Capacitor smoothing question

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lizby
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Joined: 17/05/2016
Location: United States
Posts: 3297
Posted: 04:09pm 10 Mar 2025      

  Mixtel90 said  C=1500Ah It will discharge to end point voltage in 1 hour at 1.5A
C/20     It will provide 75mA for 20h


If the second is true, it's unlikely that the first will be true. As I understand it, that's why reliable ratings of rechargeable batteries are typically quoted for a C/20 discharge rate.

I have yet to see a Chinese 18650 battery or 12V 18650 battery pack which is rated accurately. I've been looking for a way to test this reliably--it looks like the circuit from @twofingers will do it. So there's something to be added to my already overflowing to-do list.

The LiFePO4 batteries seem generally much closer to spec.
twofingers
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Joined: 02/06/2014
Location: Germany
Posts: 1518
Posted: 04:31pm 10 Mar 2025      

  lizby said  ... --it looks like the circuit from @twofingers will do it. So there's something to be added to my already overflowing to-do list. ...





You might also look for zb2l3.I bought several from Ali-Express for about 2 EUR each. The circuit is trustworthy. The batteries to be tested can have up to 15 V. Two 7.5 ohm/5W resistors should be included. The threshold voltage (cut-off voltage is adjustable).
This is probably the cheapest solution.
Regards
Michael
Edited 2025-03-11 02:36 by twofingers
Mixtel90

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Joined: 05/10/2019
Location: United Kingdom
Posts: 7446
Posted: 04:46pm 10 Mar 2025      

Sorry lizby. :)
1500mAh of course. :)

The best bet is probably not to buy "high capacity" 18650s from China. Then you'll probably be less disappointed...
lizby
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Joined: 17/05/2016
Location: United States
Posts: 3297
Posted: 06:38pm 10 Mar 2025      

  twofingers said  You might also look for zb2l3


Thanks. I ordered a couple of those. I do like the ability of your circuit to produce a graph.
twofingers
Guru

Joined: 02/06/2014
Location: Germany
Posts: 1518
Posted: 06:42pm 10 Mar 2025      

  lizby said   I do like the ability of your circuit to produce a graph.

Yes, it really is fantastic! I like it a lot!
Regards
Michael

BTW:
I use this:
https://www.printables.com/model/646235-enclosure-for-battery-capacity-tester-hw-586/related

model for 3d-printing.

And a 1 EUR charger as a holder for the 18650 battery.

Edited 2025-03-11 05:21 by twofingers