Measuring Alternator output - Mopar Tech

Phil · #1 09-09-2008, 10:00 AM

What is the correct way to measure the amount of amps your alternator is putting out? I want to check mine to see how many at idle and at higher RPM's it is putting out.

#2 09-09-2008, 10:14 AM

Do you know the amp rating for your alternator ? 100 amp 120 ? I usually just check for voltage out put with the system taxed, i was told that 3/4 of you amp rating at idle and 100% at 2000 rpm. Constant 13.5 volts to 14 volts.

MYBD318 · #3 09-09-2008, 10:25 AM

The alternator will only put out enough amps to lift the voltage to the regulated level usually somewhere around 14 volts.
To measure how much current at that time you would need use a clamp on type current probe or wire in an ampmeter or shunt. Changing the system load like lights, AC or heater blower will vary the demand and the current will be larger from the altenator.
Like dustpan stated its just easier to measure the voltage.
Sorry for the long explanation.
Mikey

Phil · #4 09-09-2008, 10:41 AM

Don't be sorry I want to learn more about this stuff. I think I have a 65 am alternator and I'd like to go to a 95 or 100 amp unit to handle the extra load I have put on the system with my nitrous kit, fuel pump and electric fan. I have bypassed the ammeter and now my volt meter will tick back and forth when the turn signal is on. I have the MP constant output regulator and it is supposed to stay at 13.5V constantly but it ticks with the turn signal between 14 and 12 and drops below 12 if I have to lights and fan on. It never ticked like that before i bypassed the ammeter but I wonder if the bypass kit messed with how the voltmeter reads and regulates now.

MYBD318 · #5 09-09-2008, 01:59 PM

If I were to guess. I bet the the voltage at the alternator stays right on during this event and that you have some serious voltage drop in the wiring from the alternator to the dash

MRL Performance · #6 09-09-2008, 05:20 PM

You are not supossed to run that regulator for normal everyday driving. Its for Race only. At least thats what MP says.

Scotty · #7 09-09-2008, 05:42 PM

I run one on my truck and it's been on there for 4 years. No problems.

Phil · #8 09-10-2008, 05:12 AM

It wouldn't suprice me that I have voltage drop...I am running the factory harness from '73.....I have got to save up the cash for a painless harness and get rid of the factory thing. I do know I need a bigger alternator with all the stuff I have added. Race only mean better right? Seriously though my car doesn't see enough street time to be considered a driver anymore. I have a factory style one on the shelf I might swap it out for a test.

Mark · #9 09-10-2008, 07:56 AM

Phil, you know as well as i do that factory harness wasn't worth a sh!t when it was new.

Phil · #10 09-10-2008, 08:19 AM

Definetly....I only used it cause it was in decent shape and I didn't have the money to buy a harness and pay to have it put in.....I still don't have the cash for that.....this is why I bypassed the ammeter. Until put that bypass kit in my volt meter never ticked back and forth with the turn signals....I really think when I bypassed that ammeter it messed with the flow for the constant output regulator.

MYBD318 · #11 09-10-2008, 09:30 AM

If you have the factory harness then you will have the square firewall connector that I'm sure by now has some melted pins like the main feed. I reworked the connector by taking out the mating pin set and passing a fresh larger gauge wire directly from the altenator through the existing pin cavity and to the fuse block. This is one of the major failure points with Ma chryslers wiring harness.
Bla bla bla...
Mikey

Phil · #12 09-10-2008, 09:34 AM

Pins are all in good condition....factory fuse panle is MIA and I ran a feed wire through to the new fuse block.

Phil · #13 09-11-2008, 10:24 AM

Well I moved the voltmeter's wire so it reads off the ignition hot side of the fuse box and it helped with the "tick tocking" when the turn signals are activated. It bothers me that it never did that before I put in the harness preserver and bypassed the ammeter. I got my alternator/battery tester out and fired up the car and turned everything on and I do need a bigger alternator....I can suck it down to 12v with everything on and below 12v if I turn the bottle heater on. I am gonn call the local alternator shop and see how much it would cost to have mine rebuilt to a 95 or 100 amp unit and make it so it puts out 60amps or so at idle and then the full 100 at 2000rpm or above.....I'll then put the stock voltage regulator back on.

Bill · #14 09-11-2008, 06:21 PM

I BELIEVE YOU DONT WANT TO DO IT THAT WAY . the new alternater with internal voltage regulater will work just fine , ehat ever you use it will use just said above ..

Bill · #15 09-11-2008, 06:22 PM

that means when your electric fuel pump kicks on you only have 65 amps turn on the radio 65 amps ect ect , then rev it up to 2000 rpm all the time to keep up / i may be missing something here please set me straight!!

the new alts have zener diodes just for what your talking about and more . buy the mancini altwith mounting kit 130 amp . 250.00$ OUCH!!!!!!!