Me and a buddy needed to go across a couple of states this spring. He bought a box van and converted it to an RV. We got to the refrigeration and he said that we would use a cooler and buy bags of ice along the way. I suggested, with my technical background and relative bravery in the subject, that we could build a real refrigerator with some thermoelectric coolers. He liked the idea and I began.
I researched all the circuits that would be needed and started to amass the parts. Aside from the peripheral circuits, I decided on using a MOSFET (35A rated)to modulate the thermolectric coolers. (off a dep cycle 12V battery) The TE's were rated at about 15V and 18A all together. I would have them run at about 8-10A along with a fan and a few LED's to provide monitoring information. The refrigerator temperature would be managed by thermistor control (btw, if you need one...I found a Radio Shack that actually caries them....try Brookings OR)
The operation and problem is as follows: The thermistor varies in resistance with temperature, high, giving a low resistance and vice-versa. I also included a trim pot. to simulate and also trim the temprature threshold for the MOSFET. Thus, as I reduced resistance on the trim pot. (in series with the thermistor) the output from the thermistor to the GATE of the MOSFET would switch on the TE's and ancillaries (fan, LED's ect.).
The problem arose when I first tried to operate it. The fan and LED's worked like a charm, however, when I hooked up the TE's, the MOSFET let out a sliver of smoke when I varied the trim pot. I found out later that the stage between OFF and ON (about 8K ohms at the pot. out of 110K) at the MOSFET would cause a need to dissipate quite alot of heat. The current that was being gated from the TE's, I assume. It works quite well, with minimal heat dissipation, with the pot. trim to to the lowest resistance.
My first question is, I have a power resistor in series with my TE's...such as about 1.5ohms to maintain my current desire of about 8-10A(such as a current limiting resistor to my LED's). What power (watts) rating should they be? And my second question is if I can decrease the range bewteen OFF and ON such that it switches quicker, nearly like a digital signal...how can I do that? I have considered and tried a Darlignton pair. Using a transistor for the small side and the MOSFET as the large side. (it didn't make any difference, this way ) Should I have used two transistors to make it a true Darlingon pair? (Sorry for my sort of poor and undetailed wording...my first draft was erased by a slip of the finger) I hope you can see my dillema. I want to have the MOSFET drive the thermoelectric coolers without undue heat disspation in short order. It works well fully on like I said. Just the bit in the middle seems to be the problem. If you need more detail of my circuit or past articulations of (such as possible mistakes), please ask. Thankyou.
I researched all the circuits that would be needed and started to amass the parts. Aside from the peripheral circuits, I decided on using a MOSFET (35A rated)to modulate the thermolectric coolers. (off a dep cycle 12V battery) The TE's were rated at about 15V and 18A all together. I would have them run at about 8-10A along with a fan and a few LED's to provide monitoring information. The refrigerator temperature would be managed by thermistor control (btw, if you need one...I found a Radio Shack that actually caries them....try Brookings OR)
The operation and problem is as follows: The thermistor varies in resistance with temperature, high, giving a low resistance and vice-versa. I also included a trim pot. to simulate and also trim the temprature threshold for the MOSFET. Thus, as I reduced resistance on the trim pot. (in series with the thermistor) the output from the thermistor to the GATE of the MOSFET would switch on the TE's and ancillaries (fan, LED's ect.).
The problem arose when I first tried to operate it. The fan and LED's worked like a charm, however, when I hooked up the TE's, the MOSFET let out a sliver of smoke when I varied the trim pot. I found out later that the stage between OFF and ON (about 8K ohms at the pot. out of 110K) at the MOSFET would cause a need to dissipate quite alot of heat. The current that was being gated from the TE's, I assume. It works quite well, with minimal heat dissipation, with the pot. trim to to the lowest resistance.
My first question is, I have a power resistor in series with my TE's...such as about 1.5ohms to maintain my current desire of about 8-10A(such as a current limiting resistor to my LED's). What power (watts) rating should they be? And my second question is if I can decrease the range bewteen OFF and ON such that it switches quicker, nearly like a digital signal...how can I do that? I have considered and tried a Darlignton pair. Using a transistor for the small side and the MOSFET as the large side. (it didn't make any difference, this way ) Should I have used two transistors to make it a true Darlingon pair? (Sorry for my sort of poor and undetailed wording...my first draft was erased by a slip of the finger) I hope you can see my dillema. I want to have the MOSFET drive the thermoelectric coolers without undue heat disspation in short order. It works well fully on like I said. Just the bit in the middle seems to be the problem. If you need more detail of my circuit or past articulations of (such as possible mistakes), please ask. Thankyou.
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