Replacing the last power supply cap

adamct · 18043

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Offline adamct

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Reply #30 on: August 09, 2013, 06:05:45 PM
Just bought 3 of the 200uf poly film caps off eBay. If MLB tested me right now, I would fail a doping test...my testosterone is off the charts!


Offline earwaxxer

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Reply #31 on: August 09, 2013, 07:14:36 PM
LoL!!! .. yep.. you are definitely hooked!

Eric
Emotiva XPA-2, Magnepan MMG (mod), Quickie (mod), JRiver, Wyrd4sound uLink, Schiit Gungnir, JPS Digital power cord, MIT power cord, JPS Labs ultraconductor wire throughout, HSU sub. powered by Crown.

Offline adamct

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Reply #32 on: August 10, 2013, 03:09:36 AM
Hmmmm....fools rush in.....

I just watched a video on the difference between start and run capacitors. The poly caps I bought are start capacitors. Am I correct that those are a no-no for use in the power supply, and likely to blow up in my face?  :-\


Offline Grainger49

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Reply #33 on: August 10, 2013, 03:58:12 AM
If it has a DC rating equal or greater than the stock cap you are fine. 


Offline adamct

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Reply #34 on: August 10, 2013, 04:10:28 AM
Therein lies the rub....I think it is rated for AC only...


Offline HF9

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Reply #35 on: August 10, 2013, 05:31:16 AM
Typically the AC ratings for a cap are notably lower than the DC ratings. I'd imagine the manufacturer probably just didn't anticipate anyone dropping their cap into an amp ;)

My DIY Audio Electronics Blog: DIYAudioBlog.com

Offline Grainger49

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Reply #36 on: August 10, 2013, 02:32:53 PM
I think you are going to have to try it and see.  If the caps don't destruct in the first 5 minutes they just might make it.  For the test put jumpers on.  Don't remove any other caps just put the new cap, only one, in parallel with the last cap.  Put some paper under it in the odd chance that it lets go.

Then move forward with confidence.


Offline adamct

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Reply #37 on: August 10, 2013, 03:48:19 PM
Check out this eBay listing, then scroll down and watch the embedded video. How dangerous is it if a cap goes belly up?


Offline earwaxxer

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Reply #38 on: August 10, 2013, 04:42:53 PM
Interesting.. Now I know the difference between a "start" and "run" capacitor.

Eric
Emotiva XPA-2, Magnepan MMG (mod), Quickie (mod), JRiver, Wyrd4sound uLink, Schiit Gungnir, JPS Digital power cord, MIT power cord, JPS Labs ultraconductor wire throughout, HSU sub. powered by Crown.

Offline adamct

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Reply #39 on: August 10, 2013, 05:05:36 PM
Grainger,

Do you still think I should try it, or just chuck them in a drawer chalk it up to a learning experience?

I've already ordered two of the 100uf oiler "run" caps at the eBay link to use instead of the last power supply cap. Unless someone tells me they really think it is safe and/or worth experimenting with the poly "start" caps, I'll leave the other two electrolytics in the power supply as-is.

Best,
Adam


Offline 2wo

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Reply #40 on: August 10, 2013, 06:52:31 PM
I have a bad feeling about them but I have no personal data to back that up.

I can say that motor RUN caps, if not your holy grail. Work pretty well for me...John

John S.

Offline Grainger49

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Reply #41 on: August 11, 2013, 03:37:07 AM
Adam,

Did the auction say "Motor Start" capacitor?  What voltage rating did they have?  What voltage will be on them?

I should point out that capacitors have a surge rating and a steady state rating.  That is one of the differences between a start, which accounts for the surge, and run capacitor that is expected to be used in steady state AC applications.  That also brings up that the demonstration was with AC, a power supply is DC. 

So I'm still at the try it point. 


Offline adamct

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Reply #42 on: August 11, 2013, 03:39:41 AM
It said "motor start-up", not "run", and they are rated for 450 VAC.

Best,
Adam


Offline adamct

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Reply #43 on: August 11, 2013, 03:45:04 AM
Also, I'm just wondering...in the video, they specifically said that motor start caps are only rated for AC. I took that to mean "don't use these for DC", not "the DC rating isn't specified" (which would imply that if you knew the DC rating, and they matched your purpose, they would be OK).

Is there a way to test these outside of the Crack? I've got a DC power supply. Actually several of them, but they are admittedly relatively low voltage (one goes up to 12 or 18V, the other is 34).


Offline Grainger49

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Reply #44 on: August 11, 2013, 04:48:07 AM
Ok, rated for 450V AC can, but doesn't necessarily, mean 636V DC.  Since we are talking about Crack here, the steady state DC is 170V.  The AC from the power transformer is 150V but paralleled to give double the current capability. 

I'm still at try one to see.  Otherwise what are you going to do with it?  Throw it away?  Wouldn't you want to see if it explodes first?  Protect your eyes and face.


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