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  1. #1
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
    Posts
    6,439

    Unhappy Mill motor failure !

    Hi Guys,

    The motor packed up on my mill last night ! No warning it just stopped. I'll strip it off the mill today and have a look at it. I must admit it was far too hot to touch. No smoke but that slight hot smell after it had stopped.

    Until I can get it fixed, everything else has to take a back place.

    FWIW, the mill is a Chinese copy of an "Optimum BF20L" with a variable speed DC motor. This will be the third motor to fail on this mill since I bought it. The original motor failed within a couple of weeks and the supplier replaced it, now this one has failed. At least it didn't smoke and leak tar all over the top of the mill.

    I'll take some pictures later.
    Best Regards:
    Baron J.

  2. #2
    Join Date
    Aug 2008
    Location
    Charlestown NSW
    Age
    65
    Posts
    1,669

    Default

    Bugger. I feel for you. Do you think you will replace it with something similar or convert to AC with a VFD?

    peter

  3. #3
    Join Date
    Dec 2013
    Age
    56
    Posts
    1,416

    Default

    Sorry to here, I'd look into something Peter has suggested.
    Using Tapatalk

  4. #4
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
    Posts
    6,439

    Default

    Hi Guys,

    Here are the pictures I've just taken !

    01-09-2019-001.JPG 01-09-2019-005.jpg 01-09-2019-002.jpg
    A family picture of the failed parts. The brush springs are toast and the screwdriver actually pushed through the brush cap, leaving a hole right through. One brush is down to about half the length it should be.

    01-09-2019-003.jpg 01-09-2019-004.jpg
    These are close up's of the brush holders and the connections to the wires. Underneath those overheated shrouds are push on spade connectors. Obviously well underrated for the amount of current that they have to carry !

    Unfortunately from previous experience I know that there are no spare parts available for these motors and I'm not prepared to pay the £100 plus plus that the dealers want for replacements, at those prices they can keep them. The new models of this mill are now fitted with brushless DC motors, which I understand are far more reliable.

    So everything stops whilst I try to sort out this mess.

    Peter, Dave, thank you for your commiserations and suggestions. When the original motor failed, I did look at replacing the motor with an AC induction motor and using belt drive. Unfortunately the physical motor size and weight would make a conversion very difficult, so I ruled it out.

    We will see how I get on with sorting this mess out. Very .
    Best Regards:
    Baron J.

  5. #5
    Join Date
    Aug 2008
    Location
    Charlestown NSW
    Age
    65
    Posts
    1,669

    Default

    What are the brushless DC motors worth? It would be expecting too much for one of them to be a direct bolt on replacement though. More than likely be just slightly different
    peter

  6. #6
    Join Date
    Dec 2013
    Age
    56
    Posts
    1,416

    Default

    Quote Originally Posted by bollie7 View Post
    What are the brushless DC motors worth? It would be expecting too much for one of them to be a direct bolt on replacement though. More than likely be just slightly different
    peter
    I think the controller cost would come in over the cost of the motor, though I haven't had much to do with them.
    I know there is a big jump in cost for CNC brushless motors and controllers compared to brushed.
    Using Tapatalk

  7. #7
    Join Date
    Feb 2008
    Location
    Australia
    Posts
    146

    Default

    Seen a few conversions done with the AC 3 phase motor on the BF20L, it fits but it looks tight.

    Can you not use the brushes they sell on ebay for grinders ect.? they seem to come in all sizes and most with a spring attached.

  8. #8
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
    Posts
    6,439

    Default

    Hi Guys,

    Thankyou for your comments.
    Sorry about being a bit slow responding, I've been away visiting family for a few days.

    Dave: Yes the controller plus the cost of the motor is a lot more than I would want to pay !

    Ch4is: I can make some new brushes, its the springs that are the hard part. I can't find a method of attaching a pigtail into the carbon, so the springs have to be copper plated to reduce their resistance otherwise they just get very hot. The pigtail effectively bypasses the spring to feed power directly to the brush.

    In actual fact the problem with these motors is that the electrical connections to the brush holders is not really capable of passing the current demanded by the motor at full power. As the loading on the motor increases, so does the current required. This causes the voltage across the motor to drop increasing the amount of current required to maintain the speed. This is the cause of the heat that has damaged the wiring in there.

    The advantage of BLDC motors is that there are no brushes. All the commutation is done electronically. Basically the motor is turned inside out. With the brushed motor the field magnets are bonded to the casing and the windings are on the armature. On a BLDC motor the magnets are part of the armature and the windings are bonded to the casing and semiconductors are used to supply power to them.

    Making motors this way has considerable advantages, not least that it is far easier to cool them.
    Best Regards:
    Baron J.

  9. #9
    Join Date
    Jun 2013
    Location
    Tasmania
    Posts
    257

    Default

    Thats sucks.

    I had the same issue on a Sieg X3. The replacement motor and controller was horrendous. I bought a 1hp tread mill motor, which is a brushed DC motor and a better quality DC motor speed control and retro fitted. It would likely work on a BF20L (which I have one of those too). The treadmill I picked up dirt cheap off Gumtree and the speed control off Ebay.

  10. #10
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
    Posts
    6,439

    Default

    Hi Hornetb,

    I agree, it does !

    I know of a number of people that have had issues with these motors and their controllers. The poor electrical connections cause considerable problems.

    I've got a couple of salvaged treadmill motors, unfortunately neither of which have the same footprint as the motor on my mill.

    I've not taken any pictures yet of the repairs I'm making to mine. Basically its a clean and refit issue, then make new brushes. I've had a suggestion from a friend that might work, which I will try.

    Watch this space because I will be posting pictures of the repairs, whether successful or not ! But I do object to having to pay for what I consider to be poor design, workmanship or both.
    Best Regards:
    Baron J.

  11. #11
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
    Posts
    6,439

    Thumbs up Mill Motor Repair.

    Hi Guys,

    I've started work on repairing my mill motor ! Warning ! Lots of pictures.

    09-09-2019-001.jpg 09-09-2019-002.JPG
    This is how the heat from the poor contacts left the push on spade connectors. I fully expected to have to prise them off the spades, but they came off with very little effort.

    09-09-2019-004.jpg 09-09-2019-003.jpg
    This is the condition of the brush holders after removing the push on spade connectors. You can see the cracking clearly in the first picture and the way the adhesive has melted and forced its way out between the Bakelite and brass sleeve. Those push on spades are copper and are just spot welded to the side of the brass sleeve.

    09-09-2019-006.JPG 09-09-2019-005.JPG
    I used a miniature wire brush in a Dremal to clean up the spade tags before tinning them with 60/40 solder.

    09-09-2019-009.jpg 09-09-2019-008.jpg
    I then used a couple of short lengths of butyl rubber covered wire and soldered them into the spade tags

    09-09-2019-007.jpg
    This is what it looks like now. I'm thinking about putting some butyl rubber sleeves over the wires and spade tags. At least if the solder decides to melt they would contain it and not let it drip onto the armature.

    09-09-2019-010.JPG 09-09-2019-011.jpg
    These pictures show the brush cap end of the brush holders. The first picture is what they both should look like. In the second one the adhesive has been scraped off the contact surface.

    09-09-2019-012.jpg 09-09-2019-013.jpg
    I mentioned previously that I would be making some new brushes for the motor. These two pictures are of the carbon bar that I will be using. This is a non copper loaded compressed carbon. It is a very hard grade, Ideal for the manufacture of some new brushes.

    09-09-2019-014.jpg 09-09-2019-015.JPG
    This is one of the old brushes stood on the new carbon. You can see the damage on the brush edges caused by vibration from the rotating armature commutator wearing away the edges in the direction of rotation. The actual commutator is in good condition with zero noticeable wear.

    Well this is as far as I've got at the moment ! I am going to use the vertical bandsaw to cut the material for the new brushes. After that its a matter of filing and sanding to get them to the right size.

    Thanks guys.
    Best Regards:
    Baron J.

  12. #12
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
    Posts
    6,439

    Thumbs up Mill Motor Repair completed.

    Hi Guys,

    Well following on from my earlier post, the mill is back up and running. Just a few pictures showing how I did it.

    09-09-2019-001.JPG 09-09-2019-002.jpg
    As I alluded to earlier, I used my vertical wood cutting bandsaw. This picture is setting up a straight edge, using one of the old carbon brushes to set the width.

    09-09-2019-003.JPG 09-09-2019-004.jpg
    I then cut two pieces of carbon to the right width. Actually about a millimetre too wide. Better to have too much than not enough. Anyway a quick rub on some fine sandpaper got rid of the saw marks and took them down to the right width. The next step was to rub about 1.5 mm off to reduce the thickness. A very dirty messy job.

    09-09-2019-006.JPG 09-09-2019-007.JPG
    And hey, they fit perfectly.

    09-09-2019-010.JPG 09-09-2019-011.JPG 09-09-2019-012.JPG
    A friend suggested drilling a small hole in the end and filling it with solder in order to secure a pigtail. To be honest, I would have been very happy if it had worked. I used a 1.5 mm drill and drilled a hole in each brush, 3 mm deep. I then clipped a short length of cored 60/40 solder, placing it in the holes. A few moments with a cooks torch rapidly melted the solder, leaving a small bubble of solder in the hole.

    At this point I was thinking, great, it works ! No it doesn't ! As soon as the solder melted, I placed a braided pigtail, dipped in rosin flux into the hole. The solder simply wicked up into the braid leaving the hole empty. I did try several times by putting another clipping of solder into the hole, but each time it just disappeared into the braid.

    So I just replaced the springs behind the brushes and reassembled the mill. It works just as it did before. If anything it seems to run a little more quiet than it did.

    Thanks Guys for following.
    Best Regards:
    Baron J.

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