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Home✈️Aircraft🚁HelicopterHelicopter Main Discussion › Parallel Charging batteries of different capacities...
05-10-2011 03:22 AM  8 years ago
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Spencer K

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Phoenix, Az

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Parallel Charging batteries of different capacities...
In a recent RC Heli magazine, there was an article on parallel charging lipo's of different capacities simultaneously. I have a paraboard, and have very good knowledge of charging batteries, but maybe an electrical engineer could chime in?

The magazine article states you may charge a 3s 5000, and a 3s 2200 at the same time. To determine the charge rate for 1c you do the following:
5000+2200=7200 total mah, therefore you choose 7.2A charge rate out of your charger, and theoretically they will charge in "harmony".

Does this work because the smaller pack (2200 mah) is more sensitive to the incoming current, consequently raising the voltage faster than the larger pack, so you get a parallel "current spill-off" into the larger pack? Any input/ Explanation would be really helpful to the electric community looking to cut-down on charge times.
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05-10-2011 03:35 AM  8 years ago
Tyler

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Chicagoland area

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Yep, it works as you suspect. Ive done it with great success. Saves loads of time with a x6 parallel board and high c rated packs.Enjoy things that money can buy IF you don't lose the things money can't buy.
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05-10-2011 04:15 AM  8 years ago
Justin Stuart (RIP)

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Plano, Texas

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I was told to NEVER do this because one pack will get overcharged and the other pack will get undercharged. In fact, I was told never to charge different brands with the same capacity or even batteries of the same brand of the same capacity of different ages. But you know what? If it works, then it works, right? I've just always been hesitant to try it.Avant RC
Scorpion Power Systems
Thunder Power RC
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05-10-2011 09:41 AM  8 years ago
martinic

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NB, Canada

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The charger charges to set voltage, not capacity, and the batteries are constantly equalizing their voltage; that's how it works. Connected batteries act as one.

Spencer K, your understanding echos my understanding (based on lots of reading on various forums and personal experience).
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05-10-2011 12:43 PM  8 years ago
red_z06

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Dumont, NJ

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Does this work because the smaller pack (2200 mah) is more sensitive to the incoming current, consequently raising the voltage faster than the larger pack, so you get a parallel "current spill-off" into the larger pack?
Think of 3s5000 as 3s2p2500 and it will make sense to you.
So, connecting another 3s2200 will just make it 3s3p7200.

In slow (1c) charging, even high and low impedance can deal with with it by inter pack balancing.

Think of a two same beaker inter connected at the bottom. One has very large diameter and the other is smaller so the capacity will be different. As you pour water, with two same orifice spout, the smaller will tend to fill up faster but the interconnect will try to keep the water level at same height (electrical potential or V). But, water will spill on smaller first unless you have a brim sensor that slows the water flow (current).

The brim is 4.2v and when the charger sees this (with mixed c rating packs), current will get lower even though the bigger pack with high c rating (worst case scenario) hasn't reached the brim yet. So, at slower rate, it will take longer to fully charge if mixed c rating is put in parallel. But, same c rating with different capacity will behave much like a one big capacity of the same rating.

Hope this helps.
www.JustinJee.com
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05-12-2011 02:41 AM  8 years ago
Spencer K

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Phoenix, Az

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Spencer K, your understanding echos my understanding (based on lots of reading on various forums and personal experience).
good to know im not crazy!
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05-12-2011 03:39 AM  8 years ago
Sam2b

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Tacoma, WA

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Here's a video demonstration, thanks to David Gray. As long as the cell voltages are very close and the cell count is the same, then you can parallel charge various capacity packs at the lowest C rating capable pack among all packs in parallel. But always stay in the same room to keep an eye on it for safety. Hope this video helps a bit more.

Watch at YouTube

_Sam B_
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