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Old 20th October 2004, 10:41 AM   #511
ljozsef is offline ljozsef  Hungary
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Default see kilowattski

...and any using BC550B?

Thanks!
Laci
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Old 20th October 2004, 06:34 PM   #512
byteboy is offline byteboy  Netherlands
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Default Bad quality electrolytic caps

Taco,

As far as I remember you used in your AlephX those Nippon Chemicon "Stubby's", 68000uF/50Volt, as sold by a number of different (surplus?) dealers?

I think there was a kind of Dutch group-buy of those caps?
Considdering the price of those caps these must be NOS (New Old Stock) and would be of a manufacturing date some longer time ago (as you mentioned already yourself)
Do you know of any other bad experiences from the other group-buy members regarding the quality of those caps?

I'm asking because I was considdering buying a number of these caps myself but after reading your posts I don't know if I still should do this.
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Old 20th October 2004, 07:23 PM   #513
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Post 6 in this thread FS: New chemi-con 50v 68000uF caps $4.00 tells how read date codes. The stubbys I bought were only a four years old.

The one's I've used seem fine.
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Old 20th October 2004, 08:24 PM   #514
Taco is offline Taco  Netherlands
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Default Re: Bad quality electrolytic caps

Quote:
Originally posted by byteboy
Taco,

As far as I remember you used in your AlephX those Nippon Chemicon "Stubby's", 68000uF/50Volt, as sold by a number of different (surplus?) dealers?

I think there was a kind of Dutch group-buy of those caps?
Considdering the price of those caps these must be NOS (New Old Stock) and would be of a manufacturing date some longer time ago (as you mentioned already yourself)
Do you know of any other bad experiences from the other group-buy members regarding the quality of those caps?

I'm asking because I was considdering buying a number of these caps myself but after reading your posts I don't know if I still should do this.

Byteboy,

I used BC Electronics 47.000 uF 63V caps. I do not exactly know how old these caps are, but I think mine are older than 4 years.

I never took part of the Dutch stubby group-buy. You can use those stubbys but take care those caps stay cool, I think mine died because of the heat in the case (~50 C) and the age of the caps itself.

Kilowattski,

you can savely use the ZTX450 or a MPSA18 instead of BC550C. I am not sure of the BC550B, maybe the hfe is a bit low.
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Old 27th October 2004, 04:11 AM   #515
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Default Irf540

Question for you guys....

I am going to build an aleph-x with ~30v rails. I intend to create a 'quiet wind tunnel' using 4 - 7" x 15" heatsinks. I have thoughts on perhaps electrically isolating each of the heat sinks from each other and the chassis. I am then proposing ~12 IRF540 for each of the 4 heat sinks without isolating the tab (no mica/silicone) for better thermal conductivity. I would like to bias it pretty hard - get the 'juice' flowin'

I have looked at the schematic and I see no problem electrically doing this. I am probably missing something. Pls lemme know if I am.

Also, does anyone have issues in not 'thermally coupling' the ccs and outputs? (eg. thier not being on the same heat sink)

(OH, why IRF540? Because I can get them cheap, and I am cheap!)

Thanks in advance
Marc
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Old 28th October 2004, 07:21 PM   #516
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I would still think about some grease. Maybe Arctic Silver is
conductive enough?
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Old 28th October 2004, 07:36 PM   #517
jwb is offline jwb  United States
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The thermal conductivity of a good silicone pad is comparable to the conductivity acheived with thermal grease, and better than a bare tab/heatsink junction. I see no reason to avoid them.

Is the extra 0.27K/W (Bergquist K-10) the killer issue in your thermal design?
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Old 28th October 2004, 09:01 PM   #518
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Mr Pass and jwb,

Thanks for your reply. Yes, i did not mention that I would of course use grease, without question. What is your opinion/experience in mounting thansistors w/out insulators? Are the thermal benefits a real advantage or is it a waste of time and effort? It seems to me that getting the heat off of the chip itself as fast as possible would be of paramount importance. Basically..in a nutshell...is it a bad idea.

Thanks
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Old 28th October 2004, 09:53 PM   #519
jwb is offline jwb  United States
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mpmarino,

Instead of just hacking and conjecturing, you should sit down and work out the thermal problem. The devices you are using (IRF540) are much worse thermally than a proper power device like IRFP244. The 540 will get twice as hot for any given power level and heatsink, owing to its the higher R-theta of the (smaller) TO-220 package as compared to the (larger) TO-247. The question is: what is your per-device power dissipation and what is the device temperature for various devices and mounting methods? Does the desired device operate at a decent temperature or do you need a bigger one?

As for the circuit's performance, you should analyze whether or not it's ok to connect, electrically, the drains of all the devices. Is it OK to have multiple current paths to the drain? Does it cause any kind of unwanted loop? How will you keep your pet aardvark from licking the electrically-live heatsink?

You might want to go through the site and read Nelson Pass' advice about substituting devices for the IRF*44 series. There's a reason people use those. It's a really nice device.

Best,
jwb
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Old 29th October 2004, 02:44 AM   #520
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Thanks JWB,

Advice taken

OH, and by the way, you're right...I wouldn't want to mourn my pet aardvark's 'pass'ing.

Sometimes my crazy ideas plague me and it helps when someone sets me straight.

thanks
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