12V Power supply
 

beerbarrel wrote:

Anyone have a source for a schematic for a 12v around 20 to 30 amp
power supply that makes use of a full wave rectifier? I've found quite
a few for a bridge rectifier but I'm not really sure how to mod them
to use a full wave rectifier. I have a nice 32v 30 amp center tapped
at 16v transformer that I would like to make use of.

Thanks...

You can use half of your bridge with this transformer to produce
something like 22 volts DC at the filter cap. Connect each end ot the
secondary to one of the AC inputs ot the bridge and connect the cap
and load between one of the DC connections of the bridge and the
center tap. If you use the + terminal of the bridge, it will be the
positive output. If you use the - terminal of the bridge, the center
tap will be the positive output.

The bridges will handle a bit more current than they are rated for,
because only two of the 4 rectifiers will be getting hot. They will
certainly need a heat sink for anything like 20 amperes out, though.

After you get that working and running a couple 12 volt headlights in
series (at least), you can start thinking about how to regulate this
down to 12 volts.

--
John Popelish

"beerbarrel" wrote in message
...
Anyone have a source for a schematic for a 12v around 20 to 30 amp
power supply that makes use of a full wave rectifier? I've found quite
a few for a bridge rectifier but I'm not really sure how to mod them
to use a full wave rectifier. I have a nice 32v 30 amp center tapped
at 16v transformer that I would like to make use of.

Are you mixing things together here?

There are full wave bridges that use a ct transformer and half wave bridges
that use non-ct transformers.

I know of no distiction between bridge rectifiers and full wave rectifiers
other than there can be full wave or half wave rectifiers and there is
usually a disctinction between encapsulated rectifier bridges and ones built
of discrete diodes and resisters.

After running a 32v ct transformer thru a full wave bridge you are going to
have way too much voltage for regulating down to 12v unless you enjoy the
extra heat.

Sounds like you intend to make a linear power supply, what sort of regulator
and pass transitors do you have in mind?
thanks, John.

beerbarrel wrote:

On Sat, 08 Jan 2005 20:42:35 -0500, John Popelish
wrote:


beerbarrel wrote:

Anyone have a source for a schematic for a 12v around 20 to 30 amp
power supply that makes use of a full wave rectifier? I've found quite
a few for a bridge rectifier but I'm not really sure how to mod them
to use a full wave rectifier. I have a nice 32v 30 amp center tapped
at 16v transformer that I would like to make use of.

Thanks...

You can use half of your bridge with this transformer to produce
something like 22 volts DC at the filter cap. Connect each end ot the
secondary to one of the AC inputs ot the bridge and connect the cap
and load between one of the DC connections of the bridge and the
center tap. If you use the + terminal of the bridge, it will be the
positive output. If you use the - terminal of the bridge, the center
tap will be the positive output.

The bridges will handle a bit more current than they are rated for,
because only two of the 4 rectifiers will be getting hot. They will
certainly need a heat sink for anything like 20 amperes out, though.

After you get that working and running a couple 12 volt headlights in
series (at least), you can start thinking about how to regulate this
down to 12 volts.



Thanks John...

I saw that particular setup somewhere while I was looking for a
schematic. I would really like to try to use the transformer as
designed if I could. It would be nice to throw it into some of the
good schematics that I've seen on the net. I might wind up using the
one secondary and the centertap if I can find something.

It does use the transformer as-designed -- it just doesn't use all of
the bridge rectifier. This is what you're trying to do:


To load
-. ,------|------o---------
)|( |
To mains )|(---. |
)|( | |
-' '------|------o
| |
| | +
=== ###
GND ---
|
|
===
GND
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de


--

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

beerbarrel wrote:

Let me rephrase what I said, or what I meant to say. I have a 32v
transformer that is centertapped at 16v. It has the diodes in place
for a full wave rectifier.

Two diodes or 4?

I want to construct a linear PS from this.
I don't really want to add a bridge to make this work in another
configuration. What I need is a schematic that allows use for a high
current transformer (30 AMP) using this configuration. I would like to
get max current out of the transformer. I realize that I could use one
of the secondaries and the center tap with a bridge to make a PS and I
might have to do that. I think that it would cut into my current
rating heavily though. Any thoughts?


--
John Popelish

Anyone have a source for a schematic for a 12v around 20 to 30 amp
power supply that makes use of a full wave rectifier? I've found quite
a few for a bridge rectifier but I'm not really sure how to mod them
to use a full wave rectifier.

Hi, Bridge rectifiers are full wave. Sounds like you want a full wave center
tap arrangment. These are very common, surprised you could not find a
schematic.
With a 32 volt center tapped xfmr, connect the center tap to common and
attach 2 rather large diodes to the other two transformer leads, and common
their anodes. You now have an unfiltered 22.6 volt full wave DC power supply.
Xfmr CT is negative, and the diode anodes are positive.
To get to a 12 VDC regulated supply add sufficient filter capacitors, and
regulator devices. A 12 volt 20 amp linear power supply requires heat sinks on
the solid state devices. I use about 50,000mfd filtering on mine, and a 200
volt 50 amp darlington transistor, as the series pass transistor regulator. I
used them because that is what I had on hand. The final design of your
regulated supply will depend on a number of factors.
73 Gary N4AST

beerbarrel wrote:

On Sun, 09 Jan 2005 16:25:55 -0500, John Popelish
wrote:

beerbarrel wrote:

Let me rephrase what I said, or what I meant to say. I have a 32v
transformer that is centertapped at 16v. It has the diodes in place
for a full wave rectifier.

Two diodes or 4?

I want to construct a linear PS from this.
I don't really want to add a bridge to make this work in another
configuration. What I need is a schematic that allows use for a high
current transformer (30 AMP) using this configuration. I would like to
get max current out of the transformer. I realize that I could use one
of the secondaries and the center tap with a bridge to make a PS and I
might have to do that. I think that it would cut into my current
rating heavily though. Any thoughts?

2

The transformer was removed from a automotive battery charger and has
2 heavy duty rectifiers pressed into a heavy aluminum plate. I have a
65000 mF cap band ready to go for the filter.

Then you have the basis for a high current supply. You could get a
slight increase in current capability by separating the two halves of
the secondary, put a 4 diode bridge in each half and connect the
outputs of those bridges in parallel, but the view is probably not
worth the climb unless you really need every ampere this thing is
capable of. And in that case you would want a switching regulator to
convert volts to amperes, instead of a linear regulator. Lots more
difficult.

Here is the data sheet for a control chip commonly used for high
current linear regulators. The application notes (figure 5) give the
general idea of what is required. You will have to come up with a
bank of pass transistors (6 to 10 TIP36, perhaps and a big heat sink).

http://cache.national.com/ds/LM/LM723.pdf
--
John Popelish

On 09 Jan 2005 23:21:57 GMT, (JGBOYLES) wrote:

With a 32 volt center tapped xfmr, connect the center tap to common and
attach 2 rather large diodes to the other two transformer leads, and common
their anodes. You now have an unfiltered 22.6 volt full wave DC power supply.
Xfmr CT is negative, and the diode anodes are positive.

You have the rectifiers connected the wrong way to get a positive
output voltage. In half wave rectifiers, two diode CT full wave
rectifiers and in bridge rectifiers, the cathodes are always connected
to the _positive_ capacitor terminal.

Paul OH3LWR

You have the rectifiers connected the wrong way to get a positive
output voltage.

You are right Paul, thanks for pointing that out. Been too long since I
thought about anodes and cathodes on solid state rectifiers. I just look for
the band or the diode symbol on the the device and hook it up.
73 Gary N4AST

This is probably the thing for you.

http://www.qsl.net/yo5ofh/projects/power_supply.gif

Geir

"beerbarrel" wrote in message
...
Anyone have a source for a schematic for a 12v around 20 to 30 amp
power supply that makes use of a full wave rectifier? I've found quite
a few for a bridge rectifier but I'm not really sure how to mod them
to use a full wave rectifier. I have a nice 32v 30 amp center tapped
at 16v transformer that I would like to make use of.

Thanks...

May I ask, first, what components, for your power supply, do you currently
have...
I gather you have the transformer.. what other components do you have...

I gather the transformer is 32 volts across the full secondary, with a
center tap??

Larry ve3fxq



"beerbarrel" wrote in message
...
On Sat, 08 Jan 2005 20:42:35 -0500, John Popelish
wrote:

beerbarrel wrote:

Anyone have a source for a schematic for a 12v around 20 to 30 amp
power supply that makes use of a full wave rectifier? I've found quite
a few for a bridge rectifier but I'm not really sure how to mod them
to use a full wave rectifier. I have a nice 32v 30 amp center tapped
at 16v transformer that I would like to make use of.

Thanks...

You can use half of your bridge with this transformer to produce
something like 22 volts DC at the filter cap. Connect each end ot the
secondary to one of the AC inputs ot the bridge and connect the cap
and load between one of the DC connections of the bridge and the
center tap. If you use the + terminal of the bridge, it will be the
positive output. If you use the - terminal of the bridge, the center
tap will be the positive output.

The bridges will handle a bit more current than they are rated for,
because only two of the 4 rectifiers will be getting hot. They will
certainly need a heat sink for anything like 20 amperes out, though.

After you get that working and running a couple 12 volt headlights in
series (at least), you can start thinking about how to regulate this
down to 12 volts.


Thanks John...

I saw that particular setup somewhere while I was looking for a
schematic. I would really like to try to use the transformer as
designed if I could. It would be nice to throw it into some of the
good schematics that I've seen on the net. I might wind up using the
one secondary and the centertap if I can find something.