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By zogdc
#199306
I came into a hand-held marine VHS receiver that seems to be fine except the LIPO battery is completely drained, and the circuit board in its charging station badly corroded (and product has been discontinued). I'm trying to figure out if it's worth it to build a replacement charger.

The specs on the battery pack are 7.4v with 1400mAh capacity. So obviously that's 2 cells. There are 3 contacts from the LIPO to the charging station but they are not labeled.

All of the tutorials and modules I've seen for LIPO chargers are for single 3.7v cells. What reading I've done on charging multi-cells suggest the charging is more complicated, and my knowledge of battery chemistry is pretty limited.

Grateful for any thoughts or information on how to proceed. For starters: can/should I hook up an ordinary 3.7v charger and will that have any effect, or is this a stupid/unsafe idea?
By jremington
#199307
If the cells in the radio were completely drained, they must be replaced. Lithium-based cells should never be discharged below about 3 V, and they must be charged with a properly designed charger.

For best results, you need a balancing charger for a 7.4V battery pack. Effectively the two cells are charged separately.
By zogdc
#199308
jremington wrote: Mon May 28, 2018 11:17 am For best results, you need a balancing charger for a 7.4V battery pack. Effectively the two cells are charged separately.
Here is a picture of the charging contacts for the LIPO pack. Obviously 2 contacts are ground and positive. The 3rd could either be: a) a thermistor or some other sensor, or; b) a second positive to the other cell. I don't see any way I could hook up a balancing charger to this.

Image
By jremington
#199310
Balancing chargers for 2S configurations have three wires, intended for case (b) of your post. Which, incidentally, would be the center tap of the battery pack, not the "second positive".
By gal
#199404
The simplest way.
8.4 V Voltage regulator output to 800mA current limiter.
I original you have thermistor to brake charging when too much current is taken by battery which get to hot.
long long title how many chars? lets see 123 ok more? yes 60

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