Xmas: 50 lights on and 50 off

[W. eWatson]

I started putting up outdoor Xmas lights (small candle shape) today, and
noticed 1/2 the string, 50, probably 100 in total, were out. Nicely
divided into two halves. I took the string to the h/w store to see if
they knew what happened. Nope. They just refunded my money. They may
have been blinking lights.

This afternoon I went out to put up a string of blinking lights, maybe
1" tall and upside down U shaped. They were all blinking. When I raised
them on a pole, 50 stopped working. I counted them. What's going on?
Both, I think, had 3 wires. The last set certainly did.

 

[W. eWatson]

It's simple. You have two strings of fifty lights in series. One
light fails and 50 lights go out.

Yes, likely so, but then which one? I thought the three stringers
somehow got around that problem.

I thought I found out a year ago something that explained all this, and
a way to repair them quickly. I don't see a bookmark on it, so off to
Google.

Ah, here's a hint. Fuses. There are two in the plug, which indicates to
me that a fuse could have blown.

Ah, there's a tester than only requires one to slip a bulb over a hole.

I see the avg life for bulbs in cheap strings ins about 3 years (seasons).
<http://www.familyhandyman.com/DIY-P...ving-Tips/how-to-repair-christmas-tree-lights>

Here's a "quick" tester
<http://www.amazon.com/Keeper-01201-Complete-Fixing-Miniature/dp/B000R8KBOK>

 

[Michael Black]

I buy new ones every year because those Chinese lights only need a
dirty look to go out. They will all light on the ground but after I do
all the work half will be out. LEDs are coming down in price.

Yes.

We still have lights from at least forty years ago. I can't remember when
they were bought, I can remember the serial strings where if one bulb went
bad the whole string went bad, so sometime in the sixties the non-series
lights came into the house. And they've stood up well.

The small bulbs of more recent origins look nice, but yes, they are
trouble (at the very least bad contacts, unlike the screw in bulbs of old)
and of course, result in a semi-serial arrangement, back to "which is the
bad bulb". But they are cheap, which has its advantages, but also the
problems.

LED bulbs are down to what good Christmas lights used to be, they only
seem expensive compared to the really cheap small throwaway strings of
recent times. Buy a set of LED Christmas lights, and they'll last
practically forever, just like those 1960s strings that are still running
fine. But unlike the old lights, the LEDs will take forever before a
light burns out, since they are LED, and unlike a lot of uses, the lights
only get used for a couple of weeks each year, so the life span of the
LEDs is nearly infinite.

Michael

 

[Desireless]

I buy new ones every year because those Chinese lights only need a
dirty look to go out.

lol I hear ya.

 

[[email protected]]

Yes, likely so, but then which one? I thought the three stringers
somehow got around that problem.

I thought I found out a year ago something that explained all this, and
a way to repair them quickly. I don't see a bookmark on it, so off to
Google.

Most now have bulbs that fail short (or some other mechanism) so that one
burned out bulb doesn't make the whole string go out. A loose bulb still
opens then entire (half) string, though.

To fix:

1) Swap each bulb with a new bulb. Use one spare, replace first bulb, take
that one and move to second, continue rotate left. Assumption #1: Only one is
bad. Assumption #2: The string itself isn't bad.

2) Get a non-contact voltage probe. Electricians use these things to check
for live circuits. Move it down the chain until it lights up.

Ah, here's a hint. Fuses. There are two in the plug, which indicates to
me that a fuse could have blown.

Two? Both sides of the line (non-polarized plug)?

Ah, there's a tester than only requires one to slip a bulb over a hole.

I see the avg life for bulbs in cheap strings ins about 3 years (seasons).
<http://www.familyhandyman.com/DIY-P...ving-Tips/how-to-repair-christmas-tree-lights>

Here's a "quick" tester
<http://www.amazon.com/Keeper-01201-Complete-Fixing-Miniature/dp/B000R8KBOK>

You can get the non-contact testers at the HD or Lowes for about a third of
that.

 

[[email protected]]

I have the lights my parents bought when I was a little kid over 50
years ago, along with what's left of the ornaments they used to hang on
the tree. They haven't seen daylight in over 12 years.

I have ornaments my parents bought for me ("ooh pretty") from 50 years ago
that have been used every year since. Most of the (unlit and non-tinsel)
ornaments are hand-made and >30 years old. I throw out lights as soon as they
start making trouble. They're too cheap (the day after Christmas) to bother
with or risk.

 

[W. eWatson]

I bought a Light Keeper Pro at an ACE h/w store yesterday. It isolated
the problem to the first four bulbs in the string that was out. My
problem may now be finding four bulbs. I guess I can cut them out of the
string and solder things back together.

Our local ACE store was out but selling them for $22. I happened to be
on a short trip 15 miles away and found them at an ACE for $17. One of
our local stores sold them at Xmas time,but was out. Not an ACE.

Interesting unit. It can solder pins down the string.

 

[ehsjr]

I bought a Light Keeper Pro at an ACE h/w store yesterday. It isolated
the problem to the first four bulbs in the string that was out. My
problem may now be finding four bulbs. I guess I can cut them out of the
string and solder things back together.

You could, but that would cause other bulbs in the remaining string
of 46 to burn out prematurely. Also with a 3 wire string, you need
to be able to figure out where to connect the wire (or the resistance
described below to bypass the open bulbs. With some of the strings
I've seen, the twisted wires make that too damn hard in my opinion.

Regarding premature burnout and resistors to replace the bulbs:
Each bulb in the original string of 50 drops a certain amount of
voltage. If the original string contains only bulbs and wires, then
each bulb drops ~ 2.4 volts (120/50). With 4 bulbs gone, you want to
find another way to drop ~9.6 (4*2.4) volts. Otherwise, the 46 bulbs
are each subjected to voltage a bit higher than normal, and will
burn out more quickly.

Probably easiest to buy another string, but if you want to proceed
and use a resistance to drop the voltage, you'll need to measure the
current drawn by a fully operational string. That will be I in the
formula E = IR. Solving for R: R = E/I. E is the voltage drop,
assumed to be 9.6 volts. It would be better to measure the voltage
drop across 4 bulbs in the fully operational string, and use that
measurement for E in the formula. R is the resistance required to
drop E volts at I current. The wattage dissipated would be I^2*R and
the resistor(s) would need to be rated at least twice that for a
safety factor. Since the resistance might touch flammable material,
you probably want a lot higher rating. More on that follows.

I don't know the specifics of your string, so I'll make up a value
for I: 200 mA. Using 200 mA and 9.6 volts, the required resistance
would be 9.6/.2 or 48 ohms, and the power dissipated would be 1.92
watts. I'd use 5 ten ohm, one watt resistors in series. That way
the dissipation would be spread across 5 resistors which would keep
the temperature lower. Whatever the actual number turn out to be,
you want to spread the heat out over a large enough area to keep
the temperature well within safe limits.

Replacing the bad bulbs with identical new bulbs, or replacing
the string, avoids all of that.

Ed