| Electronics > Projects, Designs, and Technical Stuff |
| DC Motor Questions |
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| Xnke:
So, not like how to control one...I'm running a PWM/H-bridge controller. But, I have a 4-pole, permanant magnet, lap-wound motor. It has four brushes, two + and two -, with the + brushes 180* from each other, and the - brushes 180* from each other, and + and - brushes are set 90* to each other. It is rated for 20v, 20A service, with the brushes wired in parallel. IGNORING HEAT, If I were to wire the brushes in series, would I be greeted with a happy 40V, 20A motor? Would it now run 4 times faster? As far as why we're ignoring heat, the motor has no fan and has an external port on the front housing and the brush housing for a blower to run. If the motor would be happy at 40V, but wouldn't automagically desire the full 20A current, (If current will still be based on load) then having a squirrel cage blower mounted on the rear shaft of the motor would supply plenty of cooling air. I am not finding many details on how 4-brush permanant magnet motors operate, beyond "it will be lap wound and the number of brushes is equal to the number of poles, if it is a high-current motor". Wave wound motors are for "lower current" and only ever need two brushes. Basically I've got a big brushed DC servo motor that is missing the encoder, it's in very good condition (practically new) and I wanna press it into service. Ideally it'd be a 800W 2500RPM motor, but it is a 400W motor that is ridiculously overbuilt with no fan to cool the armature. I *Suspect* it's a 1000RPM motor, but until the motor shop finds me some spare brushes (I wanna have extras if I am gonna run this thing) I won't have it assembled to test and see how the motor reacts to 40V operation. |
| duak:
Here's some observations but no answers. I've got an brushed DC instrumentation motor with two brushes located 90 degrees apart, not 180. I didn't dig too deeply and sort of found out that the armature was wound differently but I don't know why or if there was an advantage. I seem to recall seeing some servo motors in CNC machines that have 4 brushes, all placed 90 degrees apart. Not knowing for sure, I would bet the extra brushes allow for greater current and thus higher short term torque. I'd also bet that the brushes are diametrically at the same potential by way of the armature so I doubt they could be connected in series. However, I don't know for sure. I'd be interested to find out more too. Cheers, |
| jmelson:
--- Quote from: Xnke on October 24, 2018, 01:18:59 am ---But, I have a 4-pole, permanant magnet, lap-wound motor. It has four brushes, two + and two -, with the + brushes 180* from each other, and the - brushes 180* from each other, and + and - brushes are set 90* to each other. It is rated for 20v, 20A service, with the brushes wired in parallel. IGNORING HEAT, If I were to wire the brushes in series, would I be greeted with a happy 40V, 20A motor? Would it now run 4 times faster? --- End quote --- NO! The armature and commutator are wound to have 4 magnetic poles, and the field is provided by 4 magnets. Without rewinding the armature, you can't change the fact that it is a 4-pole motor. And, the commutator and brushes are set up for the same architecture. Jon |
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