Battery bank question

6 posts / 0 new
Last post
Icon
Offline
Last seen: 1 week 3 days ago
Joined: 08/18/2013 - 19:31
Posts: 240
Location: AR
Battery bank question

I am building a bank, and I have some new unused 18650s Panasonics, but bought at different times. Do these need to be matched somehow, or just installed and charged? Never having built a bank, what do I need to know?
Batteries are protected, and bank holds seven batteries in parallel.
Thanks……

kramer5150
kramer5150's picture
Offline
Last seen: 2 weeks 2 days ago
Joined: 05/19/2010 - 13:43
Posts: 1811
Location: Palo Alto CA

I have never build a bank before myself. IMHO its always a good idea to measure actual capacity of your cells if you can. It also doesn’t hurt to use them a bit and cycle them a couple times just to make sure they hold charges and deliver current. My hobby charger has a .5A discharge test that counts amp-hours, and its a decent way to approximate capacity of individual cells.

L4M4
L4M4's picture
Offline
Last seen: 17 min 6 sec ago
Joined: 12/08/2013 - 13:43
Posts: 1025
Location: Germany

If you put all of them in parallel – it doesn’t matter too much.

Only in Series they should be all pretty much the same in capacity and internal resistance

Barkuti
Barkuti's picture
Offline
Last seen: 2 hours 28 min ago
Joined: 02/19/2014 - 14:46
Posts: 1676
Location: Alhama de Murcia, Spain

Just make sure the cells are in a more or less close state of charge (voltage) before connecting them in parallel to avoid any heavy current inrush. This is unlikely to be really harmful, though. 

You may want to remove the protection circuitry in the cells, costs you a slight performance loss and the powerbank circuitry does that automatically. It is possible you may have to do it because the cells don't fit in the box anyway.

 

Ronin42
Ronin42's picture
Offline
Last seen: 22 hours 1 sec ago
Joined: 12/17/2014 - 22:17
Posts: 1537
Location: Alameda, CA

Minor point.

But maybe it was implied they should be the same model aka capacity.

If the bank your building as opposed to assembling will have cells in series then your into either a balance charger or balance circuitry in the bank proper.

If not going to go with any balance circuitry then try “bottom balancing” as opposed to full charged. Because it is more important to have them run down to the same voltage as opposed to charge up to the same voltage.

I’m not an expert but I did run in to the concept and it seems to make sense.

(“It’s good that most people can’t remember their previous lives. Otherwise
things would be a lot more complicated than they already are.”
Ajaan Lee Dhammadharo)

Icon
Offline
Last seen: 1 week 3 days ago
Joined: 08/18/2013 - 19:31
Posts: 240
Location: AR

Thanks for the replies guys… I know I’m getting smarter, cause I’m always learning that there’s stuff I don’t know.