Polarizing Alternator

940tvolvo · Post by **940tvolvo** » 16 Feb 2019, 10:23

Can anyone tell me what polarizing alternator bypasses?

lummert · Post by **lummert** » 16 Feb 2019, 15:24

It bypasses the battery warning light on the instrument cluster. Make sure this light is functioning.

93Regina · Post by **93Regina** » 16 Feb 2019, 18:10

940tvolvo wrote: ↑16 Feb 2019, 10:23 polarizing alternator

This expression suggests non-sense....still checking your muffler bearings?

Post by **mrbrian200** » 17 Feb 2019, 13:22

I looked into this - it's technical. Polarizing the alternator isn't about bypassing anything.
Alternators do not use permanent magnets. However, alternators need a bit of residual magnetism in the armature pole pieces to initially induce small field current which in turn generates a larger magnetic field, then even more current to ramp up output. Think of it being a feedback loop between increasing current and magnetism until the alternator reaches it's maximum output.

If an alternator has been unused for a very long time (time frame in years), or has been 'mistreated' this residual magnetism can be lost. Though there is nothing electrically or mechanically wrong with it, it simply can't get going without this residual magnetism present. There are also cases (note: not under normal conditions) where that residual magnetic field can be reversed north to south to the same effect: the alternator no longer works. The polarization procedure corrects both of these conditions.

If you start the car and it charges the battery while running, you need not worry about any of this: there is both residual magnetism within the alternator and it's magnetic poles are properly oriented to get the whole thing working.

I'd actually never heard of this before, but apparently it's a concern 'to be aware of' on very old vehicles, restoration projects, and non automotive power generation equipment.

940tvolvo · Post by **940tvolvo** » 17 Feb 2019, 13:35

Thank you mrbrian200 much appreciated

No, the alternator does not charge the battery when I start my car, in fact when I test the alternator it reads like the alternator is not good, putting out no charge/voltage. Only once I polarize it does the charging system work as it supposes to. And I've bought 3 alternators, 2 batteries, and a starter. I have no idea what is wrong with the car.

940tvolvo · Post by **940tvolvo** » 17 Feb 2019, 13:39

93regina

Are you asking me if I checked the muffler bearing or was that trying to imply that my (brain) bearings are loose? I am kinda slow today, and so I just need to clarify. Thank you lol

Post by **jimmy57** » 17 Feb 2019, 16:03

The rotor is magnetized by a miniscule current from the warning light circuit. On older cars the + brush circuit is connected to the warning lamp circuit in cluster via the D+ 61 terminal on alternator. On newer networked cars it is not a direct connection to lamp circuit in cluster to D+61, it is dedicated circuit in CEM. The residual magnetism in rotor is not enough to create current flow for voltage regulator unless engine is revved above 2500 and sometimes much higher. The newer cars with communication to VR still get initial magnetizing current flow on that signal D+61 terminal.
On your 940 it is a cluster warning lamp circuit feed. The small gauge slip on spade terminal wire should make a number of warning lamps light up if you switch ignition on and touch that wire to ground. If it does not then that wire may have a connection issure at the bulkhead connector at back of engine compartment on driver's side under the strut to firewall brace. The "bullet" and sleeve connection used in that plug are known to cause issues. If you run a jumper wire to the alternaotr terminal for the small gauge wire connected to battery + and it charges then the circuit is good. The alternator also uses a ground wire due to the rubber bushings and that can break and make it not charge.

Post by **jimmy57** » 17 Feb 2019, 16:11

On new cars with two path mufflers there is a damper (throttle) on a shaft through bushings. Those bushings are the honest to goodness muffler bearings.........Reality is way strange sometimes.

dm635 · Post by **dm635** » 17 Feb 2019, 17:15

To my knowledge Polarizing is done to Generator charging circuits anytime the battery is disconnected or any charging parts replaced. First time I've heard it being done to an alternator. But if it works for you.

I saw where you've been asked about the battery light on the dash. On '87 and back BMW's if the battery light on the dash does not light there will be no charging. Starting in '88 a resistor was added across the battery bulb leads so the battery would get the exciter wire circuit hot so the alternator would still charge with a burnt out bulb.

93Regina · Post by **93Regina** » 20 Feb 2019, 14:56

mrbrian200 wrote: ↑17 Feb 2019, 13:22If an alternator has been unused for a very long time (time frame in years), or has been 'mistreated' this residual magnetism can be lost.

Been kicking up RPM to 2000 or so, for a number of years to get alternator running.

cases (note: not under normal conditions) where that residual magnetic field can be reversed north to south to the same effect: the alternator no longer works.

But I have two alternators that can be spun either way, and work fine....Delco Si30...Prestolite/Leece-Neville-This alternator is equipped with a bidirectional fan which can rotate in either a clockwise or counterclockwise direction.