posted by Rantanplan on 05/17/2010
Involvement:Expert (understands the inner workings) - Ownership:1 day to 1 week
+ Looks pretty good in its dark grey finish. The design reminds me personaly a little bit of some lights from Jetbeam.
+ interior construction: LED and driver are placed in a really big pill made of brass which is screwed into the head of the light. Because of the size and high number of threads the heat transfer between pill and body of the light should be pretty good ... at least a lot better than in other XY-fire lights.
+ build quality is o.k. There are some edges which are little bit sharp and the lettering on the side is a bit off, but´s fine overall.
+ beam quality: nice and even hotspot. There are some artifacts in the beam right outside the hotspot, but I can live with that.
- quality in general: I got my light, tested it and got 2.2 amps measured at the tailcap. Later on with different 18650s I got only 1.8 amps. Well, I thought that maybe the second set (which was charged at 80% too) had a higher internal resistance. Some minutes later I can only get 1.2 amps no matter what (fine) batteries I use ... even if I directly contact the contacts at the pill with a bench power supply @ 8.4 volts. Compared to a Jetbeam M1X (gen 1), which has 500 lumen at max, my Trustfire ST-50 is clearly less bright now. I guess the driver went south ;)
- length of the battery tube: Trustfire should have made it about 3-5 mm longer, because with the usual protected 18650 (as the batteries supplied with the light) all spring are compressed to the end the batteries are on the verge to get crushed.
There are reports of other people with failing lights. Measuring over 5 amps at the tailcap can only be explained by a broken driver, so that the LED is in direct drive.
Lets do the math: A SST-50 has a nominal operating current of 5 amps, which the ST-50 should use due to info Trustfire gives us. Vf of the LED is probably around 3.6 volts, so at full power a SST-50 will need 3.6V x 5A = 18W. 18 watts of power at the LED considering a buck driver with 85% efficiency results in roughly 21W of power delivered by the batteries. Battery voltage goes down with higher loads, which means that even a good protected 18650 will sag down to 3.7V almost immediately. 21 watts from two 18650 (=7,4V) results in a bit more than 3 amps battery current. Considering (not included) losses due to resistance in all the parts of the light, it is safe to say that battery current must be above 3 amps before you can assume a fully powered SST-50 light.
The Trustfire ST-50 has a nice design and almost all the features for being a really good light worth its price. But I can´t recommend it because of the quality issues. My light doesn´t seems to be the only faulty one, check the other feedback here ...
My bottomline: I got a nice SST-50 host. I will replace the crappy driver with something better and get a decent light sometime in the future.
If your fine with the possible need to send the light back or are able to use it for a modding job, then get this light ... otherwise ... you know ;)
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