Re: ATM RE:Temperature Controller for Dew Prevention

[Bob Bond <rgb@ncube.com>]

I built one of these.  I based it on a couple of circuits I found in a
booklet I got at Radio Shack called "555 Timer IC Circuits" RadioShack Cat.
No. 62-5010.  I used the power transistors they recommend and hooked them
up the way they suggest.

I used heating elements I got at a local surplus store.  I think they were
used in coffee pots.  I have seen similar heating elements in surplus
catalogs.  They are nichrome wire with about 1 ohm resistance per inch of
wire.

                        Bob

At 06:32 PM 9/24/98 -0300, David Croston wrote:
>
>Donald Clement of San Diego/ Running Springs Wrote:
>> "Anybody have a circuit for controlling a dew prevention heater so that
>> the heated part will stay a set offset above ambient? I  starting to
>> look into a building a controller, perhaps based on an LM3911 or similar
>> part, but then why not utilize list resource first." 
>
>
>
>I too am trying to make a dew heater and controller. I have some duty
>cycle circuits based around the 555 timer chip which I understand will
>provide full voltage for a controlled cycle period and thus save battery
>life when only "low" power is required. I have two questions/ requests
>for direction:
>
>1: how can one interface this low powered (800mA) device to a heater
>circuit (say 3Amps or about 35-40watts)? I believe this should be
>possible using power transistors but would appreciate ddetails of a
>circuit and components. 
>
>2: a lot of the links given in response to Donald's message use
>resistors for the heating elements. From my rough calcs. I believe it
>should be possible to butcher and use sections cut from a trace heater
>cable available from Canadian Tire. Anyone tried this? Are there any
>problems in making connections to supply leads?
>
>If anyone with electronics savvy could advise I'd be very grateful.
>
>David Croston
>
>