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Jeff,
This scooter listed on EBay motor you recommend (ZY6812 24vdc 150w? motor) is listed as a brush motor. Does it run smoothly and quiet??

Thanks, Dick

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I see this motor is still on EBay but it is a brush type motor and not a permanent magnet dc motor. My experience with a brush motor has been too much noise.
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Provided you are reasonably sure the 24 V motor can withstand pulses of 90 V, I would give it a try. However, if it can't, you could land up with a damaged motor quite quickly.

Alternatively, if, by some type of circuit I cannot imagine, the peak output from the B controller is reduced below 90 V, I'd go ahead, but I have never met a controller that did that. It approximates 24 V by chopping up the 90 V into a series of pulses giving an AVERAGE voltage of 24, so on for about 27% of the time. I will as my brother, who has much experience of driving motors, what he reckons. It's possible something could be going on that is beyond my understanding.

Of course if KB say it is never a problem, then go ahead.

Keith,
KB states my unit is designed for permanent magnet and shunt wound motors DC motors. This control can use 120 volt AC input and is designed for 90 volt SCR rated motors. I want to use a 24 volt motor.
I am going to contact tech support by phone to get as much direction as I can to determine if the motor I want to use will safely handle the higher voltage of the 90 volt KB unit. If it is determined the 90 volt output could damage my motor I will use a 24 volt power supply as you originally suggested.
If they tell me I can adjust the trim pots to achieve my goal I will try that first.
Does this sound like a reasonable approach?
Dick
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I think the KB controller could well be OK with a 24 V motor, but the motor will be subject to 90 V spikes, and the general insulation might not be able to handle it. They may have used higher grade enamelled wire on the armature, if it is cheaper through being used on so many larger mains powered motors, but they might have used the minmum. If they used the minimum you could burned out a motor very quickly. I suspect KB would recommend against it unless you can get assurances from the motor maker that it is OK, and I don't thin it will be easy to confirm that.

The 24 V DC option I outlined before will still give good performance, and once the motor is fitted you've done the hard part.The electrics could hardly be simpler and it is more certain that it will work without trouble.

The you tube videos may help, but they are only really going through what we have already discussed.

A sewing machine motor, whether modified to go the right way, or from an overlocker, will be similar to an original Unimat motor in it's characteristics, and, has has been explained, not too god as a variable speed drive.

In your situation I would go back to the 24 V DC motor option. We know it works, there are no issues with applying high voltages to a low voltage motor, and the electrics are quite simple. The only snag I can see is making a control box, and that is largely a mechanical problem of fitting connectors through a panel. If you allow plenty of space, like making it as a box for the lathe to stand on, there will be plenty of space, and that's usually the problem.

My rule of thumb when deciding how big a control box should be:

1. Carefully design the box allowing generous space for wiring around all the components.

2. Buy a box twice that size.

3. Find you still can't fit everything in.

However, a sensible size plywood box under the lathe will be big enough, I'm sure of that. Hint - fit a baking tray on top of the wood, partly as a protection, but also to act as a chip tray. This will also influence the size of box you build..

Clark,
What resistor would I need to use in my 90 volt KB motor control to get the voltage down to 24 volts and where would I plug it in?
Or should I contact KB support for this?
Dick
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Keith,
I looked for a 90 volt motor that will work with the KB controller I have but they are all higher horse power and too large for the Unimat.
So I might end up doing as you first suggested and get a low cost 24 volt motor controller from EBay to match the motor. The manual I have for my controller stated to use only 90 volt motors.?

Dick
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On Thu, Sep 16, 2021 at 08:39 PM, OldToolmaker wrote:

I contacted KB tech support and was told to turn the potentiometer all the way CCW before turning the motor on as it could be damaged if set too high.
I am assuming I can turn it up as required once it is on. Am I correct in assuming this may be a bit of a risk to the motor as it would be easy to slip up and ruin the motor?

I would start with both MAX & MIN speeds set to zero, or as low as they go. Try varying the motor speed - if it moves at all it should be from standstill to a low speed. I would then turn the MAX speed up gently, until the revs are in the right sort of range, then pause for thought. How can you check the MAX is right for the motor? The output to it will almost certainly be pulsed, so you would either need an oscilloscope or a true RMS voltmeter to check, and I would guess you don=t have either. There are low cost pocket scope/meters out there which do both, but I'm not sure how good they are or how easy to use. The other way would be to check the motor revs, and see if it is anywhere near the rated maximum speed on no load. Rev counters can be electronic, optical, but the old mechanical types may be possible if you have any small gearboxes handy. Using a gearbox with, say, 100:1 reduction, you apply the input to the motor shaft with a bit of rubber as the coupling - just press it on - and then cunt the output rotations while timing it with a stopwatch, or just a clock with a second hand. An assistant to give Start & Stop commands would be useful.

This is a truly antique version:? . I have seen similar ones offered at tool sales, and there is nothing wrong with them in spite of being old tech. Apart from anything else the batteries don't run out!

The pointed is pressed into a recess in the end of the shaft - I assume from a centre drill - and taken out after standard time - I'm guessing ten seconds - and the number indicates the RPM, probably sufficiently accurately for your purposes. So what have you got kicking about the workshop that could be used? I have some small 100:1 worm boxes, but I think the postage to you would be a bit too much.

The remaining worry is that the maximum voltage applied to the motor - the peak voltage of the pulses, not the average voltage - may be too high for the motor insulation, or for the commutator. I tested a brushed motor one day by plugging it into the mains, 230 V here, and it went round very fast with a ring of arcing around the commutator. It was a 110 V motor. Actually it could have been just what you need, but we binned it years ago, and see the note about postage, above.

Don,
I have the manual. I understand what you are saying and I will look at that as soon as I have the motor in hand. Everything you said makes perfect sense and I am sure I can adjust the trim pots. I will keep in touch.?

Dick
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Dick:

Short answer - YUP.? You definitely want to keep that knob turned down at first.? Turning it up too high will let the magic some out of the motor.

Here's a possibility, that drive has trim pot adjustments for the MAX and MIN speeds.? I'm not sure how MUCH adjustment is allowed but it never hurts to try it.? Did you get the User/Installation manual with the drive?? If not it's available on-line - just Google kb drives manual.? It's a 16 page PDF and it's pretty self-explanatory.? The factory defaults supposedly have the MAX trim pot set to rated speed and the MIN speed set to 0 - they both should be turned all the way, one way or 'tuther.? This will let you set the upper and lower limits for the motor speed.? I'd check what the MAX trim pot is currently set to, and then with the motor running try turning that guy the other direction and see what it does.? You should get an immediate response out of hte motor.? You MIGHT have to cycle power to the drive, but I doubt it since you're adjusting an actual device.? Who knows, it might actually let you limit your max speed to what you want.? That way you still have the full Min to Max range of adjustment available on the speed pot.? And, you are taking advantage of some the drive's capabilities.

Don

I contacted KB tech support and was told to turn the potentiometer all the way CCW before turning the motor on as it could be damaged if set too high.
I am assuming I can turn it up as required once it is on. Am I correct in assuming this may be a bit of a risk to the motor as it would be easy to slip up and ruin the motor??
Dick
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Dick:

If there's a nameplate on the motor it will usually list the FLA (full load? amps) of the motor - HP or KW might also be listed on the nameplate.? From the FLA and the motor voltage you can get a ROUGH idea of the motor wattage.? Failing that, see if there is a manufacturer's name and/or model number stamped on the motor someplace.? I've used those to dig up the manufacturer's motor data before.? If the seller is unwilling to do that for you, I'd move on to another seller/motor.

You'd be surprised how much info you can find if you ask Google the right questions.

Don

Thanks, Clark!
I have one more question to ask. How does one determine the wattage of a dc motor if the seller doesn’t know or is unwilling to find out. I want to find a 24 volt permanent magnet dc motor about 150 watt.
Dick
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I think a footpedal speed controller can be added in a similar way to that resistor but to different legs of the regular speed knob. I’d looked at different footpedals that I thought might be adapted, I can’t remember if I found a good one that would work that way that was also cheap. For the Consew branded brushless motor I mentioned earlier I replaced the insides of a sewing machine pedal with a circuit supplied with the Consew controller.