Repairing Forney C-5 Arc Welder

[Markfothebeast]

I've only really taken a quick look under the top cover. I'm not familiar with the design of this type of "plug-in" stick welder. It looks like each of the transformers windings are tapped for different output currents. What confuses me is the battery charger function. How is the AC current converted to DC? There must be some type of old school bridge rectifier circuit in there.

Someone had obviously replaced the cord. The neutral wire appears to be wired as a hot leg, unless I'm looking at this wrong... The 120v outlet on the front has the neutral wired to the ground. I'm planning on replacing the 3-prong cord with a 4-prong and wiring the nuetral and ground separately.

Would it be appropriate to replace the 120v receptacle on the front, wire it to a hot leg, and separate the ground and neutral? It'd be handy to use the outlet.

The story behind this is that it apparently "caught fire" but I don't see any fire damage, at least from what I saw with a flashlight in the dark. It was used in a barn and sat close enough to open doors that it was in the elements. I wouldn't be surprised if there's poor enough resistance that a wire was smoking.

So today in the day light I plan on getting a closer look and test the windings/wiring and clean it up. I'm looking for a bit of insight on how these function. Perhaps there's a manual or wiring diagram out there? Any rough idea of its age?



-Markfothebeast-
(www.youtube.com/markfothebeast)

 

[Markfothebeast]

I forgot to mention, there's a large capacitor inside. It looks like it may have failed (bulging). What's the purpose of the capacitor? Is this part of the battery charging function? My old Miller Thunderbolt with the shunt transformer doesn't contain a capacitor. I'll get a photo of it shortly.

-Markfothebeast-
(www.youtube.com/markfothebeast)

 

[Larryjones]

Look for a selenium rectifier. They are or were common in battery chargers. That thing on the left side kind of looks like one.

 

[Markfothebeast]

I did find this service manual for the C5BT (I believe it's called). Looks similar.

-Markfothebeast-
(www.youtube.com/markfothebeast)

 

[Markfothebeast]

The cap definitely looks blown and oil covered.

-Markfothebeast-
(www.youtube.com/markfothebeast)

 

[Markfothebeast]

Thanks for the offer but I'd prefer to find a parts unit locally if I really want to go that far. Unless you're located in Western WI? I was planning on making it work properly for my dad to learn how to weld with.

-Markfothebeast-
(www.youtube.com/markfothebeast)

 

[Markfothebeast]

The C-3 and C-5/C-B/C-BT all appear to use a 20 MFD 370 Volt Oil Filled capacitor. Can anyone tell me if it is possible to use a larger MFD capacitor with the same voltage rating or higher? I have a couple large microwave capacitors but I'm not quite sure if they are the same type.

-Markfothebeast-
(www.youtube.com/markfothebeast)

 

[Bert_]

Many of the old farm welders had capacitors to improve power factor and lower the line current. They did that to keep from blowing fuses in the old 60A services.

The cord would have had a 10-50P which does have a neutral that would also have been bonded to the frame. You are on the right track with a four wire cord if you want to keep the receptacle, personally I would just use a 3 wire cord and disconnect the receptacle since I've never used it on one of these anyway.

You need to use the correct value, 20 MFD at 370V is a common size and shouldn't be hard to get. You can go higher on the voltage rating, say 440v. A motor shop would be sure to have one, electrical supply might also.

I like these Forney welders, I think they were pretty good in their time.

 

[Markfothebeast]

What would happen if I were to use a different microfarad value capacitor? I'd read an interesting amp draw test with the use of differently sized capacitors. There's quite a large drop in current with a larger MFD value. At least according to the test results.

-Markfothebeast-
(www.youtube.com/markfothebeast)

 

[Markfothebeast]

Somewhere in this post a guy posted the results of using no capacitor and different capacitor values. That's quite a dramatic difference. I'm wanting to understand how the amount of capacitance impacts the welder. I also have a Thunderbolt 225 which uses no capacitor. Perhaps I could add a cap to this unit to lower the draw?

"1. No capacitors, 1.9 Amps at idle with no load and 48.3 Amps while welding with 1/8" rods at 140 Amp setting.
2. 33 microfarads, 4.4 Amps at idle, no load and 8.8 Amps while welding with 1/8" rods at 140 Amp setting.
3. 66 microfarads, 4.5 Amps at idle, no load and 7.2 Amps while welding with 1/8" rods at 140 Amp setting."

The clampmeter is an AC/DC mid range quality uni
https://www.practicalmachinist.com/vb/general/adding-power-factor-capacitors-stick-welder-277967/


-Markfothebeast-
(www.youtube.com/markfothebeast)

 

[Bert_]

On the next page of that article he retries his test and only drops input current by a few amps.

On the Forney I would stick to the original values since I'm pretty sure the capacitor is in series with the winding and a different capacitor could seriously affect the welder. If you try to add one to the Lincoln it would not be critical since you would be adding it in parallel.

 

[Markfothebeast]

I'm only learning by means of the internet here. I would like to have more of an understanding!

-Markfothebeast-
(www.youtube.com/markfothebeast)

 

[Markfothebeast]

The capacitor is wired to one hot leg to the "on" switch and going to a transformer. Perhaps it has it has its own dedicated "start" winding like on an electric motor is what you are saying?

-Markfothebeast-
(www.youtube.com/markfothebeast)

 

[6PTsocket]

The C-3 and C-5/C-B/C-BT all appear to use a 20 MFD 370 Volt Oil Filled capacitor. Can anyone tell me if it is possible to use a larger MFD capacitor with the same voltage rating or higher? I have a couple large microwave capacitors but I'm not quite sure if they are the same type.

-Markfothebeast-
(www.youtube.com/markfothebeast)

The caps in microwaves are closer to 1 mfd at very high voltage ratings. Stick with what is in there, they are not hard to find. The voltage can be higher but do not change the capacitance. The values on those caps are pretty loose tolerance.

Sent from my SM-G900V using Tapatalk

 

[Markfothebeast]

There pretty cheap too. It's about $8 - $12 for a new cap.

-Markfothebeast-
(www.youtube.com/markfothebeast)

 

[Bert_]

The capacitor is wired to one hot leg to the "on" switch and going to a transformer. Perhaps it has it has its own dedicated "start" winding like on an electric motor is what you are saying?

-Markfothebeast-
(www.youtube.com/markfothebeast)

No start winding, the capacitor is just in series with the one winding. Just another way of connecting it. With this method if the value of the capacitor is changed it could affect the current and voltage that the transformer see's.

Sounds like your already planning on it but I would get rid of those wirenuts and clean up the wiring on that cord.

 

[RodneyW]

I have an old Marquette welder that uses that same sort of plug-in lead system I've been intending to get working. I'll be watching this thread closely.

 

[Markfothebeast]

That wiring is definitely going to be replaced with 6/3 50-AMP appliance cord with a 4-prong plug. The ground and neutral will be separated. But for now I'm going to order the capacitor. I will update once I get the new components.

-Markfothebeast-
(www.youtube.com/markfothebeast)

 

[Brandon_oma#692]

I need to replace the capacitor in my Forney c-3. Can anyone tell me if this is correct? https://www.grainger.com/product/DAYTON-Round-Motor-Run-Capacitor-2MEC7 It does not say anything about oil filled. I am clueless about capacitors other than to short them before handling.

 

[Bert_]

I need to replace the capacitor in my Forney c-3. Can anyone tell me if this is correct? https://www.grainger.com/product/DAYTON-Round-Motor-Run-Capacitor-2MEC7 It does not say anything about oil filled. I am clueless about capacitors other than to short them before handling.

How do you know the capacitor needs to be replaced?

As far as the value goes, it should be printed on the side. Sometimes they are hard to read on old capacitors.

That wiring is definitely going to be replaced with 6/3 50-AMP appliance cord with a 4-prong plug. The ground and neutral will be separated. But for now I'm going to order the capacitor. I will update once I get the new components.

-Markfothebeast-
(www.youtube.com/markfothebeast)

Obviously a little late for the OP but for anyone else reading, a #10 cord is fine for almost all of these arc welders. No need to waste money on a big heavy #6 cord.

 

[Brandon_oma#692]

How do you know the capacitor needs to be replaced?

As far as the value goes, it should be printed on the side. Sometimes they are hard to read on old capacitors.
.

Pop bang boom. Side is split open. Forney website says

We no longer carries this capacitor, however they are still available in the market. The part you need, in order to operate the machine safely, is a 20 MFD 370 Volt Oil Filled capacitor.

I can find 20 mfd 370 vac all day long but unsure about oil filled.

 

[Bert_]

Pop bang boom. Side is split open. Forney website says I can find 20 mfd 370 vac all day long but unsure about oil filled.

Any metal cased "motor run" capacitor of the correct value is what you need. Maybe not a big deal for a welder but for the most part I don't even carry 370v caps. 440V caps have better insulation and tend to last longer.

 

[Brandon_oma#692]

Any metal cased "motor run" capacitor of the correct value is what you need. Maybe not a big deal for a welder but for the most part I don't even carry 370v caps. 440V caps have better insulation and tend to last longer.

Awesome thank you