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Hobart Handler 120 Welder - No Arc

Pete Deets

Subscriber
Last Subscription Date
01/01/2020
Connect a 12v battery charger to the cap's terminals, again with appropriate polarity. Observe the voltage rise. Once it has ceased rising, disconnect the battery charger, and observe how voltage drops. If it drops fast, there's an internal leak. If it drops slow, there ain't.
A good idea but I'll throw out a suggestion for a tad bit of safety: Try to put a 12v headlight bulb or turn signal bulb in series with the battery as you charge the cap. If the cap is good you may get a little flash of light from the lamp. If the cap is shorted then the worst that will happen is the light will stay lit.

If you try this without the lamp and the cap is shorted then in very short order you'll let the rest of the magic smoke out of it accompanied by a very big BANG:yikes:and a shower of paper & foil confetti (don't ask). This is know as "peanut buttering" a capacitor...........:wave: ...........PD

Editing to add that if the lamp stays lit disconnect it fast or you'll find out what the insides of the capacitor look like..............PD
 
Last edited:

DKamp

Registered
Naw, Pete- not with a 12v battery charger.

That electrolytic cap's rating SHOULD be somewhere in the range of 50-80V, with a bleeder resistor (usually lame) and a ceramic disc capacitor to snub HF noise to protect the cap from high ESR.

If the cap goes Happy Birthday from a 12v battery charger, it was certainly way-junk to begin with... and it would POSITIVELY gone party-mode long ago during Kris's tests by simple virtue of the machine's operation- when you activate the machine, it goes full-zoot into that capacitor... at much higher than 12v, and much more current on-tap than a half-wave center-tapped EI core the size of your fist.

The battery charger's inherent limiting will not pass enough current to damage itself either. It will give a little spark, the needle might slap the peg, and that'll be the most of it.
 

Pete Deets

Subscriber
Last Subscription Date
01/01/2020
OK dkamp, if you say so. I will offer that the fellow at the bench next to me in Electricity class (over 40 years ago) would give a different answer through personal experience. He cleaned up most of his mess but there were floaties in the air all that day.........:wave:............PD
 

DKamp

Registered
If he detonated an 80V electrolytic cap using a 12v supply that was inherently current-limited, it was because his terminal polarity was reversed. Kris's hands have been through many learning experiences, they will NOT make that mistake... but you can rest assured that even if she WERE to do it, it would not be anywhere near the worst thing that'd happened in her lifetime. We can only hope that if she does, she's bold enough to send us a photo of her sporting a confetti'd tin-foil hat... it's perfect for Arizona, especially during the 'RV' time of year... :jester:

I used to teach people how to troubleshoot and repair 3-phase AC drives in electric passenger railcars... we intentionally blew electrolytic capacitors of the 1200v category as part of our safety demonstrations. One capacitor, enclosed inside an otherwise empty equipment box, fired off by a controlled power supply, so that students would intimately understand, and respect this scenario. Electrolytic capacitors can explode, but it is not 'easy' to do. Usually, when one fails, it's in a linear supply downstream of a failed bridge rectifier- it's getting AC.

And an aside note, for anyone who ever wondered:

A typical automotive 12v battery charger, connected properly, will NOT fire an 80v electrolytic. T=R*C where R is also Z of the transformer's output (Z = R + X, in this case XL). Most automotive battery chargers' transformers exhibit about 0.5 ohms of resistance, and at 60hz, XL is about 0.25ohm... so net output is about 20A.... but unlike the welding transformer, the cross section of the battery charger's EI core is typically under 44 square inches, so you'll be saturating somewhere around (5.58*44=) 250vA or so... which 'mathematically' yields 25A at 10V, but in reality, the core losses go so high that 16A will be about all it's worth. This is entirely intentional in the design... as it 1) 'helps reduce' the likelyhood of the unit's self-destruction under 'dead short' output (a totally discharged battery, or an errant short while connecting leads, as well as a reversed polarity to a charged battery), and 2) helps prevent someone from mindlessly hammering an incendiary voltage and current thrust into a plastic box full of hydrogen gas saturated in sulphuric acid.

I noted 'helps reduce', because wet-cell automotive batteries go critical much more often than anyone would like, and it's MUCH more serious an occasion than an electrolytic's graduation ceremony. There's an unfortunate reality of wet cells that electrolyte, when discharged, can freeze, distorting plates and fracturing busbars. When one decides to connect a charger, the battery 'seems' fine... and charges... and once enough hydrogen gas builds up, the damaged internals grant you a spot in the evening news, terrible ringing in the ears, and freckles that match the locations of hundreds of holes in your workshop clothes. It's a gift that just keeps on giving... So much moreso than a capacitor impersonating the Outback Bloomin' Onion.
 

Pete Deets

Subscriber
Last Subscription Date
01/01/2020
I wasn't worried about Kris but more wanted to introduce the idea of current limiting for someone quickly skimming through the thread and only seeing
Connect a 12v battery
and not seeing the word charger.

Yes, higher voltage supplies can make parts fly quite a ways and in the AM, FM & TV transmitters I have & do maintain the most interesting damage has always been Ma Nature - lightning. Things vaporize that you never would have thought possible. I'm sure in the transit world you've seen your share too. Right now the beam voltage supply in the TV transmitter I care for is rated for a maximum output of 36,000 V at 2.6 A dc steady. Only 91Kw. My goal for the day is that everyone still be able to count to 10 when they go home (or at least as far as they could count when they came in).

Fortunately I've never witnessed a wet cell go boom nor do I want to but I have seen a couple of camera bags go up in flames when a camera battery and even a 9 volter were carelessly tossed in with a spiral bound reporters' notebook that used a metal spine. Lots of stink there!

Well, so much for thread drift & I apologize for paddling down that stream.

Kris, please let us know how things come out..................PD
 

DKamp

Registered
Well, Pete... Imagine a 'little' 4-1000A tube, with 7.5kv on the plate, filled with uh....
... No, I'm not gonna suggest the actual contents... just 'something liquid, with LOTS of chemical energy'...

That's the kind of event that an 8D truck battery generates when it celebrates independence day. Nowhere near WLW's output, but nothing you want to in any proximity of. We set up demonstrations with old railway glass cells, always at a very great distance from the facility... and it really doesn't matter what TYPE, when a battery goes, it is NOT pretty. During WW2, Coast Guard Auxiliarists in sailboats were incredibly effective at crossing paths with enemy submarines, because they were effectively silent. Never happened that I'm aware of, but my flotilla commander always kept his flare gun loaded with a WP parachute flare, and if he ended up facing, his action would have been to send the flare (possibly even the whole launcher) down the hatch, as that phosphorus was going to ignite a whole host of things, particularly the batteries, in seconds. Kinda like dropping a fresh 9v in a pocket full of change... things go from whimsical to critical in just one heartbeat.
 

landreo

Registered
MIG or wire feed liners can be cleaned easily with an air gun, carb cleaner and some welding wire. That may be all that is needed.


Capacitors can be tested safely with Pete Deets' method, it is a good way to do it, i.e. slowly. I think it would be rare for a good capacitor to explode from anything other than over voltage and rare for a bad capacitor to explode from a 12 volt home battery charger but there is still a small chance which is the reason for a slow charge and discharge through a light bulb but again, the chance of something going bad through a quick charge is small. . With me, old vintage radios and such just get their capacitors replaced without testing since I assume the old paper and old style electrolytic capacitors are bad. I have a capacitor tester but unless a newer style electrolytic is visibly damaged then I assume it is good. The newer electrolytics rarely fail without some visible evidence. I will occasionally test a newer capacitor based on symptoms even if it looks good but not often.

A home battery charger will not self regulate through saturation of the core.Just the opposite. A saturated core will loose inductance and cause the primary current to increase and burn the wires and insulation. In general, it is not possible to saturate the core by a resistive load on the secondary. It will overload the secondary and primary and cause the transformer to overheat but that is not due to nor is it prevented by any core saturation. A reactive load may cause core saturation but not a resistive load. Do not think you can override the thermal protection and short the secondary without consequences. The transformer will not self regulate.

Some transformers are made from heavy enough wire that they could survive a dead short for a time, welding transformers are one type. There also are some old style specialty battery chargers, golf cart and forklift chargers, that have a separate third winding and a capacitor so they will self regulate through a type of localized saturation. They will typically make a loud hum that decreases with load. These ferroresonance transformers are not very common. The also is a type of magnetic regulation using a magnetic shunt commonly used in microwave oven transformers. I made an armature growler out of a microwave oven transformer and had to remove the shunt. Because of that it would not regulate and would then saturate the core easily. I had to limit the primary voltage to around 40 volts to keep it from melting.

Saturating a transformer core, in general, is not desirable but it comes from high primary current not a resistive load on the secondary. A saturated transformer core, in general, is not a means to self regulate nor a means to protect from an overload.
 

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