alternator exciting

INCase · Dec 26, 2011

converted FIL's 9N to 12volt (DONT send 10 pages of why not to convert). Old generator was bad and he doesn't like to fiddle with things and i had an extra alternator.

QUESTION: Has anyone had trouble with lower RPM tractors not getting enough RPMs to excite the alternator. It is a 3 wire DELCO and is wired properly.

Seems like the tractor "should" turn fast enough to get the unit to charge with it rev'd all the way up.

Has anyone had to "re-excite" a 3 wire alternator (GM Delco)? If so how do you do it. It has a wire to the idiot light and ignition switch from #1 and #2 terminal to the "BAT" term on the alternator.
Thanks!!!!

Geo-TH,In · Dec 26, 2011

I have to get my Jubilee to 1200 RPM's before the alternator begins charging. I have to rev up my Farmall C to get it to wake up too. The older alternators would begin charging the instant they started turning. My replacement alternators need some time and RPM's to wake up.
George

Chris(WA) · Dec 26, 2011

I run an alternator off a Mitsubishi on my Allis. Have to rev way up to get it to charge then it will work till I shut it off. Always wondered why myself as it would charge at idle (5-600 RPM) in a car..

pat sublett · Dec 26, 2011

I believe that the idiot light may be the key to the problem. Alt is excited through it. You might try a low restance resistor ether in parallel or series with the light.

old · Dec 26, 2011

Replace the light bulb with a diode from radio shack #276-1661 and it should excite at about 700rpm or so

JMOR · Dec 26, 2011

(quoted from post at 21:22:33 12/26/11) I believe that the idiot light may be the key to the problem. Alt is excited through it. You might try a low restance resistor ether in parallel or series with the light.

xactly, the bulb supplied a very marginal excite current to alternator. In GMs original incarnation of the system, there was a 10 Ohm, 6.25 Watt resistor in parallel with the light bulb. Sure most tractor conversions skip the resistor & many work or sort of work, but if you install it, yours will work correctly.

INCase · Dec 26, 2011

would adding a extra resistor in series with the light help? I really like the light for the FIL to check if the alt is charging. The light is a little dash light from NAPA.

The 800 Case I wired up with an alternator has a regular mini lamp factory dash light which probably has more resistance.

LJD · Dec 26, 2011

A 3-wire Delco 10SI or 12SI should charge instantly. Does not rely on any residual magnetism to excite.

A 10SI rated 61 or 63 amps must spin 1800 RPM minimum to charge.

A 10SI rated at 72 amps must spin 1600 RPM to charge.

Your crank pulley is probably at least twice the size as your alternator pulley, so worst-case the 10SI should start charging at 900 engine RPM. If not, something is wrong(alternator or wiring).

Now if you've got a huge diameter pulley on the alternator that make it run at only engine speed - then you can have a problem. Alternators usually are set up to run at 2X to 3X engine speed.

Janicholson · Dec 26, 2011

Run a jumper to the #1 lug from battery volts when just above idle. if it charges, it is not getting enough through the idiot light as you have it. Is it perchance a LED type Light? they do not work unless there is a 10 ohm resister across the bulb terminals. if it fails to charge with 12v to the #1 post, the alternator needs to be checked, Maybe it was in stock for that reason. Jim

JMOR · Dec 26, 2011

(quoted from post at 21:48:36 12/26/11) would adding a extra resistor in series with the light help? I really like the light for the FIL to check if the alt is charging. The light is a little dash light from NAPA.

The 800 Case I wired up with an alternator has a regular mini lamp factory dash light which probably has more resistance.

bsolutely NOT!!!
What did I say? I said 10 Ohms in PARALLEL with the idiot light!

John T · Dec 26, 2011

They dont need to be "RE EXCITED" so if all else is okay I question what kind of light (incandesecent or LED) your idiot light is??? If its too much resistance (like an LED can have)perhaps there is insufficient current flow for adequate initial excitation??? Instead of the light try maybe a 10 ohm resistor in its place and see if that makes a difference??

John T

INCase · Dec 27, 2011

the 9N crank pulley looks like about 6 inch (hard to get tape in there.

The alt pulley is a wide belt one and is about 3-1/4.

INCase · Dec 27, 2011

Put the jumper to the #1 and it started charging. A nice 14.3V at the battery. Shut is off and wouldn't re-excite so it looks like the idiot light isn't sufficient to get it to go.

Thanks for the help!!!!

massey333 · Dec 27, 2011

A little different take John.There is something in the wiring on Delcos that can effect the excitment,we had a super good shop,but 99%of all apps.for JD 30s &40s he did would not start until you had the engine 1900-2000 and was then fine.He would never admit or fix them,but they had to be rewired internaly.Also had 2 GM dealerships in the family and they said the same thing about some parts place rebuilders needing the alts.rewired to work properly.So it is not all black and white.

mkirsch · Dec 27, 2011

The idiot light is too much resistance. Resistance reduces voltage. The alternator is not seeing enough voltage to properly excite through the idiot light.

GM's solution was to add a resistor in PARALLEL to the idiot light. Adding resistors in PARALLEL actually has the effect of REDUCING resistance, and INCREASING voltage to the alternator excite circuit.

If you want to make it work correctly, withOUT any hacks, add the resistor mentioned earlier across the terminals of the idiot light. That will fix it.

Owen Aaland · Dec 27, 2011

(quoted from post at 12:04:12 12/27/11) A little different take John.There is something in the wiring on Delcos that can effect the excitment,we had a super good shop,but 99%of all apps.for JD 30s &40s he did would not start until you had the engine 1900-2000 and was then fine.He would never admit or fix them,but they had to be rewired internaly.Also had 2 GM dealerships in the family and they said the same thing about some parts place rebuilders needing the alts.rewired to work properly.So it is not all black and white.

I would guess that he was using a single wire regulator. Even then that would put the alternator speed at 4000 - 5000 RPM before starting to charge.

Most of the alternators I rebuild are 72 amp. When I put them on the test stand they will start to charge at between 600 and 800 RPM. That is with feeding battery voltage to the excite terminal. The more resistance you have in that wire the high the RPM will be before the alternator starts top charge. Once they start to charge the will continue to charge until the speed again drop below the 600 - 800 RPMs.

The alternator should be running at 2.5 - 3.5 times the speed of the engine crankshaft. Since the older tractor engines are not high speed you can go much higher than 3.5 and be alright.

Geo-TH,In · Dec 27, 2011

Forgot to tell you my 2005 Buick's alternator takes about 5 seconds to wake up. It's a 2 wire alternator. The second wire may go to the computer or it goes directly to the idiot light. That said, my limited experience with the newer alternators is they take some time to wake up and higher RPM's than the older ones.

My farmall has a diode and the ford has an idiot light. I've replaced both alternators with in the past year. Both take time to wake up and both need higher RPM's to begin charging. After they wake up, they will continue to charge on lower RPM's. The older alternators began charging as soon as the tractor started.

Don't worry about it. I think there may have an advantage to the lazy alternators. When my tractors are cold, I let them warm up for a minute or two before increase the engine speed and add the load of the alternator to the engine.

George

alternator exciting

INCase

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Geo-TH,In

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Chris(WA)

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pat sublett

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old

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JMOR

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INCase

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LJD

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Janicholson

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JMOR

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John T

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INCase

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INCase

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