li circuit. I am wondering how many SLAs to leave in place ...ie I could leave all 6 *110Ahr in place inititally

One point to consider if powering the BMV from the lithium bank is it will always be drawing power from that bank, even if low voltage disconnect operates. Not a significant problem if prompt recharge occurs, but could be potential issue for leisure boaters leaving boat unattended for some time. As to leaving 6 SLA batteries in place, don't really see what it would achieve? You would have the constant power wastage of trickle charging 6 batteries from the lithiums, instead of just 1. Lead acid should remain full at all times, our (pack level) low voltage alarm is set at 12.8v and never sees that in normal usage.

 

15 hours ago, MoominPapa said:

A quick report on progress with the Moomin-BMS. State-of-charge based on coulomb-counting is now functional, as is charge and discharge disconnect

Sounds very interesting. Any plans to sell it? Need any testers?

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11 hours ago, Dr Bob said:

The set up I am thinking about is having 300-400Ahr Li capacity with a 90A alternator

We've got 320ah bulk charged by 2 x 70A A127 alternators, and absorption charged with 1 alternator. 

11 hours ago, Dr Bob said:

I guess therefore that it will be up above 80% SoC when the voltage reaches 14.0v

With our setup above 2 x 70A alternators, charging at around 100a, they consistently hit 80ish% when voltage hits 14.0v. 

 

11 hours ago, Dr Bob said:

I will try it and see if the Sterling AtoB will go into float - ie 13.5V soon after it reaches the 14.0V in absorbtion. It always goes into float too soon on the LA's. If it stays in absorption too long then I will have to manually disconnect the Li's. I think by the time I get round to doing all of this, the commercial version of T&B's controller will be available and I can then buy and fit it if necessary

A lot of these controllers use time in bulk to determine absorption time, ie if bulk takes a long time, then so will absorption. The complete opposite of what you want for charging lithiums!

 

11 hours ago, Dr Bob said:

The question for me then is not so much about the relationship between voltage and SoC on the Li's (the straight line from 20% to 90% with a knee upwards when over 14V...but more about how quickly the tail current drops and what is the tail current to SoC relationship? For example, on my LA's (6*110Ahr) I will have say 30A going in as the votage rises to over 14.0V (ie in absorbtion) which then drops by half in each hour after that...so in 2hrs is down to 7.5A .....and I use that as my 100% SoC.  I guess the Li's tail current will drop more quickly but is 1%, 2%, 4% or 8% tail current 100% SoC?

Same argument with lead acid! What is 100% anyway? We take 4% tail current at 14v as 100% soc, but tempted to increase that to 5%. Current does drop much much quicker than lead acid, but still takes us over an hour to get from 80% to 100%.

 

Again, just to reiterate though, you don't ever need to get to 100% with these batteries!

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7 hours ago, Tom and Bex said:

We've got 320ah bulk charged by 2 x 70A A127 alternators, and absorption charged with 1 alternator. 

With our setup above 2 x 70A alternators, charging at around 100a, they consistently hit 80ish% when voltage hits 14.0v. 

 

A lot of these controllers use time in bulk to determine absorption time, ie if bulk takes a long time, then so will absorption. The complete opposite of what you want for charging lithiums!

 

Same argument with lead acid! What is 100% anyway? We take 4% tail current at 14v as 100% soc, but tempted to increase that to 5%. Current does drop much much quicker than lead acid, but still takes us over an hour to get from 80% to 100%.

 

Again, just to reiterate though, you don't ever need to get to 100% with these batteries!

Thanks T&B. Some good info on charging here. My questions are aimed at trying to understand if my alternator and Sterling AtoB will switch out of absorption to 13.5V before I get to 100%. That's why I am keen to know where 100% is on Li's. On lead acids you must get there. On Li's, you mustn't ( other than balancing).

From your data and my experience of the AtoB, I may just get away with using the AtoB. If not I will turn the Li's off manually short term and get a proper alternator controller.

Ok on power to the BMV. Yes I'd read that in Eric's blog. Good point.

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10 hours ago, Tom and Bex said:

Sounds very interesting. Any plans to sell it? Need any testers?

I have briefly considered if it has the making of a product, and come to the conclusion that it might, but there'l be an awful lot more engineering to do. I don't mind editing source code and re-compiling to set parameters. A buyer wouldn't want to do that. In fact you'd have to make the thing entirely independent of a PC, or face supporting PC software too (on a Macintosh, or Windows! "Just run Ubuntu" wouldn't hack it.) 

 

My plan at the moment s to use a "tractor regulator" set to 14.0v and sensing from the disconnect contactor to control the alternator charging. That's rather A127 specific, so you'd need to include some elements of the Arduino regulator to make the thing alternator generic.

 

However if you want source and some hand-drawn diagrams, you're welcome :)

 

Cheers,

 

MP.

 

Last nights software work included dredging up A-level maths from nearly 40 years ago and writing code to do linear regression on current.,voltage samples. If you model the battery as ideal cells and a fixed internal resistance, this allows you to measure the true cell voltage without the effects of discharge, as long as the discharge rate varies over the sampling period. Turns out that my 3.5Ah pack and weedy test wiring has an internal resistance of about 150 milli-ohms. I'm expecting the real thing to be closer to one or two.

 

 

 

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1 hour ago, MoominPapa said:

Last nights software work included dredging up A-level maths from nearly 40 years ago and writing code to do linear regression on current.,voltage samples. If you model the battery as ideal cells and a fixed internal resistance, this allows you to measure the true cell voltage without the effects of discharge, as long as the discharge rate varies over the sampling period. Turns out that my 3.5Ah pack and weedy test wiring has an internal resistance of about 150 milli-ohms. I'm expecting the real thing to be closer to one or two.

 

I don't know if you already know (and probably too late anyway!) but if you have some data point pairs (eg current and voltage) and want to write an equation to describe the relationship, then a really easy way to do it is to put the data into Excel, plot an x-y graph and then get it to draw a trendline, and tell it to write the equation for the trendline on the graph. Then you can see the equation you need to programme. You can choose between linear, logarithmic, polynomial (specified order),  power, exponential, moving average. Beats doing "proper maths"!

 

I wonder if/how much the "internal resistance" varies with temperature?

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8 minutes ago, nicknorman said:

I wonder if/how much the "internal resistance" varies with temperature?

According to the guy who wrote the below paper, internal resistance varies more greatly with temperature than it does with SoC. The paper is over a year old and a sample of one, so there may well be others that disagree. 

https://res.mdpi.com/energies/energies-10-01284/article_deploy/energies-10-01284.pdf?filename=&attachment=1

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1 hour ago, nicknorman said:

I don't know if you already know (and probably too late anyway!) but if you have some data point pairs (eg current and voltage) and want to write an equation to describe the relationship, then a really easy way to do it is to put the data into Excel, plot an x-y graph and then get it to draw a trendline, and tell it to write the equation for the trendline on the graph. Then you can see the equation you need to programme. You can choose between linear, logarithmic, polynomial (specified order),  power, exponential, moving average. Beats doing "proper maths"!

 

I wonder if/how much the "internal resistance" varies with temperature?

Last time I checked, Excel doesn't run on Atmel microcontrollers :)

 

The plan is to store the last 20 minutes or so of current, terminal voltage measurements in the BMS and do the regression and thereby get a  more accurate value for the sum of the cell voltages. This is essentially the point where the line crosses the zero-current axis. 

 

The Arduino SDC does support floating point, but the library takes a good chunk of program memory and isn't very fast. Fortunately is also supports  64-bit integer arithmetic reasonably efficiently, so I was able to  scale the inputs and do the calculations on large integers in implied fixed-point.

 

Linear regression only needs four "running" parameters, the sum of x, sum of y, sum of xy and sum of x^2 so the actual values from the last 20 minutes are not needed to do the calculation,  They are needed to remove the points dropping out of the calculation after 20 minutes from the running totals. I can store them as 16 bit values, so with samples every five seconds, they take up less than 1k of my available 2.5k RAM.

 

I'm hoping that this voltage number will be good enough to be able to look up in a table giving SOC versus voltage and get a useful SOC number which can be used to counteract long-term drift in the SOC derived from coulomb counting, I don't anticipate the batteries being at 100% or 0% very often to reset the boundary conditions on the integration.

 

MP.

 

 

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1 hour ago, MoominPapa said:

Last time I checked, Excel doesn't run on Atmel microcontrollers :)

 

The plan is to store the last 20 minutes or so of current, terminal voltage measurements in the BMS and do the regression and thereby get a  more accurate value for the sum of the cell voltages. This is essentially the point where the line crosses the zero-current axis. 

 

The Arduino SDC does support floating point, but the library takes a good chunk of program memory and isn't very fast. Fortunately is also supports  64-bit integer arithmetic reasonably efficiently, so I was able to  scale the inputs and do the calculations on large integers in implied fixed-point.

 

Linear regression only needs four "running" parameters, the sum of x, sum of y, sum of xy and sum of x^2 so the actual values from the last 20 minutes are not needed to do the calculation,  They are needed to remove the points dropping out of the calculation after 20 minutes from the running totals. I can store them as 16 bit values, so with samples every five seconds, they take up less than 1k of my available 2.5k RAM.

 

I'm hoping that this voltage number will be good enough to be able to look up in a table giving SOC versus voltage and get a useful SOC number which can be used to counteract long-term drift in the SOC derived from coulomb counting, I don't anticipate the batteries being at 100% or 0% very often to reset the boundary conditions on the integration.

 

MP.

 

Ah I get it now, I thought you were trying to find a “fixed” equation to describe the relationship between the parameters but as I understand you are extrapolating a dynamic data set to predict the voltage at zero current.

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In the orginal post and in a few more posts, we discussed the VSR voltage regulator that T&B used. This was a DIY/self build type device that seemed to do a pretty good job. Nick identified this was now going commercial. I contacted the guy who designed the VSR and asked if it would be available soon. I got the following response today:

 

We will not be establishing formal sales channels at this time into the UK.  However, it seems we can ship from the USA.  I have attached a PRELIM datasheet for the WS100, please do not forward it – we will be releasing a final one in a few weeks (ala, changing photo, etc).

We do have some WS100 regulators available today via Ebay.  If you search for “Wakespeed WS100 regulator” you will see a couple of options.  They are 1st gen units and the same as we will be shipping later the year, though we have made some small manufacturing improvements (mostly around the temperature probes –using sockets vs hard wired as the present ones are on Ebay).

The WS200 will be a few months away, and the WS500 (datasheet also attached) will be shipping next month in limited quantities.

There are no more of the VSR Gen3 units available, sorry.  And do wish to point out, the follow on to those is indeed the WS500 regulator.  If you have any questions on which ones might be the best fit feel free to ask questions!

And if you keep an eye on:  http://www.wakespeed.com/, it will get updated as things progress.   (We really are just now getting things off the floor, so to speak).

It looks like to control LiFePo's you will need the WS500 regulator which looks like it will be available next month. No pricing data but the WS200 is £250 ish - so the WS500 likely to be more. It certainly looks like it is perfect for the job if a bit expensive and I'd need to take the alternator apart (I assume) to fit. Looks like a plan B. Balmar seem to have something similar (very quick look) but with less functionality for £500 ish.

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I know you are all looking at ways of controlling the alternator, but surely my cheap 6 squids board from Amazon, conected to a relay would do the job of turning off the alternator? Set it for 14 volts at the battery, when thats achieved it disconnects the alternator, use something in the boat batteries drop below 14 volts, it starts charging again simples, and very cheap as the relay wouldnt be taking much load

Edited by peterboat
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10 minutes ago, peterboat said:

I know you are all looking at ways of controlling the alternator but surely my cheap 6 squids board from Amazon conected to a relay would do the job of turning off the alternator? Set it for 14 volts at the battery when that achieved it disconnects the alternator use something in the boat batteries drop below 14 volts it starts charging again simples and very cheap as the relay wouldnt be taking much load

Is it safe to just switch the alternater off Peter? I thought it could naff emm??

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15 minutes ago, peterboat said:

I know you are all looking at ways of controlling the alternator, but surely my cheap 6 squids board from Amazon, conected to a relay would do the job of turning off the alternator? Set it for 14 volts at the battery, when thats achieved it disconnects the alternator, use something in the boat batteries drop below 14 volts, it starts charging again simples, and very cheap as the relay wouldnt be taking much load

Well 2 things, firstly what is the hysteresis of your sick squid board? If it shuts off at 14v, the battery voltage will rapidly drop to say 13.6v and then if the relay closes again, you will just have a chattering relay.

 

And secondly for people who cruise their boats a lot, once the battery was fully charged and the relay opened, for the rest of the cruising day the battery would be depleted by the boat's loads. Well unless you have a LA battery as well, but that seems a fudge to me.

2 minutes ago, peterboat said:

what happens do you think when you turn off the ignition?

Nothing, for most boats. The alternator remains operating until it stops (or nearly stops) spinning

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