125vac switch in 12vdc application? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

savatreatabvr · 03-31-2013, 04:01 PM

I'm wondering if using a push button 125vac 1/3hp switch to turn on and off a 12vdc radiator fan in my truck is safe or am I creating major issues?

mgchevyparts · 03-31-2013, 04:52 PM

The amperage rating is what you need to pay attention to. You should have a relay installed and the control would go through that. You don't want to run, say 20 amps through the switch normally.

JellyBeanDriver · 03-31-2013, 05:10 PM

There is a difference between DC and AC ratings of switches and relays due to the AC arc when the switch opens extinguishes as the voltage crosses zero. Not so when switching a DC load.

So AC amps does not always equal DC amps. Also max voltage can be different.

Can't tell you if this would be a problem with your radiator fan but like the previous post, you could have this switch activate a relay.

savatreatabvr · 03-31-2013, 06:00 PM

I already had the 125vac push button switch laying around so I thought I'd be cheap and use it but rather than dealing with a relay I think I'll just go buy a 12vdc toggle switch from Autozone and save myself some headaches, lol! Thanks for the info.

mgchevyparts · 03-31-2013, 06:48 PM

Doesn't matter, you need a relay for that much current.

Pyrotechnic · 04-01-2013, 01:19 AM

Even if you do go to the parts store and get a 12V toggle switch and hook it up without a relay, you will fry the contacts out of it in no time.

**hatzie** · 04-01-2013, 02:14 PM

Way too much inrush current on a fan motor to just use a switch. GM uses a relay on the heater fan for this reason.

savatreatabvr · 04-01-2013, 06:07 PM

I thought I was pretty good with wiring until I heard the word "RELAY"! Lol but I'll take ya'lls advise and use a relay if someone could tell me what relay to buy and how to wire it up?

savatreatabvr · 04-01-2013, 06:17 PM

I thought I was pretty good with wiring until I heard the word "RELAY"! Lol but I'll take ya'lls advise and use a relay if someone could tell me what relay to buy and how to wire it up?

JellyBeanDriver · 04-01-2013, 10:54 PM

Get a 'Bosch' style relay with socket. You can get them from ebay for cheap (I think I paid $14 for 5 qty).
Usually has 30A contacts and has a drawing on them that shows the coil terminals, the common and the normally open and closed contacts.

03-31-2013, 04:01 PM	#1
savatreatabvr Registered User Join Date: Oct 2011 Location: phoenix, az Posts: 508	125vac switch in 12vdc application? I'm wondering if using a push button 125vac 1/3hp switch to turn on and off a 12vdc radiator fan in my truck is safe or am I creating major issues?

03-31-2013, 04:52 PM	#2
mgchevyparts Registered User Join Date: Feb 2013 Location: Upland, Calif Posts: 698	Re: 125vac switch in 12vdc application? The amperage rating is what you need to pay attention to. You should have a relay installed and the control would go through that. You don't want to run, say 20 amps through the switch normally.

03-31-2013, 05:10 PM	#3
JellyBeanDriver Registered User Join Date: Jul 2012 Location: United States Posts: 268	Re: 125vac switch in 12vdc application? There is a difference between DC and AC ratings of switches and relays due to the AC arc when the switch opens extinguishes as the voltage crosses zero. Not so when switching a DC load. So AC amps does not always equal DC amps. Also max voltage can be different. Can't tell you if this would be a problem with your radiator fan but like the previous post, you could have this switch activate a relay.

03-31-2013, 06:00 PM	#4
savatreatabvr Registered User Join Date: Oct 2011 Location: phoenix, az Posts: 508	Re: 125vac switch in 12vdc application? I already had the 125vac push button switch laying around so I thought I'd be cheap and use it but rather than dealing with a relay I think I'll just go buy a 12vdc toggle switch from Autozone and save myself some headaches, lol! Thanks for the info.

03-31-2013, 06:48 PM	#5
mgchevyparts Registered User Join Date: Feb 2013 Location: Upland, Calif Posts: 698	Re: 125vac switch in 12vdc application? Doesn't matter, you need a relay for that much current.

04-01-2013, 01:19 AM	#6
Pyrotechnic Registered User Join Date: Feb 2007 Location: Austin, TX Posts: 3,930	Re: 125vac switch in 12vdc application? Even if you do go to the parts store and get a 12V toggle switch and hook it up without a relay, you will fry the contacts out of it in no time. __________________ 1977 GMC Sierra Grande

04-01-2013, 02:14 PM	#7
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 4,977	Re: 125vac switch in 12vdc application? Way too much inrush current on a fan motor to just use a switch. GM uses a relay on the heater fan for this reason. __________________ 1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials... 1973-1991 GM Light Truck Service, Unit/Overhaul, Wiring Manuals, Parts Books and Some 1968-1999 GM Service Training textbooks in PDF 1988-1998 GMT400 CK service manual project 1988-1993 GMT400 CK parts books. 1967-1972 GM Light, Medium, & Heavy Truck Service Manuals in PDF Please include at least the year and model in your threads. It'll be easier to answer your questions. And please let us know if and how your repairs were successful.

04-01-2013, 06:07 PM	#8
savatreatabvr Registered User Join Date: Oct 2011 Location: phoenix, az Posts: 508	Re: 125vac switch in 12vdc application? I thought I was pretty good with wiring until I heard the word "RELAY"! Lol but I'll take ya'lls advise and use a relay if someone could tell me what relay to buy and how to wire it up?

04-01-2013, 06:17 PM	#9
savatreatabvr Registered User Join Date: Oct 2011 Location: phoenix, az Posts: 508	Re: 125vac switch in 12vdc application? I thought I was pretty good with wiring until I heard the word "RELAY"! Lol but I'll take ya'lls advise and use a relay if someone could tell me what relay to buy and how to wire it up?

04-01-2013, 10:54 PM	#10
JellyBeanDriver Registered User Join Date: Jul 2012 Location: United States Posts: 268	Re: 125vac switch in 12vdc application? Get a 'Bosch' style relay with socket. You can get them from ebay for cheap (I think I paid $14 for 5 qty). Usually has 30A contacts and has a drawing on them that shows the coil terminals, the common and the normally open and closed contacts.

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