Hey everyone!

I'm trying to make a solar charger for a specific battery I have. The solar panel is 5V 450 mA and the battery is 3.7 V at 2000 mAh. I'd like to just leave it out all day and not have to worry about overcharging the battery.

I'm pretty new to all this, but I have the panel, the battery, and a diode to prevent the battery discharging back to the panel. The last thing I need is something that will prevent overcharging the battery. Please correct me if I'm wrong!

Does anyone know of a way to get this done inexpensively? This is a pretty small set up, so I don't want to break the bank. I'm willing to make something myself or just buy something ready-made.

Thank you for all the help!

Edit: I might also end up using two panels for 5V and 900 mA - that is where the overcharge protection is really needed.

 

one here for 3.6v battery


4.2V charger


more here

 

You might be interested in post #11 in this thread, showing a way to dump excess current above a set voltage. I've been using that circuit for quite some time with an old laptop cell (Li-ion) and it's still going.

One of those cheap DC-DC converters you can get on e-bay might be another option. Charging to constant voltage is not a great strategy for Li-ion, but you did say cheap is good.

 

Here is another shunt regulator. Bare bones.
The way it works is that when the battery reaches 4.2 volts the FET is turned on and the current is "shunted" to the resistor holding the voltage steady.

 

Thanks! Do you guys know where to buy one ready-made? Or someone that would be willing to put this together?

I'd prefer to get one as quick as possible, and I think making one for me would take some time since I'm pretty new to all of this.

 

If your looking for a ready made solution these are hard to beat. Just set it to 4.2 volts.

http://www.ebay.com/itm/Auto-DC-DC-...122?pt=LH_DefaultDomain_0&hash=item4acb154e92

 

I just want to make sure my intuition here is correct. This will work just like the circuit you linked earlier right? If you set it to 4.2 volts it will charge until the battery reaches that voltage level and then hold it there.

Thanks for all the help!

 

Yes, Might even work a little better as it can boost the voltage from say 3.5 to 4.2 to charge the battery when the panel isn't in full sun.