// CAPS
awhiteguy,
I had 2 x // 100V 10.000 microF caps in an OTL amp to be used as 10.000 microF/200V.
Each rail had 4 of these caps so Ctot was 10.000 microF at + and - 150VDC.
Equalizing resistors were in place so you wouldn't expect problems.
However,no two caps are the same and after a years' use I noticed trouble,fuses blew for no obvious reason and the top cap was always getting noticebly hotter then the bottom one.
To cut a long story short one day while I wasn't in the room a fuse in one of the rails blew and a minute later that cap had all the boiling electrolyte spilled all over the amp.
Net result: I ended up replacing 8 caps for the 200 V equivalents,
I had half a days work cleaning the inside of the amp,repaint it afterwards and to top it all off I had to replace an entire carpet as well.
Total cost? Much more then the 200V caps would have cost in the first place.
Once the 200 V caps were installed the amps sounded noticebly better (sense of ease and that sense of restlessness was gone)and never have given trouble since.
Had there been a CT on the xformer this wouldn't have happened but I sure learned the hard way.
You see since no cap is equal the top one takes the inrush current and overvoltage at switch on and with the tubes being cold that represents a lot of stress,eventually weakening the cap and taking it out.
Guess you know my advice to you.
Ciao,
awhiteguy,
I had 2 x // 100V 10.000 microF caps in an OTL amp to be used as 10.000 microF/200V.
Each rail had 4 of these caps so Ctot was 10.000 microF at + and - 150VDC.
Equalizing resistors were in place so you wouldn't expect problems.
However,no two caps are the same and after a years' use I noticed trouble,fuses blew for no obvious reason and the top cap was always getting noticebly hotter then the bottom one.
To cut a long story short one day while I wasn't in the room a fuse in one of the rails blew and a minute later that cap had all the boiling electrolyte spilled all over the amp.
Net result: I ended up replacing 8 caps for the 200 V equivalents,
I had half a days work cleaning the inside of the amp,repaint it afterwards and to top it all off I had to replace an entire carpet as well.
Total cost? Much more then the 200V caps would have cost in the first place.
Once the 200 V caps were installed the amps sounded noticebly better (sense of ease and that sense of restlessness was gone)and never have given trouble since.
Had there been a CT on the xformer this wouldn't have happened but I sure learned the hard way.
You see since no cap is equal the top one takes the inrush current and overvoltage at switch on and with the tubes being cold that represents a lot of stress,eventually weakening the cap and taking it out.
Guess you know my advice to you.
Ciao,
parallel more caps...
For a given capacitance, it usually it pays to parallel a few caps. Because capacitors have some inductance and resistance to them, paralleling them reduces the effective inductance and resistance and increases capacitance. (In short, you get a better capacitor) Paralleled caps also usually end up having a higher rated RMS current than just one alone. (Basically there is more surface area to dissapate heat)
Again, there are some practical limits... ...like paralleling .01uf disc ceramics to get 40,000 uf would be a bad idea Really good capacitor... ...but really difficult to build.
-Dan
For a given capacitance, it usually it pays to parallel a few caps. Because capacitors have some inductance and resistance to them, paralleling them reduces the effective inductance and resistance and increases capacitance. (In short, you get a better capacitor) Paralleled caps also usually end up having a higher rated RMS current than just one alone. (Basically there is more surface area to dissapate heat)
Again, there are some practical limits... ...like paralleling .01uf disc ceramics to get 40,000 uf would be a bad idea
Really good capacitor... ...but really difficult to build. -Dan
Tiroth,
Your comment got me worried, as I have a huge stock of 1500uf HFQs which I plan to use in parallel arrays for my power amps. A web-search later, and I can't find anything on leakage current being a problem for paralled caps, all mentions of this as a problem are for series caps. Ripple current appears to be the problem for parallel arrays, although the solution appears to be simple, i.e. taking the + input as the opposite end of the chain to the - input, err, words are failing me ....
http://www.chemi-con.com/guide/pg9.php
Have I missed something?
Jake
Your comment got me worried, as I have a huge stock of 1500uf HFQs which I plan to use in parallel arrays for my power amps. A web-search later, and I can't find anything on leakage current being a problem for paralled caps, all mentions of this as a problem are for series caps. Ripple current appears to be the problem for parallel arrays, although the solution appears to be simple, i.e. taking the + input as the opposite end of the chain to the - input, err, words are failing me ....
http://www.chemi-con.com/guide/pg9.php
Have I missed something?
Jake
Ripple current... ...leakage current...
Ripple current should not be a problem with a big cap. To figure out ripple current, you need to look at the current that is charging, and discharging your cap. It will be roughly the same as the current your amp dumps into your speakers. If you're amp draws a lot of current, you may look into paralleling more caps. This will usually give you more RMS rated current for a the same ammount of capacitance. In all reality you shouldn't even need to look at ripple current. (at least for audio stuff!)
Leakage current is the current that moves between plates on the capacitor. A perfect cap has none, but in reality, most capacitors are a little leaky (that is, there is some resistance, usually very large between the capacitor plates, so a small ammount of current flows.) In a "leaky" cap, that current is higher, because of a lower resistance. In a very leaky cap, that current can (not always) generate enough heat to cause the cap to explode. For this reason, most large electrolytic capacitors have a vent built into them. (You can also cause a cap to blow because of overvoltage causing more current to "leak" than nomal, Ask me how I know this!)
Leakage current PER cap does NOT go up when you parallel caps. Leakage current does go up, because you have more caps. Again assuming the caps are the same size, and if one cap leaks 1mA, two caps will leak 2mA, and 100 Caps will leak 100mA. Also, keep in mind that smaller value capacitors will usually have less leakage.
-Dan
Ripple current should not be a problem with a big cap. To figure out ripple current, you need to look at the current that is charging, and discharging your cap. It will be roughly the same as the current your amp dumps into your speakers. If you're amp draws a lot of current, you may look into paralleling more caps. This will usually give you more RMS rated current for a the same ammount of capacitance. In all reality you shouldn't even need to look at ripple current. (at least for audio stuff!)
Leakage current is the current that moves between plates on the capacitor. A perfect cap has none, but in reality, most capacitors are a little leaky (that is, there is some resistance, usually very large between the capacitor plates, so a small ammount of current flows.) In a "leaky" cap, that current is higher, because of a lower resistance. In a very leaky cap, that current can (not always) generate enough heat to cause the cap to explode. For this reason, most large electrolytic capacitors have a vent built into them. (You can also cause a cap to blow because of overvoltage causing more current to "leak" than nomal, Ask me how I know this!)
Leakage current PER cap does NOT go up when you parallel caps. Leakage current does go up, because you have more caps. Again assuming the caps are the same size, and if one cap leaks 1mA, two caps will leak 2mA, and 100 Caps will leak 100mA. Also, keep in mind that smaller value capacitors will usually have less leakage.
-Dan
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