Just got another excellent older Lincoln welder, and a recommendation.

[etpm]

I have an embarrassment of welding machines. Yesterday an old friend gave me a welder he hasn't used for over 5 years and he knew I would use it. The machine in question is a Lincoln SP-100. I already had the SP-125 Plus machine. As near as I can tell the machines are identical. I took the SP-100 cover off today to check for insect nests and the like and the guts look just like my SP-125 Plus machine.
I bought my SP-125 Plus machine about 20 years ago. It was used. In an auto body shop. About a year after I bought it I took it apart because I wanted to add a purge button so I could have shielding gas instead of air in the whip when I started welding. That's when I discovered its previous life in an auto body shop because of all the Bondo dust inside.
Adding a purge button to control the gas solenoid turned out to be not as easy as anticipated because I wanted the purge button to control low voltage and the gas solenoid requires 120 volts. So I had to figure out what the circuit board inside the machine was doing to control the gas solenoid because low voltage was being used to switch the 120 volts going to the gas solenoid. Anyway, I figured out what was going on and added a push button into the circuit and ever since I have had a purge button on the panel of my SP-125 Plus.
So today I opened up the welder my friend gave me so I could clean out any wasp nests and other similar insults to welding machines and the interior looks identical to my newer SP-125 Plus machine. The circuit board that I modified in the 125 machine appears from memory identical to the SP-100 machine circuit board. All the other interior stuff also looks the same. I suspect Lincoln just changed the exterior knobs, because they are slightly different, and came up with a new model number.
The specs for the machines are also the same and the machines have the same controls, just slightly different knobs. They weld the same too. At the end of the day if a person was looking to buy a used 120 volt wirefeed machine then either model, the SP-100 or the SP-125 Plus, would be a good machine to buy. These machines are not inverter machines so they are not so light. Also, because the voltage and wire speed controls are infinite rather than stepped controls, the less experienced user may have some trouble learning to weld. But a more experienced welder will really appreciate the added flexibility when welding a challenging job. If I was on a budget and inexperienced I would buy one of these machines. There might be some trouble learning with all the flexibility but it won't take that long to get past that and the extra skill learning to run a machine that is more flexible will certainly pay off in the future.
I have put many hours on my SP-125 Plus machine. At least 400. Probably more. It sits on a cart I made that also holds a gas cylinder. So I am going to use my SP-125 Plus for welds that use shielding gas and my new to me SP-100 machine for flux core wire, AKA innershield wire, AKA inner shield wire. Now I need to make a cart for the new to me SP-100 machine. Lately I have been using more fluxcore. That SP-100 is gonna get used a lot.
Eric

 

[Harry in Ky]

I too have a Lincoln SP 100. I have no idea how old it is. I traded for it about twenty years ago from a friend who acquired it from an estate sale type thing some years before that and had never actually used it. It had a bad guide tube at the time so I bought a new Radnor gun and guide assembly for it. It seemed to work OK with flux core wire so I bought a gas bottle and built a cart for it all. I've used it ever since for any number of projects. It works great for light stuff.

I might like to try adding a purge button (some day when the weather is better) so I'm curious to know just how you did that. That first few seconds of splatter before the gas reaches the arc can be annoying.

 

[ericm979]

When I'm using my SP100 I hit the trigger for a few seconds before I'm going to weld, then cut the excess wire off and weld. That purges the hose and it doesn't get too much air in it if I don't dawdle.

A purge button would be much better.

The 100 and 125 were pretty much the same back when I got my 100 (close to 30 years ago!), the 125 just had more power.

 

[California]

I might like to try adding a purge button (some day when the weather is better) so I'm curious to know just how you did that. That first few seconds of splatter before the gas reaches the arc can be annoying.

Here's something that might work for you:

My HF MIG-180 was highly modified by its first owner.

He installed an Omron H3Y adjustable delay timer to make the gas start before the welding current. They aren't expensive, I see under $15 on Amazon.

Amazon.com

Omron lists an endless variety of voltage and delay options.

 

[etpm]

I documented the changes I made to the circuit board and if I can find I will post it. Somewhere the circuit board schematic is available because I have or used to have it. Since the specs are identical for both machines I suspect the circuit boards are the same.
Eric

 

[Harry in Ky]

Thanks. Both are interesting ideas.

 

[etpm]

I looked on the web and found where I had posted the schematic and instructions to add a purge button to rhe SP-125+ machine. See the text below. See attached .png file.

Circuit changes resulting from the addition of a gas purge switch.


Additions:
A relay, pushbutton momentary switch, diode, and several wires were added to the control circuitry.

Operation:
When the button is not pressed the welder operates normally. When the button is pressed the relay coil is energized which causes the relay to switch the connection of resistor R16 from diodes D9 and D11 to the out pin of Voltage Regulator X4. This turns on the Gas Solenoid Control opto-isolator OC11 which then turns on triac TR11. Triac TR11 then energizes the Gas Solenoid.

Circuit Changes:
One lead of resistor R16 was unsoldered from the circuit board trace that connected R16 to diodes D9 and D11. A wire was then soldered from the trace to the NC pin of the relay. A wire was soldered from the free lead of R16 to the COM pin of the relay. A wire was soldered from the OUT pin of Voltage Regulator X4 to the NO pin of the relay. A wire was soldered from the GND pin of X4 to one of the two coil pins of the relay. A wire was soldered from the other coil pin to one of two male spade connectors. Another wire was soldered from the out pin of X4 to the other male spade connector. These male spade connectors connect to the female spade connectors which are soldered to wires from the pushbutton switch. The added diode was soldered reverse parallel across the coil pins of the relay.