Ampmeter

~ If you have a volt meter just put the positive & negative leads across the battery posts with it running at fast idle. You should show 7+ volts. If not, it isn't charging.

~Leave the voltmeter hooked up & short the [F] post on the generator to the generator case [is it showing above 7.2 volts now?] if so, your generator is probably working & your problem is more than likely a bad regulator, open in the field wire running from the generator [F] post to the regulator [F] terminal, or a bad regulator ground. [try a ground wire from the regulator case to the tractor frame] ..NOTE: the regulator case must be grounded for it to work.

~If it didn't show 7.2+ volts with the [F] post grounded, leave it grounded & run a jumper wire directly from the generator [A] post to the starter big battery terminal stud on the starter [the regulator is very hard to get to on the 420 so it is much easier to use the jumper wire to the starter post]. Does it show 7.2+ volts now? If so your problem is either an open in the wire running between the generator [A] post & the regulator [GEN] terminal, a bad regulator, an open in the wire running from the regulator [BAT] terminal to the [ammeter], or an open in the wire running from the [ammeter] to the battery cable stud on the starter. Use your volt meter & check for battery voltage at the [BAT] terminal of the voltage regulator, [if you don't have battery voltage there, find out why].

~If it still doesn't show a charge, leave the [F] post grounded on the generator, turn the tractor off & disconnect the jumper wire from between the [starter stud] & the generator [A] post. Then remove the generator drive belt & re-connect the jumper wire from the [starter stud] to the generator [A] post,, the generator should start to motor, now un-ground the [F] post & see if the generator picks up speed....If the generator doesn't motor at all, you have a generator problem like- dirty commutator, burnt out armature, stuck brushes, broken wire to the armature brush, bad generator ground, or other internal problem,,,if the generator motors but doesn't slow down with the [F] post grounded, you have field problems like open in the field windings, broken field brush spring, stuck field brush, broken field wire, or other field related problem. NOTE: on that 420, 6 volt generator start it motoring with the [F] post grounded then remove the [F] post ground to see if it speeds up.

~Most people find that printing this test sequence out & taking out to the tractor will help keep things in order.

~If the tractor has been converted from 6 to 12 volts you could have the wrong generator or other change induced problems so post back if you have been converted to 12 volts...

John T. is correct in that an ammeter appears as a near-zero resistance in series with the current being measured, so it doesn't "care" what voltage system it's hooked up to.

I think both my 6V (420, 70D) and 12V (50) have stock -20,0,+20 amp scales though.

Take care Ol John T

You guys are confusing me again. Are you saying that the same ammeter will read the same if it's in a 6 volt system or a 12 volts system provided the current flow is the same ? Cause that's what I believe.

I was always told that voltmeter measured a potentional difference, and an ammeter a current quantity.

So, if you make an example analogous to plumbing, the voltmeter would measure pressure between say, the internal system pressure and the atmosphere, and the current would be measured by a flowmeter. So, as long as the flowmeter (ammeter) could stand the pressure (voltage) without exploding, the same flow meter could measure a 5 gpm flow in either a 12 psi system or a 5,000 psi system.

I think that's why the identical ammeters are called out whether 6 or 12 volts. If it was voltage dependent it would be measuring Watts.

Frank-in-Tallahassee
70D // 855

Clear as mud ???

Post back any more questions, interestign thread we got going here. Ol John T

Nope, I'm not confused about I=E/R. More important is P=I(squared)R. I understand that, too.

I was just saying that when I replied to the first question that an ammeter is an ammeter, be it 6 or 12 volt, the replies to that sounded like voltage was being brought into the mix, and I was certain that didn't matter.

Now, back to what Clooney said, and that was an ammeter would read different in a 6 volt vs. a 12 volt system. There I say no. If a 12 volt generator is putting out 20 amps, then the ammeter will show 20. If the same ammeter is put in a 6volt circuit and the 6volt generator is putting out 20 amps, then that same ammeter will read 20 amps. I know that if the current stays the same and you double the voltage, the wattage doubles. So the 12 volt generator @ 20A is putting out twice as many watts as the 6 volt generator at 20 amps.

So, that's why I said that JD was right when they offered the same ammeter regardless if for a 6 volt or 12 volt system.

An ammeter don't care.

Frank-in-Tallahassee
70D // 855

Maybe it was my misunderstanding, but in his initial post Dave asked if there was any difference between a 12 volt ammeter and a 6 volts ammeter. When the answer given was, "Yes, there is a difference, but should still show charge/discharge", I posted that that an ammeter is an ammeter is an ammeter.

I just didn't want folks trying to go out and buy something they can't get, like a left-handed monkey wrench, a bucket of steam, or a 6 volt ammeter !

Later !

Frank

When you say there is some differences between a 6V and 12V ammeter, what do you mean ? You lost me there.

For example, JD supplied the AF 2749 R ammeter for the 40/50/60/70/70D/and 80 models, which is certainly a mix of 6 and 12 volt systems. Same ammeter went on to be supplied on 720 gas or diesel, and 730 gas or diesel, electric or starting engine.....

Frank-in-Tallahassee
70D // 855

Yeah, but. Dave asked whether there was a difference between a 6 volt ammeter and a 12 volt ammeter. You said there was some difference. I just had never seen a "6" volt vs. "12" volt ammeter. You could buy different scales and ranges, but not different voltages.

If you go to the CD for example, look in the notes for the ammeter of a '50' or '60', and then read the notes for '70D', they all refer to the AF 2749 R as the sub for the previous AB 2568 R. Now if there was a different ammeter called out originally, it might have been for the scale on the gauge, but not because it was 6 volt vs. 12 volt. If some one has that original parts books, I'd sure like to see JD ever offered different black face ammeters for the 6 volt applications vs, the 12 volts applications.

I'm not arguing gauge faces or markings. I'm just saying that the way I read it from you was that there is an difference between a 6 and a 12 volts ammeter, and I say an ammeter don't care. If an old ammeter reads 20 amps and it's correct at that point, it will read 20 amps whether it's 6 or 12 volts, right ?

I understand that if it's a low output 6 volt system like on Dave's 40, they might have selected a more sensitive ammeter, so the +/- scales might have been 10 A, while a 730 diesel system with a big generator and lots of batteries might have used an ammeter with a scale of say +/-20A.

That's all I was questioning.

Frank-in-Tallahassee
70D // 855

Did you try to polarize the unit after you installed it??? With the tractor not running, momentarily connect (spark) a wire between the regulators BAT terminal over to the ARM (or GEN) terminal, and you should see a spark, then remove the wire immediately. The ARM post on the generator (larger of the 2 posts out the generator) should be the same electrical point as its connected to the ARM terminal on the VR by a wire assumign its wired correct.

If its a 3 wire VR, (BAT GEN FLD terminals) I guess its wired right??? GEN or ARM terminal wired to the ARM post on the generator, F or Field terminal wired to the gens F post (smaller of the 2) out the generator, and the BAT terminal has to be connected to the non grounded battery terminal eventually, or else it cant charge it. The usual path is a wire from the BAT terminal to the load (non battery) side of the ammeter, and the high (battery) side of the ammeter is fed from the battery, often off the starter post or even direct to the battery. Therefore, if you place a test lamp or a voltmeter on the BAT terminal on the VR it should always be HOT battery voltage, otherwise theres a problem, and even if the gen and VR are working, it cant charge the battery.

I just posted a long winded detailed troubleshooting procedure below on here or over at Rummys JD page to test a generator and VR, so look below on one of these pages and read that post or post back questions if you need more help.

Are you usign a 3 wire or a 4 wire VR???? The 4 wire has a 4th terminal labeled L for load, and if you have that post back, cuz the directions will be a bit different.

I guess its not just a 2 wire cutout relay is it???

Are you still at pos ground?? and is the new VR a positive ground model??? Some work on either polarity, some do not.

The VR has to have a good ground conenction to the steel frame of the generator. Does yours??? Try a jump ground wire to see if that helps in case you're not sure.

Good luck, God Bless the USA, and please pray for the troops.

Ol John T Nordhoff in Indiana