AC Motor Control Capacitor (?) - Page 1
Forum section: electronics / projects

author: Redstone02
author_rank: Newbie
timestamp: January 05, 2024, 08:45:36 pm
content: Hello,I am refurbishing a 1957 8mm movie projector. The 120 volt ac drive motor is a run capacitor (1 mfd, 450 vdc) and has speed control. The speed control knob appears to turn a high wattage potentiometer (ceramic and wire wound). Between the potentiometer and motor is what appears to be a capacitor but has no marking that I recognize- 5019 900vac - see photo. This capacitor (?) has a braided wire to chassis.Any ideas on what this device is?The projector: Wollensak 715. Google does not find a wiring diagram.Thanks,Red

author: Gyro
author_rank: Super Contributor
timestamp: January 06, 2024, 11:32:01 am
content: Hi, welcome to the forum.That's a brushed motor rather than any sort of induction type, so the capacitor can only be for interference suppression. Not a motor start or run type. If the potentiometer is a high wattage wirewound type, the it will be directly controlling the motor current rather than there being any speed control electronics in the yellow package.When you say "between the potentiometer and the motor", can you please clarify how it's wired? I see the bare wire that is connected to the chassis and two black insulated wires. I would have expected one black wire to go to each side of the motor. I suspect that it is a combination of an 'X' rated capacitor across the motor and two 'Y' rated capacitors going from each side to the chassis connection.The only other possibility (if the two black wires are really connected in series with the potentiometer and motor) is that the package contains an interference suppression inductor combined with a 'Y' capacitor to chassis.If the chassis is solidly grounded via the mains lead and there are no signs of deterioration or swelling, you are probably fine just leaving it as is.

author: Redstone02
author_rank: Newbie
timestamp: January 07, 2024, 06:05:52 am
content: Thank you for the help Chris. When I first pulled off the back cover, the plan was to replace belts and, after a general clean-up, button it back up. Then I saw the 65 year old capacitors. You are correct on all points: a brushed universal motor and the mystery part is in parallel with motor leads - the black wires from the mystery part goes to each side of the motor. The HD pot is the only speed control.Is the mystery part (to me) used here in the same application as the type y ceramic disk capacitor in old tube radios? The mystery part does have a braided wire going to chassis, but the projector power cord is only a two-prong non-polarized plug.Attached is a photo of the part. I don't know what looks okay and what does not when it comes to this part. I have had a capacitor pop nearby once that made me think someone shot a gun.Thanks again,Red

author: SeanB
author_rank: Super Contributor
timestamp: January 07, 2024, 09:41:54 am
content: Yes it is an interference suppression capacitor, typically 100n 275VAC class X2 between the black wires, and 2 22n 275VAC class Y capacitors between each black lead and the bare wire. you really do need to replace it, though you will not get an exact same shape one, mostly because the original is a wax filled paper capacitor, last made probably early in the 1970's. you can replace it with a single 100n 275VAC class X capacitor, and that will do the same, just not have the connection to the frame, or get a similar one.https://probe.com.au/ocart2/index.php?route=product/product&product_id=336https://www.amazon.nl/-/en/Capacitor-malfunction-filter-vacuum-cleaner/dp/B014JEILL2These 2 are pretty much the same capacitor, or at least similar function, which should be available by you to replace it. first one is identical in application, black leads, and screw terminal is the mount and third lead, second one you just use one of the blue and one of the black, and insulate the other blue and black, or connect the 2 blue together, and the 2 black together, and connect to the motor where the old black ones went.