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Main => Main Forum => Topic started by: kevinp on March 23, 2008, 01:38:58 am

Title: 12V automotive relay (Bosch style) questions
Post by: kevinp on March 23, 2008, 01:38:58 am

Hello,

Does anyone use the automotive (known as Bosch style) relays for switching 110V to their cab electricals?

I would like to trigger the coil with 12V from a molex connector on the PC PSU, which is no problem.  However, what are the contacts on the switch side rated for, voltage and amperage?  I can't seem to find a reliable answer.  I will be running a fluroscent marquee light, arcade monitor and PC speakers through the switched side.

I know on cars they're good for 30A @ 12V, some are 40A.  Ohms law would seem to indicate 3A @ 120V which is likely not enough for all these loads.  My main goal is to use the ATX power supply power button in a normal fashion and the molex connector to simply relay the hot 110V for all my other cab needs (marquee, 100V transformer, etc.)  This would allow a nice soft shutdown in windows when the button is pressed on the back of the cabinet.  I simply need a large enough relay.

Suggestions?

Title: Re: 12V automotive relay (Bosch style) questions
Post by: DaOld Man on March 23, 2008, 02:28:38 am

I think the voltage rating on a contact is based on how it will arc when opened.
Also insulation for a 12 volt  relay may be different than that of a 120 VAC one.
I really think you should play it safe and pick up one rated for 120 VAC.
Here is the one I use for my power strips:

http://www.cascadesurplus.com/catalog/product_info.php/products_id/1052

It is SPST 10Amp 250 VAC 12 VDC coil.
Very easy to hookup, and pretty cheap.

Title: Re: 12V automotive relay (Bosch style) questions
Post by: danny_galaga on March 23, 2008, 02:29:40 am

 i would stay away from using a car relay. different relays use different materials for the contacts. for 12v copper is sufficient. higher voltages result in more back emf though and more arcing so they use different materials- silver etc. i went to the equivalent of radio shack and bought something suitable. will probably cost a little more than an automotive relay but hey, youre only buying one!

heres an example:

http://www.dse.com.au/cgi-bin/dse.storefront/47e6060a03c5cf302740c0a87f9c06b4/Product/View/P8032

im sure ive seen 'bosch' sized ones around too...

Title: Re: 12V automotive relay (Bosch style) questions
Post by: danny_galaga on March 23, 2008, 02:30:47 am

shnap!

Title: Re: 12V automotive relay (Bosch style) questions
Post by: DaOld Man on March 23, 2008, 02:35:16 am

Great minds think alike...