# messing around w/small TEC

#### brodo

##### Member
got a question for the PSU/Peltier gurus...

I am messing around with a small 30x30x4.7 peltier I picked up at Fry's and I see it says the max (Vmax) - VDC is 8.10. So I am connecting the wires to a molex the red and black (should be the +5v line).

My question is, can I connect the +3 and +5 together, then connect my hot (red) wire to the combined +8v and get better results from this little guy? Or do I run a risk frying PSU and/or the TEC

I imagine if I used the +12v line I would certainly fry the TEC in an instant. I am correct with that theory, right? (I would like not to spend \$23 testing this theory)

#### Diggrr

##### Underwater Senior Member
I'd try running it at 5 volts. Most TEC's perform best when running at less than their max rated voltage.

If you combined your +3 and +5, you'd get +2 volts, and really be disappointed at your results.

OP

#### brodo

##### Member
doh!

hah ok, well I won't be trying that then. looks like I'll stick with the +5v

OP

#### brodo

##### Member
wait a sec!

so if +3 and +5 gives me +2 ... then what if I +12 and +5 will that give me +7?

then I would be 1v off my TEC's max and I should have the most optimal result?

#### Warlord2

##### Member
yes that will give you 7v

#### Since87

##### Member
Warlord2 said:
yes that will give you 7v

Whoa there!!!

Connecting a TEC between +12V and +5V will give you 7V IF the current being drawn from +5V, by the rest of your system, is greater than the current the TEC will draw with 7V across it.

Most voltage regulators are only designed for current flow to ground. In other words positive voltage regulators provide positive output currents and negative voltage regulators provide negative output currents.

Suppose the TEC draws 5 Amps at 7V. If the computer is only drawing 4 Amps from the +5V rail then to maintain +5V with the TEC installed the +5V regulator must source -1 Amp in order to maintain the voltage at +5V. Since the +5V regulator can only source positive currents, it won't be able to compensate. What will happen is that the +5V rail will go to a voltage above +5V where the current through the TEC matches the current through the components connected to the +5V rail. THIS COULD BE VERY BAD!!!

Doing this with a fan or two is one thing. The current draw on the +5V rail is almost always going to be significantly higher than the current draw of a couple fans. The current draw of a TEC is another story all together.

Unless you know the minimum current draw that your computer provides to +5V rail, and that the minimum draw is a couple amps more than the TEC will draw at 7V, do not do this.

OP

#### brodo

##### Member
this is in a test setup, with an empty 250w PSU - so the only thing on it is the HSF and the TEC.

so with that, does VERY BAD indicate a fried TEC or FAN? or PSU? because there is no computer on it.

I will wait until I get an electrical engineer reply

#### Since87

##### Member
In the case you posted, very bad means a fried PSU. In a full system very bad could mean fried PSU, MOBO, CPU, drives, etc, etc, etc.

Do you know Qmax and Imax for the TEC? I could give you some idea of results you might get at different voltages if you have that data.

If you are going to air cool this pelt, you might actually get better cooling at 5V than 7V anyway. At 7V you will be dissipating twice as much power in the pelt as you would at 5V, and you will only get a 22% increase in cooling capacity. You would need 0.18 C/W cooling on the hot side of the pelt to get any benefit from 7V at all.

OP

#### brodo

##### Member
yea it is the largest, although small on from Fry's:

30x30x4.7

Vmax=8.10
Imax=3.9

I can water cool it, air cool it or whatever, I am just trying to see how far I can push it. I am going to order a couple 50-150 pelts tonight, but I want to tinker with this thing and push it to its limits (if that produces the best results).

thanks.

later,
brodo

#### Since87

##### Member
What about Qmax? Most important spec of all.

OP

#### brodo

##### Member
damnit - no Qmax on this spec sheet .. let me try their web site..
I think it is 20
Qmax=20

#### donny_paycheck

Since87-

What if he used the -5 and +3.3? Would it yield him +8.3v with enough current to run the TEC? It sounds screwy to me so I'm betting there would be problems, but since you seem to know what you're doing here, would this be a good or bad idea?

#### JFettig

##### Hey! I showered! Senior
dude, go to bgmicro.com and search peltier, they have some peltiers there, 8 bucks for a 36 or 40watt tec

#### Since87

##### Member
donny_paycheck said:
Since87-

What if he used the -5 and +3.3? Would it yield him +8.3v with enough current to run the TEC? It sounds screwy to me so I'm betting there would be problems, but since you seem to know what you're doing here, would this be a good or bad idea?

The Antec True Power 550 Watt PSU has a 0.5A rating for the -5V rail.

Connecting this pelt from +3.3V to -5V would most likely pull the -5V rail above ground and smoke the componenents that are supposed to be running on -5V.

I doubt any PC PSU is going to have a much higher current rating on the -5V rail.

So again, bad idea. Generally, all PSU loads should be connected between one of the regulated voltages and ground.

With a Qmax of 20 Watts this pelt isn't going to be of much use in cooling anything other than maybe a GF2. When connected from +5V to ground, it would be able to cool a 10 Watt load to about 8C with decent aircooling.

OP

#### brodo

##### Member
well I am not putting it on my duron or athlon xp for sure :-} I am just f'in around with them...

I did, however, take on a dare from a friend and connected to the the +12v line. No smoke! and the pelt behaved normally.. did not appear to get any cooler/hotter.

Oh and I tried connecting the +3 and the +5 no smoke, but the power supply cut off. heh I unplugged and back in and it worked.

I have 3 78watters in the mail - going to have some fun with those!

maskedgeek - thanks! I have been looking for a good source.

#### Since87

##### Member
brodo said:
Oh and I tried connecting the +3 and the +5 no smoke, but the power supply cut off. heh I unplugged and back in and it worked.

The PSU's overvoltage protection kicked in. At least you know that works.

#### JFettig

##### Hey! I showered! Senior
peltiers are way too much fun! just dont get too curious and stick yoru tongue to it, i know from experience
i have a few myself and im about to put a few to use with dual aircooled 80watt peltiers

OP

#### brodo

##### Member
having trouble finding them

The PSU's overvoltage protection kicked in. At least you know that works.

well that's cool maybe I'll test out my other PSUs to make sure theirs work as well

.
just dont get too curious and stick yoru tongue to it, i know from experience
ha! nope, sure won't hear about that story from me - I have some good ones, funny and sad (from having the current jumpering 110 throw a screwdriver out of my hand to frying CPUs) but unless one of my dogs get their noses stuck, that'll be it. (maybe my finger, I touch them pelts alot)

-----

I have searched around and I am not having much luck finding decent peltiers for decent cost.

www.swiftnets.com has good deals on their 78w but I want to get some 80's and perhaps some 150's.

anyone have a thread they could refer me to or an online store? I am also impatient so I am hoping to find someplace that will have it to me before the weekend. swiftnets.com might be a while (48hours - 2weeks for accessory type parts).

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