Battery life

[EvilV]

And the use of a voltage/current regulator is highly recommended - series-connected diodes would not be safe enough.

I was wondering what would happen if say the output of an LM317 at 4.5volts was fed into 3 series connected nimh cells. I expect that the fully charged combined battery potential of around 4.2v would not be exceeded until the batteries stopped taking any more current,but given that the Fine Offset stations draw so little current themselves, is it possible that the no load voltage on the system could creep higher?

I ask this because I have noticed by sticking a volt meter across them that some cheaper regulated supplies deliver higher voltages than the rated one, until a load is applied. Maybe this wouldn't make any difference - I don't know, but for sure a weather station that can last a year or more on a pair of alkaline batteries, must be drawing next to no current, and might appear as virtually a 'no load' situation to a voltage regulator. I'd not be pleased if I blew the sensor / transmitter unit by fiddling about.

[beteljuice]

I think I read somewhere that 'modern' units of this type effectively go into 'stand-by' mode inbetween transmit pulses in order to acheive the battery saving.

But that might be gibberish - anyone confirm

[nking]

I think I read somewhere that 'modern' units of this type effectively go into 'stand-by' mode inbetween transmit pulses in order to acheive the battery saving.

But that might be gibberish - anyone confirm

I guess that's possible but then how would the unit for example, know the highest gust speed since the last transmit. I would imagine the energy saving comes from only sending the data every 48 secs whereas more frequent would mean more power.

[beteljuice]

I meant that the transmit 'carrier' is not left open. This being the greatest current consumer.

hmmm ...... but then how would they know if they lose contact, unless it's a time-out thing.

[Charlie]

I was trying to figure out when I said that, because I thought I said the exact opposite. It turns out the quote was edited a bit too agressively, and attributed a response to me.

It's true that the open circuit voltage could rise to 4.5 V as a static potential. Some devices could be damaged by just a few electrons at this level of overvoltage. Fortunately, none of those devices are in this station, which is lucky or they would never survive the first thunderstorm of the season! Someone else posted running their system at 4.5 V for 30 minutes with no ill effects, so I don't think this is an issue. Also, for any meaningful current to flow, the diodes will need to conduct, which means their forward volt drop is in play, dropping voltage to the ~3V as outlined.

As to the earlier post about current from garder lights, the garden warts do indeed only put out on the order of 20 ma, and this is tons for this application. There is no need for parallel segments.

I'm planning to put a meter on this beast and see how much current it takes, but I suspect it is pulsed (at least the transmitter) and I won't be able to get a reading.

[gemini06720]

One thing we should be clear about is that, except for the Davis Vantage Pro weather stations, a solar panel would be used to power the transmitter part of the station, that is the outside unit that captures the data from the sensors and transmit that data to the inside receiving unit usually called a console.

Since I cannot write about stations I know little or nothing about, I am going to write about the Davis Vantage Pro weather station. The system is composed of two units, the external ISS (the integrated sensor suite - the unit managing all the external sensors and the transmitter) and the internal receiving console.

According to the technical specifications sheets:
- the current drawn by the ISS varies between 0.14 mA (average), 30 mA (peak) at 4 to 6 VDC;
- the power produced by solar panel installed on the ISS averages 0.5 Watts / 0.75 Watts;
- the ISS is also powered by 3-Volt Lithium cell with a life expectancy of 8 months without sunlight
---- greater than 2 years depending on the amount of power produced by the solar panel (the cell is not rechargeable).

As I indicated in the first line of my message, Davis has designed its consoles (the usually indoor receiver) to also be operated/used out in the field.

For that purpose, Davis has designed a solar power supply kit. It consist of a 0.5 Watts solar panel, a 6-Volt 1.3 Amp/Hour lead-acid battery, and a regulator circuit. The console normally draws 0.90 mA average, 20 mA peak, (plus 120 mA for display lamps, plus 0.125 mA for each optional wireless transmitter received by the console - up to eight different transmitting stations) at 4 to 6 VDC - the power for the console comes either from a regulated AC power adapter or from 3 C-cells (with a life expectancy of up to 9 months).

[Charlie]

The Fine Offset is quite different from the Davis, then! While F.O. do not specify current consumption, they specify that 2 AA alkalines batteries will last 2 years in the outside module. If the batteries die from draining them, the unit consumes ~ 150 uA (0.15 mA). If they die from shelf life, the number is smaller yet. This means a garden wart solar cell supplies 2 orders of magnitude more current than the unit consumes. We've seen some batteries dying after 9 months. If this is due to power drain, the consumption is still only 0.5 mA. I based these calculations on a pair of 2700 mAH alkalines.

The "console" needs 3 AA's but is usually powered through it's USB port.

F.O. might be optomistic, but these power consumption levels certainly in the realm of possibility!

[Gina]

The garden light solar panels I have give 3v in full sunlight. I forget what they give in cloudy conditions - I'll see if I can remember to check tomorrow.

However, I've got some Energizer Lithium batteries to put in mine next time. At five pounds for six they are not exactly expensive The FO units need regular checking for corrosion on plugs etc. anyway.

[Keyz]

Well, yesterday my outdoor sensor started to deliver data without changing the batteries! But. The temp har gone up from -20C to only -5C. Maybee the RF power is dependent of the temp? I will check the batteries later.

Regards
Christer

Hi Christer,
This would tend to suggest to me your batteries have become drained, and the super low temperatures reduced the power available to the point that it could not transmit. The increase in temperature could have enabled the chemistry inside to work enough to send the transmission, but I would suggest the cells are still drained?

Unfortunately, changing to rechargables with all the solar charging being discussed here may not fix your problem due to rechargeables being particularly vulnerable to such cold temperatures. Would be interesting to see how constant charging may alleviate this issue.

I guess it tends to be a case for experimentation, or converting to mains power, or regular battery changes (Say changing right before the start of winter.)

Thankyou for highlighting this, I will be sure to report back on my battery life in my temperate climate when the batteries run out. I would say I'm in ideal conditions for a maximum length test (Max temp 30, min -5 say). Using Eveready Lithiums here, since December 09. (Interestingly, can't find Eveready Lithium's anywhere online to show anyone, but I am super positive they are not Energizers!)

Good luck!

[EvilV]

Well, yesterday my outdoor sensor started to deliver data without changing the batteries! But. The temp har gone up from -20C to only -5C. Maybee the RF power is dependent of the temp? I will check the batteries later.

Regards
Christer

Hi Christer,
This would tend to suggest to me your batteries have become drained, and the super low temperatures reduced the power available to the point that it could not transmit. The increase in temperature could have enabled the chemistry inside to work enough to send the transmission, but I would suggest the cells are still drained?

It's true that exhausted batteries would be unable to perform at low temperatures, but also, as has been discussed elsewhere here, even good alkalines suffer from a fall off in voltage, especially as low as -20c. A while back, in response to another thread on this subject, I looked up some technical papers on the Energizer site and from memory, the voltage dropped down to about one volt at that sort of temperature. Since any radio transmitter's output of RF is critically dependent upon the voltage applied to the circuit, it would be certain that dropping the voltage from 3v (2xAA in series) to around 2v, would lower the RF power considerably. Reducing the supply voltage by maybe 30%, quite likely at -20C, would reduce the RF output by about 50%, give or take. This would easily make an installation non-viable as the lower rf output might not penetrate walls from outside, even if it could do at the normally higher voltage. Warm up the batteries again, and hey presto - your radio link is miraculously restored.

Of course, it is probably pretty easy to check the voltage on the installed batteries if the transmitter is accessible.

Maybe we should be pleased we are not operating a remote weather station on the surface of Mars... NASA have been doing this stuff for years, and apart from having to send the data rather further than we have to (36 million miles to 250 million miles depending on the relative position of Earth and Mars) and the mean surface temperature is -63c, reducing seasonally down to -140C.... NASA artificially warm the batteries, or they would certainly fail and the machine would never come back to life again. It's much harder there to run out and swap the Energizers too...

[christer]

Well, yesterday my outdoor sensor started to deliver data without changing the batteries! But. The temp har gone up from -20C to only -5C. Maybee the RF power is dependent of the temp? I will check the batteries later.

Regards
Christer

Hi Christer,
This would tend to suggest to me your batteries have become drained, and the super low temperatures reduced the power available to the point that it could not transmit. The increase in temperature could have enabled the chemistry inside to work enough to send the transmission, but I would suggest the cells are still drained?

It's true that exhausted batteries would be unable to perform at low temperatures, but also, as has been discussed elsewhere here, even good alkalines suffer from a fall off in voltage, especially as low as -20c. A while back, in response to another thread on this subject, I looked up some technical papers on the Energizer site and from memory, the voltage dropped down to about one volt at that sort of temperature. Since any radio transmitter's output of RF is critically dependent upon the voltage applied to the circuit, it would be certain that dropping the voltage from 3v (2xAA in series) to around 2v, would lower the RF power considerably. Reducing the supply voltage by maybe 30%, quite likely at -20C, would reduce the RF output by about 50%, give or take. This would easily make an installation non-viable as the lower rf output might not penetrate walls from outside, even if it could do at the normally higher voltage. Warm up the batteries again, and hey presto - your radio link is miraculously restored.

Of course, it is probably pretty easy to check the voltage on the installed batteries if the transmitter is accessible.

Maybe we should be pleased we are not operating a remote weather station on the surface of Mars... NASA have been doing this stuff for years, and apart from having to send the data rather further than we have to (36 million miles to 250 million miles depending on the relative position of Earth and Mars) and the mean surface temperature is -63c, reducing seasonally down to -140C.... NASA artificially warm the batteries, or they would certainly fail and the machine would never come back to life again. It's much harder there to run out and swap the Energizers too...

Hello again. I´m using Energizer Ultimate Lithium since Oct2009 that should work OK down to -40C. Here is a link:
http://data.energizer.com/PDFs/lithiuml91l92_appman.pdf

//Christer

[cisop]

I have some battery data that might be of interest. I can't remember the make of my old weather station but it was purchased from Walmart in 2007. It was always hard on batteries. I kept track of the dates that batteries were replaced. The alkaline batteries were Duracell Copper Top Alkaline mostly. the Lithium batteries were by Eveready and they were the 1.5 volt variety.

Here is the data.

05/06/07 alkaline
06/07/07 alkaline
07/12/07 alkaline
08/14/07 alkaline
09/20/07 alkaline
10/24/07 alkaline
11/24/07 alkaline
12/24/07 lithium
01/17/08 lithium
02/11/08 lithium
03/04/08 lithium
03/26/08 alkaline
04/23/08 alkaline
05/28/08 alkaline
06/29/08 alkaline
08/03/08 alkaline
09/07/08 alkaline
10/10/08 alkaline
11/12/08 alkaline
12/12/08 alkaline
01/09/09 alkaline
02/09/09 alkaline
03/08/09 alkaline
04/08/09 alkaline
05/11/09 alkaline
06/12/09 alkaline
07/14/09 alkaline
08/21/09 new unit alkaline

30 day average for the Alkaline and about 25 for the Lithium.
I have since purchased a Fine offset branded by National Geographic. I installed it on 08/12/2009. I have not replaced the batteries yet.
i know the Lithium should be better according to the specs but in reality they did not do well. We do get cold weather here (Canada). We had one day this winter at -27.5 Centigrade and -20's are not unusual.
-
cisop

[hurring]

I am running the fineoffset 1080 unit and I am having to change batteries monthly. I have used cheap akalines, dearer akalines and have just used enegizer lithiums. We have just gone through summer so no cold weather but I feel this is using way to many batteries. I am guessing it maybe the distance I have it from the base unit and having to travel through walls
Solar charging sounds intresting, does anyone have pics of how they wired it up
cheers
Adrian

[steve]

I am guessing it maybe the distance I have it from the base unit and having to travel through walls

I don't think the transmitter knows how far away the base station is, it just transmits at fixed power and hopes the base station can hear it.

[goldrush]

Whilst as Steve says, the transmitter does not know, or even care:-0 how far away the reciever is, if it happens to be almost at the limit of reception (distance and walls etc) with "good" batteries, then the RF output is likely to fall well below that required for the particular distance, when the batteries are low.. resulting in the need to change batteries even more frequently than appears normal
Another point is that I have checked 3 or 4 units in a 20 acre field and only 1 came close to the range quoted in the spec with new batteries.