The Ford Barn

mngreen · 02-13-2015, 06:32 PM

...the 30A fuse (or breaker) at my starter blows while driving with my 1960's era 12v Delco 10si alternator, 3-wire setup on my Model A? Will the alternator still power the ignition or kill it? Or....will the alternator push out maximum current after sensing no battery voltage and fry everything?

Kurt in NJ · 02-13-2015, 08:00 PM

What side of the fuse is the voltage sensing wire hookedf to?

James Rogers · 02-13-2015, 09:54 PM

If it is hooked like it is designed to be, the engine will die. This fuse is the source for all the power in the car except for the starter.

tbirdtbird · 02-13-2015, 11:15 PM

yep, whether an alternator or not

Willie Krash · 02-13-2015, 11:19 PM

On a three wire set up the alternator should go off line. The 2 or R term are the sense terminals, once it goes to zero it should shut down.

I do believe the very early 10si employed secondary regulation. It may really depend on the regulator. A generator of course a different story.

To simplify one's thinking take amperage out of the equation. The alternator cannot make any device take more amperage. The device determines this (voltage goes up, amperage goes down).
Think of your alternator as a wall plug. It will provide 14.25V at 70° with enough mechanical input. If rated at 60 amps it will provide what ever amperage the car (device) demands up to 60 amps.

The higher that amperage demands the lower the voltage, typically on an analog system the voltage will ramp down. That is to say a good 60 amp analog alternator may produce 40 amps at 13.5+V off idle.

Just to add to the discussion I rarely if ever use an amp meter when checking alternators or generators. If all the loads the car needs are satisfied there is no need to know amperage. On a modern car if all the loads are on and the battery is seeing 13.6V or better amperage becomes a moot point.
Hope this helps. Caveat, I have been stuck in the office for over 10 years so this is from memory, what ever that is..

mngreen · 02-13-2015, 11:51 PM

Sponsored Links (Register now to hide all advertisements)

Would anything bad happen if I tested your theory by simply removing the fuse while the engine is running?

tbirdtbird · 02-14-2015, 01:06 AM

nothing bad at all.
they can be tough to get out. I put a zip-tie around them before I put them in to make removal easier. can put one on now even tho it is in place. Gives you a 'handle'

02-13-2015, 06:32 PM	#1
mngreen Senior Member Join Date: Jul 2010 Location: Rancho Santa Margarita, CA Posts: 155	What's going to happen when.... ...the 30A fuse (or breaker) at my starter blows while driving with my 1960's era 12v Delco 10si alternator, 3-wire setup on my Model A? Will the alternator still power the ignition or kill it? Or....will the alternator push out maximum current after sensing no battery voltage and fry everything?

02-13-2015, 08:00 PM	#2
Kurt in NJ Senior Member Join Date: May 2010 Location: on the Littlefield Posts: 6,159	Re: What's going to happen when.... What side of the fuse is the voltage sensing wire hookedf to?

02-13-2015, 09:54 PM	#3
James Rogers Senior Member Join Date: May 2010 Location: Asheville,NC Posts: 3,104	Re: What's going to happen when.... If it is hooked like it is designed to be, the engine will die. This fuse is the source for all the power in the car except for the starter. __________________ http://www.model-a-ford-4bangers.com/

02-13-2015, 11:15 PM	#4
tbirdtbird BANNED Join Date: May 2012 Location: inside your RAM Posts: 3,134	Re: What's going to happen when.... yep, whether an alternator or not __________________ '31 180A

02-13-2015, 11:19 PM	#5
Willie Krash Senior Member Join Date: Jan 2012 Location: Phoenix, Oregon Posts: 661	Re: What's going to happen when.... On a three wire set up the alternator should go off line. The 2 or R term are the sense terminals, once it goes to zero it should shut down. I do believe the very early 10si employed secondary regulation. It may really depend on the regulator. A generator of course a different story. To simplify one's thinking take amperage out of the equation. The alternator cannot make any device take more amperage. The device determines this (voltage goes up, amperage goes down). Think of your alternator as a wall plug. It will provide 14.25V at 70° with enough mechanical input. If rated at 60 amps it will provide what ever amperage the car (device) demands up to 60 amps. The higher that amperage demands the lower the voltage, typically on an analog system the voltage will ramp down. That is to say a good 60 amp analog alternator may produce 40 amps at 13.5+V off idle. Just to add to the discussion I rarely if ever use an amp meter when checking alternators or generators. If all the loads the car needs are satisfied there is no need to know amperage. On a modern car if all the loads are on and the battery is seeing 13.6V or better amperage becomes a moot point. Hope this helps. Caveat, I have been stuck in the office for over 10 years so this is from memory, what ever that is.. __________________ Mike Stitt "A business that make nothing but money is a poor business." -Henry Ford

02-13-2015, 11:51 PM	#6
mngreen Senior Member Join Date: Jul 2010 Location: Rancho Santa Margarita, CA Posts: 155	Re: What's going to happen when.... Sponsored Links (Register now to hide all advertisements) Would anything bad happen if I tested your theory by simply removing the fuse while the engine is running?

02-14-2015, 01:06 AM	#7
tbirdtbird BANNED Join Date: May 2012 Location: inside your RAM Posts: 3,134	Re: What's going to happen when.... nothing bad at all. they can be tough to get out. I put a zip-tie around them before I put them in to make removal easier. can put one on now even tho it is in place. Gives you a 'handle' __________________ '31 180A