Different current draw

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doublebubble asked Jun 28, '24

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.

inverter current draw

20240629-093437.jpg (7.4 MiB)

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klim8skeptic ♦ commented · Jun 29 at 01:35 AM

@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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Answer 1 · 2024-06-29T01:56:46Z

doublebubble answered · Jun 29 at 01:56 AM

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 ♦ commented · Jun 29 at 04:06 AM

@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 klim8skeptic ♦ commented · Jun 29 at 04:41 AM

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 ♦ doublebubble commented · Jun 29 at 05:04 AM

@doublebubble

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

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doublebubble JohnC ♦ commented · Jun 29 at 05:26 AM

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

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JohnC ♦ doublebubble commented · Jun 29 at 05:59 AM

@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 JohnC ♦ commented · Jun 29 at 07:17 AM

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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