Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives :: Books
Support This Site: Contributors :: Advertise


It is currently May Mon 21, 2018 12:05 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 10 posts ] 
Author Message
 Post subject: Inside "Motor Run" type capacitors.
PostPosted: Jan Sun 28, 2018 9:38 pm 
Member

Joined: May Thu 14, 2015 4:15 pm
Posts: 746
Location: Dallas, TX
I wonder if anyone knows what the insides of motor run capacitors are like.
A jukebox I'm working on uses them for speaker crossovers. I've already bought non-polarized capacitors to replace them and since the new ones are so much smaller I plan to use them to re-stuff the old ones. The old ones are visible when the top is raised. 33uF, 100volt. I wonder if they have tar holding the insides like the aluminum cap caps do. I will have to cut the retaining ring on the top, I think.
Attachment:
CrossOverE1.jpg
CrossOverE1.jpg [ 98.02 KiB | Viewed 765 times ]

Attachment:
CrossOverE2.jpg
CrossOverE2.jpg [ 93.42 KiB | Viewed 765 times ]

_________________
Tim
It's not the Destination, It's the Journey.


Top
 Profile  
 
 Post subject: Re: Inside "Motor Run" type capacitors.
PostPosted: Jan Sun 28, 2018 11:12 pm 
Member
User avatar

Joined: Jan Mon 05, 2009 4:09 am
Posts: 1221
Location: Hudson, MA
Were the originals shorted? and are the new ones electrolytic or film?

_________________
Eddy


Top
 Profile  
 
 Post subject: Re: Inside "Motor Run" type capacitors.
PostPosted: Jan Sun 28, 2018 11:21 pm 
Member

Joined: Oct Sun 18, 2015 2:49 am
Posts: 145
Location: San Angelo, TX
Yeah, the inside looks like most old caps. You can pry the serrated ring out and then the contents with lid will come out. Probably with some difficulty. The rolled up cap will probably be imbedded in tar or tar like goop. Then you can clean up the inside. If the connector rivets are aluminum, run a wire thru a small hole on the side of the lug to make a connection to new caps. Denis


Top
 Profile  
 
 Post subject: Re: Inside "Motor Run" type capacitors.
PostPosted: Jan Mon 29, 2018 1:01 am 
Member

Joined: Jun Fri 19, 2009 6:34 pm
Posts: 7646
Location: Long Island
Motor run capacitors are either oil filled metal cans, or the modern ones are metalized film in plastic cubes and other case styles. They're usually only a few uFs at 250 or 600 VAC.

What you have there appears to be a typical motor starting capacitor. They were non-polarized electrolytics, so it figures that somebody thought of using them in speaker crossovers. At full voltage and current, motor starting capacitors have a very limited duty cycle, but at the lower voltages and currents in a speaker network, they were undoubtedly fine for continuous operation.

When you remove the retaining spring and pull the guts out, you'll find a so-called "dry electrolytic" package consisting of a flat wound paper and aluminum assembly that has been covered in tar. The electrolyte was a paste between the foils. It's a bit acidic and it might burn your fingers a little if you touch it. But all you have to do is cut the leads and dump the old cap, then you can install your new one on the terminal board and stick it back in the case.

_________________
"Hell, there are no rules here--we're trying to accomplish something!"

Thomas A. Edison


Top
 Profile  
 
 Post subject: Re: Inside "Motor Run" type capacitors.
PostPosted: Jan Mon 29, 2018 6:27 am 
Member

Joined: May Thu 14, 2015 4:15 pm
Posts: 746
Location: Dallas, TX
I'm not sure of the type the originals are other than they would be non-polarized. I suspected that they were electrolytic (or paper) so planned to replace them. The printing on the case does state "60CPS" so that would be 60 Hz. The new ones are non-polar electrolytic. The original capacitor for the tweeter is NP electrolytic.
Normally with a aluminum cased electrolytic you can melt the tar with a heat gun, but I don't think using a heat gun on these plastic cased ones would be a good idea. I think the case is Bakelite so maybe a oven on low. That's why I was asking if anyone had taken one of these apart.

_________________
Tim
It's not the Destination, It's the Journey.


Top
 Profile  
 
 Post subject: Re: Inside "Motor Run" type capacitors.
PostPosted: Jan Tue 30, 2018 4:16 am 
Member

Joined: May Thu 14, 2015 4:15 pm
Posts: 746
Location: Dallas, TX
I opened up the capacitors today. The metal ring came off easier than I expected.
One of the reasons I suspected that the caps were electrolytic was the over-pressure vent hole in the top disc. Maybe they would have used the same disc with other types since they had them.
The top disc wouldn't move very far, I figured that the straps or wires connected to the terminals was holding the disc on. I put a small sharp screwdriver through the vent hole and moved it around until I broke one of the straps. With one loose I was able to lift the disc and cut through the other strap with a knife.
The case is about 3-3/8 inch tall, the tar was about an inch below the rim.
Attachment:
RunCapInE1.jpg
RunCapInE1.jpg [ 118.36 KiB | Viewed 572 times ]

Attachment:
RunCapInE2.jpg
RunCapInE2.jpg [ 122.39 KiB | Viewed 572 times ]

I have since dug out about a quarter inch of tar and uncovered the roll of foil and separator. No oil, at this point it looks like an electrolytic.
The roll is well embedded in the tar. I will either figure a way to melt the tar or find a good way to dig out the roll. Since melting the tar would be smelly, I may use something like a Forstner bit in the drill press. Perhaps using ice water as a lubricant.
Here is where the cap goes in the jukebox cabinet.
Attachment:
InteriorCabE2.jpg
InteriorCabE2.jpg [ 128.13 KiB | Viewed 568 times ]

_________________
Tim
It's not the Destination, It's the Journey.


Top
 Profile  
 
 Post subject: Re: Inside "Motor Run" type capacitors.
PostPosted: Feb Thu 01, 2018 6:59 pm 
Member

Joined: May Thu 14, 2015 4:15 pm
Posts: 746
Location: Dallas, TX
These capacitors are probably not typical motor run or motor start ones, from the outside they do look like ones.
After chilling the caps in the freezer, I used a quarter inch bit in a drill press to drill out some of the tar around the element roll. Cold water was used as a lubricant so the tar wouldn't stick. I then went back to a narrow wood chisel to remove more tar and finally the element. The actual capacitor element was very small compared to the housing. It looks to me like it was a non- polarized electrolytic.
I drilled some small holes in the discs for the new capacitor leads and soldered them to the lugs.
Attachment:
CrosovrRestufE1.jpg
CrosovrRestufE1.jpg [ 135.73 KiB | Viewed 482 times ]

_________________
Tim
It's not the Destination, It's the Journey.


Top
 Profile  
 
 Post subject: Re: Inside "Motor Run" type capacitors.
PostPosted: Feb Thu 01, 2018 11:59 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 3033
Location: Seattle WA US
Tim-
I fail to understand why you would go to so much work on the capacitor case, then restuff it with such crap as a bipolar electrolytic capacitor. Good mylar capacitors, with high enough values for restuffing projects, are available at good prices from several suppliers on the web. Here's one example : http://www.bgmicro.com/capsmylar.aspx

Bipolar electrolytics are used commercially because they are relatively cheap and small. They have no other virtues.
-Chuck


Top
 Profile  
 
 Post subject: Re: Inside "Motor Run" type capacitors.
PostPosted: Feb Fri 02, 2018 3:27 am 
Member

Joined: May Thu 14, 2015 4:15 pm
Posts: 746
Location: Dallas, TX
K7MCG wrote:
Tim-
I fail to understand why you would go to so much work on the capacitor case, then restuff it with such crap as a bipolar electrolytic capacitor. Good mylar capacitors, with high enough values for restuffing projects, are available at good prices from several suppliers on the web. Here's one example : http://www.bgmicro.com/capsmylar.aspx

Bipolar electrolytics are used commercially because they are relatively cheap and small. They have no other virtues.
-Chuck

They used non-polar capacitors in a couple of places in the changer control and I had to order from a different source for them. Since I was pretty sure the crossovers were NP E-caps, I added those in to the order also. I like to keep things as original as possible. I'm fixing up this jukebox, from 1964, for a client and they usually like to do it as cheaply as possible.

_________________
Tim
It's not the Destination, It's the Journey.


Top
 Profile  
 
 Post subject: Re: Inside "Motor Run" type capacitors.
PostPosted: Feb Fri 02, 2018 8:10 am 
Member

Joined: Sep Thu 23, 2010 6:37 am
Posts: 9653
Location: Powell River BC Canada
Your care and workmanship is impressive.


Do obliterate all the markings from the old capacitor case.

The rationale for this is important.

_________________
de
VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
ve7aso@rac.ca


Top
 Profile  
 
Post New Topic Post Reply  [ 10 posts ] 

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 11 guests



Search for:
Jump to:  
























Privacy Policy :: Powered by phpBB