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Energizer CHPROWB4 Project

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New Member
Hello I just registered as I was hoping to get some opinions or help.

Using a 5v solar panel I want to feed the DC Voltage from the panel in so that I can just leave it in the sun and it will only charge one NIMH battery at a time.

I had made a topic over at sparkfun and I will give the link,and please don't harp on me I was a bit confused at the time as I had never done anything like this. My problem right now is finding where the DC is done being converted then from there I want to try feeding in voltage from the panel and see if that works.

I am just having trouble narrowing it down.


Thanks for any help.


Super Moderator
Most Helpful Member
So, are we supposed to register at the sparkfun site and make comments over there?
do we just read the postings over there and make replies here on ETO?

You are confused?
So am I.



Well-Known Member
Most Helpful Member
i think the OP is confused too, the charger he's referring to runs off of AC line voltage...


New Member
I only gave the link as a reference so you could see how far I am.

And yes I am aware it runs off AC line voltage. But I know this can be done as I was also told so by a friend.
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Well-Known Member
Most Helpful Member
It's far simpler to start from scratch than rebuild the AC charger.

As long as you are using a "bare" solar panel (no internal backup battery).

Just feed it through a schottky diode to a single cell AA holder.
Add a simple "shunt voltage regulator" set for around 1.5V across the holder, to dump excess energy once the cell is fully charged.


The TLV431 will start to draw current if it's reference pin rises to around 1.25V.

A 100K preset for R1 and 390K for R2 should give a reasonable adjustment range.
It will only draw a minute current from the cell when there is no illumination, 3 - 4 microamps, so should have no effect on charging performance.

R4 should be OK with eg. 10K

R3 is only needed if the power source can supply more current than the shunt regulator can safely take; it should not be needed with a small solar panel.

Adjust the preset to 1.5V or a fraction less once the NiMH cell is definitely at full charge & the solar panel has full illumination.

(The first link is a variation of the example in figure 21 of the TLV431 datasheet).


New Member
I will keep this suggestion in mind. I do hope it has an auto shutoff as I would be sleeping when its charging.

Just so we are on the same page I won't be rebuilding the AC Side of the circuit. Once it gets converted to DC then goes through the filter capacitor I was hoping to introduce the panel right after the filter capacitor.

Will this work ?.

If this does not work I will go from scratch I just want to make sure I have checked all the bases.


Well-Known Member
Just to get the terms straight, the output of the AC to DC converter appears across the filter capacitor. It does not go through it.

What is the DC voltage across that filter capacitor when it is running on AC? For you idea to work, the voltage from your solar panel needs to be equal or maybe a little higher that that. (depending upon what the actual charge control circuitry is)


New Member
It measured 4.2

Since I could not adjust the panel voltage I used a DC Lab PSU to try and match it. All I got was one flash and that's it. But when I touched the panel to the cap I got flashes from the led's. Btw the panel is 5v.
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