12 volt control circuit

I'm rather new to electronics and would appreciate any advice someone has on building a 12 volt circuit to control my telescope dew heaters. They draw approximately 3-4 amps total. I would like the on\off cycle to be controllable. I have seen some circuits using the 555 timer, but not any that would handle the current of my heaters. Thanks,

Curtrw

Posted by curtrw (wellwan@autobahn.mb.ca) on 12/01/2004, at 06:04 GMT

Use a relay

You can still use the 555 astable circuit as described in the EiM article if you connect the 555 output to a relay with a 4A contact rating, and use this to switch the heaters.

See figure 3a at www.eleinmec.com/article.asp?1 for relay wiring details.

Posted by Tim Surtell on 12/01/2004, at 20:48 GMT

12 Volt Control Circuit

Thanks Tim for the advice and information on the circuit. I think it's exactly what I'm looking for. I'll definitely give it a try.

Thanks Again,

Curt

Posted by curtrw (wellwan@autobahn.mb.ca) on 13/01/2004, at 04:23 GMT

12 volt control circuit

Tim,

I appreciate your help about the astable 555 circuit to control my dew heaters. I have a couple of questions though. Is it possible to use the same 12 volt source to operate the 555 circuit as well as the 12 volt-4amp draw for the heaters? I tried it using the transistor option(NTE66) with a diode on pin 3, but had a problem with a large voltage drop(7 volts) on the output of the transistor. Would this be because I used the same 12V source? Any help on this would be greatly appreciated.

Thanks,
Curt

Posted by Anonymous on 21/01/2004, at 21:58 GMT