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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??? :D
 
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
 
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
 
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
 
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?
 
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...
 
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
 
one thing...

Not sure if it matters, but I didn't use a fixed resistor on the output of the PSU in the designer, I used a constant current source, and then set it to 4 amps...

I'm going to redo the work in PSUd2 and see if my numbers end up different to yours or different from what I remember...

Stuart
 
well...

...The chokes are large-ish, but nothing compared to the caps they are 'helping' or replacing, so for really low ripple it seemed like the right thing to do.

The ones I bought were for speaker work, crossover etc. Parts express had a good selection the last time I checked. Air cored are 'best', biggest and most expensive, especially if they are wound with wire fat enough to have a low DCR. So I went with steel cored, Erse I think made them. 14gauge wire, over a steel dogbone shaped core, not sure how many turns, but each weighs 8-12oz.

Using PSUd2 after I make up the CLC using the numbers we are talking about, ie 46vAC (0.06ohm), 1n5402 bridge, 63k(0.015ohm), 2.2mh(0.5ohm), 63k(0.015ohm). I have a 58.1v DC rail with 10mV ripple, at 5 amps continuous...

With a CLC it's not just the DCR of the transformer that lowers the rail, the almost complete removal of AC ripple makes the average output DC noticeably lower. After all there is 2.5v of ripple removed by the choke...along with 2.5v DC

HTH

Stuart
 
originally

I think I saw values in an article by NP, nowadays I start from these values and vary them in PSUd2 until I get something I can live with...

When I first used a CLC it was for a zen or Aleph amplifier that had relatively poor PSRR, so ripple reduction was critical...

Stuart
 
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K-amps said:
How does one calculate the inductance needed for a given supply? Are there rough estimates?

what you really need to estimate or choose (it's better term for situation ) is max Rdc of choke you can accept;
after that you can try to find on market max inductance for that Rdc.

more mH ,better filter .......

I'll use ~9 mH in my Babelfish,with some 0,15-0,2 ohms Dcr
 
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