Welding Tips and Tricks

I made an arc welder using two Microwave Oven Transformer. They give out 38 volts and minimum 32 volts according to input. My input is 220v but as my country is developing country the voltage is not constant and we face low voltage problem . My rod is getting stuck many time, maybe that's because I am a amateur. Anyway is 30-38 volts enough to weld metal?
I am hobby welder so I don't have to weld big metal for long time. All advices will be appreciated.

Deltawelder@101 wrote:I made an arc welder using two Microwave arc welder. They give out 38 volts and minimum 32 volts according to input. My input is 220v but as my country is developing country the voltage is not constant and we face low voltage problem . My rod is getting stuck many time, maybe that's because I am a amateur. Anyway is 30-38 volts enough to weld metal?
I am hobby welder so I don't have to weld big metal for long time. All advices will be appreciated.

Welcome to the neighborhood!

38 volts is a bit low. If you go up 50% (add a third microwave?), to around 56 volts, you'll be closer to "normal" open circuit voltage for welding, and have less trouble with sticking.

Where are you located?

Steve S

Not sure of the setup op is using but most likely is a parallel setup, so no way to add a third transformer. If by chance the setup is in series than adding a third could be done, although I wouldn't recommend that setup.
Instead, increase the wraps on your secondary coils and setup in parallel. You will lose some amps but overall should help. How many wraps did you put on your secondary coils? Are both transformers the same?

First post welcome to the forum.

Otto Nobedder wrote:

Deltawelder@101 wrote:I made an arc welder using two Microwave arc welder. They give out 38 volts and minimum 32 volts according to input. My input is 220v but as my country is developing country the voltage is not constant and we face low voltage problem . My rod is getting stuck many time, maybe that's because I am a amateur. Anyway is 30-38 volts enough to weld metal?
I am hobby welder so I don't have to weld big metal for long time. All advices will be appreciated.

Welcome to the neighborhood!

38 volts is a bit low. If you go up 50% (add a third microwave?), to around 56 volts, you'll be closer to "normal" open circuit voltage for welding, and have less trouble with sticking.

Where are you located?

Steve S

I live in Nepal.

Mike wrote:First post welcome to the forum.

Thanks

dsmabe wrote:Not sure of the setup op is using but most likely is a parallel setup, so no way to add a third transformer. If by chance the setup is in series than adding a third could be done, although I wouldn't recommend that setup.
Instead, increase the wraps on your secondary coils and setup in parallel. You will lose some amps but overall should help. How many wraps did you put on your secondary coils? Are both transformers the same?

I didn't find solid 12 Gauge wire so I used stranded 7/22 copper wire. I get 17 volts each. I tried 3/22 wire but the number of wraps won't be much. Yes the two transformers are same.

Just shows how much technical know how is lost in a " developed" country. I weld all day, with top notch equipment, yet have no idea how it all works.

Mickles.

weldin mike 27 wrote:Just shows how much technical know how is lost in a " developed" country. I weld all day, with top notch equipment, yet have no idea how it all works.

Mickles.

LOL, So do you think I can weld small things in low duty cycle with 38 volts.

generally you need 50-100v to strike an arc and 17.5-40v to maintain the arc while welding (at least thats true with most constant current welding machines) theoretically if u can initiate the arc that voltage would fall in the range to weld. have you got any way to adjust your amperage? higher current would potentially keep your voltage from dropping too low when you use a close arc.

just my thoughts feel free to correct me if im off base with it.

With microwave oven transformer welders, voltage is determined by secondary coil windings. Fewer wraps, fewer volts but higher amps. More wraps, more volts fewer amps.

@deltawelder, did you disassemble the microwave transformers or did you cut the old secondary windings out?

You probably are needing more volts, and if you need more amps you could look into building 2 more transformers. Setting up 2 sets transformers in series. Then each set would be set in parallel. Finally ran through a rectifier to go from ac to dc.

Just adding a rectifier could increase your success rate.

christhewelder75 wrote:generally you need 50-100v to strike an arc and 17.5-40v to maintain the arc while welding (at least thats true with most constant current welding machines) theoretically if u can initiate the arc that voltage would fall in the range to weld. have you got any way to adjust your amperage? higher current would potentially keep your voltage from dropping too low when you use a close arc.

just my thoughts feel free to correct me if im off base with it.

It is impossible to gain 100v with MOTs because that would require too many transformers and homemade are just for doing a little work you know, but I have learned to create ad maintain arc now. I will upload the video and photo soon. I saw in many youtube videos. They have been welding 6013 -1/8'' rod with ease with 37 Volts but 7018 big rods make welder heat real fast.

dsmabe wrote:With microwave oven transformer welders, voltage is determined by secondary coil windings. Fewer wraps, fewer volts but higher amps. More wraps, more volts fewer amps.

@deltawelder, did you disassemble the microwave transformers or did you cut the old secondary windings out?

You probably are needing more volts, and if you need more amps you could look into building 2 more transformers. Setting up 2 sets transformers in series. Then each set would be set in parallel. Finally ran through a rectifier to go from ac to dc.

Just adding a rectifier could increase your success rate.

I chopped the secondary off because disassembling is tough. I couldn't fit more wire so final output is 38 volts and many youtubers also weld using 35 volt average like guys who use car batteries for welding, Man see my pic below. I am planing to add that but doesn't the rectifier reduce output voltage.

It would reduce voltage, how much would determined by how efficient the rectifier is.
But once you get a arc started you should notice a immediate difference in arc stability. The way I would set it up is to have the rectifier where you could use it or bypass it.

The voltage drop across a silicon diode is 0.6V, so a simple 4-diode bridge (two active at each cycle) for a drop of 1.2V total. Parallelling several bridges doen not increase the voltage drop, it just spreads the current out so smaller diodes can be used. The addition of a smoothing capacitor will bring the open-circuit voltage up closer to "peak" versus RMS, negating the voltage drop across the rectifier and aiding arc-starting.

I no longer have the books to look up appropriate values, and haven't used my electronic training in many years, but there are members here with the knowledge to advise you.

BTW, if you can find germanium diodes in suitable capacities, they only drop 0.3V each.

Steve S

Otto Nobedder wrote:The voltage drop across a silicon diode is 0.6V, so a simple 4-diode bridge (two active at each cycle) for a drop of 1.2V total. Parallelling several bridges doen not increase the voltage drop, it just spreads the current out so smaller diodes can be used. The addition of a smoothing capacitor will bring the open-circuit voltage up closer to "peak" versus RMS, negating the voltage drop across the rectifier and aiding arc-starting.

I no longer have the books to look up appropriate values, and haven't used my electronic training in many years, but there are members here with the knowledge to advise you.

BTW, if you can find germanium diodes in suitable capacities, they only drop 0.3V each.

Steve S

Thanks, for the information. I will try to add some rectifier if it comes in my budget.

I was just doing a little research on this subject recently and supposedly you can use the rectifier for a automotive alternator, although there will most likely be a extra set of diodes that are not needed.

I watches these videos a while back and think they might help a little.
http://youtu.be/nTDx3sN2dhU
http://youtu.be/r6oDCbcmtWw
-Jonathan

I was going to recommend those exact videos.

dsmabe wrote:I was going to recommend those exact videos.

Beat you!!
-Jonathan

I want to say there was another video showing a setup in parallel, and 2 rectifiers on 220v power. I wasn't able to find it though.

Superiorwelding wrote:I watches these videos a while back and think they might help a little.
http://youtu.be/nTDx3sN2dhU
http://youtu.be/r6oDCbcmtWw
-Jonathan

What a coincidence, these are the same videos that gave me inspiration and information and just like him I also have 38 volts output and you now I understand it that it was my skill that made rod to stick. After some practice I can handle the arc and the transformers also don't get that hot. They only get hot when the rod is stuck. Actually I was inspired by articles f Instructables.com 4 years ago . Finding a MOT in a developing country like Nepal is hardest part because out traditional food doesn't need Microwave and the our spending capacity is also low. . I am happy that you guys helped

Well I have a new question- How much amps and volts do you need to arc weld aluminum with thinnest rod?

All along it's really a matter of having the ability to deliver the correct current. The volts will help you strike your arc, but in simple terms, you need power to melt. Power = Volts x Amps (in simple terms).

If you can't get enough amps, you'll never get that electrode to melt.

A car ignition coil delivers thousands of volts, but you can't weld with it, because it can only deliver micro-amps.

To deliver enough current you need big cross section conductors in the secondary winding. You need to be able to move a lot of electrons in the secondary circuit. You also need enough iron to adequately saturate the magnetic field in the transformer core.

Microwave's weren't really designed to work in this sort of way, but my guess would be connect the transformer windings in parallel. Have the exact same number of turns on the secondary circuit of each transformer, and - most importantly - make sure all of the windings are wound in the same direction. Connect all the starts together and connect to ground. Connect all the ends together and connect to the electrode.

That will at least give you a better current supply.

HTH

Ranger