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Topic: MAX745 Balance Charger (Read 68 times) previous topic - next topic

TimChPi

Hey guys:

I am wanting to DIY a fast charging lithium-polymer battery balance charger to charge a battery pack for RC planes, from a big laptop charger(19.5v, 135W).

Maxium is pretty clear about how charging can be arranged if it is a single cell, but there are nothing about a balance charger.

I have attempted to search for a reference design from someone else, but clearly that is very hard to be found and the only one I was able to find make zero sense to me.

What I am thinking right now is I should have a separate charging controller for each cell.
I have no idea if it is the right way to go but please tell me if you know.

And if it is, I have came through two possibility for how they shall be connected, however failed to determine which one is correct.

Please see attachment for basic sketch of the idea I have regarding how they shall be connected.

Help appreciated.

Thanks
Regards

TimChPi

Hey guys:
I think I need to clarify my balance 2 further as the diagram can be confusing.
So we know that electronics works on voltages difference, and we can have different ground references for different components if we need to.
This way, we connect the ground of charger for cell 2(7.4-3.7) to the positive of cell 1, which is the negative of cell 2.
And we connect the ground of the charger for cell 3(11.1-7.4) to the positive of cell 2, which is the negative of cell 1.

And the balance 1 is just connect ground of all charger to ground and positive to Vin and set different cell count for different cells.

Hope this explains.

Help appreciated.

Thanks
Regards

srnet

I have attempted to search for a reference design from someone else, but clearly that is very hard to be found and the only one I was able to find make zero sense to me.
Its likely that most people that know enough about how to build such a charger, would not bother, given how cheap a ready built new one is these days, £14 delivered.

Bear in mind that a great deal of care and experience is required when designing and building a LiPo charger, get it wrong and you can set fire to things, or worse.
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TimChPi

Hello:

Thank you for your reply.
I understand the point you are making.

However, the project I am dealing with requires a embedded charger that charges the battery automatically at a pre-set rate when plugged in, until a pre-set voltage.

Also, because the confined space that the project requires, a 3-in-1 board that include:
a battery charger
boost regulator
and automatic switch for switching between internal(battery) and external(plug) power source shall be desirable, where, I was not able to find one that fit into my form factor(10x15cm, max).

The battery shall be charged at at least 4 amp, but desired to be 6.

And for that, in order to design one myself I clearly need to know how to build a very basic balance charger in the beginning, just to complete the design.

Cheers

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