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WWI Ace
09-10-2005, 12:18 AM
I have 4 Thunder Power lipoly packs. All are 1320mah packs. I have two 3-cell packs and two 2-cell packs. What I want to do is put some kind of jumper connection between them to make two 5-cell packs. If I keep red wires with red wires, and black wires with black wires it will work, right? I don't want to burn them up and I want to be able to disconnect them to fly in my smaller planes. I want to use the 5-cell pack to power a 40oz. plane that I am thinking of building.

Twmaster
09-10-2005, 12:50 AM
When you say "5 cell pack" what exactly do you mean? Do you mean 5 x 3.7V? This could be acheived by putting the red from one pack to the black from the next pack then connecting the ESC to the remaining red and black wires. Can your ESC handle that much voltage? What I suspect you want is lots of current. With the packs you have putting red to red would be very bad as your 3 cell pack is 11.1V and your 2 cell pack is 7.4V. If you want to make more current not voltage you need to use identical packs as in put the 2 3S packs together or the 2 2S packs. I know folks like FMA make a gadget to do this sort of thing however I cannot say how the packs/cells might react to this sort of arrangement. I'd honestly say you are likely better off just buying a big-bad battery if you need more umpf.

Matt Kirsch
09-12-2005, 04:00 PM
If you connect a 3 cell pack and a 2 cell pack together by connecting red-to-red, black-to-black, you WILL damage the packs!!!

That's a parallel connection, and what will happen is that the two packs will try to balance each other out. The 2-cell pack will get overcharged, and there will be a fairly high current flowing between the two. It's a recipe for disaster.

To make a 5-cell pack, you want to connect them in SERIES. That's red-to-black.

Learning the difference between series and parallel circuits should by your priority at this point.

WWI Ace
09-13-2005, 01:23 AM
Matt. Thanks for the info. I didn't want to try anything until I talked to someone that knew what they were doing! So if I understand this correctly, red to red and black to black will increase my mah's. But I can only hook 3cell packs to 3cell packs and 2 cell packs to 2cell packs. If I hook a red to black and use the remaining red and black wires as my normal positive and negative connections then I will increase my voltage?? That's right isn't it? That would allow me to fly a larger plane with a bigger motor right? Sorry that I seem stupid about this, I'm just trying to learn! I've flown alot of small parkflyer sized planes with lipolys but I want to try to convert a .25 size glow plane to electric and since I'll already have to buy a motor and bigger ESC I was hoping to use these smaller packs until I could get larger ones.:cool:

Matt Kirsch
09-13-2005, 03:50 PM
You've got it. Red-to-black increases voltage, and allows you to power larger planes with larger motors.

One thing you may want to consider in making the larger packs is building wiring harnesses with connectors, rather than hard-wiring the packs together. This allows you to break the packs apart and use them in your smaller planes, or charge them individually to check on their condition.

Additional info:
Normally, you would use a 3S LiPoly pack in a .25 size (typically ~3-4 lb) airplane, drawing somewhere between 30 and 40 Amps (for ~300 to 400 Watts). Even in parallel, your 1320 packs won't handle this, but you can get the Watts you need by going with a high-voltage, low-current setup.

With a 5S pack on this size plane, the motor setup is going to be a little unconventional, and will probably need to be a geared setup using a low Kv motor.

WWI Ace
09-13-2005, 11:51 PM
Thanks Matt!! Sounds like if I'm gonna do this I might as well just get a whole new setup. Battery, motor, ESC. Oh well, it's only money I guess!

jonnyjetprop
09-15-2005, 03:31 PM
I wanted to add a couple of things to the thread. First is the Thunder Power does not recommend putting packs together in parallel. There is a little more to putting them together in series than hooking them up red to black.

Both packs must have the same level of charge. To do this, you need a DVM or a wattmeter. The packs should be within .01 volt of each other (this is Thunder Power's recommendation).

Second, Thunder Power does not recommend charging the ganged packs together as a unit, instead they want you to break the packs apart and charge them seperately.

John