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Relay Question
Hello Everyone,
I added a fan to my (front) oil cooler and the relay is borderline hot to the touch with the fan in the off position. Will you look over my schematic and see if it looks right to you? When it comes down to electrical stuff I'm not the sharpest knife in the drawer.  Thanks. Larry (1984 3.2) 
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"A good sense of humor is the best thing to have in your toolbox when working on these cars." Quote by Charles Freeborn, Pelican. |
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07-05-2012, 07:56 AM
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Registered
Join Date: Jan 2009
Location: Germany
Posts: 1,239
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Shouldn´t it look like this. I´m confused by the extra ground at the switch
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07-05-2012, 08:40 AM
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Hi
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The ground at the switch is because it is a lighted switch.
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"A good sense of humor is the best thing to have in your toolbox when working on these cars." Quote by Charles Freeborn, Pelican. |
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07-05-2012, 08:45 AM
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Registered
Join Date: Dec 2008
Location: San Antonio, Texas
Posts: 3,590
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Make sure you have an excellent ground. If not this can cause overheating.
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1973 911S (since new) RS MFI specs 1991 C2 Turbo |
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07-05-2012, 12:56 PM
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Registered
Join Date: Jul 2000
Location: So. Calif.
Posts: 19,910
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The relay should be rated higher than the anticipated current flow for the load to control. 30A should be more than adequate for a fan motor circuit.
Excess heat in an electrical circuit indicates excess current flow for the circuit components. You could connect an ammeter in series with the control circuit (switch to ground) and the power circuit (battery to load to ground) and measure the current with the switch ON and OFF. Obviously, with the switch OFF, there should be no current flow nor voltage to the relay (86). Likewise, on the power circuit, there should be no voltage applied to the load (87a) nor current flow in the 30/87a circuit. A short circuit in the coil windings of the relay could create add'l current flow and extra heat. Current flow in that control circuit should be quite small, 1-2A (but only with the switch ON). You could also temporarily connect a test light to the load circuit instead of the fan motor and see what happens. Hope this helps. Sherwood |
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07-05-2012, 02:00 PM
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Registered
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5-pin relay......
Quote:
Larry, You should be using a 4-pin relay but yours (5-pin) would work too. The problem I see with your connection is that the load (fan) should be connected to 87 instead of 87A. This is how it works: With power OFF, the coil (86-85) is not energized and the NC (normally closed) terminals (87a - 30) is at this position. Now with power ON (toggle SW), the coil (86-85) would be energized switching the normally closed (87a-30) to 87-30 (NO-normally open) configuration. Use a test light instead of a fan as load for testing your wiring set-up. An ammeter will tell you the current draw (ampere) for the load. The fan could be bad (??). So measure the current draw of the load. The load should be connected to 87 not 87a. See the wiring diagram from earlier post. Tony |
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07-05-2012, 03:34 PM
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Hi
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UPDATE:
It turns out I had a bad relay. It was bad right out of the box. I replaced it with a 4-pin relay and everything works great now. Thank you all for you input.
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"A good sense of humor is the best thing to have in your toolbox when working on these cars." Quote by Charles Freeborn, Pelican. |
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07-05-2012, 04:04 PM
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Registered
Join Date: Jul 2000
Location: So. Calif.
Posts: 19,910
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Quote:
FWIW, Bosch-style relays are manufactured all over the world. QC depends. Sherwood |
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07-05-2012, 04:35 PM
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Gretchen
