240v Motor advice

Discussion in 'General Electronics Chat' started by keat63, Jul 8, 2013.

  1. keat63

    Thread Starter New Member

    Jul 8, 2013

    I recently swapped a blower motor in a hot tub. The blower motor was a chinese 125mm Vacuum cleaner Ronning motor.
    I couldn't find the exact motor, so I replaced it with one from a Zanussi vac.

    Everything has worked flawlessly for about 6 weeks, only this weekend, the starting capacitor blew big style.

    Basically, it turns out, that the PCB for the hot tub, had a 2.0uf cap installed on the blower side of the circuit.

    The vac motor i installed has a smaller cap attached to the motor it's self.

    And I foolishly don't recall the original Ronning motor having a cap if i'm honest. Plus the fact that the PCB has a cap installed, would leave me to believe, that the Ronning motor, probably didn't have a cap.

    I've taken the blown cap out of the PCB, and everything appears to be working with all circuits on the board.

    So I guess my question really, would having 2 x starting capacitors cause one to fail ? and if so, why did it take 6 weeks ?
  2. chuckey

    Well-Known Member

    Jun 4, 2007
    There are at least three different configurations of single phase motors using capacitors:- cap in to start with a motor speed switch or a timer to take it out of circuit once the motor is up to speed. A cap start (as above) but with a different cap in all the time for running. A single cap for both start and run - no switch or timer. So the question is, what sort was the original motor and what sort is the new motor.
    The starting capacitor and the starting winding are operating quite close to resonance so an additional cap could resonate the circuit, leading to excessive currents. Also true starting capacitors are lightly made as they are only used for 1-2 seconds at a time, if they get left in circuit, they overheat and explode.
  3. keat63

    Thread Starter New Member

    Jul 8, 2013
    Not a clue.
    I would say the one on the board was left in circuit though, as it was totally burnt out.
    This thing has been faultless for about 6 weeks.
    On Saturday, I'd had the covers off to resolve a whistle caused by a small air leak, on the output tube. Nothing major, and no major components touched.
    Afterwards i did start the blower very briefly, just to ensure that it was still functioning.
    I wanted to allow the silicone on the output tube to go off, so the startup was maybe for a second (at the most)
    The unit was then just circulating water, with no blowers running, and had been for a few hours.
  4. #12


    Nov 30, 2010
    Hi. I'm a technician. Do you want to learn the electronics of this circuit or do you want to get it running?

    A 2uf motor capacitor. Probably polyfilm of some sort. The other kind is oil filled, and you can't mount them on a circuit board. They are too big. Not enough capacitance to be a start capacitor. Having 2 of them in parallel does not make one of them fail. Even having the wrong capacitance does not make the capacitors fail. It makes the motor fail. I'd say your capacitor just...failed. I carry at least 12 of them, in various sizes, in my truck and, in 40 years of replacing them, I have never known why they fail, but I do know that no external cause made them fail. How do I know? I replace them and everything runs for years after that.

    I'd say, scrape the remnants off the circuit board and clean it up real nice. Then let the new motor run with the capacitor that it was born with. Then, you can discuss philosophy, the crystal ball theory of why things fail, and why they chose that particular day to fail, and do it all from the comfort of your hot tub.

    See if the blower runs now. If it does, you win. If it doesn't, you will have to find out what other circuit board parts were killed by the capacitor going bad.

    Then again, I might be wrong.
    strantor likes this.
  5. keat63

    Thread Starter New Member

    Jul 8, 2013
    This is exactly what I did.
    I initially wondered if I'd maybe nicked a wire on re-assembly, but couldn't see anything.
    I even resorted to rewiring the blower motor back to the PCB, just in case.

    So the main PCB is now missing it's original capacitor, with the smaller cap on the motor as it was born, and everything is working as it should.

    Maybe it was just pure coincidence, that it chose the day i'd had the covers off to blow. However, paranoia does creep in.
  6. #12


    Nov 30, 2010
    By coincidence, it was July 3 when I last found a bad capacitor. It was an air conditioner. The compressor was "safetied out" on overheat and the fan wasn't running. It was the 3uf section of a 35/3 @ 370 volts. Experience tells me that when one section fails, the other will fail within a week or two. I installed (2) capacitors, a 35uf and a 3 uf because they don't sell 35/3 any more. I lit it up, adjusted the Freon pressures, and turned it off. Unhooked my gauges, put the cover on, and loaded everything in the truck. As I was leaving, I turned it back on and NOTHING ran :eek:

    By then, it was nearly dark and the mosquitoes were trying to eat me alive. I went inside and the digital thermostat was blank. A fuse was blown on the control board. I didn't have that size fuse with me, so I went home. I spent the night wondering if rats had eaten the wiring and I blew the fuse by disturbing the wires. Sometimes, everything that can go wrong, does.

    Next morning: Replace the fuse and the thermostat lights up. Never did find out why the fuse blew. The outside half of the air conditioner was still silent. Pull the cover back off and measure the obvious...the motor contactor (big relay). Bingo. The contacts are closed but they aren't connecting. It failed while I was there. That's the first time that happened in 40 years of doing repairs.

    Now...get in your hot tub and we'll discuss why the motor contactor was running when I was working on the machine and quit as I was leaving. :D