Electronics > Beginners
What kind of motor is this? Meant for AC, but can be driven with DC?
help_me_pick_username:
I took apart an old vacuum cleaner today. I found a tiny PCB with a triac and a DIP8 IC (couldn't find datasheet) that I'm guessing is some sort of MCU for turning off the motor if it's been running for too long? (Does that seem like a plausible explanation?).
Anyway, I found a motor. It's pretty big and heavy, I've attached some pictures.
I measured the resistance across contacts 1 and 4 (these were the two contacts that were connected to the PCB), and got 1.2Ω. I decided to power it with my DC bench power supply and see what would happen. To my surprise, at about 6.5v, the motor started spinning, drawing about 1.2A. I kept raising the voltage and the current remained constant at about 1.2A, and the motor kept spinning faster. The highest I went was 32v, which was the highest my PSU went, and it was still drawing 1.2A, and the high pitched whine was annoying, so I didn't run it for very long.
I don't know how the two contacts of either side are connected (continuity tester said each pair was connected, with a few ohms of resistance, but this could just be the coils, so I don't know), but the motor only worked when powered through contacts 1 and 4. I tried to power through 1 and 2, but it didn't run. Another thing to note is that the motor only runs in one direction. If I flip the DC voltage on 1 and 4, it still spins the same way.
So I have a few questions. What type of motor is this? How is it running on DC when it is meant for a much higher AC voltage? There are two brushes and a commutator, I thought that was a brushed DC motor thing?
I was wondering if the two coils on either side of the motor (the ones connected to contacts 2 and 3) were acting as permanent magnets, thus creating the same design as a brushed DC motor...? Is that even possible?
Since this is a pretty large motor, will I have to worry about damaging my power supply while driving it? Inrush current shouldn't be an issue since my PSU has current limiting, but what about when turning off my power supply? Will I have to worry about the negative voltage spike damaging my PSU? I watched this video by ElectroBOOM: https://www.youtube.com/watch?v=yO9xIVv8ryc&vl=en. In it, he solves the negative voltage spike by placing a diode across the contacts. Should I do this when powering this motor with my PSU?
If I have made some incorrect assumptions in this post, please feel free to correct me, I do not have much experience when it comes to AC or DC motors.
Nusa:
https://en.wikipedia.org/wiki/Universal_motor
james_s:
Universal motors are ubiquitous in domestic vacuum cleaners, food mixers, blenders and various other things that need a powerful, compact, cheap motor that does not require a particularly high duty cycle.
They will typically run waaaay below rated voltage. Not as powerful as on the full rated voltage of course but most will spin on 5% of rated voltage.
help_me_pick_username:
Since the motor is rated for 240v AC, does that mean I could (theoretically) run it at 240v DC?
Zero999:
--- Quote from: help_me_pick_username on December 23, 2019, 08:10:41 am ---Since the motor is rated for 240v AC, does that mean I could (theoretically) run it at 240v DC?
--- End quote ---
Yes it should be fine off 240VDC. I've tested one before running from a bridge rectifier connected to the mains, with no smoothing capacitor. A smoothing capacitor would increase the average voltage towards the mains peak voltage of 340V, which would cause the motor to run faster and hotter, than what it was designed for.
Often a TRIAC is used to switch the motor, so the on/off switch can be smaller. Did you get the part number for the 8 pin DIP? Perhaps someone here can find the data sheet. I could also be an opto-isolator.
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