How to charge two, two cell packs in a plane.

[Snoopy1]

Please see the attached sketch. The sketch is showing 2 - 2 cell packs being charged as a single 4 cell pack. I believe this works and gives me an advantage of twice the amps that each pack can be charged at from the charger. Note all this came about that I was at the field and needed to charge my flite packs back up. The only charger that I had on hand was a four cell charger that could charge at a maximum of 4 amps. (FMA 4 PLUS). Yes I know I can parallel the two packs. I just believe that if I take the time to build the wiring harness from the two batteries to the charger, it will give me some advantage. What I am not sure about is, is there something about the internal workings of these chargers that I am missing. This set up gives more power to charge with and the charger sees all four cells to balance.
Your comments and help will appreciated.

 

[Bunky.F.Knuckle]

Disconnect the packs from any switch.

Be careful in charging in parallel. If 1 pack has more voltage than the other, or cell voltages are off, your cell balance will be off and/or 1 of your LiPo or A123/LiFe pack will have greater than 8.4 or 7.2V.

Or another alternative is to purchase another FMA charger. I'm not familiar with your charger at all. I need to research it some....

From your diagram, you are charging in Series. Which means voltage increases for the packs, capacity remains the same. So, you would be charging as a 4S pack and your rated capacity ie 2600mAh or 2.6A Now, if you were charging in parallel, your pck voltage would be like a 2S pack, but your capacity would increase (double). Which does mean that you can charge at a faster rate, but still would be a MAX of 4A pertaining to your charger specs you listed.

Honestly, your best bet would to be to buy a parallel charge cord for your packs and a parallel balance cord.

 

[bigblueswope]

I don't think that will work because a 4s pack is all in series and your diagram has split the packs such that your ground is in the middle. I believe the charger will see 0 cells connected. I think what you want is a harness that connects them in series. Flipping a batt in the diagram so that battery battery 1's positive is connected to batt 2's negative.



BJ Swope

 

[Bunky.F.Knuckle]

I'm just curious...... Which Lipo are you running?

 

[Terryscustom]

FMA normally throws a "common ground" error when charging to batteries that are still hooked together in any way (switch / RX / etc.). All depends on the setup. Personally I don't risk these simple things, just remove and charge or carry an extra set.

 

[ChickenBalls]

PLEASE don't charge lipo's in a plane, even worse idea trying fake/trick the charger out to see the 2- 2 cell batts as a 4 cell. NOT and I do mean NOT a good idea. Pull em out the plane to charge.

 

[rcpilotacro]

I pull the lipo out of the plane and keep them in storage mode, charge it only the night prior, while being around it, when shite hits the ceiling with your life, you don't want the cause to be lipo. Besides storage position gives a nice long life for your lipo

 

[Snoopy1]

Thanks for all the responses from everbody. The batteries are connected in series and the charger will see the terminal voltage at 16.8 volts max. (4.2 Volts/cell fully charged. ) The "Y" is connected the same way as a four battery pack would be. Yes I agree that a second charger will do the trick and avoid any possible connection errors. Yes again at home all my batteries are balanced and brought back to storage charge ready for the next flying day. Yes to the connection between the packs while charging through the balance port the packs need to disconnect from all the switches in the plane. That one I missed. Yes that will give you a ground error. Ok will not do this.
Ok can we take this one step further as a technical discussion. the two pack are removed from the plane they are on the work bench they have both been balanced and have about the same charge, the main power leads are not connected. Like to charge as shown in sketch. WHY WILL THIS NOT WORK.

 

[Bunky.F.Knuckle]

You need to have the discharge leads plugged in, as well as the balance leads. If you have done this, then there is an error in the wiring harness.

 

[Terryscustom]

Some of the FMA chargers will let you charge only through the balance tap, but then they limit you to just over 3A charge, which I suppose is fine for 2S.

One thing I discovered by accident this past weekend with my Hitec X4 AC Plus. When you are plugged into AC power there is 13.4 vdc supplied to the 12v power-in port on the side! So, I thought I'd test out the wattage of it. I hooked up two more CellPro 4S chargers to the 12v power in on the Hitec and was charging six 2S packs at 3A each and the power supply voltage remained at 13.2v.

I guess the point is there may be a way to join two packs together, but with all the dual, quad and now tested 6-pack charging options available I don't know why anyone would risk it.