I Smoked my L4

Last week, While testing the total current draw of my L4 (Remove tail cap --- "-" lead to case, "+" lead to negative terminal of battery), the current reading initially held stable at approximately 1.37A - then very quickly, it began to rise.

The last reading I remember was 6.01A. I assumed that the Higher readings were just noise from poor lead connection, and then, I smelled the dreaded electrical fire smell.

AFTERMATH

Initially the L4 would only flicker, then after a while and with fresh batteries, I had some level of consistent output (similar to the output of a 1 x CR123 configuration).

I am assuming that somehow, with the introduction of the multimeter into the circuit, that I exceeded the circuit input levels. BTW, I was using a cheap $10 meter from wallmart.

Anyway, I sent my L4 back to surefire for repair.


I would like to ask if anyone can explain this occurance? I have tested the total current on this light, using this method many times before.

Dood, that stuff will rot your brain.

I wouldn't recommend smoking the L4. The fumes from the plastic and electronics burning can't be good for your lungs, and the HA finish will chip your teeth when you put it into your mouth to inhale. /ubbthreads/images/graemlins/crackup.gif

Weird. The shunt resistor in the meter may have been the cause of the problem, but I wouldn't expect this behavior. /ubbthreads/images/graemlins/thinking.gif

A meter cannot blow up your L4 or any other flashlight you're measuring with it. Sounds to me like you got a bum L4.
You did the right thing though - sent that sucker back to SureFire for a repair or replacement. /ubbthreads/images/graemlins/smile.gif

Sounds like your meter some how went from passive to agressive! /ubbthreads/images/graemlins/icon15.gif I wonder if the (presumed) 9V battery in themeter somehow didn't add to the Vin?!?!? /ubbthreads/images/graemlins/icon3.gif

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McGizmo said:
...I wonder if the (presumed) 9V battery in themeter somehow didn't add to the Vin?!?!? /ubbthreads/images/graemlins/icon3.gif

[/ QUOTE ]
If the meter malfunctioned, it could be very remotely possible.
I'd suggest setting the meter up exactly like he did when the L4 burnt out, and then putting the two metal probe tips on his tongue. If a sharp tingling sensation is felt on the tongue, then the meter is defective. Normally, no voltage whatsoever should be present on the meter probes.

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The_LED_Museum said:
Normally, no voltage whatsoever should be present on the meter probes.

[/ QUOTE ]

Except in the mode used to measure resistance. But on the amperage or voltage settings, you're right.

In the resistance measuring mode, voltage is present, but the current is very, very low. Typically under 1mA; not nearly enough to smoke something as robust as an L4.

With all due respect, I'm not so sure that SF should honor this as a warranty request. If they do, it's no wonder their pricess are so high, with the need to pay for non-SF induced related damages.

I would highly doubt the meter could have damaged the light. The battery in a cheap meter is usually an AA cell (or two). That would add at worst case 1.5 (or 3 volts) to the circuit. Hardly enough to do damage. Even if the voltage was added the current is highly limited in what the meter will provide. After all, that same voltage is used to measure resistance and you can, with impunity, short the DMM leads together with no significant current passing through the leads. So you can safely eliminate the meter from inducing any problems into the light.

Even if the meter was hooked up incorrectly the worst that would happen is dead short through the meter and all that could be delivered is the maximum voltage of the batteries at their maximum current. And if this current passed through the meter it would smoke the meter, not the L4.

And if you shorted to the case of the L4 you would simply provide an alternate path for the current rather than through the LED and the electronics. The LED and electronics would simply see this as dead batteries.

There is just no way that the light could have been damaged with a meter. The light is defective and needs to be replaced under warranty.

Thanks for all of the input. I do suspect a meter malfunction . and I don't mind sticking my tounge on the probes. I will let you know what I come up with. Although it is supposed to be a passive circuit, perhaps a faulty rotary switch has connected an odd functional conbination - or perhaps the 10A termial is somehow shorting to the battery voltage.

This is a super cheap meter, and I am sure that it is the cause of the problem - It is just too coincidental an occurance.

I will take the meter apart, and check for obvious signs of malfunction. I have not used the meter since the incident, but it does still power up.

I will ask Surefire for a detailed analysis of the failure - but I don't expect much of an explaination.

This Is Nascar - You are right,

They have probably factored thier fantastic warranty into the price of the light. This is a good business practice. and it was done up front, in anticipation of the cost of repair/ replacement of failed products. It was not done as a re-active stance against people blowing up their lights by doing stupid things. Am I the only one who has tested the current in this manner?

Don't get me wrong, I am not one to go running to Mommy when I damage something with an ill advised action. Quite honestly, I would have liked to investigate the problem myself, but Surefire has locked the cricuit board in so well that I cannot access it without causing damage.

So I am forced to send it in for repair, which by the way, I have provided full disclosure.

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LEDSmith said:
Thanks for all of the input. I do suspect a meter malfunction.

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Highly, as in extremely, unlikely.

I do not see how it would be posible for a multimeter to
damage your flashlight.
I have 2 dmm's that run on 2 aa
and I have 2 dmm's that run on 9 volt batterys
I guess if the 2 aa powered dmm's shorted out and provided 3 aditional volts to your flashlight circuit.
I used to have a 4 aa powered meter.
that would suck because the 2 aa meters are worth almost 3x
the cost of your flashlight.
I think if a meter failed and was providing it's internal batery voltage at the probes you would notice that the meter did not work right anymore.
something else must have went wrong.

I do appreciate how unlikely it is that the meter caused the problem. THe meter is powered by a 9V battery

Is it possible that a repetitive "ON/OFF" as in intermittent contact of the meter leads, to open and close the circuit, could have caused a current surge/ bounce - as in how power surges/ bounces when you first apply it to a circuit. could a transient from this bounce set off a chain reaction and revealed a weakness in the circuit.

Just groping for ideas.

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LEDSmith said:
I do appreciate how unlikely it is that the meter caused the problem. THe meter is powered by a 9V battery

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When you consider that one of the purposes of the meter is to check continuity on diodes, in both directions, a problem in the meter would fry diodes in a heartbeat. It would probably also smack your meter with that much voltage and full current.

The intermittent turning on and off should not affect the light. If it did why would you have a momentary push button. The high speed switch bouncing would not be a problem either.

I think you just had a bad flashlight and your timing was real good for the failure.

I had an LED light develop a short while it was in my pocket. I noticed the light getting very warm and quickly removed it from my pocket. It quickly got too hot to hold and I had to remove the batteries. The batteries were very hot. The light was not being used, just in my pocket. So it does happen.

I commend you for being honest to SureFire about the reason for the mishap. I also commend you for trying very hard to find out what happened, something that you were limited in doing due to the bezel design. If after reading your explanation, SureFire charges you for a new bezel or for repairing the fried one, the company should be ashamed of itself. I am confident that they will gladly replace your bezel, and if they can determine that you did something to cause the catastrophy, they will inform you of that determination so that it will not happen again. As you said, the price of the L4 has the cost of the most probable mishaps built into it.

Keep your fingers crossed, and let's all hope for the best for LEDSmith.

I'm not looking to get into a pissing contest with you. If you told SF what happened, then that's great. I applaud you for being honest, as your should. I have no beef with that. My issue would have been if you called SF and said "my light worked last night and today it stopped working". I'm sure you can appreciate my point here. Again, I have no issues. You did the proper thing. I hope all goes well. The L4 is a great light.

I have never fried diodes in continuity mode with any meter
but maybe I am smarter than that