Peltier devices

Hey
I know the general principal of electronics.
Voltage (volts) is pushed and Current (amps) is drawn.
But I was wondering is the same principal applies for Peltier devices; otherwise known as TEC's, Thermoelectric Cooler, Thermoelectric Module, Peltier Junction or Peltier Plate etc.
What I was wondering, is if I were to buy one of these; say a 12v 320w device, will it automatically draw the full potential 320w (27 amps (derived for P=IV)) or is there some way to limit them, so as to not draw to their full capacity, say 110w or 50w ??
This way, one could regulate heat etc by varying current, rather then just on/off ??
As I want to use one of these devices for a number of projects, but don’t want to have to carry around a huge power supply, and other reasons
So what I want to know is; can you regulate the current to a peltier cooler??
Thanks guys
Regards. Christopher Morton

It can be done using PWM. A simple PWM generator and power MOSFET should do the trick.

PWM??
sorry, i was never good with acromims
you should see me on msn lol

pulse width modulation ... your device gets its full current, but in short pulses, so the average current becomes lower.

dammit; Pulse-width modulation
I was considering dabling into it a while ago, for a rgb led board, but in the end gave in goz i thought it would be too complicated.
anyone wanna give me a hand??

isn't it a modulation of the sine wave??
as in to make it less efficient.
the device gets the same current, but it isn't 'worth' as much.
Is there anyway to do it without PWM
is there anything to stop the peltier device drawing so much??

PWM essentially means switching the device ON and OFF, if it's ON for 50% of the time, and OFF for 50% of the time, then it receives only 50% power. For a heating element (which a peltier basically is?) you can use low speed PWM known as 'burstfire control' - but in any case, while it's ON it takes full current - it's only the average that's lower.

Peltier devices aren't know for their effectiveness - you probably need to run it flat out anyway?.

Nah, i wouldn't assume so
with an ambient room temperature of 26-27 degrees; i only need to pull down to just below zero. I've heard of 5v 4w devices doing that and more, so one would assume 320w @ 12 v would do this alot easier.
thats the problem at the moment, if i could have somewhat limited the current then i could have bought the 320w module and decreased power until it was adoquite. this way i shall have to get lower power devices and shoot and miss etc; until i find a good match.

Peltier devices have a cold side and a hot side, and create a certain difference between them - is it as high as 27 degrees?. There's been quite a lot about peltiers on here previously, it may be worth searching for it?.

How large an item are you trying to cool anyway?.

meh
not very big; probably atm 10cm x 10cm x 10cm
well insulated, somewhat a very small freezer. all i need the peltier to do is hold a constant temp.
huge heat sink, I'm thinking half the size of the freezer or even bigger; with a nice big fan to get rid of excess heat.
i have no doubt it can be done; I'm just trying to do it the most efficiently i can. (don't want a huge power bill )

I designed a PWM which will just about do the 27A (you can briefly see it with that motor which i believe is 30A at 12v, the difficulty there was inductive kick, but a peltier won't have that?). It may not be ideal as it is designed to be universal by including voltage control you probably don't need. A 555, driver and power MOSFET may be simpler, anyhow:

https://www.electro-tech-online.com/threads/pwm-controller.21834/

i was looking at a peltier manufacturer ('supercool')
who state that a pulldown (T) of 27 degrees celcius is nothing.
and they can reach pull downs of upto 110 celcius with some of there modules.
and there standard just over 40.
what i have been thinking, is just get one with a greater potential then i need.
have it set on a temp on/off thermostat type device that measures temperature every 2 min (or when opened) to determine the temperature, then depending on that, whether the device will be on for the next 2 min cycle.
This way i will use the full potential of the device while still maintaining the maximum life expectancy.
all i need now is to find a suitable device; and with the help of some engineers at 'supercool' i think i will be able to do that.
i shall post back with my results from speaking with them.

illitrate you're not saying what you're actually cooling though, the 'pull down' temperature as you call it doesn't mean anything when it's attached to a load that actually generates heat. The type of device you're going to use is going to depend completly on the use it's being put to. Like is it cooling something like a static volume (a fridge) or is it coolnig at active electronics device?

Hmm, i thought i said it somewhere
oh well; its just like a freezer, but smaller. and somewhat portable for storing frozen foods.
the dimensions of the device will be (approx) 10 x 10 x 10
well insulated. so one assumes its static

trying to cool air with a peltier is an exercise in futility ... sure it's possible, but its terrible in terms of efficiency.

your best bet is going to use a large fan powered heat sink on both the hot and cold side ... since the peltier is a heat pump, it does not "generate" cold, it just moves heat from A to B ... the heat sink and fan on the cold side will circulate warm air from your storage volume to the heat pump, and the fan on the hot side will move the pumped heat off into the ambient atmosphere.

Yea thats what i was thinking actually. heat sinks on both sides, with fans.
obviously a much bigger on on the hot side, but still one for the cold side; to move the cold, around inside the container.
the other thing i was thinking; considering the volume of the container is going to be a 'static' heat, or, it wont generate heat; once the tempreture has reached 0 or below, considering good insulation, it will not require as much power to keep the tempreture there. will it??

OK let me jump in here with some practical problems.
The body of the Peltier itself is a poor thermal insulator, this is true whether it's on or off. So you may have a nice cooler box with 1" polyurethane insulation, but there's not only a 1" sq Peltier device there to conduct heat into the box but a nice big hot and cold side sink there which only helps conduct heat from outside into the box.
So using a larger Peltier than required is quite a liability. The thermal conductivity factor is higher with larger devices and this will let more heat leak on whether it's on or off.

Peltiers suffer additional efficiency problems with any form of PWM of on/off modulation, especially when low duty cycles are employed. The problem is primarily one of internal resistance.
Say the internal resistance of the device is 0.25 ohm. We can either operate it on 20 amps at 25% duty cycle or 5 amps at 100% duty cycle. Let's look at the difference:
5 amps ^ 2 * 0.25 ohm=6.25W average resistive heating
20 amps ^ 2 * 0.25 ohm * 0.25= 25W average resistive heating (it's 100W for the 25% of the time when it's on!)

That's why it's wise to use a DC/DC converter with an inductor to provide a constant current rather than PWM the device.

so do you think it would be a better alternative to have a lower wattage device on constantly, then the larger intimitidly??

As stated above, doing a freezer or even a refrigerator with a peltier is not going to produce satisfactory results. One of the big issues is that the air inside is a poor conductor for transfering the "heat" of the objects placed inside.

The only peltier based device I have seen like this that was almost of any practical use was a beverage cooler with a liquid transfer medium like water. The cans were placed into the water that was circulated by a small pump.

Essentially it was a "high-tech" version of the really old-school water powered coolers that soft drink makers used to use decades ago.

Oznog said:

OK let me jump in here with some practical problems.
The body of the Peltier itself is a poor thermal insulator, this is true whether it's on or off. So you may have a nice cooler box with 1" polyurethane insulation, but there's not only a 1" sq Peltier device there to conduct heat into the box but a nice big hot and cold side sink there which only helps conduct heat from outside into the box.
So using a larger Peltier than required is quite a liability. The thermal conductivity factor is higher with larger devices and this will let more heat leak on whether it's on or off.

Peltiers suffer additional efficiency problems with any form of PWM of on/off modulation, especially when low duty cycles are employed. The problem is primarily one of internal resistance.
Say the internal resistance of the device is 0.25 ohm. We can either operate it on 20 amps at 25% duty cycle or 5 amps at 100% duty cycle. Let's look at the difference:
5 amps ^ 2 * 0.25 ohm=6.25W average resistive heating
20 amps ^ 2 * 0.25 ohm * 0.25= 25W average resistive heating (it's 100W for the 25% of the time when it's on!)

That's why it's wise to use a DC/DC converter with an inductor to provide a constant current rather than PWM the device.

Click to expand...

I Believe this person Emailed me about doing this.
He was in Australia and If So:
His Proposed plan was a refigerator that would be at an 80 Degrees Ambient temp, and with the Inside temperature to be a few degrees Below Zero.

That is quite a feat to accomplish.
And One Inch of polyurethane insulation is almost useless.
Try 3 or 4 inches.

I agree, running Full On and Full Off is best, controlled by a Temperature Detector inside the fridge. (Not PWM.)

Additionally a Heat detector on the Heat Sink is Advisable. Since these peltier devices work on a Maximum Temperature Difference between the two sides, Getting the Heat sink Too Hot, makes them Ineffective in Cooling. If it Gets too hot, the Peltier device should shut off but the heat side fan should continue to run till it cools down.

Additionally, Creating an insulated Channel around the Cold Sink, with a fan to blow the air is best. Possibly also a Trap door that shuts, so when the Cold air fan stops, The door shuts, stopping the movement of all the air inside the fridge from leaking back through the thermoelectric module.
Especially since he is trying to get Below Zero.

The Best situation to get below zero would be a Dual case, One Peltier device to cool a chamber down from the Outside air, And another one cooling from the inside of that chamber to the inside of the Fridge. Even better is adding the Above trap doors on Both heat pumps.

Gets Rather Complicated, Doesn't it.
Can also get rather Bulky.

Hope I explained this so its Understandable.