Ace82 said:
OMFG!
I'll wait and see how long your guys's lasts, makes me wonder, why wouldn't they give us the 2 cr123a’s instead of the 18650 if the lasers can handle it? I mean they do have the 2.5W nlight LD right? Why does Jack say they’re powered at 2.4W if they’re really powered at 1.1W?
Hi Ace82,
Why would I say that they operate at 2.4W if they are operating at 1.1W????
Well, Actually I think I said they operate at ~80% of the rated diode current value, or something along those lines. Anyway, the real current at full power is 2.0 amps.
They are not being powered at less than 2 amps unless the adjustable tail is set at less than the maximum. The diode current at level 1 is just slightly over 1 amp.
The method that the GooeyGus is using to measure current is flawed.
If an amp meter is put in series with circuit, it increases the circuit impedance/resistance so much that the diode current setting is at an effective level of about -1 (if that were possible).
Below the dashed I've copied text from previous messages I've sent to customers on the subject of measuring current and why it's not as easy as it sounds and how I verified the diode current.
But 1st a couple of warnings,
Doing this will greatly reduce the life of the laser from thousands of hours to perhaps 1 or 2 two if even that.
GooeyGus isn't the 1st to try this, just the 1st to post about it. I get a ton of stories from customers and believe me it won't last long at all.
If these lasers were capable of such output, the manufacturer would capitalize on that and sell them as such, the fact is that the laser will die in a short amount of use and the manufacturer would have a very bad reputation.
One the question of overheating shutoff. There isn't any protection for overheating shutoff of the laser/diode. What the RPL has is battery protection circuit for the Lithium-ion cell. This circuit also provides ESD protection for the diode; but it won't protect the diode from over current or burn out. The way the battery protection circuit works, it will shut down when the sense voltage goes below a preset threshold of ~3V or so. If you were to use 2 cr-123 cells (6V), this battery protection would always be over-ridden.
I'm personally not against hacking, overclocking or other experiments, in fact I'm an overclocker from way back to the 80386 days.
But don't expect a warranty repair on such things, it's been attempted in the past by customers saying "it just stopped working", but upon root cause failure analysis it was found to have suffered from over voltage. The signature of laser/component failure for over-voltage is easy to determine as well as the that of excessive G-force (failure from dropping).
OK, Here's the text from other messages I've sent on RPL current measurements and the way it must be done.
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On the topic of diode current measurement. Since the RPL is a very low
impedance/resistance device, Using ohms law I*R=E, if E=~4.0 volts and
I(current)=~2.0amps, then the resistance through the entire system is
~2.0 ohms or less. To give you an idea of how a very low change in
circuit impedance/resistance affects the entire system in a major way;
the adjustable tailcap when set to diode current level 1 (which is
about 1.0 Amps of diode current) has a resistance of ~1.20 to 1.30
ohms. If the tailcap is set to level 9, the tailcap resistance is
~0.25 to 0.30 ohms and diode current will be ~2.0 Amps. So a change in
resistance of the entire circuit of only ~1 ohm or less has a huge
impact on the diode current.
Because of this, normal means of measuring current cannot be used. for
instance if a high quality bench amp meter or external power supply
were to be used, it would change the circuit because of the added
resistance meter leads and even more affected by the added internal
impedance of the meter or power supply.
The other common way that is used is by adding a known resistance in
series with the circuit (voltage sense resistor) won't work well
either because the resistor would need to be very low in resistance
(perhaps 50 milliohms or less), but also be of high precision and
large enough in power rating to handle 2 Amps of current flowing
through it.
I tried many methods of measuring diode current and here is how I was
able to measure current the most accurately.
The below procedure describes how I did it, I copied this text from an
email I sent to a customer back in June of 2006 right after receiving
the 1st RPL production units. At that time I still had a full time job
working as an engineer at Marvell Semiconductor and Optotronics was
only 1 year old and still just a "side business" for me.
------------
Hi xxxx,
Something pretty cool and impressive to tell you.
Yesterday, I brought an RPL in to work , I wanted to measure the current these lasers
use. You can't use normal means to accurately measure current because
any added resistance (like cable/ meter probe length and internal amp meter
resistance will change the circuit because these lasers are very low
impedance/resistance devices and even 0.1 ohm makes a huge
difference..
In my job we test IC's used for the read channel of hard drives and
DVD players/writers; so we have some pretty high tech test equipment.
The O-scopes we use are from a company called LeCroy (look them up at
www.lecroy.com ). A couple weeks ago I asked the LeCroy rep (who I've
known about 13 years) if they had any current probes that could
measure DC current. Most current probes measure current when the magnetic field
collapses thus only works on AC / high frequency signals. They did
have a couple of models of DC probes and said he would arrange for me to demo it
for a couple days. I told him it wasn't for work that I needed one,
but to measure current on a laser I had. Thursday he dropped it off
for me to use until Monday. The way it works is that there is a
sliding clamshell that opens, then you slide the wire you want to
measure current thru into it and then close the shell. This way, the
measurement does not affect the circuit at all since it's not
connected to the circuit at all, just around it. The probe is
connected to a LeCroy scope to take the measurement.
Here is how I set it up. I soldered two alligator clips end to end
with about 1/4 inch of heavy gauge wire between them. I then soldered
a 2.5 inch length of 14 gauge wire to the top of the lithium-ion
cell..
I then soldered the other end of this wire connected to the battery to
the point in the endcap where the copper battery connection point
meets the circuit board. I then connected the end to end clips from
the laser tube to the endcap. This gives a small length of heavy gauge
wire from the battery to the endcap to clip the current probe onto.
Now on to the meat of this email.
The current at level 9 (max power) was just a few milliamps over 2.0 amps.
I guess this amount of current is expected with a 2.5W diode. If you
look at diode specs, you will see the 2.5W diodes use about twice the
current of the 1.2W diodes in the PPL. I then turned the power down to
level 1 to see what it be there. It was right at 1.0 amps.
What surprised me the most was that when I was at my workbench
measuring the level 1 current, I looked up and saw that after just
about 1 second and a black scope probe lead that was between 2-3 feet
away from the laser began to smoke! I know black tape will smoke/burn
easily, but this is a scope probe wire about 1/8 inch in diameter and
3 feet way and this was on the lowest power setting.
