This was brought up earlier in another thread which I didnt want to hijack so started this..
Chief RA has posted a couple times about using a solar panel to directly drive one of those thermocouple coolers and I think this is interesting and hopefully Chief RA can tell us more about how it works. I think this is "cool" by the way..
A battery is a constant voltage and a solar panel is constant current so they are way different in how they power things. But what Chief RA is doing is pretty clever in how simple it is and there isnt really anything wrong with doing this.
I found this spec for a electric part of a thermoelectric cooler http://www.customthermoelectric.com/tecs/pdf/07111-5L30-25CJ_spec_sht.pdf
The reason for the link is for the V vs I curve at the bottom of the page. A resistor will have a constant slope of V vs I and this thermocouple mostly does also. The difference between the thermocouple and a resistor is an "offset" where the current doesn't start flowing until the voltage gets to 1 or 2 volts. But its still very similar to a resistor and a solar panel will power a resistor just fine. The panel will produce current which results in a voltage across the resistor simply defined by ohms law. For max power into the resistor, you would match the resistor value so that the voltage produced was the same as the panel maximum power point voltage.
Ill use the thermocoupler in that spec sheet as an example and it lists some specs of 2.5 amps at 8.6 volts. Two of these in series would operate at just over 17 volts which is of course in the ball park of the maximum power voltage of a "12 volt" solar panel. In this case of picking a solar panel to power two of these thermocouples in series, you would pick a panel peak power of 2.5 amps * 17.2 volts = 43 watts.. Just one case, there are a huge variety of thermocouples available.
This is just an example.. I dont know what Chief is using (I think its closer to 100 watts of solar). Someone will note that the conventional setup with solar, MPPT controller, battery, compressor fridge is more efficient and this is true. But.. its also WAY more complicated and expensive than one of these thermoelectric coolers plus a solar panel.. Its interesting for a smaller boat application.
Chief RA has posted a couple times about using a solar panel to directly drive one of those thermocouple coolers and I think this is interesting and hopefully Chief RA can tell us more about how it works. I think this is "cool" by the way..
A battery is a constant voltage and a solar panel is constant current so they are way different in how they power things. But what Chief RA is doing is pretty clever in how simple it is and there isnt really anything wrong with doing this.
I found this spec for a electric part of a thermoelectric cooler http://www.customthermoelectric.com/tecs/pdf/07111-5L30-25CJ_spec_sht.pdf
The reason for the link is for the V vs I curve at the bottom of the page. A resistor will have a constant slope of V vs I and this thermocouple mostly does also. The difference between the thermocouple and a resistor is an "offset" where the current doesn't start flowing until the voltage gets to 1 or 2 volts. But its still very similar to a resistor and a solar panel will power a resistor just fine. The panel will produce current which results in a voltage across the resistor simply defined by ohms law. For max power into the resistor, you would match the resistor value so that the voltage produced was the same as the panel maximum power point voltage.
Ill use the thermocoupler in that spec sheet as an example and it lists some specs of 2.5 amps at 8.6 volts. Two of these in series would operate at just over 17 volts which is of course in the ball park of the maximum power voltage of a "12 volt" solar panel. In this case of picking a solar panel to power two of these thermocouples in series, you would pick a panel peak power of 2.5 amps * 17.2 volts = 43 watts.. Just one case, there are a huge variety of thermocouples available.
This is just an example.. I dont know what Chief is using (I think its closer to 100 watts of solar). Someone will note that the conventional setup with solar, MPPT controller, battery, compressor fridge is more efficient and this is true. But.. its also WAY more complicated and expensive than one of these thermoelectric coolers plus a solar panel.. Its interesting for a smaller boat application.
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