Capacitor charging times.

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pre65
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#1 Capacitor charging times.

Post by pre65 »

I'd like to try a DIY capacitor bank between my 15v PSU and the Beresford SEG DAC and see if it's any different to the Dorado PSU enhancer.

The Dorado has (I believe) a current limiter on it's input, so if I use 2 of my Kemet 22000uf 63v low ESR soup can capacitors would I need to do that ?

Also, with my 15v @ 7 amp (max) PSU how long would 2 of 22000uf take to charge up ? Ball park figure would do. I'd probably fit bleeder resistors across the caps unless the brains consider it unnecessary if I turn the PSU off first and the SEG when the light goes out.
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pre65
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#2 Re: Capacitor charging times.

Post by pre65 »

I found an online calculator.

I'll check in my 50W resistor box and then do a calculation.

44000uf - 50R @ 4.5W = approx 6 seconds to get to 14V, peak current 300ma, as an example.
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#3 Re: Capacitor charging times.

Post by pre65 »

If I use 25R on each cap then 0-14V = 1.5 secs


25R 9W 600ma peak.

Is that better ?
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#4 Re: Capacitor charging times.

Post by Nick »

If I remember that supply has a voltage reg followed by a current source, so you won't be comparing like with like.
Is that better
Than what?
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#5 Re: Capacitor charging times.

Post by pre65 »

Nick wrote: Sat Apr 18, 2020 7:01 pm If I remember that supply has a voltage reg followed by a current source, so you won't be comparing like with like.
Is that better
Than what?
The second example compared to the first example.

ie two caps paralleled with 50R compared with two caps with 25R each.

To be honest I can't hear any difference with ,or without the Dorado. Just wanting to try something a bit different. Unless you think I'm wasting my time ?
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#6 Re: Capacitor charging times.

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ie two caps paralleled with 50R compared with two caps with 25R each.
Those are two things, but I don't understand what attribute you are using to compare then to make one better than the other.

All you have is two caps being charged through a 50R resistors and the other the same two caps being charged through 12R5 made up of two 25R resistors in parallel.
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#7 Re: Capacitor charging times.

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Nick wrote: Sat Apr 18, 2020 7:40 pm
ie two caps paralleled with 50R compared with two caps with 25R each.
Those are two things, but I don't understand what attribute you are using to compare then to make one better than the other.

All you have is two caps being charged through a 50R resistors and the other the same two caps being charged through 12R5 made up of two 25R resistors in parallel.
I have trouble trying to explain what I mean.

I'll do a diagram to show you what I'm thinking.
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#8 Re: Capacitor charging times.

Post by pre65 »

If I put a 22000uf cap across the PSU output, but without a limiting resistor, would that damage the capacitor on initial charge up ?

The PSU regulating chip is limited to about 7 amp.
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#9 Re: Capacitor charging times.

Post by Nick »

pre65 wrote: Sat Apr 18, 2020 8:02 pm
Nick wrote: Sat Apr 18, 2020 7:40 pm
ie two caps paralleled with 50R compared with two caps with 25R each.
Those are two things, but I don't understand what attribute you are using to compare then to make one better than the other.

All you have is two caps being charged through a 50R resistors and the other the same two caps being charged through 12R5 made up of two 25R resistors in parallel.
I have trouble trying to explain what I mean.

I'll do a diagram to show you what I'm thinking.
My point is that "better" is not just a simpls thing, better as in cheaper, better as in more expensive, better as in bigger, better as in smaller. Etc.
Little known fact, coherent thought can destructively interfere with itself leaving no thought at all, that’s why I prefer incoherent thought.
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#10 Re: Capacitor charging times.

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pre65 wrote: Sat Apr 18, 2020 9:18 pm If I put a 22000uf cap across the PSU output, but without a limiting resistor, would that damage the capacitor on initial charge up ?

The PSU regulating chip is limited to about 7 amp.
The cap would not care as long as its voltage limit were maintained, don't know if the power supply would like operating into a momentary short though.
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#11 Re: Capacitor charging times.

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Nick wrote: Sat Apr 18, 2020 9:28 pm
pre65 wrote: Sat Apr 18, 2020 9:18 pm If I put a 22000uf cap across the PSU output, but without a limiting resistor, would that damage the capacitor on initial charge up ?

The PSU regulating chip is limited to about 7 amp.
The cap would not care as long as its voltage limit were maintained, don't know if the power supply would like operating into a momentary short though.
So,a 1K (for example) resistor across the cap would prevent a momentary short ?
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#12 Re: Capacitor charging times.

Post by SteveH »

Hmm, a resistor, any resistor in parallel with a s/c is going to do what exactly? :D
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#13 Re: Capacitor charging times.

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SteveH wrote: Sat Apr 18, 2020 10:31 pm Hmm, a resistor, any resistor in parallel with a s/c is going to do what exactly? :D
A resistor across a capacitor will act as a bleeder resistor, and also as a load if the real load (ie my SEG DAC) is not switched on.

So I'm thinking (always dangerous :lol: ) that as the capacitor is not a permanent short the resistor will make it not blow up the power supply.

Even as I'm trying to explain things it sounds wrong. :?

For how long would the capacitor remain a short circuit ? Milli seconds ?
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#14 Re: Capacitor charging times.

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I connected 1 x 22000uf capacitor (without resistor) to the PSU output, then switched the PSU on.

No smoke or any signs of distress. :D

Next time Jean is out I'll test for sonic changes, although with my aural memory it's doubtful I'd notice anything.
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#15 Re: Capacitor charging times.

Post by IslandPink »

pre65 wrote: Sat Apr 18, 2020 9:49 pm So,a 1K (for example) resistor across the cap would prevent a momentary short ?
No, on switch-on the cap is just a very low resistance ( eg. the ESR of the cap type ) in parallel with a much larger resistance. the current just surges into the lower resistance (cap) till it's charged-up. The parallel resistor only has purpose when you switch off.
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