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Mixing Lion Energy UT 1300 and BigBattery 170Ah Battery

JAO

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I recently installed 2 Lion Energy UT 1300 105Ah LiFePo4 batteries in parallel in my motorhome. I have decided to add one more battery also in parallel. My first instinct was to simply buy a third UT 1300 to add to my existing bank, but after watching Will’s recent video on the SOK and BigBattery 12 volt LiFePo4 offerings I thought I might add a BigBattery 170 Ah instead of a third UT 1300. Both are built with prismatic cells and have their own BMS. Would mixing these two different batteries in parallel be acceptable? I called BigBattery and asked them. Their response is “not recommended.” They mentioned that it might cause an inbalance in discharging or charging cycles resulting in premature failure of one or more of the three batteries. What would be the pros and cons, and risks of going forward with mixing the two? Is BigBatteries concern legitimate? Thanks for the help!
 
IF they are both the same voltage and chemistry, and you conduct best practices per the "Wiring" in link #2 in my signature.

Different capacity batteries will share different portions of the load. Thus, the imbalance and premature wear.
 
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IF they are both the same voltage and chemistry, and you conduct best practices per the "Wiring" in link #2 in my signature.

Different capacity batteries will share different portions of the load. Thus, the imbalance and premature wear.
Thanks for your input I’m new here and don’t quite understand how to see/find the link #2 you mentioned. Could you please tell me how? Thanks again.
 
Now I see it. Thanks!
Ok, I’ve read #2 and the others. Then I reread your first answer. The two Lion Energy UT 1300 (105Ah each) and the BigBattery 170Ah battery are both prismatic cells and 12.8 vdc at full charge. Same chemistry, same voltage, different capacities. You mentioned this circumstance would cause imbalance and premature wear. How big of an issue would that be in this case? Is it correct to assume that charging the three in parallel would not be a problem since they each have their own BMS? Would the imbalance and premature wear be a big issue or a small one? Are we talking a few percent reduction in life, or a significantly bigger reduction? Thank you again, and anyone else that can shed light on this.
 
Bigger issue with high currents. Charging is generally a lower current compared to peak discharges, so charges will typically be less of an issue.

SWAG: "premature" might be a 10% reduction in cycle life of the battery that handles more than its "fair share" of the load.

I would personally choose to do this to increase capacity rather than purchase a matching set. I'm cheap as crap and pretty lazy. Hate having money (resources) laying around doing nothing.

Once established, I would test it under a heavy load and hope that the share of current is roughly equivalent to the ratio of capacities with the BigBattery taking about 60% of the total.

Note that the wiring in the batteries themselves may influence current sharing.
 
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Assuming the packs are wired in parallel, they will always be at the same voltage. The issue will be that there will be eddy currents between the packs as they charge and discharge. If there are large capacity differences these currents could cause one of the BMSs to cut out. I suspect one of the "best practices" mentioned above is to monitor those currents and to use the combined packs in such a way that the eddy currents are reduced to a safe level.
 
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Assuming the packs are wired in parallel, they will always be at the same voltage. The issue will be that there will be eddy currents between the packs as they charge and discharge. If there are large capacity differences these currents could cause one of the BMSs to cut out. I suspect one of the "best practices" mentioned above is to monitor those currents and to use the combined packs in such a way that the eddy currents are reduced to a safe level.
Thanks for responding. Regarding the last sentence in you reply, practically how would one go about doing this?
 
Bigger issue with high currents. Charging is generally a lower current compared to peak discharges, so charges will typically be less of an issue.

SWAG: "premature" might be a 10% reduction in cycle life of the battery that handles more than its "fair share" of the load.

I would personally choose to do this to increase capacity rather than purchase a matching set. I'm cheap as crap and pretty lazy. Hate having money (resources) laying around doing nothing.

Once established, I would test it under a heavy load and hope that the share of current is roughly equivalent to the ratio of capacities with the BigBattery taking about 60% of the total.

Note that the wiring in the batteries themselves may influence current sharing.
Thanks. Would the BigBattery comprise about 60% of the discharge load even when it is connected to 2 of the 105Ah in parallel? Meaning the bank would be a total of 3 batteries in parallel, a 105Ah + another 105Ah + a 170Ah.
 
practically how would one go about doing this?
I would look at the pack sizes in Ahrs and look at the max draw of devices connected to that mixed pack. If the differences are small and the pack is not used hard it is probably not an issue. If there was a draw greater than one of the packs, I would put current shunts on each pack to get a sense for what those eddy currents amounted to. As mentioned earlier the smaller pack will probably wear out earlier and its capacity will be reduced. As that happens the eddy currents will get larger.
 
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Thanks. Would the BigBattery comprise about 60% of the discharge load even when it is connected to 2 of the 105Ah in parallel? Meaning the bank would be a total of 3 batteries in parallel, a 105Ah + another 105Ah + a 170Ah.

No. Sorry. 170/(170+105+105) = about 45% of the load. I missed the 105Ah.
 
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If I might expand on this a bit, If you have two separate battery blocks of different size ((and possibly different chemistry) that are not wired in parallel, with each feeding a different inverter (example system one: 206 amp SOK 12 v tied to a 600 watt pure sine inverter and subsequent circuit. System two: 4 - 6 wet cell GC batteries 2p2s to output 12v connected to a 2000 watt inverter/charger feeding a separate circuit). Can both be connected to the same charger (110vac or solar) without issue? With different system the draw would vary between the two battery banks but the converter charging them shouldn't care, correct? The SOK has a BMS that will cut off charge at full. The Lead Acid will continue to trickle charge to maintain. Am I missing something? If the Lead Acid are eventually replaced with say a BigBattery 170 AHr 12v system. As long as they remain separate, should there be no degradation of the batteries due to balance?
 
No. The charger connection puts the batteries in parallel, so any voltage disparity between the two banks would result in a current surge between them.
 
so, Snoobler, I would need a separate charger as well to keep the two systems completely separate?
 
If this is so, than is it correct to say that in all cases you must keep all batteries in a system (power source/ battery block/ inverter/ charger /output) the same? In other words; If you start with SOK 206 AHr 12v you can only add SOK 206 AHr 12v; if you start with BB 100AHr 12V you can only add BB 100AHr 12V etc. (this is assuming Parallel installation so you are only increasing capacity not changing voltage) OR instead is it that if you start with 100 AHr 12v LiFePO4 you can only add 100 AHr 12v LiFePO4 (but it is not necessary that the Brands be the same)>
 
Snoobler, I reread the entire thread twice. Please forgive my slowness but I am just trying to clarify the points noted in my post yesterday. Mainly that being whether or not battery banks need to be of all the same size, voltage and chemistry to work together in balance or so they need to also be the same brand/model as well.
 
If you read posts #2 and #7, you can't possibly have drawn the conclusions you did or still have the same questions.
 
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