720 D regulator

With the tractor running, if you jump wire the VR's ARM and BAT terminals together, does she charge then???? If not, ground out the field post (smaller of 2 on gen) and see if she charges then. If she never charges despite the ARM and BAT VR terminals jumped together and the Field post grounded, I think the gen is bad (those 2 jumps essentially takes the VR out of the system) and probably has a bad field since the motor tests shows the arm etc may be okay, while the VR may or may not be bad also.

Let us know what happens.

God Bless the USA Ol John T Nordhoff in Indiana

When I full-field my 70D generator, it will fly right up to 20 amps. It has new brushes and a fresh-turned commutator.

Frank

I couldn't even diagnose a bad generator belt for over a week !

LOL !! back atcha ! You hoosiers putting in any corn yet ? They're mostly done down here. Isn't that wierd ?

F-I-T

1) I kinda like what ol Frank was saying there below. A loose or glossed up belt or pulley can cause low charging for sure, especially if she does better now after you had it off and replaced it.

2) When you first say above it charges 4 amps now and 8 if you jump BAT and ARM together, and 20 with the field grounded out, I think the generator may be fine (10 to 20 is about all they put out, I think clooney has some gen output current specs) but suspect the Voltage Regulator. The VR is supposed to supply different resistances to ground for the field, dependign on the state of the battery. If a dead field ground makes the generator charge and keep charging 20 amps even into a well charged battery, it sounds good and the belt cant be all that bad if she maintains a steady 20 amps. If it will charge 20 amps I cant see that the gen is all that bad UNLESS the field windings are being ran at excess current than designed for by a dead field ground and will eventually over heat and burn up. I dont have the actual field resistances inside that VR, but know it furnishes a near dead ground at low battery, with a higher field resistance at good battery or light load conditions. THEREFORE I cant say for sure the gen is good (suspect it may be) and cant say for sure if its a bad gen or only a bad VR, sorryyyyy yyyy.

My best guess IF its a bad gen, is the field windings are partly shorted somewhere. Cuz a grounded out GOOD field should slow down the motor action which you say dont happen?????

I would just run her a while if it still holds charge or close with all lights on and see what happens and check the belt situation as Ol Frank was talking about.

Puzzled in Indiana Ol John T

I don't want to interfere with the generator guru's, but had to tell you. I just solved a similar charging problem on my 70D and it turned to be an older, very slick, fan belt.

A new belt fixed it up. I wouldn't have thought that it could have that big an effect.

Frank-in-Tallahassee
70D // 855

~I presume we are talking about a 720D pony, correct? If not, none of the below will apply. [those 24 volt systems are completely different]

~First, is the generator actually charging? It must be putting out higher than battery voltage to close those cut-out contacts...With the engine running at fast idle take a jumper wire & jump the [A] post on the generator to the [BAT] terminal on the generator. Then look at the ammeter, if it shows a charge on the ammeter your generator is charging & should close the cut-out contacts [see below]... If it doesn't show a charge on the ammeter, with [A] [post still jumpered to the [BAT] terminal add a second jumper wire to short the [F] post on the generator to a GOOD CLEAN ground. If it charges then, you have a bad regulator, bad regulator ground, or open in the [F] wire between the generator & regulator. If it still doesn't show a charge on the ammeter you have probably found your problem & that is a non functioning generator. [sorry if this is redundant & you have already verified the generator output].

~If the generator checks out per above, you either have a regulator problem, the incorrect regulator, or a wiring problem.

~Is there a chance you have a 12 volt regulator? If so that 6 volt generator probably won't close those cut-out contacts until a very high RPM. It could be a polarization problem but you already polarized the generator when you closed those cut-out contacts to motor it.

~Is the regulator wired correctly? It sounds like you have the [BAT] & [GEN] terminals hooked up correctly or it wouldn't have motored, is the [BAT ]terminal on the regulator hooked to the power wire from the ammeter? How about the fuel gage wire? It belongs on the [GEN] terminal at the regulator [that's the one with the wire running to the generator's [A] post. The regulator [F] terminal obviously hooks to the generator [F] terminal.

~I guess the bottom line is...if the generator can & is producing at least 1 volt above battery voltage the cut-out points should close if the regulator is wired correctly, fully grounded, the correct voltage, & working.

~About the only other thing I can think of is that the regulator is not for your system polarity, but most of those regulators will work either polarity it's just the coating on the points are on the opposite point contact. Are you still running a positive ground?