The Stovebolt Site Forums The Shop Area The Electrical Bay Alternator vs Generator (51 half-ton)

What exactly is the benefit of using an alternator instead of a generator? I'm planning a 235/Saginaw upgrade for my truck and I'm just exploring my options. I know the consensus is that an alternator is "better" than a generator but I want to know why.

I don't intend to drive it a lot and I like the idea of keeping it looking as original as possible because I do want to start taking it to shows and whatnot.

Alternators charge at low speeds (even Idle) while generators need more RPMs to charge. Alternators will also take higher RPMs for extended speeds
Mike

Alternators also tend to put out more amps than a generator and use less power to operate. But, a generator will charge a completely dead battery, an alternator will not. Also, a generator will produce electricity w/o any power from a battery. An alternator does require power from a battery to exite the regulator and feilds.
If you want to keep original, and aren't planning on putting on extra electrical components like a stereo or electronic engine controls that will require more amperage, the generator will be just fine. Just give it a freshening up with new bearings, brushes, perhaps have the armature contacts machined true, and a new regulator if necessary. It'll work just fine.

Woody,
First let me say I am a die hard keep it original type person. I also restore antique starters and generators and up grade them etc. Cost is a big factor for a lot of folks on something like this. You can take a 10si Delco alternator with a special low rpm cut in self exciting regulator and get the benefit of cut in at low rpms and upwards of 70 amps if its built correctly. With that you can then add on about whatever electricals you want.
Now, if you want to stay origial, there is nothing wrong with the original charging system with external regulator if it is built/restored correctly along with a new regulator at the same time. I have had original generators come in the shop that have well over 50 years on them, never been touched and still working. Cant say the same for any alternator. Yes, it will cost more to restore the gen. and install new reg. but they are for the most part just a trouble free as the alternator when built like they are supposed to be built. By this I mean not just patched up but professionally restored.
It is also possible to take a stock 30 amp generator and internally match up a new armature and coils and get upwards of 45-55 amps out of the generator. Of course you then have to upgrade the regulator as well for the higher amperage output.
Just my 2 cents worth, but I still like the looks of a restored gen. under the hood.
Ken

Once upon a time I found an outfit on line that sells 12v alternators in housings that look like generators. They only did 12v so I wasn't interested. I recently took the plunge & put a 6v one wire alternator in my 38 & am happy with it so far. The only down side is you need to run a heavy gauge wire directly from the alternator to the battery which bypasses the ammeter so the ammeter doesn't show anything anymore. The only way I know it's charging is to put my multi-meter on it every so often. I suppose I could hang a volt meter under the dash but so far everythings good.

Tiny,

Why can't you wire the alternator output through the ammeter in the conventional manner?

Stuart

I had it wired that way and almost fried the ammeter. It's a 65 amp alternator and one time I cranked for a while with the key off (brain dead moment, forgot to turn the key on) so when I finally did turn the key on and the engine fired the ammeter put out way over the 30 or so amps the ammeter is made for. It pegged the ammeter for a considerable time and after that it worked but not the way it did before. Plus the wiring is too light a gauge for the potential alternator output. I called the folks I bought the alternator from and they advised running an 8 gauge wire directly between the alternator and battery. If I'd bought a 35 amp alternator there would be no problem. Lesson learned.

Right.
In order to use an Ammeter, you should shunt it. There needs to be circuitry for that though. If that's what you want, I'll sit down and whip something up.

I have an ammeter sitting around too. Nice unit, but voltmeters are so much easier to wire up.

Looking at the wiring diagram I see the battery and horn hooked to one side of the ammeter and everything else connected to the other side. Does this mean that the lead from a one wire self exciting alternator should be connected to the same side as the battery and horn?

Jim,

No! The output of the charging system is hooked to the "other" side of the ammeter...not the same side as the battery. On a AD rig, the loads and the output from the charging source would be hooked on the same terminal, which would be the -, or negative side of the ammeter.

The battery should be attached to the other side of the ammeter, the + side. If your truck uses a horn relay, this is usually used as a buss for the charging system output. The horn is normally on the load, or - side of the ammeter...I think!

Stuart

I did the switch to an alternator on my '50. I had run generators for years and as Ken said the key was getting them to work right in regard to output and the regulator. On a raining night with lights, radio and converted electric wipers, the system would discharge at idle. I don't really like the look of a modern alternator in my engine compartment, but I do like having a fully charged battery at all times. I did look into the alternator in the original generator, until I saw the $400.00 plus price tag.
Steve O

Hi Stuart,

I have the battery and the horn connected to the + side of the ammeter. Everything else including the alternator lead is connected to the - side of the ammeter. The wiring diagrams shows the horn (and cigarette lighter if installed) being connected to the same ammeter post as the battery. I guess they felt it wasn't necessary to measure the load of the horn when honking. The reason for my earlier question about connecting the alternator to the same connection as the the battery is because of an earlier post in this thread from Tiny suggesting that the ammeter be bypassed and the alternator connected directly to the battery. Doing a search and looking thru the history I can see that this subject has been beat to death, but the questions still remain and get asked over and over because it is still so confusing.

How is the horn relay used as a buss for the charging system, and how would it be wired?

My 38 has the horn relay for the accessory horns (called Town & Country in '39) connected directly to the battery (top of the starter switch), then grounded through the horn button. My regular horn does not have a relay and is connected on the (-) side of the ammeter. That was per the instructions that came with my harness.

Jim,

I think I gave bum info in my previous post. The common buss isn't at the horn relay. My diagrams show the horn relay connecting to the BATT terminal of the regulator, which would be the most direct route for a full power connection to the horn via the relay. This point isn't really important.

I can see Tiny's point on bypassing the ammeter with his new alternator, but I don't know if I agree totally.

Although a modern alternator has the capacity to supply more current than a old style generator, it's the demand on the system that will regulate this.

If the battery were run down, as in Tiny's case, the charging system would spike when the truck started and alternator began to charge. This wouldn't happen for very long, and as the ammeter isn't a mechanical gauge, I don't think it would be affected.

The typical generator could supply upwards of 30 amps. The alternator that is often used with a 6/12 swap is usually in the 50 amp range. Unless some fancy wiring is done, and regardless of which side of the ammeter the charging system output is attached, there is going to be some wire under the dash that has the potential to see the total output of the charging system.

Although I don't know this for sure, I would speculate that the ammeter is constructed internally to handle output of a modern alternator. I don't know if pegging the gauge would ruin it, but I would doubt it...it's not a solid mechanical hookup.

The only scenario I can see where the ammeter would see a huge current rush would be if the battery were run down during a hard start, and then this would only be for several seconds before it tapered off.

The whole idea with this topic is whether or not it is safe to have large current carrying conductors inside the cab. I think if done properly it's fine, but I suppose it's really a matter of personal preference.

Stuart

I realize that this is an old thread, but this is exactly what I'm looking for. I need to replace my generator and would like to use an alternator that looks like the original generator. The truck has been converted to 12V so this will be perfect.

I found a guy on the west coast that sells what he calls a "genernator" for $800 to $900 - way out of my league - but $400 would be doable.

Can anyone give me the name and number for other sources of this type of product. I've tried the usual Chevy truck part suppliers, but they've never heard of such a thing.

Power Gen - $350+