Electrical question-blade welder

[Gordon]

I have a blade welder on my DoAll band saw. It is rated 440 volts single phase and uses two wire input. I no longer have 440 but do have 220 volts single phase. Is it possible to use a transformer to get 440 volts and if so what size and or type? Since the welder is capable of welding 1" blades and I want to weld 1/2" blades is it going to just operate at half capacity if I feed in 220 volts or is it going to burn it up?

Edit: Welder is labeled as 10 amp.

 

[gartof]

Don't try to run it on 220V. You need a transformer 220V in and 440V out. 10 amps at 440V equals 20 amps at 220V.

 

[BaronJ]

Hi Gordon,

Try and find an old arc welding transformer, they often have taps on that go 220 to 480 volts. Just bear in mind that you are using it as an auto transformer. Leave the output side unconnected.
HTH.

 

[Gordon]

This probably more involved than I want to get into. I have not tried to silver solder blades but I may try that.

On the option of imputing 220v and receiving half the amperage, I have been getting mixed answers. I have been told do not try it and it should work. The welder is not usable to me as is so I could just try it but I do not want to burn it up either. What started this is I found an old coil of blade stock. I have been purchasing premade blades and thought that if I could weld these I have enough for probably 20 blades. I brought the stock to a show which makes blades and they did not really want to monkey with it because the stock was slightly corroded and they had to clean it up to weld it. I can spend the time to clean the stock if I can figure out how to weld it. Silver solder may be the easiest answer.

 

[BaronJ]

Hi Gordon,

Just to answer your first concern. Power is basically "Volts times Amps" so gartof is correct, however welding a bandsaw blade only takes a few seconds and the transformer, even if it were capable of only half the power would take longer to burn out. Now I metioned a welding transformer !

Lets assume that the maximum welding transformer output current was 100 amps at say 50 volts. If we also assume that the transformer was fed from a 450 volt supply, this means that the supply would have to provide 20 amps, to support this. (450/50=5 and 100/5=20)

From your post the blade welder requires 10 amps at 440 volts, so using my figures your 220 volt input would need to be able to supply aproximatly 20 amps. (440/220=2 so 2X10=20)

"Numbers rounded"

With respect to your blade stock, any rust, oil or dirt on the weld overlap will reduce the weld strength and take longer.


Now I would guess that the blade welder on your "DoAll" bandsaw is actually fed from a transformer anyway and if you examine it carfully you may actually find that it has tappings on it for other voltages.

The bandsaw that I have access to (440 v 3Ph 1" blade width) has a blade welder whose transformer outputs about 10 volts open circuit (that is with the contactor closed and no blade in the welder) I haven't a clue how much current is actually used, but from the thickness of the copper bar I would guess 40 to 60 amps.

HTH.

 

[GLCarlson]

A transformer is a voltage converter, not a current converter. If a transformer delivers 12 volts out from a 120 input, the ratio is 10:1; that doesn't change. It'll deliver 24 volts when fed with 240, and 6 volts when fed with 60. So putting 220 into a transformer expecting 440 input means that the voltage out will be half the expected working voltage. That may -or may not- be important, but assuming that the current drawn will double at half the input voltage makes assumptions about the welder circuit that may not be true (probably aren't, if the welder has any active circuitry, and may not be even if that's not so, as current will be limited even in that case by the winding resistance or other passive components).

Worst case, you may be attempting to operate a semiconductor controller on half its expected voltage. That could affect timing circuitry, regulators, etc- or even mean that the controller would not work at all, or would fail.

If, on the other hand, this is a simple tapped transformer with perhaps a current limiting resistor, you'll just see roughly half the voltage at the welding tips- which may be enough. How much power and what current will depend on what else is in line.

If you can have a look at the welder, do so. If there appear to be any active components (transistors/SCR/triacs) you should be careful about operation at other than rated voltage. If it's just a transformer and maybe a current limiting resistor, worth a try.

 

[Gordon]

It has been quite a while since i took it out of the saw but it does not have multiple windings for 220/440. That was my first thought. As I remember it is just a pretty straight forward resistance transformer. I am not too sure of what limits the time of the weld. I would think that whatever is used for the timing circuit would be the most likely to be damaged. I will have to remove it from the saw one of these days to take another look at it.

 

[BaronJ]

A transformer is a voltage converter, not a current converter. If a transformer delivers 12 volts out from a 120 input, the ratio is 10:1; that doesn't change. It'll deliver 24 volts when fed with 240, and 6 volts when fed with 60. So putting 220 into a transformer expecting 440 input means that the voltage out will be half the expected working voltage. That may -or may not- be important, but assuming that the current drawn will double at half the input voltage makes assumptions about the welder circuit that may not be true (probably aren't, if the welder has any active circuitry, and may not be even if that's not so, as current will be limited even in that case by the winding resistance or other passive components).

Did you actually read my post ?

"Try and find an old arc welding transformer, they often have taps on that go 220 to 480 volts. Just bear in mind that you are using it as an auto transformer."

It is clear that I said using the arc welding transformer as an auto transformer to go from 220 to 440 volts.

In my following post I went through the sums in answer to Gordon.

Worst case, you may be attempting to operate a semiconductor controller on half its expected voltage. That could affect timing circuitry, regulators, etc- or even mean that the controller would not work at all, or would fail.

If, on the other hand, this is a simple tapped transformer with perhaps a current limiting resistor, you'll just see roughly half the voltage at the welding tips- which may be enough. How much power and what current will depend on what else is in line.

If you can have a look at the welder, do so. If there appear to be any active components (transistors/SCR/triacs) you should be careful about operation at other than rated voltage. If it's just a transformer and maybe a current limiting resistor, worth a try.

There was no suggestion of feeding his blade welder anything other than its rated voltage. I would agree that one should be mindfull that there may be active devices involved.

On the bandsaw that I refered to, there is a simple contactor feeding the blade welder and yes it does have a weld timer.

 

[BaronJ]

It has been quite a while since i took it out of the saw but it does not have multiple windings for 220/440. That was my first thought. As I remember it is just a pretty straight forward resistance transformer. I am not too sure of what limits the time of the weld. I would think that whatever is used for the timing circuit would be the most likely to be damaged. I will have to remove it from the saw one of these days to take another look at it.

Hi Gordon,

Pity about that, some do have tapped primary windings. In the case of the one I refered to, the blade welder is fed from across two of the phase's via a contactor. The timer is a simple 30 second clockwork one, no electronics at all. The user simply sets the time once the blade ends are in position.

 

[bazmak]

As a first year sheetmetal work apprentice one of my jobs was to make up
the band saw blades for the blokes.The original bandsaw had a fixture
for holding the blades which had to be scarfed with a file before silver soldering
The new bandsaw had a fixture for butt welding and arc welding together
No different from a std arc welder.The few seconds the arc is active should not
cause burnout.Try it you have nothing to lose.Other than that its a simple matter to scarfe and silver solder.I also looked into it for my small bandsaw
but all I could buy was 100ft coils of blade and I didn't use enough blades
If you have the blade then its worthwhile to make up your own by either
method.Just don't do them singularly a few a time and it becomes easy
I can still 3 coil the blades as easy as yesteryear

 

[goldstar31]

As a first year sheetmetal work apprentice one of my jobs was to make up
the band saw blades for the blokes.The original bandsaw had a fixture
for holding the blades which had to be scarfed with a file before silver soldering
The new bandsaw had a fixture for butt welding and arc welding together
No different from a std arc welder.The few seconds the arc is active should not
cause burnout.Try it you have nothing to lose.Other than that its a simple matter to scarfe and silver solder.I also looked into it for my small bandsaw
but all I could buy was 100ft coils of blade and I didn't use enough blades
If you have the blade then its worthwhile to make up your own by either
method.Just don't do them singularly a few a time and it becomes easy
I can still 3 coil the blades as easy as yesteryear

When I had a little Burgess BSK Bandsaw, I scarf jointed as Barry describes but silver soldered instead of arc welding. I wonder why I never used my hand held Spot welder - ex my vehicle restoration days.
All gone now, at 86 no one wants even to insure my cars:wall:

However, I can recall 'Herbie' describing making a spot welder out of a scrap microwave.

Any chance of resurrecting his excellent post in this connection?

Norm

 

[Gordon]

I am aware of the fact that 10 amps at 440 = 20 amps at 220. Amps x volts = watts so I was wondering if fewer watts for a longer time will accomplish the same thing. For instance a 30 watt soldering iron draws .25 a and a 60 watt soldering iron draws .5 a and the 30 watt theoretically will heat up something in twice the time. I am not sure if the voltage at the weld is entirely a determining factor. A cheap arc welder operates at a lower open circuit voltage than an expensive one. Ease of welding is a factor but both will weld. When I started looking at this I figured that it would require a 4.4 KVA transformer and that did not seem right.

 

[BaronJ]

Gordon,

It's obvious that you are aware that the blade welder is simply a transformer and I'm sure that you have a multimeter that can measure AC volts, so simply feed your 220 volts into the welder transformer primary and measure the open circuit voltage of the secondary. Knowing the input and output voltages will tell you the transformer ratio. A measurement of the secondary winding resistance knowing the voltage will allow you to calculate the current, you can then work that back to get an idea of the current draw at 220 volts.

I was under the impression that you wanted to run the whole bandsaw from your 220 volt supply.

 

[ddmckee54]

Gordon:

The 4.4KVA is right. I was just looking in my Ugly's book at the full load currents for single phase transformers and a 5KVA 480/240 volt transformer is rated at 10.4 amps on the 480 side and 20.8 amps on the 240 side. If you were trying to handle the 10 amp load on a continuous basis you should go to a 7.5KVA transformer, but with your duty cycle a 5KVA will be fine.

However is it worth it? The best deal for a 5KVA transformer I could find on Flea-bay was $150, retail is going to be twice that cost, probably more. You planning on breaking/making enough blades to justify that cost?

Don

 

[Gordon]

Don: That is really the question. If I could purchase something for under $50 it may be OK but much more than that I can just pay the price for new blades. I have never tried silver soldering blades and had not really considered it until I started to look into this. Silver solder is probably the next thing to try. I used the welder on the saw when I owned my business but when I retired and brought the saw home I did not have 440 so I have not used it in the last few years.

 

[Gordon]

Gordon,

A measurement of the secondary winding resistance knowing the voltage will allow you to calculate the current, you can then work that back to get an idea of the current draw at 220 volts.

.

The problem is that I do not know what is a workable voltage for welding blades. Once I find out I still do not know if the voltage is sufficient to weld the blade.

 

[bazmak]

Silver solder is very easy.Scarfe/feather the ends of the blade,flux and cut a piece of silver solder.Clamp together with a pair of pliers and heat up to red heat..Clean off the welds.With mine many years ago if there was the slightest jolt the blokes would make me do it again.I got very good very quickly

 

[BaronJ]

The problem is that I do not know what is a workable voltage for welding blades. Once I find out I still do not know if the voltage is sufficient to weld the blade.

It is the current flowing that heats the blade ! The joint is essentialy a short circuit.

 

[bazmak]

The current required to weld a blade size say 12x1mm (12mm2) is the same as say a 4mm did welding rod.What is the power required with a welder for 4mm dia rods.I think you are worrying too much give it a go.A 4mm welding rod needs about 100 amps secondary for 5 secs

 

[BaronJ]

The current required to weld a blade size say 12x1mm (12mm2) is the same as say a 4mm did welding rod.What is the power required with a welder for 4mm dia rods.I think you are worrying too much give it a go.A 4mm welding rod needs about 100 amps secondary for 5 secs

Yes you are quite right. If it came to a pinch he could simply dispense with the blade welder transformer and use a welding set across the blade jig.