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Old 11-20-2018, 01:02 PM   #1
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Default DC crane resistors

Hey all im working on a 250vdc 30 ton overhead crane witch has a 5 speed hoist this crane has been in service since possibly the 40s and now when operating the hoist in 5th point down only the resistor bank is glowing orange any thoughts of what to look for
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Old 11-20-2018, 02:12 PM   #2
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When I worked on this type of equipment, sometimes a partial break at the resistor bank combined with dust and grim, causing too much resistance in the field circuit. So does the motor slow down or stop when in 5th step and the resistor bank glows orange. Does this system have a drum controller mounted inside a cab? Most cranes I worked on where A/C 3-phase "Wound-Rotor Motors" with 3 and 5 step operation and a resistor bank connected thru slip rings to the rotor. Weird to say the least. The DC cranes where rare and like 190X vintage such as Laclede Steel in Granite City, IL. This was over 25 years ago for me, could be wrong. Curious, what is the brand name. "PH" was the best IMO but there gone now. Been around since before 1900, chain hoist before electrification.
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Old 11-20-2018, 02:27 PM   #3
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P&H, the excavator firm, STARTED life building such hoists.

It's, AFAIK, STILL committed to its oldest units.

Like Rolls Royce, H&P largely sells its gear based upon the fact that it can never get too old for replacement parts.

They have been bought out, but are STILL operating out of Minnesota, AFAIK.

You'll chuckle: P&H got into the hoist business by buying out GE's technology! (1894)

[ There was a massive business slump during 1894. This was why San Francisco minted only ~24 dimes all that year. These were not regular production dimes, just test pieces. That's how rotten the demand was for even the common dime. (!) The mint still had no end of 1893 dimes to hand out. ]

Double check all of that, as my memory is going to He!!.
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Old 11-20-2018, 03:09 PM   #4
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No drum controller and im not sure on manufacturer it's either a Morgan or Cleveland crane however it is Cutler hammer controls
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Old 11-20-2018, 07:24 PM   #5
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Dull or bright orange? When I worked at the tower plant, our old crane's resistors would give a dull glow at high speed which the crane company verified was normal for that model. When it got bright, it meant the slack adjuster for the drum brake needed serviced.
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Old 11-25-2018, 11:23 AM   #6
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Curious, did you get a chance to find/fix the problem? Was the resistor shorting out at the rack for step-5? If the unit is D/C, chances are it's been in service since 00's (1900 vintage) Where is equipment located? ex. Power plant, Water plant, etc. Try and post some pic's. I know I will never get back to those locations again. This includes walking an "I" beam with rail down the center of it and nothing to tie off to. Don't tell OSHA, they'll have a hissy fit about that
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Old 11-25-2018, 11:30 AM   #7
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Also, welcome to the forum and please fill out your profile
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Old 11-25-2018, 11:34 AM   #8
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Old 11-25-2018, 11:44 AM   #9
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I've always known DC hoists to heat up the resistor bank good at high speed. Is this a new symptom or something someone just noticed? Burned out poles or burnt closed poles on the switching contactors would be my first guess if this is a new symptom; only bringing in more or less resistance than intended, overheating the resistors that it does bring online. Should be pretty simple to dance your meter down the contactors and do an FOP test, and run through the resistor bank and look for out of spec resistors.
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Old 11-25-2018, 09:41 PM   #10
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So i work a rotation and i have not been able to get back on the crane do to production but the crane is still working im surprised however I'd like to change the contactor tips since they are heavily worn and also I'd like to check the resistance on the resistor bank but you can't read the name plates on them

This is a new symptom for this crane

And the orange glow is very bright

Very dusty environment so there could be a short to ground

I will keep ya'll posted and i will update my profile thanks for welcoming me
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Old 12-04-2018, 01:19 AM   #11
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Hey all just a little update i found that the resistor was burned out at some point and someone moved the wires over one tap so i went ahead and changed out the resistor and no change i then made sure that all connections throughout are tight i also changed all 22 contact tips i suppose it is possible that this has always been like this and someone has just noticed but then why did the resistor burn out in the past head scratcher here oh and still no electrical prints ha ha
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Old 12-04-2018, 01:42 PM   #12
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Old 12-05-2018, 02:08 AM   #13
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I believe what you have there is going to be a series motor that operates as a series motor only in the Hoisting direction. During lowering it operates as a shunt motor. During hoisting, each point should pick up a contactor, all the way through 5A. During lowering, it's the opposite. All acceleration contactors pick up, shorting out all resistors in series with the field, and then dropping out a contactor with each point. So, in 5th point lower, all resistors should be in the circuit, carrying current. So, the longer you lower in 5th point, the more heat the resistor bank has to dissipate. Same with hoisting in 1st point. Some dull glowing would be normal. Bright glowing, maybe not so much. Can you check the current through the bank vs what the nameplate says it can handle? Banks do burn open from time to time. Moving the wires over a tap is also pretty common. There might also be "LA" or "LT" contactors that pick up and drop out with the points, but I don't remember exactly when they operate.
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