Proxxon Micromot 50 - Page 1
Forum section: electronics / beginners

author: mike_mike
author_rank: Super Contributor
timestamp: October 01, 2018, 05:02:52 am
content: Hello,I recently bought a Proxxon Micromot 50 and I saw that the power connector for this hobby drill has 3 pins. Two of them are marked with + and -. I will connect those 2 pins to 12V. But there is the third pin and I do not know the purpose of this pin.I am wondering if you could help me with the purpose of the third pin. I attached a photo with the connector. The third pin is the shortest one.I am also wondering where can I find a mating connector.Thanks in advance.

author: Brumby
author_rank: Unknown
timestamp: October 01, 2018, 05:22:38 am
content: Since it's DC - and the cord is only a coiled figure 8 (no third conductor) - my guess is that it is a polarity safeguard, so that you can't plug it into the mains adapter the wrong way around.

author: mike_mike
author_rank: Super Contributor
timestamp: October 01, 2018, 07:25:14 am
content: Thanks for the reply.One more question:The Proxxon Micromot 50 will work fine if I will power it using a 4 Amps LM317 + PNP transistor power supply adjusted at 12V ?

author: Brumby
author_rank: Unknown
timestamp: October 01, 2018, 08:41:47 am
content: Since the specifications say:Direct voltage 12 - 18V. 40W.as givenHERE- a 12V supply that can deliver up to 4A should work nicely.That is unless somebody has some specific knowledge that would question this.

author: tooki
author_rank: Super Contributor
timestamp: October 01, 2018, 09:12:03 am
content: Interestingly, the Micromot 50/E (the variable speed version) has this note: "The speed control of our 12 volt devices only works when operated via nonstabilised power supply units (e.g. all MICROMOT mains adapters). Connection to stabilised power supply units is possible. However, the devices will then operate with maximum rotational speeds (also applies to operation with batteries)."I wonder what they're doing?!?

author: Gyro
author_rank: Super Contributor
timestamp: October 01, 2018, 09:19:34 am
content: The 50/E uses a thyristor speed controller. They need a rectified but unsmoothed supply so that the voltage can drop to zero between mains cycles. With smoothed DC the thyristor just latches on, so full speed only.

author: tooki
author_rank: Super Contributor
timestamp: October 01, 2018, 11:28:30 am
content: Thanks for the explanation!

author: 6PTsocket
author_rank: Regular Contributor
timestamp: October 01, 2018, 04:45:08 pm
content: Quote from: Gyro on October 01, 2018, 09:19:34 amProxxon should have said unfiltered rather that unstabilized. A dumb style car battery charger would make the perfect power supply as long as it has the current rating. It is nothing but a transformer and rectifiers.you can get them pretty cheap and it says 5 amp, 10amp, etc. right on rhe front so you don't have to research it.Sent from my SM-G900V using Tapatalk

author: tooki
author_rank: Super Contributor
timestamp: October 01, 2018, 06:08:51 pm
content: Quote from: 6PTsocket on October 01, 2018, 04:45:08 pmWell, their documentation is all German-tinged.(As a native English speaker, but also fluent German speaker, I'm quite adept at recognizing Denglisch.In electronics, for example, you see German speakers write things like "elcos" and "trafos", mirroring the usage in German.)

author: 6PTsocket
author_rank: Regular Contributor
timestamp: October 02, 2018, 01:58:23 am
content: The bottom line is we now know what is needed and that is an unfiltered DC supply that can supply enough current. Any language confusion has been cleared up. I would still look for a battery charger if i did not have the transformer.Quote from: tooki on October 01, 2018, 06:08:51 pmSent from my SM-G900V using Tapatalk

author: mike_mike
author_rank: Super Contributor
timestamp: October 02, 2018, 05:41:02 am
content: Quote from: 6PTsocket on October 02, 2018, 01:58:23 amAre you talking about the model which has speed control or are you talking about the one which does not have speed control ?It seems a little bit complicated because I do not understand all the things you said, can you please clarify if I can use the LM317 + PNP power supply for this Micromot (the one without speed control) ?Thanks in advance.

author: Brumby
author_rank: Unknown
timestamp: October 02, 2018, 07:52:52 am
content: Your LM317 + PNP power supply will run the model without speed control ok. The one with the speed control will have an issue with controlling the speed.

author: McBryce
author_rank: Super Contributor
timestamp: October 02, 2018, 10:09:26 am
content: The original Proxxon PSU with the correct socket and drill holder only costs about $30 new. Is it really worth building something yourself for this?McBryce.

author: mike_mike
author_rank: Super Contributor
timestamp: October 02, 2018, 04:09:24 pm
content: Quote from: McBryce on October 02, 2018, 10:09:26 amI already built the LM317 + PNP transistor power supply for generally use in my workshop. So I thought that I can use it for the drill.

author: jeroen79
author_rank: Frequent Contributor
timestamp: October 02, 2018, 05:31:56 pm
content: Quote from: Gyro on October 01, 2018, 09:19:34 amThen why bother rectifying it?

author: Gyro
author_rank: Super Contributor
timestamp: October 02, 2018, 06:54:13 pm
content: 100Hz rather than 50Hz (assuming bridge rectifier). Non rectified would only give youmax50% duty cycle.

author: SeanB
author_rank: Super Contributor
timestamp: October 02, 2018, 07:15:29 pm
content: DC motor works on DC, thus you get 2 power cycles with each mains cycle with full wave rectification, rather than a single cycle and then a blocked off negative cycle. As well transformers do not like DC current fed through them, they tend to saturate magnetically and run hotter than normal.

author: TassiloH
author_rank: Regular Contributor
timestamp: October 02, 2018, 09:16:01 pm
content: I think the third pin on the plug is only polarization so that the plug only fits one way. These plugs have been in use at least for 40 years for small 12V tools - I had the Böhler "MiniTool" series as a kid (some remnants of that company are now called Kaleas), and they had a third pin molded from plastic. The cheapest way to make a suitable socket: Get some small diameter brass tubing and glue small pieces into your front panel (my late father built a power supply like that), or get an extension cord:https://www.amazon.de/dp/B0017NP2FC/

author: Brumby
author_rank: Unknown
timestamp: October 03, 2018, 12:40:49 am
content: Also, rectification allows you to offer one power supply that will suit both products. Why double up on inventory?

author: 6PTsocket
author_rank: Regular Contributor
timestamp: October 03, 2018, 02:44:25 am
content: The one that does not have the speed control requires raw DC. A regulated supply is normally filtered before the regulator. If your transformer and rectifier can run the motor, removing the filter cap and regulator would allow it to be used to feed the speed control. If you feed the speed conyrol filtered, regulated DC as your supply is now, it will only run at full speed.Quote from: mike_mike on October 02, 2018, 05:41:02 amSent from my SM-G900V using Tapatalk

author: RichKem
author_rank: Contributor
timestamp: June 08, 2022, 08:41:17 am
content: Hi,Thanks for posting this information.I understand this thread is a few years old.However, we are also having a similar conversation about the Proxxon Micromot 60 in the Model Engineering forum here:https://www.model-engineer.co.uk/forums/postings.asp?th=180327You are welcome to join in.

author: arekm
author_rank: Unknown
timestamp: October 17, 2022, 05:42:19 pm
content: Did anyone try stable/filtered DC power + simple NE555 and mosfet circuit (100Hz, proper duty cycle) to make thyristor turn on/off and thus allow speed control on proxxon device itself?(goal is to have proxxon tool powered from regular power tools (18V though) batteries while keeping speed control working)

author: Le_Bassiste
author_rank: Frequent Contributor
timestamp: October 19, 2022, 10:37:43 am
content: Quote from: arekm on October 17, 2022, 05:42:19 pmas should be clear by now, the PROXXON needs rectified unfiltered AC input to control the motor. the reason is that the speed controller usesphase angle controlon the thyristor.hence, the AC waveform has to be at least kind of sinusoidal or, triangular, for that matter. also, the motor is connected to the cathode of the thyristor, which allows (fairly) load-independant speed control of the motor:the higher the mechanical load on the motor, the further the cathode of the thyristor gets "pulled down", which in turn automatically increases the counduction phase angle of the thyristor, thereby stabilizing the r.p.m. under load. downside is the "motor boating" or "pulsing" of the controller, when set to low r.p.m. and the mechanical load is being removed.

author: Texmisure
author_rank: Newbie
timestamp: November 17, 2022, 11:11:25 am
content: I confirm, the third pin is for don't reverse the plug on psu. One transformer and 4 diodes and you power all 12v proxxon machines. One question to all, which is the diameter of the pin connector?