A series of beginner 18350 questions

[westegg]

If this is inappropriate because there are existing guides, please don't hesitate to point this out to me.

By way of background, I have never really bothered with rechargeables in the past. I tend to go on trips where space is a premium and it's much easier to source common sized primaries when I go than lug around a charger. I have now bought an Okluma and some AW 18350s 3.7v 800mah with an Xtar VP2 charger. I have some questions:

1: The Okluma runs non-protected cells - why is this? What would happen if I ran a protected cell in it?

2: When putting a new cell in the charger it initially read 3.75v and the voltage started going up from there whilst the charger told me it was not charged fully. Is this safe? Do I just trust the charger to do its job?

3: Charging at 0.25a or 0.5a - I assume 0.25a takes longer but leads to better battery life?

4: I over discharged one to 2.8v. It seems to be fine but is it dangerous?

5: Storage - the knowledge seems to be store full or partially charged. Which is best?

6: The Okluma has a low voltage warning - it flashes then drops down to a lower current/brightness. Am I ok running the cell on the lower setting or should I knock it off and recharge asap (see question 4 for what happened when I carried on running it)?

Thank you.

 

[vicv]

1: a protected cell may not fit but otherwise no problem
2: the cell came with about 30% charge. The charger is charging it and will continue to do so until it's at 4.2V. Then it'll gradually reduce current until it's full. So your charger is acting properly. When it's done check the battery with a DMM and make sure it's not above 4.2v when done and it's fine
3: correct
4: it should be fine but try not to do this too often
5: storing at ~3.8V is better for the cell long term but keeping them fully charged is worth it in my opinion as they're cheap and the whole point of having more than one cell is for them to be ready
6: when the low voltage warning starts definitely charge as soon as possible. That's what it's for

 

[westegg]

2: the cell came with about 30% charge. The charger is charging it and will continue to do so until it's at 4.2V. Then it'll gradually reduce current until it's full. So your charger is acting properly. When it's done check the battery with a DMM and make sure it's not above 4.2v when done and it's fine

Thank you. A quick follow up question - why is the cell labelled as 3.7v if it charges to 4.2v?

 

[Timothybil]

<quote>4: I over discharged one to 2.8v. It seems to be fine but is it dangerous?</quote>
2.8v is lower than is recommended for longer cell life. It is approaching the area where actual physical damage can be done to the cell. Most protected cells cut out at 2.5v, anything lower than that will probably result in irreversible changes inside the cell that can have nasty results. If you are going to use unprotected cells, you really need a DMM to check voltages on a regular basis. As others have recommended, learn your light and its behavior so that you know when you are approaching the danger zone.

 

[HKJ]

I have written a couple of articles about LiIon batteries answering some of the questions.

Here is a list: http://www.lygte-info.dk/info/indexArticles UK.html

Some of them may contain more information that you want now.

A few short answers:
2) For best lifetime LiIon cells are always delivered partial charged. LiIon batteries has an average voltage of 3.6 to 3.7 volt, the maximum is 4.2V, minimum depends on
actual cell.

3) The lifetime of batteries is usual rated at 0.2C (1/5 of rated current) charge current and is around 300-500 times. Going significantly above that charge current can reduce the cell life.

4) 2.8V is below minimum voltage for some cells, but it not anywhere near dangerous (See article).

5) There is a reason batteries are delivered partial charged. Keeping cells cool and partial charged gives the longest life.

 

[vicv]

I have written a couple of articles about LiIon batteries answering some of the questions.

Here is a list: http://www.lygte-info.dk/info/indexArticles UK.html

Some of them may contain more information that you want now.

A few short answers:
2) For best lifetime LiIon cells are always delivered partial charged. LiIon batteries has an average voltage of 3.6 to 3.7 volt, the maximum is 4.2V, minimum depends on
actual cell.

3) The lifetime of batteries is usual rated at 0.2C (1/5 of rated current) charge current and is around 300-500 times. Going significantly above that charge current can reduce the cell life.

4) 2.8V is below minimum voltage for some cells, but it not anywhere near dangerous (See article).

5) There is a reason batteries are delivered partial charged. Keeping cells cool and partial charged gives the longest life.

I believe he means 2.8v open circuit which is quite low. He has no way of measuring under load voltage unless he meant the factory low voltage driver setting of 2.8V then that's no problem but should be charged asap. If that's the case the cell should be reading around 3.2V or so. Dead but not particularly dangerous for the cell
To the op: the cell says 3.7V because that is the average voltage of the cell under load throughout its discharge but full charge is 4.2V. Hjk has some excellent articles on his site and I highly recommend spending a few hours on there getting up to speed on LI ion knowledge. It's a great resource. Also look at the stickies at the top of this section of the forum

 

[vicv]

I have written a couple of articles about LiIon batteries answering some of the questions.

Here is a list: http://www.lygte-info.dk/info/indexArticles UK.html

Some of them may contain more information that you want now.

A few short answers:
2) For best lifetime LiIon cells are always delivered partial charged. LiIon batteries has an average voltage of 3.6 to 3.7 volt, the maximum is 4.2V, minimum depends on
actual cell.

3) The lifetime of batteries is usual rated at 0.2C (1/5 of rated current) charge current and is around 300-500 times. Going significantly above that charge current can reduce the cell life.

4) 2.8V is below minimum voltage for some cells, but it not anywhere near dangerous (See article).

5) There is a reason batteries are delivered partial charged. Keeping cells cool and partial charged gives the longest life.

I believe he means 2.8v open circuit which is quite low. He has no way of measuring under load voltage unless he meant the factory low voltage driver setting of 2.8V then that's no problem but should be charged asap. If that's the case the cell should be reading around 3.2V or so. Dead but not particularly dangerous for the cell
To the op: the cell says 3.7V because that is the average voltage of the cell under load throughout its discharge but full charge is 4.2V. Hjk has some excellent articles on his site and I highly recommend spending a few hours on there getting up to speed on LI ion knowledge. It's a great resource. Also look at the stickies at the top of this section of the forum

 

[HKJ]

I believe he means 2.8v open circuit which is quite low.

I assumed unloaded. It is not anywhere near dangerous levels.

 

[ShineOnYouCrazyDiamond]

To the op: the cell says 3.7V because that is the average voltage of the cell under load throughout its discharge but full charge is 4.2V. Hjk has some excellent articles on his site and I highly recommend spending a few hours on there getting up to speed on LI ion knowledge. It's a great resource. Also look at the stickies at the top of this section of the forum

I just wanted to jump in here quickly to correct the above statement on the 3.7v markings. It's not that the cell is 3.7v under load on average - that doesn't really have anything to do with it.

3.7 volts is what is called the "nominal" voltage of the cell. It's not fully charged and it's not fully depleted, it's right in the middle. If you look at the cell as being usable in the range from 3.2 volts LVC to 4.2 volts fully charged - the middle spot is 3.7 volts.

The interesting case for us flashlight users is that we generally can't use the full capacity of a LiIon cell in a flashlight. This is because most circuits designed for LiIon cell (most specifically single cell lights) are buck converters and they will regulate down to about 3.4 volts (under load) and then run mostly direct drive where you see the LED slowly dim.

 

[Thetasigma]

1.IMR cells are recommended as protected ICRs don't do well with high current. Protected cells may also not fit due to the added length of the protection circuit and button top. A protected cell may work if it fits, but it won't do well at the high current levels.

2. 2.5V is usually the threshold below which permanent damage occurs. Li-Ion cells usually are fully charged at 4.2 volts, and mostly discharged at 3.2V. The nominal rating is 3.7V, and is just the middle of the cell's voltage curve.

4. No damage should have been done, but it may decrease the overall life of the cell discharging it so low, regularly.

5. Long term, partial is supposed to be better. Personally I keep mine fully charged since Li-Ion have a limited shelf-life anyway, and they all get used at some point.

6. The light can be used for a little while at the lower modes, but it serves as a reminder to change out the cell as soon as possible. Low voltage warnings are usually at 3V.

 

[nfetterly]

Regarded "protected" vs "non-protected" vs IMR (non-protected).

Protected Li-ion cells have a protection circuit that trips if too much current is demanded. This generally adds a bit of length which can be an issue with some lights.

"non-protected" li-ion cells do not have the protection circuit.

IMR cells are "inherently" safe chemistry & therefore do not have the protection circuit (so they are "non-protected", but "inherently" safe), they are made for high current demand. All the 18350 cells I have seen have been IMR.

Welcome to CPF.

 

[SG Hall]

Welcome to CPF westegg. [emoji4]

For a beginner you certainly ask the right questions! Well done! [emoji106]

 

[vicv]

I assumed unloaded. It is not anywhere near dangerous levels.

You're the battery guy. I was under the impression 2.8v open circuit was very low since we've always been told 3.6v was dead. Low voltage protection usually cuts lights off at 2.8V under load which bounces back to around 3.2V open so I assumed 2.8 resting voltage was quite bad. Most of the newer cells are designed for a 2.5v cutoff but my charger won't discharge below 3v so I don't know what a 2.5v cutoff bounces back to

 

[vicv]

I just wanted to jump in here quickly to correct the above statement on the 3.7v markings. It's not that the cell is 3.7v under load on average - that doesn't really have anything to do with it.

3.7 volts is what is called the "nominal" voltage of the cell. It's not fully charged and it's not fully depleted, it's right in the middle. If you look at the cell as being usable in the range from 3.2 volts LVC to 4.2 volts fully charged - the middle spot is 3.7 volts.

The interesting case for us flashlight users is that we generally can't use the full capacity of a LiIon cell in a flashlight. This is because most circuits designed for LiIon cell (most specifically single cell lights) are buck converters and they will regulate down to about 3.4 volts (under load) and then run mostly direct drive where you see the LED slowly dim.

We're basically saying the same thing. It's an average. It's a bit confusing though as the newer cells(last five years or so) really should be a 3.5v nominal cell. All the extra capacity is in the lower voltages

 

[westegg]

Thank you everyone. It's great when you find a resource online with so much genuine knowledge rather than a load of people having a punt.

With respect to the 2.8v - that was the reading when I put it back in the charger. I'm guessing charger reading should be taken with a bit of a pinch of salt. I've got a multimeter somewhere I will dig out for the future.

 

[HKJ]

You're the battery guy. I was under the impression 2.8v open circuit was very low since we've always been told 3.6v was dead. Low voltage protection usually cuts lights off at 2.8V under load which bounces back to around 3.2V open so I assumed 2.8 resting voltage was quite bad. Most of the newer cells are designed for a 2.5v cutoff but my charger won't discharge below 3v so I don't know what a 2.5v cutoff bounces back to

2.8V is very low, for some cell it may even be low enough to slightly damage the cell, but it will not make the cell dangerous.
I have written a bit more about it here: http://lygte-info.dk/info/BatteryLowVoltage UK.html