TOM make sure that your circuit is a parrallel one, not in series.Also you
cannot reduce the watt of the bulb because you will reduce the resistance of
your circuit and let pass to much current on the same bulb (burning action)


"Tom Best" a écrit dans le message de
om...
I would appreciate some help with a 12 volt question.

I set up a 7 light long string of 12 volt, 40 watt bulbs on a strand
of 12 guage, outdoor lighting, copper wire. The bulbs and bases were
standard Edison screw base types. The lights were connected to a 300
watt DC converter made for outdoor yard lights. In theory, I would
like to take the same string (with lower wattage bulbs) on sailing
trips.

In 4 days, 6 of the seven lights have burned out. One light continues
to burn at normal brightness.

Any ideas or comments on these failures apprecitated.

Thanks
Tom

"jean" wrote in message
...
TOM make sure that your circuit is a parrallel one, not in series.Also you
cannot reduce the watt of the bulb because you will reduce the resistance
of
your circuit and let pass to much current on the same bulb (burning
action)

This is incorrect. If you reduce the wattage of the globe, the resistance
will INCREASE as it will draw LESS current at the same voltage to get the
lower power.
( Power = Voltage*Voltage/Resistance). As the bulbs progressively failed, it
is obvious that they must be in parallel as they would all go out if any one
failed in a series circuit.

regards,
Mark

jean,

I'm confused on what you're saying. 40 watts is the current limit
for the bulb, period! Unless of course the voltage is too high
thereby forcing more current through. From what I see of these
outdoor converters, the voltage output is constant. Manufacturers
just don't want you to overdrive them with more wattage of bulbs
than the trancformer can put out.

-JimL

jean wrote:
TOM make sure that your circuit is a parrallel one, not in series.Also you
cannot reduce the watt of the bulb because you will reduce the resistance of
your circuit and let pass to much current on the same bulb (burning action)


"Tom Best" a écrit dans le message de
om...

I would appreciate some help with a 12 volt question.

I set up a 7 light long string of 12 volt, 40 watt bulbs on a strand
of 12 guage, outdoor lighting, copper wire. The bulbs and bases were
standard Edison screw base types. The lights were connected to a 300
watt DC converter made for outdoor yard lights. In theory, I would
like to take the same string (with lower wattage bulbs) on sailing
trips.

In 4 days, 6 of the seven lights have burned out. One light continues
to burn at normal brightness.

Any ideas or comments on these failures apprecitated.

Thanks
Tom

Watts is a measure of power. Current is measured in amperes.

JimL wrote:

jean,

I'm confused on what you're saying. 40 watts is the current limit
for the bulb, period! Unless of course the voltage is too high
thereby forcing more current through. From what I see of these
outdoor converters, the voltage output is constant. Manufacturers
just don't want you to overdrive them with more wattage of bulbs
than the trancformer can put out.

-JimL

jean wrote:
TOM make sure that your circuit is a parrallel one, not in series.Also you
cannot reduce the watt of the bulb because you will reduce the resistance of
your circuit and let pass to much current on the same bulb (burning action)


"Tom Best" a écrit dans le message de
om...

I would appreciate some help with a 12 volt question.

I set up a 7 light long string of 12 volt, 40 watt bulbs on a strand
of 12 guage, outdoor lighting, copper wire. The bulbs and bases were
standard Edison screw base types. The lights were connected to a 300
watt DC converter made for outdoor yard lights. In theory, I would
like to take the same string (with lower wattage bulbs) on sailing
trips.

In 4 days, 6 of the seven lights have burned out. One light continues
to burn at normal brightness.

Any ideas or comments on these failures apprecitated.

Thanks
Tom

jean wrote:

TOM make sure that your circuit is a parrallel one, not in series.Also you
cannot reduce the watt of the bulb because you will reduce the resistance of
your circuit and let pass to much current on the same bulb (burning action)


jean;
1) The original poster stated that he had seven (7) bulbs "in
parallel", so that's not an issue.
2) Do not understand your "reduce the watt of the bulb"
statement. It appears wrong. If you reduce the wattage LESS
current will flow (Volts x current = watts). And the resistance
will INCREASE. Basic Ohms Law!
Example: 12 volts x 1 amp = 12 watts. Resistance of lamp is
Volts/Amp = 12/1 = 12 ohms.
Example: 12 volts x 2 amps = 24 watts. Resistance of lamp is
.......12/2 = 6 ohms.
Thus: Twice the resistance results in half the wattage.

Thanks for the info. Small (important?) corrections and additional
info follows:

Seven bulbs in paralled and are 25 watts, not 40 watts. Resulting in
a total of 175 watts on a 300 watt transformer. However, one bulb
still burns at regular brightness.

The copper wire is 12 guage and stranded. About 30 feet long.

I though the low voltage yard lights were transformed to 12 volt DC
not 12 volt AC. Is that the issue?

Tom

"Tom Best" wrote in message
om...

I though the low voltage yard lights were transformed to 12 volt DC
not 12 volt AC. Is that the issue?

The light bulb would not care if it got 12 VDC or 12VAC.

It might help if you provided more detail on the "DC Converter".

Why are you using a DC converter instead of a simple AC transformer?

You said it was made for this so one would assume the voltage is correct,
but you should measure it anyway. Have the lights been on 24 hours a day, or
just a few hours each evening?

Light bulbs are rated in number of hours they can be expected to last. Some
light bulbs will last thousands of hours. Others, like a projector bulb for
example, may last only tens of hours.

Heat, shock and vibration are reasons for premature bulb failure. Some
bulbs are not rated to operate in an "upside down" position, as it will
cause the base to overheat. Make sure that the bulb is not being used in an
inappropriate application.

Perhaps if you told us exactly what bulbs you were using it would help. You
said they were in a screw base, are these the 12volt bulbs that are often
used in RVs or boats?

Rod McInnis

On Tue, 2 Dec 2003 14:01:11 -0800, "Rod McInnis"
wrote:


"Tom Best" wrote in message
. com...

I though the low voltage yard lights were transformed to 12 volt DC
not 12 volt AC. Is that the issue?

The light bulb would not care if it got 12 VDC or 12VAC.

I'm going to go out on a limb here. Assuming the voltage is in the 12
Volt range and the bulbs are of reasonable quality, there might be a
difference between AC & DC regarding these bulbs.

A 12 Volt bulb (automotive/RV type) running on AC is being turned on
and off 120 times per second (60 Hertz). Although way too fast for
general themometers, it's also experiencing a temperature change 120
times per second. By design, the bulb may be designed to withstand the
vibration associated with auto/RV applications, but not the super
rapid temperature changes.

I've noticed a similar scenario with garden lights. They use the exact
same type automotive bulbs used in some tail lights, yet last only a
fraction of the (relative) time. To save money, the transformer output
is AC, eliminating the bridge rectifier and smoothing capacitor.

I would guess that were the same string of lights hooked up to a
"smooth-ish" 12 Volts of DC, as experienced in a car charging system,
they would outlast the 12 Volts AC system every time. A liberal
sprinkling of diodes, chokes & capacitors will go a long way to
increasing the life of your bulbs.

FWIW, Tungsten filament bulbs are not the most efficient means of
lighting an area. They produce a great deal of wasted heat.

Regards.




It might help if you provided more detail on the "DC Converter".

Why are you using a DC converter instead of a simple AC transformer?

You said it was made for this so one would assume the voltage is correct,
but you should measure it anyway. Have the lights been on 24 hours a day, or
just a few hours each evening?

Light bulbs are rated in number of hours they can be expected to last. Some
light bulbs will last thousands of hours. Others, like a projector bulb for
example, may last only tens of hours.

Heat, shock and vibration are reasons for premature bulb failure. Some
bulbs are not rated to operate in an "upside down" position, as it will
cause the base to overheat. Make sure that the bulb is not being used in an
inappropriate application.

Perhaps if you told us exactly what bulbs you were using it would help. You
said they were in a screw base, are these the 12volt bulbs that are often
used in RVs or boats?

Rod McInnis

"Joe Here" wrote in message
...

A 12 Volt bulb (automotive/RV type) running on AC is being turned on
and off 120 times per second (60 Hertz). Although way too fast for
general themometers, it's also experiencing a temperature change 120
times per second. By design, the bulb may be designed to withstand the
vibration associated with auto/RV applications, but not the super
rapid temperature changes.

The thermal lag of an incandescent bulb is way too slow for there to be any
significant amount of temperature variation on a per cycle basis.

Rod