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Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059
Hmm. I'd heard about using Peltiers as power generators, the main problem is getting the low voltage output converted efficiently to useable levels.
One approach that has been used before is to charge up a capacitor using the peltier output (1000 uF 6V tantalums are good for this) and then connect it in series with the peltier to momentarily get 2* voltage; this then gets fed into the charger etc.
the efficiency of this is pretty high and the required circuitry can be as simple as a three transistor "lm3909 clone" or just a MAX660 or ICL7660.
Its very unfortunate that tunnel diodes are extinct, they are nearly ideal for this application and there is no modern equivalent that runs down to <1V. -A
Registered Member #99
Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637
Hmmm, sounds pretty neat. I wonder how long before the "cold" side warms too much? Seems that if the cold side could be kept cool without the need of any other such power, then a simple butane powered generator could be possible. Kinda like a low pressure torch built to run for long periods. 1.3volts at 1amp is very usable...Perhaps one could series two or more to increase voltage?
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
IT takes few tens of seconds, depending how evenly and how fast I heat etc.
With few peltiers, good heatsink and fan one could make fan sustain itself from the power of ''cell'' (actually a thermoelectric converter from some source of heat, some burning coal maybe or butane torch..
It needs good cooling altough, I got some real current only after throwing a block of ice on cold side..
Someone can put few hot rocks inside too (just kidding, I hope nobody here owns *that hot* rocks )
Although thing isn't really related to fuel cells.
As far as I figured out that commercial minicell doesn't require platinum at all (?) and it will be able to power small stuff like led's etc. why don't you just series two or more cells and use much simpler and more efficient mosfet boost converter..?
Registered Member #99
Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637
Firkragg wrote ...
IT takes few tens of seconds, depending how evenly and how fast I heat etc.
With few peltiers, good heatsink and fan one could make fan sustain itself from the power of ''cell'' (actually a thermoelectric converter from some source of heat, some burning coal maybe or butane torch..
It needs good cooling altough, I got some real current only after throwing a block of ice on cold side..
Someone can put few hot rocks inside too (just kidding, I hope nobody here owns *that hot* rocks )
Although thing isn't really related to fuel cells.
As far as I figured out that commercial minicell doesn't require platinum at all (?) and it will be able to power small stuff like led's etc. why don't you just series two or more cells and use much simpler and more efficient mosfet boost converter..?
I dont have the money to series enough of the fuel cells...The joule thief works alright for lighing ultrabright LEDs anyways...By the time the voltage drops below what the transistor will accept, the fuel cells has almost exhausted all its gas anyways...
I dont see how the mini fuel cell, or any fuel cell could work w/o platinum. I believe the platinum is the key to getting it to work anyways. Their methanol fuel cell membrane + electrodes all use platinum as well. I think the anode uses managanese to catalyse oxygen also, and the cathode uses platinum. Matt
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Measured current from that peltier was actually short circuit, I doubt I get more than 100-200mW from it as maximum
After checking mini has electrodes platinum-coated (wasn't apparent at first).
Can you post pics, better explanations, you can give me 1 fromchermistry, etc. about that NaOH thing?
Seems easily replicate-able but doesn't fullfil definition of fuel cell for much. I don't see why would gasses sitting on inert electrodes in NaOH dp 'something' really.
Registered Member #99
Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637
Firkragg wrote ...
Measured current from that peltier was actually short circuit, I doubt I get more than 100-200mW from it as maximum
After checking mini has electrodes platinum-coated (wasn't apparent at first).
Can you post pics, better explanations, you can give me 1 fromchermistry, etc. about that NaOH thing?
Seems easily replicate-able but doesn't fullfil definition of fuel cell for much. I don't see why would gasses sitting on inert electrodes in NaOH dp 'something' really.
Im not much of a chem buff, but I beleive the NaOH, or KOH(popular) are used in what are called alkaline fuel cells. In other words, the solution partly acts like a membrane, allowing only H+ ions to pass leaving behind e-. Since the hydrogen as a gas is H2, that leaves two e- and two H+ right?The electrons flow through the circuit to meet back up on the other side(cathode?). The OH ion also serves some purpose(general chemisrty stopped there for me )
So the platinum causes the H2 to split into protons and electrons I beleive, and the manganese somehow causes the solution to give up O2 (which recombine with H2 to form H2O. Here is how I try to explain it in simple terms.. H2 is a big bro and little bro. When big bros friends come over, he leaves lil bro behind. (Platinum is friend of big bro). Since lil bro cant stand to be away from big bro, he finds a way back!(the circuit), and thus the fuel cell.
Someone please help me out with my chemistry!I have no idea what im talking about Matt
Registered Member #193
Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022
This site gives a fairly good explanation. The NaOH solution acts like the polymer membrane (In fact, in the old days, there weren't any ion exchange polymer membranes so all fuel cells just used a tank of elecrtolyte so, from my point of view, the polymer is acting as a slightly strange electrolyte)
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
I made a small alkaline cell of my own, sort of at least.
Firstly I dipped two carbon rods in NaOH and fired them up, but after each 'charging' I could get my small motor make just a revolution or two. Voltage was about 1V, but it would start to drop as I connected voltmeter to the cell.
I tried to save created gases by wrapping the rods in cotton wool, but it worked even worse.
Later I filled entire bottle with less dense wool but it didn't help. It didn't hold small bubbles since solution was too viscous, and I would just get a big bubble burped out after a period of time.
I tried copper wires instead of graphite rods and they work as well, but positive electrode kept oxydising so I tossed them away.
Now I'm using graphite rods again with copper-zinc litz wire (from ATX cable) coiled around them.
WIre doesn't do anything itself (0V) but it keeps more gas around each electrode after 'charge'.
Most I got now is the small motor spun for few seconds.
I guess your platinum wire used same way could create some pretty good results.
Registered Member #99
Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637
Firkragg wrote ...
I made a small alkaline cell of my own, sort of at least.
Firstly I dipped two carbon rods in NaOH and fired them up, but after each 'charging' I could get my small motor make just a revolution or two. Voltage was about 1V, but it would start to drop as I connected voltmeter to the cell.
I tried to save created gases by wrapping the rods in cotton wool, but it worked even worse.
Later I filled entire bottle with less dense wool but it didn't help. It didn't hold small bubbles since solution was too viscous, and I would just get a big bubble burped out after a period of time.
I tried copper wires instead of graphite rods and they work as well, but positive electrode kept oxydising so I tossed them away.
Now I'm using graphite rods again with copper-zinc litz wire (from ATX cable) coiled around them.
WIre doesn't do anything itself (0V) but it keeps more gas around each electrode after 'charge'.
Most I got now is the small motor spun for few seconds.
I guess your platinum wire used same way could create some pretty good results.
Yea, i did this also awhile ago. I used NaOH and carbon electrodes. I got it to run my joule thief for a few seconds. If you have gas supply, you could bubble it over them. When i attempted to use methanol+KOH, i got nothing. I now beleive i got ripped off(ebay). Dont do business with Texas Supply...The platinum wire I have does catalyse H2O2 so I know its good, but the "methanol" does nothing in the pressence of the platinum wire.
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