mini lathe circuit board

The KBIC/KBLC motor controller circuit board which drives my Chester Conquest mini lathe has died, yet again.
I am fed up with repairing it (and I am usually a patient and repair-y
type guy, I nursed a Hoover washing machine which went wrong at least once a year for 40 years).
The one I bought is a HHD6-G model, 1200W 220V AC input 0-220V DC 8 Amps output, whereas the motor on my lathe is 90V DC and rated at 5 Amps.
Bit of a mismatch, but... it is a true speed controller, the speed doesn't vary with load, and so I put a resistor in series with the pot in order to prevent high speed, high current, high voltage, high power situations. It is plenty fast enough.
And - it works, much better than the KBLC did. For normal use the motor does not seem to be overheating, though later when I upgrade it (when the reversing switch arrives from China - Chinese stuff can be good and really cheap, but it takes so damn long to arrive!) I will put a thermal cutout on it. It has a fuse already.
What's good? The speed doesn't vary with load. At all, it seems, unlike the KBLC, which would do so noticeably.
More impressive, the improvement in low-speed torque is astounding. I can't stop the chuck by hand, which I could do with the KBLC.
Thread cutting has gone from just-about-doable-if-it's-small to charge-in-there-lad!
Very pleased
(except I wired it up wrong first time round and blew all the fuses and all the tracks on the input mains filter board - in keeping with the phrase: measure twice, cut once, we should have: check with a meter for stupid inattentive mistakes before applying mains for the first time!)
Peter Fairbrother
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On 10/08/17 12:28, Peter Fairbrother wrote:


Sounds like the original controller was triac or scr based, with little or no velocity feedback, hence the speed variation. If the motor is a 90 volt item, that system was probably designed for a US 115 volt line and they just backed off the phase control limit to prevent motor burnout on 240 volts. Problem with that is high peak currents in the motor and controller, which may account for the reliability problems.
Now, sounds like you have a pwm mosfet based controller, but in that case, you are chopping rectified 240v volts AC to the motor, which may cause overheating, or armature breakdown. Have bought several of those cheap pwm controllers and they work pretty well, but you need to match the pwm voltage to the motor. In this case, could be 300 volts + peak to peak across the motor. Suggest you try running that controller from a 110 volt tool transformer to see if it works, then use that instead of 240 volt mains...
Regards,
Chris
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