one more time................alt. questions

[beedees]

What is the purpose of grounding the second fiel :icon_smile_question:d terminal on a dual-field alt. when using with a single field wiring harness?

[Ghoste]

To prevent overcharging the battery.

[Plumcrazy]

The second alternator brush was originally grounded in the older single field wire alternators.  If you install a newer dual field wire alternator on a car wired for a single field wire alternator without grounding the other terminal it won't charge

[Ghoste]

It doesn't overcharge?

[beedees]

Reasonfor asking, I installed one without grounding the 2nd terminal and it lasted about 20 min.  Seemed to be charging o.k. though. Could doing this hve fried the v.r.?

[Nacho-RT74]

one field alt uses two brushes: one grounded ( without plastic isolator ) and one isolated. This alt is feeded with regulated ( pulse ) positive from mechanical regulator with a green wire, for a while negative is constant by brush grounded. When charging system needs more positive, regulator will send more power and increase the magetic field, then the output.

dual field alt use two brushes isolated, One is CONSTANT positive from ignition key ( blue wire ) and the other one is REGULATED GROUND, coming from regulator with a green wire. Regulator take the negative source from chassis and sends what charging system needs increasing negative signal so, increasing magnetic field inside the alt, Then the output. Blue wire feeding the regulator comes from same ignition key source and is the signal to regulator know if car is needing more charge.

Grounding one brush on double field alt is to make work a lates alt to electronic regulator charging system on to old single field charging system to mechanical regulators.

[beedees]

  Do I need to switch to electronic v.r.?

[Nacho-RT74]

As I stated, with just ground one of the brushes is enough to keep the original mechanical regulator, because you would be doing exactly the same than earliers Alts but on a later one.

HOWEVER...

Since you already have the expensive part of an electronic upgrade ( the alternator ), then make the complete upgrade wouldn't be bad to make because has been prooved than laters charging system is more eficient and constant. Just would need an extra wire ( blue ), electronic regulator and plug... just $50 more.

[Ghoste]

I'd still like to know about the over or undercharging part.  Reason being that until I grounded the other field on my alt, the amp guage was nearly pegged into the charge zone, if it should have been undercharging, then I have some other problem I need to address.

[Nacho-RT74]

overcharging when you ground one of the brush only happens if you are grounding the brush feeded by electronic regulator with negative since will be bypassing the negative regulator function, on elect/double field alt setup.

Other stuff is that low capacity stock alternators keep charging full scale when you press gas pedal, not really at iddle, since for a while engine is at iddle, cars allways is sucking power from batt and not from alt, so charging power keeps unbalanced. At nights that is really a headache.

Anyway will help a lot a COMPLETE description about your problem.

[Ghoste]

But mine overcharges if the other field is NOT grounded.  As long as I keep it grounded, the alt functions fine.

[Nacho-RT74]

what kind of regulator do you have ?

[Ghoste]

An electronic aftermarket one for a single field.  It does not look like the stock one it's an aftermarket replacement designed to wire up to my existing harness.

[Nacho-RT74]

weird!!!!!!!!!!!!!!!!!!!!!!!!!!!! I would say there is somekind of short with high resistance inside the alt.

Unplug completelly the alt and check continuity:
- between brushes around 5-10 ohms
- between ANY of brushes and chassis ABSOLUTELLY NO READING...

except of course if you have definitelly grounded one of the brushes, that of course it should have continuity.

[Ghoste]

Yeah?  Well then, there is a place here in town that will check them for free so for all the trouble it is to take it off, I may as well run it in there and find out what's going on with it.
Thanks Nacho.

[dm69charger]

I purchased a new 75 amp chrome alternator from Summit a couple of years back and had the same problem with overcharging.  It was a duel field unit so I grounded the one field as instructed.  The ammeter pegged the entire time.  I was on my way to a car show and smelled something starting to burn.  I reached my hand under the dash and the wires going to the ammeter were really hot.  I believe that I killed the voltage regulator and I was getting the full 75 amps from the alternator on my wires.  These wires were not meant to carry that much current.  I thought that I was going to catch my car on fire.  I unplugged the wire that I grounded and continued to the show.  The alternator was no longer charging at that point.  I was just using the battery.  Anyway, what I did was just upgraded to the two field voltage regulator 70 and up type.  I is a simple upgrade and you only need to add one wire.  It has worked a lot better since.

[Ghoste]

I haven't had a chance to look at mine yet.  Obviously, there is something really goofy with it.

[Nacho-RT74]

If you ground a double field alt AND DOES HAVE Electronic regulator, then will get max output from alt. You are sending max positive and max negative input, increasing magnetic field. That will overcharge. You can do that in case of emergency Voltage regulater goes bad in the middle of nowhere but not on regular use.

AS stated, Double field alt with electronic regulator is regulated BY GROUND not by positive. Positive is constant max input from Ignition key blue wire, same that feeds ballast, etc...

Single field alt is to work JUST with Mechanical regulator, since POSITIVE is the signal regulated, for a while negative ( ground ) is constant max input because brush is grounded.

BECAREFULL GUYS, color wires are inverted from one to another. Green on earliers is positive, and on laters is negative. On both cases, green is the regulated source.

Ground a double field alt brush WITH MECHANICAL REGULATORS is simulate the single field alt, and there is not problem on that. BUT JUST with mechanical regulators, or as stated in case of emergency Electronic Regulator went bad to arrive to a place to replace.

[MorePwr]

Ok now I'm getting confused. By the pictures can you tell if I have an electronic regulator? I've tried grounding the unused field connection on the alt (see pic)  Nothing changes. still puting out 16.5v

I replaced the alt, reg, battery cables, cleaned all connections. and bypassed the amp guage.

My over charge issue was accompanied by a pulse, very dim lights to very bright, in sinc with the amp guage. replacing all those parts did nothing. bypassing the amp guage stoped the pulsing,(So I thought) but I still have 16.5v at an idle.

Gave myself an hour or so break. when I went back out to see if id'e overlooked something. I restarted the car and the pulse is back, but only for a couple of minutes, then it stops and I'm back to a steady 16.5v...so temp?

I should add, while all this has been going on my fuel and temp guages have been intermittently working, but completely dead today.

Any help would be appreciated. thanks!

[Nacho-RT74]

you have a mechanical regulator with a later double field alt BUT one of the brushes prong is cut and is grounded with a metalic washer.

it looks you have some short somewhere or damaged regulator.

Regulator blue wire must have 12 volts coming from ignition on RUN position, that's input, and green wire with screw is output to alt brush. It should read some reading around 12, but since is a pulsating signal coult it be unnacurate to a digital multimeter. For a while Batt is more discharged or Car does need more power, then pulses are quicker to increase magnetic field on rotor captioned by stator what give more output on alt. Negative brush since is constant by chassis then magnetic field variations are drove by positive pulses.

[71_deputy]

I'll pipe in a bit there Natcho, also make sure the engine to battery and battery to rad support connections are CLEAN and TIGHT!!!!!!

your voltage reg only has one bolt- use two with toothed washers to bite into the metal for a good ground.  as a extra ground I always use a braided ground strap from the back of the engine to the bolt of the voltage reg to give the system a shorted path to follow.

John Mac

[MorePwr]

Good advice Nacho and Deputy, I'll spend today checking wiring and grounds.....I'll let ya know. Thanks

[Nacho-RT74]

Another checks:
-checking for short on green wire with ground. Unplug + side of batt and green wire from alt and check continuity with chassis on regulator. It must be have no reading.

-Check for short or no reading on rotor. Remove grounded brush and check between rotor track ( will be visible when you remove brush ) and prong of the other brush. It should have between 5-12 Ohms reading. When brush is isolated is enough check between brush prongs, but since this one is grounded...

-Another rotor check is, once you removed grounded brush, then it must be NO READING between isolated brush and alt chassis. This is a very common fail when rotor/alt fails making some overcharging reading without enough amperes, even amp on cluster missread this stuff... keep reading overcharge, but is not a real reading being unable to keep car running with batt disconected.

-Absolutelly no continuity between any of regulator terminal and chassis.

there is another several checks. I think I'll make a check guide about this, with pics.

[MorePwr]

Thanks again for all the advice. it has really helped   I've got the charging system working perfectly now with a jumper wire from the batt. to the regulator. the problem from the git go was a three volt drop to the regulator. I pulled the firewall plug and found that the volt drop is comming from the inside of the car, I guess that the next stop is the ign switch. which has been hacked by the previous owner.

I also found some commonality between the charging system and the guages. which have been acting up also...The dark blue wire from the ignition switch sends power to the guages and the regulator. according to the wiring diagram I'm looking at.

[Nacho-RT74]

Yes on standart gauges, but rallyes gauges are feeded by accesories black wire from ignition switch.

Drop on blue wire line could it be also on bulkhead plug.