Opus bt-c3100 v2.2 discharge cutoff for 18650's

Hello all,

I just picked up my first battery charger, an Opus bt-c3100 v2.2. I didn't realize there was a newer bt-c3400 v3.1 available. I have some protected Orbtronic 3400mah 18650's which protect it from discharging below 2.5 volts.
I see that the 3100 v2.2 discharges the batteries down to 2.8 volts. I've also read that discharging below 3 volts permanently increases internal resistance and reduces capacity and you should discard any 18650's that have been discharged below 3 volts. I see that the new bt-c3400 v3.1 discharges down to 3.1 volts. After plenty of searching and reading I'm not sure if I should be using the bt-3100 to discharge the 18650's. I need another charger for more slots anyway but am I actually degrading the performance of my batteries using this version of the Opus?

As far as i know li-ion capacity specification are based on an 2.8v discharge, Many CPF member have the C3100 and C3400 v2.2 and nobody seems to mind it discharging to 2.8v and quite a few people ordered the v2.2 over the v3.1 for that reason.

I cannot be sure but i think i remember Opus changed the discharge cut out to 3.1v as a lot of protection circuits are set to 2.8v and discharging to 2.8v was triggering it, causing the Opus display to show NULL (no battery inserted) when the cut out kicked in and you loose all your results.

I doubt discharging an extra 0.3v is going to reduce a cells life by much, But wait and see if smarter CPF members will disagree.

There are lots of threads on the C3100 have a read though a few.

John.

+1 with John
Most cells these days have a minimum manufacturers voltage, 2.5 or 2.8v cell/manufacturer dependent. Discharging a cell down to the opus's 2.8v ,will not damage the cell. Damage occurs when the voltage is bellow manufacturers spec and left there............If charged up straight away, any potential "damage" is minimised even when bellow the spec. In use(flashlight etc), ideally you dont want the voltage to get too low , once your close to 3v your not going to be able to get a high, maybe a medium. Most flashlights will warn(blink) or simply tell you by not letting you in higher modes. Get a feel for the light , keep an eye on the voltage and before you know it, you will be guessing the V before sitting in the charger. Most of my cells are between 3.3v and 3.8v when i sit them in the charger bays. If i know i am going to be using it next day,(like a work light ) then i top off ready to go.

Issues with the v2.2 were more around protected cells tripping iirc

So dont worry, do your required test then enjoy your fuel

:welcome:

Are you worried about longevity?

Samsung smartphones don't let Samsung phone batteries discharge lower than 3.500V ("0%"->phone turns off->phone can't be turned on again->battery taken out->has 3.550V online voltage->has 3.550V offline voltage), see my smartphone battery testing thread, i tested Samsung Galaxy Series and Samsung J Series, while they do charge them to 4.350V as the battery specification allows (3.8V nominal voltage).

Maybe this info helps.

Or gives you an idea.

Here what a distributor for Opus says about the changes:

"What does the newest version v3.1 offer over the older v2.2?
It is basically a change in the discharge for Li-ion cells. You will see the discharge for Li-ion cells terminate at 3.1V instead of 2.8V. This brings the charger in line with industry best practice for discharge. Most Li-ion cell data sheets specify 2.8V as minimum voltage for discharge. Best practice is to terminate discharge at 3.0V Because of the way this charger uses PWM for the discharge current it is better to use 3.1V.

In the past some low quality cells would trip the internal protect circuit, especially at high discharge currents. That was not so much a charger problem as it is a cell quality problem but the charger gets blamed. That situation is much improved now. The discharge and capacity measurement are now closer to industry best practice instead of just general Li-ion cell data sheet specifications. In fact the change has little affect in the measurements. The protocols for NiMH/NiCd cells are not changed."

Torchmee said:

…This brings the charger in line with industry best practice for discharge…this charger uses PWM for the discharge current…The discharge and capacity measurement are now closer to industry best practice…

Click to expand...

i didn't know that industry best practice uses a pulsating discharge current. it is true though that the MH-C9000 uses discharge pulses as discharging "current".

if that is so, then i want to have PWM discharge current too on my XTAR VP4 PLUS charger-analyzer :thumbsup:

kreisl said:

i didn't know that industry best practice uses a pulsating discharge current. it is true though that the MH-C9000 uses discharge pulses as discharging "current".

if that is so, then i want to have PWM discharge current too on my XTAR VP4 PLUS charger-analyzer :thumbsup:

Click to expand...

And do you have solid results from a well-known laboratory any proof to support your sarcastic, contrary claims?

Edit: And please Kreisler, no deleting of previous posts.

i don't understand your question tatasal. what did i claim about what?

i was quoting the previous post.

and about the MH-C9000 you can check HKJ's review, it's true.

Ok, Kreisler, let's just say it's not a claim but your sarcastic remark against "i didn't know that industry best practice uses a pulsating discharge current."

So again, (though anyone worth his intellectual salt already knows what you were really were driving at) and I quote myself: And do you have solid results from a well-known laboratory any proof to support your sarcastic, contrary (claims) remarks?

tatasal said:

Ok, Kreisler, let's just say it's not a claim but your sarcastic remark against "i didn't know that industry best practice uses a pulsating discharge current."

So again, (though anyone worth his intellectual salt already knows what you were really were driving at) and I quote myself: And do you have solid results from a well-known laboratory any proof to support your sarcastic, contrary (claims) remarks?

Click to expand...

i really really don't know what you're talking about or what you mean. seriously. i am at a loss here sorry.

( are you looking for results of discharge tests which use pulsating discharge currents in the tests? and what should these results prove? is that it what you're asking from me? )

you're misunderstanding my remark - it was a 'remark', not a 'remark against', and certainly i was not claiming anything in that post. what are you implying?

to cut your story short, i don't have data which does not disprove that pulsating discharge current does not support industry best practice results.

you've asked me a question (which doesn't compute in my salt) and i've tried hard enough to understand it and answer it.

well, i kindly suggest that we leave it like that.

other wise it is too much OT in this thread.

thanks.

Take it outside fellas!

The 3100 is a good charger. The c9000 is also regarded as a good one, but it pulse discharges while flashlights (heavy pwm excluded) don't.

What it means more than that requires diving into the dry technicalities.
As those aren't really being detailed here, the facts are as they are and there's really little disagreement.

kreisl said:

i didn't know that industry best practice uses a pulsating discharge current. it is true though that the MH-C9000 uses discharge pulses as discharging "current".

if that is so, then i want to have PWM discharge current too on my XTAR VP4 PLUS charger-analyzer :thumbsup:

Click to expand...

Seems you set the thread off the tracks for no reason. Tinderbox said nothing of the sort regarding pulsed discharge; he was commenting that the change in the discharge cutoff voltage brought it inline with Industry Standards (didn't mention which industry) and indicated the absolute value needed to be different than what is typically used because of the pulsed discharge. Implying in the end the cells will end up at the correct resting voltage compared to the alternative discharge approach.

Hmmm, I have the 3100 v 2.2 and it is discharging to 2.80v. That is with the dischcarge-test function. I sat here and watched while it happened. Is it possible I would get 3.1v using the discharge function? I doubt it, but possible.

I need some explanation why my bt-c3100 v2.2 charger keeps stopping the discharge at different cut-off voltages.
I've read on this forum, it should be 2.8V but every cell stops at a different voltage.
I've included an image to show a normal endpoint of 4 18650's discharging. (@500mA)

deadbeefAHC said:

I need some explanation why my bt-c3100 v2.2 charger keeps stopping the discharge at different cut-off voltages.
I've read on this forum, it should be 2.8V but every cell stops at a different voltage.
I've included an image to show a normal endpoint of 4 18650's discharging. (@500mA)

Click to expand...

The cutoff voltage for the v. 2.2 is 2.80v and none of those slots are there yet, so what's the issue? Since the Opus has independent channels, each cell will be doing its own thing. Maybe they're in varying states of health and the weaker ones are discharging faster? The discharge cycle will terminate at 2.80v for each and then each cell will rapidly rebound in voltage, so if you're not looking at the charger at the exact moment of termination, you'll come back and see perhaps 3.20v on the cells, but they're no longer in the discharge mode.

Chris

Chris, are you sure about the rebound of the voltages while the cells remain in the bays?
i will test this, but if I recollect all the discharges with 4 cells in the bays, the voltage remains fixed if the discharge current reaches 0'
different CELLS DIFFERENT CUTOFF VOLTAGES.

Does the discharge function always go until 2.8V? I almost think my charger is broken. its my second charger. the first one was a DOA with a defective display.
my system is, first charge 4 cells @1A, then measure internal resistance and then discharge all 4 @500mA. The finish is the picture shown.

deadbeefAHC said:

Chris, are you sure about the rebound of the voltages while the cells remain in the bays?
i will test this, but if I recollect all the discharges with 4 cells in the bays, the voltage remains fixed if the discharge current reaches 0'
different CELLS DIFFERENT CUTOFF VOLTAGES.

Does the discharge function always go until 2.8V? I almost think my charger is broken. its my second charger. the first one was a DOA with a defective dis anplay.
my system is, first charge 4 cells @1A, then measure internal resistance and then discharge all 4 @500mA. The finish is the picture shown.

Click to expand...

Yes, the cutoff voltage for 3.6v li-ions is 2.80v. The cells in the picture are still in their discharge phase. They can rebound to about ~3.30v, but that can vary depending on the cell in question.

Chris

I'm not sure my Opus BT C-3100 v2.2 is working correctly.

I discharged a protected 14500 and it only discharged to 3.48v before ending the discharge cycle. Three times it did this, ending somewhere between 3.48 and 3.6
So I tried again with a high-discharge unprotected 14500. Same results.
All tests were done at 300mA.

I just tried discharging a AA NiMH. I expected a discharge down to about 0.9v (per user manual specs), but it quit at 1.14v.

Any idea why I'm not getting full discharges?

pdirt said:

[...] Any idea why I'm not getting full discharges?

Click to expand...

How/when are you measuring the termination voltage? This must be done while it is discharging, not after it has finished (since the cell voltage quickly rebounds immediately after the discharge ends).

I find that my protected Keeppower 14500's are basically drained around 3.6v. Your charger is likely fully discharging them.