using a DC motor as a generator, for an AC motor-driven DC welder (pix posted)

(...)

--Winston

For welding you want some tens of volts at rather large current. I'd say "none of the above" unless you're into welding very thin sheet.

As a generator, a motor will put out roughly the same voltage as the nameplate voltage at the rated RPM, and the 100% duty cycle current will be around the same (short circuit current will be similar to the LRA, but proportional to RPM). Open circuit voltage is proportional to RPM for PM motors or DC motors with a fixed field voltage run as a generator.

What you want for a welder is something like an aircraft generator or maybe a truck alternator (??) that will put out a lot of current at low voltage.

Here's a guy or two who have Cheney'd around with a car alternator to make a simple welder:

You're asking for 10 times the current and 1/10 the voltage that these motors (as generators) were designed to handle. While by virtue of DC motor versatility you may be able to configure them to operate at that condition, they will quickly fail from overheating, overtorquing, or other outside-the-envelope consequence if so applied.

Not that hard to find a 5 VDC power supply putting out a regulated 200 amps from house current.

With the big-ass magnets you can get nowadays, is a homopolar generator feasible for a welder? Or is the voltage too low?

Dave

People who do this, usually use 28v tour bus alternators.

You can buy them on ebay for not too much. Sell your motor so that soneone else will keep it in their garage.

First of all it is do'able. Popular Mechanics had a long article, years ago, about building a welding machine using a surplus aircraft DC generator. I have also seen an article on the web about doing the same thing - unfortunately I can't find the URL. Try googling various combination of welder, generator, home made, etc., and I'm sure you can find it.

The only problem is that you need a low voltage, high amperage generator, say 24 volts @ 300 amps.

Bruce-in-Bangkok (correct Address is bpaige125atgmaildotcom)

There are people that haul 3 batteries and have special circuits to charge each in time.

Then they, when climbing rocks and weird stuff - bend a fender or breaks something - yank out a Ready Welder and weld up the break.

One could set up a wind mill and weld when the wind was there or use batteries and charge them up with said DC motor/generator just like cars did it in the 50's.

Martin

Mart> >

----== Posted via Pronews.Com - Unlimited-Unrestricted-Secure Usenet News==----

---= - Total Privacy via Encryption =---

If you insist on DC output (native mode), you need to find a 24 to 32 volt DC motor where all the current goes through the brushes.

Best way is to f> ol' bubba here wants to build a nice cheap DC welder, preferably that

None of the motors are suitable, as you could only get about 6-10 amps out of any of them, and the voltage would be way too high. You need closer to 35 volts than 110 to weld. If you want to build one, you need an old fork-lift motor, an aircraft starter generator, or a heavy duty bus/truck alternator. An alternator will give you "rectified AC" at a higher frequency (ripple) than you would get from a line powered transformer type DC welder. A Permanent magnet motor gives no voltage/current control. A series motor CAN be rewired to make it useable and controlable, but something with a shunt field (either shunt or compound wound) can be accurately controlled. As can the alternator.

The easiest route to take would be to buy a Miller Shopmaster 300 CC/CV AC/DC from me.

The OP could keep an eye on ebay for a used Leece-Neville 28v 200+ amp alternator. That should work very well. It should cost about $150 plus some shipping.

If you start with a good alternator, at least you will end up with a expensive (due to labor factored in) and inconvenient, but powerful welder.

I really do not see a good reason to use anything less powerful, to only end up with an expensive and inconvenient crappy welder.

----== Posted via Pronews.Com - Unlimited-Unrestricted-Secure Usenet News==----

---= - Total Privacy via Encryption =---

Look at my post prior to this one you wrote - yours is out of sequence and missed mine. A movie with two batteries.

Off roaders don't haul 3 or 4 batteries for welding. They use 2 or 3 max.

Martin

Mart> If you insist on DC output (native mode), you need to find a 24 to 32

----== Posted via Pronews.Com - Unlimited-Unrestricted-Secure Usenet News==----

---= - Total Privacy via Encryption =---

Go to forklift dealers. I've seen complete trucks chucked in dumpsters that still had motors that were too old or the brand no longer available (Lewis-Shepard is one example) that had good drive motors in 12, 24 or 36v models that were sold as scrap. The drive motors would have been perfectly functional or rebuild-able. By the way Hyster bought Lewis-Shepard, Automatic Lifts were bought by Eaton Towne & Yale A.K.A. Yale now. There are others such as Otis, now Baker.

Some of the dealers *don't* want to refurbish some of their own brands that have some age. It can become a hassle to warrant some unseen problems on high hour trucks. The motors are not the problem, some come in with questionable frame repairs or alterations that dealers can't afford to get caught holding the responsibility for somebody else that didn't know how to do the job right in the first place. Poor welding practice being a prime example. There is too much 6011 or 6013 rod in this world of repairs.

Salespeople get better commissions and less complaints on new equipment.

You might also check into golf carts. Some manufacture industrial warehouse carts that have heavy duty motors that outlast the frame. Most golf carts are 36 vdc by the way.

HTH