I want to power my FET amp(200W) from a mobile power supply. Amp requires
50VDC. It occured to me that car stereo amps use DC to DC converters that
would produce the voltages and currents that I need. Would like information
on where I could get parts/information to roll my own. I am particularily
intersted in the transformer design and where I could get one already made.
This doesnt seem to be something one can get easily as a replacement part.

Jimmy wrote:

I want to power my FET amp(200W) from a mobile power supply. Amp requires
50VDC. It occured to me that car stereo amps use DC to DC converters that
would produce the voltages and currents that I need. Would like information
on where I could get parts/information to roll my own. I am particularily
intersted in the transformer design and where I could get one already made.
This doesnt seem to be something one can get easily as a replacement part.



With those power levels you're probably dealing with custom magnetics.
There's a switcher in the '04 handbook with the right power level, I'd
consider basing your magnetics on that, or at least use the stacked
E-core idea.

Barring that you could try to get your hands on someone's surplus car
stereo equipment, and harvest the power supply section from that. You
may also want to shop the surplus suppliers for DC-DC converters. 48V
is a common telco voltage, there ought to be bricks (or combinations of
them) that would step you up from 12V nicely.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Jimmy wrote:

I want to power my FET amp(200W) from a mobile power supply. Amp requires
50VDC. It occured to me that car stereo amps use DC to DC converters that
would produce the voltages and currents that I need. Would like information
on where I could get parts/information to roll my own. I am particularily
intersted in the transformer design and where I could get one already made.
This doesnt seem to be something one can get easily as a replacement part.



With those power levels you're probably dealing with custom magnetics.
There's a switcher in the '04 handbook with the right power level, I'd
consider basing your magnetics on that, or at least use the stacked
E-core idea.

Barring that you could try to get your hands on someone's surplus car
stereo equipment, and harvest the power supply section from that. You
may also want to shop the surplus suppliers for DC-DC converters. 48V
is a common telco voltage, there ought to be bricks (or combinations of
them) that would step you up from 12V nicely.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I want to power my FET amp(200W) from a mobile power supply. Amp
requires
50VDC. It occured to me that car stereo amps use DC to DC converters
that
would produce the voltages and currents that I need. Would like
information
on where I could get parts/information to roll my own. I am
particularily
intersted in the transformer design and where I could get one already
made.
This doesnt seem to be something one can get easily as a replacement
part.



With those power levels you're probably dealing with custom magnetics.
There's a switcher in the '04 handbook with the right power level, I'd
consider basing your magnetics on that, or at least use the stacked
E-core idea.

Barring that you could try to get your hands on someone's surplus car
stereo equipment, and harvest the power supply section from that. You
may also want to shop the surplus suppliers for DC-DC converters. 48V
is a common telco voltage, there ought to be bricks (or combinations of
them) that would step you up from 12V nicely.
=====================================
A solution could be using an off the shelf 12V-DC to 115V or 230V -AC
inverter with an AC to 48V-DC (surplus) power supply unit from the telco
industry . Perhaps not so elegant and a bit bulky ,but readily available.
The AC to 50V-DC power supply unit can also be readily homebrewed with
standard components .With 115 V-AC input , a surplus 2:1 step down
transformer available from the surplus trade would do the trick.
BTW some time ago at a flea market I bought a 230V to 50V-15Amperes
transformer for equiv. US$ 0.50............yes it is a heavy beast , !
Perhaps that's why it was available for 50 cents.

Although at a much lower power level ,this is the usual way providing power
to a laptop computer in a motor vehicle.

Frank GM0CSZ / KN6WH

I want to power my FET amp(200W) from a mobile power supply. Amp
requires
50VDC. It occured to me that car stereo amps use DC to DC converters
that
would produce the voltages and currents that I need. Would like
information
on where I could get parts/information to roll my own. I am
particularily
intersted in the transformer design and where I could get one already
made.
This doesnt seem to be something one can get easily as a replacement
part.



With those power levels you're probably dealing with custom magnetics.
There's a switcher in the '04 handbook with the right power level, I'd
consider basing your magnetics on that, or at least use the stacked
E-core idea.

Barring that you could try to get your hands on someone's surplus car
stereo equipment, and harvest the power supply section from that. You
may also want to shop the surplus suppliers for DC-DC converters. 48V
is a common telco voltage, there ought to be bricks (or combinations of
them) that would step you up from 12V nicely.
=====================================
A solution could be using an off the shelf 12V-DC to 115V or 230V -AC
inverter with an AC to 48V-DC (surplus) power supply unit from the telco
industry . Perhaps not so elegant and a bit bulky ,but readily available.
The AC to 50V-DC power supply unit can also be readily homebrewed with
standard components .With 115 V-AC input , a surplus 2:1 step down
transformer available from the surplus trade would do the trick.
BTW some time ago at a flea market I bought a 230V to 50V-15Amperes
transformer for equiv. US$ 0.50............yes it is a heavy beast , !
Perhaps that's why it was available for 50 cents.

Although at a much lower power level ,this is the usual way providing power
to a laptop computer in a motor vehicle.

Frank GM0CSZ / KN6WH

On Tue, 15 Jun 2004 10:26:39 -0700, Tim Wescott
wrote:

Barring that you could try to get your hands on someone's surplus car
stereo equipment, and harvest the power supply section from that.

Why not install a high power audio and RF amplifier in the car and
feed them from a common power supply, since you can not use those two
amplifiers simultaneously anyway :-).

Take a suitable high power audio amplifier, install a switch over
relay between the inverter and the actual audio amplifier. When the
PTT is pushed, the relay switches the power to the RF amplifier. All
the other time you can listen to the music (or to a QSO) at a high
audio volume :-).

One problem is that the RF amplifier requires a unipolar +50 Vdc
supply, while audio amplifiers usually have a bipolar supply. Running
the RF amplifier from a bipolar supply would require transformer
coupled inputs and outputs and isolation of the circuit board ground
from the chassis.

Some bridged audio amplifiers may have a unipolar power supply or it
may be possible to use only the positive side of a +/- 50 V bipolar
supply (but may require rectifiers with a higher rating).

A simple audio amplifier driven from a unipolar 50 V or +/- 25 V
bipolar supply will produce about 56 or 112 W into 4 resp. 2 ohms per
channel. In a bridged configuration 110 or 220 W into 8 resp. 4 ohms
per channel.

With a +/-50 V supply, a simple audio amplifier would produce 110, 220
or 440 W into 8, 4 resp. 2 ohms into a single channel.

I think that looking at the audio amplifier power specifications (into
various loads) should give a hint of what kind of amplifier voltages
are used and thus limit the number of candidates worth investigating.
It should be noted that even if some amplifiers are rated at 2x100 W
or 4x100 W, it is very unlikely, that the power supply is capable of
delivering more than one channel at the rated power for any prolonged
time.

The audio amplifier power supply RFI filtering may be more or less
nonexistent, so you may have to add quite a lot of filtering.

Paul OH3LWR

On Tue, 15 Jun 2004 10:26:39 -0700, Tim Wescott
wrote:

Barring that you could try to get your hands on someone's surplus car
stereo equipment, and harvest the power supply section from that.

Why not install a high power audio and RF amplifier in the car and
feed them from a common power supply, since you can not use those two
amplifiers simultaneously anyway :-).

Take a suitable high power audio amplifier, install a switch over
relay between the inverter and the actual audio amplifier. When the
PTT is pushed, the relay switches the power to the RF amplifier. All
the other time you can listen to the music (or to a QSO) at a high
audio volume :-).

One problem is that the RF amplifier requires a unipolar +50 Vdc
supply, while audio amplifiers usually have a bipolar supply. Running
the RF amplifier from a bipolar supply would require transformer
coupled inputs and outputs and isolation of the circuit board ground
from the chassis.

Some bridged audio amplifiers may have a unipolar power supply or it
may be possible to use only the positive side of a +/- 50 V bipolar
supply (but may require rectifiers with a higher rating).

A simple audio amplifier driven from a unipolar 50 V or +/- 25 V
bipolar supply will produce about 56 or 112 W into 4 resp. 2 ohms per
channel. In a bridged configuration 110 or 220 W into 8 resp. 4 ohms
per channel.

With a +/-50 V supply, a simple audio amplifier would produce 110, 220
or 440 W into 8, 4 resp. 2 ohms into a single channel.

I think that looking at the audio amplifier power specifications (into
various loads) should give a hint of what kind of amplifier voltages
are used and thus limit the number of candidates worth investigating.
It should be noted that even if some amplifiers are rated at 2x100 W
or 4x100 W, it is very unlikely, that the power supply is capable of
delivering more than one channel at the rated power for any prolonged
time.

The audio amplifier power supply RFI filtering may be more or less
nonexistent, so you may have to add quite a lot of filtering.

Paul OH3LWR