Batteries in parallel with different amps on positive and negative

daromer

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But the negative and positive leg of each cell will ALWAYS have the same current ;) That doesnt change no matter what type of cell you have or how it flows. As also shown by Wolfs details about how current flow between cells not with same capacity.
1617027120879.png

As shown on the image you shoud only meassure at the red lines. If you check anywhere else you get different values. As said think of each wire as a resistor and you can calculate it with U=I*R
 

daromer

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Cheap 4-life

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Yes, usually amps in is the same as amps out.. but when charging-discharging and batteries of different capacities-resistances in parallel are happening this isn’t true. The higher capacity batteries are essentially charging (raising voltage) the lower capacity batteries thru circulating current that goes thru the busbars. Whether or not it’s shown on the positive or negative depends on which way the amps are flowing due to charging or discharging. It’s no going up in thin air. The extra amps (from the higher capacity batteries) is charging the lower capacity batteries.
 

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But the negative and positive leg of each cell will ALWAYS have the same current ;) That doesnt change no matter what type of cell you have or how it flows. As also shown by Wolfs details about how current flow between cells not with same capacity.
View attachment 24451
As shown on the image you shoud only meassure at the red lines. If you check anywhere else you get different values. As said think of each wire as a resistor and you can calculate it with U=I*R
Yes I measured at the red lines
 

daromer

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Then im pretty sure there is a measurement error to be honest. It must be or else you have energy dissapearing in nowhere and invented a black hole :D Clamp meters to me is prone to give weird numbers in some cases and yours arent far off from what i have seen. Especially with cheaper ones.
 

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Daromer, wolfs detail you are referring to how batteries of different capacity act., the batteries need to also have different internal resistance or the amp differences I’m showing wouldn’t happen.
 

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Well I’m off to work. All I can say is bench test it yourselves and you will see the exact same reading I see
 

daromer

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Im sorry but no we wont get that reading unless its something wrong. The energy flow must be equal on both sides for physics to work out.

I have done it many times with clamp meters on both neg/pos and other especially when doing solar panels where you can have 20 wires in same and then you always look at the same pos vs neg values and you always find them within spec of the clamp meter. Except if you have to migh disturbance and your clamp meter offsets wrongly.

You can have different currents going into each cells as shown by tests by Wolf and also of course standard based on u=i*r. Same is with currents on negative end vs positive end on a cell. Its always the same meassured.

Feel free to draw up or show on a video and we might be able to pin point the error in the test or if we dont just understand what it is you test. But if you test as i show in image above it is the same except clamp meters tend to vary alot.
 

Maarten

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I think it is a more complex situation.
First of all the internal resistance of the battery dictates the current of the battery, not perse the capacity of the battery. Albeit that there is a relationship between the two were usually the internal resistance is lower in a larger battery.
R=U/I -> I = U/R.
Plus because the batteries are parallel the voltage "must" be the same. When the current draw on one cell is larger due to a different internal resistance and subsequently the voltage of that battery drops, I can well be that the other parallel battery starts to 'charge' that battery. And therefor the sum of the amperage of all cells might not be equal to the total on the pack level.

I think.....
 

daromer

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Yeah sum of each battery compare to total can be complex but measuring in and out from a single cell is always the same :)

Wolf have good graphs showing the tricky part when you have different cells but it all sums out in the end measuring currents int the circuit itself.
 

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In that case all the above discussion is all for nought.:cry:
I’m sorry. To me it makes sense and no further testing is needed. The only way a higher capacity battery can balance-bring up the voltage of a lower capacity battery is to supply it with amps when they are all in parallel. If discharging the battery bank the lower capacity battery will drop in voltage slightly sooner than the higher capacity battery. The higher capacity battery then sends amps into the lower capacity battery. If the battery bank is being discharging then the power flow thru the batteries is coming out the positive and in the negative. Therefore the only way for the lower capacity battery to receive the amps from the higher capacity battery (due to the direction of power flow when discharging) is thru the negative. And that what my tests showed me.

If anyone else is interested and has the time to test this for themselves, I’d like to here about their results
 
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ajw22

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Yes, usually amps in is the same as amps out.. but when [...] this isn’t true.

May I be the first to congratulate you for having discovered new Physics. Write to all professors and publishers to have their books of the last few hundred years re-written, and submit yourself for the Nobel prize.
Seriously: current IN is _always_ _exactly_ the same as current OUT with a battery. It's such fundamental Physics, it's non-negotiable. If you're seeing something else, then you have bad measurements, or current is leaking somewhere past the sensor. It doesn't matter if the battery is connected in series, parallel, charging, discharging, short circuited, or even burning.
 

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I e
May I be the first to congratulate you for having discovered new Physics. Write to all professors and publishers to have their books of the last few hundred years re-written, and submit yourself for the Nobel prize.
Seriously: current IN is _always_ _exactly_ the same as current OUT with a battery. It's such fundamental Physics, it's non-negotiable. If you're seeing something else, then you have bad measurements, or current is leaking somewhere past the sensor. It doesn't matter if the battery is connected in series, parallel, charging, discharging, short circuited, or even burning.
i explained where the amps from the higher capacity battery to the lower capacity battery are going and why they can’t be seen on the positive but are seen on the negative of the lower capacity battery when discharging.
Also explained why when charging the amps from the higher capacity battery into the lower capacity battery are seen on the positive instead of on the negative like when discharging.
It’s not a big deal. I now know which of my batteries have a lower capacity. I’m seeing the difference on positive-negative only on the lower capacity batteries. makes complete sense to me why when charging (instead of discharging) the amps going into the lower capacity battery from higher capacity battery are seen on the opposite polarity due to the amps moving in a different direction. This confirms that there’s nothing wrong with my clamp meter or my test.

I’ll do one better. I’m about to add 2 higher capacity batteries (higher than any of the four I have) to my battery bank. I’ll be removing the two lower capacity batteries in question and replace them with the new higher capacity batteries. I’d bet the house that my clamp meter will then show that battery 1 and 2 (the higher capacity batteries out of the 4 I have now) will then have different amps on the positive and negative because they would then be the lower capacity batteries of the 4. But that still might not convince everyone or anyone but that’s ok with me
 
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Wolf

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So this is too serious of a topic to dismiss into oblivion.
This is a video I made and I am no video maker but it shows the amperage on both the neg and pos of 2 batteries in parallel.
You have seen my setup but here it is again.
1617066880250.png
Both of which are 14s80p. This is done at night with no solar input and the house running on batteries.
The inverters are drawing off of both batteries.
Battery 1 is the "Frankenstein" my first build and battery 2 is the LG pack all same 2600mAh cells,
Battery 1 tested at 185Ah with a 8.549mΩ IR.
Battery 2 tested at 207.02 Ah with a 6.1mΩ IR
I actually had to create a youtube channel. Man what is wrong with me.
Here is the video. Remind me next time to do landscape.

Wolf
 
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Cheap 4-life

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So this is too serious of a topic to dismiss into oblivion.
This is a video I made and I am no video maker but it shows the amperage on both the neg and pos of 2 batteries in parallel.
You have seen my setup but here it is again.
View attachment 24460
Both of which are 14s80p. This is done at night with no solar input and the house running on batteries.
The inverters are drawing off of both batteries.
Battery 1 is the "Frankenstein" my first build and battery 2 is the LG pack all same 2600mAh cells,
Battery 1 tested at 185Ah with a 8.549mΩ IR.
Battery 2 tested at 207.02 Ah with a 6.1mΩ IR
I actually had to create a youtube channel. Man what is wrong with me.
Here is the video. Remind me next time to do landscape.

Wolf
I knew you would test it. I will be subscribing to your channel.
Couple things. Your meter is showing amps jumping around quite a bit. Was your load varying that much. The amp differences when I check isn’t much between the polarities. As I said it was only just over 1 amp. When discharging it was 5.7 and 7.2, on the lowest capacity battery. So only 1.5amps different. Other times I checked with the meter it was only 1.3amps. I seen your meter varying by roughly .5 amps. My batteries might have capacities slightly more different than the batteries you are testing. Also your wires are all really close together. Mine are a couple feet apart. I think other wires could be causing your meter to have some interference- inaccurate readings.
 
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Wolf

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Yes my load changes consistently that much as my boiler and radiant heat circulation pumps and various devices turn on and off.
You can see that by my batrium amps doing the same thing. Wires close together on a clamp meter do not affect the results of the field that is inside the clamp. Otherwise they would be totally useless if wires close to them would interfere.
Wolf
 

Cheap 4-life

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So this is too serious of a topic to dismiss into oblivion.
This is a video I made and I am no video maker but it shows the amperage on both the neg and pos of 2 batteries in parallel.
You have seen my setup but here it is again.
View attachment 24460
Both of which are 14s80p. This is done at night with no solar input and the house running on batteries.
The inverters are drawing off of both batteries.
Battery 1 is the "Frankenstein" my first build and battery 2 is the LG pack all same 2600mAh cells,
Battery 1 tested at 185Ah with a 8.549mΩ IR.
Battery 2 tested at 207.02 Ah with a 6.1mΩ IR
I actually had to create a youtube channel. Man what is wrong with me.
Here is the video. Remind me next time to do landscape.

Wolf
Were those batteries in the video paralleled? Seems like they are in series
 

Wolf

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If both of my 14s80p batteries were in series I would be running at 48v nominal x2 which would be 96v.
So ah no they are 2 batteries each 48v nominal in parallel.
 

Cheap 4-life

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My mistake. Missed that you said 14s.

I think an important thing to realize is that the amp differences I’m seeing on the lower capacity batteries polarity is not a lot. It’s not like it’s 5amps. But the difference is there. And the higher amps does switch to the positive when charging on the lower capacity battery. The polarity amp differences aren’t there on the higher capacity batteries.

It doesn’t take much current at all for a higher capacity battery to raise the voltage (of a paralleled battery) the small amount needed to constantly keep the lower capacity battery at the same voltage. Varying loads slight difference in wire lengths, connections etc can make the amp polarity differences hard to see.

Also the amp differences are more significant (still only around 1.3amps) on the first battery I got for the bank. It is the oldest (from a 2015) and more mileage. The next oldest 2016 with similar miles has close to the same amp differences on its polarity but slightly less, like .8amps. And lastly the 2 higher capacity batteries are the same year 2018 (from same car) with less miles than the first 2. There isn’t any amp differences on the polarity of those 2 higher capacity batteries

When I checked the amps with a higher discharge and charge (roughly 12amps on each battery) the amp polarity differences are still the same small amount
 
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