So I’m measuring some battery draw on a couple of 1s li-ion lights figuring it should be a decent approximation of forward current… except it doesn’t make sense. The two lights in question are both Sofirn, a IF25a 4000K and two Sc31 Pro 5000k. Both Sc31Pro lights are pulling 1.88A off the battery on “turbo” after a factory reset of the Anduril while the IF25a is pulling just above 2 amps on turbo after the factory reset. This is using the Sofirn branded 21700 and 18650 cells as well as a Samsung INR 18650 30Q.
Now, correct me if I’m wrong but wouldn’t this mean the Sc31 Pro lights are only driving the emitter at around 1.8 amps? Also, how is the IF25a wired? This doesn’t make a ton of sense to me. For example if the SC31 Pro is rated at 2000 lumens it would need 6 amps forward current to reach that number (according to this test by djozz ). I’m using a Klein DMM on the 10A setting so while I’m losing some resolution it should still be grossly accurate. The batteries are all above 4.1vdc resting and the lights are at room temp.
Output seems appropriate for the ratings so I’m doubting my logic that battery current is roughly comparable to emitter current in a ~3v LED in a 1s light.
Basically, the reason I am doing this is to determine if I can safely swap an SST-20 or LH351D in place of the SST-40 (on an appropriate board of course). If its really driving the LED to 6A for the 2000 lumen rating then the SST-20 shouldn’t last long. THe LH351D might do better but I don’t know how long.
Interestingly, after manually configuring ramping ceiling to the highest level (1 click) the battery draw increased to 3.3A. This is still far short of 6A required for 2000 lumens per the djozz test, though it does make some sense since the factory default is supposed to be 120/150 for ceiling.
Does the brightness seem dimmer when testing with a meter? I tend to get a very low reading with the leads that came with my meter and get much more accurate numbers with 6” 10awg wire jumpers.
Hard to say, as this is a e-switch on the side I was using my 6/yo son to hold the leads while I manipulated modes… So in others words a real possibility! I have some left over 12awg strands (not as good as solid for this) from a relay harness build so maybe I’ll try again soon.
Yes, if you’re measuring the current by putting the leads of a standard DMM in series with the circuit the resistance added by the leads and the DMM will limit the current that can flow in that circuit.
And it’s not linear error, the more current you try and pass through the circuit (ie. the brighter you try and run the light) the more innacurate it will be.
As an example, with very non-factual numbers, if low mode on your light is 100ohms, high mode 20 with turbo 5, and you add 5ohms to the circuit with your DMM then low mode will be reduced to just over 95% (100/105) of it’s current, high mode to 80% (20/25) and turbo to 50% (5/10). So the brighter you go the more restricted you become.
You can mitigate this a bit by using lower resistance (thicker) cables and the higher rated input on the DMM, if there is one, but it still won’t be accurate. You need a clamp meter so the only resistance added to the circuit comes from a cable, which will be much lower than DMM.
What Marc E said, and to illustrate : the Klein tools mm600 reviewed by HKJ has 20mΩ for each probes and 50mΩ on the 10A setting, for a total of 90mΩ (without counting contacts resistance), which is pretty low for a DMM (due to the relatively low resistance of the probes).
Play on the cursors on my DD estimation tool and you’ll see the effect of added resistance
(Put ~25m for a 30Q)
You’ll see that to get only 6A with a SST40, the flashlight circuit needs to have a relatively high resistance, it should be fine with a SST-20 or LH351D.