On Sat, 4 May 2019 15:03:27 -0000 (UTC), "Dallas"
wrote:


Hi guys, the motor run capacitor for my rolling shutters tubular motor
died. The cap case size is 35mm x 78mm and this is critical because it
must fit inside the motor enclosure. I've looked at hundreds of 20 µF
capacitors and they all were at least 40mm diameter (too wide). Then I
found a capacitor that is 25mm x 56.5mm. This is tiny and I'm thinking
it must be too good to be true. Can you help me decide if this
capacitor will run this motor? The printing on the original capacitor
is:
Arcotronic – (purchased by KEMET)
Part Number C.87.7ZF2 MKP
20 µF +/-5% b
320 V~ HPF N
560-8/A1
(In the USA voltage is 120 volts)
(out of production for years, none available)
And the data sheet for the prospective new little one:
https://www.farnell.com/datasheets/2755239.pdf

It looks ok, with one possible problem. The capacitor should be
non-polarized.
https://en.wikipedia.org/wiki/Motor_capacitor
Start capacitors above 20 µF are always non-polarized
aluminium electrolytic capacitors [4] with non solid
electrolyte and therefore they are only applicable for
the short motor starting time.
I dunno about the "non solid electrolyte" since the capacitor in
question is a "solid" polypropylene metallized film dielectric. Oh
well.

I can't tell from the Farnell data sheet whether it's an NP cap.
So, I found the original C87 series data sheet at:
https://content.kemet.com/datasheets/KEM_F3063_C87.pdf
It doesn't specifically say non-polarized, but the lack of polarity
markings and an "AC" voltage rating, indicates that it's probably NP.
Yes, it should work.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558