Cumulus Support

How long do the batteries in the transmitter typically last? The manual says over 2 years but manufacturers tend to be optomistic about the life of batteries. I plan to mount in a very hard to reach spot (particularly during a Canadian winter). If the manual is correct, the batteries are effectively dying from shelf life, so replacing them with a set of lithiums should extent the life to at least 5 years, and possibly 15 or more. However if everybody is seeing them die in 6-12 months, I'll design a little solar powering unit that should not need attention for over a decade.

So have you changed your transmitter batteries? How long do you get? What are the symptoms of needing a change (occasionally missing some data, or a complete cut off instantly)?

I have not used rechargeable batteries as I believe they do not last as long.

I use "Duracell Plus", alkaline batteries -- had them in the station for just over 12 months then changed them when I was cleaning the instruments, even although there was no sign of them needing replaced. My lowest temperature during that time was -17C and the highest 28C

Hi
You don't say why the site in hard to get at - if it's a question of going up a pole I would (and do) use a remote battery box at a lower level with D cells. Well I did - but I've found if the transmission route to the base is at all obstructed the battery condition seems to be critical and any drop in voltage in the cold causes low signal strength and data errors. No to rechargeable unless you can find a way to keep the voltage close to 3V (rechargeables only reach about 1.2V to 1.3V each). I'm now using a 3.2 V mains power supply and it has made a remarkable difference to the data quality. I did actually use a 4.5V supply for a short time with no disastrous effects so maybe the transmitter would handle three rechargeables in series but AT YOUR OWN RISK. Do a search for the best batteries to maintain voltage in a Canadian winter as in my opinion the battery power is critical.
Regards
Alan

after some research i found the energizer lithium AA's should be perfect for this application. They have better extreme cold/heat tolerance, better self-discharge, better discharge / voltage profile and higher capacity than any alkaline.

you can usually buy them for about £1 per battery off ebay

Rechargables ni-cd or ni-mh have a low internal resistance, even though they might have a good mAh rating they self-discharge over time (even while they are being used) so the net result is less useable time

Thanks guys. I did find a thread in here with a poll about battery life that gave me a warm fuzzy. I agree with the lithiums - I've used them in low temp applications before - but they would not be much help if the current draw was too high (alkalines dying in a couple months = lithiums dying in twice that). Fortunately this does not seem to be the case so I think lithiums are the way to go.

As to the solar supply, putting 9 segments in series will give about 4.5 V open circuit. Add a series diode to protect when the sun goes down and you can happily charge 3 ni-cad or ni-mH AA's. Add a diode in series with the 3 AA's, and you get ~ 2.9 V which will run the unit without damage forever. The current demand is low, so the low temp effects on the batteries can be ignored in this application. (My solar garden lights work at -30C but my digital camera does not). The solar cells, if scavaged from those garden lights won't put out enough current to damage the batteries; it will be a sort of float charge.

As to why it's not accessable... it going on a pole on a snow covered sloped roof, and I am not. I know how to remotely power things, but why bother if lithiums will last 10-15 years?

Oh, one last thing - the question was how long do your batteries last but you didn't actually answer. I'm still curious...

I just got my Watson Fine Offset clone, so I can't answer the question, but I'm really interested in this. I have a fancy to make a solar charged system with three NIMH in series. I think the idea of using junk solar garden lights is a good one. You see them in skips around here when people are doing garden remodelling.

A bit of experimentation is called for I think and as long as we don't exceed the already tested 4.5 volts, I doubt we'll see any problems. In the end, we aren't measuring the weather on Mars, so if it stops or fails altogether, it isn't exactly a disaster is it?

Alkaline batteries in my transmitter lasted about 9 months. Lithium cells sound interesting - cheap enough and a lot less trouble than messing with solar panels or regulated power supplies

AH BUT... Lithium cells are 3v not 1.5 so you'd want one lithium cell and one dummy (short circuit) to give the 3v required! No?

Been checking up on this - I know CR2032s as used for motherboard BIOS batteries are 3v.

Lithium cells are very light in weight and have twice the voltage of most other types of cells. Where an ordinary (ordinary meaning non-lithium) flashlight sized battery is 1 « volts, a lithium equivalent will be 3 volts. That means you need only half as many cells to do the similar job... . This is a cost savings as well as a performance/size benefit. Lithium batteries have a very low rate of self discharge, meaning that they have a virtually infinite shelf life. Put them away now, pull them out in ten years and they'll be virtually as good as new. The actual figure on self discharge is about 1% per year, which from a practical standpoint is almost nothing.

Lithiums generally cost from two to four times that of lesser batteries. If they last only twice as long, you're at a break even point money wise, and you get fewer battery replacements for free.

Another advantage of lithiums is that their voltage stays constant until the thing is dead. Carbon-zinc and alkalines start with their rated voltage, and their voltage gets lower and lower as the battery is used, until the performance of whatever they're powering gets so crappy that you replace them.

The last paragraph is another good reason to use lithium cells for this application - the transmitter will continue at full power for the life of the battery, making them as good as a continuous stabilised supply

So a battery holder for something like a CR2032 and wires to the battery compartment of the transmitter would seem a good solution.

How about using one of the 3v solar panels from Rapid Electronics

http://www.rapidonline.com/sku/Tools-Fa ... 97/42-0240

The claimed output is 3v at 100ma load and could be used to recharge a 3.6V Lithium Battery such as CR123A. As Alan has used main powered units with outputs upto 4.5v there shouldn't be any issue running at 3.6v. One thing though, you would have to adapt the battery compartment as the CR123A is not the same physical size of an AA

I think dexterslab was talking about the 1.5v Lithium AA batteries, so these would just go into the normal battery compartment?

Ah I see - thanks Steve Just checked on this via Google and it seems they've developed a slightly different chemistry for the 1.5v lithium cells but with the same advantages as the 3v.

Gina wrote:Alkaline batteries in my transmitter lasted about 9 months. Lithium cells sound interesting - cheap enough and a lot less trouble than messing with solar panels or regulated power supplies

AH BUT... Lithium cells are 3v not 1.5 so you'd want one lithium cell and one dummy (short circuit) to give the 3v required! No?

Actually, Energizer makes a direct AA replacement...
http://www.energizer.com/products/hight ... eries.aspx

yes, sorry i should have mentioned AA

the guide for my rebranded Fine Offset says the transmitter should last for 2 years, which did surprise me and knowing what the chinese are like, somewhat optimistic. We'll see, i've only had mine for a couple of weeks.

i like the idea of solar charging, but as with a lot of things like this given two lithium AAs are about £2 which say might last a year, spending £20 rigging up some solar charger would take 10 years to pay for itself and probably add a factor of unreliability.

I have just ordered a pack of 6 Energizer lithium AA cells from Amazon.co.uk for £4.90 with free delivery. I'll probably put the other 4 either in clocks, or wireless keyboard and mouse. So that's the transmitter sorted out

Hey there!
I started my "FineOffset" station in the end of sept 2009 powered by Energizer Ultimate Lithium AA batteries.
Last week the outdoor unit stopped sending data. I think that the batteries ar dead now. Here in the north of Sweden we have had radher colt weathet the last month. Around -20C. It is still -20C so it is too cold to change batteries now as I must take down the 5 meter high steel tube to reach the unit.
I will report later when the batteries are changed.

Regards
Christer