Transient suppression for a buzz box welder? - Page 1
Forum section: electronics / projects

author: CaptDon
author_rank: Super Contributor
timestamp: May 25, 2021, 05:07:08 pm
content: I have a homebrew A.C. welder made from a 3KVA transformer with 48vac (24X2) secondary. I use some very heavy duty inductors in series with the low voltage side to control current. (Everything was free from an industrial demolition so I used it) I have never really looked at the transients on the supply line (240vac single phase) but I assume there are probably some big ones. I have several freebie GE 250HE250 MOV's but they don't clamp until over 600vac and that seems too high to prevent possible punch-through on my #10 supply side feeders rated at 600v. Is there a more modern device or one better suited? Do the commercial (Lincoln 225 for instance) units use any suppression techniques? I know this welder of mine is like Prehistoric Pete, but I mostly just weld things like 1/8" to 1/4" angle iron using iron powder drag rods like 7014 and 7018 and it actually works very well. Years ago I used the 6011 and 6013 but they were noisy and sent a shower of sparks 10 feet in every direction. Sadly, set my flannel shirt on fire years ago. Ripped it off like the Incredible Hulk!!!

author: jonpaul
author_rank: Super Contributor
timestamp: May 25, 2021, 05:35:47 pm
content: MOVs are useless and dangerous, fire hazard.600 V wire rating is not the issue, its the effect of those transients on other equipment.I would add a very heavy EMI line filter and a UL rated professional transient limited, to protect the other equipment connected.Otherwise, MOV or not, expect a lot of mysterious failures eg computers, displays, routers, anything electronic on the same power circuitBon Chance.Jon

author: CaptDon
author_rank: Super Contributor
timestamp: May 25, 2021, 06:17:29 pm
content: I agree with you 100% about the transients affecting sensitive equipment!!!! Guess I'll find anything with an aging RIFA cap that way!!! I also guess transient line to line as well as each line to neutral would be a good thing? The welder outlet is on a 50 amp 240v service (2X120) in my garage and fed from the 50A breaker in the main panel in the house. I think the underground feeder (running in plastic conduit) is #4 X3 with bare ground conductor which is the same gauge and not one size smaller. There is the required local ground rod at the garage end also.

author: james_s
author_rank: Super Contributor
timestamp: May 25, 2021, 06:24:08 pm
content: I've had a few different welders and I don't recall seeing any kind of line filter in any of them, the basic "buzz box" type are just a big transformer in a box. Usually with magnetic shunts or a movable core to control coupling used to regulate the current but your added inductors accomplish the same goal. I suppose a filter on the inlet wouldn't hurt but I don't think most commercially made welders bother with them.

author: Turbinedave2003@yahoo.com
author_rank: Newbie
timestamp: May 25, 2021, 07:58:39 pm
content: Over the past 50 I have owned several tranformer welding machines (buzz boxes) from Miller, Lincoln, and Craftsman, both tapped transformer and magnetic shunt types and none of the machines had any form of suppression on the transformer primary side. All were installed and wired into single phase 230 volt residential lighting panels. At no time did these machines induce enough voltage transients to damage household appliances and electronics. I have since moved on to inverter machines but still keep a 50 yr old Craftsman transformer machine around.I wouldnt worry about it, unless the service ampacity to your home is very low whereby welding at high currents would cause your house voltage to sag excessively.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 25, 2021, 09:47:47 pm
content: I wouldn't worry about it. Anything that's worth using, should be rated for comparable transients already (namely, EFT and ESD). As far as same vs. dedicated mains circuit, I'm not sure, there might be something there.The proper place for a MOV is at the stinger and work. It is the instant of breaking the arc, where current drops to zero suddenly (and usually pingpongs back and forth several times, making a rapid burst of very brief sparks), that generates noise. The high voltages can be clamped by something like a MOV, and the ideal location for it is as close to the contact as possible.Which is also why you should place a snubber across a relay contact, for example, not across the relay coil or solenoid or motor or whatever inductive load. You generally don't want to place MOVs across contacts, because MOVs gradually fail over time, breaking the isolation of the contact; but this would be the preferred place if not for that.The next best thing you can do with a welder, is put the MOV at the output terminals, and accept whatever noise is generated by load current times lead inductance -- a few meters of cables, strewn about haphazardly, will probably amount to a few 10s of uH inductance. That isn't a lot, but we're also talking ~100A currents, and energy stored goes as the square of current. It's probably still enough to generate that rapid-fire burst of sparks, is what I'm getting at.And this, finally, is why I'm skeptical that there's much problem with conducted mains noise -- the noise is generated by the spark, and merely carried through everything else. It's not generated by the welder, in and of itself, and indeed it's filtered to some extent by the transformer.More to the point, you've got cables laid out randomly, without regard for signal quality or RF grounding -- it's an enormous antenna, and the EMP from breaking the circuit will pretty much go anywhere it pleases. Probably as much is conducted through the transformer, as coupled through common wiring, and grounding, in the welder's encloure.These are fast events -- a spark can break down in a fraction of a nanosecond. In a nanosecond, the wave thus emitted, travels a mere third of a meter! It's an instant to us, but it very much expands like a shockwave, pushing things out of its way as it expands -- fortunately the radiation pressure is minuscule, it's hardly a physical push; it's more an analogy for the voltages/currents in conductors that the wave interacts with. (If we're talking peak voltages of 4kV or so -- a typical high-level EFT waveform -- then we're talking peak currents around 10A in free space itself (having an impedance of 377 ohm), or higher in transmission lines that have lower impedances, roughly 100 ohm for mains wiring for example.)Tim

author: coppercone2
author_rank: Super Contributor
timestamp: May 26, 2021, 05:24:26 am
content: Careful, you don't want to destroy your appliances. If you have all old shit it will be fine but the new ones are finicky IMO.MOV are not trash so long they are properly installed, you can wrap them with kapton tape with a thermal fuse under neath to try to clamp it, but I assume you mean hocky puck movs, so you wanna put a box over it and fuse that. I got a whole house protector after the power company took out 4 power strips (with exploded movs) and a plug in weather station. It is just a MOV bank inside of a oversized box that should contain fire.When lincoln designs the magnetics they probobly put some work into making sure the system does not have excess properties which result in excessive spiking.The most sensitive things are going to be the small plug in stuff with AC out-wall warts that have a rectifier inside of the thing you are powering, they are poorly protected and will be the first thing to go.I would put something like this in there and forget about ithttps://www.digikey.com/en/products/detail/tdk-electronics-inc/B72232B0231K001/634996?utm_adgroup=TVS%20-%20Varistors%2C%20MOVs&utm_source=google&utm_medium=cpc&utm_campaign=Shopping_Product_Circuit%20Protection_NEW&utm_term=&utm_content=TVS%20-%20Varistors%2C%20MOVs&gclid=Cj0KCQjwwLKFBhDPARIsAPzPi-Iq9antfXQg0kNt9V3ZZmDyj2sypQfXo4MYEPHj1H0ei1ddw2ZXmJwaAmrlEALw_wcB

author: jonpaul
author_rank: Super Contributor
timestamp: May 26, 2021, 05:38:37 am
content: Hello again,There are two sources of transients:Stored energy in the transformer core when circuit is interrupted, no limit to voltage except insulation and energy = 1/2 L (henries) * I peak squared. Perhaps a few to dozens of Joules.Welding arc generates copious RF noise that is radiated and conducted.Just run the susceptible equipment, weld away and see if the equipment is running normally or is affected.Good EMI inline filters are perhaps $20-100, heavy duty transient protectors $40-200Jon