My last couple of activations (GW/MW-013 and G/WB-005) have been cold - only a few degrees above freezing. I also noted that my LiPo batteries appeared to be losing capacity. Discharge tests at room temperature and in the 'fridge (Janis did know) at 4 deg C showed that at the lower temperature, effective battery capacity is less than half that at room temperature. Sooner or later I will have to replace the LiPo batteries and have been considering LiFePO4s. Does anyone know how these compare with LiPos in the cold?
I use LiFePO4 batteries David & I find them excellent in the cold. Expensive to buy but many claimed advantages over other battery types. Bob G6ODU was surprised when he picked up my 24aH battery on GW/NW-043, At how light it was.
73.
The temp effect is well known Dave. My Icom handy wont run at highpower when colder than 0.5C to protect the battery.
The capacity returns when the cell is warm. You can have issues with fully charging at room temperature and then taking the cells into the cold. They are effectively overcharged.
LiFEPO4s are much better. They used to be very expensive but now are much more cost effective. When my LiPOs are no more Iâll replace with LiFEPO4. In the meantime, the LiPO were so cheap Iâll use and abuse them till they no longer work.
This home made pack will run an 817 for over 2hrs and cost 3.50 ukp to make. At that price you can take 2 or 3 to allow for lower Winter capacity. http://www.flickr.com/photos/mm0fmf/7993708381/
You can have issues with fully charging at room temperature and then taking the cells into the cold. They are >effectively overcharged.
Thank you for your reply, Andy. It does lead to the inevitable questions:
a) when does the difference between charging temperature and discharge temperature become a practical issue, and
b) what is this diference for LiFePO4s?
BTW, it seems as if the chemistry is quite efficient - the calculated Ah figure for the discharge was only a few percent different from what my charger (Imax B6) says it put back.
a) when does the difference between charging temperature and discharge >temperature become a practical issue,
Richard G4ERP has real world knowledge of this ISTR. In my book, the batteries I have cost such a small amount of money I donât worry about this effect. Maybe the life will be reduced significantly. My LiPOs date from Summer 2009 and get charged in a 20-25C shack and carried out in all weathers. I think they donât hold up as well as when new but Iâve had 4.5 years of âabuseâ out of the 2x RC packs from Honk Kong which cost under 25ukp inc charger.
b) what is this diference for LiFePO4s?
I donât know! A quick search says the effect is less for LiFEPO4. At -20C capacity is 50% of capacity at 20C. The figures are worse for LiPO ISTR.
This home made pack will run an 817 for over 2hrs and cost 3.50 ukp
to make. At that price you can take 2 or 3 to allow for lower Winter
capacity. http://www.flickr.com/photos/mm0fmf/7993708381/
I think you might have problems getting that past airport security.
This home made pack will run an 817 for over 2hrs and cost 3.50 ukp
to make. At that price you can take 2 or 3 to allow for lower Winter
capacity. http://www.flickr.com/photos/mm0fmf/7993708381/
I think you might have problems getting that past airport security.
Rick
Jesus, if I were one of the security guards Iâd probably start to hyperventilate as soon as I saw that pack, or even better, THREE of that kind. Andy, did you carry them in a belt around your waist?
It went in carry on luggage once and checked luggage another time. The 1st time (Madeira) it was checked in. But youâre meant to have batteries in carry on luggage so it went to Barcelona connected to an 817 in my backpack along with a laptop, PSU, mouse, syringes, spare needles etc. In fact it was screened at Edinburgh, Amsterdam & Barcelona there and back! They normally spot my diabetic syringe and cold pack and ask about that when I fly.
My LiPOs date from Summer 2009 âŚIâve had 4.5 years of âabuseâ out of the 2x RC packs from Honk Kong which cost under 25ukp inc charger.
My 4AH LiPo packs are similarly âwell usedâ. They still amaze me when I take them off the charger as the cells are usually balanced to within 0.02V. They still give sufficient for a couple of 1 hour activations running 22W of 144MHz / 5W of HF in combination with the piggy-backed 10AH NiMHs. No ned to consult the bank manager yetâŚ
LiPoâs shouldnât be that bad at 4C - most manufacturerâs info suggests capacity at 0C is about 75% - 80% of that at 20C, which my experience supports but there is considerable variation in how different manufacturerâs batteries behave at lower temperatures, seemingly depending on the exact variant of âgraphiteâ used for the anode structure - whilst most quote -20C, some manufacturers give 0C as a minimum working temperature, others -10C. Typically capacity (when quoted) at -20C is about 40% of that at +20C.
I am not aware of any âissuesâ with fully charged LiPoâs becoming âeffectively overchargedâ when cooled, neither from manufacturersâ literature nor consideration of the chemistry of the cells. Most manufacturers quote -20C as minimum discharge temperature. If anyone has further reliable information on this Iâd be very grateful if they shared it with me.
Charging is another matter. 0C is universally given as the minimum charging temperature, below this serious damage occurs which not only reduces the cellâs capacity but also renders it more unstable in the event of abuse. Itâs always a good idea to charge LiPoâs at a slower rate to get maximum life, particularly so at low temperatures.
To return to your question, LiFePO4 batteries are significantly better at low temperatures. Manufacturerâs data suggests that they should be on a par with or slightly better than LiPoâs at 0C, where capacity should be 80% - 85% of that at 20C; and much better at -20C, where capacity should be 60% - 70% of full capacity.
Hope that lot helps!
73 de Paul G4MD
PS I sit my LiPo on top of my 817 inside itâs waterproof container when operating - the (âwasteâ) heat generated by the radio keeps the battery warm as toast!
PPS still using my first LiPo given to me as a birthday gift by Gerald in early 2009 - has lost some capacity, but still good for two 1hr SSB activations between charges
Jesus, if I were one of the security guards Iâd probably start to
hyperventilate as soon as I saw that pack, or even better, THREE of
that kind. Andy, did you carry them in a belt around your waist?
I am not aware of any âissuesâ with fully charged LiPoâs becoming >âeffectively overchargedâ when cooled, neither from manufacturersâ
literature nor consideration of the chemistry of the cells.
Your memory must be getting sporadic the same way mine now is Paul, put it down to older age, RF exposure or both!
"Post by G4MD on 25th February 2010 at 19:46
[snip]
Iâm sure a while ago I saw on the reflector a reference to problems with LiPoâs if fully charged being damaged by subjection to low temperatures. I could find no reference to this in the (internet published) literature, if the original poster recalls this and has any more info on this aspect Iâd be most interested.
73 de Paul G4MD"
"Post by G4ERP on 25th February 2010 at 21:05
Hi, Paul. It was probably me. I think I mentioned it here and also in the Handbook. This is also why the FT80 manual refers to leaving the batteries at a 50% SOC which is the safe state.
When we ship Li packs around the world we have discharge them to a known state to avoid damage at the reduced temperatures they might encounter in transit.
So, I guess charging to only 80% (say) would potentially solve two problems:
a) the effective over-charge with reduced temperature and
b) provide a lower voltage for the transceiver operating on 4S packs.
Thanks Andy, itâs coming back now⌠I put it down to the Fullers Golden Pride.
I am still unable to find in scientific or manufacturerâs literature any reference to LiPoâs being damaged at low temperatures if fully charged. Most quote -20C as the batteryâs minimum working discharge temperature but none say if youâre using it at -20C only half charge it first.
The recommendation to store and transport LiPoâs in a partially charged state is well known and founded on good scientific reasoning but I cannot find any connection to temperature.
Richard, if you are reading and can point me at any cell/battery manufacturerâs information supporting the link to âlow temperature overchargeâ phenomena Iâd be most grateful. (Got a vague idea Iâve asked that before too? sorry if so)
To All,
The answer is to keep them warm, batteries I mean. I had the cells fitted into a cartridge belt, worn under the coat and no problem keeping them above room temperature. Ah, those were the days!
Don [G0NES]
In reply to all: Thank you all for your contributions to this thread. There is much here to consider, and not just for the SOTA community. Some amateur astronomers with âGoToâ pointing equipment also use batteries in chilly conditions.
I have a LiFePO4 battery on order, and plan to do some testing before it is put in service, including charging in the âfridge (With Janisâ agreement, of course) followed by a top-up at room temperature which (I hope) might indicate the degree of overcharging when doing the reverse.
Despite Daveâs final post I want to add my point of view.
In reply to MM0FMF:
The capacity returns when the cell is warm.
Exactly.
You can have issues with
fully charging at room temperature and then taking the cells into the
cold. They are effectively overcharged.
I do not think so and I attribute this to a misunderstanding between stored capacity and useable capacity. Why should the amount of charge stored in the battery vanish in the cold and reappear in the warm?
In fact the cold slows down the charge transport within the battery. As a result internal resistance increases. This is also the reason why self discharge of all batteries is smaller at low temperatures. This means drawing the same current, voltage drop will be larger. As capacity is considered the integral of discharge current over time down to a specific voltage any voltage drop will result in not getting all charge out of the battery.
In fact I know this from my mobile phone. Having it display SOTAWatch during winter activations lying in the cold the battery indicator sometimes even drops to empty. Switching internet off and putting it in my warm pocket brings back the original reading and it runs for hours afterwards. This is due to reducing the drawn current and esp. warming up the battery.
@Dave G6DTN
To my mind charging the battery in the cold is not a useful concept to test this.
Charging in the cold is unrealistic. In fact when charging the battery you are always at a warm place: at home, in the car, etcâŚ
Charging in the cold in fact reduces the charged capacity as both CC and CV phase will be stopped too early due to internal RI drop. The battery will simply be not âfullâ. But this does not really tell anything about its real capacity.
If you really want to do a sensible test I would propose:
Charge the battery in the warm. Discharge it in the warm with very low current (C/20) to cancel out any resistance effects. Now charge the battery at the same temperature. Charge should be about the same. Now cool it down and discharge it again with C/20. I would expect no real difference. Of course increasing the discharge rate in the cold will lead to a smaller discharged capacity. In ideal after warming up the battery one should be able do discharge the remaining charge.
Thank you for your reply, Michael.
The idea behind charging in the cold and topping up in the warm is to get some idea about how much to charge the battery in the warm to avoid it becoming overcharged when it gets cold.
Your reply to Andy (MM0FMF) suggest that taking a fully (warm) charged battery into the cold should not result in putting the battery into a potentially damaging overcharged state. However, I have noticed, but I have no figures to quote, that the open circuit voltage of a part-discharged battery in the cold is less than the same battery when it has warmed up, suggesting that internal resistance is not the only thing to consider. I hope to be out on G/WB-003 tomorrow morning and will make some measurements. I have no thermometer, so will have to estimate the temperature as cold, very cold or too cold to get out of the car!
Jesus, if I were one of the security guards Iâd probably start to hyperventilate as soon as I saw that pack, or even better, THREE of that kind. Andy, did you carry them in a belt around your waist?