OK, I have 2 switches that turn on the electric fan and the electric water pump. The wiring for these 2 switches is shown below. I know I'm supposed to have a fuse to prevent all sorts of problems but I just wanted to see if this would work or not. Well it does, but with both accessories running it runs out of juice in about 30 seconds and doesn't even work with the headlights on. Is this due to the fact that they are wired improperly or due the fact that the 12v battery charger doesn't give nearly enough juice as compared to the alternator? Thanks.

BTW, my car is short the exhaust so I can't see if the alt would be enough power to keep these puppies going.




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-'82 Z28 (Pro Street conversion in progress)
-'96 Grand Am (daily driver)

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You're battery charger probably doesn't have enough "oomph", probably a 40 amp charge or so?, anyway, the fuse should be prior to the switch, not after is, you want to protect from the source, not mid-stream.

 

that's what I figured mike about not having enough juice...if you notice I said I'd put the fuse between the pump/fan and the switch...check the drawing...

 

Yeah, I see that...the fuse should protect the whole circuit...switch and all...i/e 12v Supply-fuse-switch-device....

 

Is there such a thing as a switch with a built in fuse? That would be so much easier to wire up

 

I think you should determine exactly how much current all three accessories will be drawing (two fans and one electric water pump). I would guess that each fan draws 12 amperes and the water pump 15 for a total of about 40 amperes.

I think the biggest ATC automotive fuse made is a 30 ampere (green), which means you should go with a MAXI ATC in-line fuse (looks like an ATC fuse, only bigger - Pep Boys stocks them). Like you stated in your post, that fuse should be connected to the positive battery post with a length of at least #8 AWG wire (#6 may be better - J.C. Whitney is a good source, or welding supply house (more expensive)) to the contact of your relay.

I would not bother with a fuse from the fuse panel to the relay coil if it comes from a wire already protected by a fuse (preferably under 10 amperes) but if you want to put another in to protect this circuit, fine.

I don't know what kind of relay you got from ACE hardware, but if my guess is correct (that your circuit draws over 35 amperes), then I doubt that that relay is rated for that high a current.

The highest ampere rating for a "cube" relay that I am aware of is 40 amperes, with 30 amperes being the most common (Radio Shack sells the 30 ampere). A good source of 40 ampere 12VDC "cube" relays is HOSFELT ELECTRONICS, INC (888-264-6464) - don't know if they're in the Internet. Costs $3.50/ea. Excellent source for commercial/industrial relays at good prices.

If you're switch a circuit that draws more than 40 amperes, I'd go with a solenoid which generally start with a rating of 100 amps. Newark Electronics (www.newark.com) is a good source (catalog has 1700+ pages). I got their 40F3663 15VDC relay, actually called a "heavy-duty DC power contactor) rated at 100A full load, 400A inrush current ($17.23) which is slightly smaller than an automotive solenoid which they sell also with the same ratings for $35.95 (02F1134).

We careful of using an automotive solenoid. It should be rated for CONTINUOUS use. Most automotive solenoids are intended to just provide current to the starter motor, which is not normally CONTINUOUS duty. The Newark DC power contactors (relays or solenoids if you will) ARE rated for continuous duty.

There's more to it than just slapping on a relay (solenoid)...

 

Ok, umm, I need to re-read your post like 1000 times to fully understand it but let me further explain something. I only have 1 electric fan and the 1 water pump obviously...they both are on separate lines, have separate switches and go to separate spots on the fusebox to get power...the drawing obviously confused you because I only drew one wire to represent both lines because they take the same route...so the actual amps on each line is very minimal...I'll double check the amps from the electric drive, but how many amps are with a stock electric fan?

Here we go...the electric drive said it can be used with a 10amp fuse, so I don't think it's all that powerful...

BTW, I'm getting rid of the POS Mr. Gasket electric water pump drive and getting an Aerospace Components Electric water pump. It flows better than mechanical ones, has a constant gph of 37, and it only draws 4 amps!

 

Craze,

Sorry if I did not make myself clear enough.

You are correct, if you have EACH motor on a separate fuse/wire/relay, you should be okay, especially if each circuit draws less than 10 amperes.

It's important to know FROM THE BEGINNING how much current each circuit will be using, and how far from the current source you'll be. That will tell you what size fuse, wire and relay you'll need.

To your problem of the circuit not operating more than a half minute. Are you connected to a battery charger without a battery, or a battery charger connected to a battery?

If there is a battery/battery charger combination, and the circuit dies after only 30 seconds, I'd say you have essentially a dead battery since it won't hold a charge. Will it crank the engine continuously for over 10 seconds? Does it crank the engine fast or slow/weak? Can you crank the engine with the headlights on? If you have a voltmeter (preferably digital, or DMM), how many volts do you see AT THE BATTERY TERMINALS when you crank the engine? A good battery will have > 11.0 volts. A marginal battery will have < 10.5 when cranking. Less than 8.0 volts and it's almost dead.

I would not connect your circuit to just a battery charger, since they are generally just a transformer with one diode, which gives un-filtered pulsating DC (half-wave rectified voltage), which is generally not good for DC circuits.

[This message has been edited by Stuart Moss (edited July 25, 2000).]

 

Craze,

Forgot to answer your question of how many amps a stock fan draws. That question got my curiosity up, so I went out to my '91 Z-28 with dual electric (factory) fans and measured the current with a DMM.

As you probably know, amperage is dependent upon voltage (the more voltage, the more amps the same load will draw), so I'll give you the current with the engine "off" (12.5V) and "on" (14.1V).

Also, a motor will draw more current when it starts than when it is at running. These fans used more than 20 amperes to start, and reduced current draw to 9-12 amperes (see below) upon reaching operating speed. Normally, this happens so quick (within a second), that regular "fast acting" fuses can safely be used. Otherwise, a "slow blow" fuse would be needed.

Current draw (one fan) at 12.5V was 9.8 amperes.

Current draw (one fan) at 14.0V was 12.2 amperes.

That equates to 24.4 amperes with both fans operating, engine running.

Please don't think that electric fans will provide free energy (free horsepower due to lack of a manual fan). While you'll gain SOME horsepower (over a manual fan), the engine must still provide HP to power the alternator to power the electric fan(s) - at least when the vehicle is not moving since the fans are not needed when the vehicle is at highway speed, which is when you'll see the most HP gain over a manual fan.

[This message has been edited by Stuart Moss (edited July 25, 2000).]

 

Instead of wiring it hot through a switch (too much amperage), use a relay for driving lights (a good one like Bosch; when I bought a high $ relay kit from Barry Grant for his fuel pumps that's what it came with.) Nearly all of these relays use a 5 pin connector. Run 1 wire (fused) to the power side of the relay (10 gauge). Run 1 wire to trigger the relay via a (toggle) switch (14-16 ga, only a 1-2 amp draw). One ground wire (10 ga)to the chassis. There are now two outputs: one for the fans one for the pump. Run 1 wire for each from the relay forward. I run 2 12" flexalite fans and a Meziere water pump and pull a maximum spike of 26 amps when the fans are triggered. Normal operating draw is 20 amps. Use 10 gauge wire from the relay to the fans and the amp draw will be kept as low as possible. My car does not use the rear window defogger circuit so I tapped into that to keep the circuit controlled by the ignition.

 

9.0,

The relay you described, commonly called an "icecube" relay, draws a lot less than 1-2 amperes - actually 120-150 mA (milliamps, or 0.120 - 0.150 amperes). 18 guage wire will be sufficient to power the coil (anything larger than 16 guage is overkill).

BTW, there is no need for 10 guage wire to run from the negative side of the relay coil. As stated above, 16-18 guage is fine.

You stated "...Use 10 gauge wire from the relay to the fans and the amp draw will be kept as low as possible...". The use of a larger guage wire is not to keep current draw to a minimum, but to keep VOLTAGE DROP to a minimum. The larger the wire, the less the voltage drop...and by the same token, the more current that is passed through a wire, the larger the voltage drop. Large voltage drops cause devices to operate with more difficulty...too much and it'll fail.