Yesterday I activated G/SB-006 Shillhope Law. Nothing particularly exciting about that, the hill is easily accessed via a quad bike trail, but being a 2 pointer it attracts the 3 winter bonus points. Nice.
So off I went, driving to the access point just as dawn broke on an icy landscape. Because of the forecast low temperature I had taken the precaution of carrying 2 10Ah Lipo packs. The air temperature as I left the car was -9C, I guess it did not warm up as I ascended to 500m asl at the summit.
As is my norm I first tried to activate on 7MHz but was beaten back by the wall of “contesters”, apologies to those who listened for me before I QSY’d to 60m cw.
Yes I remember: Weekends = Warc and 60m bands.
So back to the batteries:
Using the first pack I made about 40 QSO’s at which time the battery voltage had fallen to 10V, perhaps only 60% usable capacity had been available. During this time I kept the second battery pack warm by keeping it in my clothing. When I started using it it’s temperature would have been about 20C. It maintained the voltage better, but soon cooled and the terminal voltage declined. Moral of the story, I am going to make a 1.5m extension power lead so I can snuggle the battery during use and preserve the terminal voltage and capacity (or stay in doors).
Another lesson learnt.
The obvious place is in your underpants. Why? Well you can unzip your flies, extract the cable from the pack that you coiled up when dressing then rezip to keep the cold out. Reverse the process when you have finished. I suggest this action is best performed when other people are on the hill as the look on their face (before they inform the police) will be priceless.
Yes, and to be serious, I have noticed my 4Ah LiPOs “go off” when cold. But it does have to be quite cold. So around 0C, a few degrees either way doesn’t make a significant difference. But certainly when it’s -5C and below, they do have obviously less capacity. My 2 packs are 7.5 years old now and seem to take longer to charge than I remember when they are well discharged. If they are showing reduced capacity at typical GM hill temperatures, I’ve not really noticed it.
Rescue teams carry(*) thermal pads to keep Nitrous Oxide warm as apparently below about 10C it separates into Nitrogen and Oxygen, and breathing the nitrogen bit on its own could be a problem… The Medics also used to have a sterile saline bag - which in winter conditions was kept under a shirt near an armpit! ( This is if you are ever unfortunate enough to get severe hypohermia one of the issues is shock and fluid loss, so slow rewarming and a warm saline drip i/v improves your chances…). … so although the prospect of slipping a battery into your pants may seem extreme ( I presume in a fireproof bag, possibly wired to a solar panel in your headgear? ) it turns out that slipping i/v fluid up your armpit is not that unususal.
(") There were UK protocols approx 15 years ago and may now be well out of date.