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Relay wire sizes

Sonny

It’s all fun til the rabbit gets the gun.
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I’ve noticed that my rpms drop about 100 when my electric fans come on at idle.
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Voltage at the coil goes from 12.8 to 11.9. Goes back up when I rev it.

going to add the MSD relay to the coil. Based on the attached chart, do these wire awgs sound right:

relay to battery 10 awg (about 3’)
Relay to coil 12 awg (10 awg?) 5’
Ground 12 awg. 1’
Thanks!
 
relay to battery 8 awg
otherwise good.

Now check the alternator output and also check battery cell condition. What is the output at idle of alternator?? likely 15 amps
 
Sonny does that relay have a one way diode between 85 and 86 post. If it doesn't think about one.
 
Ur ground could even be smaller (#14), all it does is ground the relay.
 
Snakeoil24 is right. What is the current consumption rating of your new fans? You didn't mention what alternator you are currently running but if your existing alternator has low output at low RPMs (idle), your modifications won't matter. You may need to start looking at alternators with a higher output at idle, preferably one that exceeds the current draw of the fans. It might even be that your current voltage regulator is iffy.
However, I still have some questions. Are you planning to get the main power for the fans directly from the battery? I'm not too knowledgeable about this one so hopefully someone else can chime in, but wouldn't that put the fan draw outside the voltage regulator sensing circuit?
 
Snakeoil24 is right. What is the current consumption rating of your new fans? You didn't mention what alternator you are currently running but if your existing alternator has low output at low RPMs (idle), your modifications won't matter. You may need to start looking at alternators with a higher output at idle, preferably one that exceeds the current draw of the fans. It might even be that your current voltage regulator is iffy.
However, I still have some questions. Are you planning to get the main power for the fans directly from the battery? I'm not too knowledgeable about this one so hopefully someone else can chime in, but wouldn't that put the fan draw outside the voltage regulator sensing circuit?
Current alternator is a basic one from advance auto and is 60 amps. The fans draw 30. I have the fans driven off of the alternator, and now I have an MSD 6A ignition box wired to the battery. Condition still exists. It’s a basic car electrically, no power windows or doors, am radio, and lights. I read that going from a 60 amp to 85 amp alt doesn’t require a wire size upgrade. Sound correct? Would I need to go larger on the alternator?
Sonny
 
relay to battery 8 awg
otherwise good.

Now check the alternator output and also check battery cell condition. What is the output at idle of alternator?? likely 15 amps
new battery. Check amps at alt stud??
 
Also I never installed the relay. Figured the ignition box would do the trick. But no.
 
Current alternator is a basic one from advance auto and is 60 amps. The fans draw 30. I have the fans driven off of the alternator, and now I have an MSD 6A ignition box wired to the battery. Condition still exists. It’s a basic car electrically, no power windows or doors, am radio, and lights. I read that going from a 60 amp to 85 amp alt doesn’t require a wire size upgrade. Sound correct? Would I need to go larger on the alternator?
Sonny

I looked online and could not find a reliable source concerning the idle output of a stock Mopar alternator. I still seriously doubt that a stock 60 amp alternator & regulator put out at least 30 amps at idle. One easy way to tell would be to start the engine, disconnect the fans and check the volt gauge, reconnect and check again. Again, if your issue is only during idle and eases with an increase in RPM's, your alternator & regulator combination can not provide the demand at idle.
As for the main wire gauge. It's important to remember that amps are a measurement of consumption. You could install a 1000 amp alternator but if you system consumes a total demand of 60 amps from all devices, all in proper working condition, then that is all that will be output from the alternator regardless. If you add devices the total consumption increases. Plus, remember that stock wiring was engineered according to the maximum demand at the time. I would say that increasing the wire size is never a bad idea. Do your math and see if it's really necessary.
http://www.powermastermotorsports.com/
There's a lot of good information on Powermaster's site. Check it out.
 
Late to the party anytime for me I upgrade something I always upgrade what's involved. Your fans will pull more load at a light because of that factor the alt wiring can't give you more amps. So upgrade is needed. Also next time your looking at the alt pulley did you use the old one or upgrade it to the amps that it should be. Some alt pulleys are different size. Better yet I should say each alt pulley is made to help produce max out put so if the new is 4 inch round and the old one is 6 inch round and you used old pulley on new alt it won't produce what your after. So between the wire being wrong and the pulley being wrong then your problem will never get cured. Good luck and just my 2cents.
 
Get an amp meter and measure at idle and at 1200 rpms then determine the required maintenance amperage above the draw by 10%. You will then need to go toan independent alternator rebuilder to see if the can boost idle level output.
 
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Bearman has a point about alt. pulley diameter. The bigger pulley will turn the alt. slower and as you decrease the diameter of the pulley the faster it will turn if I recall my geometry correctly, therefore raising the amp output.
 
What do you have hooked up to the battery direct. Next put the clamp side of meter around the wire you wish to test. That will tell you the amp load of the wire. Try around the main cable at the alt at idle then run it up to 1200 you will see a difference.
 
It’s rare to find a DC Clamp Amp meter.

Your meter is reading AC Volts.

Some meters have Auto Voltage Selection meaning it automatically displays the voltage in AC or DC.
You might have to press the “Select” button to switch to DC voltage
 
It’s rare to find a DC Clamp Amp meter.

Your meter is reading AC Volts.

Some meters have Auto Voltage Selection meaning it automatically displays the voltage in AC or DC.
You might have to press the “Select” button to switch to DC voltage
 
Mine reads thru the clamp side on my voltmeter I didn't pay attention to the what he had it set on sorry folks.
 
10-4. I’m bad at electricity.
My battery reads about 12.6v at rest. Crank the engine and I’m getting 13.1 v at the battery, fans off, and reving up to 2000rpm does nothing for voltage. No increase in voltage at all.
 
10-4. I’m bad at electricity.
My battery reads about 12.6v at rest. Crank the engine and I’m getting 13.1 v at the battery, fans off, and reving up to 2000rpm does nothing for voltage. No increase in voltage at all.
Also in car volt meter shows 14v then fans come on it drops to 12.0.
 
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