Fixing welding set's built-in battery charger

Hi all,
My welding set contains a 75 amp battery charger, but it doesn't work.
I'd like to fix the battery charger so I can use it for electrolytic
de-rusting and electroplating, but I'd rather not pay for the welding
supply shop to fix it.
The welding set is a Cytringan Bantam 180 amp oil-cooled AC set. I don't
have the digital camera to hand, but it looks very similar to the
Cytrigan set shown at the top of this page, just a little smaller:
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I can take a photograph later if necessary.
My question is, does anyone know what I can expect to find if I open the
welding set, and what the problem might be? I'm assuming the battery
charger uses a single diode to produce half-wave rectified DC. You can
adjust the battery charger current using the same knob used to adjust
the welding current, but the charger current apparently only reaches
about half the welding current. There is a separate terminal for the
battery negative, and you connect the battery positive to the welding
earth. Even with no load, there is no voltage measurable between these
terminals.
I'm guessing that there's a dud diode or loose connection inside. I hope
there's nothing wrong with the transformer (it welds fine). Anyone know
what I might find inside the set, and what the problem might be?
Best wishes,
Chris
PS: Got some 6011 rods on Monday. Will try them this weekend.
Reply to
Christopher Tidy
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What are the symptoms? Does it start up when turned on? Is there a power light? Do gauges move? Is there a contactor inside? What controls it?
If I were you, I would boldly open the case and start following the symptoms and connections with a multimeter. You can, most likely, figure out just what is wrong by using logic, asking pointed questions in this newsgroup and beinf meticulous.
i
Reply to
Ignoramus11916
There are no gauges or lights, and I'm pretty sure there are no electrically-operated contactors inside.
The reason I asked here first is because the machine is really heavy (maybe 250 lbs) and full of oil. Opening it is therefore not an attractive proposition, and it means that my welder will be out of service while I'm trying to fix it. I just thought that perhaps someone could offer some guidance first?
Chris
Reply to
Christopher Tidy
There are no gauges or lights, and I'm pretty sure there are no electrically-operated contactors inside.
The reason I asked here first is because the machine is really heavy (maybe 250 lbs) and full of oil. Opening it is therefore not an attractive proposition, and it means that my welder will be out of service while I'm trying to fix it. I just thought that perhaps someone could offer some guidance first?
Chris
Reply to
Christopher Tidy
There are no gauges or lights, and I'm pretty sure there are no electrically-operated contactors inside.
The reason I asked here first is because the machine is really heavy (maybe 250 lbs) and full of oil. Opening it is therefore not an attractive proposition, and it means that my welder will be out of service while I'm trying to fix it. I just thought that perhaps someone could offer some guidance first?
Chris
PS: Apologies if people receive this message more than once. BT Internet's news server is playing up AGAIN!
Reply to
Christopher Tidy
If the charger doesn't work but the main unit does work, the two usual culplrits are a bad contact on the selection switch or a blown diode.
In most electronic equipment, switches are not much of a problem but welders tend to have high currents, dirt, open design, and not high useage of the switch. Look for cruddy contacts, buff them lightly with some soft abrasive (NOT steel wool!) and see what goes.
Simple ohm meter check from both directions shouls spot a bad diode.
Odds are good you could find the culprit in half an hour of open case diagnostics.
Christ> Hi all,
Reply to
RoyJ
The contacts in this machine are submerged in oil, and there are no vents at all, so crud can't enter. Do you think this makes it more likely that it's the diode that has failed? Would you expect just one diode or four? Any idea what a replacement diode is likely to cost?
If I open the machine, should I also change the oil? The guy at the welding supply store suggested this, but I wasn't sure if it was really necessary, or if he was just trying to make money out of a service. He said something about the oil getting contaminated with moisture.
Thanks for the advice.
Chris
Reply to
Christopher Tidy
OK, ya got me. I've never seen a fully oil submerged welder(only a similar sized pole transformer rated 4130/120/120 at 5 kva). Contacts submerged in oil does not sound like a good thing.
As for diodes, Original equipment diodes may cost an arm, leg, and first born. Suitable replacement diodes can be had for US$10 or less. Unlikely to be an exact fit in the diode block though. Could be just one, 2 in a center tapped setup (both will be blown if you have no voltage), or a full wave bridge (probably blew a couple )
Oil does get contaminated if not fully sealed. If the oil is visibly murky I'd probably want to change it. If not, why bother for home use?
Christ> RoyJ wrote:
Reply to
RoyJ
Maybe I'm just not familiar with the "welder-charger" concept, but in the above paragraph, you stated that you connect the battery positive to the welder "earth". I'm assuming you mean the ground clamp - and I don't believe that would be right. The welder electrode holder would be "positive" probably for this.... BUT like I said, I may be wrong.... Ken.
Reply to
Ken Sterling
I've been told oil makes a better dielectric than air, so there is less arcing as the contacts approach and faster quenching of the arcs that form. OTOH, the oil also should be free of water and crud which presumably starts making it more conductive.
Oil will also move heat out of an assembly faster than air convection.
I have a high voltage relay downstairs, supposedly will switch up to something like 20kv once its oil bath is filled- though I've not actually tried it... :)
Greg
Reply to
Greg Menke
The switch on my big press is supposed to be a oil bath switch. It was made that way so that it would be explosion proof in a fashion. Of course this was a long time ago and it probably came out of a cotton gin/elevator where the dust can cause explosions. My problem is that since I have to keep the press outside the bowl for the contacts will fill with water when it rains. I have to be sure and dump it before plugging it in each time.
Wayne Cook Shamrock, TX
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Reply to
Wayne Cook
Thanks to everyone for the advice. It sounds like the best idea is to cautiously open the case in a clean area, at some point when I don't need the welder for a while, and have some extra oil ready to make up for spillages. I should get the chance to do it in the next month or so.
I've also heard that oil helps to quench arcs at contacts (you got oil-filled circuit breakers, right?) but I wouldn't have thought this would be a problem with a welding transformer as you don't adjust the current while you're welding. I think the main purpose of the oil is for cooling, but it also keeps the inside dry and corrosion free. The set is similar to a pole transformer in many ways, and is also rated at 5 kVA. Fortunately the top opens, so I can get inside without draining the oil. Would you like me to post some pictures if I disassemble it?
I, too, thought of making a diode bridge to connect to the outside of the set, but it seems like a bit of a messy solution. It would be much neater to fix the battery charger. I'm also rather curious to see inside the set myself.
Will keep you informed of progress.
Best wishes,
Chris
Reply to
Christopher Tidy
Any chance this is a PCB oil? Nobody has mentioned it, I'm curious..
John
Reply to
JohnM
Yes, that occurred to me too. I'd guess a welder that is filled with oil might well be in the vintage where PCB oils were common.
OTOH I'm thinking the OP is probably as old or older than me. At this stage, what's a few minor carcinogens amongst friends.
Reply to
xray
According to the data plate, the set is filled with Shell Diala B oil, which as far as I know is not a PCB oil. Perhaps someone can confirm this?
Chris
Reply to
Christopher Tidy

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