Automated variac to control cooler motor
Automated variac to control cooler motor
(OP)
Hi,
I have a cooler powered by a small motor. The cooler motor is adjustable 0-60V (the higher voltage, the colder the cooler gets). Since a soft start is preferred, I use a typical Variac to slowly turn the voltage up in the lab.
However, I'd like to set up a simple input/output system, where the input is the thermocouple temp reading of the environment. Based on this temperature, I would like the output voltage to adjust 0-60V accordingly.
My quesetion is if it's possible to have the variac automated, without having to manually turn the dial? I know you have to change the tap manually in a transformer, and turn the dial in a Variac due to number of coil turns. I just don't know if I can vary the voltage output in some way automatically.
Appreciate your feedback. Thanks.
I have a cooler powered by a small motor. The cooler motor is adjustable 0-60V (the higher voltage, the colder the cooler gets). Since a soft start is preferred, I use a typical Variac to slowly turn the voltage up in the lab.
However, I'd like to set up a simple input/output system, where the input is the thermocouple temp reading of the environment. Based on this temperature, I would like the output voltage to adjust 0-60V accordingly.
My quesetion is if it's possible to have the variac automated, without having to manually turn the dial? I know you have to change the tap manually in a transformer, and turn the dial in a Variac due to number of coil turns. I just don't know if I can vary the voltage output in some way automatically.
Appreciate your feedback. Thanks.





RE: Automated variac to control cooler motor
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Automated variac to control cooler motor
Also, is this a DC motor or a universal motor. It surely cannot be an AC motor of any kind.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Automated variac to control cooler motor
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RE: Automated variac to control cooler motor
It could potentially become a $1k+ projrct...I really don't know what's available out there to achieve this. Hopefully not too expensive.
RE: Automated variac to control cooler motor
Secondly, you cannot simply feed a thermocouple into a variac or variac-like device to control output. As the temperature goes up, the speed goes up, then when it works and the device gets cooler, the speed goes down. It will never stay at any stable level, it will always be "hunting" up and down, eventually switcging from fully on to fully off. You need in between is what is called a "feedback loop controller" of some sort, typically a PID or at least a PI loop controller. If you don't know what that is, you have a lot to learn, Google is a great place to start.
The cheap and dirty explanation is that they take a setpoint (which you enter) of whatever temperature you want to maintain, monitor the thermocouple and then determine a process signal that would go to your variable controller (of whatever kind it needs) that powers the motor. The controller determines the proper Proportional (P) response to the signal change, Integrates (I) the rate of change in the response and Derives (D) the predictive response time.
RE: Automated variac to control cooler motor
A complete triac solution with temperature control and trigger circuits can be produced at a very low price. That is what is inside most bath-room ventilators and those particular boards can be easily produced at ten dollars or less (How I know? I designed a lot of them).
The variac solution is just wrong.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Automated variac to control cooler motor
I was thinking of a simple board with a microcontroller that can take the thermocouple input reading, and with some programming, output to some interface that can adjust the voltage to the motor.
RE: Automated variac to control cooler motor
Get my point?
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Automated variac to control cooler motor
RE: Automated variac to control cooler motor
Best regards,
Mark Empson
http://www.lmphotonics.com