Jetbeam Jet III-M output with 18650 disappointing

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Slickseth

Newly Enlightened
Joined
Aug 30, 2007
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Jetbeam claims that this light will accept an input range from 2.7v-15v. And while this may be true, I've discovered that the current to the emitter when powered by 1x18650 is just over half the output when using 2x18350.

When I bought the light, I was aware that it didn't have a boost circuit, but I assumed that it would still be able to achieve full output when running on a single li-ion. At least for a little while...

Testing current to the emitter, I found:

2x18350 (~8.0v) = 1100mA
1x18650 (~4.0v) = 660mA

obviously, the output drops even more as battery voltage decreases.

Has anyone else tested this? I'm curious if these figures are normal.

I know I can just run 2x18350 and get full output, but the stored energy of two 18350 cells is only 6.12w, while the highest capacity 18650 is able to hold 10w.
 
Are you REALLY measuring current to the emitter, or at the tailcap?

If at the tailcap, are you sure that your current measurements aren't reversed?

:popcorn:
 
I haven't tried 18350's, but FWIW, I can't tell the difference in output between 1x18650 and 2xCR123A.

I haven't measured the tailcap current for 2xCR123A, but on 1x18650 I get 790mA from a half flat (3.9V) battery.

I'll post 2xCR123A and full 18650 values tonight.
 
bullettproof said:
What does measuring at the tail do for you?? Really??
Click to expand...

It tells you how much power is going to the driver circuit in watts.

A fully regulated light will have similar power inputs regardless of cell voltage.

Power is current times voltage.

The power to the emitter is generally about 3/4 of the power input to the driver.

Therefore, you can approximate the current to the emitter by measuring the tailcap current.

My Jet-III-M tailcap current measures 850 mA on 1x18650, and 550 mA with 2xRCR123

It's better to measure both current and voltage of the cell simultaneously if you can.
 
EngrPaul said:
Are you REALLY measuring current to the emitter, or at the tailcap?

If at the tailcap, are you sure that your current measurements aren't reversed?

:popcorn:
Click to expand...

I measured the current at the emitter. I desoldered the positive wire from the emitter, and tapped my meter between the + output from the driver and the + on the emitter.


Sorry if I wasn't clear on that one.
 
You were clear, it's just a little unusual for someone to actually do that. :tinfoil:
 
My JET-lll M puts out the same amount of light whether I use 2 x cr123a, 2 x rcr123a, or 1 x 18650. Isn't that what it supposed to do, considering the advertised circuitry in it?

From Selfbuilt's excellent review of the JET-lll M. You'll notice that the output is exactly the same no matter what batteries are used.

Image1-3.jpg
 
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Have you considered that your ammeter in series with the emitter may be causing a voltage drop that the driver cannot overcome?

Example:

with 8V source, a non-boost driver can still provide good current even if you provide a voltage drop in series.

with 4V source, the ammeter could drop the voltage something like 0.7V to 3.3V at the LED, where it would have less current.

I guess you could calculate this knowing the impedance of your meter, or by placing a separate DMM across the ammeter to measure the voltage drop.
 
EngrPaul said:
Have you considered that your ammeter in series with the emitter may be causing a voltage drop that the driver cannot overcome?

Example:

with 8V source, a non-boost driver can still provide good current even if you provide a voltage drop in series.

with 4V source, the ammeter could drop the voltage something like 0.7V to 3.3V at the LED, where it would have less current.

I guess you could calculate this knowing the impedance of your meter, or by placing a separate DMM across the ammeter to measure the voltage drop.
Click to expand...

Good point. Makes me wonder...

I think what I'll do is attach the leads of the voltmeter directly to the led. If the output is supposed to be the same with 1x18650 vs. 2x18350, then the voltage at the led will be the same. If there is any deviation between the two, then I'm going to assume that a) Jetbeam's advertising is deceptive or b) I just got a faulty driver.

I'll report back later with the results.
 
i have a Jet-III M (titanium version), and JUST did a test on it yesterday.
1x18650 and 2x16340 starts off with the same light output for me according to my lightbox.
 
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EngrPaul said:
Have you considered that your ammeter in series with the emitter may be causing a voltage drop that the driver cannot overcome?
Click to expand...

This is exactly what I was wondering, especially if it's a cheap meter. (no offense intended) I don't believe all meters are created equal and can place different resistant values on the load???? Although we are talking about fairly large voltage and amp measurements as far as a meter is concerned. I wonder if how well regulated the driver is can also make a difference?

Bill
 
Hitthespot said:
This is exactly what I was wondering, especially if it's a cheap meter. (no offense intended) I don't believe all meters are created equal and can place different resistant values on the load???? Although we are talking about fairly large voltage and amp measurements as far as a meter is concerned. I wonder if how well regulated the driver is can also make a difference?

Bill
Click to expand...

Your point is definately valid. However, IF the driver is supplying the SAME current to the emitter regardless of battery voltage, even if my meter reading is skewed a bit, wouldn't it still give me the same (skewed) measurement for both tests?

Say for instance that your bathroom scale is out of calibration. And two different people (who happen to weigh the EXACT same) measure themselves on it. The reading will be wrong, but it will still be the same for both of them.

So basically what I'm saying is: regardless of whether the two measurements from the different battery configurations are showing the ACTUAL output; if the output is supposed to be the same, then the two measurements should also be the same. But mine aren't the same, which makes me think that something is wrong.
 
The problem is that the cell voltage is very close to the emitter voltage. If you look at the cree data for current vs. voltage, any minor changes to voltage will result in major changes to current.

Putting a resistance in series has a whole lot more influence on the current when the driver cannot boost the voltage.

The relationship is not linear, not like calibration error.

You could measure the emitter voltage and read current off the cree chart... this removes the ammeter from the picture.
 
Ok, I tested the voltage at the emitter using the two different battery options.
Results:

1x18650 (4.02v) = 3.6v @ 660mA tested at the emitter

2x18350 (7.98v) = 3.87v @ 1100mA tested at the emitter

As far as I can tell, the results are definitive. The output is significantly lower when using 1x18650 vs. 2x18350. Either the light is working exactly as it was designed, and Jetbeam's info is misleading, or I've just got a malfunctioning unit. Either way, I'm pissed that i am forced to use a lower capacity battery configuration in order to get full output.

Do any other Jet III-M owners care to test their lights and confirm whether or not mine is a fluke? Yes, I've seen the lumen tests, but I'm interested to see the actual voltage/current numbers.
 
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I would but, truth be told, I'm not up for desoldering the emitter right now.

Sorry.

EDIT: As promised, my tailcap readings...

2xCR123A - 5.97V, 810mA = 4.83W
1x18650 - 4.14V, 970mA = 4.06W

There's certainly more power being drawn by the driver at higher voltage, but damned if I can tell them apart on a white wall...
 
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I don't know if Jetbeam-III ST BVC has the same circuit as the III-M, but my III-ST has also a significantly lower output with 1x18650 than with 2x18350...:candle:

and - yes, it's very disappointing, as it's the more expensive, with the lower brightness and the worst beam, of all my li-on flashlights...:sigh:

right, the III-ST BVC - R2:

5794b94e63d023236b6874a97275e612aca153e7.jpeg
 
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