Opus BT-C3100 V2.2 4 Slot Battery Charger

Overall this a good upgrade on my VC4 charger, nice features for discharging cells but a puzzling quick test feature. Obviously this is more of a feature walk-through rather than a review, I am really only interested in the discharge feature. Next up is the IDST C4 charger, it looks awesome.

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  • That quick test feature would be nice if it actually produced repeatable results. One thing though is that the contact resistance from the terminals can effect the results on that as well, none of those batteries looked like they were seating in there very well, you could wiggle them around quiet a bit. Looks like a decent charger though, might get one to replace my VC2 Plus as I need more banks, but there seems to be a lot of these multibay chargers coming out now.

  • IR test is confirmed garbage on these(and pretty much any other tester) A more reliable indicator of battery health is Round Trip Efficiency, that is, how much you get out divided by how much you put in. Eg: cell took 2000mah charge and you got 1800mah discharge, so 1800/2000 = 0.9 = 90% RTE. Lower IR = higher efficiency. With this unit and very healthy cells, you can get higher than 100% RTE, see my other comment about the problem this unit has with reported discharge capacity.

  • I mentioned this on another vid of yours, the reported discharge capacity on these is ~10-15% high. You can see this for yourself by testing a good new low IR cell, the discharge capacity will be higher than the charge capacity, I've had good Panasonic cells report 200-300mah more out than in! Which is ofcourse, impossible. Also, discharging more than 3A at a time(ie, 4 cells at 1A or 2 cells at 2A) the discharge will be interrupted so the unit can cool down, greatly extending the discharge time. Some people have modified these with bigger fans. There's even 3D files out there for a replacement case bottom that takes a pc fan, I think it's on thingiverse somewhere. The good news is these units are consistent, consistently wrong, but still consistent, so for comparative purposes it's still ok, just don't compare capacities with those from any other unit.

  • I got a btc-3100 v2.2 maybe a year ago now. If you do a test cycle on 4x Li-Ion batteries at 500ma you'll get the fan to come on and you'll wish you hadn't. I found there was another level of thermal protection that would cycle the discharge on and off. I found a replacement base that accepts a 80x15mm fan on thingiverse and 3D printed it. Muuuuuch quieter. (Important because I am testing cells of unknown quality so I only test when I'm in the room.)

  • I predict that the “5500mAh” NiMH cell will not even hold 550mAh (10% of the claimed capacity). After all, if you are going to claim an outrageous capacity, why even bother making a AA cell with a respectable capacity (2000mAh+ is respectable for a good quality low self discharge AA NiMH); go big or go home, etc…

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