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Old Sep 17, 2014, 09:53 PM
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United States, PA, State College
Joined Aug 2014
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Discharging a lipo back into another power source

Here's a scenario. Say you charge up a group of LiPos and, for whatever reason, plans change and you aren't able to use them all within a reasonable time. Standard procedure suggests discharging them to storage levels to extend battery life. But discharging them using a charger is wasteful, because all that energy is just released as heat by the charger. While it might not be much energy lost per discharge, it will add up over time.

That said, there has to be a less wasteful method. Can you discharge the battery back into a power supply, for instance, a 12V Pb marine/moto battery or a portable power bank, rather than having the charger waste the energy? If so, how? Any links?

I'm POSITIVE I've seen a link on how to do this somewhere, but I cannot find it anywhere now.
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Old Sep 17, 2014, 10:17 PM
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hoppy's Avatar
Space Coast
Joined Oct 2000
20,912 Posts
Sure -
http://www.rcgroups.com/forums/showt...r#post15248986

I use that method with used/unused packs after flying.
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Old Sep 17, 2014, 10:49 PM
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United States, MN, Eden Prairie
Joined Oct 2008
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My iCharger has a regenerative discharge function that will put the charge back into the pb battery connected to the input.
Shown here starting at time 5:40
iCharger 106B+ Review and Features (9 min 50 sec)
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Last edited by Rhea; Sep 17, 2014 at 11:01 PM.
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Old Sep 17, 2014, 11:25 PM
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United States, PA, State College
Joined Aug 2014
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Yes! The iCharger is, specifically, where I now remember seeing that feature. Thanks for the info. I want to upgrade from the iMax B6 soon anyway.

In the meantime I might use that poor man's resistor-based solution.
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Old Sep 17, 2014, 11:38 PM
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Georgia
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The problem with "regenerative discharge" is the ability of the charging source battery to absorb a charge. Most automotive Pb batteries can only handle a 6A or less charge rate.
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Old Sep 18, 2014, 03:03 AM
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Upper Hutt, New Zealand
Joined Apr 2006
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Quote:
Originally Posted by kamikazeknifer View Post
While it might not be much energy lost per discharge, it will add up over time.
True...

But something like discharging half of a 4000mah 4s would be 28 watt hours. How many times do you think you'll use it? A thousand times? If you want to come out ahead you better not spend more than about $7 on this project. And that's using my electricity prices, if you're in the US most places you're going to have to spend more like under $4. And that kind of price you you're going to lose money if you have to solder up a new connector.

Now, 10,000 times? $40 you might be able to get a charger for that... That's discharging say 5 batteries every day for about 5 years.

If you're worried about the discharging being wasteful then trying to develop an alternative is far more wasteful.

Now, if you think it will be fun. Then cool. Go for it.
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