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Subwoofer amplifier power supply: 600W

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johneppen

New Member
I need some help designing a power supply for an amplifier. I have gathered that the bulk of a subwoofer amplifier is a power supply which steps up the 12V(which is standard in most cars) to 20-60volts depending upon the amplifier. Correct me if i'm wrong, but i believe this is because you need a higher voltage to send more current through your speakers(which are usually 2ohm or 4ohm). So actually it is a simple calculation involving ohm's law.
I want a power supply that can continuously supply 60vdc@15amps. My theory is to invert the 12 volt battery current to square wave, which would be 6vac correct? Then i would have to send it through a step up transformer and the windings would be 1:10 correct? My questions are as follows: where can I find a toroidal transformer which could handle this much load and be very small, what is the most ideal frequency, would a pwm need to be a part of this? If you could answer all three questions it would be greatly appreciated. Thank you!
 

kinjalgp

Active Member
Why do you want to invert the battery supply? You can directly use a transformer which will convert 110V or 220V AC to 60V AC @15A. Rectify and filter it using large capacitor bank of around 20,000uF and your supply is ready. Or you can buy a light weight Switch Mode Power Supply.
 

Chippie

Member
I thought the guy was after powering his amp from his car ?

60v at 15A is around 900w of power!!!! Serious........The biggest problem is obtaining a transformer that will handle those power levels.......
AFAIK the ETD44 is good for around 300w although not a toroid, dont know of anything higher..perhaps a search on the web might produce some results... a transformer of that physical size is gonna be big!!!


The basic invertor consists of a pwm chip.......SG3525 driving a series of Mosfets, with High speed Hi current diodes on the secondary..regulation is achived by feeding back a sample of the output voltage to the on chip comparator
 

Chippie

Member
Hmmm a lorry battery perhaps? :lol:


but dont forget that 900w is pure output power not input.......so assuming an efficiency of 75% then the actual power required to realize the 900w is going to be somewhat higher..........



With those sort of power levels you are looking at some serious ear damage.......
 

Chippie

Member
Well got to agree an extra 0 is possible..........60w would be more realistic and achievable....A 75Ah battery although fairly sizeable wont last long.....
 

johneppen

New Member
nope guys 600W is the figure.....we're goin for some serious bass. The 75 amp draw from the battery won't be a problem as long as the car is running. I was wondering if anyone knew anything about a switching power supply? I just need to find a way to keep the transformer as small as possible. Possibly a very high frequency? How about old computer power supplies. Their current capabilities are about 20A or more each. Is there some way i can take the transformer from those and use them? They are switching power supplies though, and I don't know what that really means. Thanks
 

Chippie

Member
Given the physical size of the switching type power supplies, there is a finite amount of power that can be drawn from them..........the 20 amps you quote is from the 5v rail.......assuming a std 300w pc psu, that equates to 100w.........leaving the remainder for the other rails of which the 12v rail supplies another 8-10 amps........

Even so the transformer in them is sized to provide the relevant power levels....typically 250w.......but this is at a given frequency somewhere in the region of 25khz........Increasing the frequency will allow more power but again the physical size of the transformer is the limiting factor........ a bigger transforner is needed for your appication....

HTH Chip
 

johneppen

New Member
So what your saying is that if i oscillate the 12v battery at a frequency of 25khz, take a couple of transformers from computer power supplies and unwind the primaries till i get the correct ratio I could use those? I had one other thought. How do inverters have such a small physical size( the type that invert 12v to 110v to power appliances in RVs and campers) The transformers in those must be pretty small also.
 

Chippie

Member
johneppen said:
So what your saying is that if i oscillate the 12v battery at a frequency of 25khz, take a couple of transformers from computer power supplies and unwind the primaries till i get the correct ratio I could use those.


You seem to have missed my point.......The transformer in a pc psu is small....It has certain properties in relation to its physical size.......one of which is the amount of power it can provide......in this case it is sized to provide in the region of 300w......Ok change the frequency of the pwm and you could get more power from it, but there is a limit.........and no way would you achieve 900w from it.........What may be possible is to construct 3 300w switchers and parallel up their outputs.........this could feasibly be a way of achieving the required power levels........
 

johneppen

New Member
Yeah i know exactly what you are saying, but i can obtain a few of these transformers, so if i parallel up four, five, or even six I can get the required power. This is what you are saying correct? If this is so, I should just be able to measure the frequency that is going through the original power supply and duplicate it correct? Thank you
 

arcom

New Member
What the heck are you going to do with 600W of power???
Disassemble the car with vibrations :D
 

johneppen

New Member
hey man 600W is nothing.....i know guys that have systems with 1500W+ All i wanna do is run a couple maybe 15" subwoofers.
 
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