motor run caps.

[Rob Flinn]

I just acquired a small Hammond organ. Since it is 55 years old I want to replace the original motor run cap for safety. The original is 1.25uF which difficult to find. 1.5uF is easy to find. Therefore my question is how critical is the value of the motor run cap ? Could I sub in a 1.5uF ?

 

[rock soderstrom]

I am by no means an expert on motor run caps, but I am sure the 1,5uF will do the job pretty good. Think of the tolerances in the past and all the old MP capacitors that are still doing their job even though their capacity has doubled. This will work.

Edit:

Wikipedia says that the following happens if the capacitor is incorrectly dimensioned. I still think you are close enough:

"If a wrong capacitance value is installed, it will cause an uneven magnetic field around the rotor. This causes the rotor to hesitate at the uneven spots, resulting in irregular rotation, especially under load. This hesitation can cause the motor to become noisy, increase energy consumption, cause performance to drop and the motor to overheat"

 

[rock soderstrom]

You can still buy 1,2uF/450V motor run caps at Amazon:

https://www.amazon.de/DollaTek-CBB6...a66-993a-c5172d2c6328&pd_rd_i=B07HBT6YH1&th=1

 

[Bo Deadly]

I just acquired a small Hammond organ. Since it is 55 years old I want to replace the original motor run cap for safety. The original is 1.25uF which difficult to find. 1.5uF is easy to find. Therefore my question is how critical is the value of the motor run cap ? Could I sub in a 1.5uF ?

Yes, that's almost certainly fine. It might even be better. Motor run caps are tuned to the motor coils and frequency of mains. So if the manual doesn't show a different value depending on main freq, that would indicate that they "split the difference" to accommodate both 50Hz and 60Hz markets with one cap. Unfortunately I can't seem to reconnoiter exactly if a lower frequency would demand a slightly larger cap. But a larger inductor / cap equates to lower resonant frequency so it seems to make sense that a slightly larger cap might work better.

 

[Rob Flinn]

Thanks for the info guys. I tried the motor with a 1.5uF cap today and it seems to run really well. I will install the motor back in the Hammond when I can & see if it maintains a constant pitch.