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Lipo charging

Is this a dodgy charger

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Mike Blandford13/09/2018 22:09:57
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Posted by Dave Hess on 13/09/2018 13:45:57:
I can't see any inductors to smooth the PWM. I can't see a reason to do that anyway because charging lipos doesn't need a smooth voltage. The inductor at the other end of the PCB looks like it's part of the buck converter circuit to raise the 12V high enough to charge a 6S battery - probably something like 25V.

The chargers I have use the inductor in both buck and boost modes, converting the supply voltage to that required to charge the battery. They operate using the charge current to regulate the output voltage that is controlled by the PWM mark-space ratio. The PWM frequency used is sufficiently high that the inductor, with the associated output capacitor, produces quite a constant voltage/current, in the same way any switch mode power supply works.

Mike

Dave Hess14/09/2018 00:14:35
103 forum posts
9 photos

Did you see this schematic. It seems to show the output mosfet connected directly to the battery? What's controlling the current if it's not the mosfet?

**LINK**

Nigel R14/09/2018 08:54:34
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"From my observations, I can see the charging switching on and off during the balance phase. The cell voltages rise, then drop back down again. This is what I mean by an iterative process, i.e. it doesn't do it in a single step"

The charger has to let the cells relax after a short burst of charge/discharge before it can get good readings of the cell voltage. In short, it's meant to go on and off. They only need a few seconds of "off" to get a decent reading, before going again for 20 or 30 seconds with another bout of balancing.

Nigel R14/09/2018 09:10:55
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1550 forum posts
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"It seems to show the output mosfet connected directly to the battery"

There is a direct connection from the batt negative to negative power in, which I think you have missed? It is by R15, top left of schematic.

The big inductor is the only output connected to batt positive.

Mike Blandford14/09/2018 09:45:16
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402 forum posts
14 photos

Dave, that is exactly the circuit I expected.VT13, VD4 and L1 form a buck (step down) switch mode regulator, while VT15, VD5 and L1 for a boost (step up) switch mode regulator.

Mike

Nigel R14/09/2018 17:48:51
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1550 forum posts
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.

Edited By Nigel R on 14/09/2018 17:49:24

Denis Watkins14/09/2018 17:51:48
2985 forum posts
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Posted by Nigel R on 14/09/2018 17:48:51:
.

Edited By Nigel R on 14/09/2018 17:49:24

Exactly Nigel, a Testosterone battle excludes us all, he he

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