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Old 17th November 2006, 09:20 PM   #1
K-amps is offline K-amps  United States
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Default Quick Dumb question

I am doing some simulations in PSUID... for a 2kVA toroid used in an Aleph2.

Secs are 43-0-43AC...

Question is: for a Toroid that size, what is the approximate DCR of the secondary? (meaured from center tap to any one hot side) My guess is between 0.5-1ohm... maybe lower.

I am sitting in an Airport so I cannot measure it...

Anyone have the vaguest idea of what typical values are???
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Old 17th November 2006, 09:35 PM   #2
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Default MarkG posted...

...a set of useful specs recently on the ksa100 thread.

For a ~1200va, 28-0-28 transformer from Bel Canto it was specified as 0.065ohm...the primary was 0.34(+0.13), depending on input voltage selected.

The secondary was wound with 14gauge wire, so if you are staying in the ballpark for voltages and current, the resistance will likely be proportional to the secondary voltage...ie 45-0-45 will have something like 0.1ohms...

If the voltage is significantly higher the gauge of the wire will need to diminish and the resistance is going to be increasing at a great rate.

HTH

Stuart
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Old 17th November 2006, 09:51 PM   #3
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Awesome! Thanks Stuart.

Now. since you brushed that one off... let me try and challenge u...

63v 27,000uF Panasonic TH-A series cap. Approx ESR?


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Old 17th November 2006, 09:55 PM   #4
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Found it !!

http://www.panasonic.com/industrial/...series_dne.pdf

Thanks.
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Old 17th November 2006, 10:03 PM   #5
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Default Well...

...since you only want the approx. ESR, I'd use 0.015ohms at 120hz.

I couldn't locate your exact part, but checking the panasonic catalog for all their current ranges of 27000u, 63v working caps shows surprisingly little variation, independant of size, shape, terminal type etc. The numbers seem to range from 0.012 to 0.018 ohms...

HTH

Stuart
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Old 17th November 2006, 10:07 PM   #6
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Since their Surge rating (for the 63wv parts) is 79vdc....

Am I ok using it with a +/- 60.5 vDC rails?... I know it is cutting close.... but those are the parts I have...
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Old 17th November 2006, 10:19 PM   #7
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Default I think so...

Since they have specified the surge rating, it seems like it should be safe to use it...

Might be wise to check their definition of 'surge rating', if it is limited to events that are on the order of micro or milli seconds, then it might not be the right plan to use all of it, those things are really messy when they pop, not to mention loud.

Stuart
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Old 17th November 2006, 10:25 PM   #8
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Well....

How do I go about reducing a couple of volts and keep a low impedance rail? I will bias the amplifier in the order of 20 watts pure class-A on those rails. i.e. loading the rails by about 2.25amps.... My gut is that will drop the rails by1-2vdc right there. Then I can use a CL-60 (or a couple) on the primaries of the tranny... in total my guess is I should be able to drop 2 volts...

If not; should I consider building a bridge with disctrete Diodes and use 2 in series... or even 2 bridges in series?
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Old 17th November 2006, 10:29 PM   #9
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PSU Designer tells me that reducing the load on the PSU from 300ohms (unloaded) to about 16 ohms (approximating a 2.25amp load or 20 watt class-A bias) reduces the rails to 55vdc.... does that seem in the ball park?

Seems the droop is too much... for a 2kVA trannie feeding about 108,000uF per rail in Low ESR Panasonics dropping from 59 to 55vdc with only a 134 watt (2.25Amp) load...
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Old 17th November 2006, 10:35 PM   #10
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Default I used a 2.2mH choke...

between a pair of 63k cans, on each rail. The choke is wound with 14gauge wire on a steel core and has Isat>5 amps, so not stressed in this scenario at all.

Drops the ripple to very low levels and reduces the DC by a couple of volts (at 4-5 amps total)...IIRC ripple measured ~10mV.

According to PSUd2 I would have needed something like 10x the caps for the same result without the chokes.

Stuart
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