DC Motor Starter Fried? - Page 2
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  1. #21
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    Remember the OP is using directly rectified AC, and the voltage is lower than the spec 250V. The ripple on the voltage may be enough to cause the chatter. Generally, the motor could have enough inductance to calm the chattering, but the field may not draw enough to be a "holding current" that keeps the contacts closed. Some smallish amount of capacitance on the rectifier may keep that down

    Also there is a lot of visible rust and dust. That could hold the relay magnetic circuit open just enough to require extra current to hold it in. Cleaning should then let the moving iron seat solidly on the coil pole so the chattering does not occur. Since it worked before, that is actually pretty likely. The regular use would have kept the pole face clean.

    The chattering may have had enough arcing to cause some smoke also, burning dust, fluff, etc, or just causing smoke due to the arc toasting the contacts..

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    First rule of DC repair... get it clean...Phil

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  4. #23
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    Got it. Thanks for the help. I'll do what I can to clean it up and look for obvious damage but short of divine intervention the best option may be to repower with something more modern. Most of the discussion here has been well above my head and WWII Electrician's Mates are in short supply.

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    Most are in the here after,I miss them, even though I love DC motors and controls... it would be best to re-power...Phil

  6. #25
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    Another diagnostic clue if you'll permit me. I started taking off the motor and had to remove the belt and the 80 LB cast iron belt cover and I got curious as to what the motor would do with no load - I was getting rid of it anyway so why not? I bolted it back down, set the fire extinguisher by the starter panel and fired it up. Purred like a tawny kitaen. No chatter from the starter mechanism and no smoke. I still had the inspection panels off the motor housing and saw intermittant sparking, some tiny, some that traveled the circumference of the motor shaft surface. I shut it off, waited a minute, and started it a second time. This time a stutter of two or three clicks and back to spinning like a top.

    I checked the resistance of the machine by turning the drive wheel which is spun by the belt and it turned easily, so no unusual resistance.

    Did I get my divide intervention or does this point to a particular cause? Is the sparking in the motor caused by worn brushes? It looks like the stationary arm holding whatever it holds is designed to press it against the surface of the rotating part of the motor. And that contact point is where the sparks originate.

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    Post a pic and show where it sparked...Phil

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    Here's a closeup of the arm I referred to: Motor Thingy DC Motor Thingy - Album on Imgur

  9. #28
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    So yes, a brush holder and brush.. The segmented thingy being the commutator.

    Speaking of which, the commutator is dirtier than a bum's bum. And much rust is in evidence.

    Many things are improved by cleaning the spaces between the segments, and cleaning all oil off the commutator and brushes (brushes are best replaced, because they generally soak up oil.).

    The goo that is in between the segments is conductive, since it appears to be largely carbon dust. That causes all sorts of problems, including "ring fire" and so forth.

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    You have a cleaning job to do, free the brushes, de grease the comm, (the copper thing with the slots), and clean the slots...surf the web for info, then ask here for help...you should remove the motor and remove the endbell ( mark where the wires go...Phil

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    Thanks for the comments. I will disassemble and clean that area and replace the brush(es) and clean the starter box wiring and components. I am picking up a cherry picker/engine hoist on Sat to get the motor to my bench.

    One question remains though - what does the struggling performance of the motor under the modest load of the belt drive vs the easy spin-up with zero load indicate, if anything?

    "Ring of fire" is a perfect description.

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    To clean the slots use a hacksaw blade with the teeth pointing toward you so they cut on the pull stroke. Cut the end of the blade off and you may need to grind the teeth thinner to fit your commutator. A used blade is fine because you will be using the end that doesn't saw.

    Bill

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    Ring of fire was no/bad brush contact,no power was the same problem... grind the sides of the saw blade so there is no rake to the teeth...Phil

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    As I understand the purpose, the idea is to clean the carbon and oil from the grooves, not to remove metal. I'm in no position to instruct anyone but I think the purpose of grinding the sides of the blade is to remove the "set", the lateral projections of the cutting points, not the rake. I'm not clear on me using the part of the blade that doesn't saw - that seems to contradict the suggestion of having the teeth pointed to cut on the draw stroke. If I've got the purpose right, I can figure out the rest. Thanks all.

    Phil, thanks for that explanation about the bad brushes. Funny - I thought they would be long wire brushes and not solid sticks.

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    Quote Originally Posted by ChipChaff View Post
    .......

    Phil, thanks for that explanation about the bad brushes. Funny - I thought they would be long wire brushes and not solid sticks.
    They were, on the first streetcars. Big problems all the time, almost killed the whole deal.

    Then a (Belgian engineer, I forgot his name) suggested carbon brushes, which seemed stupid due to resistance, but as you know, actually worked out perfectly.

    Edit... "Van Depoele" comes to mind as the man in question.

    Normally a saw is used on the commutator spaces because the insulation (often mica) does not wear down like the copper, and sticks up ("high mica"), causing a problem. Not sure you have that, because we cannot see, but it looks like there is oil and carbon all over the place.

    Clean it off, and clean the carbon gunk from between the commutator "segments". You may not need a "saw" at all, I'd use something softer but thin , like a pointy piece of brass, and rake that through first. If you do have "high mica", then you can fix up a saw to fit between the segments and cut it down.

    I think you may need a solvent, maybe paint thinner, and a rag or Q-tips to get all the gunk out of the "slots" (spaces).

    Then find the source of the oil. Likely the nearest bearing, and maybe just due to over-oiling, or oiling the wrong way, like dripping it on the shaft and hoping it goes into the bearing.

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    Ultrasonic cleaners work really well on commutators if you have it apart and have access to an ultrasonic cleaner.

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    In my motor shop we would use a thinned hacksaw blade to clean the slots if we didnt have to turn and undercut the comm, it cleans the slot quickly and didnt require a great amount of skill set...In the ones that need to be trued up in the lathe would go to the undercutter to have the mica cut down and then we would hand deburr the segments...this required a highly skilled man. The hack saw blade is the best tool for a newbe to use and give good result.I didnt work on the little starter motors nether 1000hp and biger..Phil

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    In the first post you said the motor was 250V DC, but then when you listed the specs, they say it is a 230V DC Motor.

    Which is it?

    Also, full-wave rectified 220VAC will give you a lot more than 220VDC. More like 310VDC or so....

  19. #38
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    Quote Originally Posted by awander View Post
    ..........

    Also, full-wave rectified 220VAC will give you a lot more than 220VDC. More like 310VDC or so....
    Not so.

    The PEAK is up there, sure.

    Rectified and not filtered, it will still act like DC at the RMS value or a little less, if the motor has enough inductance to smooth it a bit. It WILL be pulsating, and not the same as actual DC, with peaks of torque way over the DC value, and valleys of zero torque..

    The actual power will be the same, a resistance heater will still produce the same output on either AC or rectified AC, given loss in the rectifiers (minimal).

  20. #39
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    JST is right, unfiltered the dc will be the 240 volt less 1.4 volts for loss in the didoes....It does get a little tricky if there is no load on the motor, it will act as a filter and the voltage will climb up, but not to p-p...The supply voltage makes little diff.. the field will get stronger so the speed will stay the same (200 volts to 250 volts you will see little or no speed change of the motor). The field and the arm is supplied by the same supply.You will gain a little tork and heat on the higher voltage..Phil

  21. #40
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    Makes sense. Did he say it was unfiltered?


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