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Replacement for .5 MFD / 300 VDC Capacitor

Discussion in 'General Electronics Discussion' started by Tsabia, Oct 24, 2018.

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  1. Tsabia

    Tsabia

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    Oct 24, 2018
    Short story: I’ve been googling this and have also contacted customer service a Mouser Electronics and have not been able to find this capacitor. Can anyone point me in the right direction, or recommend a suitable replacement?

    Long story: Trying to repair a 1950’s Westinghouse mixer. The variable speed control doesn’t work, it only runs at full speed. Inside I found the large ceramic 300Ω 30w resistor that’s part of the speed control had snapped in half. I replaced it with a Caddock Thick Film Resistor 300Ω 30W I found online at Mouser Electronics, but there was no change in operation. That leaves the capacitor

    When searching for the .5 MFD / 300 VDC I found someone who makes replacement capacitors for vintage Sunbeam mixers. He told me that his 0.1 uf / 600 VAC capacitor should work. I installed it and the bit of smoke I saw lead me to believe that I blew the new resistor I installed. The speed control now works roughly with the contacts that make up the mechanical part of speed control vibrating audibly. I’ve read that running it this way will eventually burn up the contacts, though.

    Thanks in advance for your help.
     

    Attached Files:

  2. kellys_eye

    kellys_eye

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    Jun 25, 2010
    0.47μF is the nearest standard value and obtainable in a full range of voltages. Anything that meets or exceeds the voltage requirement will suffice.
     
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  3. Tsabia

    Tsabia

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    Oct 24, 2018
    So this would work? EE2CF644-5C62-4A54-9C0D-8D07890C23D2.png
     
    Last edited: Oct 24, 2018
  4. Bluejets

    Bluejets

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    Oct 5, 2014
    The cap and the resistor are there for a purpose.
    The cap stops or limits rf noise emitting and more importantly the resistor help eliminating the sparking across the speed control points.
    As you found, without this, the points will quickly erode away and the control will become useless.

    As a side note, i used a Sunbeam mixer with a blown speed control on a miniature cam grinder I built here. The solution here was to to use one of the phase control ( drill speed) units.
     
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  5. kellys_eye

    kellys_eye

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    Yes, that would work.
     
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  6. Tsabia

    Tsabia

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    Oct 24, 2018
    First, I would like to thank everyone for their input. My mother received this mixer in as a wedding gift in 1952 and I’m hoping to have it restored and running properly for her in time for us to make Christmas cookies.

    I installed the above mentioned capacitor and a replacement for the burnt out 300Ω/30W resistor. The resistor blew out again, so the condition that blew the original ceramic resistor still exists. The only thing I see that could be in question is a piece marked 075 -.075 -.006 MFD / 160VAC (capacitor?) that’s wired into the incoming power cord. Either that, or I’m not using the right type of resistor, or there’s something going on in the motor (which looks to be in very good condition).

    There was a website that explained the operation of these units, but I can’t seem to find it again.
     
  7. Alec_t

    Alec_t

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    Jul 7, 2015
    If the 300Ω resistor is in series with the motor winding to reduce the speed but is obviously passing excess current, then it seems likely the motor winding has a short-circuit fault.
     
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  8. Bluejets

    Bluejets

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  9. Tsabia

    Tsabia

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    Oct 24, 2018
    I followed videos I found and did the following tests:
    Field coil - continuity/balancing test and a coil-stack continuity test.
    Armature - 180 degrees bar to bar test, adjacent bar to bar, and a bar to armature stack continuity test.

    It all checked out fine.

    I did find a crack in the insulation on the coil input wire, but it didn’t appear to have shorted out on anything.

    The only thing I can think of is that the resistor I’m using isn’t up to the task?
     
  10. Alec_t

    Alec_t

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    Jul 7, 2015
    Can you bypass the speed control and wire the motor to mains via a suitably rated fuse, to test if it runs correctly at full speed? If it does, then that would suggest the OEM resistor is indeed inadequately rated (assuming it is correctly wired) but doesn't explain how it survived up to now.
     
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  11. Tsabia

    Tsabia

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    Oct 24, 2018
    The motor ran fine at full speed when the cap and resistor were blown. It continues to run well at the full speed setting with just the replacement capacitor, but increasingly choppy at lower speed settings because of the speed control points arcing.

    Am I not using the right replacement? Would you suggest I try something with a different rating? Here's a link to what I've been using: https://www.mouser.com/ProductDetai...pMlzBnuqU4w==&countrycode=US&currencycode=USD

    Below is a pic of the original capacitor along side the replacement. (I have one good one left).
    IMG_0433 (1).jpg

    Here's the mixer.
    IMG_2312.jpg
     
  12. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    That new resistor (not a capacitor) must be mounted on a heatsink. Yeah, it will likely smoke if you don't mount it on a heatsink.

    I would probably get a 50W to 100W aluminium clad resisitor. It may be sufficient in this application without being attached to a heatsink.
     
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  13. Tsabia

    Tsabia

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    Oct 24, 2018
    Oh, yes, I meant to type resistor. Thank you.

    The resistor fails immediately when on start-up. Is that consistent with the absence of a heatsink?

    I’ll see what I can find in an aluminium clad resistor as you suggested. While the need for a heatsink makes sense to me, I’m guessing it’s beyond my novice abilities to set up a reliable one.
     
  14. Alec_t

    Alec_t

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    Jul 7, 2015
    Have you checked that the centrifugal mechanism isn't seizing and that it's contacts are in good clean condition? Any crud or stiffness preventing the contacts closing effectively could result in the resistor passing current for longer than expected and hence overheating.
     
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