K
Kermit
Guest
Pulse width modulation hits the motor with the FULL voltage, so you develop FULL field strength. At low motor speeds the time in which the motor is getting full power becomes a shorter duration than the time during which the motor is getting no power. An unpowered motor when driven by mechanical means becomes a generator!
The magnetic fields built up by the motor currents grow and collapse much slower than the electricity moves, so the next motor drive pulse comes in and keeps things going in the same direction, but not before the motor has slowed itself down, by generating reversed electricity. Enough inertia remains in the spinning mass to keep things chugging along at a reduced speed.
The back EMF could be causing your troubles, the currents being felt at the brushes are not steady and the extra surges are creating more arcing and sparking on the brushes and commutator. This(low speed operation) would be much harder on the mechanical parts just mentioned because of that. With out special protection devices these pulses can destroy transistor junctions and other electronic things as well. Result is extra 'stress' on those high power silicon junction devices. Meaning a higher number of units manufactured will have power problems somewhere down the road. Building them with better electronic protection equals increased manufacturing cost. (not gonna happen at the rock bottom prices chinese wholesalers are seeing) Just put Mosfet devices in which have much larger margins of 'withstand' voltage. Cross your fingers and ship them. Many will do fine, but lots more will fail than we consumers think should.
Blackvette has the solution. Repair and replacement of parts will get you going again. Zee, periodic maintenance including removal of brushes and cleaning of motor parts you can reach will extend the life of those brushes.
For the rest of us, we have to cross our fingers as well, and hope the stresses of operation are falling on 'healthy' silicon and mechanical devices that can stand the abuse. ;D
I'm not a wiseass, but I play one on the internet,
Kermit
The magnetic fields built up by the motor currents grow and collapse much slower than the electricity moves, so the next motor drive pulse comes in and keeps things going in the same direction, but not before the motor has slowed itself down, by generating reversed electricity. Enough inertia remains in the spinning mass to keep things chugging along at a reduced speed.
The back EMF could be causing your troubles, the currents being felt at the brushes are not steady and the extra surges are creating more arcing and sparking on the brushes and commutator. This(low speed operation) would be much harder on the mechanical parts just mentioned because of that. With out special protection devices these pulses can destroy transistor junctions and other electronic things as well. Result is extra 'stress' on those high power silicon junction devices. Meaning a higher number of units manufactured will have power problems somewhere down the road. Building them with better electronic protection equals increased manufacturing cost. (not gonna happen at the rock bottom prices chinese wholesalers are seeing) Just put Mosfet devices in which have much larger margins of 'withstand' voltage. Cross your fingers and ship them. Many will do fine, but lots more will fail than we consumers think should.
Blackvette has the solution. Repair and replacement of parts will get you going again. Zee, periodic maintenance including removal of brushes and cleaning of motor parts you can reach will extend the life of those brushes.
For the rest of us, we have to cross our fingers as well, and hope the stresses of operation are falling on 'healthy' silicon and mechanical devices that can stand the abuse. ;D
I'm not a wiseass, but I play one on the internet,
Kermit
