Great! Thanks. Is WVDC the rated output voltage or the peak voltage (i.e. top of the 120hz sine curve)? I know they are fairly close, just trying to get a picture in my head of what manufacturers have in mind when they rate a cap.
AC volts are rms values, don't forget the √2 ratio between that value (a pure mathematical construction), and the real peak value.
In addition, a transformer voltage is specified fully loaded, and for the nominal mains voltage. Add 10% for unloaded condition, another 10% for mains variations, and you arrive at 1.414*1.1*1.1=1.71.
With 36VAC, that's 61.6V. 63V is just sufficient, with no additional margin.
With 53V, you're completely out, and 80V is not sufficient either, you have to go for 100V.
Bad advice 63 Vdc rated Cap is not enough for 53 Vac
53 VAC * 1.414 = 75 Vpeak
xfmr also have "regulation" issues - they give a higher V unloaded so that they meet their VA spec under load
then there is line variation - design for 10% high line V
I would use 20% over the peak rectified V as a starting point for the Derating calculation, usually another +20-25%
stacking these factors you could make a rule of thumb of using Cap Vdc rating of ~2x the xfmr Vac #
so I would use 100 Vdc rated Caps with the 53 Vac xfmr, 75-80 with the 36 Vac xfmr
If you are using it center tapped for a dual supply then each polarity is only 1/2 the peak and you could use the 63 V rated C
I have seen many underated C in commercial supplies - it can work - but it is bad design
53 VAC * 1.414 = 75 Vpeak
xfmr also have "regulation" issues - they give a higher V unloaded so that they meet their VA spec under load
then there is line variation - design for 10% high line V
I would use 20% over the peak rectified V as a starting point for the Derating calculation, usually another +20-25%
stacking these factors you could make a rule of thumb of using Cap Vdc rating of ~2x the xfmr Vac #
so I would use 100 Vdc rated Caps with the 53 Vac xfmr, 75-80 with the 36 Vac xfmr
If you are using it center tapped for a dual supply then each polarity is only 1/2 the peak and you could use the 63 V rated C
I have seen many underated C in commercial supplies - it can work - but it is bad design
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Thanks, Elvee. I assumed the outputs mentioned were open circuit and not the rated voltages. 53 volts is sorta odd to me for a transformer.
somejohndoe, ideally the cap will charge to the peak voltage and stay there, so use that value + the safety margins spelled out in Elvee's post. As a diy'er, I have to rely on the manufacturers' ratings, ie that "stay there" voltage. Including worst case and a little CYA margin is a necessary habit when selecting virtually any component.
somejohndoe, ideally the cap will charge to the peak voltage and stay there, so use that value + the safety margins spelled out in Elvee's post. As a diy'er, I have to rely on the manufacturers' ratings, ie that "stay there" voltage. Including worst case and a little CYA margin is a necessary habit when selecting virtually any component.
Today's capacitor are much less tolerant on overvoltage than before: 35 years ago, you could go away with murder, apply a quasi- permanent overvoltage of +25% to a part, and it would happily survive.
If you try the same kind of trick with a modern cap, be prepared for a loud surprise.....
That would be great except the original amp was about 6 years old. Part of the fate of modern, mass produced, price sensitive electronics. I have found some 15000uF/100V electros locally so I will use those. Didn't want to spend money but would rather have a working and safe device than a cheap but dangerous one. I had the 63V caps on hand (22000uF ones!) but I'll probably reuse the 80V caps for the 36V supply in another unit, just for caution.
63V caps is just fine for your 36V transformer. they will handle opp to 44V transformer (unloaded) and you don't drive your amps unloaded, do you?
i have used 63V caps with bouth 40V and 42V transformers for a very long time now. my class D with 42V transformer shows just under 57V with the amp running.
my class A amp with 40V transformer shows 50V when running.
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Not unless the speaker cable has fallen out...... you don't drive your amps unloaded, do you?
Not unless the speaker cable has fallen out...
even then the PSU is under load. how mutch depends on type of amp. class A A/B D or what ever. as long as your amp is connected to the PSU, the PSU is under load
44V unloaded. i am not talking about 44V sec transformer.
but lets look at that. a 2x40V transformer gives 40V under load at 115V/230V mains. not 110/220V. so its 5% rise in worst case.
BTW: thule IA150 is running 2x44V transformer and 63V caps.
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