Clarke CL250J motor controllor

I found the excellent post created a while back on the forum a couple of years ago http://www.model-engineer.co.uk/forums/postings.asp?th=38809&p=1

This board is the CL250 version ther actual pcb markings 'Xin Yun Electront SMD-FC250.

What happens is when the speed pot is advanced it goes from a standing to almost full speed, from about 10 o'clock position, the speed is controllable slightly from this point!

It works perfect on a Lamp load varying very steadily but not the motor.... yet the motor runs comfortably on a 12V DC bench top power supply.

As mentioned in the post I did some checks these are checking the post these are measuring the pot and checking the voltage between pins 2 & 3 varys between 0 & 12V. I've recapped using 105 deg. low ESR types.

If it comes to replacing the SMDs I can do that being in the trade... this fault is bugging me, thinking it's around the feedback circuitry... be interesting to see what happens on a 'dummy load' drawing an amp or two, which I've never tried yet.

The motor kicks better than the Co-op donkey when starting from a stop to full speed! This board used the open type trimmers not the multi-turn trim pots.

Clues anyone pleas? Thanks

Dave

Here's a,snap of the board, it's a FC250J not FC250 as mentioned.

Hi Dave,

You may get a bit of help from Little Machine Shop's trouble-shooting guide here:

< http://littlemachineshop.com/Reference/DriveTroubleshooting.pdf >.

If you haven't come across them before, LMS is the main US source of spares and

info for lathes which (like yours) originate from the Seig factory in China.

Andy

PS: I had difficulty reading your initial post, because a banner advert down the RH side of

my screen obscured much of it, which is why there are a lot of carriage returns and hence

wide line spacing in this reply, and in the copy of the post which I've pasted in below.

I found the excellent post created a while back on the forum a couple of years ago

http://www.model-engineer.co.uk/forums/postings.asp?th=38809&p=1

This board is the CL250 version ther actual pcb markings 'Xin Yun Electront SMD-FC250.

What happens is when the speed pot is advanced it goes from a standing to almost full

speed, from about 10 o'clock position, the speed is controllable slightly from this point!

It works perfect on a Lamp load varying very steadily but not the motor.... yet the motor

runs comfortably on a 12V DC bench top power supply.

As mentioned in the post I did some checks these are checking the post these are

measuring the pot and checking the voltage between pins 2 & 3 varys between 0 & 12V.

I've recapped using 105 deg. low ESR types.

If it comes to replacing the SMDs I can do that being in the trade... this fault is bugging

me, thinking it's around the feedback circuitry... be interesting to see what happens on

a 'dummy load' drawing an amp or two, which I've never tried yet.

The motor kicks better than the Co-op donkey when starting from a stop to full speed!

This board used the open type trimmers not the multi-turn trim pots.

Clues anyone pleas? Thanks

Dave

Unfortunately, I can't really read your post because a banner advert obscures the RH side of it

Thanks for the link Andy, I'll have a look after some sleep, just that I'm curious why 'it seems' to work OK on a dummy load course thats not inductive.... and come to think a light bulb is a constant load unlike a motor.

Thanks again, Dave

Hi Dave,

I suspect this could be a motor fault. Although the motor seems to run OK on 12 volts there still could be a fault on it when running with a higher voltage. A build up of carbon between the segments of the comutator could flash over at higher voltage. The brushes could also bounce on the comutator a higher speed particularly if they are worn down. You could also have a partial short or open circuit in the windings. measure the resistance of the motor and turn the motor a few degrees at a time noting the resistance at each position. The readings should be about the same in each position. A high or low reading in one position indicates a fault. You could also dismantle the motor and measure the resistance between each pair of adjacent commutator segments. These too should all be about the same value.

Les.

For many years I worked designing systems which ran on computers. Yes the first machine had valves so that is how long ago it was. These machines worked 7-24. Ok they had shifts of engineers but they seldom failed.

I am puzzled as to why our ‘Modern Electronic speed condolers always seem to fail after a few years at the most. Is it the components? The basic designs or what? I have one speed electronic controller which I built about 30 years ago from a kit sold by a company called ‘John Bull’ somewhere in Soho London. It was and still is used on my Emco Unimat SL.

I suppose that the electronic speed controller are used for cheapness. However there are single phase speed controllers appearing. These are used mainly on ventilation fans and I an investigating them.

For the rest all my speed control is mechanical if it breaks I can rebuild it.

I was somewhat pleased to see the review in MEW of the Warco WM240B lathe. I have two growls/grumps with it.

The first is the speed range to my mind it is skewed towards the high end. 2000 RPM is satisfactory for mild steel of 0.144” (6.4mm) diameter however its low end is 125 RPM is satisfactory for 2.3” (58.5mm) steel. However much of our work (munching away at castings and thread cutting) we really require even lower speeds down to 25-50 RPM. At a quick glance a form of ‘Back Gear’ could be fitted into the final drive pulley. My second ‘grump’ is I would like a form of tower traverse. The simplest form is that used on the Myford Super 7, but I think it could be made even simpler.

Rdgs

Dick

Thanks to Les Jones 1, it does seem a feesible explanation everything else seems to be 'up to spec', voltages, mosfets resistance.... lol, I even checked what I could of the smd resistors, leaving only the two op-amps and the relays.

There 'could' be a clue in what you say, because at 'switch on', to be exact I should say when thev speed control reachers about 10 o'clock the motor kicks off from a stop to high speed (the speed control seems to work from this point) you get that very strong whiff of carbon spark smell, but not burning or varnish smell... so yep I plan on checking the motor next time round.

Pity, I had a DC - 230V motor and controllor in two weeks ago, this kept blowing fuses and was the mosfet, this wasn't anything to do with lathes, I just forget the make now... gee, I could have lobbed that motor in to try!

One thing I did not consider was diodes and FETs breaking down under load or when driven, had this lots of times in TV's, only the substitution method works here.

The link Andy privided is very handy, I've filed it, thanks.

This unit was something I was ask to repair, I'm not the owner, I'm into making and designing pcbs from scratch using cad, not on a professional mind - no silk screening here, quite a boring job.... drilling all the holes!!!

Thanks for all the replys to date,

Dave

Stripped motor down and all looked ok, cleaned armateur whilst out. Afraid it's not the motor as I tried it on a lashed up power supply, to be on the safe side I limited the voltage to 200V.

Checking with the lamp the voltage increases evenly from 0 to 216V, so I checked the voltage with the motor as load as soon as the speed pot reaches about half past nine the voltage jumps up from 0V to about 75 volts. When running if I try to set the speed that little whisker lower the motor kind of stops and starts.

Bring back triacs and thyristors please. Plenty high voltage transistors kicking about that will handle a good few amps with a power dissapation of 300 Watts, trouble is the voltage drop across the transistor times the current it's passing produces heat!

Dave

Hi Dave,

The fact that the output when the motor is connected stays at 0 volts until the speed pot reaches the nine thirty position makes me think there could be fast spikes from the speed controller due to the motor inductance that it interprets as a DC signal and making it think it is actually giving out a voltage. It might be worth checking the snubber components across the mosfets (R42, D2 and C2) It would be interesting to see how the PWM gate drive signal to the mosfets behaves. To connect a scope to the controller would require that the lathe was fed from an isolating transformer. There is a schematic HERE for either the FC250 or FC250J (It does not say which one it is but I suspect they are similar.

Les.

I could scope the drive, but at the moment I have no isolating transformer, I can understand the snubber clamping the spikes the motor makes as it turns due to it's inductance, can't see where else these could come from and the motor at this point hasn't 'twitched', admittingly a lamp's inductance is zero compared to the motor's inductance.

One of these things that gets me curious and curiouser, just love to crack this nut.... why does the voltage suddenly jump with the motor and not light bulb.... the pwm rise time perhaps and the inductance opposing it, perhaps it's anything but a sqaure wave - just my luck that!

To make the motor faster we need a longer 'on' time and a shorter on time to make it run slower as I always understood, scoping the drive as you suggested would be really interesting - but no isolating tranny, don't fancy sending a 150Mhz HP storage scope into orbit... it's a back buster!!!

I'll sleep on it over the weekend and try another angle of approach, thanks for throwing some light.

Dave

Sorted:

Thank you to all, what it was I dunno !!!!!

I removed all the through-hole components cleaned and retinned any oxodised connections and refitted..... up on power up 'zilch' nothing.

There was no 12V supplies, after a bit of head scratching and time wasted I applied a logical approach - use the test meter! Looking at the circuit at diode FR109 the cathode is connected to the negative terminal on the bridge rectifier not in this case...

because of a corroded connection on on the topside of the board of the earthy side of C2 the 600V 47nF capacitor which connects to the negative side of the bridge rectifier on the underside of C2, this meant the dropper chain at FR109 cathode wasn't connected!

Looking at the top side missing copper land (solder connection) around C2 negative lead was never meant to be connected.... but not according to the circuit. Once this connection had been made using a hard wired link. "Eureka", all was well and running slow on the slow setting.

So I put it down to a duff connection but where?

For information the actual FET 2SK790, TIL113 opto couplers and LM324 smd op-amps are available from Cricklewood Electronics... at a very resonable price!

Dave

Edited By Sparks on 18/04/2012 20:51:50