Transformer for Heater Control

Old 06-14-12, 11:40 AM
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Transformer for Heater Control

I am looking to power a heater. According to the product specifications it will require 11.1V/26.4A to heat to 800C and 16.9V/33.1A to heat to 1000C.
The manufacturer sells an expensive temperature controller which we would like to avoid using. It has been suggested to me that I use a variable transformer and step down transformer with the following specifications (single phase).

Variable Transformer
Current Secondary: 25 A
Frequency: 50/60Hz
Primary Voltage: 120VAC
Secondary Voltage: 0-120/0-140 VAC
Power, Rating: 3/3.5 kVA (Constant Current Load), 3.6 kVA (Constant Impedance Load)

Step Down Transformer
Input: 110/220 V
Output: 8/16/32 V
Power: 1.5 kVA
I need to be able to control the voltage to the heater in order to control the temperature. My understanding is that I should connect a 120VAC 60Hz connection from the wall to the variable transformer and set to ~110V. This 110V connection then goes to the step down transformer which will be set to output 16V (or 32V if I need more than 1000C). From here I can then adjust the voltage in the variable transformer to change the voltage output at the step down transformer to the heater.

I assume that I should not be hooking this up the opposite way (step down goes to variable transformer) because of the voltage outputs/inputs specified for each of these transformers.

My first question is will this work? It seems that the power rating of the step down transformer is more than enough to power the heater and that the max power through the variable transformer will also not be exceeded.

Assuming this does work I need to ensure that the user does not overload the heater causing it to burn out. If I were to install a fuse in the system where would be the best place to install it and how do I know what specifications this fuse should have (i.e maximum current) in order to protect the heater.

Finally, when I hook this equipment up is there any guidelines I need to follow about what gauge wire I need to use and how these wires or how they should be insulated.

I do not have much experience with this sort of thing. Any help would be appreciated.
Old 06-14-12, 04:34 PM
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I do not have much experience with this sort of thing
Welcome to the forums! Not being terse, I suggest you talk to the person who suggested this set up and have them either draw it out for you or guarantee it will work if done a certain way. Without experience with transformers or electrical heating units, it may be cheaper to buy the one the manufacturer offers which will, by the way, be UL certified. There's too much at stake.....heating units, fire hazard, how will you house it, etc. IF you burn out the heater, will it cost more than the control unit from the manufacturer??

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