i need about 100amps at 12 volts

[Steerpike]

That Kinetic thing is just an expensive car battery. And at $600, you'd still save money by selling you exsting amp and buying a mains powered 1000W amp.

[Steerpike]

Originally Posted by anwaypasible

see.. i figured if i do one +12 and one ground combined with one +3.3 and one ground, there would be a simple addition taking place.
i understand the added current from the +3.3 would only be a fraction (also known as 'only an extra 100watts that the powersupply is helping my amp produce').

Noo.. If you series-wire two power supplies to get the sum of their voltages, the available current is the smaller of the two individual supplies (i.e., the current of the !2 v supply). Currents do not add in a series circuit.

your saying if i did the one +12 and one ground combined with one +3.3 and one ground.. WITH ONE POWER SUPPLY that the two rails are going to float/bleed/fight and then shorten the life of something?
(or are you saying that the combining of two power supplys will do that?)

You physically cannot do it with a single power supply. The (-) connections of both the 12v and the 3V are the same point electrically.
To do what you want, you'd need to connect the (-) of the 3V section to the (+) of the 12v section. Only possible with 2 supplies.

What i was saying also. if you take two 12V supplies, and parallell wire them, to add the current (amps), still only giving 12V total, they will fight over what the voltage should be. Neither will be putting out exactly 12.000000V.

i thought that there would simply be more stress on the filter caps and more stress on the step down transformer.. but nothing cross-eyed unless

Depends on the magnitude of the voltage difference. At best, the supplies will just run hot. At worst they wil burn out, or less catastrophic, just shut down due to overcurrent protection.

[anwaypasible]

Originally Posted by Steerpike

That Kinetic thing is just an expensive car battery. And at $600, you'd still save money by selling you exsting amp and buying a mains powered 1000W amp.

the 'car battery' lets out high amperage at almost a dead short they say.
even the cheapest one they offer is 'stronger than 100 one farad capacitors'

besides.. it is sealed up tight so i could re-charge it in the house with no ventilation.
they go on ebay for starting $105

[event horizon]

I'd forget the computer PSUs myself, you'll need to do a heck of a lot of messing about as has already been suggested Getting them to current share is a nightmare with special feedback circuitry needed so they both contribute equally, that is unless you stick a dirty great big low resistance resistor on the positive output of each supply to force current sharing (but it's going to be very lossy).

Your best bet if you are determined to do this is either to purchase something already designed for the job - read loadsamoney Or find 3 surplus high current 5V supplies & connect the outputs in series. You'll need a diode (100A plus) accross the output of each supply (reverse connected) just in case one of the supplies goes down so they don't want to destroy themselves, but it can be done.

I happen to have 3 x 750W 5V (150Amp) supplies here to test car amps so i know it can be done, you'll need one hell of a decent mains supply though unless they are power factor corrected.

[anwaypasible]

Originally Posted by Steerpike

You physically cannot do it with a single power supply. The (-) connections of both the 12v and the 3V are the same point electrically.
To do what you want, you'd need to connect the (-) of the 3V section to the (+) of the 12v section. Only possible with 2 supplies.

What i was saying also. if you take two 12V supplies, and parallell wire them, to add the current (amps), still only giving 12V total, they will fight over what the voltage should be. Neither will be putting out exactly 12.000000V.

you have said something here that has struck my interest.
so the power comes in from the transformer and are the +12 and +3.3 rails connected to the same transformer?
because if they had the same electrical connection the +12 rail could suck up all the juice leaving the +3.3 to dwindle down and feed from a (if any) capacitor that is not being re-charged because the +12 rail is being a hog.
yes..? no..?

does the +3.3 rail have its own transformer? (i'm thinking it would be smarter)
because if not.. then the +3.3 would have to have voltage regulation, but using the same current bank.

see i was under the impression that there are more than one current bank to use.
but if the +12 and the +3.3 have the same 'bank account'
it would be wise for me to simply use the +12 rail ONLY and suck the blessid thing with the amplifier.

i guess that question can only be answered by looking inside for more than one transformer though eh?
am i right or wrong about that.

[event horizon]

Originally Posted by anwaypasible

does the +3.3 rail have its own transformer? (i'm thinking it would be smarter)
because if not.. then the +3.3 would have to have voltage regulation, but using the same current bank.

No, they are all run off of the same transformer. Generally the output with the highest current is the regulated output, the others including +12 tend to get regulated by the amount of turns on the transformer & the output inductor. They'll be linked on the ground line so can't really be split.

If you increase the output voltage on the main regulated output then all the voltage outputs will generally follow suit, that is unless they are followed by a post regulator such as a power mosfet controlled by other circuitry.

[aardvarkash10]

why are you trying so hard to make your life miserable?

Its a car amp - so emulate whats in a car.

Get a battery (not a pissy little one - get a 17 plate commercial vehicle one) and a (say...) 25A continuous battery charger.

Done.

Now go "oonst oonst" yer heart out....

[russo]

As said before, the car amp as an SMPS that takes the 12v input and convert it to 60-0-60v or more to feed the amplifier, so why don't you just open the amplifier, disconnect the smps from the amplifier and use a centertap transformer rated for the current and voltage supplied by the smps originally?
Would be easier and a lot cheaper than your initial idea.

[anwaypasible]

Originally Posted by event horizon

I'd forget the computer PSUs myself, you'll need to do a heck of a lot of messing about as has already been suggested Getting them to current share is a nightmare with special feedback circuitry needed so they both contribute equally, that is unless you stick a dirty great big low resistance resistor on the positive output of each supply to force current sharing (but it's going to be very lossy).

Your best bet if you are determined to do this is either to purchase something already designed for the job - read loadsamoney Or find 3 surplus high current 5V supplies & connect the outputs in series. You'll need a diode (100A plus) accross the output of each supply (reverse connected) just in case one of the supplies goes down so they don't want to destroy themselves, but it can be done.

I happen to have 3 x 750W 5V (150Amp) supplies here to test car amps so i know it can be done, you'll need one hell of a decent mains supply though unless they are power factor corrected.

so you are saying literally daisy chaining power supplys in series rather than parallel (just like series and parallel with speakers) is beneficial, but only if the supplys are of the same rating?

i am understanding that there is circuitry with IC chips that could or could not help the situation.

what about the power supplys being ran off the same 60hz wave.
i mean i think that would set the timing of the transformers in sync (especially if they are the same)
and then the rest of the current is direct/constant.. so i am failing to see where/how the circulation would be taking place.

the filter capacitors would heave-ho eachother?
the difference in transfomers would heave-ho eachother?
the (if any) feedback circuitry would cause a heave-ho between the two supplys if wired in parallel?

because this is where i'm confused at.. i dont see the electricity as an ocean of water yet.

[anwaypasible]

Originally Posted by event horizon

No, they are all run off of the same transformer. Generally the output with the highest current is the regulated output, the others including +12 tend to get regulated by the amount of turns on the transformer & the output inductor. They'll be linked on the ground line so can't really be split.

If you increase the output voltage on the main regulated output then all the voltage outputs will generally follow suit, that is unless they are followed by a post regulator such as a power mosfet controlled by other circuitry.

this makes me think that the step down transformer drops the 110v down to 5v or 3.3v and then uses another step up transformer to provide the +12v

am i speculating different design options here?