Changing a rechargeable flashlight from 220 to 110 volts

[VicHanson]

There are a bunch of cheap rechargeable flashlights available here in Peru, I assume they are made in China. I have not been able to find anything like them on the web and am wondering if they are available in the U.S. The latest ones I bought are Opalux brand, but they are sold under other names as well. They come in various sizes, from four to about 20 LEDs. I want to take some of the 15 LED lights back to the U.S. to use them in my camper build. They only cost $5.20, but are very bright and run up to 20 hours on a charge. The problem is they only come in 220 volt models here. I assumed there would be a transformer inside that could be rewired to use 110v but there isn't one, only a capacitor, a couple of resister and some diodes, along with two 4v batteries. Are there any electronic techies here that could tell me how to change them to charge with 110v?

Or actually better for the camper I guess would be 12v. If I wired 3 of them in series could they be charged from the 12v house battery? I drew up a wiring schematic, I think I got everything tracked down right. It's a PDF file and for some reason they don't insert, but it is below.

It's been over 40 years since I studied electronics (and haven't used it for almost that long), so had to look up how to read a resister. There is even an on-line calculator now - how easy!

Thanks if anyone can help.
Vic

View attachment 15 LED lights with battery and charger pdf.pdf

 

[iigs]

I think the easiest solution for using these in the US would be a simple step-up transformer, something like:

http://www.fullcompass.com/product/295054.html

That is the first one I found, and it's $17. It should be possible to do better.

They could probably be trivially adapted to run on 110V directly, but judging from the schematic they're relying on some undocumented aspect of the circuit (the internal resistance of the batteries?) to ensure the voltage isn't exceeded. Since they're so cheap you might try hooking them directly up to 110V to see if they work.

If you want to charge them with 12V, I don't see any problem with charging three of them in series. For best results make sure they're identical (same size batteries) and ensure that they're all in a similar state of charge (completely discharged) and health (i.e. all roughly the same age with the same number of discharges). Deviating on any of these could result in one getting undercharged and one getting overcharged, possibly causing a failure or fire.

 

[VicHanson]

Thanks, iigs.
I'll probably just go with 12v charging unless someone else comes up with some ideas on modifying them. Have been thinking about just trying it on 110v too, might just work.

Vic

 

[VicHanson]

Finally got the light discharged when I had access to a 110 v. source, it seems to have charged up fine on 110v. So I guess the voltage source is not a problem.