# charging batteries with a low voltage source

Discussion in 'The Projects Forum' started by hornsc, Jan 9, 2009.

1. ### hornsc Thread Starter New Member

Jan 9, 2009
2
0
Hi
I am trying to power a fan that draws about 4volts and 0.1A. I have a low voltage DC source of 0.5volts which isn't powerful enough even if I use a DC/DC converter. So using this I hope to charge some batteries which could then power my fan. What is the best way to do this?

Any suggestions are much appreciated,
thanks

2. ### thingmaker3 Retired Moderator

May 16, 2005
5,072
6
Use the converter to increase voltage to a level high enough to charge your battery. You will need some means of limiting current to avoid loading down your supply. Then all you'll need to do is wait a very long time while the battery charges.

3. ### Bernard AAC Fanatic!

Aug 7, 2008
4,240
414
As always-more questions, what current can the 1/2 V source supply? Maybe its a solar panel or thermocouple and candle? I have trouble with a 4 V converter.

4. ### hornsc Thread Starter New Member

Jan 9, 2009
2
0
Thanks for replies guys, The source supply is a thermo electric generator. Across a 180 ohm resistor the TEG is outputting about 0.8 volts, so a power of around 4mW. So that implies a current of 4.4mA if my maths is correct!!

5. ### Audioguru New Member

Dec 20, 2007
9,411
896
You might need to charge a battery for months at a power of only 4mW.

When the voltage is stepped up to 4V then the current will be stepped down to only 1mA or less.