Totally Confused

[hicrop10]

As many of you know I’m restoring my B87,which has been in the family since new.I was always under the assumption it was positive ground being it was built in 1964.My electrician friend tells me it’s negative ground,he had a test gauge that says so.My question is how do I check to verify what it is?The truck has a voltage regulator and a generator,generator is not working so I’m getting that fixed.

[Geoff Weeks]

1st look at the generator regulator, sometimes they are marked as to polarity.

2nd does the truck have a working ammeter? If so hook up the batteries and turn on all the lights, wiper, heater etc and see which way the ammeter needle moves. If it moves toward the + side of the ammeter you have the wrong side of the batteries going to ground, if it moves toward the - side, you have the correct side grounded.

 

There is very little to do to switch from one polarity to the other on the old generator system trucks. Everything will function just fine on the reverse polarity with the exception of some electric gauges, most will read correctly but some types will read backwards. Of course any modern radios will be damaged with the wrong polarity. Alternators will be damaged, but not generators.

Once you have determined which polarity, all you need to do is "polarize" the generator. This is most easily done at the regulator. With the engine off, jump momentarily from the "bat" terminal to the "A" or gen (not the F or field) terminal to establish the magnetism in the field poles shoes of the generator. That is it!

If you still can figure out what it was from the get go, choose one polarity (I would suggest neg ground as it will make any accessories easier) and set it up for that polarity.   

[mowerman]

lol I’m no help… but  its hard to tell anything when you got everything stripped out good luck

[hicrop10]

7 hours ago, Geoff Weeks said:

1st look at the generator regulator, sometimes they are marked as to polarity.

2nd does the truck have a working ammeter? If so hook up the batteries and turn on all the lights, wiper, heater etc and see which way the ammeter needle moves. If it moves toward the + side of the ammeter you have the wrong side of the batteries going to ground, if it moves toward the - side, you have the correct side grounded.

 

There is very little to do to switch from one polarity to the other on the old generator system trucks. Everything will function just fine on the reverse polarity with the exception of some electric gauges, most will read correctly but some types will read backwards. Of course any modern radios will be damaged with the wrong polarity. Alternators will be damaged, but not generators.

Once you have determined which polarity, all you need to do is "polarize" the generator. This is most easily done at the regulator. With the engine off, jump momentarily from the "bat" terminal to the "A" or gen (not the F or field) terminal to establish the magnetism in the field poles shoes of the generator. That is it!

If you still can figure out what it was from the get go, choose one polarity (I would suggest neg ground as it will make any accessories easier) and set it up for that polarity.   

1st-the voltage regulator is marked mp,the fellow that I have dealt with the past 50 years tell me that mp stand multiple polarities (positive or negative).The generator is not working so he’s going to try and find parts to rebuild it.I don’t have anything else wired up yet.

[Geoff Weeks]

Can't say I've seen "MP" on the regulator, but that doesn't matter. Regulator (even those that are marked for polarity) will function fine on either. It was just the point material was place on the points that were optimized for one polarity. It made them last longer in the days where generator and point (mechanical) regulators were common.

 Now it doesn't pay to make and stock two regulators for every application. They make one, and figure it will last long enough. So little call for mechanical regulators these days. It has been like that for 30 years or more.

I have two trucks from the 40's and both regulators are still going strong. One I'm sure is the original, the other may be or may have been replaced at some point. 

 

If you have the truck wiring stripped out and are starting from scratch, then I would wire neg ground until I found something that didn't work right (gauge). then decide if it is better to replace that with a neg ground unit or switch to positive ground. 

[mowerman]

I was thinking the same thing…. I really can’t add much here … bob

[Vladislav]

5 hours ago, Geoff Weeks said:

Can't say I've seen "MP" on the regulator, but that doesn't matter. Regulator (even those that are marked for polarity) will function fine on either. It was just the point material was place on the points that were optimized for one polarity. It made them last longer in the days where generator and point (mechanical) regulators were common.

 Now it doesn't pay to make and stock two regulators for every application. They make one, and figure it will last long enough. So little call for mechanical regulators these days. It has been like that for 30 years or more.

I have two trucks from the 40's and both regulators are still going strong. One I'm sure is the original, the other may be or may have been replaced at some point. 

 

If you have the truck wiring stripped out and are starting from scratch, then I would wire neg ground until I found something that didn't work right (gauge). then decide if it is better to replace that with a neg ground unit or switch to positive ground. 

Geoff, how about the starter? I also have two trucks from the 40's. And a battery was once put wrong on one of them by my guy. To my great surprize the truck started (gas engine) and drove a few hundred meters to my shop. And I found out the mistake on the next day.

But the other one is diesel. And when I tried to apply different polarity to the cranking motor while its rebuild (reassembly) it spinned oppositely.

[Geoff Weeks]

9 minutes ago, Vladislav said:

GAnd when I tried to apply different polarity to the cranking motor while its rebuild (reassembly) it spinned oppositely.

older direct drive starter will spin the same direct on either polarity (as you found out). PMGR (permanent magnet gear reduction) starter will spin backwards on reverse polarity. 

To reverse direction on a wound field motor, you need to reverse the current in the field relative to the current in the armature. If you reverse both, they still spin the same way. With permanent magnets for the field, they will stay the way they were magnetized when the motor was made, and by reversing the flow through the armature, you have reversed the armature relative to the field, and vola, it spins the opposite direction. 

[Vladislav]

21 hours ago, Geoff Weeks said:

older direct drive starter will spin the same direct on either polarity (as you found out). PMGR (permanent magnet gear reduction) starter will spin backwards on reverse polarity. 

To reverse direction on a wound field motor, you need to reverse the current in the field relative to the current in the armature. If you reverse both, they still spin the same way. With permanent magnets for the field, they will stay the way they were magnetized when the motor was made, and by reversing the flow through the armature, you have reversed the armature relative to the field, and vola, it spins the opposite direction. 

Interesting. But my old Leece Neville acted opposite. I checked out photos I made during its rebuild and the field was wire coils not permanent magnets. Interesting both its terminals are insulated off the body but I don't see any reason how that could affect field-armature connections. When I put different polarity it spoon different directions. To the moment I just have forgotten which terminal should be connected to which pole and made the test. Also a point the tag on the starter mentions its rotation (clockwise).

[Geoff Weeks]

Vlad, I can't explain what you have observed, I only know theory (magnetic poles are determined by direction of current through the coil) and in practice, with trucks I have had that have been reversed at least twice in their lifetime.

When the current direction is reversed the N and S pole is reversed, but because both are in series, both the armature and field poles are reversed together,  so the relative positions to the two magnetic fields (armature and field) remain the same and the motor spins the same direction. When you reverse one relative to the other, it will spin "backwards.

It is why generators don't care which polarity, they just need the shoes polarized before they are spun for the 1st time. You don't have to "spin them backwards" when the polarity is changed.   

[Vladislav]

52 minutes ago, Geoff Weeks said:

Vlad, I can't explain what you have observed, I only know theory (magnetic poles are determined by direction of current through the coil) and in practice, with trucks I have had that have been reversed at least twice in their lifetime.

When the current direction is reversed the N and S pole is reversed, but because both are in series, both the armature and field poles are reversed together,  so the relative positions to the two magnetic fields (armature and field) remain the same and the motor spins the same direction. When you reverse one relative to the other, it will spin "backwards.

It is why generators don't care which polarity, they just need the shoes polarized before they are spun for the 1st time. You don't have to "spin them backwards" when the polarity is changed.   

Yes, I understand. And what you're telling makes sence definitely. To explain my case I should take the manual and research the starter electrc schematic. But that needs time and attention of which I recently am very short. I will keep the subject on my mind since it's very remarkable and well new to my "modern car" experience.

Also it sounded very surprizingly of a generator to be able operating for both polarities if pre-magnetized. I have a generator for that same truck I'm going to put my hands on either but didn't so far. The voltage regulator is mechanical too and I recently reassembled it with body painted and terminal nuts/washers galvanized. But the inside looked so virgin I saw no reason to disturb it. It needs to be tested though but my current plan is just to install both the regulator and generator on the vehicle when it's ready to start the engine in the chassis and look for actual work. If a trouble I'm on here asking help

[Geoff Weeks]

I would be surprised if the regulator doesn't work just fine from the get go. I had a few from the early 40's still working fine. They really did a good job when they made those.

As long as the commutator isn't bad or someone didn't cranked down on the current regulator and burn the windings, the genny should be good also. Just lube the oil cups and make sure it spins easy.

I have purchased I don't remember how many off E bay and once cleaned up they work just fine. I don't buy ones that look like they have been under water or all broke up, but just good generally used condition

You can test a generator by "motoring" it. Connect the battery across the output (A or Armature) and the case and it should start to spin.

[Vladislav]

Thank you. I will try. Just when I get myself to the task. Currently have to offset my activity to another project.

[T-Mack1]

A lot of interesting things here.  Here's my few bits of wisdom I've learned.

-Not all alternators will be damaged when reversing polarity.  Only ones with build in rectifiers (diodes).  Alternators with external rectifiers like the Leece Neville system on our '57 firetruck (B85F) should be ok.  BUT,  the rectifier will have to have the output wires switched (big sparks otherwise).   If it is a "case grounded" rectifier, identified by only having one output wire, you would have to isolate the case to switch polarity.   Our original Selenium rectifier and the new solid state one we now have, have isolated Pos & Neg outputs, so one output wire goes to ground.  

- Electric motors without permanent magnets use how the windings connect to the brushes and commutator that they rub against, to create the magnetic field to "pull" the rotor (spinning part) around.  It uses the "Opposite poles attract" theory as a pull (or the "Like" poles repel as a push).  So, it doesn't matter if the "Positive is pulling a Negative", or if the opposite happens and a "Negative pulls a Positive" .  It is still pulling in a direction set by the windings.

- Many older (non-solid state) voltage regulators work basically on a voltage "threshold" principle, where it looks at voltage level, not voltage polarity.  There are theories to explain it, but simply,  If the voltage is too low it sends more voltage to the field to create a higher output voltage.  Once it get to the desired voltage ( the threshold) it holds the field steady.  If the voltage goes past the threshold voltage it reduces the field down a little.   All this is done at almost the speed of light.