I'm trying to relearn stuff from 40+ years ago. I'm looking for any suggestions for a circuit that will switch OFF a LiPo charger at or approaching full charge. My thought is using a current sensor with an Op Amp and using the voltage output that when falls to a predetermined value causes a relay to switch off the supply to the battery. Obviously the switching off value would probably need to be set for each LiPo device. I understand LiPo dependent devices do have overcharge protection, if they come from quality manufactures. I like redundancy in systems. Any suggestions would be appreciated.

 

For maximum Cell-life-expectancy,
a Li-Po Battery should not be stored in a fully-charged condition.
Therefore, it is best to only fully charge the Cell shortly before it's eminent use is expected.

Roughly "half-charged" is supposed to be best condition for storage.

Usually, Li-Po-Cells can be charged very-hard if the Cell-Temperature is closely monitored.

These guidelines would indicate that fully-charging a Li-Po-Cell,
and then turning-off the charger,
and letting the Cell just sit there in that condition,
is not an ideal plan.

There are Cell "dis-chargers" specifically designed to reduce the
Cell's Voltage down to more appropriate "storage-levels".

Li-Po-Cells are normally shipped from the manufacturer with a "~50%" charge for all of the above reasons.
.
.
.

 

For maximum Cell-life-expectancy,
a Li-Po Battery should not be stored in a fully-charged condition.
Therefore, it is best to only fully charge the Cell shortly before it's eminent use is expected.

Roughly "half-charged" is supposed to be best condition for storage.

Usually, Li-Po-Cells can be charged very-hard if the Cell-Temperature is closely monitored.

These guidelines would indicate that fully-charging a Li-Po-Cell,
and then turning-off the charger,
and letting the Cell just sit there in that condition,
is not an ideal plan.

There are Cell "dis-chargers" specifically designed to reduce the
Cell's Voltage down to more appropriate "storage-levels".

Li-Po-Cells are normally shipped from the manufacturer with a "~50%" charge for all of the above reasons.
.
.
.

Thank you for your reply, some of what you say I didn't know. With respect to my LiPo devices they are all used each day on my bike and need to be recharged after 5+ hours of riding time. There is a GPS, three cameras, extreme I know but the way others use bike paths and roads I want all the evidence if hit. lights and radar. As previously indicated I like redundancy.

 

I would suggest a Charger that can be Voltage-Limited,
this way You can charge the Cell(s) to ~3.6-Volts, ( roughly "half-charged" ),
and leave them in that condition indefinitely.
The second half of the Charge would be at maximum-recommended-Current
which should only take ~30-minutes max, ( depending on the type and size of Cells used ).

The type of Li-Po Batteries used in RC-Model Cars, Planes, Quad-Copters
are designed to withstand severe Charging-abuse,
and can quite often be fully Charged in as little as ~10-minutes.
But You will $Pay$-dearly for this type of high-Current Charging-performance.

Max-Amp-Batteries
.
.
.

 

My thought is using a current sensor with an Op Amp and using the voltage output that when falls to a predetermined value causes a relay to switch off the supply to the battery.

That could be done.
What is the battery voltage?
What is the "predetermined" current value?

 

Welcome to AAC.

This does seem redundant in the most literal sense of ”unnecessary” but if it makes you happy…

My suggestion would be you just buy a LiPo protection board of the sort that usually goes right on the cell. They are small, cheap, provide over-voltage protection (among other things) and you’d just need to connect the charging power to one side the cell to the other.

This assumes a 1S configuration. If any are in a battery (multi-cell) configuration, they will have to be treated specially.