Lowest voltage on unprotected cell...

[Robocop]

I am testing out a new light made by Peak and it is designed for multiple battery combinations. It workd best on two R123 cells and I have several of these for testing. Some of my samples are protected and some are not.

I believe the light has a 2V cutoff built in however it starts to flicker rapidly as a warning on low battery right around 2.3V. My question is that if this light is designed to use rechargeables surely it must be used only with the protected versions correct? If I have 2 of the R123 cells inside the light and run it until it flickers how bad will this kill these cells at 2.3V total ?

I searched and found many threads warning against low voltage use of unprotected cells however never found any concrete numbers as to just how low or just how fast it will kill the cells? If I do discharge 2 cells down to a total of 2.3V will it instantly kill the battery or is it a long term process?

I am curious as I am testing this light and know many use the unprotected versions of cells. I know there is little difference in cost of protected and non-protected however I do need to have all the info I can in order to give any suggestions to the maker of this test unit.....thanks for the help.

 

[legtu]

i think 2v(or 2.3v) is a bit too low, but that will also depend on the current draw.

at these low voltages, you're more at risk of encountering cell voltage reversal which is really bad. it can render the reverse-charged battery unstable, or worse, a 'spectacular' battery fireworks...

 

[Robocop]

Thanks for the input however I am not really sure as to the current draw of this light. It has an adjustable knob to change the current however at full power it gets hot fast so I assume it is pushing the cells pretty hard.

Peak is on to something with this light as it is very bright and well thought out however maybe it is best for me to use protected cells only in this light. Thanks again and if you are curious as to the light check the Peak forum in the manufacturers section for my post.

 

[DM51]

You should definitely only use protected cells in this light.

The adjustable knob sounds interesting (!!) and it sounds as if full power should only be used in very short bursts. Overheating batteries is not a good sign. If you are using R123s, the maximum safe current will be 1.5A, but for continuous use a better limit would be 1.2A. I haven't checked your other post yet, but I assume Peak has supplied information about the current draw.

The voltage to aim for with a Li-Ion cell is 3.5v at rest (ie after discharge). Under load, a cell that goes a little below 3.0v during use can rebound to 3.5v at rest, depending on the load.

If the cell is taken down to 2.3v under load, it probably won't even rebound to 3.0v. If it is reading below 3.0v at rest, real damage has been done to the cell, and it may not be possible to recover it.

If it is reading only 2.3v at rest, the best thing to do would be to get rid of it straight away.

 

[cy]

Robo, depends upon mfg spec's and when cell is measured. some state 2.5v in min discharge voltage, others higher.

what's really important is how long cell remains below 3v. a cell can rest and bounce back above 3v.

for all practical purposes, when a li-on cell goes below 3.5v. it's almost empty. very little to be gained by going below 3v and risk damaging cell.

best practice when using bare cells is to yank cell, immediately when light dims. then quickly measure cells voltage. do this for a few cycles and you will know exactly where cell is at. goal is to yank before 3.5 is reached.

best to only use protected li-ion cells in series. especially since protected cells are so readily available now. I'm using bare li-ion cells mostly because that's all that were available at the time.

some lights like surefire A2 will not take anything but bare cells due to internal diameter.

really favor lights that can operate with single li-ion cell. almost every light I actually use are switched to rechargeable cells.

I'd be interested in finding out if peak's proto light will support 17670 or 18650. being able to support 1x 18650 or 2x CR123 would be a real advantage.

greatest danger using li-ion cells occurs during re-charging. it may be worthwhile to read link below.

 

[coppertrail]

I wanted to know the answer to this question as well. I have some Protected RCR123A/18650 cells on the way. Their PCB cuts them of at 3.0V/cell.

I read the "Charging Li-Ion Batteries" article from batteryuniversity.com

Here's a paragraph from the article that discusses discharge voltage:

"Extreme low voltage must also be prevented. The safety circuit is designed to cut off the current path if the battery is inadvertently discharged below 2.50V/cell. At this voltage, most circuits render the battery unserviceable and a recharge on a regular charger is not possible.
There are several safeguards to prevent excessive discharge. The equipment protects the battery by cutting off when the cell reaches 2.7 to 3.0V/cell. Battery manufacturers ship the batteries with a 40% charge to allow some self-discharge during storage. Advanced batteries contain a wake-up feature in which the protection circuit only starts to draw current after the battery has been activated with a brief charge. This allows prolonged storage."

The cells I have ordered cut off at 2.75V and cut the charge at 4.2V.

 

[DM51]

That is OK. They should rebound to well above 3.0v even if you do let them go down to the low-voltage cut-off. For best results, pull them before they get that low. That goes for all protected cells if you want to get maximum cycle life out of them. And if you charge them to 4.15v instead of 4.2v, you will get even more cycles.

Be particularly careful if you are discharging them under a very light load, as the rebound will be less.

 

[coppertrail]

That is OK. They should rebound to well above 3.0v even if you do let them go down to the low-voltage cut-off. For best results, pull them before they get that low. That goes for all protected cells if you want to get maximum cycle life out of them. And if you charge them to 4.15v instead of 4.2v, you will get even more cycles.

Be particularly careful if you are discharging them under a very light load, as the rebound will be less.

Thanks DM, I had heard about the 4.15V charge cutoff being the "sweet spot" for max number of cycles. I generally do not let mu current protected cells drain below 3.5, a habit which I wil observe with these new cells whenever possible.

 

[LEDite]

Robocop;

I have been using lithium #18650 cells for several years.

Taking a Sanyo, Sony or Panasonic cell down to 2 Volts for a short period of time will not hurt them.

Just be sure to charge them at 0.1 C until they get to 3 volts or so.

Larry

 

[Robocop]

Cy the new light will indeed run from one 3.7V cell and is designed for several ranges of batteries while using the same body. I believe the maker states it can be powered from 2.5 V all the way up to 9 Volts however the brightness depends on how much power is going in and thus far the best option has been 2 R123 cells for me.

Regardless I am thinking these low ranges will be way too much for my un-protected cells and I really want to keep them in good shape as they are used for several of my incandescents......I think I will use only protected cells in this light and I appreciate the advice.

 

[Robocop]

Peak is a little slow to respond at times however I have sent them several comments on this light. I did speak with their tech. who did say the circuit was designed to pulse quickly when warning of lower voltages however I now see this light is only for protected cells.......They have not responded to many of my e-mails nor in the beta testing Thread however if any here would like to see the light I have a few pics in this thread http://www.cpfmarketplace.com/mp/showthread.php?t=166500

 

[SilverFox]

Hello Robocop,

The key is the resting voltage.

Let's see if I have this correct... You have 2 cells in the light and the resting voltage for the 2 cells in series is 2.3 volts?

If that is correct, you are most likely doing damage to your cells.

A Li-Ion cell that is over discharged gets into a situation where the electrodes are being dissolved. This results in lower mid point voltage, less capacity, and more heat being developed during discharge.

You can still get some use from the cells, but at reduced performance.

Depending on the brand of cell, you can reduce your cycle life to 10 - 125 cycles. The big problem is the copper shunts that are formed during over discharge. As they short out heat is given off, and we come closer to thermal run away.

The best performance and cycle life comes when the discharge is limited to 3.0 volts under load.

Tom

 

[Robocop]

Hey SilverFox good to hear from you as always......

The biggest problem for me when testing this light is that I did not understand some of the specs written in the manual. It stated that the light had some form of battery management system. I copied and pasted the makers comments below...

The electronics monitor the battery input voltage and the current through the primary inductor. This is done so as not to over-stress low voltage batteries and cause premature battery failure. The output voltage to the LEDs is thusly reduced as is the maximum light output. This is a constant current, voltage boost type circuit. Any battery combination between 2.0 volts and a maximum of 8.5 volts may be used. Input voltages above 7.5 volts will not increase the light output, the system will limit the maximum current through the primary inductor and shut down. A 2.0 volt supply will provide a maximum of 1.5 watts of power to the LEDs.


Now after reading that I was curious if the light somehow detected the use of unprotected cells however now do not think that it does. I do know that the light begins to strobe slightly when the voltage reaches a certain point however this is a constant point not affected by the power source. It looks to me like this strobe begins at around 2.3V and if I waited until I noticed the strobe at that voltage then my 2 unprotected R123 cells would be destroyed or even one of the 18650 cells if being used.

For my next e-mail to the maker I am thinking that I should recommend they add a disclaimer to allow the use of only protected cells in the Li/Ion version. Regardless I now see that 2.3V is way too low for 2 R123 ran together to be taken down to and very risky on even one 18650 cell.