I am looking for opinions on PS cap sizing.
The amp in question is a ML 27.5 Class A amplifier (all solid state). The cap is from the low level PS circuit. It is rated at 1900ufd @150VDC with only 85VDC across it. I've temporarily put 1100ufd in cct and it works fine.
Given that the following are what's available to fit the physical size, and money is not an issue what would you choose? Just curious.
The available values are:
2700@200VDC CDE
2400@100VDC Mallory
5000@160VDC CDE
4700@100VDC United Chemi-con (cheapest)
Dan
The amp in question is a ML 27.5 Class A amplifier (all solid state). The cap is from the low level PS circuit. It is rated at 1900ufd @150VDC with only 85VDC across it. I've temporarily put 1100ufd in cct and it works fine.
Given that the following are what's available to fit the physical size, and money is not an issue what would you choose? Just curious.
The available values are:
2700@200VDC CDE
2400@100VDC Mallory
5000@160VDC CDE
4700@100VDC United Chemi-con (cheapest)
Dan
The problem is physical size. They are held in with their screw terminals and one very unyielding clamp. Paralleling is not an option because of that.
What I'm basically concerned with is 100V units not standing up with 85V on them (long term) and/or putting too much capacitance on the rectifiers. There's a fair bit of heat in this amp.
What I'm basically concerned with is 100V units not standing up with 85V on them (long term) and/or putting too much capacitance on the rectifiers. There's a fair bit of heat in this amp.
I think that 100V would be a bit short for the 85V. If you got 10% more mains (not unusual) you're up into the low 90's, and although the cap will not explode it will shorten it's life. Is the 85V what you measured or what is in the manual? This may differ.
I also would be hesitant to increase the capacitance too much, you may actually get more higher-order harmonics on the supply lines. Going from 1900 to say 2700 uF seems OK, but I wouldn't go to 4700.
Jan Didden
I also would be hesitant to increase the capacitance too much, you may actually get more higher-order harmonics on the supply lines. Going from 1900 to say 2700 uF seems OK, but I wouldn't go to 4700.
Jan Didden
Jan, or anyone else who knows, this is a little off topic I guess, but still related. Is it possible to use high value caps in combination with small caps to take out high frequency noise. I've seen this quite often in PS's, where there's a big cap and a small, maybe 0.1uF cap paralleled accross it, and wondered if that's what it was for.
Cheers,
Steve
Cheers,
Steve
For the stuff I do at work, we derate capacitors by 60%, to give longer life. It's mil stuff, so reliability is critical. For an 85 Volt rail, I would specify a cap with at least 150V rating. The 2700uF/200V part sounds like it's closest to the right capacitance value, and the 200V rating will help insure it's longevity.
The data sheets for capacitors typically give a lifetime of 2000 hours running a cap at it's rated voltage. The more you derate them, the longer they last. Temperature also is a factor. Some of the newer caps, like the conductive polymer types, are claimed to not need derating, but we derate them anyway. (Those are low voltage caps anyway, so they don't apply to your case).
Cheers,
bg
The data sheets for capacitors typically give a lifetime of 2000 hours running a cap at it's rated voltage. The more you derate them, the longer they last. Temperature also is a factor. Some of the newer caps, like the conductive polymer types, are claimed to not need derating, but we derate them anyway. (Those are low voltage caps anyway, so they don't apply to your case).
Cheers,
bg
baggystevo82 said:
Whats feeding the cap? A trafo/ recifier or a regulator? If the latter. You could blow the regulator which may not be designed for a high current charge-up of the larger (4700uF?) cap.
As others, I'd also say 2400uF of at least 160v may make it "live" longer.
K-
PS: In some Krell pre-amp, I saw burnt 63v caps with 56v supplies. The 100v parts were ok... i.e. did not heat up as bad. So in a power on and forget circuit, I'd go with lots of voltage headroom.
True, forgot about that. Although isn't it better to put regulators after smoothing and storage caps? Either way, with any change in capacitor it may be worth checking that both it and surrounding components will survive. Duncan Amps PSU deisgner would be useful, and you could put a number to any improvements that a change in capacitor value might bring.
Steve
Hello bagystevo, good to meet you again
Those small capacitors in parallel with the bigger one makes some big difference when you work with radio frequencies . Also in audio we can find a lot of people using it (i do always), the reason explained to me some years ago is that electrolitics condenser is made with spiral form, alike a shorting diameter coil (or opposite if you want it is real too)... if you have a coil, together with capacitance, you will have some resistance to hi frequencies to pass througth the electrolitcs that is constructed this way, so, if oscilates, or if some hi frequency signal is captured in mains wiring ( the longest and magnificent aerial you can have, capturing magnetic signal from all the town and the field), and those mains wiring sometimes interrupted by a heavy transformer to low down voltage...here HF signals stops...but others conections, doubled in multiples of radio frequencies captures always signals that enter your home transformer and sometimes goes to your amplifiers because electrolitics do not let them pass to the ground because of coils resistance... the inductance of the coil acting as resistance, and some designers thinks that using 100 Megahertz transistors the amplifiers will work better in 10000 cicles... and sometimes, harmonics are worst, but they know very well the reasons and secrets that i cannot discuss here. This small capacitor is alike a short for those signals, also a short for ultrasonic signals and can be helpfull.
If all those ideas is something woddoo, or not, do not change the mains reason...beeing good or not beeing good, it is so cheap that is better to put them everywhere, as a precaution... this medicine, if do not put you good again, also cannot kill you!
Carlos
Those small capacitors in parallel with the bigger one makes some big difference when you work with radio frequencies . Also in audio we can find a lot of people using it (i do always), the reason explained to me some years ago is that electrolitics condenser is made with spiral form, alike a shorting diameter coil (or opposite if you want it is real too)... if you have a coil, together with capacitance, you will have some resistance to hi frequencies to pass througth the electrolitcs that is constructed this way, so, if oscilates, or if some hi frequency signal is captured in mains wiring ( the longest and magnificent aerial you can have, capturing magnetic signal from all the town and the field), and those mains wiring sometimes interrupted by a heavy transformer to low down voltage...here HF signals stops...but others conections, doubled in multiples of radio frequencies captures always signals that enter your home transformer and sometimes goes to your amplifiers because electrolitics do not let them pass to the ground because of coils resistance... the inductance of the coil acting as resistance, and some designers thinks that using 100 Megahertz transistors the amplifiers will work better in 10000 cicles... and sometimes, harmonics are worst, but they know very well the reasons and secrets that i cannot discuss here. This small capacitor is alike a short for those signals, also a short for ultrasonic signals and can be helpfull.
If all those ideas is something woddoo, or not, do not change the mains reason...beeing good or not beeing good, it is so cheap that is better to put them everywhere, as a precaution... this medicine, if do not put you good again, also cannot kill you!
Carlos
Carlos,
Looking on your biography I believe you been there, surfing on
the resonance peaks of high Q caps.
With electrolytics having a "practical" ESR the Q is not that high
and the resonance will be accordingly. It is ananother story with
film caps and the like. Theese guys have, almost, only the rated
capacitance and lead inductance and can get peaky.
Check out www.evox-rifa.com, if I remember it they even have
some software where you can see the resonance etc for their
caps. Furthermore they have very nice papers and stuff about
lifetime calculations etc, not to mention their link library.
/Brasilian cigars are even better than Cohibas / Mattias
Looking on your biography I believe you been there, surfing on
the resonance peaks of high Q caps.
With electrolytics having a "practical" ESR the Q is not that high
and the resonance will be accordingly. It is ananother story with
film caps and the like. Theese guys have, almost, only the rated
capacitance and lead inductance and can get peaky.
Check out www.evox-rifa.com, if I remember it they even have
some software where you can see the resonance etc for their
caps. Furthermore they have very nice papers and stuff about
lifetime calculations etc, not to mention their link library.
/Brasilian cigars are even better than Cohibas / Mattias
Hahaha. I like the way you tell you ideas!
Surfing on may be "travelling with your brain"...or delirating, or
"dreamin beeing wake up"..... beeing drunk and having some "visions". I like this way, i think its the most kind way to say, you completely wrong!. Good!, can be strange for you,but this mades me think about you as a very kind person, and with a clever sense of humor.
OK!, i will see the informations you direct me, in my country we say that things with the idea the man is "big crazy", something completely out of control, or "viajando na maionaisse", travell with a maionaisse, becoming very drugged using only simple maionaisse.... a very funny words here.
If not intention, you make me feel "wondering", "travelling", this is kind way to do the things,
My deep congratulations for you, no common people of this part of the world with so much humor.( not ironic, real empathy, good)
Carlos
Surfing on may be "travelling with your brain"...or delirating, or
"dreamin beeing wake up"..... beeing drunk and having some "visions". I like this way, i think its the most kind way to say, you completely wrong!. Good!, can be strange for you,but this mades me think about you as a very kind person, and with a clever sense of humor.
OK!, i will see the informations you direct me, in my country we say that things with the idea the man is "big crazy", something completely out of control, or "viajando na maionaisse", travell with a maionaisse, becoming very drugged using only simple maionaisse.... a very funny words here.
If not intention, you make me feel "wondering", "travelling", this is kind way to do the things,
My deep congratulations for you, no common people of this part of the world with so much humor.( not ironic, real empathy, good)
Carlos
Carlos you are right....
.......I did absolutely not mean you are wrong in any way.
On the contrary, I believe you are quite right.
When I say surfing I mean you have digged into tons of HF stuff.
Believe me after 30yrs of experience you have probably seen things
that have not yet been given a deeper theoretical analysis on.
The software on the evox-rifa page just gives you an idea of how caps
may work in a circuit, without using breadboards and instruments.
However, and you're the one to know, nothing beats real hardware
hook-ups.
/ Regards / Mattias
.......I did absolutely not mean you are wrong in any way.
On the contrary, I believe you are quite right.
When I say surfing I mean you have digged into tons of HF stuff.
Believe me after 30yrs of experience you have probably seen things
that have not yet been given a deeper theoretical analysis on.
The software on the evox-rifa page just gives you an idea of how caps
may work in a circuit, without using breadboards and instruments.
However, and you're the one to know, nothing beats real hardware
hook-ups.
/ Regards / Mattias
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