High RPM'S to Excite the Alternator

KCTractors · Apr 27, 2009

I have a Moline 602 with the Delco 3 wire alternator on it. I have the field wire, wired to a idiot light, but I still have to rave up the rpm"s to get the alternator to excite. I wired a Ford 800 with John from La"s idea with the auto switch and works great. Starts charging at low rpm"s. Any idea, I was thinking of using a auto switch on the Moline , but I thought that idiot light was supposed to do the same thing.

rvirgil_KS · Apr 27, 2009

You might try adding a 10 ohm 5 or 10 watt resistor across the idiot light (such as Radio Shack #271-132) or replace the idiot light with a 1.5A @ 50 Volt (or greater) diode. (Radio Shack 276-1661 has good sturdy leads) White band end of diode toward alternator.

Check this link, on left under albums click on "Newest Uploads" and go to diagram for MM Letter Series with Alternator. It should be close to the way the 602 is wired
MM Letter Series with Alternator

old · Apr 27, 2009

Most likely problem you have is a light bulb that is to big as in to many watts. That is one reason I use the Radio shack 276-1661 diode

Jon Hagen · Apr 27, 2009

Some of the GM cars of the 70's had two "gen" indicator lights wired in parallel for a faster excite, one exposed one hidden. Mechanics that did not know the second hidden indicator light existed, would about rip their hair out in frustration while trying to fix a slow alternator excite problem. Replace the burned out hidden bulb and all was well.

How fast does your alternator turn ? My 4020 JD has a large alt pulley on it,s three wire alternator and turns so slow that the gen light normally does not go out until atleast 1300 engine rpm.

440roadrunner · Apr 28, 2009

(quoted from post at 20:52:45 04/27/09) Most likely problem you have is a light bulb that is to big as in to many watts. That is one reason I use the Radio shack 276-1661 diode

No, other way around. smaller wattage bulbs are higher resistance. A LARGER wattage bulb is what you want. I agree that the "fix" is to use a diode.

JDemaris · Apr 28, 2009

What exactly are you calling "high RPMs?"

Most Delco alternators have a minimum cut-in speed of 1200 RPM, but it can vary depending on exactly what regulator is stuck int there. When mounted on auto or truck engines, the engine speed to alternator speed ratio is usually at least 2.3 to 1, but many are up to 4 to 1. Tractors sometimes a litle slower at 1.9 to 1. At 2.3 to 1, and an engine idling at 600 RPM, the alternator is spinning at 1380 RPM.

It can depend on many things and not all alternators are the same, even when the same model #. There are several different regulators that can be installed and all have different cut-in values. Pulley size also changes things.

Some 12SIs and 17SSIs can self-excite with no field current and no self-excite regulator installed, if run fast enough. All depends on the condition of the residual magnetism.

KCTractors · Apr 28, 2009

I have to throttle it up to full throttle. I am going to try the diode system. Thanks Guys

Duner Wi · Apr 28, 2009

Diode installed the correct direction or correct size bulb both work well. Your choice.

steve in wi · Apr 28, 2009

on my pentibone lift, it always runs at low rpm,s.. i but on a smaller pully on the alt, makes a big difference in charging,don't have to rev it up high...just a thought...

buickanddeere · Apr 28, 2009

Steve in win and jdemaris have the answer.

High RPM'S to Excite the Alternator

KCTractors

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rvirgil_KS

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old

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Jon Hagen

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440roadrunner

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JDemaris

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KCTractors

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Duner Wi

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steve in wi

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buickanddeere

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