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dian
03-16-2017, 12:42 AM
i was thinking i could put to use an stick welder i never got ridd of. i have this and would hook it up to the welder, rectify the output and drive (and maybe regulate) a 12v dc motor with it.

anything wrong with that? would the device really be good for 4000w? would it manage the transition from 50v to 25v from the welder maintaining constant output voltage? I guess a motor doesnt mind the chopped up current.

http://www.ebay.com/itm/261192160445?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

edit: or i might get something else.

lugnut
03-16-2017, 02:48 AM
I don't know anything as to your question, but I do know the most electric welders have only a 20 to 50% duty cycle. Some one here should be able to tell how long you could operate a motor at what ever your load would be. ????

macona
03-16-2017, 03:22 AM
Most stick welders have an open circuit voltage of around 80v. So you are going to have to deal with that, they were intended as a constant current power supply so the voltage will change depending on the load.

You would have to look at the manual to find at what current it is rated for 100% duty cycle to find out what you can get out of it for an extended period.

PStechPaul
03-16-2017, 03:42 AM
An SCR controller like that will probably not work well on a low voltage DC motor. The 4000 watts is based on 220V and 18 amps, and it will probably only safely handle about 10 amps. It may or may not work on the 25 or 50 volts of a welder, and at 10 amps you will only have 250-500 watts. It will certainly have poor load regulation. If you really want a DC supply of 100 amps or so from a welder, you would probably need to rectify the AC using some high current rectifiers, followed by maybe 200,000 uF capacitors, and a PWM controller on the DC. It would need some husky MOSFETs or maybe an IGBT module from a VFD. Ideally you might want to make a buck converter.

As for duty cycle, generally that is based on the inverse square of the overload. So a 25% duty cycle would apply to a 2x overload. A welder rated at 100 amps 25% duty cycle should safely provide 50 amps continuous and 150 amps at 10% duty cycle, based on heating. But there will also be a maximum ON time, so the 25% might be 1 minute on and 3 minutes off, and perhaps 5 minutes on and 15 minutes off.

dian
03-16-2017, 03:49 AM
well, not really, the idle voltage is around 50v and drops to the welding voltage of 25v at around 30 a. its a 130 amp transformer, so i dont worry much about duty cycle. im interested to know if that $6 gadged will stabilise the voltage over 1000w as well in the transition phase of the transformer (it fits the palm of your hand) or if i would need something else to do it.

if i understand correctly, i could hook the thing up to 230v and get 4 kw of 12 v out of it, but thats hard to believe. and its not the point, the idea is to find a use for the welder. for a big motor, could i controll the amps with the welder, as opposed to voltage regulation by the box?

vpt
03-16-2017, 07:07 AM
I mentioned this awhile ago because I saw the one guy on myth busters use a tig machine to power an electric motor. Worked fine for him on the show but it was a tig. From what I understand there isn't a real lot different between a tig power source and a stick. Only thing that might be an issue is most stick machines don't go as low in amps a as a tig.

J Tiers
03-16-2017, 10:04 AM
1) That controller does not regulate voltage. It regulates duty cycle.

2) That controller only works on AC. They do not work on DC

3) 12 V is probably below the useful range of operation of that controller, since it is intended for 220V. It may not even function the way it is supposed to.

4) Welders are not a wonderful power supply for this.

5) The whole deal is the most fantastical kludge I have heard talked about in months. Try something else.

BCRider
03-16-2017, 01:41 PM
As already pointed out the transformer in that sort of welder is specially designed to work in more of a constant current mode than in a constant voltage mode. So you can expect a lot of variation in the voltage it provides if your current needs change much. And that will mean that whatever you use as an output regulator will need to deal with that wide shift in input voltage to the regulator.

Also as mentioned the 220v dimmer you linked to would not be usable as a voltage regulator on the output. It's too crude for that. And given how most such dimmers work it would swing wildly due to the changing voltage from the welder as the current needs change.

What sort of motor are you thinking about running with your welder? I ask this because you can buy some pretty darn powerful 12v power supplies these days for darn cheap. You could sell your old welder and afford to buy a new supply and voltage controller and have a bunch of money left in your pocket and a LOT more room in the shop.

MaxHeadRoom
03-16-2017, 02:57 PM
There are many PWM DC 555 based controllers on ebay for a few $$.
You would just need a 12v secondary transformer and a bridge rect.
What size (torque) is the motor?
BTW you Can run a DC motor from a Triac controller by fitting a suitable bridge rectifier on the output of the Triac.
Max.

Paul Alciatore
03-16-2017, 03:26 PM
Can you use your welder to power a DC motor?

Sure you can.

1. Sell the welder. Get a good price.

2. Buy a suitable power supply for your DC motor.

dian
03-17-2017, 01:23 AM
well, first of all, stuff like that doesnt get sold, it gets scraped and you pay for that, at least in this part of the world. then lets make a few things clear. this is a transformer (or whatever the correct name would be) that puts out ac. a tig puts out dc. at anything over 30 amps the voltage will be between 27v and maybe 24v. a tig will put out something around the ionisation voltage of argon, which is 16v.

so now, if i have a 1kw 24v motor, i rectify the current and drive it. yes? no? i have a few of the regular (if that means anything) 35a rectifiers around and i remember you can get them in 50a for nearly nothing. an idea behind it was to have a current regulation to regulate torque. obviously there will be not many 1kw 24v motors around, so lets say a 200w motor would have to operate from the "transition voltage" probably around 45v. a 400w motor would probably see 35v. rectified, unstabilised dc, that is. here the idea is that it will be easier to get the voltage down from 45/35v than from 230v.

so what contraption do i use to do that? the triac contoller mentioned? can you point me to such a device?

paul, how do you come up with 250-500w? 220v x 10a = ?

"1) That controller does not regulate voltage. It regulates duty cycle. 2) That controller only works on AC. They do not work on DC"

j., doesnt it regulate voltage by the duty cycle? no idea. and i am talking about ac.

J Tiers
03-17-2017, 01:31 AM
...

j., doesnt it regulate voltage by the duty cycle? no idea. i am talking about ac.

Yes, based on a constant input voltage. Your voltage will vary with current, so there will be an interaction that will have results I cannot predict without thinking about it more than I wish to..

But the other issue is it runs on 220V. You have 1/10 of that. It may or may not work reasonably on that. Most likely not, because there is usually a minimum voltage to activate the circuit. That can be set in the design, but it varies with design voltage. So if it will operate down to 5% duty on 220V, it might only work to 30% or 50% duty with a low voltage.

You have a voltage mismatch between that controller and what you have for voltage, AND the welder is not the best supply voltage device for the purpose.

It is a "lashup" a "rig", a "kludge", "cobbled up", "jerry-rigged"... You may have fun with google and those terms.

BCRider
03-17-2017, 02:50 AM
Dian, as Jerry and others have pointed out you cannot use that triac controller on your welder. It need the 220 volts on the input side to work. And to have any hope of putting out a stable power on the other side it needs to see a stable voltage on the input. The welder is not going to give it that stable voltage. So it won't regulate anything. It likely won't work at all. Or at best will work very poorly. And it will certainly not work with the radically changing voltage put out by the welder that changes with the amount of current drawn.

On top of this there's the current issue. The dimmer is rated at 4000W. At 220v that is 19 amps. But you want to run a 1Kw motor that needs a max of 24 volts. But that's 42 amps at full power. Power = voltage x current. So even if the triac dimmer did work you would be trying to pull twice the current through it that the device is rated for. And that could easily see it burn out in a blink.

The welder has a variable output. if you want to try it you should just use that adjustment. You'd still need the diodes. And from the looks of it you'd need the 50 amp versions to be sure. And a big heatsink for them as well. Then just use the current adjustment on the welder to dial up the speed. You would mostly be dialing up the current. But as the motor speeds up it'll use the current and the voltage will set itself. And if it gets to where it's pushing 41 amps through the motor you'll find that the voltage is at 24 volts. If it's going to work at all that would likely be the best way to do it.

darryl
03-17-2017, 04:32 AM
I think you'll find that the welder can't be left powered for extended periods of time without getting hot, even with low or no load. It's not even close to ideal for this purpose, in my opinion.

Having said that, any kind of 60 hz transformer based power supply (which the welder is) can have its output rectified and filtered to provide dc voltage to a load. When the current requirement is high, the output filter capacitance has to be high. If the transformer is capable of high output power, then the rectifiers have to be rated for very high current as well, partly to supply the load demand, and partly to charge the high capacitance during initial inrush. A welding transformer may have a shunt which helps to limit and/or regulate the output current, but this also changes the output characteristic to something less suitable for running a dc motor. Without the shunt, the transformer- as wired- will probably overheat in minutes. Adding turns to the primary can overcome this, but now you're looking at difficult modifications. I deal with this when I re-purpose microwave oven transformers.

Not sure what your main objective is- just to make use of a welder that isn't being used for anything else currently, or the need to run a powerful 12 volt dc motor. If you're wanting to re-purpose the welder, maybe it would be better to make a spot welder out of it-