AFAIK, the Opus BT-C3100 does trickle charge Li-ion cells (as said in the conclusion of the OP), which would be a bad thing. When the batteries are full, the charger stops charging entirely and only when the voltage falls below a certain value it starts charging again, and so on.
[quote=RobertB]
[quote=congo]
It already has that ability, but you have to get at a hidden switch on the bottom of the mainboard. I cut a small hole to access it with a probe. Works fine. You can also set it for higher voltage cells that way. Also works fine.
Resistance could be better, but it does sort of work. It seems to be better on the Zanflare C4. I’ve found a ‘reasonable’ correlation between the Opus and Zanflare IR. No good at all on the Lii-500-should be improved or removed.
If you want to go through the hassle putting in a superior fan isn’t too hard.
I also use a 5A laptop power supply for mine. Overall I think it’s my best charger now, certainly the most versatile, especially when I want higher charge and discharge features. The C4 and Li-500 are much more limited there.
I think the IR accuracy depends on the unit, the care in placing the cells, AND the quality of the cells seem to affect it….a lot. Decent cells seem to have ‘reasonably’ consistent readings. As the cells become more degraded, meaning higher IR, the readings show MUCH more erratic readings and less consistency. OTOH, that shows the cells are going to hell, so it’s still useful info. 
Because I will put in an 18650 to charge and it will say for example, 90. Take the cell out and put it back in the same slot, it will read 53, take it out put it back in the same slot it will read 125, and so on. And many other have reported the same thing
[quote=flydiver]
[quote=RobertB]
I have a hole cut in mine as well, for the occasional 4.35v setting. But that flimsy little switch is likely to fail. They need a slot selection setting for storage. Yes, they need to update the fan, and that was the other thing. 5A power supply needs to be included. And you still can’t fit 4 26650’s side by side.
It’s been 2+ years. They need to update this stuff
I’ve tried cleaning both terminals on the charger and both ends of the cell. Seems to make no difference. All 60 of my lithium ion cells are inside the same room with the charger, inside the house. So they are all the same temp.
So what irks me is that no one can keep milliamps and milliamphours straight,
“charging currents to choose from including 200,300,500,700,1000,1500,2000 mAH”
“to get the exact readout of mA to see if your cells capacity is infact true to what the label says.”
both should be the opposite, good day.
I'm running the test/discharge on two 26650 protected batteries at .5A and the fan does not come on with my opus. Is that normal? I thought fan should come on when discharging.
Did the fan turn-on when plugged? It should run when plugged, then turn-off.
The fan is temperature controlled. It will only run when the factory calibration for temperature threshold is reached, and run only when the threshold is reached.
I don't know if it came on when I first plugged it in. Good to know it's temp controlled thanks. I may take the risk and let it run as long as things don't seem to get too hot and when the test cycle is finished I will make sure the fan turns on when plugged in.
Anyone know where I can get a 12v car adapter to fit the opus charger?
It uses DC 5.5x2.1mm plug, isn’t it? Maybe something like this will work:
(it indicates up to 1.5A only though, which may not be powerful enough if charging at full speed)
I noticed the BT-C3400 comes with a car charger plug and was hoping to get that one as it looks a little more sturdy.
That is the one I purchased , OPUS BT-C3100 V2.2 Charger. I use it on all rechargeable batteries. So far so good.
I purchased 10 EBL 18650 Li-ion 3.7V 3000mAh Rechargeable Batteries on Ebay for $16.00 and tested them at 2600 mah so i kept them. Then i purchased 4 LG HG2 18650 3000mAh 20A Batteries | Authentic Original Battery LGDBHG21865 on Ebay and checked them at 1800 mah 
so i’m returning them for a refund.
This charger is a big help for me, bad for Ebay, Never buy from them again.
yes it is a great charger i’ve had it for about 2 years now and it is still running strong
and for the battery problem, the place I buy all of my batteries is: https://www.imrbatteries.com/ (link is external) every cell I have ever purchased from this site was real and I trust them, this is another site in case the first one was out of stock or vise versa https://liionwholesale.com
I just bought this charger and it behaves the same way for the IR test.
HKJ says to take the lowest reading when jiggling, rotating, putting the cells a few times in and out as chargers do that. I got the SM8124A tester and confirmed a few times that the lowest IR reading from the chargers is accurate. The chargers use a different method to determine cell IR than my tester, so I add 60% more from what my tester shows and so far it always ends up at the lowest IR reading from any charger.
@klrman: Thank you for filling me in. Sounds like there’s a method but a bit of a squirrelly one. 
I have a MiBoxer C4-12 on the way so I’ll have two references. I got a great price for one on Amazon Prime Day (according to some our other members).
:+1: 
No problem. All my chargers annoyed me first too with their swinging IR readings, but I finally got the hang of it and always double check with my tester as a backup and it has always been consistent now.
Hello guys,
I just came across this deal on BT-C3100 on BG (no affiliate):
https://www.banggood.com/Opus-BT-C3100-V2_2-4Slots-LCD-Display-Smart-Intelligent-Universal-Battery-Charger-p-1183072.html
Do you think this deal is legit? (I’m considering the fact, the price is double at local shops).
BT-C3100v2.2 for $34
Thanks