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Negative ground conversion : what about OD ?

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matt78

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Hello.

Due to a faulty dynamo, I'm seriously thinking of fitting an alternator instead of trying to overhaul the old machine.
I know that a negative ground conversion must be done, and carefully read all the related posts, in order to list all the mods that are required : battery, ignition (and sometimes fuel pump, depending on its type. Guess that the one fitted on my BN1 isn't a matter) terminals swap, and some additional equipements if they exist...

But what about the OD solenoid terminals ? None of the posts deal with this element, despite it is fitted on all our cars... As far as I know, the magnetic field direction induced by a winding changes when the current flows in the opposite way. So, provided a negative ground conversion is done, the magnetic field generated in the solenoid should act in the opposite way and try to expel the plunger, instead of pulling it.
Because there's no information about this point, I suppose that I'm wrong and that there's no need to care about, but could somebody explain why ?
Thank you in advance.

Matt
 
matt78 said:
...As far as I know, the magnetic field direction induced by a winding changes when the current flows in the opposite way. So, provided a negative ground conversion is done, the magnetic field generated in the solenoid should act in the opposite way and try to expel the plunger, instead of pulling it.... I suppose that I'm wrong and that there's no need to care about, but could somebody explain why ?
Click to expand...

A magnet is still a magnet even with a change in polarity. Different polarity would only be apparent if it was acting on another magnet (like in a permanent magnet DC motor).
 
Geo Hahn said:
A magnet is still a magnet even with a change in polarity. Different polarity would only be apparent if it was acting on another magnet (like in a permanent magnet DC motor).
Click to expand...

I'm out of my league electrically, but I wonder if the coil in the solenoid takes a 'set' or 'bias'--don't know the correct word--and needs to be re-polarized like a generator's field coils after the conversion?
 
Bob_Spidell said:
I'm out of my league electrically, but I wonder if the coil in the solenoid takes a 'set' or 'bias'--don't know the correct word--and needs to be re-polarized like a generator's field coils after the conversion?
Click to expand...

No, it doesn't. The current through the solenoid coil sets up a magnetic field that will attract a ferrous metal armature (plunger) no matter which way the current flows through the coil. The overdrive solenoid works the same with positive or negative ground. The difference with the generator is that the armature is carrying current and spins in the magnetic field caused by the stator windings, so the direction of current is important.
 
BJ8Healeys said:
No, it doesn't. The current through the solenoid coil sets up a magnetic field that will attract a ferrous metal armature (plunger) no matter which way the current flows through the coil. The overdrive solenoid works the same with positive or negative ground. The difference with the generator is that the armature is carrying current and spins in the magnetic field caused by the stator windings, so the direction of current is important.
Click to expand...

Yeah, sorta figured that, but there was a special on questions so I bought. After I wrote, I realized no one ever mentioned having to re-polarize a fuel pump after a conversion--only reverse a cap or diode--and the coil in the fuel pump has a similar purpose to the coil in the solenoid.
 
Fuel pumps can be tricky. Most are like the solenoid but there are positive and negative grded pumps. Pump will usually not work unless you have it wired correctly.
Mav
 
And some (well, me anyway) add a diode to the OD relay which would need to be reversed if polarity is changed. But that is non-stock and thus not a concern for most situations.
 
Geo Hahn said:
And some (well, me anyway) add a diode to the OD relay which would need to be reversed if polarity is changed. But that is non-stock and thus not a concern for most situations.
Click to expand...

Why you do that!!!--?
 
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