04-17-2012, 03:37 PM
Hi Peter,
In my experience, *all* Chinese machines' DC motors run hot - whether in the small mills, lathes or the accessory power-feeds - it's just a fact of life, economics being what they are. Many (if not all) of the motors have been "optimised" to reduce the amount of (expensive) copper by using thinner-gauge windings and (relatively cheap) higher-temperature winding insulation and varnishes to allow higher than expected running temperatures :(
The real killer is actually running them at low speed delivering high torque (actually or close to stalling is the worst), where:
a) The fan isn't rotating fast enough for sufficient ventilation, causing the temperature to rise *significantly*
b) The speed of rotation doesn't generate enough back-EMF in the armature windings and the current rises significantly too...
Once a DC motor gets close to stalling, the current can be several times that at full-load *at the rated speed*, which is why even the cheap DC motor drives have current-limiting built in - and some importers are specifying additional fuses between motor and controller (a *very* good idea!).
I've used a WM14-alike as power source for a flexible drive for extended periods (well over an hour at close to its maximum speed, porting a cylinder head when my German-made drill press had died) and the motor was uncomfortably hot to touch by the time I'd finished, but it doesn't seem to have suffered any harm, even with heavy grinding loads - so far, anyway!
I've also used it for some very odd things, like spinning a 6" ally disc with pieces of hard-disk magnets glued on to simulate the CDI pickup on my son's motorbike, while reverse-engineering an unobtainable Japanese ignition system... 6 magnets at 2150RPM gives a good approximation of its 13,000RPM redline
Dave H. (the other one)
In my experience, *all* Chinese machines' DC motors run hot - whether in the small mills, lathes or the accessory power-feeds - it's just a fact of life, economics being what they are. Many (if not all) of the motors have been "optimised" to reduce the amount of (expensive) copper by using thinner-gauge windings and (relatively cheap) higher-temperature winding insulation and varnishes to allow higher than expected running temperatures :(
The real killer is actually running them at low speed delivering high torque (actually or close to stalling is the worst), where:
a) The fan isn't rotating fast enough for sufficient ventilation, causing the temperature to rise *significantly*
b) The speed of rotation doesn't generate enough back-EMF in the armature windings and the current rises significantly too...
Once a DC motor gets close to stalling, the current can be several times that at full-load *at the rated speed*, which is why even the cheap DC motor drives have current-limiting built in - and some importers are specifying additional fuses between motor and controller (a *very* good idea!).
I've used a WM14-alike as power source for a flexible drive for extended periods (well over an hour at close to its maximum speed, porting a cylinder head when my German-made drill press had died) and the motor was uncomfortably hot to touch by the time I'd finished, but it doesn't seem to have suffered any harm, even with heavy grinding loads - so far, anyway!
I've also used it for some very odd things, like spinning a 6" ally disc with pieces of hard-disk magnets glued on to simulate the CDI pickup on my son's motorbike, while reverse-engineering an unobtainable Japanese ignition system... 6 magnets at 2150RPM gives a good approximation of its 13,000RPM redline
Dave H. (the other one)
Rules are for the obedience of fools, and the guidance of wise men...
(Douglas Bader)
(Douglas Bader)