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Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
I've looked around on the internet quite some time, and noticed there are a few different designs based off of MOT's into welders. I've got 4 mots, now, (ones a little smallish...so I don't think I'll use that one?)
All of them are in good shape. I know in order to weld with them, I need to rewind them to act as step down transformers. Now this is where my questions come in;
Most of the designs have two mots. However, I've seen designs that have as many as 4, and the primaries are all connected in either series or parallel, as this apparently increases output current/ output voltage, and thus gives a hotter arc, or better welding characteristics. I've got 4 mots, as said before, and I don't know how I would wire them up. I know MOT's run in saturation, so would connecting them in series prevent this?
And when connecting them to the mains, do I have to use two separate breakers, or just one? I have 15 and 20 amp circuits in my house. (there's 30, 40, and 50 amp ones, but they're all used by large appliances)
As far as connecting the secondaries up, if I run them in parallel, they need to be near the same voltage, or at the same voltage, correct? And if in series, how many of them should I put in series to get an effective arc? I understand arc welding (with a 15 to 20 amp circuits, at least, this is what people say) works best at around 70 - 90 amps, at around 35 - 50 volts. I'm not sure that's going to work so well on my breakers.
And, at last, what about PFC? Since they're technically inductive loads, I'm pretty sure I'm going to need some sort of PFC capacitor. How do I calculate the value, and what kind of capacitor should I look for? (I know not electrolytic. :) )
I also think I would just use the 3 similar ones. I would use them in series, but I have no scientific reason for that, I just think they would share the current better.
Registered Member #3343
Joined: Thu Oct 21 2010, 04:06PM
Location: Toronto
Posts: 311
Induction:
Forget the power factor issue. Actually the good manufacturers of arc welding machine (buzzbox, stick arc weders ) do not use caps anymore to improve the PF .
A confortable welding secondary voltage is in the range of 45 to 80 volts ac., in the NO load conditition.
When the arc is stablished the voltage at secondary is in the range of 20-30V. That means the magnetic shunt and winding resistance will absorve 15-50V
So if you have 4 MOT, ALL FOUR ARE IDENTICAL and the available power source (your outlet) is 115V ac, all primaries are to be connected in parallel, in order to be supplied with 115V ac. If you want to feed with 230V ac, connect the 4 primaries in a serial parallel connection.
In no load condition, the secondary of each mot to provide 13V ac, in such way that total secondary connect in series will provide 52Vac, That is a good confortable voltage to the operator .
Do not forget that MOT are very designed to work in INTERMITENT SERVICE, that is work 10 minutes and rest 20 minutes. Iron induction is in the range of 1.5 teslas, to save space and cost of cooper and iron core. Due the iron losses by high induction a fan is reqired to cool down core and windings.
However the best option is to buy a second hand buzzbox, that you can get very cheap. Or dig a burned one in a scrap yard and rewind primary and secondary, Keep in mind that the cost of cable, terminals, plugs, box, etc are more expensive that the wire and insulation required to rewind the buzzbox
See " arc starter " thread in the High Voltasge Forun
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Another MOT question; This time, Welding!
