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Flash the Field?

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Ramrod
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PostPosted: Wed Jun 06, 2007 6:46 pm    Post subject: Flash the Field? Reply to specific post Reply with quote

GT is a 6v Pos gnd '49 8N front mount. I am about ready to wrap it up and hand it over to the paint shop, last thing is the genny which came back from shop today. Genny man is top notch, never misses, says it is all fixed up and tested good, I believe him. I have stripped all old wiring, and installed a new wiring harness from TSC, a new ballast resistor for front mount coil from CNH, and a new VR from CNH labeled '6 volt Pos Gnd'. Installed genny tonight before church and when I reconnect the batt cable, I get a spark and see full tilt discharge (-30) on ammeter. I couldn't spend more time to trouble shoot, but after church, all the tractor guys got together and we figure all it can be is the cut out in the new VR is in wrong state. Will flashing field reverse that state and remove short from the system (maybe)? The wiring is so simple with new harness that I believe it is correct, and tractor starts and runs very well. Am I on the right track? To flash field, I connect battery and momentarily connect field to armature on VR, correct? I need to do this every time I disco battery too? This system is way too simple for me to get my techie mind around (yet).

 
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Bob
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PostPosted: Wed Jun 06, 2007 7:17 pm    Post subject: Re: Flash the Field? Reply to specific post Reply with quote

If you are seeing a short before ever starting it up, you have a wiring problem, or a bad voltage regulator. The cutout points in a new regulator would be "open", and stay that way until startup, when the generator begins to charge, and pulls them shut.

A conventional regulator for a generator does not stick in one "polarity state" or the "other", but could be defective, or maybe someone else tried it, started the tractor, and welded the points shut, then returned it, and you got stuck with a ruined regulator?

NOTE... A voltage regulator doesn't require "flashing" or "polarizing", but the generator MAY, to restore the residual magnetism in it's field polepieces.

If it was working for the generator guy, and he knew it was to be polarized (+) ground, and it hasn't been apart or banged around since he "ran" it, it shouldn't even need polarizing, although it NEVER hurts to do that.

 

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Jack-Illinois
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PostPosted: Wed Jun 06, 2007 7:25 pm    Post subject: Re: Flash the Field? Reply to specific post Reply with quote

No - the cutout is spring loaded to hold the points of the cutout open. The contacts could be welded shut from something prior, but flashing the system will not cure that either. I say re-check your wiring or have someone else check it. It is easy to overlook our own mistakes. You could take the belt off and see if the generator spins, but that would only prove that is where the load is. I think you are right in suspecting that.

 
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Dell (WA)
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PostPosted: Wed Jun 06, 2007 8:45 pm    Post subject: Re: Flash the Field? Reply to specific post Reply with quote

Ramrod.........NO NO NO!.......NO FLASHIE THE FIELD. Thats the WRONG thing to do with the 3-wire 6-volt 8N-genny. UNDERSTAND???

Based upon yer brief description, YOU MISS-WIRED the genny barrel studs. (and its eazy to do)

Yer genny barrel studs are actually labeled FIELD (this is an INSULATED post) and GND. (look closely) You have 2-skinny wires connected to the genny barrel from yer 4-terminal squarecan voltage regulator.

The skinny BLACK with RED tracer is GROUND at both ends of the harness (genny barrel and squarecan VR attaching screw)

The skinny BLACK with WHITE tracer is the INSULATED FIELD stud to squarecan "F" terminal.

Iff'n you incorrectly grounded yer field and fielded yer ground as I suspect, then yeah, SPARKIES!!!

It should be intuitively obvious, UN-CROSS yer genny barrel wiring and 'vola' yer correctly wired. Even though the colors are incorrect, electrons don't know the difference, isn't that amazing???

You'll be real lucky you iff'n you didn't MELT yer genny barrel wire insulation.

Surprizingly enuff, yer genny didn't gitt hurt by being miss-wired. Wiring harness and squarecan voltage regulator, different story.

Consider it a $15 lesson in how to wire yer simple tractor electrics......... respectfully, Dell

 

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Bob
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PostPosted: Wed Jun 06, 2007 8:52 pm    Post subject: Re: Flash the Field? Reply to specific post Reply with quote

Dell,

This is an "A" type system, right?

How is reversing the GND and FLD at the generator going to cause a dead short BEFORE he's ever started it, when he first connects up the battery???

If he WERE to start it, it would charge like HELL, 'cause it's "full-fielded", but there will be NO short before startup.

If he's told us the story exactly as it happened, up to this point, something else is wrong... other mis-wiring, or a shorted VR.




 

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Phil(NJ,Az,Sask)
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PostPosted: Wed Jun 06, 2007 9:02 pm    Post subject: Re: Flash the Field? Reply to specific post Reply with quote

[QUOTE]I connect battery and momentarily connect field to armature on VR,[/QUOTE]

If this a Class A GEN:
NEVER Connect the Field Terminal of the VR to anything but the field terminal of the GEN (its the VR relay Ground connection)

Class A & B GEN
You Polarize the Field poles by Momentarily Connecting the VR BAT term to the VR Armature Term. This provides voltage to the hot side of the Field coils & thus current flow via the VR Field Term.

JMHO

 

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Phil (NJ,AZ,Sask)
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PostPosted: Wed Jun 06, 2007 9:10 pm    Post subject: Re: Flash the Field? Reply to specific post Reply with quote

Bob,
Yep! Most likely Battery & Armature are Swapped (Mis-wired).


 
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Ramrod
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PostPosted: Thu Jun 07, 2007 4:08 am    Post subject: Re: Flash the Field? Reply to specific post Reply with quote

Dell, I will get into it some more this afternoon, but one more thing. The original VR was mounted isolated from gnd on rubber mounts. The new VR is mounted directly to chassis. Should it be isolated from ground when mounting? I don't thionk I have damaged anything yet, it was only connected for long enough for me to glance at ammeter and see short. A few seconds would do damage? What happens to the VR when it is damaged, burnt points maybe?

 
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Dan
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PostPosted: Thu Jun 07, 2007 5:40 am    Post subject: Re: Flash the Field? Reply to specific post Reply with quote

Keith - only because I know you are a NAA man - I suspect if you polorized your genny the same way you do on an NAA, you have damaged your expensive VR. You see, the NAA and later tractors are a "B" circuit system and you polorize by sparking "BAT" to "FLD", the 8N and earlier (with the exception I think of the very earliest 9Ns) are an "A" circuit system - and you polorize the generator by sparking "BAT" to "ARM". If you mix these up, you damage the VR (I know, I have done this also). This will cause the ammeter to peg -30 due to the internal VR contacts being stuck together. You can see for yourself by removing the outer cover on the VR with the ignition off - both contacts should be open, I'll bet one is closed right now. Solution - new expensive VR - sorry.

HTH,
Dan

 

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Ramrod
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PostPosted: Thu Jun 07, 2007 5:48 am    Post subject: Re: Flash the Field? Reply to specific post Reply with quote

I have never polarized a genny before, OW is a 12v system with a simple Delco solid state alternator/VR. Being a tech for all my life makes hi tech stuff easy for me. This low tech stuff is harder for me to visualize. I need to see a schematic showing the inner workings of the VR/Genny circuit so I can see it in my head, then it's no problem to troubleshoot. Right now, I'm just making rookie mistakes. I will crack the new VR and see if I can unstick and file the points tonight. This is the last thing on GT before it goes to paint and afterwards, back to work.

 
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Bob
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PostPosted: Thu Jun 07, 2007 6:06 am    Post subject: NO! Reply to specific post Reply with quote

On an "A" circuit regulator, both sets of contacts WILL NOT be open "at rest".

The large, HEAVY cutout contacts will be open, however, the field relay contacts will be CLOSED, whether there is one field relay (combination voltage and current), or two (one for overcurrent regulation, and one for voltage regulation).

Having these contacts closed at startup "full-fields" the generator, 'til it comes up to speed, and current and/or voltage regulation kicks in, and the appropriate contacts begine to vibrate, limiting volage and current ot a safe level by interrupting field current.

 

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Dan
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PostPosted: Thu Jun 07, 2007 6:13 am    Post subject: Re: NO! Reply to specific post Reply with quote

Thanks for the clarification Bob. I am sure my "new" VR came with these contacts open at rest. It has worked fine for several years now.

Dan

 

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Bob
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PostPosted: Thu Jun 07, 2007 6:30 am    Post subject: Re: NO! Reply to specific post Reply with quote

The cutout relay is "N.O.".

The field "relays" are "N.C.".

ALL the "relays" are "up" (away from the coil/core) at startup, so they appear the same at first glance. However, the contact arrangement is just the opposite, the field units' contacts are actually "closed".

 

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Dell (WA)
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PostPosted: Thu Jun 07, 2007 7:23 am    Post subject: Re: Flash the Field? Reply to specific post Reply with quote

Ramrod.........ah yes, the rubber baby buggy bumper mounted squarecan voltage regulator. Originally used because of "fragile" relay pivots inside the V/R and bouncing tractors on ruff ground. Which is also one of the reasons for a seperate GROUND wire between the genny barrel and the V/R.

New modern squarecan V/R are much more stout and don't need shockmount. Not only that, but modern replacement V/R's don't fit the old V/R attachment nutplates. Replacement V/R's need a flatplate adapter that usually comes with NEW V/R.

To get a V/R with flatplate adapter, order 8N10505B. The 8N10505C comes without adapter........HTH, Dell

 

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Ramrod
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PostPosted: Thu Jun 07, 2007 8:00 am    Post subject: Re: Flash the Field? Reply to specific post Reply with quote

Good info Dell, thanks. I just talked with my CNH guys, they will take back the Blue VR and exchange me for the correct black 8N10505B - 'no problem'. Maybe that will get GT up and back to work.

 
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