How much trouble am I flirting with?
October 6, 2010 10:12 AM Subscribe
Does a 120V AC -->12V DC power supply need an RF choke when used to power a small DC motor?
I'm building a small machine (an electric spinning wheel), and I'm in a bit over my head on the electronics. I plan to use a generic 12v DC power supply of the sort normally used to power LCD monitors and the like. This will be connected to a cheap reversible speed control, driving a small (~3.5A) brushless DC motor. I'm wondering whether it would cause some sort of havoc if I cut the 12v wire from the power supply short (thereby losing the integral RF choke) and hardwired it directly to the controller.
If you can answer this, please talk to me like the n00b that I am. I understand parallel and series, AC vs. DC, W=V*A, Ohm's law... and that's about it.
I'm building a small machine (an electric spinning wheel), and I'm in a bit over my head on the electronics. I plan to use a generic 12v DC power supply of the sort normally used to power LCD monitors and the like. This will be connected to a cheap reversible speed control, driving a small (~3.5A) brushless DC motor. I'm wondering whether it would cause some sort of havoc if I cut the 12v wire from the power supply short (thereby losing the integral RF choke) and hardwired it directly to the controller.
If you can answer this, please talk to me like the n00b that I am. I understand parallel and series, AC vs. DC, W=V*A, Ohm's law... and that's about it.
Best answer: ...and to expand that a bit, the choke is probably there because the supply is meant for more sensitive equipment, whereas a DC motor and its controller are very insensitive to high-frequency noise.
posted by springload at 10:29 AM on October 6, 2010 [1 favorite]
posted by springload at 10:29 AM on October 6, 2010 [1 favorite]
Best answer: Another way to think about it is that the motor itself will likely act like a big RF choke -- as springload says, it's most likely there to help damp out RF noise from a switching power supply, which your motor is almost certainly going to completely ignore and/or damp out itself.
posted by range at 10:41 AM on October 6, 2010
posted by range at 10:41 AM on October 6, 2010
Response by poster: Thanks, springload; I'll probably give it a shot. If it doesn't work so well, a replacement power supply is only $10 or so.
Additional thoughts are, of course, welcome.
posted by jon1270 at 10:43 AM on October 6, 2010
Additional thoughts are, of course, welcome.
posted by jon1270 at 10:43 AM on October 6, 2010
Best answer: You don't need the choke. It's a supression device that attenuates noise from the load (motor) back to the AC mains. Your brushless motor shouldn't make a lot of RF noise. Fire it up close to a portable AM radio tuned to no channel and see.
If you want to keep the choke in the circuit, cut it out and unthread the wiring . You'll note that there's usually a white stripe on one of the two wires. Just remember to hook it up that way when you shorten it.
It is non-essential to the operation of either the motor or the power brick.
( You ARE using a brushless DC motor driver, no? )
posted by FauxScot at 12:04 PM on October 6, 2010
If you want to keep the choke in the circuit, cut it out and unthread the wiring . You'll note that there's usually a white stripe on one of the two wires. Just remember to hook it up that way when you shorten it.
It is non-essential to the operation of either the motor or the power brick.
( You ARE using a brushless DC motor driver, no? )
posted by FauxScot at 12:04 PM on October 6, 2010
Response by poster: You ARE using a brushless DC motor driver, no?
I believe so. (Confidence inspiring, isn't it?) It's definitely a DC motor controller, and has supposedly been tested fairly extensively with the same motor by another internet denizen. There's room for a bit of doubt as to whether it's intended specifically for brushless motors, as the specs are a bit vague and don't indicate one way or the other.
posted by jon1270 at 3:23 PM on October 6, 2010
I believe so. (Confidence inspiring, isn't it?) It's definitely a DC motor controller, and has supposedly been tested fairly extensively with the same motor by another internet denizen. There's room for a bit of doubt as to whether it's intended specifically for brushless motors, as the specs are a bit vague and don't indicate one way or the other.
posted by jon1270 at 3:23 PM on October 6, 2010
Send me the details on the motor and the controller and I'll take a look, if you'd like. (I realize you are primarily interested in the ferrite choke.) If you got the motor and control recommendation from someone already using it, you're probably OK.
posted by FauxScot at 6:40 PM on October 6, 2010
posted by FauxScot at 6:40 PM on October 6, 2010
This thread is closed to new comments.
posted by springload at 10:25 AM on October 6, 2010