Ford NAA Voltage Regulator problems

Tim Crawford

New User
I have a 1954 Ford NAA, bought it two years ago.
The amp meter on the tractor has never indicated
that there was any current flow from the generator
into the battery. When you turn the key on the
amp meter reads about +4 amps,this is the opposite
of what I would expect but it does give a reading.
Then as I try to start it the ampere meter does
move as the motor is being rolled over, again this
is what I would expect. Once the tractor starts
the ampere meter goes back to +1 amp and does not
move, it sits at +1 amps when the tractor is shut
off too. My thought was that the generator was
bad or the voltage regulator is defective, but I
have been able to determine that the generator is
producing a charge. I have looked at the brushes,
there is very little wear. So that being said I
decided to buy a voltage regulator the one on the
tractor looks to be pretty old. I bought a
voltage regulator that would fit a 6-volt Ford NAA
B circuit, it said it would also work 600, 700,
800, 900. I took the old one off and it had a
rattle, I opened it up and one of the screws had
fallen out of one of the plates. I decided to
put the new one in since I had already bought it.
I got the new one in and verified that the wires
were hooked up correctly, ground was to the ground
wire on the generator, the BAT was hooked into the
terminal block, the FLD was connected to the field
post on the generator, and the ARM was connected
to the armature post on the generator. I then
turned the key on and the ampere meter indicated
+4 amps just like it did with the old voltage
regulator. I then started the tractor. The
ampere meter went back to +1 as it usually did and
stayed there for about 5 seconds, then the needle
jumped to -30 amps and stayed there for 15-20
seconds. The generator started to make some
strange noises, and then the amp meter needle
started to jump from -30 to -20, back to -30, down
to -10, up to -30 it was all over the place and it
would stay mostly at -30 amps but it stayed at
other settings for 15-30 seconds at a time. I put
a multimeter on the battery as the tractor was
running and it indicated that the battery was
getting 18-22 volt charge. I shut the tractor off
and checked the generator and it was very hot. So
I guessed I fried the voltage regulator some how.
I went and bought another voltage regulator and
very carefully installed it and verified the
wiring was correct. I started the tractor and the
very same thing happened! What is happening here?
Do I have the wrong voltage regulator? Could it
be bad wiring, a short in one of the wires? The
wires are wrapped together in a harness so I can
only see the ends and the ones connecting to the
generator have a number of cracks in them. Are
the my new voltage regulators reparable? I opened
the one up and there was no sign of any damage,
like melted wires everything looks fine. Could I
have a mismatch with the generator and the voltage
regulator, could I have an A-Circuit generator?
The previous owner may have put an A-Circuit
generator on the tractor not knowing? Is there a
simple way I can tell what type of generator I
have? There are a lot of questions here I hope
someone can give me some advice on what to do
next. Thanks.
 
(quoted from post at 15:54:56 07/28/13) I have a 1954 Ford NAA, bought it two years ago.
The amp meter on the tractor has never indicated
that there was any current flow from the generator
into the battery. When you turn the key on the
amp meter reads about +4 amps,this is the opposite
of what I would expect but it does give a reading.
Then as I try to start it the ampere meter does
move as the motor is being rolled over, again this
is what I would expect. Once the tractor starts
the ampere meter goes back to +1 amp and does not
move, it sits at +1 amps when the tractor is shut
off too. My thought was that the generator was
bad or the voltage regulator is defective, but I
have been able to determine that the generator is
producing a charge. I have looked at the brushes,
there is very little wear. So that being said I
decided to buy a voltage regulator the one on the
tractor looks to be pretty old. I bought a
voltage regulator that would fit a 6-volt Ford NAA
B circuit, it said it would also work 600, 700,
800, 900. I took the old one off and it had a
rattle, I opened it up and one of the screws had
fallen out of one of the plates. I decided to
put the new one in since I had already bought it.
I got the new one in and verified that the wires
were hooked up correctly, ground was to the ground
wire on the generator, the BAT was hooked into the
terminal block, the FLD was connected to the field
post on the generator, and the ARM was connected
to the armature post on the generator. I then
turned the key on and the ampere meter indicated
+4 amps just like it did with the old voltage
regulator. I then started the tractor. The
ampere meter went back to +1 as it usually did and
stayed there for about 5 seconds, then the needle
jumped to -30 amps and stayed there for 15-20
seconds. The generator started to make some
strange noises, and then the amp meter needle
started to jump from -30 to -20, back to -30, down
to -10, up to -30 it was all over the place and it
would stay mostly at -30 amps but it stayed at
other settings for 15-30 seconds at a time. I put
a multimeter on the battery as the tractor was
running and it indicated that the battery was
getting 18-22 volt charge. I shut the tractor off
and checked the generator and it was very hot. So
I guessed I fried the voltage regulator some how.
I went and bought another voltage regulator and
very carefully installed it and verified the
wiring was correct. I started the tractor and the
very same thing happened! What is happening here?
Do I have the wrong voltage regulator? Could it
be bad wiring, a short in one of the wires? The
wires are wrapped together in a harness so I can
only see the ends and the ones connecting to the
generator have a number of cracks in them. Are
the my new voltage regulators reparable? I opened
the one up and there was no sign of any damage,
like melted wires everything looks fine. Could I
have a mismatch with the generator and the voltage
regulator, could I have an A-Circuit generator?
The previous owner may have put an A-Circuit
generator on the tractor not knowing? Is there a
simple way I can tell what type of generator I
have? There are a lot of questions here I hope
someone can give me some advice on what to do
next. Thanks.
hich battery terminal is grounded to tractor chassis?
 
(quoted from post at 16:48:54 07/28/13) The positive terminal cable is grounded.
asked that because of your apparent backwards reading ammeter. A 'B' vr on an 'A' gen would not charge. 18 to 22 volts across battery lead posts (not cable ends) does not sound right. Typically it takes some significant time of overcharging to raise battery voltage into that range. Could be a bad battery......can go that high with bad battery. If behavior has been same & battery staying charged for 2 years, why are you looking into the charging system??
 
Well the battery was not staying charged. I would
put a battery charger on it for several hours
before I used it then it would start 5-6 times
before I would have to re-charge it. I then thought that it was the VR because the
ammeter never indicated that there was any charge
coming from the generator. It did register a +4
when the key was turned on indicating that the
ammeter was detecting a pull from the battery.
When the tractor was started I would have thought the VR
would be in control of the charge and show some
sign that the charge being created by the
generator was being regulated by the VR and was
trickling into the battery. I assumed that there
was something wrong with the original VR because
when I put the 2 new ones on the ammeter went nuts
indicating there was something different happening
with the new VR. The idea that the ammeter is
working the opposite of what it should does not
bother me. I am concerned as to what is happening
when the ammeter maxes out and the generator gets
so hot that there is no way you can touch it with
your hand. The 18 to 22 volts across battery posts
did sound very high too but that was while the
tractor was running and the ammeter going nuts.
With the tractor shut off the battery measures 6.5
volts. Am I not correct in thinking that a VR is
there to feed a charge as is needed for the
battery and for a 6 volt system it would be in the
8-9 volt range. Based on the voltage readings this is working like I am
running wires directly from the generator to the
battery? If I fried the VR would it allow a charge
that high to the battery or would it work the
opposite and you would see no flow? I may be
asking too many questions at one time here. Sorry
for the rambling.
 
The VR does 3 things, 1)connects/disconnects battery to generator armature terminal when Armature voltage exceeds a preset value (high enough to charge a battery. This is so that it does not connect if so low that battery would discharge back into generator. 2)Senses voltage of battery and controls generator output by modulating field current, such as to apply only enough charge current to maintain a specified battery voltage. 3) senses generator current so as to not exceed the rated generator output & thus damage generator AND also senses a reverse current as when battery is discharging into the generator & disconnects gen to battery accordingly. SO, to answer your questions, a VR failure could result in keeping battery connected after shutdown of engine (cut out contacts fail to open/stuck closed) & this will discharge battery & heat generator in minutes. It might never connect batt to gen so all charging/discharging by generator does not exists...just as though you removed gen from tractor. If field contacts remain closed/stuck & never open regardless of voltage, then in time battery will overcharge, excess voltage & excess current will heat battery and generator, sometimes to destruction. If field contacts never close, then generator output will be very minimal to zero.
You can "temporarily" remove the VR from consideration & prove generator working, by placing a jumper wire on generator between ARM and FIELD terminals AND a second jumper wire between the gen ARM terminal and that side of ammeter which is not connected to the battery. Should see charging amperes as well as an increase in battery voltage. Be sure ti remove ARM to ammeter jumper when engine is turned off. Suit yourself as to whether or not you leave present wiring on generator ARM & FIELD terminals..if all is wired correctly it doesn't matter, but one more step toward removing more things from circuit would be to disconnect them.
 
This is a lot of good stuff. I am going to have to take some time to digest it and see what I want to do. I noticed that based on my description of the spike in the ammeter that you have not suggested a reason for this behavior, leading me to believe that there is no one single reason for this type of behavior and correcting it is not a simple tweak. It puzzles me that I have put two new VR on the tractor and both reacted the same way the ammeter needle went off the chart. This would lead me to believe that the components that make up this circuit do not match and that there may be a mismatch between the VR and the generator. (A circuit generator vs B circuit VR) I really appreciate your help and the information you have provided. The tractor is on hunting property and won't be able to try any of this until I can get back there. The generator only gets very hot when the tractor is running, One final thing I did before leaving the hunting land was I disconnected the field wire on the generator and then ran the tractor. The ammeter then does not move(no spiking), the generator does not get hot, and the voltage across the battery post on the running tractor reads 9-10 volts. I am guessing that would mean the generator is creating a charge, but the VR is not functioning and closing the set of points(because I disconnected the field wire)that causes the ammeter to spike and overheat the generator. Thanks again for you thoughts.
 
" I disconnected the field wire on the generator and then ran the tractor. The ammeter then does not move(no spiking), the generator does not get hot, and the voltage across the battery post on the running tractor reads 9-10 volts." Something wrong with that picture. With field wire disconnected, the gen should not output enough voltage to even begin to charge the battery, so where is this 9-10 volts coming from on a 3 cell 6volt battery?? Maybe you don't have a 6v battery or maybe you need to try another voltmeter?

To further elaborate on mis-match of "A" VR on "B" gen or "B" VR on "A" gen, in both cases, there will be no field current & no output.
I might look toward intermittent conditions for the kind of radical jumping ammeter readings that you report. Maybe wiring shorting or bad/loose/intermittent gen and/or VR grounds.
 
You can remove the generatoe and take it to a reliable electrical shop and have it tested. Then you would know if the generator is really doing it"s job or not. I also have a NAA and had V.R. problems. I bought a good V.R.(Little more expensive) from NAPA and haven"t had any problems since. Also,...did you polarize your generator for a B circuit? You may want to ask about proper polarization. There are people on this site that can help in that topic.
 
You stated "I might look toward intermittent conditions for the kind of radical jumping ammeter readings that you report. Maybe wiring shorting or bad/loose/intermittent gen and/or VR grounds."

This made reminded me that after i put the first VR on I did drive the tractor down a path in the woods, it was bumpy, when I would hit a bump the VR would in most cases jump to a different level, maybe from -30 to -20, then hit another bump it would jump back up. I even raced the engine while not moving ant the ammeter would go back to +1 for a time until it got jostled some more. Could this be that the field on the generator may be grounding against the generator housing and jostling it causes it to ground at vearious levels? Boy I wish I had access to the trator I would like to try some of these things.
 
If it has 4, then it is an 8volt battery & with 12v gen & reg, it will always think the 8v battery is low & try to pump full output current into it in trying to bring it up to 12v charging voltage of about 14v. This would be a definite problem.

2.2 volts per cell
3 cells=6.6v
4 cells=8.8v
6 cells=13.2v
varies a few tenths depending on whether of charge, on float, idle (not connected), temperature, etc.
 
It may be that it only has 3 caps since when I have tested the voltage after a full charge on a battery charger it only registers 6.5 volts but then if I am charging it with a 6 volt charger that would also make sense that it only charges to 6.5 volts. Since I have no way of visually checking the battery at the moment this will remain a mystery.

You stated in one of your other replies to my posts "I might look toward intermittent conditions for the kind of radical jumping ammeter readings that you report. Maybe wiring shorting or bad/loose/intermittent gen and/or VR grounds."

This reminded me that after I put the first new VR on I did drive the tractor down a path in the woods, it was bumpy, when I would hit a bump the ammeter would in most cases jump to a different level, maybe from -30 to -20, then hit another bump it would jump back up. I even raced the engine while not moving ant the ammeter would go back to +1 for a time until it got jostled some more. Could this be that the field on the generator may be grounding against the generator housing and jostling it causes it to ground at vearious levels? Boy I wish I had access to the trator I would like to try some of these things.
 
(quoted from post at 11:19:00 07/29/13) It may be that it only has 3 caps since when I have tested the voltage after a full charge on a battery charger it only registers 6.5 volts but then if I am charging it with a 6 volt charger that would also make sense that it only charges to 6.5 volts. Since I have no way of visually checking the battery at the moment this will remain a mystery.

You stated in one of your other replies to my posts "I might look toward intermittent conditions for the kind of radical jumping ammeter readings that you report. Maybe wiring shorting or bad/loose/intermittent gen and/or VR grounds."

This reminded me that after I put the first new VR on I did drive the tractor down a path in the woods, it was bumpy, when I would hit a bump the ammeter would in most cases jump to a different level, maybe from -30 to -20, then hit another bump it would jump back up. I even raced the engine while not moving ant the ammeter would go back to +1 for a time until it got jostled some more. Could this be that the field on the generator may be grounding against the generator housing and jostling it causes it to ground at vearious levels? Boy I wish I had access to the trator I would like to try some of these things.
e can guess forever, but with too many unknowns to do any good. Need to know if battery, gen & reg are 6/8/12v?
 
I agree until I can get back to the tractor, and get all the right information, plus do some other things there is no way to diagonose the problem. Thanks to all for the back and forth discussion. I will let you know how things are going when I have done some of these things.
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top