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One of my projects require a hefty amount of amperage - and as such I want to use 2 LiPo 2S batteries, in parallel. In addition, I am regulating the voltage using multiple DC-DC step down converters ("UBEC" - https://www.hobbyking.com/hobbyking/store/__4319__TURNIGY_3A_UBEC_w_Noise_Reduction.html).

The 'trivial' approach would be to use parallel the batteries while being used (and charge them separately). Does this present potential cell imbalance issues/dangers? How does this behave with the multiple DC-DC converters?

Since I am using at least 2 DC-DC UBEC converters, I was thinking maybe I can get away with just connecting the 2 batteries negative terminals together, having each battery power half of my load. Would this work? Do I need to join the negative/"ground" terminals at the battery or after the DC-DC converters?

Thanks!

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I don't have time to answer your whole question, but probably the most important part is regarding the batteries. Putting the the batteries in parallel is OK if they are the same capacity and age and the same charge when they are put together.

Simply connect positive to positive and negative to negative and you are done. You do not have to take them apart to charge them. They will immediately balance as they charge with respect to being in parallel. The batteries in series still need to be balanced. You can consider the two batteries that you have connected in parallel as just one larger capacity battery and then continue with your project and make your connections as needed.

Hope this helps.

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  • \$\begingroup\$ Thank you. This solves the battery issue, leaving me with the DC/DC converters problem. To my understanding they cannot be paralleled. The remaining question is whether I need to connect their ground/neg terminals together, or because they both feed from the same battery(/batteries), this is not required. \$\endgroup\$
    – eranrund
    Apr 22, 2014 at 17:40
  • \$\begingroup\$ @eranrund -I am sorry, but I can't seem to figure out exactly how you are trying to connect the dc-dc converters. Maybe if you describe it in a different way I might be able to help. \$\endgroup\$
    – Filek
    Apr 22, 2014 at 23:22
  • \$\begingroup\$ thanks, let me try to elaborate. My setup consists of 2 LiPo batteries and 2-3 DC/DC converters. This powers a control board and few LED strips. The current consumed by the strips exceeds the 3A a single DC/DC converter can provide, so I would need to use a few of those. One of the DC/DC converters would power the control board and a few LED strips, while the other one would power the rest of the strips. All strips are controlled from that control board. In addition, I would like the control board to be able to monitor the 2 battery voltages. I hope this gives a better picture. Thx! \$\endgroup\$
    – eranrund
    Apr 24, 2014 at 2:46

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