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| Connecting different-sized lithium batteries in parallel. |
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| xani:
Hi, I have a bunch of batteries (from recycling used laptop batteries) that are fine (tested for excessive self discharge and such), same type but of varying capacity (say ~20-30% difference). I want to connect around 6 of them. Due to nature of use (it's a backup power supply for rPI) I do not really care about max current or getting full capacity out of every cell. My gut tells me they will just charge/discharge proportionally to their capactity and as long as I match voltages to avoid battery-to-battery flow during connecting it should be fine. Am I missing something ? |
| Wimberleytech:
--- Quote from: xani on November 05, 2019, 04:33:06 pm ---Hi, I have a bunch of batteries (from recycling used laptop batteries) that are fine (tested for excessive self discharge and such), same type but of varying capacity (say ~20-30% difference). I want to connect around 6 of them. Due to nature of use (it's a backup power supply for rPI) I do not really care about max current or getting full capacity out of every cell. My gut tells me they will just charge/discharge proportionally to their capactity and as long as I match voltages to avoid battery-to-battery flow during connecting it should be fine. Am I missing something ? --- End quote --- I would not put them in parallel unless they were mounted in a fireproof box! |
| xani:
--- Quote from: Wimberleytech on November 05, 2019, 09:03:56 pm --- --- Quote from: xani on November 05, 2019, 04:33:06 pm ---Hi, I have a bunch of batteries (from recycling used laptop batteries) that are fine (tested for excessive self discharge and such), same type but of varying capacity (say ~20-30% difference). I want to connect around 6 of them. Due to nature of use (it's a backup power supply for rPI) I do not really care about max current or getting full capacity out of every cell. My gut tells me they will just charge/discharge proportionally to their capactity and as long as I match voltages to avoid battery-to-battery flow during connecting it should be fine. Am I missing something ? --- End quote --- I would not put them in parallel unless they were mounted in a fireproof box! --- End quote --- And why exactly? They were in parallel to begin with, just in pairs of 2 |
| mariush:
Can you sort them out by capacity and then use 3 of the lower capacity in parallel, and then in series with two of the higher capacity in parallel ? Use a switching regulator to step-down to 5v. |
| xani:
--- Quote from: mariush on November 05, 2019, 10:47:26 pm ---Can you sort them out by capacity and then use 3 of the lower capacity in parallel, and then in series with two of the higher capacity in parallel ? Use a switching regulator to step-down to 5v. --- End quote --- Can't, the device I'm using it with (UPS Pico, a raspberry Pi ups board) is the one doing the charge/discharge and it supports only single cell work. |
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