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  #1   Report Post  
Dave Platt
 
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Default simple Power Supply design help needed

Hi, I'm building a power supply to run a 12vdc car stereo in my room.
The power amp is a 300w ADS Power Plate 300. At 12.5v I need a 24A
supply? This seems wrong somehow.


You may need _more_ than that. If the amp is actually capable of
creating 300 watts of clean audio output power, it's likely to
actually be drawing 500-600 watts of total power (amps are not 100%
efficient), and you may need 50 amps or more.

If the "300w" is marketing puffery, or if you're willing to run the
amp at quite a lot less than its full output capacity, the actual
needs might be a lot less than that.

I thought I'd use the xformer from
a surplus 12v battery charger with an LM317 but I have the feeling
something needs review here.


Darned right. An LM317 by itself is limited to 1.5 amperes, I think.
It's not going to cut it.

I'd appreciate any observations others
may have. Thanks for your time, pm.


You're likely to need a hefty DC supply to run an amp of this calibre
indoors.

Using a battery-charger transformer and rectifier bridge is probably a
reasonable starting place. You'll need a good-sized filter capacitor
following the rectifier bridge. You'll need a hefty set of pass
transistors - the commonest linear-supply design of this sort uses
multiple 2N3055 transistors (TO-3 cases) in parallel, with ballast
resistors, and a set of big heavy heatsinks. Take a look at the LM317
data sheet - I believe you'll find details on how to use external
transistors such as 2N3055s as external pass-elements, to boost the
LM317's current capacity. For supplies in the 25-50 ampere range I
suspect you'll need an external driver transistor or two inbetween the
LM317 and the pass transistors, to provide the necessary amount of
base drive current. You'll need to design in current-limiting
circuitry (straight limiter or foldback) to keep your supply from
frying its transistors, or starting a fire if the outputs are
accidentally shorted.

If all of this still seems a big overwhelming, you could just buy an
Astron switching power supply (see www.hamradio.com for one source),
or just decide that using an auto amp in a home setting is more
trouble than it's worth, and buy an amp designed for 110 volt operation.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
  #4   Report Post  
Sofie
 
Posts: n/a
Default simple Power Supply design help needed

"perry mason" wrote in message
Hi, I'm building a power supply to run a 12vdc car stereo in my room.
The power amp is a 300w ADS Power Plate 300. At 12.5v I need a 24A
supply? This seems wrong somehow. I thought I'd use the xformer from
a surplus 12v battery charger with an LM317 but I have the feeling
something needs review here. I'd appreciate any observations others
may have. Thanks for your time, pm.

-----------------------------------

perry mason:
You will very likely need a hell of a lot more amps than a LM317 @ 1.5A can
deliver. Also it is very unlikely that your surplus 12 volt battery
charger can deliver enough current to be useful in building the kind of
heavy duty power supply that is certainly going to be required for your set
up....... 24 amps at an absolute minimum with an actual requirement of
almost double that if indeed your 300 watt amp can really deliver 300 watts
RMS ... and that you intend to run it at high volume levels and are
expecting clean performance.
To build a safe and proper 12 volt power supply that can deliver enough
current for your apparent needs is not going to be an easy, novice task, nor
will it be cheap.
Do a search on the internet for power supply and electronic equipment
suppliers and most certainly Ebay for power supplies that are already built,
you can most probably buy something cheaper than if you built it.... and if
you purchase a quality built unit it will likely include important safety
shutdown features to protect your stereo equipment, your home and the power
supply against over-voltage and fire starting short circuits.... very
important when dealing with this kind of metal melting current.
A possible low-tech solution for you would be for you to use that 12 battery
charger that you have to keep an automotive battery continually topped
off.... then you can run your high power stereo system through a suitable
fuse directly from the battery. If the charger is an "automatic" type that
will reduce to a trickle charge when it senses that the battery reaches a
fully charged condition you can leave it hooked up all the time whether you
are using the stereo or not. The main drawback to all of this would be
that if you intend to run your stereo at very high volume levels on a
continuous basis the battery may run down after approximately an hour or so
unless you give it a chance to charge up with the stereo shut off or turned
down to easy listening levels.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -


..
..


  #5   Report Post  
Sofie
 
Posts: n/a
Default simple Power Supply design help needed

"perry mason" wrote in message
Hi, I'm building a power supply to run a 12vdc car stereo in my room.
The power amp is a 300w ADS Power Plate 300. At 12.5v I need a 24A
supply? This seems wrong somehow. I thought I'd use the xformer from
a surplus 12v battery charger with an LM317 but I have the feeling
something needs review here. I'd appreciate any observations others
may have. Thanks for your time, pm.

-----------------------------------

perry mason:
You will very likely need a hell of a lot more amps than a LM317 @ 1.5A can
deliver. Also it is very unlikely that your surplus 12 volt battery
charger can deliver enough current to be useful in building the kind of
heavy duty power supply that is certainly going to be required for your set
up....... 24 amps at an absolute minimum with an actual requirement of
almost double that if indeed your 300 watt amp can really deliver 300 watts
RMS ... and that you intend to run it at high volume levels and are
expecting clean performance.
To build a safe and proper 12 volt power supply that can deliver enough
current for your apparent needs is not going to be an easy, novice task, nor
will it be cheap.
Do a search on the internet for power supply and electronic equipment
suppliers and most certainly Ebay for power supplies that are already built,
you can most probably buy something cheaper than if you built it.... and if
you purchase a quality built unit it will likely include important safety
shutdown features to protect your stereo equipment, your home and the power
supply against over-voltage and fire starting short circuits.... very
important when dealing with this kind of metal melting current.
A possible low-tech solution for you would be for you to use that 12 battery
charger that you have to keep an automotive battery continually topped
off.... then you can run your high power stereo system through a suitable
fuse directly from the battery. If the charger is an "automatic" type that
will reduce to a trickle charge when it senses that the battery reaches a
fully charged condition you can leave it hooked up all the time whether you
are using the stereo or not. The main drawback to all of this would be
that if you intend to run your stereo at very high volume levels on a
continuous basis the battery may run down after approximately an hour or so
unless you give it a chance to charge up with the stereo shut off or turned
down to easy listening levels.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -


..
..




  #6   Report Post  
Richard Crowley
 
Posts: n/a
Default simple Power Supply design help needed

"perry mason" wrote ...
Hi, I'm building a power supply to run a 12vdc car stereo in my room.
The power amp is a 300w ADS Power Plate 300. At 12.5v I need a 24A
supply? This seems wrong somehow. I thought I'd use the xformer from
a surplus 12v battery charger with an LM317 but I have the feeling
something needs review here. I'd appreciate any observations others
may have. Thanks for your time, pm.


From what we can perceive as your understanding of
electronics, even if you had an adequate transformer (which
seems unlikely from your description), a proper schematic,
and a kit of all the components, you would still likely find it
very difficult to successfully build such a power supply.

Where did you get the 24A figure? What is the fuse rating
on the amplifier? 24A seems too low assuming the unit is
really 300W because it is very unlikely to be 100% efficient.


  #7   Report Post  
Richard Crowley
 
Posts: n/a
Default simple Power Supply design help needed

"perry mason" wrote ...
Hi, I'm building a power supply to run a 12vdc car stereo in my room.
The power amp is a 300w ADS Power Plate 300. At 12.5v I need a 24A
supply? This seems wrong somehow. I thought I'd use the xformer from
a surplus 12v battery charger with an LM317 but I have the feeling
something needs review here. I'd appreciate any observations others
may have. Thanks for your time, pm.


From what we can perceive as your understanding of
electronics, even if you had an adequate transformer (which
seems unlikely from your description), a proper schematic,
and a kit of all the components, you would still likely find it
very difficult to successfully build such a power supply.

Where did you get the 24A figure? What is the fuse rating
on the amplifier? 24A seems too low assuming the unit is
really 300W because it is very unlikely to be 100% efficient.


  #8   Report Post  
Arny Krueger
 
Posts: n/a
Default simple Power Supply design help needed

"perry mason" wrote in message


Hi, I'm building a power supply to run a 12vdc car stereo in my room.
The power amp is a 300w ADS Power Plate 300. At 12.5v I need a 24A
supply?


Depends what you want to do with the power amp.

Actual current needs depend on the load impedance and the peak-to-average
ratio of the music you intend to play.

This seems wrong somehow. I thought I'd use the xformer from
a surplus 12v battery charger with an LM317 but I have the feeling
something needs review here.


Others have correctly pointed out that a single LM317 lacks the current
capacity required. You might want to look at a commercial 12 volt regulated
power supply to see what it really takes to do the job.

I'd appreciate any observations others may have. Thanks for your time, pm.


My first observation is that in this day and age, you can often buy for far
less than it costs to make. Paying $130 or so for a 12 volt 30 amp power
supply may seem like *lots*, but check out your bill-of-materials price for
a comparable build-your-own project.

Secondly, most car audio equipment will work well with 12.5-15 volts, and
more DC volts means more peak power which can provide a sonic advantage. 18
volts is the point where amplifier overvoltage protection if any, might
start causing issues.

Thirdly, a regulated power supply may not be required if you can get ripple
and regulation under control in a purely passive design. Car audio gear is
designed to work with relatively noisy power. There is generally another
switchmode power supply inside the amp, between the battery input and the
power to the audio stages. On a sonic-benefit per $$$ spent on capacitors,
it's the output of the switchmode inverter inside the of the amp where the
value often is.

Fourthly, the peak-to-average ratio of even highly compressed music is at
least 8 dB, which means that with a suitable capacitive reservoir (remember,
there is already one such reservoir inside the power amp) you might be able
to get away with 4-10 times less average current coming from your power
supply than what you would need if you were delivering sine waves into a
resistive load. In cars "stiffening capacitors" are often snake oil, but in
your application 100,000 uF or so can let you get away with a far more
modestly-sized power supply.




  #9   Report Post  
Arny Krueger
 
Posts: n/a
Default simple Power Supply design help needed

"perry mason" wrote in message


Hi, I'm building a power supply to run a 12vdc car stereo in my room.
The power amp is a 300w ADS Power Plate 300. At 12.5v I need a 24A
supply?


Depends what you want to do with the power amp.

Actual current needs depend on the load impedance and the peak-to-average
ratio of the music you intend to play.

This seems wrong somehow. I thought I'd use the xformer from
a surplus 12v battery charger with an LM317 but I have the feeling
something needs review here.


Others have correctly pointed out that a single LM317 lacks the current
capacity required. You might want to look at a commercial 12 volt regulated
power supply to see what it really takes to do the job.

I'd appreciate any observations others may have. Thanks for your time, pm.


My first observation is that in this day and age, you can often buy for far
less than it costs to make. Paying $130 or so for a 12 volt 30 amp power
supply may seem like *lots*, but check out your bill-of-materials price for
a comparable build-your-own project.

Secondly, most car audio equipment will work well with 12.5-15 volts, and
more DC volts means more peak power which can provide a sonic advantage. 18
volts is the point where amplifier overvoltage protection if any, might
start causing issues.

Thirdly, a regulated power supply may not be required if you can get ripple
and regulation under control in a purely passive design. Car audio gear is
designed to work with relatively noisy power. There is generally another
switchmode power supply inside the amp, between the battery input and the
power to the audio stages. On a sonic-benefit per $$$ spent on capacitors,
it's the output of the switchmode inverter inside the of the amp where the
value often is.

Fourthly, the peak-to-average ratio of even highly compressed music is at
least 8 dB, which means that with a suitable capacitive reservoir (remember,
there is already one such reservoir inside the power amp) you might be able
to get away with 4-10 times less average current coming from your power
supply than what you would need if you were delivering sine waves into a
resistive load. In cars "stiffening capacitors" are often snake oil, but in
your application 100,000 uF or so can let you get away with a far more
modestly-sized power supply.




  #10   Report Post  
Andy Dee
 
Posts: n/a
Default simple Power Supply design help needed

perry mason wrote:
Hi, I'm building a power supply to run a 12vdc car stereo in my room.
The power amp is a 300w ADS Power Plate 300. At 12.5v I need a 24A
supply? This seems wrong somehow. I thought I'd use the xformer from
a surplus 12v battery charger with an LM317 but I have the feeling
something needs review here. I'd appreciate any observations others
may have. Thanks for your time, pm.

Run it from a car battery with charger.

A



  #11   Report Post  
Andy Dee
 
Posts: n/a
Default simple Power Supply design help needed

perry mason wrote:
Hi, I'm building a power supply to run a 12vdc car stereo in my room.
The power amp is a 300w ADS Power Plate 300. At 12.5v I need a 24A
supply? This seems wrong somehow. I thought I'd use the xformer from
a surplus 12v battery charger with an LM317 but I have the feeling
something needs review here. I'd appreciate any observations others
may have. Thanks for your time, pm.

Run it from a car battery with charger.

A

  #12   Report Post  
Arny Krueger
 
Posts: n/a
Default simple Power Supply design help needed

"perry mason" wrote in message

On Fri, 7 Nov 2003 11:02:17 -0500, "Arny Krueger"
wrote:

"perry mason" wrote in message


Hi, I'm building a power supply to run a 12vdc car stereo in my
room. The power amp is a 300w ADS Power Plate 300. At 12.5v I need
a 24A supply?


Depends what you want to do with the power amp.

Actual current needs depend on the load impedance and the
peak-to-average ratio of the music you intend to play.

This seems wrong somehow. I thought I'd use the xformer from
a surplus 12v battery charger with an LM317 but I have the feeling
something needs review here.


Others have correctly pointed out that a single LM317 lacks the
current capacity required. You might want to look at a commercial 12
volt regulated power supply to see what it really takes to do the
job.

I'd appreciate any observations others may have. Thanks for your
time, pm.


My first observation is that in this day and age, you can often buy
for far less than it costs to make. Paying $130 or so for a 12 volt
30 amp power supply may seem like *lots*, but check out your
bill-of-materials price for a comparable build-your-own project.

Secondly, most car audio equipment will work well with 12.5-15
volts, and more DC volts means more peak power which can provide a
sonic advantage. 18 volts is the point where amplifier overvoltage
protection if any, might start causing issues.

Thirdly, a regulated power supply may not be required if you can get
ripple and regulation under control in a purely passive design. Car
audio gear is designed to work with relatively noisy power. There is
generally another switchmode power supply inside the amp, between
the battery input and the power to the audio stages. On a
sonic-benefit per $$$ spent on capacitors, it's the output of the
switchmode inverter inside the of the amp where the value often is.

Fourthly, the peak-to-average ratio of even highly compressed music
is at least 8 dB, which means that with a suitable capacitive
reservoir (remember, there is already one such reservoir inside the
power amp) you might be able to get away with 4-10 times less
average current coming from your power supply than what you would
need if you were delivering sine waves into a resistive load. In
cars "stiffening capacitors" are often snake oil, but in your
application 100,000 uF or so can let you get away with a far more
modestly-sized power supply.


Thanks, that's really what I was looking for. Roughly, what kind of
voltage rating do the caps need?


25 volts working voltage generally suffices, IME.

I assume I would have to parallel
values to come up with a 100,000 uF total.


Actually you can find commercial caps that run up past 1,000,000 uF - that's
a Farad or more!

The really big caps are called "stiffening caps" and can be found in car
audio shops and on eBay for around $50-100. I found a surplus cap that is
rated at something like half a Farad for about $30 on eBay. It does a nice
job of stiffening a surplus (eBay, natch) 15 volt 20 amp switching power
supply to power a (true and genuine) 60 wpc carsound amp for home use. I
think said amp is called a "200 wpc" amp by some but after you dust off the
spec sheet, its about 60 wpc.

One problem with all this shucking and jiiving with car sound amps is that
by the time you provide them with power, your investment is beginning to
approach or exceed the cost of a cheap 100 wpc stereo receiver.

Also, the amp has a switch
labeled "low power". I'm not sure what that does technically but if
you depress it while it's playing the volume drops drastically so
maybe the design could be a lot less demanding. It doesn't have to be
very loud. 3/4 volume with the low power switch in is still plenty
loud, it just doesn't have the visceral punch car stereo owners look
for. I see now there is an automotive style 20A fuse plugged into the
bottom of the power amp. The exact model is a Power Plate 120, so
maybe that's 60W per side. A whole different requirement.


Well a fuse will carry more than rated current for short periods of time,
but periods of time that can give the perception of increased loudness.
Suffice it to say that with suitable backing capacitance, a power supply
that can provide enough continuous power to blow the fuse would be
sufficient. I think you'd find that the classic 30 amp 0-15 volt power
supply commonly used to service car audio components would do a nice job for
you.



  #13   Report Post  
Arny Krueger
 
Posts: n/a
Default simple Power Supply design help needed

"perry mason" wrote in message

On Fri, 7 Nov 2003 11:02:17 -0500, "Arny Krueger"
wrote:

"perry mason" wrote in message


Hi, I'm building a power supply to run a 12vdc car stereo in my
room. The power amp is a 300w ADS Power Plate 300. At 12.5v I need
a 24A supply?


Depends what you want to do with the power amp.

Actual current needs depend on the load impedance and the
peak-to-average ratio of the music you intend to play.

This seems wrong somehow. I thought I'd use the xformer from
a surplus 12v battery charger with an LM317 but I have the feeling
something needs review here.


Others have correctly pointed out that a single LM317 lacks the
current capacity required. You might want to look at a commercial 12
volt regulated power supply to see what it really takes to do the
job.

I'd appreciate any observations others may have. Thanks for your
time, pm.


My first observation is that in this day and age, you can often buy
for far less than it costs to make. Paying $130 or so for a 12 volt
30 amp power supply may seem like *lots*, but check out your
bill-of-materials price for a comparable build-your-own project.

Secondly, most car audio equipment will work well with 12.5-15
volts, and more DC volts means more peak power which can provide a
sonic advantage. 18 volts is the point where amplifier overvoltage
protection if any, might start causing issues.

Thirdly, a regulated power supply may not be required if you can get
ripple and regulation under control in a purely passive design. Car
audio gear is designed to work with relatively noisy power. There is
generally another switchmode power supply inside the amp, between
the battery input and the power to the audio stages. On a
sonic-benefit per $$$ spent on capacitors, it's the output of the
switchmode inverter inside the of the amp where the value often is.

Fourthly, the peak-to-average ratio of even highly compressed music
is at least 8 dB, which means that with a suitable capacitive
reservoir (remember, there is already one such reservoir inside the
power amp) you might be able to get away with 4-10 times less
average current coming from your power supply than what you would
need if you were delivering sine waves into a resistive load. In
cars "stiffening capacitors" are often snake oil, but in your
application 100,000 uF or so can let you get away with a far more
modestly-sized power supply.


Thanks, that's really what I was looking for. Roughly, what kind of
voltage rating do the caps need?


25 volts working voltage generally suffices, IME.

I assume I would have to parallel
values to come up with a 100,000 uF total.


Actually you can find commercial caps that run up past 1,000,000 uF - that's
a Farad or more!

The really big caps are called "stiffening caps" and can be found in car
audio shops and on eBay for around $50-100. I found a surplus cap that is
rated at something like half a Farad for about $30 on eBay. It does a nice
job of stiffening a surplus (eBay, natch) 15 volt 20 amp switching power
supply to power a (true and genuine) 60 wpc carsound amp for home use. I
think said amp is called a "200 wpc" amp by some but after you dust off the
spec sheet, its about 60 wpc.

One problem with all this shucking and jiiving with car sound amps is that
by the time you provide them with power, your investment is beginning to
approach or exceed the cost of a cheap 100 wpc stereo receiver.

Also, the amp has a switch
labeled "low power". I'm not sure what that does technically but if
you depress it while it's playing the volume drops drastically so
maybe the design could be a lot less demanding. It doesn't have to be
very loud. 3/4 volume with the low power switch in is still plenty
loud, it just doesn't have the visceral punch car stereo owners look
for. I see now there is an automotive style 20A fuse plugged into the
bottom of the power amp. The exact model is a Power Plate 120, so
maybe that's 60W per side. A whole different requirement.


Well a fuse will carry more than rated current for short periods of time,
but periods of time that can give the perception of increased loudness.
Suffice it to say that with suitable backing capacitance, a power supply
that can provide enough continuous power to blow the fuse would be
sufficient. I think you'd find that the classic 30 amp 0-15 volt power
supply commonly used to service car audio components would do a nice job for
you.



  #14   Report Post  
tweak
 
Posts: n/a
Default simple Power Supply design help needed

On Thu, 06 Nov 2003 20:39:41 GMT, perry mason
wrote:

Hi, I'm building a power supply to run a 12vdc car stereo in my room.
The power amp is a 300w ADS Power Plate 300. At 12.5v I need a 24A
supply? This seems wrong somehow. I thought I'd use the xformer from
a surplus 12v battery charger with an LM317 but I have the feeling
something needs review here. I'd appreciate any observations others
may have. Thanks for your time, pm.


Just go to radio shack and buy a heavy duty power supply.
It'll be in the 13.1-14 volt range at 1.8 to 4.3 amps.
Radio shack sell tons of these for people building up home theatre
systems using car audio amps as a cheap solution.
  #15   Report Post  
tweak
 
Posts: n/a
Default simple Power Supply design help needed

On Thu, 06 Nov 2003 20:39:41 GMT, perry mason
wrote:

Hi, I'm building a power supply to run a 12vdc car stereo in my room.
The power amp is a 300w ADS Power Plate 300. At 12.5v I need a 24A
supply? This seems wrong somehow. I thought I'd use the xformer from
a surplus 12v battery charger with an LM317 but I have the feeling
something needs review here. I'd appreciate any observations others
may have. Thanks for your time, pm.


Just go to radio shack and buy a heavy duty power supply.
It'll be in the 13.1-14 volt range at 1.8 to 4.3 amps.
Radio shack sell tons of these for people building up home theatre
systems using car audio amps as a cheap solution.


  #16   Report Post  
tweak
 
Posts: n/a
Default simple Power Supply design help needed

On Thu, 06 Nov 2003 20:39:41 GMT, perry mason
wrote:

Hi, I'm building a power supply to run a 12vdc car stereo in my room.
The power amp is a 300w ADS Power Plate 300. At 12.5v I need a 24A
supply? This seems wrong somehow. I thought I'd use the xformer from
a surplus 12v battery charger with an LM317 but I have the feeling
something needs review here. I'd appreciate any observations others
may have. Thanks for your time, pm.


Just go to radio shack and buy a heavy duty power supply.
It'll be in the 13.1-14 volt range at 1.8 to 4.3 amps.
Radio shack sell tons of these for people building up home theatre
systems using car audio amps as a cheap solution.
  #17   Report Post  
tweak
 
Posts: n/a
Default simple Power Supply design help needed

On Thu, 06 Nov 2003 20:39:41 GMT, perry mason
wrote:

Hi, I'm building a power supply to run a 12vdc car stereo in my room.
The power amp is a 300w ADS Power Plate 300. At 12.5v I need a 24A
supply? This seems wrong somehow. I thought I'd use the xformer from
a surplus 12v battery charger with an LM317 but I have the feeling
something needs review here. I'd appreciate any observations others
may have. Thanks for your time, pm.


Just go to radio shack and buy a heavy duty power supply.
It'll be in the 13.1-14 volt range at 1.8 to 4.3 amps.
Radio shack sell tons of these for people building up home theatre
systems using car audio amps as a cheap solution.
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