run capacitor terminal wire melting

I have a RPC, and I smelled something burning, turned out to be one of the run capacitors wire was melting, its one of 12 capacitors in a series. Is this capacitor bad and need replacing or is something else causing this. It hadnt been running but 10 mins or so.

I'd have to suggest that it's definitely a clue......

And, they make ohmmeters for that....

Have you disconnected that cap and measured it for capacitance and/or ohmmeter resistance?

1) capacitance should measure near what it is labeled

2)the ohmmeter should eventually settle down at an open circuit (it will measure a short at first, until the cap charges up.... assuming it ever does, which is doubtful)

jaddy said:

... its one of 12 capacitors in a series ...

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Wait, what???
Is this some kind of a home-brewed kluge job? Why 12 caps in series?

Sounds almost as though someone could not find the right capacitance value, so they wired up 12 in a row and added them together. Unfortunately the CURRENT flowing through them all is still the total it would be for one, so if they used smaller caps, they likely could not handle it. That wire was probably just the weakest link.

Jraef said:

Wait, what???
Is this some kind of a home-brewed kluge job? Why 12 caps in series?

Sounds almost as though someone could not find the right capacitance value, so they wired up 12 in a row and added them together. Unfortunately the CURRENT flowing through them all is still the total it would be for one, so if they used smaller caps, they likely could not handle it. That wire was probably just the weakest link.

Click to expand...

I tend to be a little tolerant of descriptions.... a "series" of capacitors could be a row of them which are actually connected in parallel. or not.

12 in series would have to individually be so large (12x the needed value) that I discounted the possibility. Maybe that's being too ?????

As JST and Co have implied, if the capacitors are connected in parallel, that one's definitely bad. Cut it out and replace it.

Check the capacitor that has the wire that is melting. JST details how in post #2. If it checks out, replace the wire. I have replaced wires in several "factory built" RPC's that are not crimped properly.

Bill

I checked the cap, it was ok. Guess, bad connection, cleaned it working fine. Thank for the help

jaddy said:

I checked the cap, it was ok. Guess, bad connection, cleaned it working fine. Thank for the help

Click to expand...

It will likely happen again. I had that issue with a 10hp converter I built about 12 years ago that is still in daily operation at my friend's home shop.

The problem is the wires at the end of the parallel string have to support the total amp load from all the caps combined whereas the wires at the front of the string of capacitors only take the amp load from one capacitor. Proper wire crimp will only delay the problem and not solve it as the total amp load turns the top of the capacitor into a heating element. Last capacitor of 4 was burning the spade terminals out about every 6 months or so.

Easiest solution that solved the issue for good was to eliminate the daisy chaining of the capacitors and run separate wires from each capacitor to a central terminal block. This way, the wires and the crimped spade terminals had to only carry the amp load from one capacitor vs the total load.

That^^^^

Spades also have a current limit, which is around 30A or so... More than that and you need to do something else.

The wire is hot...

jaddy said:

I have a RPC, and I smelled something burning, turned out to be one of the run capacitors wire was melting, its one of 12 capacitors in a series. Is this capacitor bad and need replacing or is something else causing this. It hadnt been running but 10 mins or so.

Click to expand...

Heh heh...

Troubleshooting is so much fun!

So I see he's already figured it out, but I'll throw in my two cents' worth...

When troubleshooting, look at the symptom without prejudice.... meaning...

The wire is melting because it is hot. Now, take it from there... the next clue, is that the wire is hot.

I had a guy with a locomotive... not a passenger, but a work-train... and a certain fuse kept blowing on one of the traction inverter systems... it had two (one for each end), and only the one end would blow. He had the truck (bogey) with the motors rebuilt... changed the trucks, changed all the GTO's (yep, older), all the snubber caps... damned near everything... just kept blowing... The drive tech support group, engineers, and their best techs fought it for months... then they gave up and parked it...and there it sat.

I had a few spare hours in my training schedule, so I checked it out. I shut the power down, removed the fuseholder, cleaned the wiring connections TO the holder, reinstalled it on rubber isolators, put it back on, and sent it out to a test track in the middle of the night, worked perfectly.

Problem is, the fuseholder backplane (insulator) was affixed to a framework mounted rigid to the railcar chassis... in an area under the bolster. Well, they used this particular locomotive to pull a small platform-type spot-tamper that had a 1,000 gallon water tank and sprayer, and they'd pull it out to a work area, and run the tamper with it coupled to the locomotive, 'cause the tamper was small, it'd jump around. Of course, the tank had 8000lbs of water in it when they started, but they'd run out of water after running the sprayers for 5 hours 'cause the sprayer nozzles had been removed 'cause they'd always clog up with dust because the filter screens were gone from the strainer. So they'd run the last 3 hours with no water, which made everything really dusty... and of course, when they got back, they'd run the whole works through the car-wash to get all the dust off, particularly the end bolster facing the tamper. Did I mention that the sprayer's pipes soaked the bolster down well too? Having it come out as a flood, rather than mist, the tamper splashed crud all up under the bolster, onto the traction motors, n' stuff, hence their reasoning that the motors needed a rebuild.

So two things were happening: First, the connections were getting a daily bath of iron rail dust, nasty water, and ballast dust... THEN they were hitting the fuse panel that was feeding the inverter with a pounding from the (now rather light) spot tamper bangin' on the coupler about two inches away.

The bad connection made the fuse a bit too warm, and the tamping vibration finished it off.

"More than that and you need to do something else. "

Oddly I've never seen a solder connection to a lug terminal like that fail from
heat.

And I've seen about a thousand crimp lugs that were improperly crimped or
failed from weak tension.

re; Troublehooting. I was taught to RTP ie read the problem. It works for life as well as electrical stuff. First what broke, second how is the thing supposed to work, third is it. Go from there.....

Then there is

"Fix what you know is wrong".