Motor Capacitor Replacement

Thread Starter

cheahdk

Joined Apr 26, 2017
4
Hi all,

Recently I've blew a motor (run) capacitor from a Yaesu G5500 rotational unit for amateur satellite ground station uses. I can just make identical replacement but I've found someone claiming that the circuit below would be a better replacement for a motor capacitor.
upload_2017-4-26_23-40-41.png

So how does this circuit work like a motor capacitor especially when AC voltages are involved? Even if it theoretically works, is it a good choice to use electrolytic capacitors for this purpose?
 

MaxHeadRoom

Joined Jul 18, 2013
28,492
The caps are back to back making them bi-polar.
What is the motor type?
I see by the sheet it is a 24v AC PCM induction motor.
Never seen that arrangement before also the caps seem rather large values?
Max.
 

MaxHeadRoom

Joined Jul 18, 2013
28,492
I see the original is 100μf which I assume is because it is lower voltage and high current motor.
Once you get into that size, non-electrolytic can get expensive and Large.
I also see there are two identical motors, what is the markings on the original cap?
Max.
 

#12

Joined Nov 30, 2010
18,224
That circuit just doesn't look right. Maybe I'm short on coffee today, but I can't seem to see how it works.
Where is the motor supposed to be connected?
Regardless of that, oil filled run capacitors are much more reliable than aluminum electrolytics.
You had one go bad? This is a rare event. As Max said, what exactly is the size you originally had?
 

MaxHeadRoom

Joined Jul 18, 2013
28,492
From the
As Max said, what exactly is the size you originally had?
According to the manual the 24vac PCM motors have 100μf each, that is why I would be interested in data from the originals. As oil filled for that size will be Large.
Max.
 

Thread Starter

cheahdk

Joined Apr 26, 2017
4
The capacitor is to be connected at the terminals that control the motor direction as seen in the 2nd last page of the manual
upload_2017-4-27_15-49-58.png
 

MaxHeadRoom

Joined Jul 18, 2013
28,492
  1. I understand having the capacitors in this way makes it bipolar, but how does the diode help here?
The diodes enable ordinary electrolytic caps to be used, each diode shunts any voltage across the cap when the cycle is opposite to the polarity of the cap.
Max.
 
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