Peltier effect in psychological study

[ke5frf]

How do you get less than 2V across a 1 ohm resistor with 3 amps flowing through it?
V=I*R=3*1=3V

Actually, read the comment in context of the entire thread, as this was a series resistance topic.

 

[Roff]

please read my comment again.

Do you mean the one I quoted?

All it takes is less than 2 volts to be dropped across a 1 ohm resistor at 3 amps to create more than 5 watts and destroy it.

I read it again. It still doesn't make sense.

 

[ke5frf]

OK, perhaps I jumped a little by simplifying 2x3=6.
The argument got off tangent on me. Yes, the resistor would have to have another value I suppose. Point was that a resistor placed in the circuit will drop several volts across it. I was using rounded math (because I am lazy) in the progression of the thread.

Point is still made, the question was asked how you could get 3 amps across a one ohm resistor and produce 8 (or 9) watts. In a series resistance where the other resistive element is sharing the voltage it doesn't take much.

Fair enough?

YES I didn't think it through or state it correctly. I should have said "all it takes to create 6 watts across (A RESISTOR) at 3 amps is 2 volts. Wouldn't that be the case if the peltier resistance was just a bit higher and the series resitance a bit lower?

My bad. Sorry for letting an error get by. I was trying to defend my original math for the purpose of helping the OP.

 

[ke5frf]

Yeah, the resistor would have to be .667 ohms my bad.

 

[ke5frf]

I have to admit, I have a compulsive personality and sometimes churn things in my mind and feel the need for further comment.

This thread started with a query about peltier circuits. I happen to work with peltier circuits daily and have seen more than my share of commercially produced devices and schematics with peltier control elements. I have yet to come across a series resistance for the purpose of current limiting. The reason is logical and simple. A regulated voltage suffices to current limit because the load regulates the current itself when the source voltage is stable.

So, the comment struck me as wasteful an unnecessary. I did not wish to insult the OP. I just realized it wasn't needed.

I also considered that temperature control would be important here. I contemplated that a better way to protect the cell from overvoltage and current was a fuse. So I offered these comments to set the OP in the right direction.

I certainly didn't mean to have the entire breadth of my electronics knowledge and experience insulted when I pointed out that a 5 watt resistor wouldn't be sufficient. This especially shocked me considering that I knew this to be true.

I am always humbled by the gurus and wiz's on this site whose knowledge dwarf mine. Roff is a good example of someone who really knows his stuff. I admit I get a personal measure of satisfaction when my relatively weak wit finds fault with theirs (which is extremely rare). This site has a bit of competitive nature which is healthy and OK.

The key is to know when you make a mistake and be humble enough to admit it. Electronics is a vast field and it is the sum of our knowledge, not individual superiority, that makes this site an asset.

Sorry to get on a soapbox.

 

[kinarfi]

Good grief Ke5frf, what does all this have to do with torturing someone with heat or cold?

 

[Vizier87]

Since the main part is about producing heat, what heating element is gonna be used? You're just gonna heat up the resistor?

 

[ke5frf]

Good grief Ke5frf, what does all this have to do with torturing someone with heat or cold?

It doesn't.

LOL. Perhaps he is a sadist. But I will assume that the experiment is carried out responsibly and that the guinea pigs are voluntary and likely getting paid (college kids earning beer money) and have signed a waiver. My conscious us clear

 

[Lewishodgson]

Just to reassure list members that I am not a sadist!
I am a Chartered Psychologist and Director of Neuroscience at a laboratory based at a UK University.
All volunteers on our studies give their informed consent and our work is strictly regulated by the ethics committee.
Contact heat administered with peltier element in a probe that is held upon the skin is often used in pain research (Fruhstorfer et al., 1976). It has been developed meanwhile into powerful tools with modern computer-assisted apparatus for quantitative sensory testing in clinical neurophysiology (Verdugo and Ochoa, 1992).
I hope that sets some minds at rest and reassures those who have been kind enough to provide helpful advice and suggestions that they have not been party to any form of unethical conduct.

 

[kinarfi]

Just to reassure list members that I am not a sadist!
I am a Chartered Psychologist and Director of Neuroscience at a laboratory based at a UK University.
All volunteers on our studies give their informed consent and our work is strictly regulated by the ethics committee.
Contact heat administered with peltier element in a probe that is held upon the skin is often used in pain research (Fruhstorfer et al., 1976). It has been developed meanwhile into powerful tools with modern computer-assisted apparatus for quantitative sensory testing in clinical neurophysiology (Verdugo and Ochoa, 1992).
I hope that sets some minds at rest and reassures those who have been kind enough to provide helpful advice and suggestions that they have not been party to any form of unethical conduct.

If your asking questions about how a peltier device works and plan to touch people with it, you better be or have some people that are very savvy about controlling the device so you don't injure you're volunteers, and if you can't afford to buy equipment that has passed all the safety protocols and building your own, may the public beware and be warned.
You better think about what your doing, even if you or your people are savvy.
kinarfi