Alternator welder

Quote:

---

Originally Posted by bobwills

Im still a bit confused. So whats a diode trio and what does it do that you would have to remove it sometimes. And ok so your saying to open it up and just put a wire grounding out the regulator. Is that really all you all are saying to do. Sorry i dont understand too much. Not the best on some of these types of things. But hey ya gotta learn somehow.

---

Hey no problem man.

The diode trio is a small solid state component that bleeds off a bit of juice from the alternator output, to energize the field coil. But the field coil needs to be energized before the the alternator can produce any juice. So it's a catch 22.

When the alternator is installed in a vehicle with a so called "idiot light", the initial field energizing current is provided by the battery, through this light. When the light goes out, the alternator is providing its own energizing field current (actually it's called "excitation" current) and the alternator becomes self sustaining.

So if you leave in the diode trio and hook up according to Blasphemy's schematic, then the rheostat will provide no control whatsoever, because the diode trio will be providing all the field current.

And yes, while you have the case open, you can solder a lead to the test terminal, (the one you would otherwise be grounding with a bolt in the threaded hole) and bring it ouside the case. Then it can easily be grounded to the case.

But a much neater way is to leave the diode trio in, and achieve control by wiring the rheostat between the test lug and the case. Then you only need a shot of juice from the charger or a battery to initiate the field excitation. To boostrap it so to speak. Then the alternator becomes self sustaining as explained above.

Cheers,
rivets

Ok so i do need the diod then unless i put the reostate switch between the voltage regulator and the casing, am i gettng it right. I think his way would work ad wouldnt. the reostate part would control the amps but the way he described to bypass the voltage regulator wouldnt. What i think would work is just ground the voltage regulator out always and then the reostat goes on the left wire which starts the feild then goes to the battery or charger controling how stong of a feild is is created changing the amperage. But maybe a strong feild all the time and controling the amperage from the voltage regulator would be better. I dont know.

If you use a rheostat on the bottom side of the field coil (short out the regulator), you will still ultimately be powering the field proportionally off of the output. This will yield a positive feedback device which is extremely unstable. When you are not welding, the output voltage will increase, which in turn gives the field more voltage which causes the output voltage to increase even more... and you can see where this is going. Anyway, that will happen until the max reverse voltage of one of the diodes is exceeded, and it fails. If you are running the alternator with no output load, and you short the field, the process I described will happen nearly instantaneously.

The feature of shorting the regulator was intended to be used at engine idle speeds with the alt connected to a battery. The low speed will limit the total output power available, to where the starting battery will be able sink all of the available output current and keep the output voltage from swinging unacceptably high.

I think the easiest and fastest way to mod the alt is it take it apart, remove the diode trio, and run two wires out to power the field externally from a stable voltage (or current) source.

I've done this basic thing. The alternator I used was a 3g ford 130amp model. When turning about 6000 rpm (alternator rpm), and with 13.8v across the field coil, it produced just shy of 100 volts on the output. It was attached to a 17.5hp gas engine. Arc starting with a 1/8" 6011 was very easy. I could hardly keep up with burn off, and by the time i got to the end of the rod a few seconds later, the stub was glowing orange. These alternators are capable of pushing far more current than the published rating (at least under the described conditions).

Two such 130 amp alternators running in parallel were able to drag the engine down; though, the engine did not stop. What happened was that as the rpm decreased the alternator output power also decreased until the required torque at the given rpm was equal to what the engine was capable of producing (at that rpm)

A misunderstanding of this situation is this is basis for the fallacious statement that an electric motor HP is somehow not equal a gasoline HP which is also not equal to a diesel HP.

Quote:

---

Originally Posted by parkour

A misunderstanding of this situation is this is basis for the fallacious statement that an electric motor HP is somehow not equal a gasoline HP which is also not equal to a diesel HP.

---

Yeah I misstated my information. Electric motors have lots of torque and this keeps it from bogging. Diesel's have a lot of torque too, but they tend to bog. Gas have torque but not nearly as much as diesel or electric, causing bogging. If you put a 100 amp alternator on each of these power sources at the same rpm, same belts, same HP at RPM, etc, the best performance will come from the electric motor, second best diesel, last would be gas. Just for the torque keeps you spinning without bog. It's much easier to stall a gas than electric. Like we have a cutter that had a 40HP gas factory installed, we swapped it for a 15 HP electric. The electric does better even though the gas is 2.6 times the HP rating. HP gets you going, torque keeps it going at desired RPM.

Summary,
Yes HP to HP is equal. I accidentally goofed and made it sound like it wasn't equal. I meant to be referring only to torque.

Thanks for bringing this point up Parkour, :cool: :)
ILP

Quote:

---

Originally Posted by parkour

If you use a rheostat on the bottom side of the field coil (short out the regulator), you will still ultimately be powering the field proportionally off of the output. This will yield a positive feedback device which is extremely unstable......

---

Excellent point Parkour.

The voltage can't rise indefinitely however, as eventually the core will become saturated. But your're right - the diode PIV will likely be exceeded.

Was thinking of self sustainability so that the welder could be wheeled anywhere away from an external power source, or have to carry a battery.

Hmm. Will have to try and think of a way to limit the field voltage to a defined maximum, when fed from the alternator output.

Or maybe cobble together a bridge with a number of diode pairs in series.
e.g. two diodes in series would effectively double the PIV rating of the pair.

Ah, the things we learn on this forum.
May not be so simple after all.

@Bobwills
I think you should listen to Parkour unless you want to experiment in how much reverse voltage the diodes can stand.

Cheers,
rivets

Quote:

---

Originally Posted by Rivets

Was thinking of self sustainability so that the welder could be wheeled anywhere away from an external power source, or have to carry a battery. Hmm. Will have to try and think of a way to limit the field voltage to a defined maximum, when fed from the alternator output.

---

Questions:
1> How many amps does it take to excite the primary coil in a 50-60 amp alt?
2> Could an external after market 12v voltage regulator be used to keep the voltage in the appropriate range?
http://www.parts-express.com/pe/show...artnumber=7812

Thanks,
ILP

How many amps to excite the field coil you mean? It doesn't take much at all to get "some" voltage out of the output side. Hell a 9v battery will energize the field enough to light a couple light bulbs with the output. As for what it takes to get welding current out of the output, you will need a volt meter to find out. I'm energizing my field with a battery charger that has an AMP gauge on the front of it, when I have the max current knob cranked up the ammeter on the battery charger is pegged out but I'm only getting 8.67v at the field. My battery charger is only an 8 amp and its just not enough to FULLY energize the field coils. At full power I should have around 13-14.3v at the field terminals, but w/o a bigger charger I'm not sure how many amps that would take.

Yeah field coil. Well obviously that 1 amp voltage regulator link wont work. But would using a higher current voltage regulator work for keeping the field voltage under 15v? I gather from reading the posts, that we are looking to keep the voltage under control, not amps for say. I'm assuming the coil's resistance will keep the current in appropriate parameters as long as the voltage is limited to 14volts +/-?? I think the maximum voltage on most of those automotive diodes normally is 20volts although I've seen some that are 16vDC, just FYI.

Quote:

---

Originally Posted by I_Love_Plasma

Questions:
1> How many amps does it take to excite the primary coil in a 50-60 amp alt?
2> Could an external after market 12v voltage regulator be used to keep the voltage in the appropriate range?
http://www.parts-express.com/pe/show...artnumber=7812

Thanks,
ILP

---

1> Based on Blasphemy's numbers, 11 to 13 amps for his particular alternator. (Assuming "pegged" is 8 amps).
2> Maybe, but not the one you indicate. The max input voltage is only 35 volts, and the max output current is only 1 amp.

Cheers,
rivets

Yeah 1amp wont cut the mustard. LOL Thanks for answering. So would the principle of an aftermarket external regulator work then?

I think i love plasma has something going there. What if its like a 24v regulator. Cause some things use 24v cause you see 24v battery chargers and jump starters. So then maybe them 24v systems might have a 24v alternator meaning theres a 24v voltage regulator in it.

I think what im gonna try is to just ground the voltage regulator out. And put the reiostate between the battery or charger and the wire that starts the field. Does will it work all like that cause that seems to be what ive heard about a lot.

Quote:

---

Originally Posted by bobwills

I think what im gonna try is to just ground the voltage regulator out. And put the reiostate between the battery or charger and the wire that starts the field. Does will it work all like that cause that seems to be what ive heard about a lot.

---

Bobwills,

You will still have to remove the diode trio.

Cheers,
rivets

Why does it have to be removed. Whats its purpose in the alternator too?

Quote:

---

Originally Posted by I_Love_Plasma

So would the principle of an aftermarket external regulator work then?

---

Yes, in principle.

The issue would be how to regulate a varying voltage of up to 100 plus volts to a constant 13 or 14 volts and stiff enough to source say, 15 amps.

Cheers,
rivets

Quote:

---

Originally Posted by bobwills

Why does it have to be removed. Whats its purpose in the alternator too?

---

Bobwills,

See post #41 above.

Cheers,
rivets

Hey this just popped into my head. If bobwills mower has a factory installed alternator he could use that what 10-25amp alt to power his field coil! :) That would be really simple, you know.

Yeah I see i think maybe. But still dont really know how come you gotta take it out. Is it to raise the volts or what? And what ill do on that part is just use the battery on the mower maybe. Or have another battery on there that is alone and it goes to the altornator then have the output of the altornator also run to the battery. Or would i run into a problem with the higher loltage running to a 12 volt battery. Im not really sure.

Quote:

---

Originally Posted by I_Love_Plasma

Hey this just popped into my head. If bobwills mower has a factory installed alternator he could use that what 10-25amp alt to power his field coil! :) That would be really simple, you know.

---

ILP,

This had also popped into my mind. I once repaired my neighbours 12.5 HP lawn tractor that had two alternator coils. One for the headlights @ 2 or 3 amps, and the other for the deck electric clutch and battery charging @ 4 or 5 amps. Still a little shy of requirements.

But if Bobwills' has a 10-25 amp juicer that could be a very different story.

Cheers,
rivets

The mower its going on is a old thing. so it prolly aint got much.