Q Regarding Homemade Spot Welder

[SE18]

Guess I should have provided my source and photos. Here's the youtube I followed, pretty much the same without the frills:

The advantage of that design (not my design, not my youtube video, I just copied it) is that the arms come out and you can spot weld things in hard to reach places a spot welder COTS type can't

Here's photos of my spot welder. I use a foot pedal for turning power on and off. Additionally, there's alight switch in the back of my unit that turns the power on (so 2 power devices). The coating on the wires gets pretty hot when welding, you can see a partial melt in one of the photos. I never did take a voltmeter or amp meter. The winding with the thick part has 2 loops.

 

[RJSakowski]

Guess I should have provided my source and photos. Here's the youtube I followed, pretty much the same without the frills:

The advantage of that design (not my design, not my youtube video, I just copied it) is that the arms come out and you can spot weld things in hard to reach places a spot welder COTS type can't

Here's photos of my spot welder. I use a foot pedal for turning power on and off. Additionally, there's alight switch in the back of my unit that turns the power on (so 2 power devices). The coating on the wires gets pretty hot when welding, you can see a partial melt in one of the photos. I never did take a voltmeter or amp meter. The winding with the thick part has 2 loops.

If you notice in the video, his electrodes turn black rather quickly as well. One issue with his design is the relatively poor contact area between the cable and the electrode, both electrically and thermally. That sort of contact is fine for a hundred or so amps but when you get into the realm of spot welding amperage, there is a lot of resistance. Resistance equals heat. Your method of connecting the cable to the electrode is a significant improvement over the original method but still leaves only two lines of contact . Commercial spot welders use either a threaded or tapered connection. Since the insulation meltdown is occurring in the vicinity of the lug, it points to a high resistance connection. Even for much lower current requirements, I don't rely on a crimped connection.

While cutting your electrodes from a length of wire is convenient, you really need a better way to make the electrical connection. I would suggest getting some larger diameter material for your electrode and turning a point on the electrode ends. You can pick up some 3/8" or 1/2" copper rod on eBay for less than $15. If you make a connector by boring a hole for the electrode in a split block, you can make a clamp that gives you almost 360 deg. contact. For the wire connections, I would use a similar clamping method. This will minimize both the thermal and electrical resistance.

As far as your transformer is concerned, your transformer looks rather small. I would use a transformer from a microwave or other appliance rated at 1 kw or more or with an input current rating of more than 10 amps. This should help to insure that you will not be over heating your primary winding. Running two transformers in parallel presents problems because of the awkward geometry of you secondary windings.

Bob

 

[SE18]

Thanks for your insights, Bob. Very helpful suggestions. Thanks for analyzing the problem and looking thru what I provided. Big help