help with a DC motor controller....

[mike3]

Hi ... I would like to ask for some help from the very informed members of this site ... I have been lurking a while ... I have just won a Micro-Mark .82500 mini-lathe on Ebay .. and it is missing the DC motor controller .. I know i can buy that from LittleMachineshop.com .. for I think 89.00 .. but I have some experiance in Electronics ... My Question is .. does or have any here have a simple diagram .. to build a DC MOTOR controller...that would work with this lathe?.. with parts list ... I like to roll my own stuff as I can ... and I like the idea of a separate ..away from the actual lathe control box .. You Guys here have also inspired me to get my feet wet with a CNC mini mill ... I have the Homier mill all the electronic parts... the 282 oz steppers Dan Mauch was selling ... and the power supplies ... but havn't started retofitting yet .. as I havn't any maching experiance as of yet .. I figured to start with the lathe and a few good books .. I found a Amazon.com ... but anyway I would really appreciate any help ....

Mike...

[Al_The_Man]

Mike, If you want to build a controller from the ground up with descrete chips, You can obtain alot of info from the IC manf applications sites, here is Motorola for a start
http://www.freescale.com/webapp/sps/...XGrrlPY7r8f7sz
I once built a very simple one for a servo valve with a single National LM759 and a couple of resistors.
All of the major IC manuf have data/Application sheets that have a whole range of circuits Harris, National, Motorola, Maxim, Allegro.
I have also got everthing from free samples to complete sample circuit boards to populate.
Al

[mike3]

Thanks.. Al ... for the web site ... It gave me the idea to use a H-bridge circuit I found on the net.. but replacing the 511's with 200 volt 20 amp mosfet's ... am i right .... I will try to post the circuit below or the web site ... Thanks again .. Mike

[tachus42]

Unfortunatly this circuit isn't going to do the job - the maximum voltage for this circuit is 15 volts or so. I think you need 110 volts at about 4 Amps for the motor on the lathe. This circuit i found comes closer to what you need. You will need to provide a separate low voltage supply for the 3525 and a higher voltage supply for the motor. It includes a current limit which is pretty manditory for a 400 Watt motor. Get the 3525 data sheet and make sure you understand the circuits operation if you decide to build something based on this.

[mike3]

Thanks for the new diagram .... Looks like it will do it for me with a few mods ... Thanks again and to Al also,,, this way at least if I fry the control sometime in the future .. I will have no problem fixing it...


Mike.....

[RotarySMP]

The 7x mini lathe motor is rated at 110VDC.

This circuit is for 8-35VDC as far as I can see. I checked the ST electronics site for the data sheet :

http://www.st.com/stonline/books/pdf/docs/4286.pdf

Since Q1 is a 100V mosfet, is the plan to separate the control circuit from the power circuit? Could someone please draw a sketch of how to do this. I have been wondering how to make a higher powered DC controller also.

To drive a 110V motor you probably want a 200V capable mosfet right?

[tachus42]

For a 110 volt motor you would probably use a supply of about 150 volts (110 ac rectified) with a 200 volt mosfet. A 10 watt 2700 ohm resistor and a 1 watt 10 volt zener to provide a 10 volt supply for pin 15 of the 3525.The resistor would be in series with d3 and the zener between ground and pin 15 . Pin 13 (vc) would be connected to pin 15 instead of 16 as this would give better gate drive for most mosfets. VR2 sets the chop frequency and dosn't really need to be variable, replacing it and r4 with a 6k8 resistor should give a frequency of about 20kHz. R7-R9 set the current limit and their parallel resistance should be 0.6/Amps ie for 4 amps, .15 ohms . VR1 should be a trim pot to set minimum speed and VR3 is the speed control proper.

[Al_The_Man]

I am not familiar with the motor on your machine but if it is a 110v universal motor and you want speed control, there is a schematic and link to the data sheet for a surplus treadmill motor control that was posted on the Metalworking dropbox about 5 years ago http://www.metalworking.com/dropbox/...s/treadmot.txt
These 2hp treadmill motor controllers are no longer available asfaik. But they use the Motorola tda1085 ic that motorola actually designed for washing machine motors.
I have had one of these controllers on my bandsaw for the last 5 years and it works great.
Al

[mike3]

Thanks.. Guys... I am building the circuit above .. with a 200 volt 20 amp mosfet ...thanks for the idea Tachus to get the needed voltage for the 3525 ...and your other input ... I havn't worked in electronics since the early 70's .... so I am rusty and things have changed alot ,, I recieved the Lathe today .. It does have the motor ... to test the motor .. I hooked up a large bridge rectifier .. with 110 .. and used a variac to control it ... works just fine. . Again ... thanks ,, I knew someone here .. would have an answer...

Regards,,, Mike

[bunalmis]

Originally Posted by mike3 Thanks.. Al ... for the web site ... It gave me the idea to use a H-bridge circuit I found on the net.. but replacing the 511's with 200 volt 20 amp mosfet's ... am i right .... I will try to post the circuit below or the web site ... Thanks again .. Mike

Who draw this schematics? Totaly wrong. Use Mos driver IC visit the
http://www.irf.com

populer driver IC IR210X family. IR2103 IR2104....

[RotarySMP]

Tachus42, thanks for posting mods to up thevoltage of the SG3525 circuit above. I printed the circuit, and note each of the changes you suggested (and understood them

Bunalmis, thank for the link, I downloaded the datasheet for the IR2103. Do I understand correctly that the IR2103 doesn't do the PWM Choppering part which the SG3525 incorporates? Do you know of a sample circuit to do the same job as the SG3525 circuit above.

[tachus42]

The value i gave for the power supply resistor i gave was a little high it will not quite supply enough current - it should be about 2000 ohms to supply 75 mA (45 is needed for the gate drive and 20 for the chip plus a liitle spare). Reducing it will increase the power disipation above 10 watts so a good alternative would be to increase the gate resistor to 330 ohms.