Proxxon Micromot 60 Drill Went BANG!!!!

My Proxxon Micromot 60 Drill Drill Went BANG!!!

As you can see from the photos below, it is easy to insert the power connector in reverse which causes the original 1uF Electrolytic Capacitor to go BANG!

Not only does this scare the life out of you is also means there is no suppression capacitor on the motor which results in a less smooth and noisy motor.

Simply replace the original capacitor with a high quality 100nf Polyester film or Ceramic Capacitor which are non-polarised (Also know as a 104 capacitor)

I found a 100nf capacitor to work best and this is a standard value for small DC motors.

Choosing a non-polarised capacitor will ensure that if you make the same mistake in future your Proxxon drill/grinder will simply rotate in reverse

Photo below shows the 1uf Original Electrolytic Capacitor next to the New 100nf Polyester Film Capacitor.

Disclaimer:

This is NOT engineering advice so do not UNDER ANY CIRCUMSTANCES follow what I do!
 

Edited By Richard Kent 1 on 07/06/2022 14:26:15

In the picture it looks to me that the centre pin is offset from the pos and neg pins so I fail to see how you inserted it the wrong way, unless the dark spot is another socket aperture that needs an insulated peg fitting to prevent incorrect plug insertion.

Emgee

Emgee - If I was YOUNG and CLEVER like you I would never have put that connector in the wrong way

Unfortunately the plug is somewhat obscured when viewed from above and to make matters worse the pins still ensure an electrical connection even when the connector inserted the wrong way

Problem is easily solved with a replacement non-polarised capacitor though




Disclaimer: This is NOT engineering advice so do not UNDER ANY CIRCUMSTANCES follow what I do! 

Edited By Richard Kent 1 on 07/06/2022 15:00:31

Well done for getting it going again Richard. However, Proxon must have a good reason for using a 1 uF capacitor in the first place. I would have looked for a 1 uF 100 V ceramic capacitor instead which should fit in the same space.

Russell

Russell Eberhardt - Russell, thanks for your input. I thought the same as you --- "However, Proxon must have a good reason for using a 1 uF capacitor in the first place"

However, I tried both a 1uf and 0.1uf (100nf) and I found to my surprise the motor quieter and smoother with the 100nf capacitor.

100nf also seems quite a common size for this application - Also known as a 104 capacitor.

As for the voltage rating. The higher the better within reason.

I read somewhere that a suppression capacitor should have a voltage rating of at least 3 times the working voltage so if you use a capacitor with a higher working voltage it is not a disadvantage.

Normally a manufacturer will choose an electrolytic capacitor due to their capacitance density and low cost. However, they have the disadvantage of having low tolerance to reverse polarity.

However, as you can see this physically larger capacitor fitted fine.

If I had one of those O-So-Silly-O-Scope things (oscilloscope) I would be able to give you more details about how effective this capacitor is at suppression.

Russell, this tool will work without the capacitor but will not give optimum performance.

I think the BANG!!! caused more harm to me than it did the drill! - Like a FIRECRACKER going off right next to you! 

Disclaimer: This is NOT engineering advice so do not UNDER ANY CIRCUMSTANCES follow what I do!

Edited By Richard Kent 1 on 07/06/2022 16:34:18

Edited By Richard Kent 1 on 07/06/2022 16:36:30

That connector does seem a bit of a silly design.

Hi,could you please put a clear picture of the plug and socket on .

I have thought about getting one of these.

Maurice

@Maurice Taylor - Maurice, see below.

You also have the option of swapping out the collet system for a 3 jaw chuck.

I have a 3 jaw chuck on order from Chronos.

The Micromot 60 is fitted with a collet system with 6 interchangeable collets as standard but I wanted the option of using drill bits which are outside the range of the collets.

I also have a Dremel but the Proxxon is a much better tool for various reasons including low noise level and smoothness.

See photos below of the connector..............

Edited By Richard Kent 1 on 07/06/2022 18:23:10

Only Proxxon know why they fitted a 1uF electrolytic, and they are therefore are more likely to get it right than Richard's suck it and see method or my guesswork.

My suggestions as to their reasons:

1. Drill was tested in an EMC lab and the capacitor value is targetted on reducing interference on particular frequencies to satisfy legal requirements.
2. The value is chosen to reduce commutator sparking across a range of loads
3. To protect the power supply's electronics by filtering out low frequency muck and slowing voltage swings down to help the regulator, if there is one!
4. To improve motor torque faced with varying loads by providing a low impedance current source close to the motor. (1uF is low for that.)

To keep costs down, their choice might be a compromise that reasonably satisfies more than one requirement.

100nF ceramic is sensible and almost universal for reasons 1 and 2. That Proxxon went for the much higher value of 1uF is a clue they were worried about something else as well. My guess, it's the power supply. An oscilloscope would show if the power supply was unhappy. Not so good for detecting poorly suppressed motors, an old fashioned LW/MW radio is better for that.

Unless one of the motor experts knows different, I wouldn't worry about the exact value. 100nF may not have been good enough for Proxxon, but it's better than nothing!

Dave

Edited By SillyOldDuffer on 07/06/2022 18:26:25

SillyOldDuffer - You quoted ............"Only Proxxon know why they fitted a 1uF electrolytic, and they are therefore are more likely to get it right than Richard's suck it and see method or my guesswork."

I've heard WORSE from BETTER  

Having said that I tend to agree that they chose a 1uF for a reason and yet the drill runs quieter and more smoothly with 100nf.

My guess is this capacitor is mainly there for RFI suppression reasons as capacitors which are used for this purpose are normally mounted as close to and directly across the motor.

As an aside, the PSU is deliberately half wave rectified and speed control is achieved with a thyristor.

Disclaimer: This is NOT engineering advice so do not UNDER ANY CIRCUMSTANCES follow what I do!
 

Edited By Richard Kent 1 on 07/06/2022 18:57:12

Don't encourage him, please.

Hi Richard ,thank you for the photos.

Maurice

Maurice Taylor - You're welcome.

I wanted to let you know that once I started using this tool I doubt I will ever go back to using anything else.

They are quite expensive but the quality and smoothness is on a different level.

If you search google for Proxxon you will see a site called germantools.

Their prices are quite good.

I don't want to post any links out of respect for the rules of this forum as it will be seen as promoting or advertising.

I hope that helps.

Edited By Richard Kent 1 on 07/06/2022 18:50:01

Hi Richard ,I can see why the plug was inserted wrong, It’s a bad design ,if the pins were the same length ,it would not fit the wrong way.

Maurice

Maurice Taylor - Great observation - never considered that until you said it - Perhaps you should put that suggestion to Proxxon.

Knowing the plug design is at it is I'm guessing it would be easier to upgrade the capacitor to a non-polarised one rather than modify the plug but the choice is yours.

If I purchase any more of these 12V Proxxon tools I think the capacitor upgrade will be the first thing I do.

It's not that the exploding capacitor does the tool any harm, it just scares the life out of you!!

By the way these tools run at between approximately 12V-18V depending on the speed setting.

I prefer the speed control on the transformer rather than on the tool but Proxxon do various options.


 

Disclaimer: This is NOT engineering advice so do not UNDER ANY CIRCUMSTANCES follow what I do!

Edited By Richard Kent 1 on 07/06/2022 19:18:08

Richard

"I wanted to let you know that once I started using this tool I doubt I will ever go back to using anything else.

They are quite expensive but the quality and smoothness is on a different level."

Can't disagree with you there. I have had a Proxxon IBS/E drill for a few years and haven't used my Dremel since. I even use it on a bracket fixed to my CNC mill for engraving.

Russell

Russell Eberhardt -

I don't have one of these, so I can't have a play.
Here's a wild guess though; the cable appears to be twin only, no third wire, so maybe the offset pin isn't an electrical connection at all, but a means of operating a microswitch inside the PSU.
i.e. there should be no power available to the tool unless the plug is fully inserted.
Maybe in this case the switch, if there is one, has jammed closed, so there is a power output even when the tool is unplugged.

Bill

@peak4 - Bill, The middle 'polarising' pin simply fits into a hole in the plastic casing of the PSU and is not electrically connected, nor does it operate any kind of switch.

I have double checked and can confirm that the middle pin plugs into a blind hole.

I think Maurice Taylor  is correct in saying it is just a bad design. If the middle pin was longer you could not insert the plug at all if you had it the wrong way.

See photo below..............

Edited By Richard Kent 1 on 07/06/2022 22:14:13