I've been playing around with peltier modules in the kitchen. Arguably too much according to some of the other house dwellers.
Something has been seriously bothering me. The majority of modules quote their delta T as being around 65 - 67C, when pumping zero watts of heat.
I have now been through quite a few different modules and setups, yet don't see anything like that in terms of the dT. In each example, I am not trying to pump heat, I am trying to find the maximum delta T.
The lowest I can manage is around -8C with a hot side temperature of about 35C. Giving a delta T of around 40, not 65+.
Trying different compounds
I'd managed to loose my tube of heatsink compound. So started by using inappropriate things like vaseline, bike grease, bike grease with electrolytic powdered copper in it (mixed to a thick paste), ice to couple the thermometer to the heatsink and so on.
Giving up hope of ever finding the tube of white grease, after weeks of looking for it, I bought some silver CPU compound.
Results? All of them performed in the same way, indicating there is not a lot of heat being moved. It would make bigger difference if there was a significant amount of heat trying to get through it.
Different heatsinks
I have a few at hand and thought I'd try them all, even though that shouldn't affect the delta T by much.
Result? Again, all of them pretty much the same delta T coming out
Different fans
I've tried both a low CFM 12V 120mm case fan and a mains powered monster from a microwave.
Result? No change!
No insulation, a sponge covering the top or foamed in place
I wondered if perhaps I wasn't insulating the cold side well enough, and that it was pumping enough heat from the atmosphere that the delta T wouldn't drop any lower.
I first tried running the element by covering the cold side and it's thermometer with a sponge, with a recess cut out of it for the thermometer.
I then wondered how effective the sponge actually was, so removed it. The temperature rose by a few degrees on the cold side. Not a lot.
To test it in the other direction, I then tried spraying the cold side with expanding polyurethane foam to completely seal it off from the atmosphere. The next day, I repeat the test and get the same delta T! Despite that it should now be pumping next to 0 watts from the atmosphere.
Spanning the voltage / current curves
I have spent many, many hours tweaking the voltage / current and leaving it for an hour in between to find the optimum for the module. I have found said 'sweet spot' more times than I can count, and the delta T is far from 'sweet'.
Checking the power supply
The supply can easily manage these elements, which are 12709's - 15V maximum, 12V optimum (it's actually more like 10 or 11 optimum), 9 amp maximum (actually more like 5-6 amp optimum).
I checked the voltage with my multimeter, lest the displays on the front be false. Nope. Correct.
I then swapped it over to an entirely different supply.
Same delta T!
What this prooves
The fact that swapping the heatsinks, fans, grease, supplies, insulation and drives is doing next to nothing to the delta T means the module is not pumping much heat at all (so should be able to obtain it's maximum delta T), that I have found it's optimum and that it is being run with an appropriate heatsink / fan for the test.
What I suspect is happening
The resistive heating in the element is providing the heat load that is countering the delta T of the element. Naturally, the thing warms up whether it's pumping any heat or not, as it has resistance and there is current flowing through it.
And that the delta T quote is the instantaneous delta T at switch on in some funky setup in a lab.
So....?
Has anyone ever managed to get the full delta T quoted out of one of these in continuous operation?
The elements I'm trying are the Chinese ones. But, checking both their current and resistance figures, they are basically identical to the Western ones that cost a lot more.
This has been sat there for weeks as I've been trying different arrangements. But I didn't think to take photos of it all since it'd take about that long to upload and comment them all.
I've tried mounting that with various different things. It doesn't make much difference as there's next to no heat being pumped anyway. I'm now going to tape it down.
Then completely cover the cold side with polyurethane spray on insulation.
These are the best numbers I can get out of it. The hot side is barely over room temperature, and the cold side is at a delta T of just 34C.
Sweeping through the voltage / current curves with different grease, fans, heatsinks and so on all produce a curve similar to this.
I'm going to try lowering the voltage to 6V, which is the maximum of another supply I have.
The meters on the front match the multimeter reading.
Running it from a different supply, I get pretty much the same delta T at 6V.
No shortage of current from that!
And the thermometer is reading correctly. These digital ones aren't perfect. I've been using two here. I'm comparing them to an expensive mercury / nitrogen thermometer that conforms to one of the British Standards for laboratory use. Both the digital ones show a temperature about a degree wrong compared to this, but no more.
Here's one of them in the freezer, reading a much lower temperature and around what I would expect from the freezer.
It's so low because someone's left the super freeze on by mistake.
I have seen one of these elements reach around -17C under similar conditions, but can't for the life of me repeat it. Why are these reading so far off their delta T's? This module has a dT of 67-68C, and a Qmax of around 77C according the custom thermoelectrics PDF. These Chinese ones have a resistance of about 1.1 to 1.3 ohms. My maximum delta T occurs around 5 amps, which would means this module is pumping around 25w of it's own heat? So where on earth does a delta T of 67 come from?
Something has been seriously bothering me. The majority of modules quote their delta T as being around 65 - 67C, when pumping zero watts of heat.
I have now been through quite a few different modules and setups, yet don't see anything like that in terms of the dT. In each example, I am not trying to pump heat, I am trying to find the maximum delta T.
The lowest I can manage is around -8C with a hot side temperature of about 35C. Giving a delta T of around 40, not 65+.
Trying different compounds
I'd managed to loose my tube of heatsink compound. So started by using inappropriate things like vaseline, bike grease, bike grease with electrolytic powdered copper in it (mixed to a thick paste), ice to couple the thermometer to the heatsink and so on.
Giving up hope of ever finding the tube of white grease, after weeks of looking for it, I bought some silver CPU compound.
Results? All of them performed in the same way, indicating there is not a lot of heat being moved. It would make bigger difference if there was a significant amount of heat trying to get through it.
Different heatsinks
I have a few at hand and thought I'd try them all, even though that shouldn't affect the delta T by much.
Result? Again, all of them pretty much the same delta T coming out
Different fans
I've tried both a low CFM 12V 120mm case fan and a mains powered monster from a microwave.
Result? No change!
No insulation, a sponge covering the top or foamed in place
I wondered if perhaps I wasn't insulating the cold side well enough, and that it was pumping enough heat from the atmosphere that the delta T wouldn't drop any lower.
I first tried running the element by covering the cold side and it's thermometer with a sponge, with a recess cut out of it for the thermometer.
I then wondered how effective the sponge actually was, so removed it. The temperature rose by a few degrees on the cold side. Not a lot.
To test it in the other direction, I then tried spraying the cold side with expanding polyurethane foam to completely seal it off from the atmosphere. The next day, I repeat the test and get the same delta T! Despite that it should now be pumping next to 0 watts from the atmosphere.
Spanning the voltage / current curves
I have spent many, many hours tweaking the voltage / current and leaving it for an hour in between to find the optimum for the module. I have found said 'sweet spot' more times than I can count, and the delta T is far from 'sweet'.
Checking the power supply
The supply can easily manage these elements, which are 12709's - 15V maximum, 12V optimum (it's actually more like 10 or 11 optimum), 9 amp maximum (actually more like 5-6 amp optimum).
I checked the voltage with my multimeter, lest the displays on the front be false. Nope. Correct.
I then swapped it over to an entirely different supply.
Same delta T!
What this prooves
The fact that swapping the heatsinks, fans, grease, supplies, insulation and drives is doing next to nothing to the delta T means the module is not pumping much heat at all (so should be able to obtain it's maximum delta T), that I have found it's optimum and that it is being run with an appropriate heatsink / fan for the test.
What I suspect is happening
The resistive heating in the element is providing the heat load that is countering the delta T of the element. Naturally, the thing warms up whether it's pumping any heat or not, as it has resistance and there is current flowing through it.
And that the delta T quote is the instantaneous delta T at switch on in some funky setup in a lab.
So....?
Has anyone ever managed to get the full delta T quoted out of one of these in continuous operation?
The elements I'm trying are the Chinese ones. But, checking both their current and resistance figures, they are basically identical to the Western ones that cost a lot more.
This has been sat there for weeks as I've been trying different arrangements. But I didn't think to take photos of it all since it'd take about that long to upload and comment them all.
I've tried mounting that with various different things. It doesn't make much difference as there's next to no heat being pumped anyway. I'm now going to tape it down.
Then completely cover the cold side with polyurethane spray on insulation.
These are the best numbers I can get out of it. The hot side is barely over room temperature, and the cold side is at a delta T of just 34C.
Sweeping through the voltage / current curves with different grease, fans, heatsinks and so on all produce a curve similar to this.
I'm going to try lowering the voltage to 6V, which is the maximum of another supply I have.
The meters on the front match the multimeter reading.
Running it from a different supply, I get pretty much the same delta T at 6V.
No shortage of current from that!
And the thermometer is reading correctly. These digital ones aren't perfect. I've been using two here. I'm comparing them to an expensive mercury / nitrogen thermometer that conforms to one of the British Standards for laboratory use. Both the digital ones show a temperature about a degree wrong compared to this, but no more.
Here's one of them in the freezer, reading a much lower temperature and around what I would expect from the freezer.
It's so low because someone's left the super freeze on by mistake.
I have seen one of these elements reach around -17C under similar conditions, but can't for the life of me repeat it. Why are these reading so far off their delta T's? This module has a dT of 67-68C, and a Qmax of around 77C according the custom thermoelectrics PDF. These Chinese ones have a resistance of about 1.1 to 1.3 ohms. My maximum delta T occurs around 5 amps, which would means this module is pumping around 25w of it's own heat? So where on earth does a delta T of 67 come from?
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