Amadeal VM25L Uneven Motor Brush Wear

[noel shelleyParticipant @noelshelley55608]

Richard where abouts are you ? Noel.

[MacolmParticipant @macolm]

For such circumstances I keep an old security light with high wattage mains halogen lamps, for example 1000 watt. With the mains supplied to the circuit under test via this, a dead short merely makes the lamp shine at full brightness. Something like a electric drill motor running on light load will scarcely light it, and the voltage dropped will be small. From cold to full brightness, the resistance of a halogen lamp increases by more than ten times, so a cold 1000 watt lamp might be perhaps 5 ohms. Lamps could be connected in parallel, and will share the current well due to the rapid resistance rise with current.

Unfortunately such lamps are no longer available to purchase new, but almost certainly available second hand.

[Richard Kirkman 1Participant @richardkirkman1]

Hi Noel,

The mill is based in Darlington.

Hugh from Amadeal reached out and provided me with some testing instructions for a lathe with a similar circuit board. I found that the Speed controller seems to be the issue. I will order a new one and fit it in a few weeks.

Posting the testing as well for anyone else in the future.

COMPLETE CJ18 ELECTRONICS CHECK
We can check a couple of things first to see if we can diagnose the fault. Since the control box trips
the electrics (i.e. doesn’t blow a fuse), you can check to see if it is the motor, filter board or the
speed control board that is causing the issue. The speed control board is the large board in the
middle of the control box, that is mounted on an aluminium backing.
First it is best to check the motor. To do so, unplug it from the filter board (the small board at the
bottom that slides out). It will have a green or orange two pin connector into the filter board.
Between these, there should be between 3-13 ohms resistance. You can check multiple coils by
turning the motor by hand and letting the multimeter settle and hopefully should still read in in that
range. If you use a 9V battery or a DC power supply on these two wires, the motor should spin very
slowly (make sure you remove the belt to test this otherwise it will not turn very easily). Leave the
motor disconnected for the rest of the testing. Also, it is recommended to check the condition of the
motor brushes. If this is fine, we can check the filter board.

If you disconnect two wires into the speed control board, labelled L1 and L2 (both usually red), these
should be 240V AC between the two wires. Please be careful! This is effectively mains power so is a
very high voltage and can injure you. If that is fine, the filter board would seem to be functioning.
However, since you say it trips the fuses as soon as you switch on the machine, this test may not
work as it may be the filter board that has had issues.

You can check the speed control board by plugging L1 and L2 back in and then use the multimeter on
A+ and A- on the same board. These need to be on the spades, not the wires, so one way to check, is
to slide the multimeter tips into the plastic cover over the spades for these two. The voltage reading
for this will be DC with a minimum of 0V and maximum of about 230-280V. This range can be
checked by adjusting the potentiometer on the front of the control box. The output voltage will
increase and decrease with turning the potentiometer up and down respectively.
If you find the filter board does not respond correctly, you can still test the speed control board. You
can plug live and neutral directly into L1 and L2 (respectively), after removing the L1 and L2 cables
from the filter board. Then check A+ and A- as I have mentioned in the previous paragraph. Please
note, doing this bypasses the switches and fuse on the control board, so it may trip your circuit
breakers. You can still increase and decrease the voltage output using the potentiometer on the
front.

When testing the filter and speed control board, it uses mains power, so please be careful! If you are
unsure, stop and please let me know! If you could test for any of these and get back to us, I will be
able to advise what to do next. I hope we can diagnose the issues with this!

SPEED CONTROL BOARD CHECK
Another test would be to check the speed control board as this will determine if the motor is actually
receiving the voltage it needs. If you unplug the motor and two wires on the speed control board
(this board is the one with many wires connected with spade connectors and is on an aluminium
backing) which plug into A+ and A-. The wires are usually black, but this is not always the case. Use
your multimeter on the 600V DC setting (or similar voltage above 200V) on the two spade on the
board to test the voltage. Please be very careful with the high voltages to not short circuit or touch
anything with the main power on. Then switch the machine on as if you were to operate it and turn
the potentiometer (the dial on the front) up. When off, the voltage should be 0V, when on max it
should be around 200-280V and should increase linearly between the two points. If you could do this
test for us, we can determine if the electronics are working or faulty.

[Richard Kirkman 1Participant @richardkirkman1]

Finally home, and a new speed controller board arrived.

Fitted it last night and put everything back together- The mill seems to have come back to life. It feels a lot faster than before too, but i don’t have a speed readout as the tachometer/display doesn’t work and i’ve never been able to figure it out.

Either way, i will take some cuts this afternoon and see if it goes bang again.

[Richard Kirkman 1Participant @richardkirkman1]

Mill was working fine, but I spent a few hours yesterday taking quite heavy cuts.

Hugh from amadeal did mention to me that the 600w motors (which this machine has) occasionally had an issue with overheating and was fixed by replacing with a 750w motor (which they are able to provide).

During my heavy use, the motor became extremely hot. I did not notice as I had the cover on, which I suspect significantly reduces airflow, too. After some time, the motor made some funny noises and wasn’t happy, so I investigated.

It appears the source of the increased wear on the brushes is the overheating motor, as one brush had died again.

It could also be me using the machine too vigorously, but I don’t think I was too far out of the realm, just in duration for a hobby machine.

Luckily, I had the remaining brush from the last death, then could clean the motor out, allow the mill to cool, and take the milling more gently.

Next steps – New brushes, and an inquiry at the cost of a (slightly) larger motor. However, I rarely do milling this heavy, so it is unlikely to be a repeating problem.

Thanks to all for helping me along with this

 

[JasonBModerator @jasonb]

What do you class as a heavy cut? Cutter size & type, metal being cut, speed, depth and width of cut, feed rate, etc

These benchtop machines work best when run towards the top of their speed range taking smaller amounts of metal off each pass which in the end takes about the same time to remove metal as a single heavy pass. See my couple of articles in the “workshop” section of the site about getting the most out of your mill (not including smoke)

[Richard Kirkman 1Participant @richardkirkman1]

I was running around too speed for the lower gear, taking 2-3mm depth of cut, varying widths. Using a 50mm face mill with 4 inserts, on cast iron. Feeding it as it felt okay. The motor never bogged down or slowed in the cut.

 

I will have a look at the articles, thanks Jason

[Robert Atkinson 2Participant @robertatkinson2]

I’m late to this thread.
As mentioned by others test with a “old fashioned” incandesent light bulb connected in place of motor.
It is very difficult to measure the output of the speed controller with a basic multimeter. It’s even worse with no load. To get meaningful readings you need a true RMS meter or specialist ISOLATED oscilloscope. Een then we hav nothing to compare the measurements to.
DO NOT bypass the fuse.
It’s likely the brush failure has caused a short circuit which has damaged the speed control PCB.

Brushes should wear evenly. Uneven wear is a sign of an underlying fault. The brushes pictured by JasonB are a good example. The one on the right has a twisted or otherwise shortened braid . This compresses the spring reducing contact pressure. The reduced pressure causes hot running and excessive wear. As Grindstone Cowboy has already said glasspaper aka sandpaper is the gorrect material for cleaning commutators and shaping brushes.

Robert.

[JasonBModerator @jasonb]

That is quite deep, spin it up faster in the high speed range and reduce cut to 0.5mm to start with. Also get some inserts intended for aluminium and non ferrous as they put a lot less load on the machine in terms of the motor and it’s rigidity.

Bit of cast being cut with a 50mm cutter (5 insert) 2000rpm almost full width of the cutter.

[Richard Kirkman 1]

On Richard Kirkman 1 Said:

Mill was working fine, but I spent a few hours yesterday taking quite heavy cuts.

…

During my heavy use, the motor became extremely hot. … After some time, the motor made some funny noises and wasn’t happy, so I investigated.

It appears the source of the increased wear on the brushes is the overheating motor, as one brush had died again.

Persistently taking heavy cuts with a small motor could be root cause:  hobby machines aren’t up to it, and a 600W motor is on the dinky side!

The motor getting very hot coupled with rapid brush wear and funny noises might be due to a very aggressive session, but I’m pretty sure the motor was damaged earlier and using it risks blowing the electronics again.   

…Next steps – New brushes, and an inquiry at the cost of a (slightly) larger motor. However, I rarely do milling this heavy, so it is unlikely to be a repeating problem.

Sorry, I’m confident a new motor is required because Richard’s motor destroys brushes and makes funny noises.

I think what’s happened is this:

• Excessive hard work in the past overheated the motor enough to melt some of the insulation inside.
• Now some windings are shorted together causing the motor to pull excessive current whenever they are under the brushes, plus shorted turns act as an electromagnetic brake when the motor is spinning.  In both cases electricity is converted to heat, not motion.  The windings get extra hot, likely to short more turns inside the motor,  AND brushes burn out rapidly.  The forces and heat involved cause the windings to loosen and might explain the funny noises – the motor is falling apart internally.

Try this – leave the motor running without doing any cutting.  How quickly it overheats relates to how many turns are shorted, which depends on the extent damage inside.  It should slowly get warm: getting hot quickly means it’s very sick.

A motor run with shorted turns is likely to destroy itself and another control board.   Therefore replace the motor and don’t thrash it in future – ten minutes work then 10 minutes cooling off.  The exact on/off ratio can be adjusted by testing how quickly the motor gets hot with the back of a hand: it should never be too hot to touch!

If the mill must be worked hard then fit a more powerful continuously rated motor with beefed up electronics.  Chinese brushless industrial sewing machine motors are popular.   Or buy a bigger mill!

Dave

 

[Robert Atkinson 2Participant @robertatkinson2]

Looks like the forum gremlins have been at work. Several posts became visible up after I’d posted and theter is a poert from another topic…

[Dave HalfordParticipant @davehalford22513]

Richard,

Buy a power meter plug and run the mill through that, then you can watch the consumption as you stress the mill if you see over 1kW consumption with the 600W motor it’s toast.

I had a faulty 3/4HP induction motor that drew 10A and hit 60C in 10 minutes.

[BazyleParticipant @bazyle]

I was looking at a 30v motor spec yesterday that has a 2 min on/10 off duty cycle spec. Obviously severely stressed but for an application which expects use for 20 seconds a few times a day should be fine (ie cheaper). As ong as it doesn’t encounter children playing with it.
My first B&D single speed drill recommended that if it got hot you should run off-load rather than stop to allow the fan to cool it. It might be worth a test from cold off-load full speed to see if it runs cool and hence running like this 50/50 duty between passes would be better than resting off.

[john fletcher 1Participant @johnfletcher1]

Connect a filament type bulb ( the type we all used to have in our homes, not Led type) to the motor supply connections, then wind up and down the speed controller, the bulb should go bright or dim. That tests the speed PCB part. The commutator looks good to me, don’t start skimming it, it just need a clean up with glass fibre stick or some very fine glass paper, NOT emery. Carry out an insulation test on the armature on its own, wrap a short length of fuse wire around the com, twist it tight, connect one meter lead to the fuse wire, other lead to frame, your looking for infinity or very near. Next the field coils, one lead to frame other to the coil end, same value. You can run the motor using a car 12 volt battery, it will revolve slowly, here a large Variac come in handy as you can wind up the speed up and down. John

 

[Richard Kirkman 1Participant @richardkirkman1]

Jason- Thanks for the video link- Yes i was using aluminium inserts, and I did start with 0.5mm cuts. Actually I started with 0.2mm cuts and took it up from there to see what the mill was happy with.

I did not consider trying the full 2000rpm as i thought that would be too fast. I will try it next time i’m milling.

Dave-The funny noises only happened when the mill was failing- i suspect the point of failure when the brush broke and the noise i heard was the electricity jumping like a popping noise.

From what everyone’s said, it looks like it could be a combination of issues, me pushing the mill too hard for too long, insufficient airflow for the motor, underpowered motor for that amount of work, or the motor is damaged from the last ‘misuse’.

So, I have ordered a 750w upgraded motor from Amadeal. Same fixings as the 600w motor so should be easy to fit and solve my problems. I would have done more problem solving, but at this point I just want a working Mill- Will update in due course!

 

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