Battery Charging Possibilities

[Macgyverasb]

Is it possible to charge a 7.4V 850mAh lipo battery on a 10V 4mA power source?

Inquiring minds want to know. Thanks everyone!

 

[davenn]

Is it possible?

Yes ... with appropriate circuitry

but it's going to be a very slow charge

 

[NascentOxygen]

Is it possible to charge a 7.4V 850mAh lipo battery on a 10V 4mA power source?

Inquiring minds want to know. Thanks everyone!

Yes, possible but only just. It will take a long time, and you may need a custom designed quite unique charging circuit.

 

[rbelli1]

quite unique charging circuit

Unique does not properly describe this type of circuit. Most of the usual suspects (Analog Devices, Maxim, National, etc.) produce devices that will certainly work with that level of input. They also go very low voltage and even higher voltage with lower currents.

Advanced or innovative would be better adjectives to use. The good news is that you get that cutting edge technology at a relative low per unit cost.

BoB

 

[NascentOxygen]

Most of the usual suspects (Analog Devices, Maxim, National, etc.) produce devices that will certainly work with that level of input.

I'm surprised to learn that, given that it sounds like such a narrow niche market. Can you point to an IC that can directly charge an 850 mAH cell while drawing less than 4 mA total?

 

[rbelli1]

http://www.linear.com/product/LT8490.

This cycles rapidly to discharge the input capacitor then let's it recharge and repeat. It is designed for solar panels but I don't see why it could not be used for any high impedance power source.

BoB

 

[NascentOxygen]

http://www.linear.com/product/LT8490.

This cycles rapidly to discharge the input capacitor then let's it recharge and repeat. It is designed for solar panels but I don't see why it could not be used for any high impedance power source.

BoB

Seems that the 8490s quiescent current is not going to leave anything for the battery.

 

[rbelli1]

It is true that some portion of the operating temperature range will completely swamp the OP's input power and uses most of that power over the rest. I know that it is not really efficient for 10V 4mA but I found this one after only a few minutes search. The last time I did any real research into this type of circuit was a couple of years ago. The goal was 5V 2mA. I remember I found something that may have worked even that low but it was cost prohibitive so we just went with a larger battery.

A two chip solution would probably be best. Use the same technique but have the charge operation completely shut down during capacitor charging from a harvester. Boosting to a higher intermediate capacitor voltage would probably help.

BoB