Ac/ Dc Ark Welder

scarecrow · Aug 16, 2008

I have the thinking of buying a DC ark welder I came across this one on eBay
http://cgi.ebay.ie/ARC-WELDER-MMA-W...yZ113743QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
I was wondering if anybody had one of them they look very cheap

I have also been toying with the idea of converting my AC too DC but I can't find any decent plan for doing this there seems to be a lot of theories on how to do this from the very simple to the very complicated and hard to find out just how successful it is :confused:

any help would be welcome

GeorgeB · Aug 16, 2008

If you are primarily interested in the DC side of things, you can get an inverter welder even cheaper than that. I paid £59 for mine. It only goes up to 70 amps and it will not do AC but so what? My transformer based arc welder meets my needs for AC and higher amperages.

My main objective in buying my DC inverter was to try TIG welding thin plate on the cheap. What's your main objective for DC? For normal arc welding, I've decided I prefer AC.

Mikey D · Aug 16, 2008

Have you seen the duty rating

nuff said

shenion · Aug 16, 2008

Another "Giant" welder. Others have reported poor support from ebay sellers of these.

Converting AC to DC requires adding a suitable bridge rectifier, some caps and protection devices. An additional reactor will help too.

It depends on how your welder is designed. Some are easy to modify (those with a separate reactor.)

The hard part is the diode bridge. They are expensive and you need ones well over the rated current of the welder.

GeorgeB · Aug 17, 2008

shenion said:
The hard part is the diode bridge. They are expensive and you need ones well over the rated current of the welder.

Sources might include an old MIG welder which has failed in some way but still has a good diode module and a few other useful bits, perhaps.

Can you use diodes from an automobile alternator? These will do high currents, presumably, but can they handle much more than 14 volts?

scarecrow · Aug 17, 2008

I had noticed the duty cycle and thought it looked a bit small the reason for buying or converting is that DC seems to produce better Welds especially for out of position welding the only problem is most of my out of position welding is done on machinery and I would need about 200 amps for some of the heavier repairs

The ark welder I was thinking of converting is just an air cooled to 260 amp
it is just your typical air cooled welder has anybody got or know where I could get a wiring diagram with all the parts and the order they should go in

shenion · Aug 17, 2008

GeorgeB said:
Can you use diodes from an automobile alternator? These will do high currents, presumably, but can they handle much more than 14 volts?

It depends on the type. Some use diodes that will avalanche over about 20V.

I have a Motorcraft 200A alternator in my DIY welder. I tested it by hooking it up to 120VAC through a resitance. I was surprised to see it handled the 160V P-P signal with no problem. I have it outputing up to 45 OCV for welding.

Older alternators tend to be a bit better. Cards typically have 150V spikes on the power (caused by solenoids, or motors turning off.) So they should be able to handle the voltage. If you can find a cheap used alternator, then it might work. However for 200A, you will need to find a real heavy-dudty alternator (most are less than 100A.)

scarecrow · Aug 17, 2008

While having a look around I came across one of these rectifiers http://www.gallawa.com/microtech/diode.html I am just wondering if they would be suitable

shenion · Aug 17, 2008

That link is about testing some HV rectifiers. Not any particular part.

scarecrow · Aug 17, 2008

shenion said:
It depends on the type. Some use diodes that will avalanche over about 20V.

I have a Motorcraft 200A alternator in my DIY welder. I tested it by hooking it up to 120VAC through a resitance. I was surprised to see it handled the 160V P-P signal with no problem. I have it outputing up to 160V P-Pfor welding.

Older alternators tend to be a bit better. Cards typically have 150V spikes on the power (caused by solenoids, or motors turning off.) So they should be able to handle the voltage. If you can find a cheap used alternator, then it might work. However for 200A, you will need to find a real heavy-dudty alternator (most are less than 100A.)

now you loss me 120VAC 160V P-P 160V P-P has left me stretching my head I've tried to find out what that is all about but to no avail starting to feel like im in over my head I thought I could just buy the parts and build it myself
the rectifier I was trying to show you was from a microwave but it looks on the small side

scarecrow · Aug 31, 2008

Doing loads of research on this one trying to figure it out and is starting to look simple-ish I couldn't find a bridge big enough for what I wanted so have decided to build my own I found these diodes and I'm just wondering if they are suitable http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=360079324780&ssPageName=ADME:X:RTQ:US:1123 I couldn't get any in reverse polarity so if I wire them this way it should be the same thing

I also found this reactor coil http://surpluscenter.com/item.asp?UID=2006092120542394&item=1162&catname= which I think would be suitable any help is very much appreciated

shenion · Sep 1, 2008

Looks good, be sure to have a good size heat sink. Rather than wires, you can use flattened copper pipe (3/4" will do) as bus bars. You can do two bars horizontally as the A/C input and two vertical as the + and - outputs. One side of each diode bolts to one bar, the other will be soldered in a hole drilled through the opposite bar.

Surge suppression would be a good idea, some MOV's on the input and output would help. A motor run capacitor (4 to 20uf) on the +/- output side will help also (one on the AC input side will help prevent emitted noise.) The more capacitance on the output side, the better. I have 69,000uf on my generator/welder (three, 23,000uf caps in parallel.) That really increases the arc stability and makes arc starting easier. The caps need to be rated for twice the AC voltage.

The reactor looks good, wish I had found on rather than make one; the wire used cost me about that much. If you use caps on the bridge, then you will need a reactor.

scarecrow · Sep 1, 2008

I have ordered the diodes got them for $21 each I have also ordered the reactor now I just to keep my eyes open for some heat sinks I'm not sure how to wire the reactor I have downloaded the hobart stick mate manual
http://www.hobartwelders.com/om/0900/o950b_hob.pdf and I'm still not 100% sure also I don't see any capacitors on their welder I can pick up motor run capacitors locally is there a difference between starting capacitors and run capacitors and I'm not sure what a MOV is or what it does or what size I would need

shenion · Sep 1, 2008

Start capacitors are only rated for starting up (intermittent use).

Run capacitors are rated for continuous use.

The reactor goes in series with either the + or - output; after the capacitor.

MOV - Metal Oxide Varistor

A MOV will clamp voltage spikes that may cause the diodes to break down. A 200-400v will do. Here's what one looks like.

In the schematic of the Stickmate, Z1 is the reactor. You can also see the MOV across the output (double triangle part across R.)

It has caps across all 4 diodes (probably 0.5uf.) One across the output will help. Using 4 helps eliminate radiated noise.

scarecrow · Sep 1, 2008

I'm not sure what voltage the welder is . With these capacitors do http://cgi.ebay.com/100uF-100-uF-10...Z4662QQcmdZViewItemQQ_trksidZp1742.m153.l1262
and these ones for the Bridge http://cgi.ebay.com/ws/eBayISAPI.dl...Track=true&ssPageName=VIP:watchlink:middle:us how do I measure the voltage of the welder

shenion · Sep 2, 2008

The welder is probably 90VAC or less. You want 250V or higher caps.

Both those you listed are low current caps.

You would want a metal can, heavy duty. Something like this.

I used big, screw-terminal, computer grade caps on my Miller similar to these. I have 60,000uf bolted to buss bars (2 caps in parallel.) Makes the arc a soft hiss.

They are expensive, new they are like $45/each. You can find deals used ones.

You can use four 0.5uf 250V caps, 1 across each of the diodes. Look for ones with metal cans and leads.

Your profile shows Ireland but you post links to the US ebay. I woudl think there would be more deals there.

scarecrow · Sep 3, 2008

hi shenion I have been searching for capacitors and came up with these http://cgi.ebay.ie/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWAX:IT&item=150288006217 the 0.5uf 250V caps are harder to find I found some but don't think they are suitable http://cgi.ebay.ie/FENDER-TELECASTE...ryZ42455QQssPageNameZWDVWQQrdZ1QQcmdZViewItem http://cgi.ebay.ie/DS28023-CAPACITO...47363067QQihZ007QQcategoryZ4660QQcmdZViewItem http://cgi.ebay.ie/ws/eBayISAPI.dll...Track=true&ssPageName=VIP:watchlink:middle:ie some of the capacitors are both start and run and there is also AC/DC capacitors I presume it doesn't make a difference. is 50uf 50000uf on the capacitors I hope it is or I'm going to need a lot of
them and I can't seem to find a MOV anywhere overhear American eBay seems to have a much greater choice thanks for all your help so far

shenion · Sep 3, 2008

6 of the last ones will do across each of the diodes to prevent radiated interference. 1 each on the AC in and DC out will help too.

The 0.5uf caps will help protect the diodes and get rid of noise. Large caps, will increase the arc stability as it maintains the current between AC cycles. It also provides a surge of current for starting the arc. You would need several orders of magnitude to have much effect. My miller has the 4 0.5 uf caps like the last link but I added 60,000uf to increase the arc stability.

Search for "Metal Oxide Varistor". Usually are about $1 each

scarecrow · Sep 5, 2008

I was just wondering how to wire everything up when I have all the parts put together am I anywhere close with this diagram

something doesn't seem quite right

shenion · Sep 5, 2008

I assume you mean 0.5 uf instead of 75 fu

Looks fine.

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