Conveyor speed controller failure?

[julianf]

Some swarf got into the contactor that controls this -

I replaced the contractors, and the other motor in the machine runs, but this one does not.

The other motor is just full power all the time, but this board is a speed controller for a conveyor belt.

It may not be clear in the photo, but bottom right is an illuminated power switch (post contacts etc) that takes 240v from out of sight and switches the two red cables (live and neutral, 1ph).

The potentiometer (top right) should be the speed controller and the black, white and earth are for the conveyor motor.


My query -

The machine was operating fine. There was visible swarf ingress to the contactor so I'm almost certain that was the initial issue.

But I'm unclear as to the possible knock on as to why it's not working now.

There is a single IC on the PCB, and a couple of transistors (I assume). No visible damage to anything.

I've not yet hunted for a schematic, as I'm only on my phone, but I suspect there may not be one.

I'm wondering if anyone recognizes this design of speed controller and can offer any advice?

Thank you.

 

[julianf]

This is the plate on the motor -

 

[julianf]

Testing the LM324N -

9v DC on VCC
Output one varies with the potentiometer, but (i cant remeber exactly) somthing like 0.3v range.
Outputs two and three show 0v against ground.
Output 4 is a stable (does not change with potentiometer) voltage.

Im sorry i cant remember the exact numbers, but, basically, one changes a little tiny amount, two seem dead, and the other is constantly high.

 

[Erie Fred]

Motor name plate narrows things down allot.
So it's a simple 180 vdc controller.
Very common, however I can't help much further.
EDIT: this looks similar:

https://www.surpluscenter.com/_MoreSpecs/AS11-2269.pdf

Or this:

https://www.surpluscenter.com/_MoreSpecs/UM11-3304.pdf

 

[eddie49]

It is a DC motor, running at quite a high voltage ( 180 ) but low current - just 1 Amp.
The controller will be a PWM ( pulse-width modulated ) type, with a timer chip - NE555 - or an Op-amp generating variable-width pulses, amplified by the small transistor and driving the motor by the large one on the heatsink - probably a MOSFET.
Easiest first attempt at a fix would be to replace all three semiconductors.

 

[m_c]

That's most likely just a basic SCR type speed controller.
Beware that the potentiometer wiring is likely sitting around half of mains voltage, so don't go probing it with your fingers!

If you want a cheap replacement, you'll find various on eBay/Ali/etc.
If you want something more supported, RS stock suitable Sprint drives for reasonable money such as - https://uk.rs-online.com/web/p/motor-controllers/8209549
Or the other popular choice are KB drives, which axiscontrols stock in the UK - https://www.axiscontrols.co.uk/products-services/products/dc-variable-speed-drives KBIC is the generic all rounder drive with various options, but IIRC they do a couple simpler options.

 

[eddie49]

Using a voltmeter to check the LM324 Op-amp is probably not going to show pulses, you would need a 'scope.
The small and large transistors could be checked with an Ohmmeter, after taking them out-of-circuit.

 

[eddie49]

That's most likely just a basic SCR type speed controller.
Beware that the potentiometer wiring is likely sitting around half of mains voltage, so don't go probing it with your fingers!

If you want a cheap replacement, you'll find various on eBay/Ali/etc.
If you want something more supported, RS stock suitable Sprint drives for reasonable money such as - https://uk.rs-online.com/web/p/motor-controllers/8209549
Or the other popular choice are KB drives, which axiscontrols stock in the UK - https://www.axiscontrols.co.uk/products-services/products/dc-variable-speed-drives KBIC is the generic all rounder drive with various options, but IIRC they do a couple simpler options.

Very true.
If the black-white-green supply cable is AC mains, and as there is no sign of a bridge rectifier, then it will be an SCR-based circuit.
So the DC output is half-wave ...? And how do they make the 9v VCC ....?

 

[m_c]

Very true.
If the black-white-green supply cable is AC mains, and as there is no sign of a bridge rectifier, then it will be an SCR-based circuit.
So the DC output is half-wave ...? And how do they make the 9v VCC ....?

DC output is a bit noisy, but works for the intended purpose.
9V is just a combination of diodes and resistors IIRC. The basic circuit is pretty crude circuit, but I've not looked at an actual circuit diagram for quite some time, so can't really remember many details about them. The commercial offerings typically have load compensation added, so the output speed is more stable compared to the bare bones circuit which can be prone to slowing under load.

 

[julianf]

Using a voltmeter to check the LM324 Op-amp is probably not going to show pulses, you would need a 'scope.
The small and large transistors could be checked with an Ohmmeter, after taking them out-of-circuit.

You mention pulses -

There's very little going on on the PCB. I'm sure a clock could be derived somehow or other, but I don't see any of the common "clock" stuff?

Am I really expecting pulses?

 

[eddie49]

The four op-amps in the LM324 chip can be cross-coupled to create variable-width pulses, for example:

How to DIY PWM Speed Control with LM324? - Electronic Components Distributor - SMBOM.COM

Create a PWM speed control circuit using LM324 and MOSFET, adjusting load speed from 0 to 100% by changing the duty cycle of the output square wave. Electronic Components Distributor

www.smbom.com

In that circuit the power driver is a MOSFET, on your controller it will be an SCR.
If you can read the number on the power semiconductor on the heatsink, we can confirm that it is an SCR, and identify the Gate and Cathode pins. There should be variable-width trigger pulses of about 3v between those pins, with positive on the Gate.

Replacement AC-mains-to-180v-DC motor speed controllers are available, e.g.:

Pardon our interruption...

 

[sako243]

Sprint drive

Fairly sure that's the brand of one I had one of those go pop on a well undersized motor running at full speed with no load.

Motor was off the machine, had accelerated up to speed and was just sitting there and bam main RCD in the building got tripped and magic pixies came out.

Confirmed with the manufacturer that the motor was well within spec, I'd not made any mistakes wiring it up and configuring it so it just got sent back to the distributor for a full refund and rolled my own.

 

[julianf]

This is the transistor that (i assume) does the switching -

I cant read the writing with my eye at all, and the best i could do was this photo.

The problem is that the large resistors are in the way, and their leads are not "slack" enough to bend them for line of sight.

Text almost looks like "BTY5Y" but clearly isnt (as nothing comes up with a google search for BTY5Y)

Can anyone more familiar with these things than me recognize it?

Thank you.

 

[julianf]

I went and had another look -

Its got to be "BT151"

then "500R"

 

[dan treg]

looks like bt151 to me

 

[dan treg]

ok posts crossed its a thyristor or similar

 

[jsf55]

BT 151 500r

Google Search

 

[julianf]

Thank you.

My next confusion is what this one is -

BT169D ?


The other one is clearly marked "2n6027" which was easy enough.