Burned out LED bulb on new bulkhead compass

[CloudDiver]

I've been slowly working on installing a Plastimo Mini Contest bulkhead compass on my C-22. It was a lot of work to actually 'shrink' and shape the mounting hole from a previous larger compass using thickened epoxy.
Anyway, I tested the blue LED illumination light with a 9V battery, worked fine. So I soldered on some 26 ga leads to extend the wires and tested again. Worked fine for two touches on the 9V battery... then, nothing.
Did I burn the resistor out? I thought the 'grain of wheat' size LED bulbs were usually 5 or 6 V LEDs with a 12 or 14 v resistor, about 80 milliamp draw? I was fairly certain a 9V battery would not have the amps to burn out the resistor. What's a better way to electrically test such things when your electrical system isn't fully installed?

So there are LED bulbs all over eBay and other places on the web, I'm sure I can get a replacement pretty cheap. I have a local electronics store that has tons of components, might be able to get it there too. Plastimo makes a replacement kit for the Compass LED, but I can't find any online sellers in the US that have them.

 

[flynhi4u]

Some leds are polarity sensitive, try reversing the wires.
I got a 12 V led for our compass so there were no resistors involved. Works great and only draws .25 amp.

Sam

 

[CloudDiver]

Some leds are polarity sensitive, try reversing the wires.
I got a 12 V led for our compass so there were no resistors involved. Works great and only draws .25 amp.

Sam

That was the first thing I tested, before I soldered on the extensions or the bulb quit working. This one is polarity sensitive, it would only work when red was on the positive battery terminal. I believe the resistor would be in-line on he positive lead.

 

[Justin_NSA]

First off, ALL Light Emitting Diodes are polarity sensitive. That's how a diode works. You are biasing the P and N materials to get conduction. Reverse the polarity and you stop conduction. I don't see how an LED bulb rated for a 12V system could get damaged by a 9v battery. Is the battery still good? Maybe it's too low now to trigger the bulb. Have you tried a new battery?

 

[CloudDiver]

First off, ALL Light Emitting Diodes are polarity sensitive. That's how a diode works. You are biasing the P and N materials to get conduction. Reverse the polarity and you stop conduction. I don't see how an LED bulb rated for a 12V system could get damaged by a 9v battery. Is the battery still good? Maybe it's too low now to trigger the bulb. Have you tried a new battery?

Yes I did. It was a fresh 9V out of the package. After the second test failed I tried another battery from the package and no joy.

 

[Benny17441]

Did you use a heat sink when soldering? Heat travels rather quickly by thin wires and could have damaged the electric component. The use of a heat sink to capture heat is always advisable when working with electric components.

 

[CloudDiver]

Did you use a heat sink when soldering? Heat travels rather quickly by thin wires and could have damaged the electric component. The use of a heat sink to capture heat is always advisable when working with electric components.

No, but the solder was fairly far down the wire from the resistor. With wire that small it solders very quickly with little time for heat to travel far. After the soldering on the wire extensions the led did work when tested on the 9V battery, two touches for about 2 seconds each. On the third touch the led no longer worked.

 

[Ken Cross]

Infant mortality is common in the world of solid state electronics. High dollar industries shake and bake for many cycles (sometimes costing thousands of dollars) before sending equipment out. Inexpensive items like we would install are usually not tested to near the standards. Early failure of electronic equipment is a normal part of the world of electronics.

Another possibility is damage caused by electrostatic discharge. This is also a huge problem for solid state electronics (Otherwise known as electrostatic Sensitive devices (ESD).
You will likely never know the real cause of the failure. Just replace it.

Ken

 

[CloudDiver]

Infant mortality is common in the world of solid state electronics. High dollar industries shake and bake for many cycles (sometimes costing thousands of dollars) before sending equipment out. Inexpensive items like we would install are usually not tested to near the standards. Early failure of electronic equipment is a normal part of the world of electronics.

Another possibility is damage caused by electrostatic discharge. This is also a huge problem for solid state electronics (Otherwise known as electrostatic Sensitive devices (ESD).
You will likely never know the real cause of the failure. Just replace it.

Ken

I agree... Is there a better way to tests 12V components when your electrical system isn't complete (no power yet) and you don't want to invest in an expensive 12V power supply? I'm just wondering if using a 9V battery to test a single led was reasonable or stupid? My reasoning was that led bulbs function from any source of voltage above 5V and the 9V battery wouldn't push enough amps to harm the bulb.
I can order Led bulbs with attached leads and resistors off the web by the dozens for about $10... Any tips on building your own from scratch? I have a Fry's electronics locally, but I'd have to solder the resistor and wires on myself.

 

[Davidasailor26]

From your description it's not clear to me - does the LED you used have a built in resistor? An LED itself really has no significant resistance, and it will burn out pretty quickly if it's put in a circuit with no other current limiting resistor. LEDs each have data sheets that show how much current they can carry, but generally that amount is way less than what a battery can provide.

 

[CloudDiver]

From your description it's not clear to me - does the LED you used have a built in resistor? An LED itself really has no significant resistance, and it will burn out pretty quickly if it's put in a circuit with no other current limiting resistor. LEDs each have data sheets that show how much current they can carry, but generally that amount is way less than what a battery can provide.

I would have to slice off the shrink wrap at the base of the led bulb to say for sure, but judging by the slight bulk there I assume that it does have a resistor.

 

[Ward H]

What David said. A plain LED which would not take the over voltage of 9v.
80mA would be way too much current. Most LEDs are something like 3v or less and around 30mA.
Was there a circuit board the LED was supposed to be connected to or are you retrofitting the LED?
Thinking back to my model train days when I did a lot of things with LEDs, working with them can get tricky. Especially with variable voltages and possible spikes. There is a current limiting component I used that worked well. Forget what they are called. Best was to build a small board with voltage regulator and resister to limit the voltage and current. Google might turn something up easy to build.

Edit - You posted while I was writing. Sounds like there was a resister in line. Maybe it was just bad luck. I would think the resister would have to be sized for 14v to protect the LED. If it was, 9v should have been safe.

 

[Ken Cross]

I would have to slice off the shrink wrap at the base of the led bulb to say for sure, but judging by the slight bulk there I assume that it does have a resistor.

If it is a bare LED, he's right, it should fail quickly. A current limiting resistor is a minimum to operate it. Better LED lighting parts actually can have quite sophisticated electronics in them. From your text I assumed it was a light designed for 12 volts (came with compass??) If not I do stand corrected. I have had pretty good luck with individual LEDs that came with resistors in heat shrink at the base.

I was gonna have you send my your address in a PM so I could just mail you some, but I can't find them. Sorry.

Ken

 

[flynhi4u]

You could just buy a 12 volt led bulb. Assuming your wanting to run it off a 12 volt battery in the boat.

Sam

 

[walt]

Sounds like what you bought has a diode to light up the display and a current limiting resistor. You should not have burned out the diode with what you did.. but I guess it did burn out. Probably easier to buy something that already has the current limit resistor but if you did want to DIY..

Here is a spec for a typical blue LED that might be used in an application like lighting up a display http://www.cree.com/~/media/Files/Cree/LED Components and Modules/HB/Data Sheets/C5SMF C5SME RJS GJS BJS 201.pdf

Assuming for this simple low power application that your circuit is just a resistor in series with the LED..

The blue version of this LED has a forward voltage of 3.4 volts (blue LEDs will almost always be between 3 to 4 volts forward voltage). Figure 1 in that spec shows the forward voltage vs current and what you will notice is that the voltage doesn't vary much over a wide current range.

Here is an example of how to choose the resistor value. If the battery voltage is 13 volts and the LED is at 3.4 volts, then there will be 9.6 volts across the resistor. To set the current at 20 ma, use ohms law

9.6V = .02 * R Calculate R = 480 ohms (standard 5% values are 460 or 490 ohms.. you could use either value and 460 will be a little brighter.

You have to be careful of the power in the resistor but that is also easy to calculate P = V*I = 9.6 * .02 = .192 watts. So you would want to use at least a 1/4 watt resistor. High temps and high battery voltage will result in slightly higher current so you may even go to 1/2 watt for the resistor.

 

[Jacktar]

The led that comes with the plastimo 101 context has a resister built in to the red wire end not at the bulb. You may have nuked it when you soldered the extension wires. It is is designed for crimp connectors. Any 12 v led will replace it. Some even come with a built in resister and dont have a polarity problem. Try model railroad sites for cheap ones.

 

[bawlmer]

Cloud. A couple of things. The LED and the resistor came as an engineered package. It was designed to work in the vicinity of 12 volts. Also a nine volt battery should not have the current to burn up a resistor if the LED shorted. If the resistor did fail you would definitely smell it. Try testing it on 12 volts before you tear into the package. LEDs have a trigger voltage that needs to be exceeded before they turn on and your nine volt batteries may not be hitting that voltage consistently. You can use your car battery if needed. The LED package will only draw as much current as it needs. Hope that helps.

 

[Bosman]

If you have a multimeter on your boat, use the diode check feature...you should get "some" resistance one way, and none the other. If the circuit is open both ways, LED is unfortunately burnt or the resistor disconnected from the wires inside the compass.

Another method is described here: http://www.brighthubengineering.com/robotics/60933-how-to-test-led-lamps/

 

[CloudDiver]

The led that comes with the plastimo 101 context has a resister built in to the red wire end not at the bulb. You may have nuked it when you soldered the extension wires. It is is designed for crimp connectors. Any 12 v led will replace it. Some even come with a built in resister and dont have a polarity problem. Try model railroad sites for cheap ones.

Yup... Bingo Jacktar. If the resistor was built into the end on the red lead, I cut it off when I cut off the crimp end to solder on the extension wire. The tiny hole that passes through me bulkhead (laterally) isn't big enough for the crimped wires to pass through, but plenty of room for two strands of 26 gauge wire. That explains perfectly why it worked on the 9V battery before I soldered the extension on, but failed when I tested it again on the extensions.

I'll have to get a new one...

 

[flynhi4u]

Jacktar nailed it! Great thing about this forum, I learned from other peeps problems.

Sam