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Old May 19, 2015, 03:57 PM
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Tim Lampe; Hobbico R&D
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Champaign, IL
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Question
Convert two 2S packs to one 4S pack (?)

Hi guys.

I have two 2S LiPo packs I would like to convert to a 4S pack in series. I know how to join the discharge leads to do this (connect a positive and a negative lead from each pack to each other and connect the remaining + & - leads to a discharge connector - say Deans or what have you).

But what I want to do is "permanently" series these packs by soldering two of the discharge leads together and mating all the balance wires together into a single 4S balance connector so I can charge (and balance) the pack as one 4S pack.

So, what do I do with the balance wires? I think the answer is to "Y" the two negative (black) balance wires together and connect into the negative port in a 4S balance plug (that has five receptacles for five wires). Then, connect the remaining four wires into the other four ports of the balance plug.

Other than the negative wire that goes on the end, does the order of the rest of the wires matter?

Will I then be able to charge (and balance) the battery as a 4S pack?

Thanks.

Tim
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Old May 19, 2015, 04:38 PM
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Tim Lampe; Hobbico R&D
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Never mind for now, but go ahead and chime in with comments/suggestions if you have any.

I found this after doing a google search;

I'll show you my work after it's done.

Tim
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Old May 20, 2015, 02:39 AM
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Yes, what you've found with Google is correct. The heavy link that goes between cell 2 and cell 3 in your diagram will in your case be the black lead from one pack (cells 1 and 2) soldered to the red lead of the other pack (cells 3 and 4).

You can dispense with either the black balance wire from one pack or the blue balance wire from the other, so that you end up with only five balance wires instead of six. But you've got to be careful that you pick the right ones -- the one you get rid of must be one of the two that connects to the cell 2/cell 3 junction.

Edit: Here's my edit of your diagram to better explain what I've said, using the actual colours of your wires
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Last edited by abenn; May 20, 2015 at 02:51 AM.
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Old Yesterday, 10:10 PM
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Tim Lampe; Hobbico R&D
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Champaign, IL
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Thanks for your comments abenn.

I got my new 4S battery pack made up yesterday. I know it's a basic concept and process, but I've never "built" a pack before. After getting all the wires soldered I connected my LiPo checker and what do you know, nothing went up in smoke and all the cells were "on-line." Then I applied some kapton tape and heat shrink (but forgot to take pics of the finished product).

Well, now I'm off and running!

Tim
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Old Yesterday, 11:21 PM
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Nice work, KRP!

mw
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