Desk-top Soldering Press! (with L.E.D)

I was getting tired of having to heat up my soldering iron just for one thing, so i created my own solution. This is very sturdy and reliable. Believe it or not, it solders wires better than a regular soldering iron and it has a L.E.D. for light! (Big thanks to guyfrom7up for helping me with the power supply)

here is the model i have for the pedal. here

I made this whole thing out of just a sewing machine pedal and some wire. it is able to solder up to 14 gauge wire. this will take about an hour to build and it will cost however much you pay for a sewing machine pedal. (there cheap). i used a broken one.

The second you make a connection between the solder and the two electrodes, it instantly sucks the solder on to the wire and will NOT come off! yes, this does have the same concept as Coldheat but is way better. you don't have to hassle over making a connection. it is also way more powerful.

By the way, those sewing machine pedals are filled with carbon plates and electrodes, dont throw them away!

Below is a video of it in action!

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Step 1: Materials and tools

Almost everything is taken from the actual pedal itself. the rest are very easy to get.


sewing machine pedal
16 gauge wire
electrical tape
alligator clips (3)
Carbon rod 9i took this from a dry cell battery)
a piece of metal
L.E.D. and its power supply
12v 4amp power supply.

Wire Strippers

*********** Before you start, you must take apart your pedal. open up the back, and you should see a concrete like block. crack that open and you will hit the mother load of carbon. you need the carbon and the spring.
I made one but it doesn't melt the solder. I use a power source of 15v 500mA and it only make sparks when I move the wires and doesn't melt the solder. any suggestions?
kruser495 (author)  tgferreira1841 year ago
you need higher current. something like 2-4 amps
Wait a sec, where does the power come from? I must keep missing it. _?_ -
I also don't really understand it :/
Ooh I see now!

but you have to wrap the soldering wire around the connection?
I already have a soldering iron from radioshack and I don't think i could get my hands on a carbon rod, from a battery anyway. So I was wondering if I could make this from my existing soldering iron and maybe another way to get some carbon some otherway. By the way this is really cool.
DON'T take apart an alkaline they have bad smelling chemicals in them, only take apart carbon zink ones, they are harder to find because they are obsolete, but the dollar store still has them. sorry about replying two years later.
I thought AA and AAA batteries had carbon rods in them. Just cut off the top and pull out the rod. At least that's what I thought another instructable said (or was it a science website?)
 If you can't get a sewing machine pedal for the carbon, get carbon-zinc or heavy duty batteries (which is just a fancy name for a better-built carbon-zinc) and take them apart for the carbon rods.

All sizes of carbon-zinc have carbon rods in them. C and D cells have some nice thick rods.
kruser495 (author)  electronicfreak226 years ago
you take the carbon out of the pedal itself. thanks dont forget to rate!
matdogg6 years ago
i have one question, what if the wires have no solder on them? then you would have to use the solderin iron (or gun) to add solder, then solder it with this?
kruser495 (author)  matdogg3 years ago
wow ^
get solder, wrap it around wire, use
jaysbob6 years ago
Just for curiosity sake, would you be a happy camper after sticking your finger between the two electrodes? I don't mean anything intentional (not that dumb) but as far as accidentally brushing up against them with a bare hand or other exposed skin?
kruser495 (author)  jaysbob6 years ago
not even close. you wouldnt get shocked even at 50v at 4 amps. only if your hands are VERY wet then you might get a slight tingle. but this is very safe.
That is not true, and dangerous to say. 50V can shock you, it depends very much on how dry or damp your skin is. I've known people with such dry skin that touching a 120Vac line barely tickles them, and others whom 25V causes a tingle. At only 10mA, you feel the tingle. As little as 60mA across the chest cavity can cause fibrillation, which means certain death without -immediate- medical attention. Add to that, your physical reaction to being shocked. I know a lot of techs who suffered bad secondary injuries when they yanked an arm away or jumped away and tore arms and hands open or bashed heads/arms/legs into surrounding objects. At very low current levels, this is you body reacting to the fear and pain of being shocked, at even modest current levels this is your muscles involuntary constriction from the electric current and can be quite severe. 50V with damp skin can cause more than a tingle, it can cause enough current to kill. Add to that, a large part of the danger with voltages/currents on the lower edge of danger is But if you puncture the skin, 12V can kill you, if it is across the right parts of your body. Most of the resistance is in the outer skin layer of dead cells. And 4A will cook you! If you have a 50V source that can put out 4A, and the worst happens and your skin gets punctured, that's 200W being dissipated in your body.
Don't mean to be mean, but in order to get .06 amps across the heart (i thought it was .02, whatever) at 12 volts then the resistance between both your hands must be:

12 = x times .06

12 / .06 = 200 ohms

if it's 20 mA then

12/.02 = 600 ohms.

you body has wayyyy more resistance than 600 ohms.

also, on an upcoming spot welder that operates on 12 volts and stores it in a capacitor, same principal.

the power supply could give 1000000000000 amps and it still won't matter. It's the voltage that allows the amps to travel.
You aren't being mean, we're just disagreeing on some points. That's why I mentioned puncturing the skin. Internally, your body does have a very low resistance, most of the resistance is in the skin. I've done experiments and your body's internal resistance is in the range of 100 to 500 ohms. 20 or 60mA, I'd not want to risk either amount across my chest cavity. It is true, it isn't -just- the amps, it requires enough voltage -and- low enough resistance -and- a complete path. This "spot solderer" should be fairly safe, as described. The 25V only appears across two closely spaced points and the transformer isolates it from everything else, including ground.
Be careful when doing the internal body resistance measurements there was a safety bulletin way back when I was in the navy about a tech who was playing around with an old Simpson 260 meter on the r x 1 scale (1.5 v dc) he put one lead into a cut and the other into his mouth, when he fell to the floor those looking on thought he was playing but he was DRT ( dead right there) the major components of the body are basically salt and water and the resulting circuit was short circuit enough to rupture the battery in the meter blowing the fuse in the process.
cold dry skin on a healthy person can be as high as 5 to 10 M Ohms but it also can be as low as 300 Ohms on a sweaty sick person the U.S. Navy defines high voltage as 30 volts for this reason
So always be careful when dealing with electricity and have fun
I forgot to say - if shorting the leads together on the lowest Rx1 scale caused the battery to explode and the fuse to blow, then why was I and every other tech who used the Simpson 260 able to zero-set it?

The ohms scale can't ever put out enough current to blow a 1A fuse. The meter inside it is a 50uA full scale meter, and the Ohms scale works by putting the battery, meter, and a resistor in series with each other, with the zero-set in parallel with the meter. So the maximum current at short circuit is -very- low. 

The fuse is there to protect when using the current scale.
I have to look at that report askance. I am not saying you didn't receive the safety bulletin, I am saying I think it was incomplete or seriously exaggerated by someone.

Put a dead short on a 1.5V battery and it won't rupture. And at 100 ohms, the lowest value I measured, that is still only about 15mA, not enough to blow the 1A fuse in a Simpson 260.  I can believe that a person with a bad heart -might- be susceptible to a current that low or that they would overreact and be killed by contact with the floor, but not that it ruptured the battery and blew the fuse.

kruser495 (author)  Polymorph6 years ago
i dont care.
well... just like in welding, its the amps that cause the heat. and its amps that cause death! In order to cause death it would have to flow through the heart. touch one electrode w/ your right hand and the other w/ your left, maybe. but the voltage also has to be high enough. blah blah blah. point in case. brushing up against it with a DRY hand should produce nothing. brushing up with a WET hand could produce a spark and possibly a burn. and putting your finger inbetween is just stupid and will probably give you a burn.(I haven't tried it obviously)
Dang! This would be the dingus for off-gridders. Just hook up to 12 gel or car battery, charged by solar panel, or whatever, and solder away. I'll have to start making proper connections now. No excuse to go dinking around with them wire nuts, or Marrettes or whatever they are called.
 Careful about connecting a car battery to this. The 12V 4A transformer is inherently current-limiting. In fact, if you were looking at the voltage from the transformer, my guess is that it drops very low when you are soldering.

A 12V car battery can put out hundreds of amps into a short like this, causing the carbon to glow red hot and throwing out burning lumps of metal and creating lots of UV.

Think about "Cold Cranking Amps". That is the current rating of your battery at its worst, when it is very cold, and into a starter, not a short. Well, not a total short, the carbon rods have some resistance, but not much.
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kruser495 (author)  jeffreystylus6 years ago
cold you think coldheat is better. hahaha. ask anyone here. the point of this was to not have to heat up your soldering iron just to solder ans l.e.d. or two wires. coldheat is the absolute worst device ever made. ask anyone.
 A friend of mine bought a coldheat, they just don't work well.

What you've built here is a home-built version of the resistance solderers used by manufacturers. I think Boeing uses them.

However, be very cautious about soldering semiconductors. If the wires being soldered are making good contact, it should be fine.

This type of solderer is great because it dumps the heat right into the connection, and as you've pointed out it has zero warmup and is cool in between.

To clarify, I was never trying to say that this is dangerous with normal caution. As you pointed out, 12V won't push much current through unbroken skin, and the current would all run through a finger caught in it. You'd have to push hard enough to break the skin, at which point, shock or no, you'd yank your finger out. The biggest hazard from shocks is secondary injuries.

I would wear goggles if you don't wear glasses already, just as you should be doing when using a soldering iron. I've known a few techs who thought it would never happen to them, then it happened and they ended up wearing an eyepatch and being in a lot of pain.
No, the cold heat device was the worse idea ever... the concept of cold heat is fantastic... LoL... Ask any one... they used the poxy cheap ones till they broke. What would you expect when you push a device to points it wasn't designed for.
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I made it with a soldering tip for the top nail, It works great
can you explain that in more detail im intrested what you did
I just took one of my hollowed soldering iron tips, screwed the screw into it (it fit great) then i just did the rest normally
csaxe215 years ago
Hey, great idea. I'm going to try to make one but just a couple of questions... For when buying the pedal, the site offers some different models. Which do I get between the RM100N is a counterclockwise for multifunction machine making straight stitch, zig-zag, buttonholes, etc. RM100S is a clockwise rotation for the mini sergers (overlocks) and coverstichs Then it also offers 110 or 220 V for the voltage. So which one do you have? Also, for the 12v 4amp power supply, do you know where I can buy one/what they look like and the price? Thanks a lot, Great Idea!
kruser495 (author)  csaxe215 years ago
i have the rm100n. if you live in the us and your power is 120v, then get the 110v. you might be able to hook it up to a car battery, or a battery charge ( for cars). i had built mine from parts i got from radioshack. let me know if you need any more help! thanks.
Hey, for the carbon rod that you said you took from a dry cell battery, how'd you do it? Would a C Duracell work? Or a D? Thanks
Plasmana5 years ago
That is a very clever Idea! I am going to make one of those!

5 stars!
trekman6 years ago
How do you attach the top electrode to the piece of metal that is taped to the top lever? The schematic for the power supply shows a fuse on the primary side. What size fuse? The transformer in that schematic is from Radio Shack but the only one like that is 2 amp. It that hot enough? They have a 12 volt @ 3 amp that is cheaper.
kruser495 (author)  trekman6 years ago
the transformer you are talking about that is 2 amps is actually a center tap transformer. so it would be 12v 4 amps. the electrode isn't attached to the metal. it is held by and alligator clip. the metal is just there to act as a heat sink when it gets hot. the fuse is not important.
I don't agree that the fuse isn't important - it's there to protect you and your equipment! If you short something accidentally (which is easy if you're not super-careful) you'll end up burning out the transformer or something. A 1 or 2A fuse is probably fine on the primary side. Also, with a CT transformer like the one from RadioShack you can't get 12V @ 4A if it's rated for 2A. If you use both taps you'll get 24V @ 2A.

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