Opus BT-C3100 charging voltage

[wight]

@Ouchyfoot

If your going to toss that cell, could you remove the protection circuit and see what happens? Just curious.

If that Nitecore cell is protected and didn’t disconnect at 4.45v, over-voltage protection is pretty much non-existent. Looks protected though, doesn’t it?

[dazed1]

What does Ri means?

[Helios1 (Helios-)]

Internal Resistance

[dazed1]

Shouldn’t it be IR then?

[Adoby]

That would be Infra Red.

By convention resistance is R. You add a subscripted suffix to specify what resistance. On this forum you have to use the advanced editor to write subscripted. You can select editor in your profile settings.

It should have been: R_i or even R_internal or R_battery

You can do the same with voltage and current

U_ab

I_a

[dazed1]

Thank you.

[FrickelFreak]

As promised I measured R_i (<- now with correct subscription!!! Tanks Adoby ): 134mΩ, that's not really good, but not too bad for a protected cell either. By far no reason for me to toss the battery (Capacity is still good as well). Even 1.5A should not be a problem since Nitecore specifies 2A as max. charge current for this cell.

I guess the charger is just a little over-eager at pumping current through the cell.

For me this means that I'll monitor the voltage when charging a new cell and select current accordingly. (The monitoring voltage part is what the charger should do on its own actually, but since it's the Dreamcharger, I guess it's dreaming a little bit too much )

@HKJ

@FrickelFreak

Thanks for that! So I guess my charger is not defective and the high voltage is indeed normal. But the used cell (Nitecore NL186) is not that old and should be ok. I did not measure Ri though, I will do that. Maybe the PCB has a high resistance… But would you say this is tolerable and the cells don’t suffer too much or should we select the current so that the voltage stays below, lets say 4.3V all the time?

The high voltage will only happen when the cell has a very high Ri and you use to high charge current. It will not happen with a good 18650 battery, except if the charger is faulty.

Definitely select a lower current!

I'm still not sure if I got a faulty unit though, or if it's just poor engineering and any other BT-C3100 would act the same way as mine.

Maybe some of you guys could check the voltage on your chargers as well. (It's really simple, just clamp DMM test leads between battery and the charger contacts and watch how high the voltage will go)

I think this would be interesting for everyone who uses this charger, as there is no indication of the actual voltage during the charge process, so you wouldn't even notice if the charger slowly damages your cells through high voltage!

@wight

If that Nitecore cell is protected and didn’t disconnect at 4.45v, over-voltage protection is pretty much non-existent. Looks protected though, doesn’t it?

That's what I was thinking too!

Over current protection is working though (I already "tested" that ). Maybe it doesn't have over-voltage protection, or it isn't fast enough to react to the pulsed voltage, or it always resets immediately when the voltage drops again, nobody knows...

btw.: HKJ, what would you consider a "good" cell in terms of internal Resistance? I looked at some figures on your webpage and 130mΩ is on the high side, but still within the average variance...

Thanks!

FF

[HKJ]

@FrickelFreak

I think this would be interesting for everyone who uses this charger, as there is no indication of the actual voltage during the charge process, so you wouldn't even notice if the charger slowly damages your cells through high voltage!

@wight

If that Nitecore cell is protected and didn’t disconnect at 4.45v, over-voltage protection is pretty much non-existent. Looks protected though, doesn’t it?

Thinking a bit more about it, the problem may be that the over charge protection in the NiteCore disconnects briefly. That would explain why the voltage is that high.

The reason for that disconnect would be a high Ri and a very sensitive over charge protection in the battery.

@FrickelFreak

btw.: HKJ, what would you consider a “good” cell in terms of internal Resistance? I looked at some figures on your webpage and 130mΩ is on the high side, but still within the average variance…

Generally I do not use Ri and do not really have a good idea when a battery is dead. There is also the problem that Ri measured with DC will vary with method.

When I tested the V1 of the charger I got about 50mOhm for a fairly fresh cell.

[FrickelFreak]

Wow, you're a fast one!

@HKJ

Thinking a bit more about it, the problem may be that the over charge protection in the NiteCore disconnects briefly. That would explain why the voltage is that high.

The reason for that disconnect would be a high Ri and a very sensitive over charge protection in the battery.

That's an interesting possibility! It would mean that the battery itself would'nt even see the high voltage, right?

But to confirm this, tests involving oscilloscopes comparing voltages at both ends of the protection circuit would be necessary and that's a little overkill for me.

I'll just keep using the charger, keep a close eye on it and keep in mind that it sometimes may be a little "dreamy".

Thanks anyway, things are much clearer for me now and I know how to deal with it!

[HKJ]

@FrickelFreak

That’s an interesting possibility! It would mean that the battery itself would’nt even see the high voltage, right?

Correct.

I have seen it a few times before, here is an old example:

Here it happens at the end of charge and not during the charge, but look at the red curve how it goes above 4.5 volt.

[FrickelFreak]

Yeah, that must be it! You can see the voltage jumping to 4.5V exactly after it reaches 4.25V and the protection kicks in.

[deckart]

I have been thinking about buying some nitecore batteries.
When you take yours apart, can you tell what factory made the base cells ?
Thx.

and regarding these disturbing dreamcharger behaviors,
do other chargers , like i4 , do these odd things.
I bought a dreamcharger but it has not arrived.
I knew I would regret it.

[FrickelFreak]

[quote=deckart] I have been thinking about buying some note ore batteries. When you take yours apart, can you tell what factory made the base cells ? Thx. [/quote]

Sure, but that won't be anytime soon as the battery is still good and should still be usable for quite some time.

@deckart

and regarding these disturbing dreamcharger behaviors,

do other chargers , like i4 , do these odd things.

I bought a dreamcharger but it has not arrived.

I knew I would regret it.

I don't know about other chargers, but I would buy the BT-C3100 again. You have to keep in mind that it is a low priced device considering all its functions. You could expect it to master all of it's features perfectly if it was double or even triple the price.

I'm sure Opus could have made it to charge with true constant current, with realtime voltage monitoring, measure the charge capacity correctly, give us a higher quality/stronger PSU, etc., but then they wouldn't be able to sell it for this killer price.

The i4 propably doesn't do these odd things, but it can only charge with 4x375mA, this is ridiculous and it takes ages for a decent 18650 to charge. Also it cannot measure discharge capacity, which is a very useful feature and the opus does this pretty accurately.

After all I still think value for money is okay.

[deckart]

I am not trying to argue.
It’s ok for the money.
But faults keep turning up and most of us
have not received ours yet.
The higher voltage could ruin our batteries
and make them unsafe.
And then what is next ??
It’s an opus nightmare. !!

[dazed1]

I think the situation with overcharge is because of the bad cell, but i could be wrong.

[Ejected_Filament]

@deckart

I am not trying to argue.
It’s ok for the money.
But faults keep turning up and most of us
have not received ours yet.
The higher voltage could ruin our batteries
and make them unsafe.
And then what is next ??
It’s an opus nightmare. !!

From what I understand the higher voltage is not reaching the battery, its a quirk caused by the protection circuits on batteries. When the battery reaches 4.25v, the circuit trips creating high resistance. The charger peaks voltage to try to ‘crack’ it, but cant as its the protection circuit braking the circuit. Maybe the battery itself has high resistance too, so that is likely not helping the situation getting to 4.25 in the first place?? Thats a guess, I dont know. And 4.25 v is pretty much within the specs of most chargers with 4.2v + or - .05v

Based on my comprehension of the statements by HKJ, there isnt an issue involving the higher voltage readings. They are as expected.

Better PSU, and the readings of input charge mah is corrected.

V2 took care of some other stuff.

In the end, for $39 youve got a decent charger on its way to you. No need for regrets.

[kloppholz]

I’ve tested with an older protected 16340 that I had. Otherwise I’ve only new KP 14500 that I would not risk for a test.
The voltage dropped from 4.14V to 3.1 and within a minute back to 4.14V.
I took the cell out and measured with a DMM: 4.54V (hold the connection for 20 seconds). The voltage didn’t went down.
If the voltage cannot reach the battery, would be the protection circuit store “so much” energy?
No problems with unprotected cells.
.
My i2 charges the same cell to 4.19V (DMM reading after finishing charging).

[HKJ]

@kloppholz

I’ve tested with an older protected 16340 that I had. Otherwise I’ve only new KP 14500 that I would not risk for a test. The voltage dropped from 4.14V to 3.1 and within a minute back to 4.14V. I took the cell out and measured with a DMM: 4.54V (hold the connection for 20 seconds). The voltage didn’t went down. If the voltage cannot reach the battery, would be the protection circuit store “so much” energy? No problems with unprotected cells. . My i2 charges the same cell to 4.19V (DMM reading after finishing charging).

If it was the battery you measured to 4.54V, it is time to replace the battery in the DMM.