Welcome to BLF ” Dazed and Confused ” 
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I would not leave it unattended while charging. Does it emit any electrical smells ?
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I had to bend the movable negative contacts towards the positive contacts to get any contact on big batteries like a 26650.
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Here is a good tear-down thread to look at. Review: Opus BT-C3100 V2.1 (with teardown and video)
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If you keep hearing strange noises when the fan is off, you probably should not use it until determining what that is. 
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Please come back here and keep asking, guys with a lot of experience are in and out here so try to give them time to notice this thread.
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You did not make a bad choice, the Opus BT-C3100 v2.2 is a good charger, I use mine a lot with no problems.
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I had some AA NiMh that tested between 0 and 5 mAh each. I ran a full refresh cycle on each battery twice. Then they tested at 500 to 600 mAh. Thats like new for some brands. Totally worth the time.
To lube, the fan needs to be taken out, a sticker on the back removed, THEN you can access the bearing. FWIW pretty much all computer fans are similar and can be lubed that way.
Clean up the area well to get the lube off, cut a new disk of duct tape or similar and seal it again. Put a sticker (I use easily removed painters tape) on the outside and date it.
I used the same tape sticker process to track my batteries, until I got one of those labelers. It’s a good idea to be able to track their status over time.
I also have an Opus BT-C3100 charger (version 2.0). I’ve had it for years and never had an issue with the charger or the fan. The fan has been quiet since I first got it and I’ve never lubed it.
I also hear a slight fast ticking sound that you are concerned about Dazed and Confused. I believe that is from the pulse charging and shouldn’t be a concern. But maybe you’re hearing something different? Either way, just monitor it for awhile until you feel comfortable that it is working properly.
Be very careful with silicone spray lubes. Some of them use solvent carriers that act as plastic glue, similar to the type of solvent glues used in plastic model assembly. I inadvertently ruined a plastic calculating device that used rotating rings marked in increments by not reading the directions on the spray can and ended up gluing the rings solid.
I've had a Opus 3100 2.2 for a few years. It's always worked well. I stand it on end when in use, fan end up, to let natural convection aid with heat removal.
slmjim
Be aware that the thermal protection may fail so don't leave it unattended :(
https://budgetlightforum.com/t/-/61627
The BT-C3100 has temperature sensors, but the software ignores them during the charge cycle. At least that’s what I observed.
Thanks everyone. I’ll leave the fan alone for now, and it sounds like other people have heard the very faint fast ticking, which is reassuring. I think I’m good to go! I’ve chucked a bunch of AAAs on refresh, and I’ll see what happens.
I do plan to use it in a car overnight when camping too, and picked the Opus because it supposedly had protection from overheating. It seems from the comment above like it is designed to do that, but in practice maybe not?
I’ve never seen it shut off while charging an 18650 because of heat. And I allowed one to go as high as 190F (88C) just to confirm. So yea. Apparently there is a software bug.
I’ve charged at 1000 milliamps in all 4 slots many, many times and never had an issue with heat. The fan does a good job keeping the temps down.
I have no doubt NeutralFan, but that’s because your batteries are good. If you pop in a battery with very high IR, no fan can stop the thermal runaway. Apparently they didn’t test that software feature, and it has a bug.
Hmm, how does it (or should it) sense the cell’s temperature? Conduction through the springy-thing?
I assumed “thermal protection” was just for the innards, not the cell itself.
You can see the cell temp sensors at the top of this pic.
The doodads wired to “TH1” through “TH4”?
Huh… interesting.
THermistors, yea.
Some poor guys have been hooking all those up, and they aren’t even fully functional.
They don’t look to have any actual physical contact with the cells, though.
Just like drivers with thermistors on the driver, vs on the LED’s board. Takes a (long) while for the driver to start heating up when the LED itself could be blue in the face and screaming for help.
The cell touches the charger in this area. And inside it is the sensor. There is no way that paper thin layer of plastic has enough R value to stop 190F from cooking the temperature sensor.
The BT-C3100 is basically the same charger as the BT-C3400. For reference, the quote below is from the BT-C3400 manual (which is more concisely and clearly written than the BT-C3100 manual):
https://images-na.ssl-images-amazon.com/images/I/51TCfcbvBaL.pdf
I do not have a method to determine if the charger always behaves this way.
Yes, the "Discharge - Refresh" mode has increased the capacity for some of my older NiMH batteries. I have never used this mode for Li-ion batteries though.
I have the BT-C2400 (aka BT-C2000) and BT-C3400 (aka BT-C3100) chargers from OPUS.
The BT-C2400 (aka BT-C2000) only supports NiMH and NiCd batteries, but I prefer it for these types of batteries because during the "Discharge - Refresh" mode, the discharge current is set to one-half of the charge current (but this may not make any appreciable difference besides making the process faster while still using a low discharge current for better conditioning and a higher charge current for more consistent full-charge termination detection). With the BT-C3400 (aka BT-C3100) the same current is used for both discharging and charging in this mode. I also prefer that the BT-C2400 (aka BT-C2000) does not have an internal cooling fan and does not use sliding rail battery contacts but I do understand why these are required for the BT-C3400 (aka BT-C3100) to charge Li-ion batteries. Also, the more secure and tight snap-in battery contacts of the BT-C2400 (aka BT-C2000) seem to provide a more consistent battery internal resistance measurement during the "Quick Test" mode.
If you want to spend a very long time conditioning and forming NiMH batteries at very low current rates check out the PowerEx MH-C9000 charger (that only supports NiMH and NiCd batteries) and read the section concerning "Break-In Mode (IEC capacity analysis)" in the instruction manual below:
https://powerex.helpdocs.com/manuals/user-manual-mh-c9000-wizardone-charger
If the electrical utility power provided to your residence is not 100% stable, be aware that if the BT-C3400 (aka BT-C3100) charger experiences a power reset due to a utility power glitch while in the "Discharge - Refresh" mode or any other mode, it will resume in "CHARGE" mode at it's default current of 500 mA, no matter which mode you were previously using. This happens to me occasionally.
I am not aware of any analyzing charger that can resume operation at the same point in the same mode after a power reset, so the above statement is not a complaint about the BT-C3400 (aka BT-C3100) specifically, but is only a warning concerning analyzing chargers in general.
Just a comment on internal resistance measurement with the slide contacts on the BT-C3100 (and presumably other similar chargers). I find that wriggling the cell a bit to make a clean contact and then maintaining firm finger pressure on the slide while the measurement is taken will make the readings much more consistent. Because the reading is quick, it is normal to do such testing one cell at a time.
On brand new authentic cells the readings are close to those reported by HKJ, who is using much better equipment.