PSUD2 question

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#21
^ unless you are plugging in a value like 2 ohms for ESR 😛 according to the formula a 10,000 uF cap has an impedance of around 0.01 ohms at 100Hz.... the ESR of a good 10,000uF cap will be around 0.05 ohms. so plugging in 2 ohms as per the original post surely does make a difference!! (it certainly does in spice!!)

Obviously with smaller caps and low frequencies the impedance due to reactance will dominate. Sorry just butting in because I'm learning from this too 🙂 I have a vague idea of how things work but tend to gloss over the actual theory (especially when it involves equations) 🙄

Tony.
 
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#22
Here's where practice intrudes- in a high voltage circuit, you're unlikely to find 1,000u, much less 10,000u! 😀 In the C1 position, you'd arc the rectifiers. In the C2 position, the sheer size and the ESR will probably not have a major effect because of the choke.

In any case, once the O/P is confident in his ability to do the basic calculations, the right numbers can be plugged into the sim.
 
#25
SY said:
Here's where practice intrudes- in a high voltage circuit, you're unlikely to find 1,000u, much less 10,000u! 😀 In the C1 position, you'd arc the rectifiers. In the C2 position, the sheer size and the ESR will probably not have a major effect because of the choke.

In any case, once the O/P is confident in his ability to do the basic calculations, the right numbers can be plugged into the sim.
Click to expand...

That will teach me not to look carefully at the schematic!! I didn't realize that this was a valve supply with such small caps... I've never used anything less than 1000uF in a power supply for smoothing caps as I've only ever done SS! Sorry for side tracking!

Tony.
 
#26
At the 60hz level adding the ESR increased the impedance by .015 ohms, which is nothing really added to 132 ohm

At the 960hz level adding the ESR increased the impedance by 8.54 ohms, which is more than doubling the impedance since it started out at 8.3 ohms, and making a total of 16.84 ohms.
 
#31
OK, so now you've spotted something important- the capacitive impedance is infinite at DC, drops proportionately with frequency, and has the ESR as an asymptote. You also understand that for small caps (like 20u), the ESR is not going to be a big contributor- in your sim, you can see this by varying it from 0.1 ohm to 2 ohms and seeing the difference in the output voltage and ripple.

Now there's one more complication that you'll need to learn about (equivalent series inductance), but that's not a big issue at the low frequencies you're working with, and you can put that off for another day.
 
#32
jazbo8 said:
The manufacturing tolerance of the VT rectifiers and/or the series resistance of the choke will swamp out the effect the ESR of the filter caps, they're the least of your worries... Remember that you are not building for NASA, just a geetar amp ;-)
Click to expand...

Yes they will swamp it as far as values go; but they are in different parts of the circuit thus have different impacts. You can't disregard cap ESR because of transformer or diode ESR.

Jan
 
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