Can someonr explain the idiosincracies I have observed in a peltier module?

In scrounging parts for the watermaker I cam across an interesting
surplus assembly. I was really after the 1 gpm flowmeter and stainless
needle valve but it came with a really strange device. One of those
things you just sense is to good to throw away. This thing is a pair of
hollow black anodized aluminum blocks about 4.25"x1.75"x1" with pipe
fittings on each end. They are bolted together with what appears to be
a couple of 1.5" square Peltier modules separating them.

Being a curious sort, I did the natural thing and took it apart to play
with the Peltier modules. First I put them on the VOM to check
resistance. They seems to float around between 19 and 22 ohms. Then I
wired it to a DC power supply and slowly cranked up the voltage. While
one side slowly got warm and the other cooler I could not get it higher
than 3 volts and the current never got above .25 amps. Changing
polarity did not make any difference.

This does not seem to fit any of my perception of the rules of
electricity. What is happening?

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

Lol. Actually, you can refer to the West Marine "West Adviser" that
discusses refridgeration methods. One of them is called something like
thermoelectric, and that's what you've discovered. If memory serves,
reversing the polarity should reverse which side gets cold and which side
heats.

Can't quite remember how the whole thing works, but I believe there are two
dissimilar metals separated by a waferthin membrane.

Peltier coolers actually made a big splash in the days of overclocking 486
and early Pentium chips. People found that by cooling the chips they could
inch up the overclocking a little more while retaining reasonable
reliability. Of course they spent more on the peltier cooler than the 486
chip was destined to be worth a month or two later, but I guess it was more
about the fun.

Nowadays you find the coolers in cig-lighter plugin portable coolers, small
refrigeration installations in boats, and even in the form of a mini-fridge
that Sharper Image sells for about $100.

They're good for periodic use, but typically they lack sufficient
insulation, and the result is that over the course of a weekend their low
amperage current drain adds up to a high amphour drain when compared to a
more robust system with freon and adequate insulation.

I'm not sure whether I consider them a gimmik or a useful item. They only
lower ambient temp by 40 degrees, so on a 90 degree day, your stuff's going
to spoil. But why I consider them gimmiky is the fact that many of them are
advertised as coolers / warmers (taking advantage of the results of polarity
reversal). For some reason something that both cools and warms seems like a
toy, but I can't say why it feels that way to me.

I actually did end up purchasing one; the Sharper Image mini-fridge version.
Why? Well, I like to go spend weekends on my C27 a couple times a month.
And that boat is really too small for built-in refrigeration. Yet I hate
having to bring the ketchup and maio home every weekend so that it won't
spoil during the week. I don't rely on the peltier-cooled fridge for
cruising, because its consumption becomes more than my 210ah capacity can
sustain. But it is great for sitting plugged into shore power all week,
keeping my mustard from spoiling between weekend visits to the boat.

Dave

"Glenn Ashmore" wrote in message
...
Can someonr explain the idiosincracies I have observed in a peltier
module?

In scrounging parts for the watermaker I cam across an interesting
surplus assembly. I was really after the 1 gpm flowmeter and stainless
needle valve but it came with a really strange device. One of those
things you just sense is to good to throw away. This thing is a pair of
hollow black anodized aluminum blocks about 4.25"x1.75"x1" with pipe
fittings on each end. They are bolted together with what appears to be
a couple of 1.5" square Peltier modules separating them.

Being a curious sort, I did the natural thing and took it apart to play
with the Peltier modules. First I put them on the VOM to check
resistance. They seems to float around between 19 and 22 ohms. Then I
wired it to a DC power supply and slowly cranked up the voltage. While
one side slowly got warm and the other cooler I could not get it higher
than 3 volts and the current never got above .25 amps. Changing
polarity did not make any difference.

This does not seem to fit any of my perception of the rules of
electricity. What is happening?

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

Peltier modules are pretty neat. You can get more info from a company
called MELCOR. They sell all kinds of Peltier devices, from individual
chips to whole assemblies. http://www.melcor.com/teccover.htm also has
some links to "handbooks" and product information. I'm not sure I can
explain the phenomenom that you observed, but you might try emailing MELCOR
and asking them. If you do get something back, please paste it back to this
thread.

I bought some modules from them a long time ago. At the time, a 1" unit
cost around $25, and I was thinking of using them in a cacaded arrangement
to replace the freon-driven system on my Norcold fridge. Then I learned how
"efficient" they were. Oh well. I do use one of the larger cooler type
units on many occcasions I have filled it with pop and beer and left it
plugged in on my boat all week. When I go out the next weekend, I'm stocked
up with a cooler full of COLD drinks! I have since fixed the Norcold, so
now I just use the peltier cooler for "additional capacity" for parties.


"Glenn Ashmore" wrote in message
...
Can someonr explain the idiosincracies I have observed in a peltier
module?

In scrounging parts for the watermaker I cam across an interesting
surplus assembly. I was really after the 1 gpm flowmeter and stainless
needle valve but it came with a really strange device. One of those
things you just sense is to good to throw away. This thing is a pair of
hollow black anodized aluminum blocks about 4.25"x1.75"x1" with pipe
fittings on each end. They are bolted together with what appears to be
a couple of 1.5" square Peltier modules separating them.

Being a curious sort, I did the natural thing and took it apart to play
with the Peltier modules. First I put them on the VOM to check
resistance. They seems to float around between 19 and 22 ohms. Then I
wired it to a DC power supply and slowly cranked up the voltage. While
one side slowly got warm and the other cooler I could not get it higher
than 3 volts and the current never got above .25 amps. Changing
polarity did not make any difference.

This does not seem to fit any of my perception of the rules of
electricity. What is happening?

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

SNIPPED

Try

http://www.peltier-info.com/

Adam

An interesting snippet from this site about resistance measurements on
Peltier modules:

Can you test a TE module with an ohmmeter? No - the DC voltage that an
standard
ohmmeter applies will cause a temperature change (Peltier Effect) which will
in
turn cause a voltage to be generated (Seebeck Effect) which will cause the
ohmmeter to read goofy (drifting, and even a 'negative' resistance. So, then
use the "diode test" position on the ohmmeter? No - even though a TE module
is
constructed of an array of N and P doped semiconductors there isn't an
actual
diode junction. A resistance test can be made with an LCR meter which
measures resistance using an AC voltage. Using a HP 4274A LCR meter I have
measured a few ohms for small modules and a fraction of an ohm for larger
ones.
While one does not usually see the resistance parameter specified on
manufacturer's data sheets it is probably not a bad of a check of a module's
health, especially if more sophisticated test methods are not available.


"Adam Aglionby" wrote in message
...
SNIPPED

Try

http://www.peltier-info.com/

Adam