I have a fuel cell that produces between .4 and .9 VDC, with current increasing as voltage decreases, max current of 2 A. This .4 volt, 2 ampere condition is the most powerful. I would like to use the fuel cell to drive a motor, let's say 6 V. Is there any way to step .4 V to around 6 V? Is there some way I could turn the steady signal into a wave, without using semiconductors (so that I can avoid the .6 V voltage drop) so that I can step up the voltage with a transformer? Thank you!

--vsnyder@mines.edu

You may want to look at some of the robotic sites (BEAM), it's a similar situation with solar cell powered motors.
This site has a few solar powered motors that might be useful for ideas:

http://www.solarbotics.net/library/c...e_t1_gbse.html

Can you run two of the fuel cells in series? You'll have more luck finding a conversion solution with a 0.8V minimum than with 0.4V. I recently did a similar search with solar cells in mind, and came across a nice line of LED drivers made by Zetex. The ZXSC3xx series will work off input voltages as low as 0.8V. I sent you a PDF of the datasheet.

http://www.zetex.com/frame.asp?page=...link=spotlight

both the Zetex parts and the 1381 mentioned in the first link can be found at digi-key.

You could build a DC-DC Step Up or Boost converter. THe LM3488 looks like a nice one for a good price. A DC-DC converter switches current through an inductor to generate an output voltage. Thay can be up to ~90% efficient and because they use a feedback loop to keep the output voltage steady you dont have to worry about the .7V drop you are talking about.

Brent

Originally Posted by bmcculla

THe LM3488 looks like a nice one for a good price.
Brent

Yeah, except for the fact that the minimum input voltage is 2.95v.

Looks to me like the lowest input voltage I can use is .5 V with a synchronous boost converter, which has a maximum power output of half a watt. I was hoping for some simple way to use just a few capacitors or something to vary the signal (wave or pulses), so that I could use a transformer, which would put out all the power I put in. (As you can probably tell, I really don't know much about electronics.) If anyone has anyone suggestions, I would love to hear them. Otherwise, I'll go with the synchronous boost converter. Thank you for all the help, everyone!!!!!

vsnyder@mines.edu

Thanks for the correction Ron

Brent

What synchronous boost converter IC did you find that can start up and run off of 0.5V? Just curious.

Search for "synchronous boost converter" at www.digikey.com, and you'll see the list I've been looking at. Several claim to operate down to .5 V--not sure about the start-up, though....

The start-up voltage is usually higher than the minimum operating voltage. For the LTC3400, the worst case startup voltage is 1V (0.85V typ), and the worst case operating voltage is 0.65V (0.5V typ) @ 25C.

The LTC3423 will work off input voltages as low as 0.5V, but needs a separate supply of at least 2.7V to operate its internal circuitry.

I suppose I could use that IC that requires a seperate power source for its internal circuitry, and power it with a watch battery. Am I correct in assuming that the more current I put into this IC, the more I'll get out?

vsnyder@mines.edu

Originally Posted by VSnyder

I suppose I could use that IC that requires a seperate power source for its internal circuitry, and power it with a watch battery. Am I correct in assuming that the more current I put into this IC, the more I'll get out?

vsnyder@mines.edu

You could power it from a rechargeable battery that is trickle charged by the output of your converter. Or, if you could start it on battery power then automatically switch over to powering it from the output with a diode OR as soon as the output comes up.

Not a bad idea. Panasonic makes a nice line of coin-cell rechargeable lithium batteries (3V), also available through Digi-key.

http://www.panasonic.com/industrial/...h/manglith.htm


here are some more notes on low-voltage DC-DC conversion:

http://www.maxim-ic.com/appnotes.cfm...mber/364/ln/en

http://www.maxim-ic.com/appnotes.cfm...mber/188/ln/en
(Digi-key doesn't carry the MAX866, but they do have the newer MAX1678)

While we're on the topic of stepping up very low voltages (~ 1.5V and under), here's a simple open-loop boost converter I stumbled across. It works down to 1V, and uses a couple of 2N3904s.

http://www.e-insite.net/ednmag/conte...es/70501di.pdf
(scroll down to "Single cell lights any LED")

can anyone suggest an equivalent to 1381... I asked the electronics storeguy and he gave me LM336 Z25. my circuit which is a beam solar photopopper. isnt working. can anyone suggest a site which gives equivalents or let me know if lm336z25 is really a good subsititute for 1381. search for 1381 solar engine, and thats the one that i m trying to make.

thanks.