i have a 2.1 unit and the fan start to have PROBLEMS… sometimes it is hard to start, and make a lot of noise………
Xtar QC may not be all that much better, as my VP1 under charges by 0.05V as well. https://budgetlightforum.com/t/-/26570#comment-582820
Still, I’m quite happy with what the Opus can do for the price and although I’m not experiencing this issue with my unit, I’m very encouraged to see the company engineer actually provide detailed info, like what trace to cut on the board to correct the issue. I’ve never seen that type of support from any other manufacturer. Frankly, if I could exchange both my I4 and VP1 for a new Opus, even with the under charging issue, I would!
KuoH
Perhaps in this thread, post # 319: $37.99 for Opus BT-C3100 V2.1 with OP3100 ( clearance) & $38.99 for Opus2.2 without using the coupon @GearBest
IMO. any fan this small in any device is going to have problems unless they use a REALLY high end fan with great bearings. I’d say there is about no chance of that. Learn how to take it out, open it up, and put some high quality oil in once in awhile.
I have to do that routinely on the little crap fan in my hobby charger (Accucell-6). Good charger, lame fan. I expect the Opus to be the same.
Best lube I’ve found is high end silicone grease for diving, though any quality thin oil will work. Just a little……
or just buy a cheap laptop cooler & usb adapter.
I bought one for $5 & I put Opus on top of it while charging. 1000% more effective than Opus’s tiny little fan. In fact, I rarely see it working anymore because Opus doesn’t think it’s necessary.
Thanks for the quality review, off to buy one now 
Can you please show your solution on the pictures, llink to the cooler,....?
Here you go.
Bought the cooler 6 months ago from ebay for my wifi router, but changed my mind. The one shown by the seller was black, and he sent me the ugly green one.
I actually don’t use this cooler anymore because it takes too much space on my desk. So, I use a cheap 120mm fan (around $2, 35-40 CFM) with a metal grill and an old 12v adapter I found somewhere. I don’t even remember where I got the adapter from. Perhaps from old router, modem, portable speaker or something.
It takes a little space, and it works better because the fan blows unobstructed. I use some plastic spacers (from old motherboard feet) to lift it up a bit from the table.
Serville, thanks. So if I understand correctly additional fan is running all the time powerd by 12V and is not controled by the Opus. I'm guessing it is only needed when doing discarges.
yes the fan is powered separately by 12v adapter, and is always running.
I use a small power extension with on/off switch, where the Opus adapter & 12v adapter are plugged into.
I just use the switch to power on both the opus charger & fan instantly.
Charging or discharging, they will be powered on/off together. I like it that way because I’m known for my laziness 
It’s a cheap chinese fan with low RPM (1500-2000 rpm max, 40 CFM max), so it’s very quiet.
I don’t see a need for Opus internal fan anymore, so I pulled off the fan cable inside, reversed the 120mm fan to suck hot air from the bottom. No more whining now….so annoying.
Make sure the laptop cooler is blowing up. The OPUS fan blows up and out the back, so if the laptop cooler is blowing down, they will be fighting each other and you will end up with LESS airflow.
Thanks for the laptop fan idea.
I have received my unit a few days ago.
My only complaint was its high pitched fan noise, like a plane taking off.
I have used my idle laptop fan with it, and now there is no annoying noise from the unit.
update: It is better to have the fan over the unit, instead having it under.
There is no vents under the unit, but can cool better over the unit.
There is some vents under the batteries that air can flow into the unit.
I think the high-pitch noise is because the small fan has very short fan blades. To improve CFM /increase airflow, it has to work at high RPM. The problem is, it also has very narrow wind passage, so everytime it increases its RPM, the noise frequency becomes higher & higher creating high-pitched sound. When you use additional cooler, the internal temperature inside the charger is improved, hence it suppreses Opus from increasing its own internal fan’s RPM.
The fan in my Opus lasted 2 days and it went totally wonkers. It appears that someone put grease in the bushing (which shouldn’t be necessary for genuine oil-lite bushings) but they completely missed the shaft.
FWIW; it is a 12V fan; You can remove the fan blade if you remove the pink o-ring that holds it in. I used a safety pin to wedge it out of its groove. The magnet forces will hold the fan in place. Although this is standard practice, the o-ring doesn’t serve a real purpose in this fan.
I used a pin as an oil dropper and used a very light bicycle chain oil (similar to sewing machine oil) to lubricate both the shaft and the bushing while they were apart.
One of the problems is that the fan blade is simply not balanced to any degree. Once it is placed in the Opus housing, the vibration noise is amplified 10 fold even with the dabs of Fijik. But this isn’t the worst of it. If that was all, it would workable.
When I re-assembled the unit, I also left the beauty cover off as this just made the noise worse. I also left the o-ring and sticker off so I can maintain the bushing with oil without disassembly: put oil in the groove and push the fan blade into the bushing to get lubrication in there.
When the blade really goes nuts, the wobble from hell, it sounds like a baby bird getting mauled. There is no way I would let this charger run without being nearby. Sad, as this is the most I’ve spent on a charger in 6 years of flash-a-holism.
In short, this unit has juts made my “don’t bother” list. Yes its nice to characterize cells; yes it is nice since it does NiMh and NiCd; having an internal V-selector is kind of odd; Every bay seems to have a mind of its own on accuracy; and yes, mine had the J1 jumper bridged, and slot 1 is dead-on. Others are still high.
one can only hope XTAR will come up with unit like this… it will likely be a winner over this “thing”.
Good Day fyesilova, 
If You look carefully, You will see that there ARE vents under the unit...
Best Regards,
George
Yes, You are right, but they are not visible if you look at directly (90 degree)
I think it gets cooler from top.
While charging at 1000mA at 4 bays and laptop fan is under the unit. it has started to run the tiny fan.
When I put it on top, the tiny fan has stopped.
That is because the temp sensors are in the case right next to the positive terminal. If you put the fan on top, you are cooling the sensors, but not the underlying thermal problem. You really want to get airflow over the entire PCB inside.
i got this charger from the GB but i have only one problem with it , it is terminating charging at low voltage about 4.15 i don’t know why and it reads about .05 more than the actual reading with My DMM so is there is any solution for this ?
Yes, it is documented in the group buy thread that you need to remove solder blob "J1" for units reading 0.05v too high (i.e. terminating charge 0.05v too low). I did this mod on mine. I'll see if I can find the post with pics and link it back here.
EDIT - here we go, that wasn't so hard to find: https://budgetlightforum.com/t/-/28487?page=6#comment-666674 . Start at post#319 and read down a few posts (esp. pics in posts #325).
-Garry
Thanks for the detailed review. I recently got the “Powerfocus” version from Banggood and have been impressed with its features.
Apparently there are similar devices that have a USB output to charge smartphones/battery packs, etc…I haven’t been able to figure out if the same features (refresh, test, etc…) are available on that port though. Anyone know of devices that would do that? It seems like a “connector” problem ?