Sgt Raven
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I think it would depend where you install the shunt. Between the charge controller and the battery, I think would show the charge going in.
Finally found a LiFePO4 BMS with Low-temp Charging Protection
- Thread starter Will Prowse
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Right, but it's only going to show the 5 amps of charge to the battery.
Sgt Raven
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Shouldn't it show the total amps flowing thru the wire? If I put my clamp meter on the output wire of my charge controller. I would expect to see the total output in that wire. Assuming it is before where the load is drawn from the circuit.
The power from the solar charge controller gets dumped into the "system". A load can pull that power off the system before it ever hits the battery. I've seen this happen on my trailer and it's kind of a pet peeve of mine that I'm not able to track it very well. The BMV-712 can tell me at the end of the day that 80 amps went into the battery. But the solar charge controllers produced 120 amps. 40 amps got sucked up by the inverter or other loads.
OverkillSolar
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If you want to see charge and discharge current separately you will need 2 external shunts, otherwise it all adds up in the bus bars before the BMS has a chance to measure it.
Stupid Monkey
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I'll have a good search through this thread, but has anyone had balancing issues with this BMS?
I'm now 10 months into use, generally never gets to top balance so I'm plugged into mains rather than solar and allowing a top balance. However despite the app "flashing" to say balancing the pack is just not balancing. Like 100 hours now at 13.75v on the charger - low enough to not trigger over-voltage while high enough to hit the balancing voltage (set at 3.45v per cell). Balancing indicated on the "blue elephant" app and "yellow elephant" android apps but no actual balancing is occurring.
I'm now 10 months into use, generally never gets to top balance so I'm plugged into mains rather than solar and allowing a top balance. However despite the app "flashing" to say balancing the pack is just not balancing. Like 100 hours now at 13.75v on the charger - low enough to not trigger over-voltage while high enough to hit the balancing voltage (set at 3.45v per cell). Balancing indicated on the "blue elephant" app and "yellow elephant" android apps but no actual balancing is occurring.
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I think my app will show which cells are balancing. But it's been a while since I've looked at the cell page of the app.
Post your parameters, maybe there's something in there that isn't set right.
Post your parameters, maybe there's something in there that isn't set right.
Stupid Monkey
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Cheers - yes the App shows balancing (both apps) - now found link to a newer version will try that. Balancing shown, but voltages not getting closer to each other.... will try new version of app and post up either way.
New app link from earlier in thread - https://github.com/FurTrader/OverkillSolarBMS/raw/master/Android_app_xiaoxiangBMS_3.1.1015.apk
New app link from earlier in thread - https://github.com/FurTrader/OverkillSolarBMS/raw/master/Android_app_xiaoxiangBMS_3.1.1015.apk
That's the version I'm on. I've been using that version since I first installed the BMS.
Sgt Raven
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100 hours? My 30A charger set at 13.8V will go from 12V to full in about 8 hours or so.
I have to charge my tablet up first and I'll go put mine on the charger and see what's up.
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Stupid Monkey
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100 hours of top balancing (with non happening).... 30 hours for a charge.
So 8 hours for your full charge is 8*30 = 240aH .... I've a 900 amp hour bank
I've got the latest version now of the "blue elephant" app, and loaded the standard LiFEPO4 setting to see if that will kick start the actual balancing ...
Sgt Raven
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My tablet is running Android 7 and I have blue elephant v3.1.1001 it's not fully supported with my older OS, but seems to work OK.
Not sure I want to chance updating to the latest version and find out it doesn't work at all.
I have to ask, did you parallel top balance your cells before putting them in series?
The BMS balancing current is really low. I am not sure what it is on the 12 volt version, but I believe it's 70 ma's on the 24 volt version which I have. 100 hours at 70ma's would be 7 amps.
You can set the voltage to start balancing in the app. Mine is set to 3.4 volts. You can also set the delta to start balancing. Mine is set to 15mv's. This is what's recommended by Steve at overkill and is indicated in the manual.
My delta at the top when my 8 cells are fully charged is less than 100mv's. Looking at the voltages on your screenshot, I am sure your delta would be much higher.
mikefitz
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Your cells are way out of balance , perhaps far too much for the bms to deal with. The balance current bleed off is quite small, 10s of mA.
It looks from the values that the cells have not been top balanced before battery assembly. I wired the cells wired in parallel and under constant supervision charged to 3.65 volts.
I found having carried out the balancing process and reconnected as a battery pack, the cells are balanced within 5mV of each other over the discharge range down to 3v per cell. (12v battery)
Under 'function settings' 'charge balance' and 'balance enable' need to be 'on'.
Under 'parameter view' the balance turn on volts and balance precision are shown, default valued are 3.4 volts and 0.015 volts.
Mike
Sgt Raven
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I started with my lowest cell at 3.366V and a split of 0.022V and charging at 30A. It rapidly dropped to 22A charging and a split of 0.014V. Only one of the 4 cells is above 3.400V and it isn't flashing like it does when top balancing. I'll go back and check it again in a little bit.
I top balanced the cells to 3.65V before building the pack and my 12V battery is composed of 4 280AH Eve cells.
Stupid Monkey
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yes, no, sort of .... there are 24 cells, in 6P4S. I gave them 10 days parallel with 10A charger and increasing voltages but then worked out it was going to take another month so built it into a battery, charged it with my 30A charger and then while watching the BMS top balance I "helped" it with a ~150w load until it was close and left it top balancing. since then I would imagine 800-1000 kwhrs of charge/discharge full time living in a van 0.2C max discharge and 0.1C max charge for 8 months - so not hard use at all.
Yeah, left it balancing - but even if it was low those numbers would be getting closer, and they just arent -
I don't think they are that out of balance that much, I watch it charge and they rise to 3.39 together (with charge voltage) then once the current drops cells 2/3 drop a little and 1/4 rise. Even taking to 3.65v/cell cell 2&3 don't get to 3.4 after that dont even get as close as to when there is a full charge current on.
I've also checked the bottom balance / low volt disconnect a few times in December due to not having power - and the cells are balanced 2.92-3.05 at my inverter cut off drawing full enough capacity too.
I've ordered a balancer anyway - to assist if i get this working, or to to the balancing otherwise. If i can be bothered to dismantle I may do a manual top balance again next week.
Sgt Raven
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The normal answer in your case. Is charge it as a battery to get it close and then parallel the cells to finish off the top balance the first time. You should have to only do this one time in the beginning. Most the people that have a balance problem never did a proper top balance at the start. I can't remember how many times this has come up. Yes it is extra work to do it right the first time, but the results seem to be worth it. But it's your cells and your battery.
So your cells are mostly balanced at the bottom. I agree with Sgt Raven. Active balancing might get you where you want to be, but there is nothing like parallel top balancing and the method he posted is popular and fairly quick compared to the regular method.
Sgt Raven
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I only had four 280AH cells and it took me 3 days to top balance them without doing anything special. I started out with my dual channel 5A per channel power supply hooked up wrong and only throwing 5A for 2 days. I got that worked out with some help on here and finished them off in one more day. So it would have taken less than 3 days if I started off with it hooked up correctly. At 10A, you should have been able to top balance them at 4 a time in 18 days or less. 6 groups of 4 might have taken 12 days total, if my case played out with yours. Since I really did 2 days at 5A and one at 10A.
Who knows, I could be FOS, too. I'm just spit balling here.
ETA: from 3.29V to 3.40V took forever. Then from 3.40V to 3.65V was super fast.
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It took me a little more than 5 days to top balance my eight 280ah cells. IMO it was worth every minute of it. I used the 12 amp version of the Riden.
The latest version of the Overkill manual is awesome and explains top balancing. There are many other sources and well. One of my favorites is Nordkyn Design. That one should be required reading for all beginners...lol.
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