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Old 21st September 2012, 06:03 PM   #1301
danielwritesbac is offline danielwritesbac  United States
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Quote:
Originally Posted by DF96 View Post
Adding a bypass cap to a circuit with too much inductance could make things worse, unless enough damping is present. As others have said, the cap bank itself is not always the best place for any bypass. The outcome depends on many things, including the detailed layout.
Oh, right. Probably should have been an RC?
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Old 21st September 2012, 08:03 PM   #1302
AndrewT is offline AndrewT  Scotland
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500VA 240:35+35Vac

Vrso=28.4mVac
Vpso=241Vac
Vsso=74.3Vac
Rsso=1r0
N = 240/74 = 3.243

did the Calcs shown on the sheet by hand but used N=6.486 (for a 37Vac single secondary)
k = 0.999786
L11 = 0.0058
L12 = 0.00014
Lm = 26.9942

Are my calculations correct with that N value? Or do I need to use 3.243

What do the numbers mean?
What do they tell me about my transformer?
Are the numbers any good for these simulations with the 120VA transformers.

I don't have any small 35+35Vac transformers.
I do have a variety of small 25+25Vac, 225VA, 300VA and 30+30Vac, 120VA, 160VA,transformers.
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Old 22nd September 2012, 07:09 AM   #1303
AndrewT is offline AndrewT  Scotland
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I left out the winding resistances.
Rprimary = 1r33
Rsecondary 0r09 (both secondaries in series measure 0r18)
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Old 22nd September 2012, 06:12 PM   #1304
gootee is offline gootee  United States
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Thanks, Andrew! I will try those parameters in the simulator as soon as I can.

You did it correctly, for the single-secondary model.

I will not use your model parameters for a 120 VA transformer model. At first I will try it as is, i.e. as a 250VA secondary of a 500VA transformer, with the given voltages etc, and compare its behaviors to those of my derived scalable model.

Then I will try to per-unitize it, as I did for my original model with Terry's guidance, to make it scalable. It should be very helpful and enlightening to have a scalable model that was derived from a larger VA-rated transformer.

Tom

Last edited by gootee; 22nd September 2012 at 06:30 PM.
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Old 23rd September 2012, 02:04 AM   #1305
gootee is offline gootee  United States
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Quote:
Originally Posted by danielwritesbac View Post
Paralleling 2 caps cuts the inductance in half and that's an excellent idea for less noise other parts of an audio circuit, but did not help the individual units make less noise and did not make the caps charge at precisely the same time, since they're not quite perfect. SO how many caps can you parallel before reciprocity failure occurs turning the good idea to bad? Same question as how many slightly different noises can we stack before the slight differences add up to awful?
Ah, practicality invades.
The earlier idea of a horde of 1000u caps directly at the outputs of an audio amplifier board, was a good idea with the very worst dullest performance. Well, we're going to need to revise that to a smaller number of bigger caps, but then the question of how many persists.
How many noises are tolerable?
How many noises are needed?
Symmetrically and considering several larger values, I've guessed six as a rough estimate for the maximum number of caps that should be in a paralleled grouping, although more caps/groupings could be added with the separation of a long trace, a cable, a diode, or a resistor. However, the Real number of caps that can be paralleled before the good idea turns bad, will vary depending on the model and value of cap.
But, do we have a rule of thumb for it?
Maybe a guideline? Something simple?
Daniel,

Paralleling reservoir caps and paralleling decoupling caps are not primarily about having less noise. In either case, it's mainly about enabling the current to flow more-easily and thus more-accurately, when called upon, because the impedance of the supply will be lower with paralleled caps. Since the current, in both cases, directly becomes the sound, paralleling more reservoir or decoupling caps (while not necessarily increasing the total capacitance) should always tend to give more-faithful reproduction of the sound, with lower distortion (steady-state or transient distortion or both).

If good layout practices are used, then the only reason, that I can see, to limit the number of paralleled caps, would be running out of space for them.

Unequal charge and discharge rates should not be a problem. But if they were, then increasing the number of paralleled caps seems like it should mitigate any associated effects, on average.

It is difficult for me to imagine how adding caps in parallel could create any noise, unless maybe the layout/current-routing is problematical, possibly with regard to star grounding. Or it might be possible that they are exposing a problem with some other part of the circuit.

Regards,

Tom

Last edited by gootee; 23rd September 2012 at 02:08 AM.
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Old 23rd September 2012, 02:57 AM   #1306
gootee is offline gootee  United States
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Quote:
Originally Posted by AndrewT View Post
500VA 240:35+35Vac

Vrso=28.4mVac
Vpso=241Vac
Vsso=74.3Vac
Rsso=1r0
N = 240/74 = 3.243

did the Calcs shown on the sheet by hand but used N=6.486 (for a 37Vac single secondary)
k = 0.999786
L11 = 0.0058
L12 = 0.00014
Lm = 26.9942

Are my calculations correct with that N value? Or do I need to use 3.243

What do the numbers mean?
What do they tell me about my transformer?
Are the numbers any good for these simulations with the 120VA transformers.

I don't have any small 35+35Vac transformers.
I do have a variety of small 25+25Vac, 225VA, 300VA and 30+30Vac, 120VA, 160VA,transformers.
Do you also have the numbers for VPSS, VRSS, and RSSS?
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Old 23rd September 2012, 03:38 AM   #1307
TonyTecson is offline TonyTecson  Philippines
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Power Supply Resevoir Size
Default paralleling caps

Hi Tom,

we all know that caps labled 4700/50volts are not exactly 4700ufd so that paralllelling them is actually paralleling several uneqaul value caps....did you simulate for those effects as well?
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Old 23rd September 2012, 06:03 AM   #1308
fas42 is offline fas42  Australia
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Quote:
Originally Posted by Tony View Post
Hi Tom,

we all know that caps labled 4700/50volts are not exactly 4700ufd so that paralllelling them is actually paralleling several uneqaul value caps....did you simulate for those effects as well?
I'll just step in for Tom here, since he hasn't responded ...

Somewhat unequal values makes absolutely no difference whatsoever, even if they are film caps. There is no such thing as matching, or anything like that coming into play here. If you happen to have a 2200, 3900, 4700, etc, on hand you can happily parallel them all up, especially if they're electrolytic, with absolutely no effect either one way or the other. The only thing that matters to any degree is the instrinsic parasitic characteristics, ESR and ESL, which can vary per the one capacitance rating. For example, Panasonic FCs can come in two different shaped cans for a certain value, and those two will have different ESR and ESL!

Frank
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Old 23rd September 2012, 09:25 AM   #1309
AndrewT is offline AndrewT  Scotland
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Hi G,
looks like my head is not in one place just now.
Yes, I have those numbers.
Vpss = 4.8Vac
Vrss = 0.22Vac
Rsss = 1/6 r (6 1r0 in parallel)And they run cold, you don't need a high power resistor, and you don't need to remeasure the resistance while it is still hot !

Shame it took 3 posts for the same test results.
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Last edited by AndrewT; 23rd September 2012 at 09:31 AM.
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Old 23rd September 2012, 09:28 AM   #1310
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by AndrewT View Post
500VA 240:35+35Vac

Vrso=28.4mVac
Vpso=241Vac
Vsso=74.3Vac
Rsso=1r0
N = 240/74 = 3.243

winding resistances.
Rprimary = 1r33
Rsecondary 0r09 (both secondaries in series measure 0r18)

Vpss = 4.8Vac
Vrss = 0.22Vac
Rsss = 1/6 r (6 1r0 in parallel)

did the Calcs shown on the sheet by hand, but used N=6.486 (for a 37Vac single secondary)
k = 0.999786
L11 = 0.0058
L12 = 0.00014
Lm = 26.9942
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