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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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Rectifier added after factory assembly? Was Help please with PWMsewing machine pedal
On Wednesday, September 9, 2020 at 4:05:35 AM UTC-4, Cydrome Leader wrote:
wrote: Did you mess up the timing of the motor by chance? The angle of the brushes makes a huge difference. maybe? How's the motor run with no speed controller? The brushes are sleeved and fit in only one way. About the only other 'unusual' possibility is that Eric has a Euro version - which has flat paper caps in the motor. They should be REMOVED and NOT REPLACED! Peter WIeck Melrose Park, PA It's only somewhat related to this, but I have a precision drill press with a real goofy looking manufacturer supplied speed controller. I called them up about something unrelated and and issue of weird bursts in speed came up. You'd have no load on the motor and it would randomly start to race. The suggested fix was to open the speed controller and cut out a bridge rectifier that turned the AC output of the triac speed controller and just let the motor get AC. So, the rectifier no longer turned AC output of the controller to DC? So, the controller wasn't used after that? It worked fine after that. I'm not sure why they added a bridge recitfier in the first place, or why removing it made a difference but it did. Didn't they need DC to the controller's resistor circuit? The motor is pretty similar is size to a sewing machine motor, and the standard universal motor type deal. The whole controller is cobbled together looking so I can't even tell if they added the rectifier or the OEM did. Oh, the rectifier was added after the original sale. I'm sort of tempted to try the drill press with a properly designed industrial speed controller (Dart Controls), with and without the bridge rectifier to see how it behaves. |
#2
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Rectifier added after factory assembly? Was Help please with PWM sewing machine pedal
bruce bowser wrote:
On Wednesday, September 9, 2020 at 4:05:35 AM UTC-4, Cydrome Leader wrote: wrote: Did you mess up the timing of the motor by chance? The angle of the brushes makes a huge difference. maybe? How's the motor run with no speed controller? The brushes are sleeved and fit in only one way. About the only other 'unusual' possibility is that Eric has a Euro version - which has flat paper caps in the motor. They should be REMOVED and NOT REPLACED! Peter WIeck Melrose Park, PA It's only somewhat related to this, but I have a precision drill press with a real goofy looking manufacturer supplied speed controller. I called them up about something unrelated and and issue of weird bursts in speed came up. You'd have no load on the motor and it would randomly start to race. The suggested fix was to open the speed controller and cut out a bridge rectifier that turned the AC output of the triac speed controller and just let the motor get AC. So, the rectifier no longer turned AC output of the controller to DC? So, the controller wasn't used after that? Correct. The chopped up AC was no longer full wave rectified into choppy DC. I never looked at the waveforms, but they were probably awful. It worked fine after that. I'm not sure why they added a bridge recitfier in the first place, or why removing it made a difference but it did. Didn't they need DC to the controller's resistor circuit? There was no feedback from the rectified output. I keep thinking it was a wall mounted light dimmer or something cheap like that inside the box, but with an electronics-looking knob. The motor is pretty similar is size to a sewing machine motor, and the standard universal motor type deal. The whole controller is cobbled together looking so I can't even tell if they added the rectifier or the OEM did. Oh, the rectifier was added after the original sale. It was added at the factory. My only modification was to remove it, as the support people suggested. I'm sort of tempted to try the drill press with a properly designed industrial speed controller (Dart Controls), with and without the bridge rectifier to see how it behaves. I haven't run this test yet, but will soon. |
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