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Cheap LiFePO4 BMS?


jetzi

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13 hours ago, Tom and Bex said:

There is always  commercial REC BSLRD (Bi-stable latching relay driver) which I'm using for my overcharge protection.

https://www.solar4rvs.com.au/rec-bi-stable-relay-driver-bslrd-for-bottom-end-sw

And here:

https://www.off-grid-systems.de/REC-Touch-Display-BMS-4S-16S-Q_2

 

Alternatively another low powered solution is a motorised battery switch as used by me (for my loads) and Dr Bob. No complicated electronic circuits to build and understand, but maintaining the advantages of low parasitic power drain.

https://www.bepmarine.com/en/701-md

 

If starting again though, I'd be looking for a BMS with direct support for bi-stable relays. 

 

Tom

Hello Tom 

 

Chargery have just released a DC contactor that works specifically with the BMS. It only requires the one contactor which works with faults on either the charging and discharging cycles of my Li. The real benefit is that it only consumes 11ma which is a massive improvement on my current setup and simple plug and play install ?

 

Peter 

 

 

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2 hours ago, nicknorman said:

The BEP seems to take 12mA when switched off. Maybe not a lot but surely an aim should be to have as close to zero power consumption as possible, if the battery has to be switched off due to low SoC. 12mA for a month is 9Ah.

Which is why I'd do it differently next if starting again. 12ma is not much, and certainly much better than a relay, but as you say, not ideal if bms operates due to low cell voltage. Not really a problem as liveaboard, but could see it as potential problem if leaving boat for period of time. 

 

Having said that, we've got no plans to change any of the current set up. It's in and working, and requires no interventions from us. Having just completed a full discharge cycle (just for my curiosity), they measure exactly the same capacity as when installed 2 years ago. 

 

Maybe if we change boats again in a few years I might look at changes, but in a few years a lot can change with lithium technology for boats! Just look how many on this forum have now got then compared to a couple years ago!

 

Edited by Tom and Bex
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2 hours ago, Tom and Bex said:

 

 

Maybe if we change boats again in a few years I might look at changes, but in a few years a lot can change with lithium technology for boats! Just look how many on this forum have now got then compared to a couple years ago!

 

Yes battery tech is making massive moves pushed along by Ev's.  When I started building my battery pack 18650 cells were the way to go. Now lifepo4 has come along and changed the game again. I'm waiting for 26650 (A123) cells to come down in price then I'll make another powerwall based on those. 

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7 hours ago, redwing said:

Finally got my 3 Valences in. I bought them from James at the end of Jan and they sat unmonitored  for over 7 months on the boat whilst I was at home.  

I bought theRS485 cable as recommended by Richard. I messed up the Tyco connector (the A and B data pins on a Valence diag are the wrong way round) so bodged the pins together and was able to read their voltages etc via Valence software. 

Voltages read 13.340(battery12) , 13.352(bat9)  and 13.231(bat23) which was in line with my voltmeter readings. The spread was between 6-8, 2-4 and 1-4 mV. The SOC readings seemed way out @ 95.69 , 21.18 and 36.00.

I charged them individually with Iskra 175 alternator via refurb Sterling 60a B to B on custom setting of bulk 13.8 and float 13.5 and monitored by BMV712. 

I let them settle and plugged them in to software again. Voltages read 13.382(12), 13.627(9) and 13.480(23) with spreads of 6, 38 and 18. The balance was active on battery 9 and then voltage came down to 13.480 with a spread of 18mV. The internal balancing on the Valences works when not on charge but connected to software. 

Paralleled em up and charged again via Sterling . They settled to 13.4 ish and have been down to 13.2 in use (parallel with 440aH LAs) and I haven't charged them via Sterling since. Solar (set at 13.8bulk 13.4 float) has had them back up to 13.4 by midday for last few days but we've had some sun and I'm not a heavy power user. 

 

I have a BEP motorised switch but not connected to BMV yet as I can't find a wiring diag. Any chance Bob or Tom could point me in direction of an idiot-proof source

 

All ok so far I think. Any comments (polite ones) and tips welcome. Thanks to all for your knowledge and experience to get me this far

SOC can only be reset by charging to full, at which point the balancing takes place as well, I have done this once in 3 years. I now happily charge to 13.9 bulk 13.8 absorb and 13,4 float and never plug in as they are always ok, I do a similar regime with the 36 volt valence batteries for drive, I really cant be bothered to check them as they always seemed to be ok in the past, the BMS on the 36 volt batteries can be reset if it goes flashing red through being over discharged. I have stripped a 36 volt battery to play with it, if you try to charge the cells without the BMS it does end in knackered cells I can assure you.

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1 hour ago, Dr Bob said:

 

What is the voltage variation like?

Have you got straps to hold the bank together?

They were all on 3.26v. I used the copper links supplied to connect the -ves together, then measured the voltage differences between the positives. Several were within 1millivolt, none were more than 5 millivolts.

 

Obviously I’ll top balance them before installation, but gliding week coming up so it will have to wait a week.

 

No straps, the casing it pretty rigid ribbed plastic (not thin aluminium, like some) and anyway my intention is to wedge them into the battery box, which has thick wooden sides.  The sides won’t come right to the top of the batteries but I suspect it will be OK.

 

 

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  • 3 weeks later...
On 24/09/2020 at 19:04, peterboat said:

SOC can only be reset by charging to full, at which point the balancing takes place as well, I have done this once in 3 years. I now happily charge to 13.9 bulk 13.8 absorb and 13,4 float and never plug in as they are always ok, I do a similar regime with the 36 volt valence batteries for drive, I really cant be bothered to check them as they always seemed to be ok in the past, the BMS on the 36 volt batteries can be reset if it goes flashing red through being over discharged. I have stripped a 36 volt battery to play with it, if you try to charge the cells without the BMS it does end in knackered cells I can assure you.

Thanks Peter, that would explain the SOC. I'll leave them as they are. There was some balancing going on when I plugged in the software after initial charging to 13.8 

 

There's a video from a van man who has fitted used Valances that may be useful to anyone else thinking of fitting them

 

https://www.youtube.com/watch?v=XXkIcYY0KxU

 

 

On 24/09/2020 at 12:58, Dr Bob said:

Here is the wiring diag.

 

the black wire from the plug (the one with green/red/black) goes to the relay connector on the BMV and then back to the black connector on the switch ( I think - I hope!!!). ie you are breaking the black line from the plug to switch when the relay on the BMV kicks in.

 

Its easy to test. Wire it all up then change the relay voltage setting to a lower voltage than currently present and the relay should operate.

I seem to remember on 'glitch' and that was to ensure that the main battery +ve connectors were in place - ie if you isolate the output line from the BEP, it wont operate. Not sure if that was just me!

 

 

Thanks Bob

 

Havent got round to it yet as have had to leave boat again. Will let you know how I get on

Edited by redwing
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  • 3 weeks later...

Since this is a bit of a niche topic I thought I'd continue this thread rather than starting a new one...

 

My BMS is set up to trip the charging relay at low temperature. But a better solution would be to warm the cells up so that they can be charged safely.

 

I've been told to use soil warming cables or vivarium heating pads for this purpose, as they apparently come in 12V versions with thermostats. The reptile ones especially have temperature control in the right range (0 to 35 degrees). The ones I find online are 240V though.

 

I did find plenty of thermostatically controlled car seat warmers which sound ideal, but I expect I need a thermostat that is much cooler - shutting off at 5 degrees or so.

 

I know that keeping them in the cabin goes a long way towards keeping them warm, but the room they're in does get cold if I'm not in it and running the diesel heater, and don't want to rely 100% on that. I would love to hear any suggestions or how anyone else has solved this problem.

 

How's everyone's installs coming? Would love an update @redwing and @nicknorman!
 

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1 minute ago, ivan&alice said:

Since this is a bit of a niche topic I thought I'd continue this thread rather than starting a new one...

 

My BMS is set up to trip the charging relay at low temperature. But a better solution would be to warm the cells up so that they can be charged safely.

 

I've been told to use soil warming cables or vivarium heating pads for this purpose, as they apparently come in 12V versions with thermostats. The reptile ones especially have temperature control in the right range (0 to 35 degrees). The ones I find online are 240V though.

 

I did find plenty of thermostatically controlled car seat warmers which sound ideal, but I expect I need a thermostat that is much cooler - shutting off at 5 degrees or so.

 

I know that keeping them in the cabin goes a long way towards keeping them warm, but the room they're in does get cold if I'm not in it and running the diesel heater, and don't want to rely 100% on that. I would love to hear any suggestions or how anyone else has solved this problem.

 

How's everyone's installs coming? Would love an update @redwing and @nicknorman!
 

Mine are under the back steps next to the central heating pipes so are way over 5 degrees but in the past the boat has been empty and the batteries are fine in the winter 

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25 minutes ago, ivan&alice said:

How's everyone's installs coming? Would love an update @redwing and @nicknorman!
 

No progress yet, unfortunately. Lots of coding to do for the BMS, but I’ve been really busy with various other things. In order to start, I need to “get into the zone” which means 100% concentration on the task and no distractions!

The alternator regulator has been performing flawlessly, but still charging the LAs for the time being.

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12 minutes ago, ivan&alice said:

Since this is a bit of a niche topic I thought I'd continue this thread rather than starting a new one...

 

My BMS is set up to trip the charging relay at low temperature. But a better solution would be to warm the cells up so that they can be charged safely.

 

I've been told to use soil warming cables or vivarium heating pads for this purpose, as they apparently come in 12V versions with thermostats. The reptile ones especially have temperature control in the right range (0 to 35 degrees). The ones I find online are 240V though.

 

I did find plenty of thermostatically controlled car seat warmers which sound ideal, but I expect I need a thermostat that is much cooler - shutting off at 5 degrees or so.

 

I know that keeping them in the cabin goes a long way towards keeping them warm, but the room they're in does get cold if I'm not in it and running the diesel heater, and don't want to rely 100% on that. I would love to hear any suggestions or how anyone else has solved this problem.

 

How's everyone's installs coming? Would love an update @redwing and @nicknorman!
 

We ended up using these heated mats. (See photo) They are available on eBay, search for "camper van heating mat" They are rated at 220w/m2. They can be cut down lengthways to fit the size of your enclosure.

We have 3 wired in series which, from memory, draws about 1 amp at 12V. In our setup this provides enough heat to maintain the cells above 5 deg C when the ambient temperature is at about -10 deg C.

We've fused both the +ve and -ve supply feed to the battery heater circuit so that a single fault e.g short to +ve battery terminal could not cause a meltdown.

--

Craig

20190120_180444.jpg

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2 hours ago, ivan&alice said:

 

I know that keeping them in the cabin goes a long way towards keeping them warm, but the room they're in does get cold if I'm not in it and running the diesel heater, and don't want to rely 100% on that. I would love to hear any suggestions or how anyone else has solved this problem.

 


 

I just keep the boat warm!

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1 minute ago, peterboat said:

So do I except wh9i ain't there 

...and then we isolate the Li's and leave it on shore power with the battery charger topping up the LA's.

Fire up the stove when we get back and the boat's always above freezing in a few hours.

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2 minutes ago, Dr Bob said:

...and then we isolate the Li's and leave it on shore power with the battery charger topping up the LA's.

Fire up the stove when we get back and the boat's always above freezing in a few hours.

If it's really cold I put the whispergen on its timer, it comes on twice a day and boat is double glazed and well insulated so its fine 

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6 hours ago, Craig Shelley said:

The past couple of months have been fairly heavy going with this project - a final push to get a BMS designed, built and installed. We're beginning to see light at the end of the tunnel.

The MK2 prototype is now installed although more work is needed to move the current the measurement functionality across to the new system.

 

Just a quick re-cap on this project so far:

12 CALB 210Ah batteries purchased from EV Support in 2017, and installed with no BMS.

The only means of monitoring for the first year was via a 5 digit panel volt meter, and 3 ammeters.

A under/over voltage cut off switch was implemented using a BlueSea Systems remote controlled switch wired to two off-the-shelf voltage switch modules.

In 2018, a rudimentary means of estimating state of charge was lashed together using a raspbery pi zero and a waveshare ADS1256 module.

A few op-amps in a breadboard provide some level shifting and scaling for the ADC. Two years later, this lash-up is still running in on a breadboard on the top shelf of the electrical cupboard.

The means of logging data via a google sheet, and plotting using the graphing facility has proved to exceed our expectations regarding reliability and flexibility. It's extremely useful to be able to view the live graphs from anywhere using the google sheets app and it has the ability to share access with family members etc...

 

Time eventually came to build a MK2 unit to overcome some of the limitations, and make a proper installation. Also by this point, I was beginning to get a little nervous about what might be going on with the individual cell voltages. We have only ever carried out spot checks on the cell voltages, but there's never a convenient time to do it. Looking at my spreadsheet, the last measurements were taken nearly a year ago!

 

By this point I have a reasonable idea of what was needed, and what I wanted! I was hoping that an off-the-shelf system would be available by now, as what we're doing isn't exactly novel, and we're not alone in needing a means of precisely measuring multiple voltages. Each time i've looked, the available systems haven't satisfied our specific needs. For instance, many of the multi-cell monitoring solutions are designed for long strings of cells in series, not series-parallel combinations. Also i'm not convinced by the accuracy if the individual per-cell PCB modules as the ones i've seen just rely on the built-in reference within the microcontroller. Having become accustomed to seeing the overall pack voltage displayed with mV resolution and how useful this is whilst observing charge/discharge, I was determined to design something at least as good, but also had an accuracy to complement this resolution. i.e. able to measure the 12V pack voltage within few millivolts.

 

Our setup adds extra complication in that we have 12 cells to monitor. Whilst we could add connecting links between the cells to reduce the number of voltages which need to be monitored, we've chosen not to add the links for the following reasons; Firstly it would be a bit awkward due to the physical layout. Second I believe it might reduce the fault resilience of the pack i.e. 1 faulty cell might then take out 2 more cells. Finally it would not be easy to measure the individual performance of the cells without breaking the links.

 

The system I've ended up designing, for the most part follows a very traditional layout of ADC, instrumentation amplifier and multiplexer. It provides 30 measurement nodes with a somewhat unusual, but flexible multiplexing scheme. It is possible to measure differential voltages between any two nodes; therefore only 5 nodes are needed per battery pack. This scheme enables the polarity of the measurement to be taken in forward and reversed directions. By subtracting the reversed measurements it is possible to eliminate voltage offset of the signal path. A precision voltage reference IC is available via internal nodes 31 and 32 to allow the system to continually self-calibrate.

 

The C code for the raspberry pi is now fully written, I've ended up reusing most of my old python script for uploading the data samples to google sheets. The next phase is to produce some meaningful graphs/dials on the google sheet using the data. I've ended up doing a fair bit of verification work on this prototype unit, even checked it against a reference standard. At 10V the measurement error against the standard was less than 1.5mV. This equates to an error of 0.015%, which is acceptable and well within the spec of the reference IC. It's possible to further reduce this either by using the trim facility available on the reference IC, or by software calibration. I don't think it's necessary to go that far.

With the system installed on the boat, a comparison of the sum the individual cell voltages, with the measured overall voltage was found to give a discrepancy of less than 100uV on each of the packs.

 

So after 3 years without balancing, the battery pack isn't looking too bad. We'll need to leave the monitoring system to gather more data across a range of SOC. Initial data with the cells with a light load and at about 75% SOC is showing a maximum cell to cell variation of 2.5mV.

 

There's still a lot of work to do on this project. The next job is to retire the old lash-up system but to do that the battery current measurement signals need to be moved onto this MK2 system.

 

I've drastically underestimated how time consuming this project would be to complete. My biggest oversight so far has been the time taken to build of the prototype unit. I wish i'd gone straight to PCB. After all i'd gone to the effort of properly drawing up the schematic. Due to the way i'd drawn the schematic, I underestimated the sheer number of interconnections needed - well that's 8 days i'm not going to get back!

Making the cable assemblies also seemed to take forever. At least the end is now in sight!

 

 

 

err .........................    what   ??    :unsure:

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2 hours ago, Murflynn said:

err .........................    what   ??    :unsure:

I use a victron BMV to measure voltage and isolate the Li's in emergency and have a cell monitoring unit (off the shelf) to show me cell voltages (only 4 cells - cant understand why Craig has 12) and have not had to do any cell balancing in the last 12 months. Siiiiiimple!

Craig just has a complicated system. It can be done much more simply.

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3 minutes ago, Dr Bob said:

I use a victron BMV to measure voltage and isolate the Li's in emergency and have a cell monitoring unit (off the shelf) to show me cell voltages (only 4 cells - cant understand why Craig has 12) and have not had to do any cell balancing in the last 12 months. Siiiiiimple!

Craig just has a complicated system. It can be done much more simply.

Yup

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23 hours ago, Craig Shelley said:

We ended up using these heated mats. (See photo) They are available on eBay, search for "camper van heating mat" They are rated at 220w/m2. They can be cut down lengthways to fit the size of your enclosure.

We have 3 wired in series which, from memory, draws about 1 amp at 12V. In our setup this provides enough heat to maintain the cells above 5 deg C when the ambient temperature is at about -10 deg C.

We've fused both the +ve and -ve supply feed to the battery heater circuit so that a single fault e.g short to +ve battery terminal could not cause a meltdown.

Thank you for the suggestion. I think I found what you suggested. It says it is 67W/m and 30cm wide, which should be plenty to put under the whole battery (I presume under is best, on top of a layer of insulation).

 

That suggests it would draw around 6A?

 

Do you use a thermostat with it? There's a cheap board which has a 10A relay - I expect I can wire it on the load side of the BMS and set this to 5 degrees and allow it to heat the battery as and when required.

19 hours ago, Craig Shelley said:

Our setup adds extra complication in that we have 12 cells to monitor. Whilst we could add connecting links between the cells to reduce the number of voltages which need to be monitored ... I believe it might reduce the fault resilience of the pack i.e. 1 faulty cell might then take out 2 more cells. Finally it would not be easy to measure the individual performance of the cells

Do you mean to say the cells are blocks of 4 in series x 3 blocks in parallel? When I was first planning my system I intended to do the same, so that I could monitor each of my 16 cells individually. I was convinced against it at the time but the reasoning has become a little less clear over time! I think it was because the series then parallel configuration would allow more opportunity for the cells to unbalance, not to mention a lot more wiring.

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45 minutes ago, ivan&alice said:

Thank you for the suggestion. I think I found what you suggested. It says it is 67W/m and 30cm wide, which should be plenty to put under the whole battery (I presume under is best, on top of a layer of insulation).

 

That suggests it would draw around 6A?

 

Do you use a thermostat with it? There's a cheap board which has a 10A relay - I expect I can wire it on the load side of the BMS and set this to 5 degrees and allow it to heat the battery as and when required.

Do you mean to say the cells are blocks of 4 in series x 3 blocks in parallel? When I was first planning my system I intended to do the same, so that I could monitor each of my 16 cells individually. I was convinced against it at the time but the reasoning has become a little less clear over time! I think it was because the series then parallel configuration would allow more opportunity for the cells to unbalance, not to mention a lot more wiring.

On my car batteries they are 5 in parallel then in series because that is what the makers recommend 

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1 hour ago, ivan&alice said:

Do you use a thermostat with it?

We currently have no thermostat. I cut the heater film into 3 separate sections, one for each battery enclosure. The heaters were then wired together in series instead of the original parallel configuration. That reduced the overall power to a level sufficient to provide a gentle heat which, from memory, eventually reaches an equilibrium temperature approx 20 degrees above ambient. This enables the heaters to be left on without any means of control. Fuses provide basic protection for over current, and the switch is a guarded and illuminates to give a very clear indication that the heaters are powered.

As the new monitoring system gives us better visibility of battery temperature, it is theoretically possible to automatically control the heaters. I doubt we'll ever get around to making that happen.

1 hour ago, ivan&alice said:

Do you mean to say the cells are blocks of 4 in series x 3 blocks in parallel?

There are 3 separate enclosures, each containing 4 cells in series. The -ve and +ve wires from each enclosure connects to the busbars.

20190214_191725~2.jpg

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On 04/11/2020 at 01:21, Craig Shelley said:

The past couple of months have been fairly heavy going with this project - a final push to get a BMS designed, built and installed. We're beginning to see light at the end of the tunnel.

The MK2 prototype is now installed although more work is needed to move the current the measurement functionality across to the new system.

 

Just a quick re-cap on this project so far:

12 CALB 210Ah batteries purchased from EV Support in 2017, and installed with no BMS.

The only means of monitoring for the first year was via a 5 digit panel volt meter, and 3 ammeters.

A under/over voltage cut off switch was implemented using a BlueSea Systems remote controlled switch wired to two off-the-shelf voltage switch modules.

In 2018, a rudimentary means of estimating state of charge was lashed together using a raspbery pi zero and a waveshare ADS1256 module.

A few op-amps in a breadboard provide some level shifting and scaling for the ADC. Two years later, this lash-up is still running in on a breadboard on the top shelf of the electrical cupboard.

The means of logging data via a google sheet, and plotting using the graphing facility has proved to exceed our expectations regarding reliability and flexibility. It's extremely useful to be able to view the live graphs from anywhere using the google sheets app and it has the ability to share access with family members etc...

 

Time eventually came to build a MK2 unit to overcome some of the limitations, and make a proper installation. Also by this point, I was beginning to get a little nervous about what might be going on with the individual cell voltages. We have only ever carried out spot checks on the cell voltages, but there's never a convenient time to do it. Looking at my spreadsheet, the last measurements were taken nearly a year ago!

 

By this point I have a reasonable idea of what was needed, and what I wanted! I was hoping that an off-the-shelf system would be available by now, as what we're doing isn't exactly novel, and we're not alone in needing a means of precisely measuring multiple voltages. Each time i've looked, the available systems haven't satisfied our specific needs. For instance, many of the multi-cell monitoring solutions are designed for long strings of cells in series, not series-parallel combinations. Also i'm not convinced by the accuracy if the individual per-cell PCB modules as the ones i've seen just rely on the built-in reference within the microcontroller. Having become accustomed to seeing the overall pack voltage displayed with mV resolution and how useful this is whilst observing charge/discharge, I was determined to design something at least as good, but also had an accuracy to complement this resolution. i.e. able to measure the 12V pack voltage within few millivolts.

 

Our setup adds extra complication in that we have 12 cells to monitor. Whilst we could add connecting links between the cells to reduce the number of voltages which need to be monitored, we've chosen not to add the links for the following reasons; Firstly it would be a bit awkward due to the physical layout. Second I believe it might reduce the fault resilience of the pack i.e. 1 faulty cell might then take out 2 more cells. Finally it would not be easy to measure the individual performance of the cells without breaking the links.

 

The system I've ended up designing, for the most part follows a very traditional layout of ADC, instrumentation amplifier and multiplexer. It provides 30 measurement nodes with a somewhat unusual, but flexible multiplexing scheme. It is possible to measure differential voltages between any two nodes; therefore only 5 nodes are needed per battery pack. This scheme enables the polarity of the measurement to be taken in forward and reversed directions. By subtracting the reversed measurements it is possible to eliminate voltage offset of the signal path. A precision voltage reference IC is available via internal nodes 31 and 32 to allow the system to continually self-calibrate.

 

The C code for the raspberry pi is now fully written, I've ended up reusing most of my old python script for uploading the data samples to google sheets. The next phase is to produce some meaningful graphs/dials on the google sheet using the data. I've ended up doing a fair bit of verification work on this prototype unit, even checked it against a reference standard. At 10V the measurement error against the standard was less than 1.5mV. This equates to an error of 0.015%, which is acceptable and well within the spec of the reference IC. It's possible to further reduce this either by using the trim facility available on the reference IC, or by software calibration. I don't think it's necessary to go that far.

With the system installed on the boat, a comparison of the sum the individual cell voltages, with the measured overall voltage was found to give a discrepancy of less than 100uV on each of the packs.

 

So after 3 years without balancing, the battery pack isn't looking too bad. We'll need to leave the monitoring system to gather more data across a range of SOC. Initial data with the cells with a light load and at about 75% SOC is showing a maximum cell to cell variation of 2.5mV.

 

There's still a lot of work to do on this project. The next job is to retire the old lash-up system but to do that the battery current measurement signals need to be moved onto this MK2 system.

 

I've drastically underestimated how time consuming this project would be to complete. My biggest oversight so far has been the time taken to build of the prototype unit. I wish i'd gone straight to PCB. After all i'd gone to the effort of properly drawing up the schematic. Due to the way i'd drawn the schematic, I underestimated the sheer number of interconnections needed - well that's 8 days i'm not going to get back!

Making the cable assemblies also seemed to take forever. At least the end is now in sight!

 

Photo shows prototype MK2 unit assembled onto lid of diecast enclosure.

 

That does sound like a lot of work, but a very interesting project to keep you out of trouble! Also very interesting to see the different ways people go about solving the same problem. In my case I used a single chip solution for cell string voltage measurement (you’d need 4, one for each string). I used an embedded microprocessor because IMO something like a Pi has a lot of unnecessary overheads which consumes a lot of power, and I went straight to PCB (no other option due to sIze of chip footprint).

I can see that keeping the 4 strings separate has some value in terms of added information about individual cells, but IMO this benefit is not worth the fourfold increase in complexity, wiring etc with inherent reduction in reliability. Just my opinion though!

 

Question: what is the average current consumption of your system?

Edited by nicknorman
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