Muliple Peltier elements: parallel or series?

I think that you are not thinking your physics through in a thorough way.

Consider your 150x150mm table, being oh-so-carefully held at temperature by one gawdaful big Peltier device (or a bunch of them in parallel, whatever).

Now consider some smartass (me, if I'm in your lab), putting a 2cm cube of something good and warm (or good and cold) on your table.

What happens to your average temperature?

What happens to the temperature right underneath the hot thing?

What happens to the temperature elsewhere?

Me, I think I'd go with a bunch of small Peltiers glued to a moderately thin (I'm visualizing 1/8") plate, each with a thermistor or other easy to use temperature probe placed in a pocket of the plate, smack in the center of the Peltier device.

Then a controller for each device, with whatever tuning is necessary so that the controllers don't get into fights and make temperature oscillations that are unstable spatially as well as in time.

How many devices and coolers you use depends on how uneven the anticipated thermal load will be on the plate, how tightly you feel you need to control its temperature, and on the thermal conductivity of your plate.

You may do much better with a fan-powered Sterling engine.

Or, for a complete demo, have one TE element complete with lots of hype, and one "150 year old technology" Sterling engine for comparison...

CANDLE-powered Sterling. Oops.

Of course, TECs are 60-year-old technology....

Cheers

Phil Hobbs

wn

th step up transformer.

scillator.

Hey, speaking of thermopiles I heard Hamamatsu has a new line of them.

I can't find a spec sheet or price though.

George H.

You are using the wrong junction for this purpose. There are far better junctions made specifically for this, although the thermocouple in a gas furnace will almost do it. About 3 or 4 in series will light an LED plenty brightly, in fact you'll need a current limiting resistor. I think they use copper and iron, nothing exotic at all, and in a gas flame, I think you get 600 mV out of these. A candle flame should be a bit less, so 4 junctions at 400 mV each should light a red LED.

Jon

This is called a millivolt system, still fairly common. Uses no mains electricity. It basically uses the same thermocouple used in the common gas safety controls on water heaters and furnaces. The solenoid coil is a small number of turns of heavy-gauge copper wire, and the current to operate the solenoid is up to several Amps.

Jon

Those must be thermopiles, a single Cu-Fe thermocouple would produce MUCH less voltage.

Interesting thanks.... punching numbers...

George H.

_____________________________________________________

Again, I may be mis-remembering the exact quantity of propane. It might have been 100 pounds.

What do the numbers look like for 1000 gallons and one year? We used it to run a mountain top microwave relay site with no commercial power within miles. We refueled it in the summer. It lasted for more than 5 years until development brought power closer to the site (an old fire tower). The most important thing is to get the combustion products out of the shelter as a lot of water vapor is produced. It sure beat solar because of the problems with snow.

I believe the efficiency was much better than 0.5 % , more like 5% or better.

Back of the envelope shows 13%

Regards, tm

Yup. My father designed a TEC refrigerator in the late '50s or very early '60s, complete with a solid-state power supply (string of Germanium DO-3 PNPs). I had a couple of them in the basement to play with when I was a kid. It was designed to go in a car but never made it past prototype. It got beat out by Styrofoam disposables. ;-)

step up transformer.

oscillator.

Peltier Coolers are almost always totally worthless. Their delta T across the heatsink usually EXCEEDS their intended delta T drop

See <

step up transformer.

oscillator.

Nonsense.

If you try cooling a CPU or a voltage regulator with one, you deserve what you get. But many kinds of instruments would be far harder to build without them. Oh, and of course the telecom infrastructure wouldn't work without them either, because Peltiers are what keep all the DWDM lasers from scribbling across neighbouring channels.

Cheers

Phil Hobbs

ong

you

very

tion

, so

ound

k.

r the

lder

are

that

l.

fety

end.

est

any

eat

for

ype,

rly

a kid.

t beat

you can get plenty of 12V TEC refrigerators/coolers but I don't think they have much if any smarts in them, they just say something like "up to 20'C below ambient"

-Lasse

Fifty years ago you couldn't. ;-)

I think he implies that in his paper. Certain special applications are ideal for TECs.

tm

ng

nt

ion

as

it

und

So

es,

re

at

On

he

d.

r a

EG)

say

an

ore

nd

ave

Oh propane. I was getting my numbers from here.

But don't worry about exact numbers

George H.

rown

st

ny

with step up transformer.

oscillator.

r to

one: (928)428-4073

text -

Hi Don,

I've used TEC's successfully in two applications. Diode laser temp control. (done before) And controlling the temp of a permanent magnetic. The trick for the magnet was to just stabilize the magnet at whatever the room temperature is... and not try and drag it to any specific temp. (This is to do NMR and we can adjust the frequency to whatever the B field is.)

As Phil H. said the great thing about TEC's is they 'go both ways'.

George H.

Setting up a straw man and then knocking it down is an old rhetorical amusement, but IMO it's beneath engineers of Don's calibre. Of course he's been in the biz for probably 50 years or more, and so feels entitled to take the occasional potshot from his porch, and who's to say that isn't OK.

I bought a copy of his TTL Cookbook in about 1974, when I was 14 years old, and it helped me a lot back then, and for several years thereafter. I was also intrigued by his TV Typewriters, but since I couldn't type they weren't that compelling. They were really just a tease anyway, aimed at those of us who didn't have our own private PDP-10.

However, saying that "Peltier coolers are almost always totally worthless", when in fact they enable most of modern communications and the Internet, is just plain nonsense, and needs to be called out. Maybe it'll improve Don's aim. ;)

Cheers

Phil Hobbs

Well, saying "they enable most of modern communications and the internet" is a bit Algoreish in its own right. :)

I have yet to see a 10 gig SFP long haul module that is cooled. I would guess a good bit of the Internet uses them.

tm