In reply to GW7AAV:
Sorry if this reply goes on a bit, but I feel very strongly about debunking the myriad myths that have grown up around LiPos…
From what I just read
Sadly there must have been more misinformation written about LiPo batteries than almost any other technical subject we encounter. Even crossed-field antennas
the problem at sub-zero temperatures in LiPOs is not a reduction in voltage but a over voltage.
Not true. As the cell temperature reduces the terminal voltage drops. To about 3.4V for a fully charged cell at -20 deg C, actual figure quoted seems to vary a bit with manufacturer. Realisable capacity also drops, to around 60% of the cell’s capacity at +20 deg. C, again varying a bit betwen manufacturers.
In fact some radio control operators store their LiPos in the freezer over night prior to use
Won’t hurt them, storage at down to -20 deg C is OK and freezers generally maintain -18 deg C
because they think they get more power out of them, which seems to suggest there is something to it.
Well they don’t, which seems to suggest they don’t know what they’re talking about
I think the issue is not that they do not work at -10 but that you may
be doing gradual permanent damage
No you’re not, you’re operating them within the manufacturer’s stated safe conditions
but from what I read storing the cells in the freezer like the RC guys are doing may well be plain dumb.
That’s true! Presumably they warm them up before use so what’s the point?
One manufactures sheet I just saw says the operating range is 20-25°C,
which suggests either they are airing on the side of caution or even
the makers don’t really know.
Don’t know where you found that, but it’s so ridiculous I’d suggest it’s not on a bona fide manufacturer’s data sheet. The makers do really know, and they publish the information.
To summarise (and this information is on every manufacturer’s data sheet I have ever found, so probably applies to the vast majority of cells available)
LiPo’s can be safely discharged at temperatures over a range of -20 C to +60C, although terminal voltage and capacity are reduced at lower temperatures, particularly below freezing.
LiPo’s should be charged at temperatures above 0 C and below 45 C
LiPo’s should be stored at temperatures between -20 deg C and +45 deg C. If being stored for any length of time, storing at a terminal voltage of about 3.75V per cell is optimal to minimise degradation.
LiPo’s should never be allowed to reach a temperature greater than 80 deg. C
Having said that, if anyone has definitive information to the contrary I would be most grateful to be made aware of it.
73 de Paul G4MD