Alternator requirements

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Dr Jay
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Alternator requirements

Post #1 by Dr Jay » Sun Jul 15, 2018 5:10 pm

Need a bit of help.
I installed an electric radiator fan.
Sooo after 1 hour of really great performance (fresh head, 268 comp cam, added to my combination at same time) the ignition (MSD and DS2 distributor) blinks off.
Soo I suspect the alternator could not hold voltage at low RPM. I decided on a 75 amp Powermaster retro alternator. Will it be enough?
Power nothing, no radio, no ac!
Blessings,
Dr Jay

1978 F100 Shortie, Lowered front and rear, 300 .030 over, 240 head, Clifford, Holley 390
252 Comp Cam, Cloyes, Fuel Inj. exhaust manifolds, MSD 6A, TOD, 9"

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Re: Alternator requirements

Post #2 by SteveP » Sun Jul 15, 2018 7:20 pm

Do you have a working voltmeter and/or ammeter so you can tell what the alternator is doing?
I'm running an electric fan full time with 2 smaller auxiliary electric fans on a stock 60 amp alternator with no problems. (DSII ignition)

86f250straight6
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Re: Alternator requirements

Post #3 by 86f250straight6 » Sun Jul 15, 2018 11:11 pm

What brought you to the conclusion that the alternator was bad? I would do what SteveP said grab a multimeter and start testing. There a several fusible links built into the wiring that could have fried causing these issues. The alternator charge wire has a fusible link built in, and if its still stock is barely enough to keep up with charging the battery.
I'm trying to build a truck that I can't break :bang:

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Dr Jay
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Re: Alternator requirements

Post #4 by Dr Jay » Mon Jul 16, 2018 12:03 am

Sure, I have meters and tools. I did not think the alternator was broken just a bit undersized. Ignition would shut off at idle, I thought that meant low voltage once the battery was depleted from carrying the the new fan. I’ll check it when I’m back in town. I’m hopeful since a 60 amp carries yours that I’ll be fine with a 75!
Thanks
Blessings,
Dr Jay

1978 F100 Shortie, Lowered front and rear, 300 .030 over, 240 head, Clifford, Holley 390
252 Comp Cam, Cloyes, Fuel Inj. exhaust manifolds, MSD 6A, TOD, 9"

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Re: Alternator requirements

Post #5 by GPGoverMPG » Tue Jul 17, 2018 7:42 am

Everything may be OK. Sometimes we try to pull to may amps through the ignition switch. You may try connecting fans and other accessories through relays. That moves the large current draw out of the switch. Good luck
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jason832
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Re: Alternator requirements

Post #6 by jason832 » Tue Jul 17, 2018 10:34 am

The ignition itself will pull very little at idle and can run on fairly low voltage.

Look up a 3g alternator swap. They're cheap and can be had in 130 amp versions. Everything can be found in a junkyard for like 30$

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Re: Alternator requirements

Post #7 by 1986F150six » Tue Jul 17, 2018 11:06 am

Dr. Jay,

Regarding a 75 amp. alternator... My 1986 F150 with factory A/C came with a 60 amp. alternator. The alternator died [old age], so I took it to a local alternator/generator/starter repair shop. They are "old school" and I have used their services before. It would have been ready in a day, but they told me they had one already rebuilt "on the shelf". I swapped with them and was on my way for $75. I was extremely pleased to find that this Motorcraft alternator was rated @ 75 amps, not 60. The wiring was identical and I have been using it for about 2 years. I was having no issues before, but am happy to have 25% more capacity.

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Dr Jay
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Re: Alternator requirements

Post #8 by Dr Jay » Tue Jul 17, 2018 1:00 pm

Should have done the alternator shop deal....
I had to have a first generation small case.
That bracket jams the alternator right up against a heat shield and the exhaust manifold. I was afraid I could not get good clearance for connections.
I really think my stock alternator is 40 amps.
Blessings,
Dr Jay

1978 F100 Shortie, Lowered front and rear, 300 .030 over, 240 head, Clifford, Holley 390
252 Comp Cam, Cloyes, Fuel Inj. exhaust manifolds, MSD 6A, TOD, 9"

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Re: Alternator requirements

Post #9 by SteveP » Tue Jul 17, 2018 10:34 pm

As GP Grover commented, you may be pulling too many amps through the ignition switch and overheating something.
I'm running my fans through relays directly off the battery through a fuse block. The main fan relay is controlled through an oil pressure switch so it runs whenever the engine is running but stops when I shut the engine off. At first I controlled it through a temp sender but it kept running for several minutes after shutdown. I control the aux fan relay with a manual switch.

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Dr Jay
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Re: Alternator requirements

Post #10 by Dr Jay » Wed Jul 18, 2018 7:56 am

Yep, you are right, no relay in my setup. I ran it off solenoid “I” post.
It all seemed so simple. Hahaha
Blessings,
Dr Jay

1978 F100 Shortie, Lowered front and rear, 300 .030 over, 240 head, Clifford, Holley 390
252 Comp Cam, Cloyes, Fuel Inj. exhaust manifolds, MSD 6A, TOD, 9"

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Dr Jay
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Re: Alternator requirements

Post #11 by Dr Jay » Sat Jul 28, 2018 8:19 am

So after some testing and observing, when the fan cut on, the idling engine would stall. Not from low battery charge or poor alternator output, battery voltage held.
That one ignition circuit would stumble enough to reset the MSD.
Common wisdom was true. Relay with the ignition circuit as the trigger and a direct connection to the battery for the primary load for the fan fixed the problem.
Then ...... the Radiator probe temperature switch died.
I’m looking for a durable alternative there.
Blessings,
Dr Jay

1978 F100 Shortie, Lowered front and rear, 300 .030 over, 240 head, Clifford, Holley 390
252 Comp Cam, Cloyes, Fuel Inj. exhaust manifolds, MSD 6A, TOD, 9"

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Dr Jay
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Re: Alternator requirements

Post #12 by Dr Jay » Sun Jul 29, 2018 10:15 pm

And my scenario continues.
Recap, head replaced, cam swap, electric fan swap.
Then motor stalled as fan cut on (repaired with wiring change and relay addition and now an air temp radiator switch) I swapped alternators and replaced the regulator while I was convinced of voltage drop.
Now it runs out fine, temp gauge holds the middle, fan cuts on when I stop, cycles in a reasonable way.
When I turn the engine off, it seems to warm up, the temp gauge swings up but still inside the normal bracket.
It seems hotter under the hood. I swapped in a 160 degree thermostat for the 190 degree deal. Gauge dropped while running. Still heats up after cut off. No AC. Manual 4 speed.
Wisdom?
Blessings,
Dr Jay

1978 F100 Shortie, Lowered front and rear, 300 .030 over, 240 head, Clifford, Holley 390
252 Comp Cam, Cloyes, Fuel Inj. exhaust manifolds, MSD 6A, TOD, 9"

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Re: Alternator requirements

Post #13 by bubba22349 » Mon Jul 30, 2018 9:17 am

:hmmm: It is normal for the engine to heat up after its shut down. I think you will need to do a little relay rewiring (ie so that its powered all the time) in that way the fan can still run after engine is shut down to cool down the engine. Go back to the 190 T Stat too. Good luck :thumbup: :nod:
A bad day Drag Racing is still better than a good day at work!

I am still hunting for a project car to build but with my current low budget it's not looking so good. My Ex- Fleet of Sixes these are all long gone! :bang: 1954 Customline 223 3 speed with O/D, 1963 Fairlane project drag car with BB6, 1977 Maverick 250 with C4, 1994 F-150 a 300 with 5 speed.

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Dr Jay
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Re: Alternator requirements

Post #14 by Dr Jay » Mon Jul 30, 2018 10:14 am

Thank you!
It was happier with the 190 degree thermostat.
I started with the fan wired solid to battery cable terminal...sensor actuated.
I sweated running the battery down. It stayed way cooler under hood. (Battery never discharged)
Blessings,
Dr Jay

1978 F100 Shortie, Lowered front and rear, 300 .030 over, 240 head, Clifford, Holley 390
252 Comp Cam, Cloyes, Fuel Inj. exhaust manifolds, MSD 6A, TOD, 9"

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THE FRENCHTOWN FLYER
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Re: Alternator requirements

Post #15 by THE FRENCHTOWN FLYER » Mon Jul 30, 2018 2:30 pm

It won't hurt a thing to let it heat up after shutdown. All mine do.

[EDIT: Although, concerns over fuel injectors being "cooked" after shutdown is what led Ford to develop their crossflow head design for this engine. Ultimately, in the short term, Ford added a little squirrel-cage blower to cool the injectors after shutdown; and for the long term they decided to just go with the 4.2 V6 which would also enable them to droop the hood line lower.

Sad.
Ah, what could have been...]

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1986F150six
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Re: Alternator requirements

Post #16 by 1986F150six » Tue Jul 31, 2018 2:32 pm

Mr. FTF, didn't Ford also experiment [prototype] with variable displacement and turbo for the 4.9L?

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Re: Alternator requirements

Post #17 by THE FRENCHTOWN FLYER » Tue Jul 31, 2018 5:22 pm

Yes, and Yes.

The variable displacement program was using Eaton cylinder disablers on a U-flow head.

The turbo program was on a crossflow head (there may have also been a U-flow turbo program - the memory fades). This engine was the real deal - Carillo rods, forged pistons, etc. and reportedly ran like a 460, which it was intended to replace. Amazingly, I have a friend who found a complete crossflow, turbo experimental prototype engine in a scrap yard near Detroit. It now resides in his Austin Healy sports car. Wicked fast.
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1986F150six
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Re: Alternator requirements

Post #18 by 1986F150six » Wed Aug 01, 2018 11:44 am

And, wasn't there a prototype 2 barrel log intake manifold, with the barrels parallel to the engine?

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