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12 Volt LED Monitor Lights

09/10/2017 10:31 PM

I'm trying to use 12 v LED lights to tell me when my 12 v solenoid valves turn on. i wired the LED's in parallel with the solenoid valves and the LED's burn out when the valve turns on. does it need a surge suppressor or something?

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#1

Re: 12 volt LED monitor lights

09/10/2017 10:37 PM

You need to check the 12V LED operating current specification. Sometime you need to add a resistor to the 12V LED. Try to add a 3/4 watt, 500 ohm resistor in series with the 12V LED. it will prevent the LED from burnt.

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#2

Re: 12 volt LED monitor lights

09/10/2017 11:31 PM

Just buy some of these and duct tape them to the solenoids you want to monitor.

Hover over the photo and left click for details.

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#3

Re: 12 volt LED monitor lights

09/11/2017 3:18 AM

Without a series resistor to limit the current, <...LED's burn out...> [the presence of the apostrophe is incorrect] is inevitable.

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#4

Re: 12 volt LED monitor lights

09/11/2017 7:31 AM

Have you got a spec., or, can you tell us the part code of the LEDs?

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#5

Re: 12 Volt LED Monitor Lights

09/11/2017 11:28 AM

You need to add a resistor in series with the LED. You are calling it 12 volt, but if it is burning out when connected in the manner you describe, it's not likely that it is a 12 volt LED. Search google for how to determine the value of that resistor.

12V ---/\/\--->|--- 0V

You also need to connect the LED in parallel to the solenoid. If you connect it in series, the solenoid will not see the 12 volts that it needs to operate.

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#6

Re: 12 Volt LED Monitor Lights

09/11/2017 11:30 AM

I see two possible scenarios here. First is what many here have identified. That your LED assembly is not actually a 12V LED assembly. A current limiting device (resistor) must be placed in series with the lamp. The second possibility is that the LED is actually getting blown when the solenoid is first turned OFF. A reverse biased diode in parallel to the solenoid/LED assembly will limit the flyback voltage to just the turn ON voltage of the diode. This diode must be current rated to handle the full current of the solenoid and not the tiny current of the LED. Other devices (transorb, RC circuit) can be used to snub this flyback voltage but details on the LED, solenoid and possibly wiring must be known to control this flyback.

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#19
In reply to #6

Re: 12 Volt LED Monitor Lights

09/17/2017 5:30 AM

GA

First good answer when reading from the top, though any good solenoid design would normally have a reversed biased Diode to limit the flyback anyway!

But I think you are right, its probably been forgotten in this example, as was the limiting resistor too!!

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#20
In reply to #19

Re: 12 Volt LED Monitor Lights

09/17/2017 9:07 AM

You are correct that the solenoid driver circuitry might contain flyback protection for itself. However, without knowing the cable length, transmission impedance (a spike will be a very high frequency signal) or how the driver flyback protection is configured the flyback could still be the culprit.

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#21
In reply to #20

Re: 12 Volt LED Monitor Lights

09/17/2017 11:33 AM

Good point!

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#7

Re: 12 Volt LED Monitor Lights

09/11/2017 2:56 PM

If the LED burns out when the solenoid is energized, then I have to ask... Is the LED is connected with the correct polarity? Reverse polarity could kill it, although I'm thinking the reverse avalanche voltage is probably higher than 12 volts.

http://microcontrollerslab.com/light-emitting-diode-working/

Another possibility is that LED burns out when the power is removed from the solenoid. When power is removed from the inductive coil in the solenoid, the magnetic field collapses and a reverse voltage appears across the solenoid and LED. This voltage could easily exceed the reverse breakdown voltage. To protect the LED, a diode should be connected in parallel so that it is reverse biased when the solenoid is energized as shown in the diagram below.

http://www.industrial-electronics.com/articles/article_title/Solenoid-Valves.html

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#9
In reply to #7

Re: 12 Volt LED Monitor Lights

09/12/2017 12:08 AM

A flyback diode may slow down the release of the coil. --- if that is important.

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#14
In reply to #9

Re: 12 Volt LED Monitor Lights

09/12/2017 11:42 AM

Quite true, just a diode will maximize the release time. Once an EE knows the details of the solenoid inductance, reverse breakdown voltage of the LED and maximum allowable release time then a suitable snubber network can be designed.

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#15
In reply to #14

Re: 12 Volt LED Monitor Lights

09/12/2017 12:14 PM

Somewhat similar circuit - I once used a standard red LED, 20k resistor and 1N4004 diode in series as a 110vac pilot light. The 1N4004 provided the reverse blocking the LED does not have.

The circuit replaced neon indicator lamps that had seen better days.

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#8

Re: 12 Volt LED Monitor Lights

09/11/2017 11:07 PM

You need to limit the current to your LED with a resister or a constant current regulator.

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#10

Re: 12 Volt LED Monitor Lights

09/12/2017 1:12 AM

Let's make things simple.

There is no such a thing such as a 12V LED. Light Emitting Diodes usually (always?) have a voltage drop of less than 1V when turned ON, so you would definitely need more than "just the LED".

Since you do not know what you are doing, there are commercial assemblies sold for your application, called PILOT LIGHTs. Get a 12V one for a few USD and stop burning your test equipment pointlessly.

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#11
In reply to #10

Re: 12 Volt LED Monitor Lights

09/12/2017 9:40 AM

?? "no such a thing such as a 12V LED" ...??

12v LEDs , more 12v LEDs , and MORE, and even 12v LED light strips ...

He could be using one of these, or multitudinous others......

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#23
In reply to #11

Re: 12 Volt LED Monitor Lights

09/22/2017 10:36 AM

Those are not just Light Emitting Diodes, since they have "Built-in resistor for 12 Volt DC operation (9~14.8 range)" or they incorporate them as an additional element. Just like "pilot lights".

Anyway, as in this thread the issue was the demagnetizing current of the coil, those would very likely have burned down as well.

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#24
In reply to #23

Re: 12 Volt LED Monitor Lights

09/22/2017 11:10 AM

?eh?... read, Re-read, and triple-read the OP:

"I'm trying to use 12 v LED lights to tell me when my 12 v solenoid valves turn on. i wired the LED's in parallel with the solenoid valves and the LED's burn out when the valve turns on. does it need a surge suppressor or something?"

The "poor newbie" (total of 4 posts at CR4 as of today) bought some "12v LEDs" <something probably similar-to what I linked>

I did NOT reply-to the OP... YOU did.

I replied-to *your* post, in which you had asserted:

"Let's make things simple. There is no such a thing such as a 12V LED. Light Emitting Diodes usually (always?) have a voltage drop of less than 1V when turned ON, so you would definitely need more than 'just the LED'."

My post had absolutely NOTHING to do with "solving his problem". It was meant to acknowledge (without "hearsay", but rather, with solid links), that he ALREADY HAD "more than 'just the LED'..."

Ergo : if you wish to tell somebody that those products "...are not just Light Emitting Diodes..."

feel free to contact the manufacturer(s) by chat/phone/or email and tell THEM.

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#12
In reply to #10

Re: 12 Volt LED Monitor Lights

09/12/2017 9:48 AM

That is not quite true. There are dozens of LED assemblies of various sizes, intended for 12V use in cars and boats. Here is a device which looks just like a simple LED but in fact contains an integral current-limiting resistor and is intended to be driven by a forward voltage of 10-14V. Note that the reverse voltage is only 5V.

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#13
In reply to #10

Re: 12 Volt LED Monitor Lights

09/12/2017 10:12 AM

If you really know of any LEDs with a forward voltage of less than 1½V then please let Suresh know for this thread:-

http://cr4.globalspec.com/thread/114495

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#16

Re: 12 Volt LED Monitor Lights

09/12/2017 5:10 PM

I am adding to my original question I have about burnt out LED’s. I am trying to monitor 12 solenoid valves that are in a 1.5 square foot area. All the valves are controlled by a Schneider Electric Smart Relay SR3B261BD module with Zeliosoft 2 programming software. Each of the 12 valves runs on independent but synchronized lagging and delayed timing with the valves on and off in 10 and 20 second timing cycles. I bought 100 cheap 12 v LED’s hoping to use them as monitoring lights. They would burn out immediately after the solenoid would cycle. I tested the LED’s on a 12 v dc power supply and they light up fine. I liked Ivanov327950’s idea of using pilot lights. Will incandescent 12 v bulbs burn out same as the LED’s? I need them mounted to the solenoids and not in a remote box so I can see the 12 valves cycling. Any further help would be appreciated!

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#17
In reply to #16

Re: 12 Volt LED Monitor Lights

09/12/2017 6:49 PM

If they are truly 12v LEDS, try a 1N4004 diode in series with the LED.

Dirt cheap and may fix your problem.

If not, try adding an additional freewheeling diode around the solenoid.

There, a 10 cent solution.

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Participant

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#22
In reply to #17

Re: 12 Volt LED Monitor Lights

09/19/2017 3:31 PM

PERFECT! I tested one 1N4004 diode in series with my LED around a solenoid and its cycling without burning out! I bought 250 diodes for $8.00 on amazon so its a 3 cent fix!

thank you for the help!!!!

Brian

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#25
In reply to #22

Re: 12 Volt LED Monitor Lights

09/23/2017 6:34 PM

Years of tinkering finally pays off!

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#18
In reply to #16

Re: 12 Volt LED Monitor Lights

09/12/2017 9:58 PM

12V incandescent bulbs will not burn out on one cycle as an unprotected 12 LED lamp will. However, incandescent bulbs burn out faster than their expected lifetime when they are frequently cycled ON/OFF. Once you lick your problem of blowing out your LED with a suitable protection circuit they should last for millions of cycles.

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