capacity testing

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renton83
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capacity testing

Since discovering I can salvage 18650 cells from old laptop battery packs I have wanted a way to accurately measure what condition they are in. I’ve been reading on measuring capactity and some chargers claim to measure it but from what I see they just measure internal resistance for the most part. I have seen this cool device for only a few bucks but it seems to be a great way to accurately measure capacity, anyone here have experience with something like this. tester

XXX-Man
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I have one like that and it’s not really accurate. But it can give you some general info about capacity.

You can get Liitokala Lii-500 and you get good capacity test and good charger for low price.

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renton83
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I already have a few good chargers I just want a dedicated tester. So for a accurate test you want a variable resister that changes resistance as the current drops?

XXX-Man
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renton83 wrote:
So for a accurate test you want a variable resister that changes resistance as the current drops?

Not really.

This one measures current, time and voltage and calculates Ah. This should be enough to get good reading.
One I have and looks the same just doesn’t do some of the measuring or calculating as it should and gives weird readings sometimes.

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renton said, …I have wanted a way to accurately measure what condition they are in.

What do you mean by “condition”?

To know if they are good or bad, just add a small charge up to a set voltage, e.g. 4.0, then let it set for a week and come back and measure the voltage, then another week later measure again.

If the voltage holds at the set point then it is a good cell, if it drops then the cell in not good.

If you want to know capacity over a given voltage range, then you can just measure voltage, current and time in seconds as you discharge it thru a fixed resistor. Plot out the current time history and integrate under the curve to get capacity.

L4M4
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Or just pay 20$ for a Lii-500 an let that thing do all the work while you sleep.

I also have a ton of Laptop-Pulls – I tested them all with my Lii-500 and threw all of the <2Ah cells away.

renton83
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I should have been more specific, I know which cells are good because I’ve been checking to see if they hold voltage I just want to know what capacity they have. My plan is to make power packs with them for charging devices so I want a idea of what the capacity is.

Lexel
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My best guess is getting a decent analysing charger

If you want do fast discharge tests there are some that can do 1A discharge per slot
like Miboxer C2-4000 or Opus BT – C3100 V2.2

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renton83 wrote:
I should have been more specific, I know which cells are good because I’ve been checking to see if they hold voltage I just want to know what capacity they have. My plan is to make power packs with them for charging devices so I want a idea of what the capacity is.

Do they have any wrap on them with numbers. If you can discharge them after fully charged, that will give you a exact capacity at a certain discharge current. I use a hobby charger but that may be a little more than you wanna spend to just find out the capacity of each cell. But a hobby charger will let you charge a pack probably quicker no matter if the cells are series or parallel. Just food for thought.
If you can find out the cells make and model it should be easy.
There are other ways to get a rough idea of capacity.