you guys are smart.. :D help :(

SkinnyBoy · 13th May 2005, 04:36 PM

basically....

I have 1000VA of transformers.... 9volts AC....

once rectified, how much capacitance to i need to keep the DC up with full load on the transformers, which is 80amps or so...

the mains is 50Hz... DC output from the rectifiers is around 12.5volts with a small load (lets assume 12volts under full load, they are big transformers)

THANKYOU!!

pinkmouse · 13th May 2005, 04:39 PM

What's your application? Caps only reduce ripple.

SkinnyBoy · 13th May 2005, 04:55 PM

its to run a car amp, in the house....

edit: and maybe to jump start a car if it has a flat battery

SkinnyBoy · 13th May 2005, 05:33 PM

is ripple the right word?

I mean.. with a small load, and no capacitors, the DC voltage drops to 9 volts... while the AC stays constant.... ripple??

tiroth · 13th May 2005, 06:09 PM

Download PSU Designer and find out. I suspect the answer is that you need a heck of a lot more voltage to maintain 12V at 80A. If you are ok with a lot of rail sag, then the requirements aren't as difficult.

SkinnyBoy · 13th May 2005, 06:16 PM

Quote:

Originally posted by tiroth
I suspect the answer is that you need a heck of a lot more voltage to maintain 12V at 80A.

I'm abit confused by that statement...

SkinnyBoy · 13th May 2005, 06:19 PM

ok... how about YOU download it, and tell me the answer

simon5 · 13th May 2005, 06:31 PM

The easy way out would be to buy a supercapacitor from a car audio shop. I guess 1 F should be enough. I would also put two smaller ones in parallel... maybe a 1 mF and a 1 uF.

You could also use Maxwell Ultracapacitors...

SkinnyBoy · 13th May 2005, 06:34 PM

Quote:

Originally posted by simon5
The easy way out would be to buy a supercapacitor from a car audio shop. I guess 1 F should be enough. I would also put two smaller ones in parallel... maybe a 1 mF and a 1 uF.

You could also use Maxwell Ultracapacitors...

yeah, but would 1 farad actually be enough? or would 2 farads be better? or, is 1 farad overkill?

THATS my question

tiroth · 13th May 2005, 07:12 PM

Ok. 4.5-0-4.5 tranny, full wave rectified into 1F of capacitance. Assumptions: 1.1m source resistance, 2m capacitor series resistance. (better than you will see in reality!)

Load: 150m (80A draw at 12V)
RMS voltage: 6.6V
Ripple: 321mV p-p

Load: 300m (40A draw at 12V)
RMS voltage: 8V
Ripple: 232mV p-p

Load: 1.5R (8A draw at 12V)
RMS voltage: 10.2V
Ripple: 88mV p-p

That's what I meant by "you need more voltage."

13th May 2005, 04:36 PM	#1
SkinnyBoy Banned Join Date: Nov 2002 Location: Adelaide, Australia	you guys are smart.. :D help :( basically.... I have 1000VA of transformers.... 9volts AC.... once rectified, how much capacitance to i need to keep the DC up with full load on the transformers, which is 80amps or so... the mains is 50Hz... DC output from the rectifiers is around 12.5volts with a small load (lets assume 12volts under full load, they are big transformers) THANKYOU!!

13th May 2005, 04:39 PM	#2
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	What's your application? Caps only reduce ripple. __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

13th May 2005, 06:31 PM	#8
simon5 diyAudio Member Join Date: Nov 2004 Location: Québec, Québec	The easy way out would be to buy a supercapacitor from a car audio shop. I guess 1 F should be enough. I would also put two smaller ones in parallel... maybe a 1 mF and a 1 uF. You could also use Maxwell Ultracapacitors... __________________ DIYaudio for President !

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13th May 2005, 04:55 PM	#3
SkinnyBoy Banned Join Date: Nov 2002 Location: Adelaide, Australia	its to run a car amp, in the house.... edit: and maybe to jump start a car if it has a flat battery

13th May 2005, 05:33 PM	#4
SkinnyBoy Banned Join Date: Nov 2002 Location: Adelaide, Australia	is ripple the right word? I mean.. with a small load, and no capacitors, the DC voltage drops to 9 volts... while the AC stays constant.... ripple??

13th May 2005, 06:09 PM	#5
tiroth diyAudio Member Join Date: Dec 2001 Location: Pittsburgh, PA, USA	Download PSU Designer and find out. I suspect the answer is that you need a heck of a lot more voltage to maintain 12V at 80A. If you are ok with a lot of rail sag, then the requirements aren't as difficult.

13th May 2005, 06:19 PM	#7
SkinnyBoy Banned Join Date: Nov 2002 Location: Adelaide, Australia	ok... how about YOU download it, and tell me the answer

13th May 2005, 07:12 PM	#10
tiroth diyAudio Member Join Date: Dec 2001 Location: Pittsburgh, PA, USA	Ok. 4.5-0-4.5 tranny, full wave rectified into 1F of capacitance. Assumptions: 1.1m source resistance, 2m capacitor series resistance. (better than you will see in reality!) Load: 150m (80A draw at 12V) RMS voltage: 6.6V Ripple: 321mV p-p Load: 300m (40A draw at 12V) RMS voltage: 8V Ripple: 232mV p-p Load: 1.5R (8A draw at 12V) RMS voltage: 10.2V Ripple: 88mV p-p That's what I meant by "you need more voltage."

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