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Ripple current of motor run caps?

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Posted on February 3, 2016 at 16:29:27
andy evans
Audiophile

Posts: 4382
Joined: October 20, 2000
 Can motor run caps handle high ripple as the first and/or second caps in a CLC supply at 450v? Thinking of a stage amp 50W, like 2x6L6 for instance.

I was looking at 500v caps and the usual suspects at 47uF or 68uF are pretty small in size. Waiting for delivery of these Vishay caps, which actually do state good ripple current in the data sheet. I'm reading .56A at 120hz.

Wondering which way to go here, and what kind of ripple current figures to shoot for in a 50w tube amp, which should be around 120mA.

 

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RE: Ripple current of motor run caps?, posted on February 3, 2016 at 18:12:56
Michael Samra
Dealer

Posts: 36118
Location: saginaw michigan
Joined: January 30, 2005
 Andy
Absolutely! The ripple current is really more of a problem when you have higher capacitance electrolytics and they tend to create more heat as the caps charge and discharge into a load. The motor run has oil with cooling properties,not to mention it's a much larger cap.. Since switch mode power supplies became the norm,ripple current is looked at much closer than in the past,at least from my experience.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: Ripple current of motor run caps?, posted on February 4, 2016 at 09:54:40
Caucasian Blackplate
Industry Professional

Posts: 8313
Location: Seattle
Joined: June 18, 2004
 Download PSUD and model your power supply. Look at the line for IC1 and the value under the Max column. That will give you a decent approximation for the ripple current seen by the first cap.

There are a lot of factors that go into how much ripple current the first capacitor sees, so there is no one size fits all answer to what number to use for a 50W 6L6 amp.

 

RE: Those aren't motor run caps, posted on February 4, 2016 at 18:40:04
Russ57
Audiophile

Posts: 3754
Location: South Florida
Joined: November 16, 2001
 Motor run type caps are usually rated 20+ amp range. These days I think it is better to call them "oil filled metalized polypropylene" caps. Used to be we were talking about AC rated caps used with motors. Today we can get caps intended for use in UPS, VFD, etc. that are DC rated and intended for your exact usage.

 

RE: Those aren't motor run caps, posted on February 4, 2016 at 19:16:44
Michael Samra
Dealer

Posts: 36118
Location: saginaw michigan
Joined: January 30, 2005
 Motor run type caps are usually rated 20+ amp range. These days I think it is better to call them "oil filled metalized polypropylene" caps. Used to be we were talking about AC rated caps used with motors. Today we can get caps intended for use in UPS, VFD, etc. that are DC rated and intended for your exact usage.

Agreed..This is why they are so frequently used in high current application and even 440v 3 phase circuits running huge compressors.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: Ripple current of motor run caps?, posted on February 4, 2016 at 19:19:51
Lee of Omaha
Dealer

Posts: 1800
Location: Omaha NE
Joined: September 8, 2006
 Motor run caps are designed to operate their entire lives in high ripple, every cycle.

 

I'm talking about plain metallised polypropylene, posted on February 5, 2016 at 04:48:50
andy evans
Audiophile

Posts: 4382
Joined: October 20, 2000
 I was referring to the typical plastic encased metallised polypropylene caps, which I assumed were not oil filled like the older metal jacket ones.

They are also rated for high ripple? They're usually marked 450vAC

 

RE: I'm talking about plain metallised polypropylene, posted on February 5, 2016 at 10:55:33
Michael Samra
Dealer

Posts: 36118
Location: saginaw michigan
Joined: January 30, 2005
 Andy
The larger caps rated in AC voltages of 370vac or higher are usually used in motorrun applications which are higher current.So obviously the 440vac caps are as well..They can be dry as well..I only mentioned the oil caps because that's what so many use being you can get then so cheap.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: Just went by your link, posted on February 6, 2016 at 20:30:30
Russ57
Audiophile

Posts: 3754
Location: South Florida
Joined: November 16, 2001
 Your link was for a standard aluminum electrolytic cap. Motor run caps are a non-polar film cap. Very different items (IMHO).

For a power supply in an amp I'd look at the ASC X386S for a nice sounding, affordable, current production, cap. ASC also offer caps intended for DC power supply filtering but I have no experience with them. It might be worth contacting them as these days more and more motor run caps are clearly labeled as "only for 50-60 hertz operation".

I can say "once upon at time" the GE brand 440VAC motor run caps also had a 1,000 VDC rating.

On your side of the pond it may make more sense to look to Epcos/Siemens/Sikorel.

 

RE: Those aren't motor run caps, posted on February 7, 2016 at 19:39:54
jorisdallaire
Audiophile

Posts: 356
Location: Quebec city
Joined: July 26, 2012
 The plastic-cased ones are not oil-filled, that is why they are smaller in size. They will handle the high-ripple high-current no problem as well.

I have tried them in your exact usage, and found they sound less good than oil-filled motor-runs (big metal oval cans).

Joris

 

RE: Ripple current of motor run caps?, posted on February 7, 2016 at 21:15:03
hennfarm
Audiophile

Posts: 535
Location: Oregon
Joined: October 8, 2008
 Hvacbrain prc10

 

RE: Ripple current of motor run caps?, posted on February 7, 2016 at 21:15:58
hennfarm
Audiophile

Posts: 535
Location: Oregon
Joined: October 8, 2008
 Prc100

 

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