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Tractor Talk Discussion Forum

Three wire alternator with only one wire connected

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R. Smith

07-06-2004 21:10:59




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Greetings... A friend of mine has a MF 202 (think that's what she said) that always has the battery running down. I glanced at the alternator the other day and even though it was a three wire alternator it only had one wire leaving at the output lug... no other wires that I could see plugged or not plugged. Can the alternator function properly or charge at all without the "sense" line and the "exciter field tap" wire connected? (Had no idea of the proper names until just a few hours ago) Just wondering. I told my friend that I'd post a message at this site to see if anyone might be able to shed some light on the matter. Sure would appreciate any help. Thanks.

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cannonball

07-08-2004 05:10:08




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 Re: Three wire alternator with only one wire conne in reply to R. Smith, 07-06-2004 21:10:59  
if the alt is a one wire she might not be racing the engine up enough to kick off alt...if she is the could have bad diodes ...unhook the wire from back of alt..hookup light tester ,if you have problem in alt light will burn ,,have nice day may god bless



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john in la

07-08-2004 03:47:34




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 Re: Three wire alternator with only one wire conne in reply to R. Smith, 07-06-2004 21:10:59  
Look over this WEB SITE



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Mike (WA)

07-08-2004 09:07:19




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 Re: Re: Three wire alternator with only one wire c in reply to john in la, 07-08-2004 03:47:34  
Great site- I printed it out for future reference, but missed a substantial portion on the right side because the text is too wide. Even misses some when you set print to "landscape" mode (sideways). Is there any way to narrow it up so it will print the full width of the site?



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john in la

07-09-2004 03:56:40




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 Re: Re: Re: Three wire alternator with only one wi in reply to Mike (WA), 07-08-2004 09:07:19  
Do not know. Have never tryed to print it out. I just saved it to my favorites so I always have it. If you think the web site my go away you can tell your computer to make available off line and it will down load a copy to your hard drive.



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Butcher

07-07-2004 18:32:01




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 Re: Three wire alternator with only one wire conne in reply to R. Smith, 07-06-2004 21:10:59  
Gary and Justin are correct. A three wire Delco will charge if you rev the engine up to a certain RPM. I have one on my 1750 and it works great. I also have used old LULL lifts that had the same setup.



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Gary

07-07-2004 16:30:03




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 Re: Three wire alternator with only one wire conne in reply to R. Smith, 07-06-2004 21:10:59  
I have a self exciting alt on my old tractor. It has only one wire going to the ign switch. No regulator. It is a 21 amp delco made to be this way. you need to rev the tractor up to get it to start charging. After that it will charge at an idle. It will run a full set of lights ect.. Disconnects when you shut the tractor off. No regulator, no extra wires, nothing. It works GREAT! I have convereted many old tractors to this system. I would not do it any other way. Gary

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Ron

07-07-2004 02:20:43




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 Re: Three wire alternator with only one wire conne in reply to R. Smith, 07-06-2004 21:10:59  
Without knowing what type of alternator you have I can only give you a general answer.

If it's a Delco and it has an internal regulator then it will not charge. However, they can be modified internally to be a "one-wire" alternator. This is becoming more popular with old tractors that have no electrical demands beyond recharging the battery after starting.

If it's an external regulator alternator, then no, it cannot charge without a regulator.

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justin j

07-07-2004 16:55:08




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 Re: Re: Three wire alternator with only one wire c in reply to Ron, 07-07-2004 02:20:43  
most 3 wire delco alternators WILL self excite with only the output wire hooked up. ive done a few 12 volt conversions that way. i just go to napa and by an alternator for a "Chevy pickup" and bolt it on my tractor instead.



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Ron

07-07-2004 17:20:54




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 Re: Re: Re: Three wire alternator with only one wi in reply to justin j, 07-07-2004 16:55:08  
They would have to be defective to do so. That's why the kits are available to convert them to "one wire".

Chevy pickup? There are at least a half-dozen different Delco alternator models that have been used on Chevy pickups.



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Bob

07-06-2004 22:37:00




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 Re: Three wire alternator with only one wire conne in reply to R. Smith, 07-06-2004 21:10:59  
It is possible to function without the #1 and #2 terminals used IF it has the proper aftermarket voltage regulator installed. Unless you know the complete history of the alternator, WHO KNOWS what's in there for a regulator, as there are MANY aftermarket units, usually not clearly identified, even with the regulator in out of the alternator.

Try this: check the voltage at the large stud with the engine at 1/2 to 3/4 throttle. If the alternator is charging, you will get 13.5 volts to 14.75 volts.

If the alternator is NOT charging, you will get 12.5 volts, or less.

If it is NOT charging, shut down the engine, and connect a jumper wire from the #2 terminal (voltage sense) to the output stud of the alternator. Connect another jumper wire to the #1 (excite) terminal, and leave the other end free.

Start the engine, and rev it up a bit, as before.
(CAREFUL OF THE FAN AND OTHER MOVING PARTS!!!)
Now, momentarily touch the free end of the test lead dangling from #1 to the large output stud. This should excite the alternator, and the voltage should come up to the range previously mentioned.

If the alternator works now, install a permanent jumper from #2 to the large output stud, and connect a wire from a switched 12 Volt source to the #1 terminal. If you stop here, the engine probably won't shut off due to the alternator backfeeding through the wire to #1. To prevent this, use and "idiot light" with a small bulb such as a 194 spliced into the lead to #1, or obtain a 2.5 amp 1000PIV diode (Radio Shack), and splice it into the wire instead of the idiot light. Toward one end of the plastic body of the diode, there will be a white band printed around the diode. This indentifies the CATHODE END of the diode, which is the end you connect to the wire going to the #1 terminal on the alternator.

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Jon H

07-07-2004 12:03:04




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 Re: Re: Three wire alternator with only one wire c in reply to Bob, 07-06-2004 22:37:00  
I would also bet the alternator Has been fitted with a 1 wire regulator.
That being said,I have on atleast two occasions Had a 3 wire Delco 10SI alternator with a stock three wire regulator self excite without any power to the Regulator excite wire (#1).
I use a home built alternator/generator test stand where I disconnect the battery when the stand will not be used for a day or so. I use a Delco regulator plug with both #1 and #2 wires connected together and fed power through a small ammeter to read field current draw. The alternator output is connected to a large ammeter and a carbon pile to test output,and all this powered by a Battery. At least twice I have connected a repaired 10SI Delco to the test stand and spun it up only to see the voltage come up to normal,but not indicate any output to the battery/carbon pile. In both cases I had not connected the battery to the test stand,yet the alternator had excited itself from residual magnetism in the rotor poles,just like one with a 1 wire regulator. A sensitive stock 3 wire regulator can self excite the stock alternator,but should charge unregulated if the #2 (sense) terminal is not connected to output voltage. The 1 wire regulators work without a sense wire connected,so I suspect they read system voltage internally from the Diode trio.

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