Caps for PSU

gengis · 21st April 2005, 01:45 AM

I need some help for picking out PSU capacitors, in the process of collecting parts for an amp. Have picked one 1000VA transformer, 60V AC, 8.33A supply per channel; amp rail +/-90VDC.

Capacitor options:

1.) 100V, 18000uF, Max ESR=17.5, Max Ripple current=10.5 A
2.) 100V, 18000uF, Max ESR=0.018, Max Ripple current =10.4A
3.) 100V, 22000uF, Max ESR=0.015, Max Ripple current =12.5A
4.) 150V, 22000uF, Max ESR=15.4, Max Ripple current =15.6A

I am only going to pick one style of the caps (4 per channel), please also explain the reasons for picking the particular cap.
Thanks.

Sch3mat1c · 21st April 2005, 03:24 AM

All of them should be acceptable, though there's no need for the excess rating (150V) and expense of the last one.

Hmm, 8.3A is a lot of DC, won't ripple be up around say 20-30A? Then you'll need to get smaller (say 5-10mF range) caps and parallel a few.

Or you could get a higher voltage transformer and choke filter it (ripple current will be almost negligible), but chokes of a suitable spec are unfortunately hard to come by.

Tim

AndrewT · 21st April 2005, 08:06 PM

Hi,
you're obviously planning a big amp and this will entail high ripple currents.
I second last recomendation to use multiple caps on each rail to increase the total ripple capacity. It has the other benefit of reducing ESR, provided you keep cable short.
The ESR for the first & last are suspiciously high, could they be milliohm?
You may find that 4 * 4.7mF & 2 *10mF are cheaper than 18mF.

AndrewT · 21st April 2005, 08:15 PM

Hi again,
nominal voltage of transformer is 60Vac
unloaded voltage assuming 3% regulation will be 61.8Vac
rectified voltage will be 87.4Vdc less 0.3 for lo current diode loss = 87.1Vdc
Plus 6% incoming mains voltage will raise your unloaded voltage to about 92.3Vdc.
That leaves about 7% spare as a safety factor. Capacitor life should be OK if you keep them cool, another reason to reduce ripple current and case temperature.

gengis · 21st April 2005, 09:38 PM

Thanks for the reply.

It is E. Holton's 800W Mosfet amp.
I ordered the boards and collecting parts now.

He recommend the third choice:
3.) 100V, 22000uF, Max ESR=0.015, Max Ripple current =12.5A

I planned to have 4 of them or 88000uF per channel.

21st April 2005, 01:45 AM	#1
gengis diyAudio Member Join Date: Feb 2005 Location: Midwest--IA	Caps for PSU I need some help for picking out PSU capacitors, in the process of collecting parts for an amp. Have picked one 1000VA transformer, 60V AC, 8.33A supply per channel; amp rail +/-90VDC. Capacitor options: 1.) 100V, 18000uF, Max ESR=17.5, Max Ripple current=10.5 A 2.) 100V, 18000uF, Max ESR=0.018, Max Ripple current =10.4A 3.) 100V, 22000uF, Max ESR=0.015, Max Ripple current =12.5A 4.) 150V, 22000uF, Max ESR=15.4, Max Ripple current =15.6A I am only going to pick one style of the caps (4 per channel), please also explain the reasons for picking the particular cap. Thanks.

21st April 2005, 03:24 AM	#2
Sch3mat1c diyAudio Member Join Date: Jan 2003 Location: Milwaukee, WI	All of them should be acceptable, though there's no need for the excess rating (150V) and expense of the last one. Hmm, 8.3A is a lot of DC, won't ripple be up around say 20-30A? Then you'll need to get smaller (say 5-10mF range) caps and parallel a few. Or you could get a higher voltage transformer and choke filter it (ripple current will be almost negligible), but chokes of a suitable spec are unfortunately hard to come by. Tim __________________ See my Electronics webpage -- the home of Vacuum Tube Drag Racing. The key to being a successful Audiophile: "I reject your reality and substitute my own!"

21st April 2005, 08:06 PM	#3
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, you're obviously planning a big amp and this will entail high ripple currents. I second last recomendation to use multiple caps on each rail to increase the total ripple capacity. It has the other benefit of reducing ESR, provided you keep cable short. The ESR for the first & last are suspiciously high, could they be milliohm? You may find that 4 * 4.7mF & 2 *10mF are cheaper than 18mF. __________________ regards Andrew T.

21st April 2005, 08:15 PM	#4
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi again, nominal voltage of transformer is 60Vac unloaded voltage assuming 3% regulation will be 61.8Vac rectified voltage will be 87.4Vdc less 0.3 for lo current diode loss = 87.1Vdc Plus 6% incoming mains voltage will raise your unloaded voltage to about 92.3Vdc. That leaves about 7% spare as a safety factor. Capacitor life should be OK if you keep them cool, another reason to reduce ripple current and case temperature. __________________ regards Andrew T.

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21st April 2005, 09:38 PM	#5
gengis diyAudio Member Join Date: Feb 2005 Location: Midwest--IA	Thanks for the reply. It is E. Holton's 800W Mosfet amp. I ordered the boards and collecting parts now. He recommend the third choice: 3.) 100V, 22000uF, Max ESR=0.015, Max Ripple current =12.5A I planned to have 4 of them or 88000uF per channel.

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