ARC AAA LE dims near magnet?

[phlashlight]

Got my ARC LE AAA about 3 weeks ago carry it with me all the time great light. Today I was using it next to a small relatively strong magnet and as the head of the ARC got close to the magnet it started to dim somewhere between full strength and "moon" mode and returned to original brightness when moved away from the magnet, tried this 3-4 more times to make sure I wasn't seeing things and had the same affect.
This is not a detrimental problem and I am not complaining, (I realy like my ARC LE) but I am curious if continuous exposure to a magnetic field would damage the electronics, shorten its life or cause other problems.
And is there a SIMPLE explanation as to why it does this?

 

[The_LED_Museum]

My regular Arc also does this.
I'm guessing it's because the ferrite core cannot desaturate fully when it's engulfed in such a strong external magnetic field, so the inductive kick or spike it is able to create is smaller.

Someone wuould need to ring up a jig of some sort so the current could be monitored while passing a very strong magnet over the head.
If the current drops as the LED dims, then there should not be any risk to the circuit.

Assuming the inverter uses an AC signal, there should also be no residual magnetic field left in the toroid either, even after a lengthy exposure.

 

[phlashlight]

Yes that's what I was thinking exactly!???? The magnet gets close and the light gets dim!?? I appreciate the help but I didn't understand a bit of it?? As long as you think it wouldn't harm the light. This is a great forum and I realy wish I understood every thing that is talked about, but I will just stick to what to those things that I understand, and try to learn as I go. thank you Stingmon.

 

[Spidey82]

so it is another way of using the arc in moon mode to save batt????
Linfeng

 

[phlashlight]

It doesn't get quite that dim, and I have no idea about how it would effect battery life but I suppose it is possible that it may work as sort of dimmer switch?

 

[Steelwolf]

How powerful a magnet are we talking about here? Standard fridge door stuff or the cobalt stuff they use in the NightStar self-generating flashlight?

Because... if you walk around with a magnet that powerful in your pockets, there's gonna be some serious problems, especially near TVs, computers, magnetic storage media, anything that uses an inductor...blah blah blah.

Not to mention the potential problems to certain of your organs.

 

[Gransee]

Yes, Craig is right, the inductor is being dampened by the magnetic field.

It won't hurt the flashlight, and it does take a close proximity to a good magnet to cause the dimming. The level of dimming indicates how strong the particular magnetic field is.

Your garden variety refrigerator magnet will not be strong enough to cause any noticable effect. I used a rare earth model to cause the effect.

Without running more tests, I would imagine that the power consumption drops under these circumstances because the coil has a higher impedance.

The flashlight is most sensitive to the field near the top part of the battery. This may be caused by the steel in the battery wicking the field down into the flashlight.

I imagine a donut magnet of the right size could be used as a dimmer, although it would be a hassle to carry.

Peter Gransee

 

[The_LED_Museum]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Steelwolf:
How powerful a magnet are we talking about here? Standard fridge door stuff or the cobalt stuff they use in the NightStar self-generating flashlight?<HR></BLOCKQUOTE>

I got it to dim with the magnetic holder they make for Trek 3-AA lights (or does it go with the PLW-3?). That has a rectangular ceramic magnet.

Much more dimming was evident with a ceramic ringed samarium cobalt speaker magnet, like the kind you find on the back those $5 car speakers.

So you don't need anything exotic or hard to find, just something reasonably strong.

 

[phlashlight]

The same magnet has the same effect on my krill light as well, similar circuit?
The magnet in question is from an old Mac computer hard drive, the magnet quite small but strong, about 1/16 of an inch thick and ¾ of an inch square. I have no idea what material/type magnet this is but it is quite strong.

 

[The_LED_Museum]

Any circuit that depends on a powdered ferrite core will show alterations when that core is exposed to strong magnetic fields; typically those found at either pole of the magnet.

DC-DC and DC-AC inverters, AF and RF circuits and 1:1 isolators using any kind of ferrite core inductors will all be affected to some extent or other if a strong enough magnet is brought near or "swiped" across the inductor's core.

 

[PeLu]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by phlashlight:
It doesn't get quite that dim, and I have no idea about how it would effect battery life but I suppose it is possible that it may work as sort of dimmer switch?<HR></BLOCKQUOTE>
When the core saturates, it's inductance goes down, that means it has less virtual resistance and the battery current will go up. I expect a shorter battery life then.
A test will show how much. Who is willing to donate 2 AAA cells and try it?

 

[The_LED_Museum]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by PeLu:

When the core saturates, it's inductance goes down, that means it has less virtual resistance and the battery current will go up. I expect a shorter battery life then.
A test will show how much. Who is willing to donate 2 AAA cells and try it?

<HR></BLOCKQUOTE>

Well, I don't have the batteries to donate, but I can try to hook up a meter and see if the current changes...

Yup, it goes way up.
The quickly thrown together test setup, using an unknown battery, registered 123mA with no magnet, and 195mA with magnet; and that was with only a moderate exposure... the test clamp was steel, and mitigated the effect substantially by "absorbing" or redirecting the magnetic field away from the Arc's head.

I'd imagine the current would shoot up way past 200-250mA if I had a proper test setup that didn't interfere with the magnetic field.

 

[The_LED_Museum]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by PeLu:
Hmm, you do not have DC here, so what your meter says may be right or not. Only a runtime test will do it. Actually you can use rechargeables .-)<HR></BLOCKQUOTE>

I connected the meter in series with the battery. So there is DC there.
Even if the meter were wrong, just watching it rise sharply when the magnet is broght near the head and then fall back off when it is removed proves the current increases.

I have some "AAA" NiMH cells (600mAh) I got for my green laser pointers, so if I don't let them discharge too badly inside the Arc, I can use those for this test.

 

[The_LED_Museum]

Anyone up for a test?

The battery shortage is - at least temporarily - over.

Let me put together a nice chart, and I'll start as soon afterwards as practical... let's shoot for 3pm to start at the top of an hour.

(Hint: if I had a stopwatch I wouldn't have to wait until the top of an hour)

 

[phlashlight]

I tried the magnet against my CMG infinity and to my surprise it has no affect I'm not into the electronics part of my flashlight affliction but I was actually surprised that it had no affect both single cell designs driving a white LED.

Is it just because it's a totally different circuit or are they of similar designs with different components. SIMPLE explanations for people like me please.

 

[The_LED_Museum]

Here's the magnet test, now in progress.

Without the magnet, the light registered 3.46mA on the solar cell, with the magnet, only 0.83mA on the same cell in the same orientation. Test is being started with magnet, and Panasonic alkaline batteries, provided by William at Texas Tactical (thanks!!!)

 

[The_LED_Museum]

This behavior seems to be flying in the face of earlier measurements. And if it goes for more than another couple of hours, chances are I'll end up falling alseep here and missing the inevitable downfall... thus wasting a battery.

Remind me never to start a test later than noon again.
Especially on the night we lost our bid for a Seattle World Series. :-/

 

[Gransee]

Hmm! So I was wrong about the current dropping. This would rule out the "donut dimmer" as a pratical retrofit.

Peter Gransee

 

[PeLu]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Stingmon:
Well, I don't have the batteries to donate, but I can try to hook up a meter and see if the current changes.<HR></BLOCKQUOTE>

Hmm, you do not have DC here, so what your meter says may be right or not. Only a runtime test will do it. Actually you can use rechargeables .-)

I cannot understand why Peter Gransee thinks that the impedance goes up. When you have a coil, it's impedance will go down when the core saturates.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Stingmon:
Any circuit that depends on a powdered ferrite core will show alterations when that core is exposed to strong magnetic fields<HR></BLOCKQUOTE>

Any ferromagnetic core will saturate when the magnetic field gets too strong. Only an air core will resist .-)

 

[PeLu]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Stingmon:
I connected the meter in series with the battery. So there is DC there.<HR></BLOCKQUOTE>

Why? As the Arc AAA's circuit is made that small, I assume it will not have to many and too large capacitors in it. Therfore the load current at the battery will be AC of an undefined waveform. I don't have an oscilloscope here to check it. Peter Gransee may clarify it (but he should not waste too much time for such questions .-)
But why care? People are not interested in load current, they are only interested in runtime.