Hi,

Using my multi-meter, is there any way to determine the voltage of a
working individual mini-bulb from a set for a Christmas tree? One set needs
2.5 v bulbs, another 3.5, another 6.

Thanks,
Dugie

On Dec 21, 6:36*pm, "Dugie" wrote:
Hi,

Using my multi-meter, is there any way to determine the voltage of a
working individual mini-bulb from a set for a Christmas tree? One set needs
2.5 v bulbs, another 3.5, another 6.

Thanks,
Dugie

Good question, complicated answer.

Start with a 2.5 V power supply, see how bright the light is, if it is
dim, try 3.5V and then 6V. But there is more to it than just the
voltage, there is also the current rating.

Even if there are 35 lamps in series across 120V, leading to a
conclusion of 3.5 V per bulb, different strings of 35 lamps may have
different currents. If you put a 3.5 V bulb from a low current string
into a string that has a higher current level, due to lower resistance
lamps, the 3.5V lamp will have too much current through it and light
up very brightly before burning out.

The only sure way to tell if a bulb is compatible with a particular
string of lights is to run the string of lights at half brightness or
lower, using a variac or lamp dimmer, put in the bulb in question, see
that it is equally as bright as the other lamps in the string, and
then increase the voltage gradually to make sure that the bulb in
questions stays the same brightness as the other bulbs in the
string.

Just measuring cold bulb resistance with a multimeter is not a very
reliable indication of the bulb as different bulbs have different
changes in resistance when they are heated to illumination levels.

H. R.(Bob) Hofmann

"hr(bob) " wrote in message ...
On Dec 21, 6:36 pm, "Dugie" wrote:
Hi,

Using my multi-meter, is there any way to determine the voltage of a
working individual mini-bulb from a set for a Christmas tree? One set needs
2.5 v bulbs, another 3.5, another 6.

Thanks,
Dugie

Good question, complicated answer.

Start with a 2.5 V power supply, see how bright the light is, if it is
dim, try 3.5V and then 6V. But there is more to it than just the
voltage, there is also the current rating.

Even if there are 35 lamps in series across 120V, leading to a
conclusion of 3.5 V per bulb, different strings of 35 lamps may have
different currents. If you put a 3.5 V bulb from a low current string
into a string that has a higher current level, due to lower resistance
lamps, the 3.5V lamp will have too much current through it and light
up very brightly before burning out.

The only sure way to tell if a bulb is compatible with a particular
string of lights is to run the string of lights at half brightness or
lower, using a variac or lamp dimmer, put in the bulb in question, see
that it is equally as bright as the other lamps in the string, and
then increase the voltage gradually to make sure that the bulb in
questions stays the same brightness as the other bulbs in the
string.

Just measuring cold bulb resistance with a multimeter is not a very
reliable indication of the bulb as different bulbs have different
changes in resistance when they are heated to illumination levels.

H. R.(Bob) Hofmann

Very complicated. Thank you, Bob.
I forget to write: 250 lamps, "straight line" (meaning the same as in series?), 110/120v AC. I don't think I am motivated to try your innovative dimmer solution, but it's close. Sounds almost like fun.
The math for 250 lamps of 2.5 volts across 120v doesn't seem to work out either.

Dugie

Note: for YOUR message only, my replies aren't indented with . I inserted them manually. As a test, any other messages I replied to have the ""

"Dugie" wrote in message
...
"hr(bob) " wrote in message
...
On Dec 21, 6:36 pm, "Dugie" wrote:
Hi,

Using my multi-meter, is there any way to determine the voltage of a
working individual mini-bulb from a set for a Christmas tree? One set
needs
2.5 v bulbs, another 3.5, another 6.

Thanks,
Dugie

Good question, complicated answer.

Start with a 2.5 V power supply, see how bright the light is, if it is
dim, try 3.5V and then 6V. But there is more to it than just the
voltage, there is also the current rating.

Even if there are 35 lamps in series across 120V, leading to a
conclusion of 3.5 V per bulb, different strings of 35 lamps may have
different currents. If you put a 3.5 V bulb from a low current string
into a string that has a higher current level, due to lower resistance
lamps, the 3.5V lamp will have too much current through it and light
up very brightly before burning out.

The only sure way to tell if a bulb is compatible with a particular
string of lights is to run the string of lights at half brightness or
lower, using a variac or lamp dimmer, put in the bulb in question, see
that it is equally as bright as the other lamps in the string, and
then increase the voltage gradually to make sure that the bulb in
questions stays the same brightness as the other bulbs in the
string.

Just measuring cold bulb resistance with a multimeter is not a very
reliable indication of the bulb as different bulbs have different
changes in resistance when they are heated to illumination levels.

H. R.(Bob) Hofmann

Very complicated. Thank you, Bob.
I forget to write: 250 lamps, "straight line" (meaning the same as in
series?), 110/120v AC. I don't think I am motivated to try your innovative
dimmer solution, but it's close. Sounds almost like fun.
The math for 250 lamps of 2.5 volts across 120v doesn't seem to work out
either.

Most likely the bulbs are in series strings of 50 2.5V bulbs. The 5 strings
are very likely in parallel. This is how they set them up. This is how the
math works. Is it one long string with a single AC power plug?

"Chuck" ! wrote in message news:aO%aj.263034$Fc.161956@attbi_s21...

"Dugie" wrote in message
...
"hr(bob) " wrote in message
...
On Dec 21, 6:36 pm, "Dugie" wrote:
Hi,

Using my multi-meter, is there any way to determine the voltage of a
working individual mini-bulb from a set for a Christmas tree? One set
needs
2.5 v bulbs, another 3.5, another 6.

Thanks,
Dugie

Good question, complicated answer.

Start with a 2.5 V power supply, see how bright the light is, if it is
dim, try 3.5V and then 6V. But there is more to it than just the
voltage, there is also the current rating.
snip
H. R.(Bob) Hofmann

Very complicated. Thank you, Bob.
I forget to write: 250 lamps, "straight line" (meaning the same as in
series?), 110/120v AC. I don't think I am motivated to try your innovative
dimmer solution, but it's close. Sounds almost like fun.
The math for 250 lamps of 2.5 volts across 120v doesn't seem to work out
either.

Most likely the bulbs are in series strings of 50 2.5V bulbs. The 5 strings
are very likely in parallel. This is how they set them up. This is how the
math works. Is it one long string with a single AC power plug?

It is seemingly "one long string" with one AC power plug, but some parts have say 4 or 5 wires twined together, so as you write, it's 5 parallel strings.

I'd like to extend the wires of a bulb enough to be able to measure the working voltage with the set on. Now, if I measure the AC current in an empty socket, with the probes completing the circuit, I get a reading of about 135 volts. I'll use alligator clips to avoid the shock of learning. :-)

Dugie

It is seemingly "one long string" with one AC power plug, but some parts
have say 4 or 5 wires twined together, so as you write, it's 5 parallel
strings.

'd like to extend the wires of a bulb enough to be able to measure the
working voltage with the set on. Now, if I measure the AC current in an
mpty socket, with the probes completing the circuit, I get a reading of
about 135 volts. I'll use alligator clips to avoid the shock of learning.
:-)


It's just simple math. 5 segments of 20 lamps making a 100 lamp string, this
is common. Each segment is 120V across 20 lamps, so 6V lamps. The other
common arrangement is two sections of 50 lamps each, with 2.5V lamps.

http://christmas.howstuffworks.com/c...as-lights1.htm

http://www.planetchristmas.com/Minis.htm

Just count the number of bulbs that go out when you remove a bulb from a
working string...
then divide 120 volts (if in North America) by the number of bulbs in each
section,

10 bulbs would be 12 volt bulbs
20 bulbs would be 6 volt bulbs
50 bulbs or so would be 2.5 volt bulbs
These are nominal voltages, Some strings use a few more bulbs and run not
as bright.


"Chuck" ! wrote in message
news:AP%aj.263038$Fc.921@attbi_s21...
http://christmas.howstuffworks.com/c...as-lights1.htm

http://www.planetchristmas.com/Minis.htm

"Ray" wrote in message
news:W43bj.2018$DP1.1297@pd7urf2no...
Just count the number of bulbs that go out when you remove a bulb from a
working string...
then divide 120 volts (if in North America) by the number of bulbs in
each section,

10 bulbs would be 12 volt bulbs
20 bulbs would be 6 volt bulbs
50 bulbs or so would be 2.5 volt bulbs
These are nominal voltages, Some strings use a few more bulbs and run not
as bright.

Now that was a good common-sense troubleshooting response. Right to the
point. Excellent!