Arc welder diode?

[Steverlord]

Hi everyone,
I currently own a Century AC230 (see pic).


I'm going to get a Century ACDC 230/140 (see pic)


for very cheap but the seller says the welder "needs a diode".

I don't know what a diode is, what the price would be, or if I could even FIND one for this particular welder.

Any thoughts on where I might get a diode for this welder?

Thanks in advance!

[SweetMK]

A diode lets current flow one direction,, kinda like a valve,

AC current goes back and forth (like a swing) 60 times a second,,

The diode(s) redirect the current flow from AC to DC,,

When you open up the welder,, you will see these diodes,,
they probably look like this



The one in the pic is 200 amp rated, and it costs $16 on Amazon,,,

[Steverlord]

Oh man this is great! Thanks for showing me this.

So if the welder is 230 amperage the diode needs be around 230-200 rate?

Again, I'm a beginner.

[SweetMK]

If you look at the pic you posted,, the DC output is 140 amps,,

If I was doing it,, I would probably use 300 amp diodes,,
or, when you open it,, look at the rating on the diode in there now,,,,,,,,,,,,

[Steverlord]

Yes. Of course 140 for DC and therefore 200 or even 300 diode.

I'm going to take your suggestion and simply match the rating of the original diode with the new.

I think I'm getting it ! ����

[Insaneride]

A FULL WAVE RECTUMFRIER uses four of those diodes that SweetMK showed and usually for that type of package two will be case positive and the other two case negative. The reason is for easy mounting to a common heat sink. I suggest you open it up and see whats inside the box.

Heres an example of a different package in 150 Amp

https://www.amazon.com/s?k=bridge+di..._ts-doa-p_2_12

The 200 amp version should be fine because two diodes are used per half wave and in my mind that gives 400 amps per half wave should you decide to use single diodes.

[yooper]

If it's a full wave bridge , 140 amp DC output , the diodes need to be a minimum of 70 amps , a slightly larger would be ok , 100 amp at the max...

[Louie1961]

I wouldn't go with anything more than 100 amp diodes. You gain nothing by going higher. I bet that machine actually has 70 or 75 amp diodes.

[Steverlord]

Yes. Understood. Thanks for your help and the link!

[yooper]

OEM diodes are 70 amp ,

https://www.centurytool.net/860_476_...60-476-666.htm

Link to manual ,

https://c.searspartsdirect.com/mmh/l...M/L0805389.pdf

[Louie1961]

OEM diodes are 70 amp ,

https://www.centurytool.net/860_476_...60-476-666.htm

Link to manual ,

https://c.searspartsdirect.com/mmh/l...M/L0805389.pdf

This post probably needs to be made a sticky. Such good info here.

[Insaneride]

Good links yooper. Those 70 amp diodes for 100 amp mig are unavailable tho. The manual was dated 1999 but I thought that was a 1970's machine. Semiconductor technology has advanced a long way since then so the 200 amp diodes SweetMK showed will work just fine if they fit. The manual shows the diodes as all the same polarity using three different heat sinks for polarity. Using a higher amp rating would be an upgrade and last longer imo. I recently replaced some SCR's and DIODE's in a motor control pcb. The originals from 20 years ago were 400Volt but the replacements in same package are improved 600Volt for a 180VDC motor. Advancement in technology has come a long way in 20 years. The most important thing for replacement is fitup to the heat sinks as long as the diodes are rated for minimum of 70A anything higher is an upgrade.

[StandarDyne]

I've never done it, but isn't there a simple way to test diodes with a VOM meter? (In case you only need to replace one of the four diodes...)

[Insaneride]

Yes you can test diodes but its a good idea to replace all four with matching diodes. If one failed the others arent going to be much better.

Testing diodes with an Ohmeter works but they are non linear and you will get different readings using different ranges on a Ohmeter. Some DVM's have a DIODE range that measures voltage drop. For Si voltage drop should be 0.707 volts but Ive seen newer diodes drop 1.4 volts.

[whtbaron]

You got me looking... I found this Youtube had a bit more explanation....

[yooper]

Good links yooper. Those 70 amp diodes for 100 amp mig are unavailable tho. The manual was dated 1999 but I thought that was a 1970's machine. Semiconductor technology has advanced a long way since then so the 200 amp diodes SweetMK showed will work just fine if they fit. The manual shows the diodes as all the same polarity using three different heat sinks for polarity. Using a higher amp rating would be an upgrade and last longer imo. I recently replaced some SCR's and DIODE's in a motor control pcb. The originals from 20 years ago were 400Volt but the replacements in same package are improved 600Volt for a 180VDC motor. Advancement in technology has come a long way in 20 years. The most important thing for replacement is fitup to the heat sinks as long as the diodes are rated for minimum of 70A anything higher is an upgrade.

I saw they were unavailable but posted it to show the oem were 70 amp , any generic diode will replace them .

[Steverlord]

Hey everyone, OP here. Very grateful for everyone taking time to help out.
Hoping to get the 230/140 running with new diodes by end of week.

Thanks again!

[Steverlord]

Wow! Prices on diodes vary greatly. From one single diode at $155 ...to a pack of five diodes for $15.

Curious: Is there a reason for the huge price difference? All were 100amp rated.

Anyway, thanks for all the help.

[ktech]

Diodes, in addition to an amperage rating, also have a voltage rating and a power dissipation rating.
I'm guessing the lower cost diodes have much lower power rating.
The power rating specifies the diode's ability to with stand the heat generated when there is current in the diode.
All diodes have a voltage drop when current is flowing in the forward direction. This voltage times the current will represents the watts generated.
The heatsink is to dissipate these watts.
Ktech

[Insaneride]

Wow! Prices on diodes vary greatly. From one single diode at $155 ...to a pack of five diodes for $15.

Curious: Is there a reason for the huge price difference? All were 100amp rated.

Anyway, thanks for all the help.

Plus one on what ketch said but also supply and demand and advanced technology is on your side with amazon_ supply.

Also, some of that package style comes with a pigtail some don't. I see 5 pairs or ten diodes for $15 but no pigtails so you would have to use your old pigtail and solder or buy with pigtails for $15 each.

You need to know the bolt size for your heat sink. I measured a similar diode that was 1/4-28 but it 35 amp so the 70 amp could be a larger bolt size. I'm sure those 200 amp are close to 1/2" bolt.

[Sberry]

Someone told me,,,,,,,,,,,,,,,,,,, is often poor troubleshooting.

[Insaneride]

Someone told me,,,,,,,,,,,,,,,,,,, is often poor troubleshooting.

Some one told me that strawberry wine will make you go blind.


For the OP, it looks like your diode package is DO-5 or 1/4-28" threads. Measre the studded threads for 1/4". You can get them in 85 amp in that package but the 70 amp seems more common. I think EBAY_ has them in 100 amp DO-5 but better deals on Amazon_ for 70 amp. Be sure to order the correct polarity. I think yours are case negative but verify. I didnt see any with pigtail leed so you will have to reuse the old one. The torque is 25-30 inch/lbs and I would use heat sink grease or mica washers or both. It will help them last longer.