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# LED indicator keeps failing

C

#### [email protected]

Jan 1, 1970
0
We have a line that uses a bunch of tri color led indicators. They
are listed to work with voltages of 12-24 VDC.

They fail within hours to a few months. Since the system runs at
24VDC, I figured putting a 820 ohm resistor to drop the voltage to
about 15 vdc when illuminated would fix everything. Well it does not
seem to be so.

FWIW, the indicator is a P+F LED18-RYG-P.

Any ideas on what might be killing these things or how to protect
them. All the other components of the systems (plc's, motion systems,
sensors) are working fine and not failing on us.

Thanks,

Wes

J

#### John Fields

Jan 1, 1970
0
We have a line that uses a bunch of tri color led indicators. They
are listed to work with voltages of 12-24 VDC.

They fail within hours to a few months. Since the system runs at
24VDC, I figured putting a 820 ohm resistor to drop the voltage to
about 15 vdc when illuminated would fix everything. Well it does not
seem to be so.

FWIW, the indicator is a P+F LED18-RYG-P.

Any ideas on what might be killing these things or how to protect
them. All the other components of the systems (plc's, motion systems,
sensors) are working fine and not failing on us.

I'd suspect reverse spikes.

J

#### Jason von Nieda

Jan 1, 1970
0
We have a line that uses a bunch of tri color led indicators. They
are listed to work with voltages of 12-24 VDC.

They fail within hours to a few months. Since the system runs at
24VDC, I figured putting a 820 ohm resistor to drop the voltage to
about 15 vdc when illuminated would fix everything. Well it does not
seem to be so.

FWIW, the indicator is a P+F LED18-RYG-P.

Any ideas on what might be killing these things or how to protect
them. All the other components of the systems (plc's, motion systems,
sensors) are working fine and not failing on us.

Thanks,

Wes

Wes,

Assuming 2.0v LEDs, with a resistor of 820 ohms you are putting around
27mA through the LED. A lot of common LEDs are rated for 20mA constant
so it sounds like you are overdriving the LEDs just a bit, which could
account for the differences in how quickly they fail.

You might try something a little closer to 1400 ohms to get ~15mA
through the LED.

I tried to find a data sheet for that part to find out the actual rating
for the LEDs but couldn't find one easily. The numbers above are just
safe(ish) guesses.

Jason

H

#### Homer J Simpson

Jan 1, 1970
0
They fail within hours to a few months.

What is the failure mode? Have you put a line voltage monitor on the system
to look for spikes?

--
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C

#### [email protected]

Jan 1, 1970
0
Jason von Nieda said:
Wes,

Assuming 2.0v LEDs, with a resistor of 820 ohms you are putting around
27mA through the LED. A lot of common LEDs are rated for 20mA constant
so it sounds like you are overdriving the LEDs just a bit, which could
account for the differences in how quickly they fail.

You might try something a little closer to 1400 ohms to get ~15mA
through the LED.

I tried to find a data sheet for that part to find out the actual rating
for the LEDs but couldn't find one easily. The numbers above are just
safe(ish) guesses.

Jason

The led's already have a limiting resistor in the package. I added an
additional one.

Thanks,

Wes

C

#### [email protected]

Jan 1, 1970
0
Homer J Simpson said:
What is the failure mode? Have you put a line voltage monitor on the system
to look for spikes?

I don't have a line voltage monitor. I do have a fluke 12 that I put
in min-max mode to monitor voltage. It didn't show any spikes but I
doubt it is fast enough.

WEs

C

#### [email protected]

Jan 1, 1970
0
John Fields said:
I'd suspect reverse spikes.

I was thinking of adding a diode to protect against that. There are
some power control relays that get switched in and out > 5000 times a
day. I need to look to see if snubbing diodes were installed across
the coils.

Wes

J

#### John Fields

Jan 1, 1970
0
I was thinking of adding a diode to protect against that. There are
some power control relays that get switched in and out > 5000 times a
day. I need to look to see if snubbing diodes were installed across
the coils.

---
Good idea. Try this too: (View in Courier)

+--[<1N4002]--+
| |
1>--+---[GRN>]----+
|
|
+--[<1N4002]--+
| |
2>--+---[WHT>]----+
|
|
+--[<1N4002]--+
| |
4>--+---[YEL>]----+
|
|
3>----------------+

H

#### Homer J Simpson

Jan 1, 1970
0
I don't have a line voltage monitor. I do have a fluke 12 that I put
in min-max mode to monitor voltage. It didn't show any spikes but I
doubt it is fast enough.

If you can't see/detect the fault causing condition, you have to guess at
what it might be and try 'fixes' to deal with it. It's down to too much
forward voltage / current or too much reverse voltage or too high a
temperature.

--
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..
..
..
..
..
..
..

R

#### Rich Grise

Jan 1, 1970
0
I don't have a line voltage monitor. I do have a fluke 12 that I put
in min-max mode to monitor voltage. It didn't show any spikes but I
doubt it is fast enough.

I don't think John was talking about line spike protection, but more
switched-inductor spikes.

Reverse-parallel diodes sound like a very good idea.

Cheers!
Rich

P

#### Peter Bennett

Jan 1, 1970
0
We have a line that uses a bunch of tri color led indicators. They
are listed to work with voltages of 12-24 VDC.

They fail within hours to a few months. Since the system runs at
24VDC, I figured putting a 820 ohm resistor to drop the voltage to
about 15 vdc when illuminated would fix everything. Well it does not
seem to be so.

FWIW, the indicator is a P+F LED18-RYG-P.

Any ideas on what might be killing these things or how to protect
them. All the other components of the systems (plc's, motion systems,
sensors) are working fine and not failing on us.

Newark says those things are $92 per each, apiece!!! For that price you should get a personal visit from the manufacturer to find the problem. -- Peter Bennett, VE7CEI peterbb4 (at) interchange.ubc.ca new newsgroup users info : http://vancouver-webpages.com/nnq GPS and NMEA info: http://vancouver-webpages.com/peter Vancouver Power Squadron: http://vancouver.powersquadron.ca C #### [email protected] Jan 1, 1970 0 Peter Bennett said: Newark says those things are$92 per each, apiece!!!

For that price you should get a personal visit from the manufacturer
to find the problem.

One would think. I recently sent an email inquiry to P+F concerning
the problem. I thought someone engineering had checked but you never
know. The Lean manufacturing stuff.... More like cut to the bone...

There are about 10 of these things on the line. My adding limiting
resistors to each extended their life a bit but has not solved the
problem.

I'm going to check my toolbox and see if I have the 1N4002's and put
them in whenever the line goes down.

I will also look for any contactors that might not have snubbers
across the coils.

I sure appreciate everyone's comments. I work maintenance and would
like to fix it for good rather than swap in parts.

Wes

C

#### [email protected]

Jan 1, 1970
0
I will also look for any contactors that might not have snubbers
across the coils.

Replying to myself. I took a look at all the control panels, the
prints show diodes across the coils of all contactors with 24VDC
coils. I didn't find a single one actually in the control panels.

I think I have just had my first practical example of why those diodes
are so important.

Thanks all,

Wes

D

#### Don Klipstein

Jan 1, 1970
0
We have a line that uses a bunch of tri color led indicators. They
are listed to work with voltages of 12-24 VDC.

They fail within hours to a few months. Since the system runs at
24VDC, I figured putting a 820 ohm resistor to drop the voltage to
about 15 vdc when illuminated would fix everything. Well it does not
seem to be so.

If an 820 ohm resistor drops 9 volts, then the current is about 11 mA.
If an internal-resistor LED has 15 volts across it and is conducting 11
mA, it will be dissipating about .165 watt - which sounds a little high to
me for an induicator LED.

Meanwhile, I would suspect spikes, maybe reverse ones.
FWIW, the indicator is a P+F LED18-RYG-P.

Which colors are failing? If red is holding up, what shade of green is
the green?

Most RYG indicators have older tech LEDs (the green is yellowish) but
the superbright greens from the late 1990's and later that are pure green,
whitish green or bluish green are often static sensitive.

- Don Klipstein ([email protected])

C

#### [email protected]

Jan 1, 1970
0
If an 820 ohm resistor drops 9 volts, then the current is about 11 mA.
If an internal-resistor LED has 15 volts across it and is conducting 11
mA, it will be dissipating about .165 watt - which sounds a little high to
me for an induicator LED.

Meanwhile, I would suspect spikes, maybe reverse ones.

Which colors are failing? If red is holding up, what shade of green is
the green?

Most RYG indicators have older tech LEDs (the green is yellowish) but
the superbright greens from the late 1990's and later that are pure green,
whitish green or bluish green are often static sensitive.

- Don Klipstein ([email protected])

These are 'high powered' led's. The green (really is green) go first,
yellow second, reds seem to last. See recent post where I found all
diodes that were supposed to be across contactors missing.

http://wess.freeshell.org/usenet/sci.electronics.basics/scan0004.jpg
(this is a datasheet from p+f)

Thanks,

Wes

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