Can a bridge rectifier be replace with a different type machines rectifier ?

[Welder Crafts]

Hello I got a MIG Welder that has a fried Bridge Rectifier or what I believe may be a bridge rectifier.
It has about 15- 20 diodes.
Would I be able to use a different type MIG welders Bridge rectifier instead of trying to source an original?
Don't know what brand welder it is not much info on it
All that is written is Special Car MIG 120. l
I've tried getting a wiring diagram but no luck with Google unfortunately.

Any help is appreciated thanks

 

[gaz1]

you can strip it and check each diode replace whats needed

Cebora Magna 150 Special Car

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[Welder Crafts]

I was thinking to do that but the diodes seem to be press fit and kinda having trouble finding them online

 

[Welder Crafts]

 

[gaz1]

 

[mtt.tr]

As long as it can handle the current crack on

Only thing that I can see being wrong would be the voltage drop

 

[graffian]

look for car alternator diodes.

 

[Welder Crafts]

I'm trying to find the same diodes as the originals.
Can anyone give me some insights?
The Diodes are Marked M or a Motorola looking M then TV 256R

 

[Welder Crafts]

look for car alternator diodes.

Them alternator diodes look similar to the ones that are on my bridge rectifier. Only prob now is finding the right one

 

[eddie49]

Generally I would not recommended "fixing" these multi-diode rectifiers.
It is likely that more of the original diodes will fail. Sometimes they go short or open, other times the pigtail leads just fall off, maybe due to some kind of metal fatigue?
In theory all the diodes were originally matched, so that they have the same forward volts drop ( as mtt.tr suggested ) - and therefore resistance, in order to share the load current equally. The diodes would at least have all come from the same batch.
Some of the diodes may have "reverse polarity" - the case is the anode - so you may have to source two types.
They are not easy to press into the plates - do not use a hammer! When stripping and re-assembling the plates, the shouldered insulating washers often break up.
Complete replacement rectifiers are available on eBay - search "MIG rectifier", e.g. from the Seller "yorweldsupplies", who are Tech-Arc in York. Otherwise you could risk possible VAT, duty & handling charges on importing a cheaper Chinese one ( e.g. from eBay or Alibaba ), or build one out of paralleled diode bridge blocks:

Replacment Rectifier for MIG Welder

I have a 250 Amp single pahase Mig Welder which had a diode short circuit in the rectifier. The replacement rectifier was available but...

www.boatdesign.net

 

[Ross365]

A basic bridge rectifier consists of a minimum of 4 diodes, so any more than that and they are just running diodes in parallel to enable a higher current.
The current capacitor of diodes has increased enormously over the years, so that for a given physical size, modern diodes pass much more current than old ones.
Finding the old ones may be very hard now, and there is not much point in doing that. I think you have to find out what was the current and voltage ratings of your existing diodes were to move forward. I'll ask some mates I have who are in to this sort of stuff.

 

[Welder Crafts]

Generally I would not recommended "fixing" these multi-diode rectifiers.
It is likely that more of the original diodes will fail. Sometimes they go short or open, other times the pigtail leads just fall off, maybe due to some kind of metal fatigue?
In theory all the diodes were originally matched, so that they have the same forward volts drop ( as mtt.tr suggested ) - and therefore resistance, in order to share the load current equally. The diodes would at least have all come from the same batch.
Some of the diodes may have "reverse polarity" - the case is the anode - so you may have to source two types.
They are not easy to press into the plates - do not use a hammer! When stripping and re-assembling the plates, the shouldered insulating washers often break up.
Complete replacement rectifiers are available on eBay - search "MIG rectifier", e.g. from the Seller "yorweldsupplies", who are Tech-Arc in York. Otherwise you could risk possible VAT, duty & handling charges on importing a cheaper Chinese one ( e.g. from eBay or Alibaba ), or build one out of paralleled diode bridge blocks:

Replacment Rectifier for MIG Welder

I have a 250 Amp single pahase Mig Welder which had a diode short circuit in the rectifier. The replacement rectifier was available but...

www.boatdesign.net

I was looking to replace all 24 diodes with stud type diodes.
On this rectifier all the diodes are the same

 

[Welder Crafts]

A basic bridge rectifier consists of a minimum of 4 diodes, so any more that that and they are just running diodes in parallel to enable a higher current.
The current capacitor of diodes has increased enormously over the years, so that for a given physical size, modern diodes pass much more current than old ones.
Finding the old ones may be very hard now, and there is not much point in doing that. I think you have to find out what was the current and voltage ratings of you existing diodes were to move forward. I'll ask some mates I have who are in to this sort of stuff.

That's what it looks like on the actual rectifier 6 run in parallel for each side totalling to 24 meaning 12 for the input and 12 on the output side.
My issue now is finding the value for the existing diodes so I can find a similar replacement that I can bolt onto the rectifier plates

 

[mtt.tr]

If I was going for the cheap option I would make my own stud mounted array.

 

[eddie49]

I was looking to replace all 24 diodes with stud type diodes.

That is certainly an option. You may not need 24. The original assembly used 6 diodes per "effective" diode, which for a 120A MIG means a 20 Amps rating per diode. You can probably source modern 40-Amp small stud diodes. When fitting them, you may find that you have to increase the spacing between the aluminium plates, or drill clearance holes for the anode tags.

 

[mtt.tr]

That is certainly an option. You may not need 24. The original assembly used 6 diodes per "effective" diode, which for a 120A MIG means a 20 Amps rating per diode. You can probably source modern 40-Amp small stud diodes. When fitting them, you may find that you have to increase the spacing between the aluminium plates, or drill clearance holes for the anode tags.

I had a quick look on rs and found some 60a diodes for £8 EA.

 

[Ross365]

This is all very do-able, just needs a sound plan. Assuming you buy new diodes, best check what their needs are in terms of heat sinking, but it's almost sure to be less than the old ones. I mailed a mate asking for info on the old ones.

 

[eddie49]

I had a quick look on rs and found some 60a diodes for £8 EA.

Yes, but then you could get 8 of these, putting two in parallel at each diode location for a 140 Amp bridge, for less than 23 quid including postage:

1 x 70HF120 70A 1200V High power rectifier metal stud type rectifier diodes BE | eBay

Find many great new & used options and get the best deals for 1 x 70HF120 70A 1200V High power rectifier metal stud type rectifier diodes BE at the best online prices at eBay! Free delivery for many products.

www.ebay.co.uk

 

[mtt.tr]

Yes, but then you could get 8 of these, putting two in parallel at each diode location for a 140 Amp bridge, for less than 23 quid:

1 x 70HF120 70A 1200V High power rectifier metal stud type rectifier diodes BE | eBay

Find many great new & used options and get the best deals for 1 x 70HF120 70A 1200V High power rectifier metal stud type rectifier diodes BE at the best online prices at eBay! Free delivery for many products.

www.ebay.co.uk

Crazy how cheap stuff like this is now.

 

[Welder Crafts]

I had a quick look on rs and found some 60a diodes for £8 EA.

Wouldn't the 60 amp diodes cause a difference within the lower mig welding settings? Or does it not make much of a difference?