Allied lithium SOC meter

[Pat911]

What CP241 says is correct and will work except to better balance the current between the batteries, both batteries should be connected together with as thick a cable as practical. Then ALL positive connections (loads and charger) go to one battery and ALL negative connections go to the shunt which will be connected to the other battery.

The way you have it connected now will force the first battery to work harder than the second as it sees lower resistance to the controller.

Cheers
Pat.

[urungus]

Hi, really appreciate the advice. However I’m confused about the suggestion to attach everything to battery A, because the official diagram from Allied (ignoring the shunt for now) shows the large cables going to battery A and the smaller charging cables going to battery B:

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And a second diagram from Allied shows the 12v step down converter attached to the battery furthest from the system positive and negative. Since system positive and negative (those are the big wires, right ?) are attached to battery A, the official diagram would suggest connecting the 12v converter to battery B wouldn’t it ?

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Is Allied wrong about the wiring of their own batteries ? Or does the introduction of the shunt change things ?

[Pat911]

Allied is wrong! It will work but it is not “best practice”

The battery closest to the motor controller will bear the majority of the load current. The batteries will equalise afterward but you’re still stressing that first battery with higher currents than the others under load. Also when charging, the closest battery will charge faster than the other.

By connecting positive to one end of the parallel bank and negative to the other, you’re balancing the currents better between each battery. It will work perfectly with two batteries but with three or more it will still stress the outer batteries more than the inner ones. Still better than connecting both positive and negative to one battery though.

Cheers
Pat.

*Images courtesy of BattleBorn batteries and The 12v Guru.

[CP241]

Good point pat. I had not thought about wiring it that way. I may have to try and move my pos or neg pack lead (whichever is less work, of course ) and see if it makes any difference.

I assume it probably won’t, at least nothing really measurable as I have a stock controller/motor so current demands are “low” and I’ve got 1/0 cables bridging them together. But certainly wouldn’t hurt to try :)

[Pat911]

In theory there will actually be a performance decrease as your controller will see a slightly higher resistance to the pack. This will definitely not translate to a real world performance drop off and may actually be a performance increase as the current demand is now shared equally between the two (or more) batteries and there will be less voltage sag from the pack itself, compared to the sag the first battery may have experienced before.

Of course, without knowing battery internal resistance (including BMS) and cable resistance I am only speaking theoretically. In reality, I don't think you'll see any performance change at all, but that first battery will thank you with an increased life.

Allied may have chosen their configuration for one of two reasons:
1. Their Engineers (if they are even engineers) are inexperienced and only have theoretical, not real world experience, as this is a novice mistake.
2. Depicting the connections as in the diagrams I linked to could possible confuse the layman that it is a series connection as that's what they would be replacing, and connecting two or more 48v batteries in series and connecting them to a cart would be bad....really bad.

Cheers
Pat.

[CP241]

Originally Posted by Pat911

In theory there will actually be a performance decrease as your controller will see a slightly higher resistance to the pack. This will definitely not translate to a real world performance drop off and may actually be a performance increase as the current demand is now shared equally between the two (or more) batteries and there will be less voltage sag from the pack itself, compared to the sag the first battery may have experienced before.

Of course, without knowing battery internal resistance (including BMS) and cable resistance I am only speaking theoretically. In reality, I don't think you'll see any performance change at all, but that first battery will thank you with an increased life.

Allied may have chosen their configuration for one of two reasons:
1. Their Engineers (if they are even engineers) are inexperienced and only have theoretical, not real world experience, as this is a novice mistake.
2. Depicting the connections as in the diagrams I linked to could possible confuse the layman that it is a series connection as that's what they would be replacing, and connecting two or more 48v batteries in series and connecting them to a cart would be bad....really bad.

Cheers
Pat.

I agree with you completely and it makes total sense. I just never thought about it, I never paid attention to their diagrams. I was anxious, dropped them in and hooked them up the easiest way possible (wherever the cables were closest too lol) and it’s been that way ever since. But the more I think about it, I’m gonna move the pack + wire for sure. Less work than moving the shunt and all the negatives.

I’ve actually got some overall housekeeping to do with the wiring down there since I rewired and moved some stuff around. May as well take out that allied meter while I’m at it lol. I’ll make an afternoon project of wire management and make a date with some flex loom and zip ties

[Pat911]

Nothing like a good afternoon project I say.

[urungus]

Thanks for these great insights, does this new diagram look right ?

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[CP241]

Yes

[urungus]

Awesome. One last question, I was watching a video with a different brand of battery and they are screwing the shunt directly into the negative terminal of the battery (see attached screenshot). Is that what should be done with the Allied batteries too (I had envisioned a short thick cable connecting the shunt to the battery) ? If so, do I use the existing terminal screw that came with the battery (I am thinking it might be too short to accommodate the shunt), or is there a replacement screw that comes with the shunt ?

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