I built a small set up in the garage last night that was unfortunatly not turning fast enough to weld. It was working but not enough amps to weld with. if your using and electric motor succesefull to weld, what size motor and what size pully?

I have a ford alt 90 amp. 2 1/2 and a 1/2 horse motor 1750 rpm w/ 2 1/2 inch pully . I think If I went to a 6 inch pully on the motor It might work, what do you think, any ideas?

that'll work or just adjust engine speed with a hand throttle.

-Steve

Originally posted by offroadr35
that'll work or just adjust engine speed with a hand throttle.

-Steve

Ummmm....I may be wrong but I think he's talking 'bout a 2 1/2 and a 1/2 horse electric motor.:D
I'm not sure your 1750 motors are going to be fast enough even with a 6" pully.
If you read the article over in the tech section you'll see he starts out welding with the engine at 2500 RPM and odds are the crank pully is already 6" or larger.


I remember years ago reading an article in a magazine where they turned a push lawnmower into a welder by putting a belt on insted of a blase and running it out to the alt. via the grass chute.

alternator on a push mower makes a good jumpstart machine also.

OK I my ratio is 1 to 1 with a 2 1/2 inch pully with a 1750 rpm electric motor. I think I should be like 8 to 1 at the least. Has any body else done this? Changing motors would be expensive since the faster you go the the more horsepower motor you need, and Higher horsepower electric motors are expensive when you can only run single phase motors

sorry, i misread.

Ok i know there are some mechanicle engineers (spell check might help here! ) that lurk this board so how about it ???? 63 people have read the thread...so far.... somebody must have a freaking comment. even if they think I am out of my Freaking skull....

You need to know how fast you want to spin the alternator before you can do the math to size the drive pulley...

MY exact reason for posting the question!!! Boy at some point I should lay off of the tequila. Tooooo bad Love tequila.

Mechanical Engineer (in training) here.... just do a small engine and connect it via belt to the alternator. The small engines have pretty good RPM outputs, with a briggs and stratton 10hp motor IIRC putting out about 3600rpm at peak HP. HTH :D

Dude....10hp is good but all you need is 5 hp....just look at the portable welders that have these units on them....an keep the pullies small to ensure good speed.....and please don't ask for ME's about this.....

Still no acctual experanice Thabnk you coyte and fuykk rewversa for you cvain attenpt ......WoW I just read what I wrote.. I freaking drunk... has any body done this???????????????????????????????anybody at all even the lowest newbie ,,,,please post. MY drunken stuper may wear off bu tyour answer will be forever ingrained in electronic type. besides think of the fun I will Have next tiem I read them////

http://oak.cats.ohiou.edu/~weinfurt/gaswelder.html

- jack

Have you checked the open circuit voltage?

I run a 140 amp alternator on my homebrew welder on my truck. Does about 36 volts per 1000 engine rpm. I find 3/32" rod burns great at about 1600 rpm, or about 58 volts....open circuit.

Just for a point of reference.

Sounds like you need to up your pulley ratio.

Jay

Originally posted by ItsaCJ6

I have a ford alt 90 amp. 2 1/2 and a 1/2 horse motor 1750 rpm w/ 2 1/2 inch pully . I think If I went to a 6 inch pully on the motor It might work, what do you think, any ideas?

You are having problems with the first law of physics, which is the conservation of energy. You can't get more energy out than you put in. 1 hp is approximately 750 watts and to weld with the 90 amp alternator, you will need at least 25 V @ 90 amps or approximately 2500 watts to maintain an arc with a 3/32 rod. To generate 2500 watts, you will need a minimum of about 3.5 hp.

In order to get the maximum power from the alternator, you need to turn it at about 6,000 RPM, so you will need a bigger pulley on the engine.

Well if I did my math correctly here is what you do. A 6" pulley has a circumference of 2x3.1416x3=18.85. A 2.5 inch pulley on the alternator would have a circumference of 2x3.1416x1.25=7.85. You then divide, 18.85/7.85=2.4 or the alternator pulley will spin 2.4 times as fast as the electric motor. If your motor spins at 1750 rpm the alternator will be turning at 4200 rpm. To play with different ratios, the last number in the circumference formula is the radius of the pulley.

No need to crank the circumference formulas.....

6" / 2.5" = 2.4:1

Jay

Got a 6 inch pully yesterday and today I tried it. it works. however like Pin head points out, this size motor will not turn the alternator fast enough under load to pull enough amps to weld much or for long. I will look for another power source. Gas or Electric. for a new power source, but this is what I had laying around and for 15 bucks I can weld Thin gauge steel as long as I want.

To Roktoy or anyone else out there who has done a homebrewed onboard welder, can you give me a link to a site with some info, I just got a 140 amp prestolite the size of a volleyball off a school bus and would like to see if it would be a doable project for me

Just to add to voltage and amperage welding fundimentals, when you first strike the arch, your voltage is high (amperage is low), durring the weld process your voltage is low (12-36v) (& amperage is high). So the higher the rpm, the purtey your beads will look ;) ezer to weld, etc etc

Pick up a welding book (library) or take a class at a near by community collage.

SMART ASS

Originally posted by Pin Head


You are having problems with the first law of physics, which is the conservation of energy. You can't get more energy out than you put in. 1 hp is approximately 750 watts and to weld with the 90 amp alternator, you will need at least 25 V @ 90 amps or approximately 2500 watts to maintain an arc with a 3/32 rod. To generate 2500 watts, you will need a minimum of about 3.5 hp.

In order to get the maximum power from the alternator, you need to turn it at about 6,000 RPM, so you will need a bigger pulley on the engine.

Originally posted by ChiScouter
To Roktoy or anyone else out there who has done a homebrewed onboard welder, can you give me a link to a site with some info, I just got a 140 amp prestolite the size of a volleyball off a school bus and would like to see if it would be a doable project for me

Using an externally regulated alternator....basically you wire up 12V straight to the field terminal (I do run an inline toggle switch). Ground clamp to alternator case. Stinger to output terminal. Engine speed sets output voltage....higher the speed, greater the output voltage.

Cookin' in no time :D :D :D

Jay

SmartAss.. Yes I undersatnad about the Voltage Amperage equation. I basicly built this for a test. To see if the average guy with crap laying in the garage could Mc Giver up a welder for under 50 bucks. and yes its more than possible. one thing to keep in mind is that Alternators by their design create their own magnetic feild. so the more load, the more magnetic feild, the greater the resistants. If I had a permant magnet alternator I would have a fixed High end out put, but the resistants would be way lower. this would give me stable voltage and amperag but at lower rpms. I have a source for a 24 volt / 100 amp permanent magnet alternator for about 100 bucks I am thinking of testing this idea out.

Sweet, keep me and others POSTED so to speak ;) :D

If I had a permant magnet alternator .....


Those are called generators and all the old cars had them.:D

Originally posted by ForestCam



Those are called generators and all the old cars had them.:D

Hmmmm I've got a generator, has anybody used one for an on-board welder?

Alternators and generators are wound differently and they produce electricity differnetly but essentialy the same thing yes.

Hey big guy doesnt 2 x radius = diameter ? LOL