Diodes

[domains]

What size Diodes would I need to covert AC to DC... does amp of the Diodes matter?
12A 200V expl... what am I looking for Need 4 diodes
.
120v welder capacitor 20mf 450v... No load about 46v

could I get 80amps of DC out of this?

Found this here.... http://www.machinebuilders.net/forum/forum_posts.asp?TID=4067&PN=1


Looks kinda easy... but is rated for a 240v welder

 

[shenion]

They will need to handle the full output current of the welder. So, for a 140 amp welder, they will need to be 140 amp diodes.

The output voltage will not change, it should be stated in the manual or on th e specifications plate on the welder.

This thread may be help on doing the change.

 

[domains]

Cool thx... And I don't have to change my capacitor right? plus it will help I think?

Checking link you posted

 

[shenion]

Read the thread. The existing capacitor is on the input side. You will need several on the output side.

There is more than just diodes. There are filter caps for noise and to protect the diodes; heat sinks for the diodes (4 diodes.) Also, a reactor and surge suppressor. Large capacitors can be used to increase the arc stability.

You will probably spend more converting it than you did on the welder.

 

[domains]

The link I posted had no filter caps... or maybe I don't understand what they are?

I can get 4 diodes cheap here.

 

[shenion]

They are there to protect the diodes and also reduce emitted noise.

When you break the arc, the voltage will go up to a huge voltage to try and maintain the arc. Similar to how a old points car ignition worked. The voltage will go high enough to cause the diodes to break down and become a short.

I bet the guys in the thread have mysterious diode failures and their VCR's start flashing 12:00 any time they use the welder.

Where they go is shown in the thread i linked to.

 

[domains]

In this kit... http://www.proto-power.com/dc_cheater.html

theres 12 diodes but no caps.

 

[shenion]

Just because it has no diodes does not mean they are not a good idea. Go look at the schematic for any professional arc welder (and most MIGs), you will see 4 diodes across the rectifier bridge.

 

[eddie49]

In your previous post, shenion, I'm sure you meant to say "capacitors", not diodes....

 

[shenion]

yes, capacitors.

 

[domains]

I talked with a machinist today that tried diodes without filter caps and said it was almost like welding AC...
he said its not worth it. He said the voltage would jump.

thx for tip.