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!! :D
 
simon5 said:
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 :D
 
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."
 
Adding more capacitance doesn't help unless your transformer/recitifiers can supply infinite current. Adding more capacitance just changes the conduction angle, which may not help you if you are already pulling down the tranny's voltage. You need to start with more voltage.

The 1.4x rule is only true if you are drawing lightly on the supply. As load increases, you begin to get only 1x RMS, and then even less than that as impedance losses add up.
 
skinnyboy:
what if I had 2000VA of toroidals, and only put the same 80amp load on them, are you saying I still wouldn't get 12volts, as I am only starting with like 12.7 unloaded?
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Hi skinny, you would use a 2000va instead of a 1000va that is specified for the
job just to get a 0.7v better regulation, gee you are smart, i would suggest you
used a 3000va to get even better results
you would get better regulation thats for sure but the returns are small there are
better ways to tacle this problem without regulation, put load and Vtr into the
equation and save the capacitance for filtering
cheers
 
mastertech said:
Hi skinny, you would use a 2000va instead of a 1000va that is specified for the
job just to get a 0.7v better regulation, gee you are smart, i would suggest you
used a 3000va to get even better results
you would get better regulation thats for sure but the returns are small there are
better ways to tacle this problem without regulation, put load and Vtr into the
equation and save the capacitance for filtering
cheers


umm... wtf is your problem? I asked a question... I didn't say I was going to do it... now, if you wouldn't mind... **** off..
 
The answer is you need more than 12V on any transformer you'd care to be carrying around with less than one person, to put out 12V 80A due to the voltage sag with higher current output.

Depending on the power supply section of the car amplifier, you might be just fine with a very low voltage but likely not.

Another route is to scratch-build a supply to suit the amplifier section... that is, bypass the switching supply in the amplifier altogether and make up a 35-0-35 or 70-0-70 or whatever it makes internally to supply the amp.