Discharging: Constant Current vs Duty Cycle

[SilverFox]

The question has occasionally come up wondering if a batteries capacity is different during a constant current discharge verses pulsing it off and on like we normally use our flashlights.

I have been playing around with the new CBA software, and one of the features is that you can set it to discharge according to a duty cycle. I set this duty cycle to 1 minute on and 1 minute off.

This battery pack is one of my TigerLight battery packs that has developed higher internal resistance and has been retired. Hence the (bad) in the title. It was interesting to watch the voltage drop as the load was applied.

At any rate, here is the graph.

Tom

 

[Bullzeyebill]

Tom, what would that graph look like if you used one of your "good" battery packs? Would we see a recovery of the pack, instead of the steady drop you see with the "bad" pack, with each turn on.

Bill

 

[SilverFox]

Hello Bill,

The good packs hold 7.0 - 7.2 volts during the constant current discharge. I would imagine that the duty cycle would be similar with less drop in voltage when under load.

Tom

 

[Cemoi]

Thanks a lot Silverfox, this is exactly what I was waiting for, see this thread.

I'm looking forward to similar plots with your best performing NiMH

 

[SilverFox]

Hello Cemoi,

Don't hold your breath...

While it usually takes 15 - 20 minutes to put together a discharge graph with the various notations, this particular plot ended up being a lot more complex. It actually took more than 2 hours to get it to the point where I could show the comparison.

I may find time to throw one in from time to time, but don't expect them on a regular basis.

Tom

 

[Bones]

Thanks SilverFox.

Theory is all well and good, but your real world examples are far good-er.

 

[Burgess]

Very interesting graph, SilverFox.

:thumbsup:



Wish you had time to test an Alkaline AA cell, in that manner.


Not to mention, Eneloop AA.


And Energizer Lithium L91 AA.



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[Cemoi]

I may find time to throw one in from time to time

A couple of comparisons (e.g. on the Eneloops, and on high capacity AA NiMH cells like the Maha Powerex 2700) would do.
I wonder if the "bonus Wh" - which seem to be granted by allowing the battery to rest - are real bonus, or if they are only "borrowed" from the total Wh provided by the batery. In other words, is the total energy that can be squeezed out of a battery independent from the discharge pattern?

 

[Burgess]

That's precisely what i've always wondered.


Is anything truly being gained, by letting a cell "rest" ?


Inquiring Minds wanna' know.



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