Circuit required to balance charge 2-cell LiPO and output series volt/Amp SOLVED

Model Engine glow plug driver 2 each 3.7v (2600mA) LiPO batteries. To charge require balanced (be able to measure each cell) lead (3.7v/2600mA). Switch (2 position 4 pole) to change from series (use) to Parallel (charging)

To use output required 3.7v/5200mA

What is the wiring diagram (schematic) to make this possible.

New to circuitry, can solder and understand diagrams, your assistance would be greatly appreciated

by stephenc63
June 25, 2018

Not sure that I understand your question. 1. Are the batteries 2600mA or 2600mAh? 2. Why do you need to measure each cell when they are in parallel? 3. Two cells in series would be 7.4V, but you say 3.7V.

by mikerogerswsm
June 25, 2018

Yes, you are right, I missed the 'h'.

The measuring during charging cycle in series (+ - to + - connection) to prevent unbalanced over/undercharge of each cell requires a balance lead (inc. lead from the junction between each cell).

To be able to measure each cell (3.7v + 3.7v = 7.4v) measure between lead 1 & 2 = 3.7v,

lead 2 & 3 = 3.7v,

between leads 1 & 3 = 7.4v

In the discharge cycle (powering a glowplug), the batteries are in parallel (++ lead - - lead). Glowplugs requires the higher amperage to 'glow' thus parallel, same voltage double current.

My math regarding the series/parallel may be incorrect causing confusion.

by stephenc63
June 26, 2018

Then surely you can retain the parallel connection when charging. Treat it as one 3.7V cell 5200mAh cell.

by mikerogerswsm
June 26, 2018

Thank you, could you send through a circuit diagram for wiring this up?

by stephenc63
June 26, 2018

2 Answers

Answer by mikerogerswsm

ACCEPTED +1 vote
by mikerogerswsm
June 28, 2018

Please note that the batteries should be at the same voltage before before connecting together. perhaps link them via a 1k resistor until of equal voltage.

by mikerogerswsm
June 29, 2018

Answer by stephenc63

Thank you mikerogerswsm, Really appreciate the time you have put into answering my question. Regards Stephen

+1 vote
by stephenc63
July 01, 2018

A pleasure, Stephen. Had another look at the resistor value, could be as low as 10 ohms for fast initial balance. Now go racing!

by mikerogerswsm
July 01, 2018

So, please excuse my ignorance, what is the best position to include this resistor?

by stephenc63
July 01, 2018

It's not part of the circuit, just use it when connecting the two cells to get the voltages equal before wiring them together. Else they could go bang or ballistic or obey hex instruction CFF (catch fire and forget).

by mikerogerswsm
July 02, 2018

Thanks Mike. Have wired up per your instructions... I am using a Revolectrix CellPro Multi4 charger to charge this device.

Works like a dream, the cells can be monitored as they charge, output is as required.

Once again thank you for your advice. Regards Stephen

by stephenc63
July 03, 2018

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