Using dew straps without controller

[Phil Hart]

Kendrick, Dew-Not and other controllers for dew straps switch the full 12v from the battery on/off with varying amounts of 'ON' time determining how much power is consumed and given off as heat in the dew strap.

If I want to simplify things (ie. avoid the controller) for a dew strap on a widefield lens setup, can I simply put a resistor in series with the dew strap to give the dew strap say 6V continous and still get some useful heat out of the strap? Would this be much different in practice to 12V from the controller 'ON' 50% of the time?

cheers
Phil

[mill (Martin)]

Phil you can do this.
Just measure the resistance of the dew strap and then put a resistor of the same value in series to get 6 Volt over the dew strap.
A 5 or 10 Watt resistor will do.
Just make sure that the resistor is not touching anything plastic because it will get warm.

[stringscope (Ian)]

Hi Phil,

I agree with Mill that this is a viable option.

An alternative is to determine approximate power requirement and then custom build an appropriate heating element to run off 12 volts. This option would be more power efficient as there is no power drain from the inline resistor. And no thermal plume from the resistor.

For normal Southern Victorian winter nights I am guessing a 4-6W heating strap at 12 volts would be about right. If you would like, let me know the required circumference and I might have one you can borrrow.

Cheers,

[Phil Hart]

Originally Posted by mill

Phil you can do this.
Just measure the resistance of the dew strap and then put a resistor of the same value in series to get 6 Volt over the dew strap.
A 5 or 10 Watt resistor will do.
Just make sure that the resistor is not touching anything plastic because it will get warm.

thanks Mill!

Originally Posted by stringscope

Hi Phil,

I agree with Mill that this is a viable option.

An alternative is to determine approximate power requirement and then custom build an appropriate heating element to run off 12 volts. This option would be more power efficient as there is no power drain from the inline resistor. And no thermal plume from the resistor.

For normal Southern Victorian winter nights I am guessing a 4-6W heating strap at 12 volts would be about right. If you would like, let me know the required circumference and I might have one you can borrrow.

Cheers,

hi ian!.. and thanks!

can you point me to a supplier of the heating straps? happy to buy my own if i can find ones ready to go with 12V without the controller. for lenses with 72mm filter diameter so nothing large.

cheers
Phil