Simple - Power Supply Design - Low Voltage Landscape Lighting
Peter Procenko
I want to build a power supply for my low voltage 12VDC Lighting.
I have the following components:
120 VAC - 13.8 VAC Transformer 20 Amp
Diotec DB3504P Full Wave Bridge Rectifier 35 Amp
I want to supply about 500 watts in total that are split across 5 seperate
runs
What size/type capacitors/resistors should I use, to smooth out the
waveform.
Where should I put these in the circuit ?
Any help would be appreciated.
Sincerely
Peter
John Miller
> I want to build a power supply for my low voltage 12VDC Lighting.
> What size/type capacitors/resistors should I use, to smooth out the
> waveform.
Before you get too far into this, are you sure the lights wouldn't be just
as happy running from 12V (rms) AC?
--
John Miller
Email address: domain, n4vu.com; username, jsm
For adult education nothing beats children.
Fred Bloggs
You have a 20A,RMS x 13.8V,RMS=276Watt maximum capability transformer
for an essentially resistive load. It will not be possible to drive
500W of lighting without seriously overheating the transformer.
Walter Harley
news:kvLmc.75233$ZJ5.1...@news20.bellglobal.com...
> Hello
>
> I want to build a power supply for my low voltage 12VDC Lighting.
>
> I have the following components:
>
> 120 VAC - 13.8 VAC Transformer 20 Amp
> Diotec DB3504P Full Wave Bridge Rectifier 35 Amp
>
> I want to supply about 500 watts in total that are split across 5 seperate
> runs
You say your transformer is rated 13.8VAC * 20A = 276W.
You are not going to get 500W out of a 276W transformer, I'm afraid.
By the way, you will need to be careful; the 13.8V refers to the RMS
voltage. The peak voltage is 1.4 times higher, sine waves being what they
are; that is, 19.3V. If you rectify the 13.8VAC and pass it through a
filter, you'll get the peak voltage, minus some ripple. If the bulbs are
really rated for 12VDC, that could be a problem.
A sufficiently powerful transformer would need to produce (500W / 12V =)
42A. So your bridge rectifier won't cut it either, I'm afraid. But if it
did, you'd need to be aware that the voltage drop across the rectifier would
be around 2V, maybe more at those currents; so it would itself be
dissipating 2V*42A = 84W. It'll get quite hot, even if it's attached to a
good heat sink.
Surely it would make more sense to just purchase an appropriately rated
12VDC power supply?
Paul Mathews
> Peter Procenko wrote:
> > I want to build a power supply for my low voltage 12VDC Lighting.
> <snip>
> > What size/type capacitors/resistors should I use, to smooth out the
> > waveform.
>
> Before you get too far into this, are you sure the lights wouldn't be just
> as happy running from 12V (rms) AC?
It's interesting to note that filament lamps generally have a longer
life when operated on AC.
Paul Mathews
Dorothy Bradbury
> life when operated on AC.
Hence a DC to pulse-width-modulation dimmer on cars, they
tend to still pulse the power even on full so the bulb life is boosted.
Usually because it is near impossible to change the bulbs!
--
Dorothy Bradbury
N. Thornton
> You say your transformer is rated 13.8VAC * 20A = 276W.
>
> You are not going to get 500W out of a 276W transformer, I'm afraid.
Well, you will, but maybe not for too long. But add forced air cooling
and an overheat cutout and it may work. But if you do that it needs to
be in a fire-safe box just in case it dosent work out.
What is the regulation of your transformer? With the extra load the
13.8v will drop a bit. And what kind of 12v rated bulbs are they?
Domestic or car? Car 12v bulbs arent 12v, theyre more like 13.6.
A better solution though would be to reduce the wattage of your light
bulbs. Gardens really dont need much power at all. Or run 250w on this
transformer and put the rest on another one later.
Regards, NT
Roger Gt
"N. Thornton" wrote
: "Walter Harley" wrote
:
: > You say your transformer is rated 13.8VAC * 20A = 276W.
: > You are not going to get 500W out of a 276W transformer, I'm
afraid.
:
: Well, you will, but maybe not for too long. But add forced air
cooling
: and an overheat cutout and it may work. But if you do that it
needs to
:
: What is the regulation of your transformer? With the extra load
the
: 13.8v will drop a bit. And what kind of 12v rated bulbs are
they?
13.6.
:
: A better solution though would be to reduce the wattage of your
light
on this
: transformer and put the rest on another one later. Regards, NT
Running your 12V lamps on 10V will make them last much longer. If
long life is an issue, check out the tables for this at
http://www.fxl.com/documents/lamp_life.htm
If the lamp rated at 13.6, then normalize the chart for that
rather than 12V.
Half the lumens in exchange for 900% increase in life is not a bad
deal for garden lamps!