# SMPS Current Regulation

#### Vish Ram

Joined Apr 25, 2017
12
Hi Experts,

I've SMPS (AC to DC) which gives output of 12V, 20A, 240W,

& I've to attach Peltier device (TEC1 12706) with SMPS, but
Confusion is Peltier have max. Current rating as 6A, but SMPS is giving 20A,
So how to limit o/p of SMPS to 6A, so it wont damage Peltier,
how current regulation is done in SMPS,

Ashish

#### Alec_t

Joined Sep 17, 2013
14,382
Welcome to AAC!
Is the Peltier device rated to be connected to a 12V supply? Can you post a link to its full specification?

#### ronsimpson

Joined Oct 7, 2019
3,147
Can you post a link to its full specification?
data sheet
From what I read at "link" you should see 5 to 6A at 12V. So the 20A reading indicates something is really wrong.

#### BobTPH

Joined Jun 5, 2013
9,174
As I understand it, he didn’t measure 20A that is the rating of the power supply.

I am tempted to answer that it is okay if the Peltier is rated at 12V, but I am not sure about that. I think Peltiers act like diodes in series, so that would suggest that current limiting might be needed.

Bob

#### ronsimpson

Joined Oct 7, 2019
3,147
I think it looks like a 2 ohm resistor but....
Look at current & volage in the 4V to 18V range. It looks relatively linear like a resistors. Not perfectly but close.

#### Vish Ram

Joined Apr 25, 2017
12
As I understand it, he didn’t measure 20A that is the rating of the power supply.

I am tempted to answer that it is okay if the Peltier is rated at 12V, but I am not sure about that. I think Peltiers act like diodes in series, so that would suggest that current limiting might be needed.

Bob
Yes, the o/p voltage of SMPS is 12V & Current is 20A,
But input to Peltier required is 12V & 6A,
so which component, do i need to connect, simply resistor or something else also.
Thanks

#### Alec_t

Joined Sep 17, 2013
14,382
If the device is accurately specified as drawing 6A at 12V under all circumstances then it should be directly connectable to the 12V power supply and will draw only 6A. That is comfortably below the maximum 20A rating of the supply. It is essentially the load, not the supply, which decides the current in this case.

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#### BobTPH

Joined Jun 5, 2013
9,174
The reason I am cautious about this is that I had a TE cooler that blew up two power supplies that were properly rated for it. 119’th on my todo list is a current limited supply for it. I find many articles on the web that suggest a CC supply should be used.

Bob

#### ronsimpson

Joined Oct 7, 2019
3,147
The reason I am cautious about this is that I had a TE cooler that blew up two power supplies that were properly rated for it.
Tell us more.
I think you have a 12V 6A Peltier and connected it to a 12V 6A supply and they died. It looks like the Peltier might draw 5.5 to 6.5A and the little supplies just could not do it.
Now you have a 12V 6A Peltier and a 12V 20A supply. That is good. The new supply should run one just fine and not get warm. Run two in parallel and be warm but could run three and be hot.

#### BobTPH

Joined Jun 5, 2013
9,174
I am not the TS.

I don’t remember the details of the two supplies that were destroyed. The first was the one it came with, the second was intentionally oversized, I think 5A when 3 was supposedly required. This was one if those mini refrigerators that were popular a decade or two ago.

Bob

#### Alec_t

Joined Sep 17, 2013
14,382
The reason I am cautious about this is that I had a TE cooler that blew up two power supplies that were properly rated for it.
I've not used a Peltier device, but it occurs to me that if the hot and cold sides of an un-powered one are initially at or near the same temperature then the thermo-electric voltage between its terminals is ~zero. At switch-on, won't it therefore look like a short-circuit to the power supply? Hence the 6A rating presumably applies only for a specific (maximum?) temperature difference between the hot and cold sides?

#### Vish Ram

Joined Apr 25, 2017
12
If the device is accurately specified as drawing 6A at 12V under all circumstances then it should be directly connectable to the 12V power supply and will draw only 6A. That is comfortably below the maximum 20A rating of the supply. It is essentially the load, not the supply, which decides the current in this case.
Thanks for clearing my doubt, it means - I can connect Peltier directly,

1 more query, if I've 3 Peltier device of same rating, I can connect them in parallel without any other component, with same SMPS power supply, right ?

#### ElectricSpidey

Joined Dec 2, 2017
2,839
Yes, but you are getting close to the max current rating of your supply.

#### Alec_t

Joined Sep 17, 2013
14,382
Thanks for clearing my doubt, it means - I can connect Peltier directly,
I originally thought that, but in the start-up circumstance of the hot and cold sides of the Peltier being at or near the same temperature that might not be advisable. See post #13. See also post #10 regarding a CC (constant current) supply.