power crossfeed to MD65 lathe

Ian

A previous article in ME December 2000 pages 544-546, Yes that long ago! , I was constructing the electronic control from the circuit design and parts lists .

After 2 completely new attempts, ie new components and boards, I could not get the motor to work. After checking(I am not an electrical engineer) I found that I had 14volts after the diodes but no further volts from thereon in.

Has anybody used this design and can offer any ideas as to why it does not work, apart from the obvious that that I am at fault in some respect, and offer any suggestions for a possible commercial speed controller for a complete beginner that is easy to wire up

any advice welcomed

Ian

I have not built the circuit but looking at the schematic there appears to be two errors that would prevent it from working.

The emitter lead of the 2n3055 transistor is not connected to anything, it should be connected to the minus power supply line at the bottom of the schematic.

The diode (D1) at the collector of the 2n3055 appears to connected backwards. As shown it will not pass the plus voltage to the transistor. ( this would explain why you are not reading a voltage here.)

John

ME4134

Edited By Ady1 on 15/02/2017 01:14:20

Hmm - not sure about that aspect. Looks to me as though the current goes around the diode via the motor then the power transistor to reach negative rail (via the missing connection?). Replacing the diode the 'correct' way round would lead to release of magic smoke I fear.

The only error with the schematic is that the emitter of the 3055 should be connected to the negative supply rail, the bottom line under the transistor. The diode connected to the collector of the 3055 is a catch diode which with the parallel capacitor serves to protect the transistor from back EMF transients generated by the switching due to the PWM signal applied to the transistor base.

I agree with David. The diode D1 is there to protect the circuitry from back emfs generated by switching an inductive load (the motor) in the collector of the transistor. Connecting the emitter of the 2N3055 to the negative rail should do the trick. Presumably since this is a major omission a search of the following editions of ME would turn up a correction. It might be worth a look if you have them just in case there are other problems with the published circuit.

Regards

Graham

Ian

Gentlemen, thankyou for your immediate help, it is most gratifying to have an answer to my tweet(?)

I will amend the circuit as you have all indicated and let you know the results

I was not able to receive later editions of the mag. but corrections could have been made.

Special thanks to Ady1 for the research to enable the diagram and article to be highlighted

Regards to all

Ian

Ian

Issue 4138 Page 64 carries the corrections. I don't have immediate access to my copy but someone else on the forum may have a better data retrieval system than mine!

Regards

Graham

I was just about to type that there were corrections published... but I won't.

Neil

I fully agree with assessment that the diode is correct as published. After I wrote that I had second thoughts about my reasoning, as soon as the transistor was turned on there would be nothing to limit the current except the diode and transistor, and as David said probably accompanied by "magic smoke". Sorry about that.

Well done, Ady1

MichaelG.

Ian

thankyou Ady1, I will keep you all posted when I amend the circuitry and test. Fingers crossed

Again, thankyou all

Ian

Ian

Anybody who needs a simpler method of powering a cross slide might be interested in a further article I had in my files from way back.

This method uses a secondhand car wiper motor or an electric window operator obtained cheaply from car breakers etc.The article was by David Machin in Model Engineer December 1994(yes, I know am going back but there are members, who like me are approaching 80 years and have accumalated lots of articles for when they retired. Iam only now finding the time " to get a round toit" The articles ended on pages 226 - 229, 17 February 1995 but this last part gives the circuit diagram and constuction details of the electrics. Constuction of the alterations to the slide,box housing the electrics, etc were made in the previous 8 issues.Reference is made to the actual alterations and drawings produced by the well known supplier A Hemmingway who according to the article supply some of the castings.I opologise that I do not have the previous issues but if anybody is wanting to try this method I can send copies by email of this part, if addresses are made available

I have an MD65 but, until the batteries died, just used my drill with a socket that fitted the handle nut. My replacement drill because I hadn't got round to sorting the batteries has now died too.

The problem with the circuit diagram is also that it is drawn cack-handed. The convention is input on the left and flow to the right and make sure your output stage switch doesn't look like it's upside down. It is one of the pitfalls when articles are introduced from another hobby/discipline - bit like seeing an electronics mag showing 'milling ' in a pillar drill. Hopefully our current editors take advice appropriately when straying from their specialisations.