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Solar Lipoly Charging rate question
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Solar Lipoly Charging rate question

by displacedtexan on Mon Jul 19, 2010 2:56 pm

I have a quick question about your Solar Lipoly Charger project.

On your page you say:
The charger will automatically 'dial down' the charge rate to match what the panel can give.


So I have some panels that are rated at 6v @ "up to" 400 ma. My question is what should I set my charging current as? I understand that I will rarely get 400 ma, but I would like to use that current when I get it.

Also, wouldn't you want use an inductor to help smooth out changes in the current when the sun goes behind the clouds?

Thanks!

displacedtexan
 
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Re: Solar Lipoly Charging rate question

by ktownsend on Mon Jul 19, 2010 6:42 pm

You'll want to be very careful approaching 6V, since it's the upper limit for the MCP73833 (with an absolute maximum rating of 7V).

By changing the value of R4 you can easily increase the charge rate to (up to) 400mA. I think that would be something in the neighbourhood of 2.5K for the resistor.

As for an inductor, there are compromises in everything. Solar power as a primary source is often a worst-case scenario, though, since in a matter of seconds your supply level can drop several orders of magnitude. It's wonderfully convenient, but definately takes some extra consideration to integrate into any system, though there's lots of information out there on it.

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Re: Solar Lipoly Charging rate question

by displacedtexan on Tue Jul 20, 2010 12:53 pm

ktownsend,

Thanks for the reply and the info.

I thought in order to charge Li ions batteries, you had to charge at a constant current until a certain voltage than at a constant voltage until a certain higher voltage is reached.

I was curious how this was done with a solar panel that has such a varying current.

So I assume I just cut the traces on the surface mount R4 resistor and solder the appropriate value in the through hole? Or do I leave the traces and calculate the appropriate parallel resistance? Beginners and the questions they ask!

Thanks!

DT

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Re: Solar Lipoly Charging rate question

by adafruit on Tue Jul 20, 2010 4:55 pm

constant current doesnt mean the current has to be constant (confusing no?) just that you cant exceed a certain current :)

you can do either, but removing the 10K may make calculation easier

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