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I need to take the controller board from a 2-cell battery (2 x 3.7v) to a single power supply (1 x 7.4v). The board has 3 wires, "B+", "B-" and "BC". The two cells are wired in series to "B+" & "B-" and the piece of wire that acts as a bridge, is also directly connected to "BC".

So, I'm guessing B+- is getting 7.4v and BC is getting 3.7v. Now that I only have one 7.4v output in my Psu, I'm not sure how to wire this. I've tested the following:

  • PSU+ to "B+" in board, PSU- to "B-" in board Did not work
  • PSU+ to "B+" in board, PSU- to "BC" in board Did not work
  • PSU- to "B-" in board, PSU+ to "BC" in board Did not work

As that was not successful I'm wondering If I can replicate the 2-cell setup just with one . I mean, getting a 7.4v output to B+- and another 3.7v positive wired to BC. Is that possible? I'm very lost at this.

Thank you so much.

Note: Why would I want to use that controller board if I have a Psu? Well, the device I want to power has to recognise a propietary power source via an ID chip wich this board has.

Diagram

Kevin Reid
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Guille Roldán
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    You do not have one 7.4V cell. You have one case with two 3.7V cells internally connected in series. If you can't get that internal connection out ... I don't think you can use that controller. –  Jan 31 '18 at 11:19
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    If you have a 2S lithium battery without a "center tap", you shouldn't use that battery at all. Lithium batteries need to be balanced. – Dampmaskin Jan 31 '18 at 11:21
  • My new 7.4 cell is not exactly a cell (I explained it that way for simplicity). Let say it's a one-output 7.4v psu. – Guille Roldán Jan 31 '18 at 11:34
  • The Li pack is indeed a 2-cell pack and i also agree that Li cells should be balanced. But fact here is that this IS a 2-pack cell without mid connection brought out. You could try to make a voltage divider between B+ and B- and connect half pack voltage to BC. – gommer Jan 31 '18 at 11:36
  • To be complete: make that a high impedance voltage divider. Not suer if it will work though. – gommer Jan 31 '18 at 11:48

1 Answers1

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Proper comment as a semi-answer.

In contrast to my previous comments. While you could try to make a virtual mid connection, its strongly reccomended to not try this. It's dangerous if it would work.

This is a 2-cell pack. If indeed it does not bring out the mid-connection, you should not charge nor discharge it.

Please read this question and answer.

gommer
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  • My new 7.4 cell is not exactly a cell (I explained it that way for simplicity). Let say it's a one-output 7.4v psu. There's nothing to charge actually, but I need to use this board between my Psu and my device because the device has to recognice a valid power input to work (It has a kind of ID chip). – Guille Roldán Jan 31 '18 at 14:51
  • in that case you can safely try to make the virtual midpoint. But that module will still protect against max charge and discharge current, balancing and over- and undervoltage. – gommer Jan 31 '18 at 15:17