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Electric fan relay/diode protected

6K views 8 replies 5 participants last post by  EOD Guy 
#1 ·
I'm using a larger relay, unknown amperage. Its one of those round relays with two 1/4 studs that the power wires connect to. It has a sticker on it that says diode protected. Beside one of the studs is stamped with a 0, nothing beside the other stud. I'm using 8 ga. to run power to it an the same to the fan. The wire coming from the battery does it connect to the stud with the 0 stamped beside it or to the other ? Any ideas? I know that voltage won't flow back thru one of those connections but I'm not sure which one to use for incoming voltage from the batt.
 
#4 ·
After looking at it again there's a 0 stamped next to the connection that that turns on the relay coming from the fan controller box also. The battery is in the trunk I'm getting voltage from the starter solenoid, I have a resetable 40 amp fuse on that wire, then that same wire is connected to the relay/solenoid stud that has an 0 stamped next to it. Then the stud without an 0 that wire goes to the fan, supplying voltage to it. Then the wire coming from the fan controller box which turn on the relay/solenoid has an 0 stamped next to it also. No instructions on how to wire up this relay/solenoid. I guessing that the connections with 0 are the ones that will shunt excessive voltage to ground.
 
#5 ·
Don't take offense here...... there is no excess voltage shunted to ground. If it did that there, would be lot's of smoke and some fire works.........

Your description is confusing. With out seeing your particular setup, the wiring is pretty straight forward....

Pwr from the starter solenoid to one large stud, the other large stud should go to the fan motor. solenoid mount is probably the ground for the internal coil, should be a third terminal (usually smaller) which is the other side of the internal coil and is connected to the fan controller. Easy way to test it is with a 12v battery and a test light/probe, hook it up.... if the light lights....it's correct.

If there is a 4th terminal, it may be hot on energize, Ground or another input for energizing the internal coil....... with out testing impossible to tell as I assume you don't have the spec sheet.

Personally I'd go with a Bosch type 70 amp relay, avail just at about any audio install place, that way you're sure how it should be wired and if it goes south, you can quickly replace it without a lot of "which wire went where"....lol
 
#6 ·
There are (2) circuits to consider when wiring a relay that you describe.
The power switching for the fan is a set of contacts that close when the relay coil is energized. Which of larger studs is used for battery wire or the fan wire shouldn't matter. However, it is possibe that there is an internal connection from one of the large studs to the relay coil +. In that case the battery connection (stud) must be observed.
The relay coil studs may have a + or - marking.
The circuit for control of the relay coil should be an ignition ON souce. But, if you use a temperature controller sender that controls the ground side the relay coil connection must be ungrounded.
If you do not have the instructions, It's important that this relay be tested to be sure which way it is wired.
Is any other info such as brand etc. that can googled?

vicrod
 
#7 ·
I'm using a larger relay, unknown amperage. Its one of those round relays with two 1/4 studs that the power wires connect to. It has a sticker on it that says diode protected. Beside one of the studs is stamped with a 0, nothing beside the other stud. I'm using 8 ga. to run power to it an the same to the fan. The wire coming from the battery does it connect to the stud with the 0 stamped beside it or to the other ? Any ideas? I know that voltage won't flow back thru one of those connections but I'm not sure which one to use for incoming voltage from the batt.
What you have is a solenoid. Like a ford starter solenoid.
It is not rated for continuous duty and will overheat and fail if left on for a long period of time.
The diode suppression is to equalize any current flow when the magnetic field lapses in the coil circuitry as when the power is turned of. It suppresses any inductance that occurs when the magnetic field lapses (like an ignition coil) and protects other components from the surge of current /voltage that would otherwise flow on the circuit.
You need to get a good relay,like a bosch style. If you are going to be powering up a circuit with over 40 amps I would recommend a solenoid that is rated for continuous duty.
Usually continuous duty solenoids are metal jacketed (not always) but that is a generalrule you can use to ID one. Motorhomes use them sometimes in the battery to battery circuitry
A bosch 40 amp relay is almost always sufficient for a single fan circuit.
EOD guy can help you with a good working configuration for the fan relays if you run 2 or more.
 
#8 · (Edited)
Your right is isn't a continuous solenoid which is what I need. I was warned about that. The fan I'm using is a single Ford Thunderbird fan, 2 speed, 18 ins. wide, its a big fan. I'm only using the high speed, disabled low speed. The fan controller is a single speed. A few months ago I blew out a fairly expansive coil in the HEI, didn't know if kick back voltage was the reason why. So I wired in this solenoid to see if it would cure the problem, didn't know about continuous solenoids at the time. Theirs only 3 terminals on the this solenoid, its grounded when bolted to the core support . I've read about using two 30 amp. relays but didn't want to go that route. I was trying to understand how using a diode protected solenoid worked more or less. It is working for now but summer is on its way an it will be running longer. So its either a Bosch 70 amp.relay or a continuous solenoid.
 
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