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Josh Campbell

Wed Jan 23 2013, 07:31PM

Registered Member #5258 Joined: Sun Jun 10 2012, 10:15PM
Location: Missouri - USA
Posts: 119

Nothing ground breaking here just wanted to share. A friend asked me if there was a way he could charge his iPhone on camping trips using some sort of heat generated electricity since heat is easy to make/get in the woods but electricity is not.

The answer was of course yes, and doable in an hour or so with parts on hand. A peltier junction, heat sink, heat transfer plate, and a heat source.

I used an alcohol burner I whipped up with two coke cans and some fiberglass, since holding the blow torch made it hard to do anything else.
I fashioned a female usb cable (power only) and hooked up a phone. The voltage dropped a bit but was still able to charge the phone. I didn't do much more as far as how much current could be drawn, how fast the phone charged or all that, may come back to it later but for now it works and he is happy.

Update:

The new configuration yields the same output voltage (peeks around 5.1V) I expected less because the heat has to travel further and through a larger surface. But the added cooling on the heat sink from the ice water (to simulate a cold stream out in the woods) must have made up the difference.

The leads kept coming unsoldered from the heat so I routed them down into the cooling water and stripped back a small section to allow heat near the solder joint to dissipate.

This peltier junction appears to supply .26 watts at 5 volts. Current can go higher but the voltage drops of course.
I thought I took a picture showing the short circuit voltage and current (voltage on the Sperry and dc current on the Fluke) but I guess I didn't. I'll do it again later.

It runs for about 10 minutes on 20mL of alcohol. Later I may figure how much power is output during that period and look up the energy potential in that amount of ethanol to show the efficiency and such... Maybe later, I'm board with this now.

klugesmith

Thu Jan 24 2013, 08:43PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Strong work, Josh! Great idea, great implementation. Ready to fly.

Have you any ideas for keeping the hot air plume away from the cold-side fins?
How does the performance of those commodity Peltier-effect modules change with temperature?

My brother once made something like that, heated by a woodstove, to run an electric fan for circulating air in the room.

The same concept provides a steady 100 watts of electricity to the Curiosity rover on Mars.
Some exhaust heat from the radioisotope capsule is piped into the instrument compartment, to keep that warm. Not much different from the power and heating system on Viking landers in 1976, whose thermal power today is more than 50% of when they were new.

teravolt

Fri Jan 25 2013, 02:01AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

good work 2bytes, I didn't know a peltier junction in the revers. what i would be kool is to replace your stove with a solar collector

Ash Small

Fri Jan 25 2013, 10:21AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Not much good if you've no phone signal signal, though.

Avalanche

Fri Jan 25 2013, 01:58PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

I did something similar to this a long time ago, using a hurricane lamp as the heat source. Rest of the setup was pretty much the same.

Be careful not to overheat your peltier module - I did and I killed it. Keeping the temperature differential across the peltier constant is important for a constant power output, but keeping the absolute temperature low enough to not kill the peltier is just as important if you are going to be using it for long periods! Mine went open circuit, I'm not sure what temperature it got to (or if the junctions are held together with solder)

Shrad

Fri Jan 25 2013, 02:31PM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780

junctions are held by solder and a peltier module can break apart projecting its hot junctions and harm you (tiny bits of hot metal are painful when they are everywhere on you hand, experience talk)

the best would be to glue the peltier to another heatsink, and dip the heatsink into boiling water so temperature never reaches that pint but still provides excellent heat transfer

Steve Conner

Fri Jan 25 2013, 02:59PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I wonder if a fan attached to the heatsink would make more extra power than it would take to run?

Josh Campbell

Fri Jan 25 2013, 09:40PM

Registered Member #5258 Joined: Sun Jun 10 2012, 10:15PM
Location: Missouri - USA
Posts: 119

klugesmith:
I changed things up a bit, I'll post some more pics soon. After a while the heat rising through the peltier junction and the hot air rolling around the heat transfer plate caused the heat difference between the two sides to be very little, so little potential was observed across the peltier junction. Just a proof of concept, but needs some work obviously.

teravolt:
Thx, yep they do. Now I need to make a tiny fire powered SSTC.

Ash Small:
Next project, peltier junction powered cellular RF power amplifier.

Avalanche & Shrad:
You are both correct, over heating your peltier junction will cause the solder joints to melt at the typical temperatures. I have a good amount of these on hand from another project so I pushed one above it's rated failure temperature. As the solder begins melting the junction still functions. As far as I can tell the seebeck effect continues long after the solder melts, failure only occurs when solder bridges the short gap between the top and bottom of one of the small peltier elements. If you look closely in the photo showing 5.1V on the meter where the positive (red) lead is exiting the peltier junction you can see a small ball of molten solder oozing out.

Steve Conner:
My first guess would be yes it would take more power than it helped create but possibly with a well designed brushless motor/driver you might be able to find an equilibrium at least to prevent over heating. Not necessarily making more power, but keeping the power generation going without device failure.

Patrick

Sat Jan 26 2013, 01:16AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

please correct me if wrong.

is fire enough of a plasma for plates and a magnet to draw current out of the flame directly?

Ash Small

Sat Jan 26 2013, 01:28AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Patrick wrote ...

please correct me if wrong.

is fire enough of a plasma for plates and a magnet to draw current out of the flame directly?

Flame is enough of a plasma to pass current between two plates, etc., so I assume it would work. I'll try and find some links tomorrow if I get the time.

EDIT: Heat tends to adversly affect most magnets, though. I do have some high temp. neodymiums, but can't remember offhand what temp. they will stand. They aren't as powerful as the 'normal' neodymiums.

EDIT 2: Actually samarium cobalt:

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