Simple DC speed control

A much needed item for workshop use and (in theory) aimed at the non 'geek-speak' constructor? Perhaps not!! An incomplete article - have to buy at least two issues to get the full story ... and the detail!!!

If someone produced an article for constructing a SIMPLE engineering item and waffled on about using EN75369cobalt/chromiumsteel mix in proportions of 3% of one to 5% another and that the production process entailed blah de blah and the ultimate strength could be modified by increasing other blah de blah, I suspect that there might be a little irritation. However electrics apparently are quite incompatible with the K.I.S.S principle e.g. List the required components, show a suggested layout and installation order, test for continuity etc .

I appreciate that to do so would deprive MTM of a second (or third) £4,80 purchase but there is going to be one less of those anyway!

rgds

Bill.

Bill,

my thoughts deleted 

Edited By John Rudd on 01/06/2015 11:14:49

You can please some of the people all of the time, and all of the people some of the time.

May I respectfully suggest that those who know how to please EVERYONE, ALL ALL OF THE TIME, sit down and write me some articles, naturally on topics in their area of expertise!

Neil

http://www.maplin.co.uk/p/mfa-panel-mounted-speed-regulator-module-rn41u

An almost identical circuit ready made on a pcb. Does the world really need another 555 speed controller?

.

Probably not ... and nor does it really need another model steam engine [etc. etc.]

But surely the main point of the article was to convey some understanding.

MichaelG.

http://www.maplin.co.uk/p/mfa-panel-mounted-speed-regulator-module-rn41u

If you read the questions it is said that "this product will not support a 12v car windscreen wiper motor" which is what a lot of us use for motorising purposes.

To be honest, I enjoyed the article, and felt it gave a useful and interesting explanation of some aspects of the device. I've a friend who has already sent for the components, and I expect to do the same for the items I can't source from my electronic junk box. What interested me most was that I have a board which will substitute for the potentiometer to provide speed control from the computer.

I suppose its a variation on the "different strokes for different folks" theme; but this one certainly suited me.

Marcus

Out of curiosity what max revs does a car windscreen wiper motor achieve?

On speed controllers one interesting aspect is giving more or less constant speed with load. Usually applied to mains voltage universal motors but in principle should be possible on low voltage dc too. I spent some time looking for a circuit and came up with nothing.

John

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Edited By John W1 on 03/06/2015 10:22:19

"write me some articles, naturally on topics in their area of expertise!"

Point 1. ... If I had the expertise, I would not be looking for a SIMPLE DC speed controller!!

Point 2. ... If you want a treatise on helicopter rescue or 747 technical systems, ask away!! Can't imagine an overwhelming interest.

Simple is as simple does, and that article, whatever else it may have been was NOT, ( for the non Geek-speak fraternity,) simple. One continues to live in hope that someone in the wiggly and straight amp community will write for the non-indoctrinated!

rgds

Bill

I use a wiper motor for the table feed on my vertical milling machine, it has a 3 speed control via home made resistors, made from nichrome wire from an electric heater, wired across a home made rotary switch. Direction of travel is obtained by a double pole On, Off, On switch. Motor is fed with 17V DC from my work shop low voltage supply.

Ian S C

John,

The principle for low voltage dc motors is to use either closed loop control or pulse width modulation (PWM) control. In both instances, the control circuit monitors the back emf and adjusts the controller as necessary to control the speed. There are 2 books by Roger Amos, "Practical Electronics for Railway Modellers", and "Practical Electronics for Railway Modellers 2" which go into these circuits in some detail. Fairly obviously, the circuits therein are designed for small scale model railways with their comparatively low currents, but it should not be too difficult to use higher rating output transistors.

Regards,

Peter G. Shaw

Thanks Peter. I did know about the back emf aspect so now I know where to look for suitable circuits. It's odd really as the old electronics magazines printed designs regularly but I don't see any on the web. I did work on electric vehicles some time ago but not on this particular aspect.. There is another control - the field windings if motors have them available. Trouble is that this can make them rev so fast that they may explode.

John

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Edited By John W1 on 03/06/2015 16:37:45

I use the speed controler off an old battery drill for my wiper moter if you find which wires are for the fastest speed on the moter then use these then you can go at fast speed or down to nothing,and you can use forward and reverse switch its worked ok for me at the moment i use a motorcycle battery as power untill i get hold of a differant sorce.Kevin

In 1975 they were quite exciting, I can't believe they remain the "go to" device for this sort of thing 30 years on!

Steve

Just found this one on ebay ... looks very promising.

Having the pot on flying leads is good for repairability.

MichaelG.

So don't these moaners want to learn anything? You can go out and buy a ready built loco, dividing head, whatever, but where's the interest in that? Personally I don't read the step by step "chuck a piece of 1" bar, drill 1/2" blah blah " articles as the don't contribute to what I already know, but I don't moan about them as there are beginners out there who don't know how to do it.

Full marks.

Now if this article was written for Electronics today it might , nay, would come in for some flack but aimed at the unwashed of this parish ?

All you need is a nugget of information to get the grey cells or sludge in some cases, working.