Opti-power fully charged at 4.18v per cell

[Guest]

Laurence notes above that is you are using a CellPro PL8 it by defualt has a cold weather ambient setting that says if the ambient is below 15C then go to cold weather charge condition which would stop the charge at 4.1v. This is to protect the packs I can be disabled from memory. Worth baring in mind as the weather gets colder do not over charge your lithium,

[Eckchaz]

Never had a problem with Turnigy (std's) but instead of ordering another 3 for the same price inc delivery, I've just ordered my first pair of Opti's

[cjcj1949]

Could Optipower confirm that lipos should be charged to a lower voltage below 15C? I thought that lipos charged to 4.20V lasted longer at low temperatures than high temperatures. I know that cellpro have this low voltage limit and I know it can't do any harm, but I haven't seen any published information on this. I haven't noticed lipo voltage dropping with temperature, but equally I haven't measured it. If the volts do drop that much then all chargers that don't measure temperature would be dangerous when used below 15C.

[LaurenceGough]

The other thing to be aware is fully charging your pack in a warm area then letting them sit in the cold, you really need a warm box to store them in if so.

It feels bloody cold at these temps so you will know when the packs will suffer...

[scallybert]

The other thing to be aware is fully charging your pack in a warm area then letting them sit in the cold, you really need a warm box to store them in if so.

I thought that charging in a warm ambient then moving to a cooler ambient was *the* problem (as the capacity decreases, and the pack becomes effectively overcharged), and the answer was to reduce the end charging voltage in the warm ambient.

Have I missed something, etc ?

[LaurenceGough]

That is the problem - I probably could have worded my post better, I have a problem with that hehe...

If you charge them warm - you have to keep them warm or damage will happen.

I think vice versa applies but I never go back in with full packs .

[scallybert]

[...]If you charge them warm - you have to keep them warm or damage will happen.

Right. This is why it makes no sense to me that the chargers recognise low ambient temperature (at charging time) as a reason to partially charge. It should be the temperature differential that's important - and the charger can't know about that.

[cjcj1949]

Right. This is why it makes no sense to me that the chargers recognise low ambient temperature (at charging time) as a reason to partially charge. It should be the temperature differential that's important - and the charger can't know about that.

This may or may not be a rumour. It depends on which website you look at. If you look at storage information the consensus is that storage is better at lower charge and temperature values. Only Cellpro reduce the charge voltage at low temperature. I think they mention 55F in one document and 50F in another. This is good advice, in the sense that the lower you charge a lipo the better, and the less you discharge it. Using a lipo at low temperature is another issue and not related to the original charge voltage. Charging and using lipos at 30 degrees C does make them work better. As far as I can see there is no problem in charging to 4.20V above 5 degrees C. In fact if you time your flights, then charging to 4.10V could cause more damage than 4.20V as you will end up at a lower discharge voltage.

Perhaps its a matter of opinion at the moment and nobody knows.

[Guest]

Guys this whole area is a bit unclear and to that end we are going to get hold of an environmental enclosure and actually do the work so we can offer definitive information. As I understand it storing a LIPO at a cooler temperature is good for it as long at its above 0 degrees C and the cell is in a storage condition. If you were to charge a LIPO in a warm condition say 18 to 20C it would cut-off at 4.2v/cell. If you we to charge that cell to 4.2v/cell at 5C then warm it up it would go to more than 4.2v/cell.

There is a lot on the net about this but much of it is very contradictory. It is well known that people like electric pylon racers charge cells to 4.2V and maintain them at 30C in a warm box prior to use so that maximum power is extracted at time of use. I have seen a cell in a warm box where the thermostat failed and the box got to 70C and the cells were seriously puffed just about ready to explode (75C is considered self ignition temp).

So we will investigate this area and report back in due course which will take a little while. In the meantime the CellPro defaults are noted below.

The CellPro PL8 defaults are:-

COLD WEATHER CHARGING WITH CELLPRO PL8
We have been contacted a couple of times in the past few days by people asking why their lithium is no longer charging to 4.2v/cell with their PL8? The answer is it is doing exactly what it is designed to do in cold weather. The default condition of the PL8 is that the cold weather setting is ENABLED. This means that at 10 degree's C ambient the charger will charge to 4.1v/cell i.e. at 10C or lower the cell voltage cut off point is 100mV lower. The cold weather settings are in PRESETS and range from: NONE (will charge to 4.2v/cell irrespective of ambient) 0 C, 5C, 10C. The available variable mV cut-off settings are: -50mV, -100mV, -150mV, -200mV. Default is 10C and -100mV = 4.1v/cell. So if you find your lithium is not reaching 4.2v and its cold this is the reason. It is dangerous to charge lithium cells (anybodies brand) to 4.2v per cell at less than 10C if you do and then warm those up they will potentially increase in voltage beyond 4.2v/cell hence the safety factor built into the CellPro PL8.

Andy

[scallybert]

Guys this whole area is a bit unclear and to that end we are going to get hold of an environmental enclosure and actually do the work so we can offer definitive information.

Thanks, most useful.

To clarify, it seems we currently believe that both of: fully charging at room temp, and moving to <10 deg C; and fully charging at <10 deg C and moving to room temp; can cause pack damage.

[I'd previously only heard the former.]

[cjcj1949]

Its the Gospel truth.

[Ashley Davis]

When you take a lithium pack from warm to cold it will suffer a drop in capacity. This causes a rise in voltage as the charged state will effectively increase as the capacity decreases. This results in damage. If you move a cold pack to a warm room it's capacity will increase with the temperature rise and the voltage drops as a result, no damage should occur due to this.

The reason I believe (and this is my best guess) the PL8 only charges to 4.1v in the cold is that the expectation is that you have flown the pack and are now field charging in the cold. The pack if it's flown may well be quite warm inside but the ambient temperature outside is cold. This creates a dangerous scenario where by the pack has it's full effective capacity due to it's internal heat but if the charger charges it to full capacity then it is quite obvious that it will cool either during or after charge and this could lead to an over charge condition. Therefore the PL8 takes the decision to only charge to 4.1V in the cold and avoids this particular scenario.
The other interesting scenario is the automatic 1C/2C/3C charging on the Cellpro range, these calculate the pack capacity by measuring voltage changes based on current. I suspect this process may yield incorrect results in the cold whereby again it may be safe to only charge to a lower termination voltage.

[dav20043]

When you take a lithium pack from warm to cold it will suffer a drop in capacity. This causes a rise in voltage as the charged state will effectively increase as the capacity decreases. This results in damage. If you move a cold pack to a warm room it's capacity will increase with the temperature rise and the voltage drops as a result, no damage should occur due to this.

The reason I believe (and this is my best guess) the PL8 only charges to 4.1v in the cold is that the expectation is that you have flown the pack and are now field charging in the cold. The pack if it's flown may well be quite warm inside but the ambient temperature outside is cold. This creates a dangerous scenario where by the pack has it's full effective capacity due to it's internal heat but if the charger charges it to full capacity then it is quite obvious that it will cool either during or after charge and this could lead to an over charge condition. Therefore the PL8 takes the decision to only charge to 4.1V in the cold and avoids this particular scenario.
The other interesting scenario is the automatic 1C/2C/3C charging on the Cellpro range, these calculate the pack capacity by measuring voltage changes based on current. I suspect this process may yield incorrect results in the cold whereby again it may be safe to only charge to a lower termination voltage.

I think you have that backwards

[jamiem]

Ashley's explanation looks correct to me based on previous knowledge? What part looks backwards, Dave??

[cjcj1949]

I think voltage is unlikely to rise with drop in temperature. It sounds a good argument though based on capacitance and charge storage. It's probably true for a capacitor. I think volts from batteries are caused by chemaical reactions that tend to depend on absolute temperature according to Arrhenius? I think. I'm not a Chemist but I must make a measurement of change in voltage with temperature. I don't think its that important though as we all know that lipos are crap at low temperatures and its best to use them between 20 and 30 degC.