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doublebubble asked

Different current draw

Asking for advice, we have 3 x 240ah lithium batteries connected together as per the crude drawing attached but this basicallywhat we have, all cables are 70mm2 and of the same length connected to busbars, I haven't shown the fuses but all batteries are individually fused also a 400amp T class fuse at the multiplus, all batteries are at the same state of charge I.e. 13.5v but I'm seeing a different current draw between battery one and the other two, as an example, battery one may have a draw of 0.31v as compared to battery 2 & battery 3 measure a draw of 0.16v, do I need to be concerned? or do I need to reconfigure some wiring.20240629-093437.jpg

inverter current draw
20240629-093437.jpg (7.4 MiB)
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klim8skeptic avatar image klim8skeptic ♦ commented ·

@doublebubble it's unclear if you are measuring voltage or current. confirm.

have you fully (and I mean FULLY) charged each battery?

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doublebubble answered ·

Thanks for the reply, just to be clear I am not an electrical expert, the batteries have been in for 10days now and when fitted all three were at 13.31v, I'm only measuring the current from each battery on their individual cables with a clamp meter, at every single connection from each battery, through the fuses to the multiplus all measure 13.5v, is my configuration of paralleling these batteries correct.

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klim8skeptic avatar image klim8skeptic ♦ commented ·

@doublebubble Given your battery leads are all the same length, current should be about equal. As long as the cable lugs are clean, flat, free from burs and torqued properly.

all batteries are at the same state of charge I.e. 13.5v

Just because the batteries all read 13.5v, does not mean they are all at the same Soc. Differences between Soc can give different current measurements.

Hence the question, have you fully charged the batteries?


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doublebubble avatar image doublebubble klim8skeptic ♦ commented ·

All batteries are at the same state of charge? Now I see your point, is it feasible to disconnect down to one battery and charge it with the multiplus one at a time then reassess as that is the only lithium charger apart from the solar. Hopefully it's not a connection issue as all leads, crimps, equipment are all brand new, I can say there was a certain amount of care putting this together but maybe the battery charge was overlooked.

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JohnC avatar image JohnC ♦ doublebubble commented ·
@doublebubble

Check the resistance over your individual fuses too. This may be contributing to the imbalance you see.

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doublebubble avatar image doublebubble JohnC ♦ commented ·

How can U check each connection for resistance? I only have the basic electrical tools, multimeter, clamp meter etc.

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JohnC avatar image JohnC ♦ doublebubble commented ·
@doublebubble

Your multimeter should have Ohms. But remove any source of V if testing in situ. Or remove the fuses to test them. You're not looking for much difference here, so be methodical.

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doublebubble avatar image doublebubble JohnC ♦ commented ·
Yeh gotcha, thanks for the tip, I'll do as you mentioned and see if something shows up, I guess I'm just looking for a higher resistance reading at each terminal and fuse + holder. On a side note would it be the connection between the higher current draw battery run to the positive busbar, as no.1 battery has the higher current draw.
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doublebubble answered ·

I need to revisit my original question as I'm still seeing a different current draw, as per the suggestions above I have gone through it all with no indication that there is an issue with the wiring/connections, yesterday I was running our hot water service which has a 1200w 240v element, measuring the current draw from each individual battery came in at no.2 & no.3 battery having a current draw of 20.2amps whilst no.1 battery had a current draw of approximately 12amps, can anyone shed some light on why? Should I be concerned? What is confusing is that after a couple of weeks into the use of the system it was the other way around with no.1 battery drawing twice as much as no.2 & 3 so for some reason that has reversed with no change in the set-up, could no.1 battery have an internal fault? Each battery has its own internal BMS.

Thanks in advance

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