Real Bull Controller box question

[sacentre]

I hope I'm in the right forum. Apologies if not.

Is anyone else using a lathe with this controller box (see photo)? I bought it to replace an older controller which didn't come with a tacho but the KBIC-240D controller board is the same.

I have a question about the RPM display. After about half an hour, the digital display starts flashing "8888" about twice a second. It clears if I switch off and on again. Is this some form of temp/overload signal or could it be a fault somewhere?

TIA

Trevor

 

[markba633csi]

Do you have the speed sensor and magnet installed? In other words is it reading correctly and then suddenly start flashing 8888?
-M

 

[sacentre]

I have the opto-isolator and the slotted disk installed (I'm not aware of any magnet) and the RPM reading appears to be accurate then it suddenly starts flashing "8888" until I switch off and on again.

 

[markba633csi]

OK you have an opto system rather than magnetic/ hall effect type.
Not sure what It could be- possibly interference from the motor getting into the sensor leads? Have you tried repositioning the wires?
Does the failure occur after a period of time even if the motor is not run? If so then the problem would be isolated to the readout itself

 

[sacentre]

Thanks for the help. No, the display remains at "0" indefinitely with the motor not running. If I turn the chuck by hand, of course the reading goes up then settles back to "0" again. As for interference from the motor, I guess I can dismount the box and move the encoder lead around and see if that helps. I'm assuming you either don't have this type of controller or you have one but don't see this problem?

 

[markba633csi]

I don't have one but have experience with electronics. Either the encoder is picking up EMI (electromagnetic interference) or there is motor noise coming thru the power supply to the readout. It may require adding some filter capacitors on the readout power supply lines or the encoder.
Experimentation is key if you don't have an oscilloscope to view the noise directly.
Be careful when working on live circuits around the motor control section
-Mark
PS is this a brush-type motor or brushless?

 

[sacentre]

It's a brush motor. I get the EMI possibility but how might we explain the regular .5 sec timing of the "8888" display. It would have to be getting the timing via the on board crystal I imagine. Then there's the fact that the problem only occurs after I've been runing the lthe for half an hour which seems to suggest a thermal issue. I'm a complete novice where electronics theory is concerned.

One thing I didn't mention till now as I didn't think it was relevant, is that because this box was designed to fit the Real Bull CJ18A and its clones, the mounting holes didn't match up with my much older lathe so I discarded the original plastic box and fabricated an almost identical one out of aluminium. All the guts are in exactly the same layout as the original. I suppose it's possible that might have contributed to EMI interference.

The only thing to do now is dismount the box from the lathe and see if the behavior changes by moving the encoder leads around a bit.

Thanks again for the interest and helpful advice.
Trevor

 

[markba633csi]

I discounted the thermal angle since you reported the issue doesn't occur if motor stopped- it points to a noise pickup problem
You might want to double check that- leave it on for several hours and see if it fails spontaneously. Make a hypothesis and then test it.
-M
PS by the way, it's almost certain the readout operates on a low voltage like 6 or 12 volts dc. There may be a stepdown transformer or they derive a low voltage supply in some other way like a capacitor input supply from the 120 volt line (the latter presents some shock hazard; no isolation)
If you can break the readout power free and run it from a battery instead it might help you zero in on the problem faster. By all means, be careful
Post some pictures of the inside of the controller if possible so I can advise better
It just occurred to me the 8888 might be a self diagnostic if the encoder stops outputting signal or gets disconnected-? maybe

 

[sacentre]

Thanks again, Mark. Here are some photos and short video clips. The display started flashing after about 5 or 6 minutes when I tried it this morning (clips 1 and 2). It usually takes much longer than that. I got the box off and ran it again. Same thing after about the same time. I pulled the 2 white ribbon cables away from the innards somewhat (clip 5) but it made no difference. If I disconnect the 3-way encoder cable while it's flashing and reconnect it, the display resets and works normally until until after 5 mins or so when it starts flashing again.

As you suggest, I'll try running a separate DC supply and see if that makes any difference. It's 5v according the silk screen printing on the PCB. That'll take me a while though.
Thanks again for your patience and invaluable help.
Trevor

 

[markba633csi]

OK now, when it's working normally and you disconnect the encoder what happens? Does it do 8888?
I see a small transformer in there, that must be for the readout power. The speed controller looks just like a KB electronics SCR drive or clone.
Very reliable, as long as you don't go poking around in it with power applied.
Other observations: It looks like the readout board has a large IC which might have a recognizable part number- and it's a dual in-line IC and possibly in a socket which makes for easy replacement.
My feeling is the opto interrupter may be flaky- here's where I would break out the oscilloscope, but maybe you could monitor the output with a multimeter if you turned the spindle slowly by hand. It should be giving a 0 to +5 volt squarewave signal to the readout board