One Wire Alternators

From time to time I see posts concerning the aplication of one wire alternators on tractors. Typically the post has to do with the RPM threshold required for the alternator to begin charging. Currently, there is one of these discussions in progress on the John Deere forum.

I understand that the alternator must energize itself when configured as a "one wire" and some amount of RPM is required for this. However, a generator must also energize itself. I thought an alternator was to be an improvement over the generator...?

What prevents the construction of a proper functioning self energizing alternator?

A generator has a permanent magnetic field. So all it takes, it to spin it up to a high enough speed to make the requlator kick in... You can always pull start a generator tractor with a dead battery, as long as the battery is not a short.

An alternator must use battery voltage to create a magnetic field.. so it can never start by pulling with a dead battery.

A one wire uses an tiny amount of electricity to put and keep... a very small magnetic field on the alternator,, and spinning it up to a high speed to finally sense enough voltage to kick in a charge,, very similar to a generator.

A conventional alternator using the ignition sense lead to turn on the alternator and magnetize it so it requires a working ignition lead through a diode or warning light to activate it. It does not have the bleed resistor in it. This type will charge as soon as it it spun... does not require to be spun up to a higher speed to start charging. And it will not have a small bleed current when turned off.

In my opinion, FWIW, that's a darn good answer. I tend to get more long winded in my responses lol.

As you know one of many advantages of the alternator is its use of low (magnetizing) current slip rings and small light "brushes" unlike the high current and segmented brush wearing commutator on a generator..........Improved power curve versus the 1/2 cycle chop chop chop pulsing DC waveform a genny produces...........Its more efficient, power to turn it versus power it generates..........

John T

BOTH generators and alternators have a slight residual magnetism in the soft iron poleshoes or rotor segments.

I don't think "a generator has a permanant magnet field" is a true statement in the conventional sense of the term "permanent magnet", as a generator that sits unused for a long time often has to be polarized to restore it's "residual magnetism" so it will charge.

Any alternator will produce a small AC voltage from it's stator windings at startup due to residual magnetism in the rotor, it's often NOT enough to get past the forward voltage drop of the diode trio and electronics in the regulator to get turned to DC and feed to the slip rings and rotor.

Kits to change a standard alternator into a "one wire alternator" are often sold as "having special low forward voltage drop diodes" in the diode trio and a special regulator to create enough DC from that little bit of AC to send the rotor to generate more magnetism and MORE voltage output, bringing the alternator "on-line".

I have one wire's on my 8N and '56 chev.
Don't have to REV either one to get them charging.

"as a generator that sits unused for a long time often has to be polarized to restore it's "residual magnetism" so it will charge"

In addition Id "guess" if it sat there with the armature removed magnetic field strength will drain off faster just like if a horseshoe magnet has its keeper removed??????

John T

One big reason folks have trouble exciting a "1 wire " alternator on an old slow turning tractor engine is that they choose the wrong size "1 wire" alternator. The rotor poles on an alternator are much smaller than a generators pole shoes, so it needs to spin faster than a generator to induce enough voltage to excite the field rotor.

Most people try to use a very high output "1 wire" alternator, usually in the 60-72 or 100 amp range, to replace their 20-30 amp generator. Part of that fault may be with the parts store that stocks only very large output "1 wire" alternators to reduce inventory, as in many cases, a large alternator can replace a small one without problems.

My experience with the "1 wire" Delco SI series alternators is that the "small" stator windings of the 37 amp "1 wire" alternator will excite at less than half the rpm it takes to excite a 60-72-or 100 amp "1 wire" alternator. Thus making the 37 amp "1 wire" alt ideal for those old slow turning engines, plus if your using the original wiring harness, a 37 amp alternator will not overload / overheat the wiring that previously was connected to a 20-30 amp generator.

Also that old husbands / mechanics tale of a "1 wire" alternator draining your battery is false for any " 1 wire Delco built in the last 40 years. A modern "1 wire" Delco SI series alternator has the exact same internal wiring as the "3 wire" alternator, their is no added connection to battery power to discharge the battery. Very easy to confirm this fact, just disconnect the BAT wire from the alternators output stud and using your multimeter, measure the current flow to the alternator, be it "1 wire or "3 wire", you will find it to be exactly the same, a few miliamps lost through the rectifier diodes which are the exact same part in either "1 wire" or "3 wire " alternator.

Well I don't claim to know all the innards of a alt. We put a one wire on my 1945 B. Local shop wired it up with a low speed pick up. The top rpm for a JD B is around 1,000. Works fine. Around 75.00 bucks. Made it 12 volt while we were at it. Tractor has a mag made it simple.

In the past there has been some discussion about one wire alternators on this site. There are some that hate them. I have 3 older tractors with one wire alternators and prefer them to any other. I wired them myself and haven't had any problems with them draining the batteries when idle. The ones that I have say that you need to throttle up to 1000 rpm in order to excite them to charge. Who doesn't run a tractor above 1000 rpm anyway?

Hello Indiana Ken,

One wire ac generator with prolerly sized pullies will charge at any engine speed. GM one wire require the
generator speed to be 1 and 5/8 faster then the engine. Then it will charge at any enging speed,

Guido.

I have several machines that have been converted to 1 wire alternators and have never had any problems
including reving to start charging. They just always work for me. They are cheap, simple, and reliable
as far my experience goes.

Hello jon f mn,

In one word.......YEP! They do just fine, Just get them spinning at the right rpm,


Guido.

One advantage the alternator has, once the threshold has been met, the alternator will continue to charge even at lower RPM as long as it isn't shut off.

With a generator, every time it falls below the charge threshold speed, the charge rate will fall off or stop charging until it is sped back up.

I see this discussed quit often on here, I have put one wire alternators on several tractors and race cars. Local Generator Shop Guy told me years ago that GM had lots of Different Regulators For inside Alternators, he got the ones that started generating when it starts turning. I have never had any problems with Of them. As many tractor friends have done the same things. Shop closed up a few days ago. Owner passed away. We lost a lot of Electrical knowledge.

Thanks to all who answered. As a 8N, 6 Volt liddite - this has long been a puzzle to me. I had never considered the effect of the diodes in the circuit. From the posts it appears some of the "one wires" do boot up at a low RPM. However, I will be sticking with my generator for the foreseeable future.

"Local Generator Shop Guy told me years ago that GM had lots of Different Regulators For inside Alternators, he got the ones that started generating when it starts turning."

The trouble with that story (AFAIK) is the "GM" didn't make "one wire alternators" (or regulators for them) in the common 10 SI or 12SI models. There MAY be exceptions to that, but I have never seen one "in the real world".

The "one-wire regulators" and alternators that are available in those common sized are aftermarket bastardizations of the actual GM products.

Larger-framed Delco "brushless" alternators (used on semis, for example) ARE self-exciting, but have a LOT more "soft iron" to retain residual magnetism.

When I got a minute, I'm gonna run an alternator slow on my test stand, and read the AC voltage output of the stator and the DC output of the diode trio PLUS get a 'scope waveform photo of the stator output and post all that on here and see how much discussion and discord that will cause!

Bob,

I will be watching for the post.

Ken

I see some of the alt parts outfits sell a special "1 wire" regulator that replaces the diode trio with two little jumper wires from the outer two stator terminals to terminal studs on the regulator. supposed to excite at very low rpm.

Are you sure they are simply wires, or could they be discrete Schottky diodes in an insulating tube?

If not, they are used with a special regulator that likely has Schottky (low forward voltage drop) diodes inside it, IMHO.

I suspect the Schottky diodes are in the regulator, ,but very hard to tell what the "jumper wires" are from a grainy 2 inch photo.

I'd be interested to see your results, too. Especially the waveforms from the diode packs. I'm always willing to be educated.

(quoted from post at 12:17:33 09/05/16) I suspect the Schottky diodes are in the regulator, ,but very hard to tell what the "jumper wires" are from a grainy 2 inch photo.

Click to expand...

have one of those. I believe the stator connection is to signal the reg that there is some activity, i.e.that rotor is turning and that it is time to provide field power from battery to rotor. Presumably more sensitive and quicker that could be done with diode trio being able to gen enough output to kick in charging.