I'm trying to create a 2s3p battery pack for a robot. I have 6x Eastshine e35 cells (which is a protected version of LG MJ1 cells). Is a 2s3p pack out of protected cells used with a balance/smart charger the same as a 2s3p cell with a BMS system? Is it going to be equivalent in terms of safety and performance ?
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\$\begingroup\$ Your protection will not balance the pack whereas a good BMS will balance it. Saftey-wise, there is not much difference but in terms of performance and long life, there is. \$\endgroup\$– winnySep 9, 2016 at 7:48
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1\$\begingroup\$ @winny : he's adding a "balance/smart charger" to the "protected cell" option, and comparing it to a "BMS system" so the first option isn't merely protected cells. I think it would be a fair question to ask what these terms mean, but it needs links to the product datasheets. \$\endgroup\$– user16324Sep 9, 2016 at 9:35
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\$\begingroup\$ yeah. I will be still balance charging it using a balance charger. The question is that if this setup should be equivalent to a bms setup. here is the battery specs link. I plan to use a 2s3p setup and include the balance JST plug to charge using this charger: link \$\endgroup\$– Geraldo RamosSep 9, 2016 at 15:02
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\$\begingroup\$ Oh! That's quite a different question. \$\endgroup\$– winnySep 10, 2016 at 22:36
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\$\begingroup\$ It is not equivalent, for sure. In a BMS, there is one charge FET and one discharge FET. If the discharge FET turns off, then the whole pack is prevented from discharging. And similarly for the charge FET. In the pack you propose, each cell has a charge and discharge FET with separate autonomous control. Maybe under some conditions, one cell could have its protection circuit cut out for some reason, while other cells remain in-circuit. I think you can see that this would then create a major imbalance during charge or discharge. I don't know that this is likely, but it seems possible. \$\endgroup\$– user57037Oct 4, 2017 at 4:45
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2 Answers
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Personally I would go for a battery pack with protected cells and balance charger and a BMS. Generally protection built into batteries is really a lat resort for protection and safety and shouldn't be depended upon. A BMS will make sure nothing bad happens to the battery and balance charging them will ensure that everything is balanced and back up the job of the other two safety features.
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I have used 3s4P lithium-ion batteries for similiar application with only balance/smart charger. Nothing bad happenned but since I am dealing with BMS, I understood thah I was only lucky. So, as I understand from your battery, all cells are individual so you have access all nodes. Buy a simple passive cell balancing card for 2 cells and use it. For parallel battery cells, BMS is not needed.
