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Gday Lester
This is my first post as i have just joined the IIS forums,
but i have been playing with designing and building PWM dewcontrollers
( manual and thermostatic ) for a few years now.
You dont "need" a fancy controller, but it makes life easier ( in some ways )
as you can set the heating level to suit the conditions.
Using seperate sets of switched resistors will work, but "you" need to switch them, you have limited settings ( hence can drain a battery when not reqd ), but as a benefit, they will produce no RFI.
PWM controllers allow you unlimited power levels ( almost ), can be easily converted into thermostatically controlled units ( so they only heat when required, thus preserving yr batteries ), but all PWM controllers put out RFI, depending on the type of heater element and wiring used.
This may or may not affect other things nearby.
As such, its a tradeoff in what you want.
Just remember, if you put too much heat into the OTA, you risk creating thermals.
Andrew
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