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spot welder

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Gregory

Member
I have made a spot welder from a microwave transformer .
I removed the primary windings and rewound the winding with 10mm wirer there is 3 raps of wirer on the iron cor.
The volts in the primary is 240 V and the secondary is 3.4 volts.
I do not know what current it will produce .
But I am not happy wit the results.
How can I improve the welding current.
Do I increase the voltage.
Or increase the the windings This is can not be done unless I change the wire size on the secondary.
I would I be better to implement a cap.?
 

Gregory

Member
I have made a spot welder from a microwave transformer .
I removed the primary windings and rewound the winding with 10mm wirer there is 3 raps of wirer on the iron cor.
The volts in the primary is 240 V and the secondary is 3.4 volts.
I do not know what current it will produce .
But I am not happy wit the results.
How can I improve the welding current.
Do I increase the voltage.
Increase the the windings This is can not be done unless I change the wire size on the secondary.
I would I be better to implement a cap.?
 

marcbarker

New Member
You say you removed the 240 V pri.

Are you applying 240 AC to the original HV secondary?
 

marcbarker

New Member
That would explain the poor performance.....

I suppose a possible workaround is obtain another microwave transformer and use its HV secondary* to feed into the present transformer's primary, which is really the secondary acting as a primary in reverse...er..I think.... I dunno now, I'm lost :eek:

* Suitable contestant entry into 2010 Darwin Awards
 
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Gregory

Member
I have removed the 240V primary winding and replaced it with 10 mm copper wirer
I now us the original secondary as the primary.
I have attached photo's
Have I removed the wrong winding.?
 

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marcbarker

New Member
Have I removed the wrong winding.?
"Have I removed the wrong winding?" he says! :) What winding have you removed?

Looking at the picture...what's that 'thing' there in the middle?, sitting between the windings? it looks like it's made of iron...

And another thing... i get the gut feeling there's too many turns.
 
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chemelec

Well-Known Member
I Doubt he removed the Primary. In his Picture, it LOOKS like the primary is there.
That is too big of wire to be the Secondary.
And those Push Lugs are the 220 Line.

The Laminations Between the Primary and the Secondary is a "Current Shunt".
It Prevents the Primary from Overload, Even on a Shorted Output.

Removing those laminates Will allow for More current out, But Possibly a Blown Breaker Also, due to higher input current.
 

RODALCO

Well-Known Member
Just having a good look at you photo's and comparing it with one of my spare MOT's.
You have removed the correct winding (HT) and the 240 Volts winding is in place in your MOT.
You need to take the iron shunt out.
As most MOT's are about 800 to 1200 Watts, put a 2.4 kW electric heater in series to reduce (control) your current and perhaps reduce the secondary to 1 or 2 turns.
 

Mr RB

Well-Known Member
Yeah the primary is intact. I would think he needs more turns on the secondary to improve its power transfer into a few ohms of steel as the target. Maybe 10, maybe 20 turns. And good copper tips for the weld electrodes.
 

Gregory

Member
The Iron shunt is that the Iron plates between the windings.?
The 2.4 electric heater you have indicated to place in series is that a heater element.
Is this a fixed resistor to control the current.
If I do not use this Heater element will the current be to severe.
I will supply a photo and point to the plates in question as it is as good as a 1000 words.
Thank you
Greg.
 

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marcbarker

New Member
In arc welders the 'current shunt' is adjustable

Arc welders don't have resistance ballast, and I've never (yet) seen a welder with a heating element to regulate their power.
 
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Gregory

Member
is the plates I have pointed to in the photo are they the Iron shunts.
Could you make a sketch of the heater that is mentioned and what should I do to increase the current
1 Increase the number of turns in the secondary.
2 Decrease the number of turns in the secondary and increase the wirer size.
3 Or increase the iron field size.
Can you give me help with this problem as I wish to make the welder do It's job.
Or am I better to dump this Idea and try a capacitor welder ?
Greg
 

chemelec

Well-Known Member
is the plates I have pointed to in the photo are they the Iron shunts.
Could you make a sketch of the heater that is mentioned and what should I do to increase the current
1 Increase the number of turns in the secondary.
2 Decrease the number of turns in the secondary and increase the wirer size.
3 Or increase the iron field size.
Can you give me help with this problem as I wish to make the welder do It's job.
Or am I better to dump this Idea and try a capacitor welder ?
Greg

My Microwave Transformer is 110 Volts on the Primary and I have 2 Turns on the Secondary.
I am using 1/2 Inch Flattened Copper Pipe as the Secondary Wire, And VERY SHORT Copper Pipe LEADS to the Welded Joint. It Works.
And I Didn't remove the Shunt Plates.

For Spot Welding, you need HIGH Current, But not much Voltage.

And as you Increase the Turns, You REDUCE Current.
But Since your on 220 Volts, the 4 Turns should be OK.

I Suggest Bigger Wire and Shorter Lengths to the Weld Spot.
 

colin55

Well-Known Member
Remove the "iron shunt" and let us know if the current is sufficient. Generally, increasing the number of turns will allow a higher current to flow.
You can make your own secondary wire by putting 10 or more strands together and lightly twisting them. Use this for the secondary. You need more than 3v. I would try 12v to 15v.
 
Hi,

the wire you have used appears to be PVC coated, if so I would strongly suggest that this is not ideal as the PVC will in all likelihood melt in operation. I would suggest that you use magnet wire or something with a high temperature withstand in its place.

Cheers
Andrew
 

Mr RB

Well-Known Member
Remove the "iron shunt" and let us know if the current is sufficient. Generally, increasing the number of turns will allow a higher current to flow.
You can make your own secondary wire by putting 10 or more strands together and lightly twisting them. Use this for the secondary. You need more than 3v. I would try 12v to 15v.

Like I said, 10 to 20 turns. 3v open circuit is way too low for a spot welder for steel.
 

Gregory

Member
I removed the iron shunt and the current did increase but not enough to weld.
I have dismantled the transformer and rewound the secondary using 34 wires as shown in the photo's.
What I would like to know is would it be advisable to place the Iron shunt between the windings.?
If so How thick should the Iron shunt be.?
Will this winding be big enough to give me the amount of current ?
 

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colin55

Well-Known Member
You haven't got enough turns.
It looks like the transformer produces about 2v per turn. You need at least 8-10 turns.
 
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