Can You Charge a 7.4V 850mAh Lipo Battery with a 10V 4mA Power Source?

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Discussion Overview

The discussion revolves around the feasibility of charging a 7.4V 850mAh lithium polymer (lipo) battery using a 10V 4mA power source. Participants explore the necessary circuitry and the implications of charging efficiency, particularly in the context of low current sources.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • Some participants propose that it is possible to charge the battery with the specified power source, but it would require appropriate circuitry and would result in a very slow charge.
  • Others argue that a unique or advanced charging circuit is necessary, suggesting that existing devices from manufacturers like Analog Devices and Maxim could potentially work with such input levels.
  • A participant questions the availability of integrated circuits (ICs) that can charge an 850mAh cell while drawing less than 4mA total, indicating skepticism about the practicality of the proposed solutions.
  • One participant mentions the LT8490 IC, which is designed for solar panels, suggesting it could be adapted for high impedance power sources, but raises concerns about its quiescent current potentially consuming most of the input power.
  • Another participant reflects on the inefficiency of charging at 10V 4mA and suggests a two-chip solution that would involve shutting down the charge operation during capacitor charging from a harvester, indicating a more complex approach may be necessary.

Areas of Agreement / Disagreement

Participants generally agree that charging is possible but remain divided on the specifics of the circuitry required and the efficiency of various proposed solutions. There is no consensus on the best approach or the practicality of the suggested ICs.

Contextual Notes

Participants express uncertainty regarding the efficiency of charging circuits at low current levels and the specific characteristics of the proposed ICs. Limitations in the discussion include the lack of detailed specifications for the charging circuit and the potential inefficiencies associated with the components mentioned.

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

Inquiring minds want to know. Thanks everyone!
 
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Macgyverasb said:
Is it possible?

Yes ... with appropriate circuitry

but it's going to be a very slow charge
 
Macgyverasb said:
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.
 
NascentOxygen said:
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
 
rbelli1 said:
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?
 
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
 
rbelli1 said:
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.
 
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
 

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