RSU

I made one using a micro wave transformer. I removed the high voltage secondary and wrapped a couple of loops of large diameter wire around the secondary. It puts out around 3 Volts and 200Amps

I use a Variac Transformer to control the voltage to the transformer.

I made a foot switch from an electrical outlet box and a N.O. switch.

And I made my own tweezer soldering tool.

I think if you removed the high voltage out put wires and replaced it with a couple of loops of large diameter wire you should be able to get the same results.

Bernd

You will KILL yourself

 if your taps are on the 2nd dary, output side of the transformer you will eletrocute your self. 6-12 VDC out put voltage is safe to use. Mine is 24 volts because I know what to touch and what not to touch. 120VAC and up is asking for trouble. Buy a battery charger for $25-30 bucks and live to tell about it.

Carter

Still Alive

Had it for three years now, still alive. I figured it would bring the net nammy's out in short order.

Do you know how a welder works?

Bernd

Well

Bernd,

I would believe the 3 Volts, But the 400 amps is a bit of a stretch!

OUTPUT> 3V X 400A = 1200W  THUS INPUT>   1200W / 130V = 9.3A. OK I'll buy that.

You need to be careful with all those Joules available, you could hurt yourself. You could adjust the variable transformer to output 24 volts for a safer operating mode.  That thing looks like something out of a Frankenstein movie!

Regards, John

Those who want the Government to regulate matters of the mind and spirit are like men who are so afraid of being murdered that they commit suicide to avoid assassination. <> Harry S Truman

A ballast is not a transformer

A metal halide ballast provides a short start pulse (in conjunction with a couple of capacitors) and then regulates current to compensate for bulb temperature. This can be done with an inductor (auto transformer) or an electronic equivalent. There is no secondary as such.

Here's a link with the relevant schematic.

pqe

Pushing them Amps

John,

Your close, but no cigar. Putting in a full 120 volts I get 90 amps on a Fluke meter. I'll take a picture if you want to see some fireworks. It will melt a 1/8" stainless steel rod in a couple of seconds.

Ok, I'll admit I screwed up somewhere. I'm now wondering where I got the 400 from. Will have to try a fresh battery in the Fluke meter. Maybe I had the wrong scale on the meter.

Bernd

Electrocuting myself

No I won't because I removed the secondary (that's the way you spell secondary by the way) have been removed and those large black cables wound around about 4 times. It gives you a step down transformer that out puts around 3 to 4 volts alternating current. Your car battery has about 800 amps cold cranking power at 12 volts direct current, more lethal than the transformer. I love it when people don't know what they are talking about. Makes it easy for me to stick there foot in there mouth.

Bernd

 GO FOR IT

GO FOR IT

I'm pretty impressed with

your design there Bernd.  Not everyone has the knowledge to construct something like yours.  That's why manufacturers get the big bucks.  Variacs are not cheap if you buy them new.

DYI RSU

The unit I built came from searching the net. If you Google "resistance soldering unit" you find many "how to's" on building one. There is no high voltage used other than the 120 volts to the primary of the transformer. The secondary windings are removed and replaced with the larger diameter wire. Heavy duty welding cable can be used for that. At about 3 or 4 turns around the secondary side will give you anywhere from 3 to 6 volts at a very high amperage. That's what is needed to create the heat. Remember you are actually creating a short circuit in order to heat the spot you are soldering. If you take your Weller soldering gun apart you'll see it works on the same principle.

I think the misconception of electrocuting oneself by using a "Microwave Transformer" comes from the fact that many think you will be using the high voltage the transformer puts out. You don't. They don't read far enough to understand the transformer is actually modified into a step down transformer. One reason for using a microwave transformer is that it is a heavy well built transformer and can easily be modified for resistance soldering use. 

I realize many don't have that kind of knowledge. All it takes is a bit of searching on the net to find the answers. The only real danger from one of these units is if you accidentally short out the low voltage high amperage side of the RU. The foot switch controls the primary side of the circuit to the transformer, so the only time current flows is when you step on the foot switch. At least with the unit I built.

What can kill you is not understanding how something works.

Bernd

Test

@ John,

Did a bit of testing this morning on RUS. The transformer puts out 3 volts AC. When shorting the terminals out right at where they come out of the box, approximately 1 to 2 inches from the transformer I get 270 amps. Doing the same with the twezzer's at 3 feet of cable length I get 3 volts at around 70 amps. So the amperage drops off the further you are from the transformer with only 3 volts pushing the current through.

I'm now wondering where I ever came up with 400 amps. I stand corrected that this DYI unit puts out 70 amps at 3 volts when using a 3 foot wire.  So that makes this a 210 watt unit instead of a 1200 watt unit. Correct?

It does the job I need. That's what counts.

Bernd

DIY Tweezers

Bernd,

Can you tell us a bit more about the tweezers?

What do you use for the "electrodes"

David

The RSU Tweezers

Sure thing David.

Material used in construction of the tweezers. The main part is a 1/4" square about 4" long piece of brass. It's milled down to 1/8" square for the rest of the length, 3 3/4". That square part is fitted in a 1/8" slot milled into a Bakelite material and glued in. I made the terminals from a piece of 3/16" diameter brass rod. Drilled appropriate holes for a hold down screw and for the heavy duty wire going in. The ends of the 1/4" square brass had holes drilled for 1/8" stainless steel rod and retaining screws. I covered the top and bottom with an adhesive backed foam rubber for insulation. The wires are stripped from a large cable that was used at work to power 480 Volt 200 Amp machines. It's metric wire. I measured the wire and came up with an equivalent of approximately 7 to 8 gauge wire.

And while we're on the subject of RSU's I'd like to add a couple more pictures.

When the use of a microwave transformer is mentioned some don't read further down the post to see the end result of using one and they claim that one can get electrocuted. That's understandable, but you will not be using the transformer with the high voltage secondary.

Here's a picture of two microwave transformers as they come out of the microwave oven. It shows what is called  a vertical or horizontal wound transformer.

After removing the secondary windings, which will be the smaller diameter wire, a large piece of wire is wound several times around the secondary. Depending on the number of times one winds the wire around will give you a voltage from 1.5 to 6 volts AC at a high amperage. Mine measures at around 400 amp's right at the output at the ends of the wire, at approximately 3 volts. This is very large gauge stranded wire. Once you get out to about 3 feet or so the amperage drops off to about 65 to 70 amps. The further away you get from the terminals the more the amperage drops. Using larger wire to wind around the secondary will increase the amperage. If you used a solid bar you get the highest amperage the transformer is capable of delivering.

If you have a Weller Soldering Gun, this is what it looks like on the inside. It works on the same principal as the transformer in the above picture, only smaller.

I hope this clears up some misconceptions about building your own RSU.

Bernd

Tweezers

Thanks, Bernd,

This may finally get me started

David

To rewind the secondary what

Rewinding Secondary

Tom,

Not sure what the wire size is. It's at least 3/8" diameter. A good wire to use is welding cable. Should be able to get that at any welding supplier. Sorry that's the best I can do on wire size.

Bernd

Getting Started

David,

No problem. Always like to help out in situations like this. Have anymore questions just ask away.

Bernd

So Bernd...

3/8" wire? That sounds like about #6 or #8 AWG. Unless that transformer is cranking way past 1200 watts, that's a bit of overkill. I'm using a 100-watt soldering gun with a split tip and it's soldering rail to PC board ties in under a second with both parts pre-tinned. Best of all, no construction to speak of. Bad part, it won't work well with detail parts.

Overkill

Yes I've often been accused of over kill on a project, like using to many screws to hold something together.  

I've usd the RSU to solder heavier pieces of brass like .060" and it's nice to be able to heat the part up fast to solder before other parts fall off. I think, now that you mention it, it was #8 AWG. The soldering iron trick I saw used by Joe G on the O scale forum. Ya, it's a bit bulky for detail parts.

There was an old machinist that told me once you need a big lathe. I asked why. He said you can turn small parts on a big lathe, but you can't turn big parts on a small lathe. I applied that principle to the RSU. I can solder small parts with a big RSU, but I can't solder big parts with a small RSU.

Bernd

RSU (old school)

I built my RSU using a surplus vacuum tube filament transformer.  I'm guessing it was a 6 volt 20 amp capacity transformer.  These are hard to find nowadays since there are no filaments to power but it might be worth a look on the web.  I built it about 25 years ago and if you do the math, I have a 120 watt soldering unit.  Ample for most needs.  I used welder's gouging rods for my electrodes, sharpened in a pencil sharpener.  I bought a large pack of them when I was doing this because I didn't know what to expect in the way of lifespan but these have not eroded since I made them (many hundreds of solder joints) and they get the current to the joint beautifully because with carbon electrodes, resistance decreases with the temperature increase.  A foot switch to operate the transformer keeps both my hands free to handle parts and electrodes and you can't leave the current running after the solder melts or you have melted everything.  120 watts doesn't sound like a lot but when it's concentrated at a pinpoint, things get red hot in a hurry.

I'd include pictures but I'm away from my normal home for the winter.  I made the handles out of parts from my junk bins.  With the low voltage, all you have to worry about is the heat at the joint and getting your foot off the switch when the solder melts. 

Good luck.  For me, it was an easy, interesting and fun project.  I would not dream of soldering feeders to rail any other way.

Rich U

RSU thread revived

Hi Rich,

Wow, an old thread revived. Some pictures would be nice. I've got some of those carbon electrodes to. The ones I have are copper coated. A friend in the gauge one live steam hobby made me aware of them. I need to revamp my unit. Especially the tweezers. Mine are very handy to use.

Bernd 

"What can kill you is not

"What can kill you is not understanding how something works." -- best reply ever. 

Electrocuting myself... knot! :D

After the snarky comment about 'secondary'... I'm wondering about the other readers.  'They're' all waiting for you to march over 'there' and stick 'their' foot in 'their' mouth!  :O  So there!  :D

Its not the voltage

Speaking of killing you its not the voltage its the current and the path through your body. About 100 to 200 milliamps will kill you, if the path is across your heart.

That is why people can have the millions of volts from a Van de Graf generator make the hair stand on end, its only a few microamps.

So that 70 amps can kill doesn't matter its only 3 volts. As long as the proper precautions are taken, insulated tweezers, and other things, you‘ll be fine. Don't grab those tweezers with your sweaty hands and accidentally step on the switch.