exciting alternator coils

Note that most alternators today are regulated by shorting the field to ground. This is because it's simpler to do with an electronic regulator. Many of the older alternators, however, were regulated on the battery side of the field. The point here is that you can't say with absolute certainty that shorting the field to ground will excite the field; on some alternators this could blow the regulator.

My experience has been that the "regulator bypass" feature isn't the greatest diagnostic tool. I once had a car that would blow up a regulator within a minute or two of installing a new one. The alternator appeared to be OK, using the regulator bypass. However, once I pulled it apart I found two blown diodes; it was charging just enough to appear to be OK.

You've got that bass-ackwards. The #2 terminal is the terminal already connected to the battery, usually even with the key switch "OFF". #1 is the excite terminal.

One thing I meant to mention in my other post is that it is possible to by-pass the internal regulator for testing purposes by inserting a small screwdriver in a certain hole in the back of the alternator, no more than 1/2" to avoid contacting the spinning rotor. Which hole will become obvious once you look inside a disassembled alternator. The regulator has an extra tab that lines up with the hole in the back of the alternator. When you insert a small screwdriver and short this tab to ground, the alternator is full-fielded.

With alternators you do not need to do this and on some alternators you could damage the unit doing something like this.

Are you sure it wasn't a GENERATOR you saw this done with and not an alternator?

Charles

Charles

Make? Internal or external regulator?

If you are referring to older GM's or Ford's with external regulator, connecting full battery voltage to the "F" terminal on either will "full field" them, in other words, put them in full, unregulated charge.

If you know your make and type, myself or other's can advise you further.

On either system, if the generator has sat unused for a long time, or has been apart, it may need to be polarized. This is done with the engine "off" by momentarily jumpering the "BATT" and "ARMATURE" terminals at the voltage regulator or cutout. This served to restore the minute residual magnetism that lingers in the field pole-pieces of the generator during periods when the machine is shut off, yet is enough to "excite" the generator into charging when the machine is again started. If a machine is changed from positive ground to negative ground (or vice-versa), polarizing the generator before restarting can avoid damage to the cutout or regulator, and possibly to the generator.

In my previous post, I mentioned temporarily connecting battery voltage to the "F" terminal on a Ford or Delco with external regulator to test for maximum output, or to narrow down whether the problem is the alternator or the regulator.

On Chrysler alternators with external regulators, there are generally two insulated brushholders that supply current to the rotor, and by disconnecting system (regulator)wiring and grounding one and applying battery voltage to the other, the alternator may be checked for maximum output.

On common Delco internally regulated alternators,
the #1 terminal is fed "excite" voltage when the key is on, usually through a resistor, a lamp bulb (idiot light), a diode, or a combination of light and diode or resistor. The #2 (voltage sensing) terminal is connected the the large output stud, or for greater accuracy, as near to the battery as possible. If the tractor is running and not charging because the circuit connected to the #1 terminal has failed, momentarily touching a test lead supplying 12 Volts from the battery to the #1 terminal will "excite" the alternator, and it will charge as long as the engine remains running.

A "one wire" alternator offshoot of the above Delco needs only the large output stud connected to the battery, and will charge once the engine is started and "revved up"

Newer internally regulated alternators come in such a wide variety of hookups that it is almost impossible to troubleshoot any of them without a service manual pertaining to that manufacturer.

Some foreign alternators (certain Bosch and Nippondenso models) connect similarly to the Delco, and others have hookups all their own.

The heck of it is, without experience and the proper manuals, it is so easy to do $100's of damage to a newer system you're not familiar with!

I hope the "raving" is of some use to you! Good Luck!

Check out the link below for more Delco info.

• Mad Electrical