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Electric Motors/Repulsion induction


QUESTION: I have a P&H Harnischfeger 500 lb. host 1/2 HP motor which usually will hum but not turn. If it starts, it runs OK. The brushes are badly worn, and this is an old unit, probably 1960's. Is it practical to replace brushes and put it together, or should more detailed troubleshooting ensue before seeking brushes? Thanks.

ANSWER: George,  wow that is old,    but cool,   

Here is the deal on brushes,   and I am trying to remember  the last PH that had brushes was a series motor I believe,   not a DC motor with rectifier     

Regardless,   the problem is more likely the lack of brush spring tension to the brush surface,

IF you send a sample brush and spring to, you can call them first,  if they have that brush and can identify it by the nameplate, and they will tell you, we are 100% sure our database says these brushes belong in that hoist,   sometimes they have few repeatable instances so they cannot be sure,       then they will send you the right brushes and you are done,

Next is to send them a sample and you need to get new springs,   however the springs are configured  if they are on the shunts fine,  if they are not get new ones,   

New brushes and weak springs is a waste   

What the condition of the commutator is  no one can know, except you said it runs OK    is OK sorta good, very good,  right on the money no problems   or just OK    ??

If it runs nicely as OK    then I would say new brushes will work, with new springs,     if OK is just OK   in other words it picks but not as smooth or is jumpy or sporadic    then yes you should tear down the motor  and turn the commutator and undercut the mica sections between the bars,  

No matter what the new brushes will have a different radious than the commutator because it is for sure worn some   to what degree  again no one knows,   

Most of the time on hoists there is no access to the commutator for seating stone,    so it is really hard to get the new brush at the radious of the comm  so it gets full contact,  

I have done this if there is no way to get to the brushes at the comm through some sort of cover plate or just an open frame,     

If it is blind,  get you a white brush seating stone,    take a small amount of the stone and crush it to about a tablespoon full,    

Put one brush in,   pour a small amount of crushed seating powder down the next open holder,  hopefully by hand you can rotate the armature and get some of the powder under the brush   then take it out and look    you will see if the radious changed   

Then repeat  I think you have two brushes maybe four,   but most likely two,  

You don't want tons of powder in there but it wont hurt much,   if anything   a big over amount could clog   but it is rare,  just enough in there to try and get the brush starting to seat    after a while they will seat in,  but they could arc  doing so,  sometimes that is no big issues if it is a lot it could be a big issue,   

If OK means truly OK   then just get the brushes  get new springs if they are not on the shunts,  get new caps if applicable.

Now it very unlikely you will find these brushes at like ACE or any hardware store    and you wont know what the original length should be,  so I would get them from Helwig,  but they are going to charge you some kind of minimum   it depends,  say the brushes and everything is $25 for one set,  the minimum might be $75.00   get three sets,     a waste probably  but better than spending $75.00 for one set,    

You might be able to get OEM brushes by digging down to PH   by model,   maybe,     that will work too,  whichever is more cost effective,    

You could send me photos of the existing brushes and of the bottom so I can see the wear and the sides so I look for burn patterns and any other photos relevant to the brushes or armature you can get at,        

PH is one of the more complicated type hoists so if you go to take it down,   take photos as you go so you can reference later and mark all parts    where they mate up    use a tiny drill bit   one drill mark on the drive end housing to the shell so they line up,  two drill marks on the non drive end   and every other part that mates   use a small tiny drill bit you can see,  like  1/32  just a little pin punch looking mark  use a drill depth rig if you have one,

The marks will look like a punch but smooth and round,   punches rough up edges  and can actually fracture parts so it is best to drill your mating marks     marking pencils and markers tend to get rubbed off,  so do it with a drill   very easy and very quick     

Then try as best you can to make the radious of the new brush fit the radious of the comm as it is,   and if the brush has not worn to the shunt    in other words clear worn and the shunt is now contacting the commm  that is the worst  if there is still brush   but just worn to a nub  that is fine,  now you put in new ones with new strong springs, caps whatever configuration  and you should be good to go,       

Let me know as you go along and if you need help or have questions  I will help you along the way,      it is of course always better to tear everything down    but sometimes that is very time consuming and a mess you dont need,     it is an old hoist,  so how much time and effort is up to you,   

let me know if anything bothers you or are not certain about,   

---------- FOLLOW-UP ----------

QUESTION: Great explanation and assistance, Wil!  I torn down the unit. I think P&H refers  to it as a repulsion induction type motor. Following your previous advice to others, I went to Helwig and obtained the brushes. Also found some loose connections and questionable wires in the control box, all of which I can fix. Replaced the bearings. The only remaining part is the round wire brush springs. One of the four is missing the open end of the "J" which contacts the brush. So, it pushes on the brush with a single wire ("I") instead of a "J". The tension seems adequate, but I resist re-assembly with that condition, so that is the latest search. Helwig gave me a reference, which gave me another reference which I am still pursuing. Fortunately, this is for a charitable operation and I am retired, so I don't have to justify the hours. I just hope I can find some springs. Thanks. George A.

OK  It is old  repulsion induction motor,   has either brushes that ride constantly on normally a flat surface segmented Commutator.  What you need to look at next is the mica between the sections,       normally it is "undercut several thousandths down so the brushes are not riding on the very hard MICA    which is basically a rock,

This takes some doing, you really need a hand undercutter,  and about the only place that is going to have one is a motor shop   and if you can get the rotating portion out,   they can throw it in a lathe and cut it flat, then undercut those mica segments,   

If it appears fairly flat,  you can take a hack saw blade,   you might have to even grind it thin,  and saw out the sections,     but this is something a motor shop should really do,   

An undercutter has an adjustable guide so you hand cut one,      then from there on you have a guide for the rest,   it has a tiny "wheel"  that is the guide then the blade is just like a tablesaw blade and it cuts the remainder,   however some of these end up being flat and if so no guide  because of the angle,          

This is a true antique  might be worth something if you were to go to say   vintage tools .com    or any antique site that deals in industrial antiques      that is probably worth checking out,       

Next if you can figure a way to guide a dremel with a cutting blade,  you could cut it that way but if you miss and put scratches all over it needs to be machined flat for sure,     

Now maybe it is still undercut   in that case, take a hack saw blade, and cut a hook in the end, if too wide grind the sides,      now gently drag the length of each section  and remove the gunk and carbon.

As to the broken spring,    the distance between the j end of the spring and the pressure pad on the brush should not be enough to cause much problem    at first  but if you look and it looks like the j portion is there so when the brush wears it follows it down the holder,   yea you need a new spring,    where to get one of those good luck      helwig will make them for you but the cost is going to be out of sight,       if the I portion looks like it will not interfere with the brush as it wears    or really not so much interfere but say it lays down on the side of the brush box,     now no pressure,        it is ok if you add to the pressure pad on the top of the brush if it has one, or even a folded piece of card board so long as it is not wedging the brush   that might work,   

But if the brush will wear and the I of the spring will follow with pressure    should be OK,

You can get like a postal scale, there are charts all over the internet     electric motor brush spring pressure chart    is your key words,      so much per sq inch   in pounds or ounces   depending on the size of the brush        if the I wont hang or stop following   if the pressures are all the same when tugged on by the postal scale,    [you will have to rig up a way to fasten an alligator clip or something to each spring and then measure]

If they are all relatively close  you got it,       

Now some rep ind motors ride all the time on the surface,  some have a spool and spring loaded device that centrifugally opens and lifts the brushes off the surface once it gets to a certain speed,       so look for that  if it is brush lifting those things get full of gunk and stick,    then you are in the starting circuit the whole time and that will burn up the start circuit,         but should be simple to tell,

You might try Eurton, they probably have or know where to find most any old vintage part if there are any,    and probably know yours by the hoist data       try them by phone and see what they say,  they have brush spring scales for sale,    they are pretty cheap or used to be,   but anything like a postal scale will work if you fab up some way to grasp the spring,

If there is a groove in the surface the width of the brush it should be machined flat,   and then undercut  not a huge project but a tedious one on your own,       past that if the brushes fit and the one spring wont just stop pushing      go for it,,,,,,,,,

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Three phase/ AC DC single phase motors, controls, any problems or failures, motor installation, performance issues, connections. All other electric motors/gearboxes/apparatus. Specialty repair concerns, obsolete motors and solutions. Other mechanical or specialty equipment. See my profile under Home/electrical at this site


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