Hi all I just put together two lights with cree xml2 led’s and 3.04 Amp rated driver boards, but when I test them with my multimeter I am only reading about 1.5 amps to 1.3 amps, what gives? I don’t think it’s the multimeter because they are similarly bright to the old drivers that were installed.
TheFlasher. This forum has lots of threads with the same question. Nine times out of ten it is the DMM leads. The meter may be rated to 10 amps but the leads are not. What are you using as a power source? If your using batteries what brand are they? We need as much information as you can give us to try and help you.
Sorry for not being clear enough, and I was never able to find a good answer to my question after searching before posting. I am used to forums and try my best to find what I need before asking. Thanks for the welcome.
The batteries are panasonic 3400mah from mtnelectronics and one is protected and one is unprotected.
It’s not just the multimeter that is telling me its not full power, visibly I can tell that it is not at 2.8/3.0 amps. The brightness does not change between using the multimeter and just putting the light together and using it so obviously the multimeter leads are not causing some increase of resistance
The multimeter seems accurate to me because the previous drivers in the lights I have were rated at 1 amp and the multimeter read that accurately so why now would it be wrong?
Here's a quick test: when you are on high mode running the current through the multimeter, short one of the leads to the flashlight bypassing the multimeter. If the brightness increases visibly at all, your leads are restricting the current significantly and giving you inaccurate readings. The 1A and 3A are completely different when you're talking about thin leads... my DMM was fairly accurate up to around 1.5A with the stock leads, but wouldn't read over 2A with any light I had! Also, these XM-L2's high forward voltage requirement makes them very sensitive to any increase in resistance.
Well if you’re getting the same low readings on two different drivers from two seperate places, you’ll probobaly have to rule out the dmm first… I just went through this, and got a Mastech meter on reccomendation by forum members here, and it is pretty accurate with the stock leads. I dropped the 30 bucks to rule it out, and threw away 2 meters.
I tried it doing the shorting the leads that gitira6 mentioned and that is the only way I notice the brightness difference but it still seems pretty subtle, not quite half the output (Although I understand perceived brightness vs output.) What I mean is I would expect a more noticeable difference if its running at less than half the power…I still feel like there’s something more to it. Maybe my soldering is increasing resistance too much? Maybe the tailcaps? The springs are low gauge and my soldering looks pretty solid…
Use some heavy gauge wire about 10 inches long. Heavy gauge speaker wire, old household cord off of something that doesn’t work anymore, even small wire will work if you tie several together to decreasing resistance, keep them short. The most commonly used wire is high strand count silicone wire (very flexible), can be found at hobby shops or online. Needs to be AWG 16 or larger, I use 14 AWG. You can shove the wire down in the lead terminal holes and use the other end just as bare wire or you can buy the appropriate banana plugs and make a set just for measuring high currents that plugs right in.
This is the most common cause of low tail cap readings. Another common cause is not having the leads in the right lead hole or the DMM isn’t set to measure current. You have switched through all the modes I guess to make sure your in high mode, right? You could also try measuring the current with the driver out of the light (directly connected to the battery and led), that would rule the light out if it doesn’t increase the current.
I ordered some bananaplugs and thick wire and soldered one myself:
If you don’t want to build leads on your own you can check hobbyking.com, this shop sells a lot of charger leads with banana plugs on one side and some fancy connector on the other side, just cut the connector and you will have decent multimeter leads.
Brightness is not detectable per eye very good, just if you compare it like you now did.
If you will do it with 30seconds time between in a room you will not be able to determine it by eye.
This effect gets even harder with increasing total brightness.
I tried this experiment very often with strangers, point 2000lm or 1000lm on the Livingroom wall, no one will see a difference…
Another effect can be a regulated driver which will regulate the constant current even if the DMM leads have a lot resistance. So you can’t determine if you DMM once measured correct values that it will do that again with another driver…
If your leads would have a resistance 0.2ohm the voltage drop on 3A would be 0.6V, the remaining battery voltage would be around 3.4V on very fresh batteries and this is the point were a nanjg with xml2 will fall out of regulation very fast….
Ignore if you have tried this
when testing tail cap current on a Qlite or 105c driver , you need to cycle through the modes to get high?
Perhaps you are on medium and getting 1.3A
You have to short out with DMM leads , then do again till you see the light changing intensity, till you get high.