After 4 months had to replace transmitter batteries. Normal?

[AaronJones]

I'm having similar problems. My station is located nearly 100' from the computer, and the signal passes through several walls. I upgraded the antenna on the receiver to a real 450 MHz whip, which helped a lot. I replaced the steel rods in the solar screen with nylon, which helped some more.

But even with lithium cells I start getting dropouts after 4 months or so. Once it loses contact it typically takes many hours to re-sync.

So I'm going to try the PowerGenix AA cells, based on NiZn chemistry. They produce 1.65 volts fully charged, which gives exactly 3.3 VDC to the transmitter. These cells are rechargable, so even if I need to change them every 6 months or so it won't cost a fortune. My only concern is the self discharge rate, about 8% a month. I doubt that I'll get more than 6 months per charge, but that's OK. I may install an external battery holder so that I don't have to take apart the screen every time I change batteries.

Amazon sells them.
I can't get to the station for 10 weeks, I'll report back once I've got the new cells installed.

You can download the datasheet for these cells.

[philcdav]

Hi guys.

How about some lateral thinking ?

Try modding the rx aerial by including a reflector?

Some simple designs made from card and foil could give 3 dB gain for a few pennies.

Add one to the tx also. Get another 3 dB?

Its all in the forum already

[gbee]

Not two years old and put in three sets of batteries. I know my drain is high and position could be better but I seem to be getting three to four months on batteries.

I'm using Alkaline's ~ Lithiums don't like a slow draw and they went flat pretty quickly and were disappointing for the money [put these lithiums in your flashgun].

[Charlie]

Lithiums don't like a slow draw and they went flat pretty quickly and were disappointing for the money [put these lithiums in your flashgun].

I'd be very interested in the source of this information. Everything I've read is exactly the opposite - indeed they will supply low currents up to a decade or more, while the alkalines die sitting on the shelf in a little over a year.

[AllyCat]

Hi,

Well, I half agree with Charlie (and not with gbee), NON-rechargeable Lithiums should indeed have a very good shelf (and low drain) life, but so should Alkalines. Most Alkalines have a "sell by" or "best by" date at least 5 years ahead, even the cheap "heavy duty" cells should be good on the shelf for a few years. It's the rechargeable NiMH and NiCd (and to a lesser extent Lithium Ion, etc.) that have a terrible "shelf" life, typically losing up to 10% each month.

gbee's transmitter is obviously "faulty" because it should run for at least a couple of years with Lithiums or good alkalines. I wonder if the fault causes it to draw excessive current above some threshold voltage (perhaps 2.5 - 3.0 volts). Lithiums start at about 1.7 volts (each) and remain above 1.5 volts for much of their life (so the drain would be high) but Alkalines start at about 1.6 volts and fall approximately linearly down to typically 0.9 volts at their (nominal) End of Life, so the average drain might be much less (and thus give an apparently better life).

I don't believe that Lithiums have a much greater capacity than good alkalines (perhaps +20%) but their excellent low temperature performance and more stable voltage over life may give far superior results in some applications.

Cheers, Alan.

[AaronJones]

Hi guys.

How about some lateral thinking ?

Try modding the rx aerial by including a reflector?

Some simple designs made from card and foil could give 3 dB gain for a few pennies.

Add one to the tx also. Get another 3 dB?

Its all in the forum already

At 433 MHz / 0.7 meters a parabolic reflector is a substantial object, over 5 times the size of one for a wireless router. Cardboard and foil won't stand up to wind and rain at this scale. It won't be few pennies and it won't be pretty, at least not one I would make.

I'll try goosing the battery voltage a bit first; I'm cheap and lazy.

[Charlie]

Hi,

Well, I half agree with Charlie (and not with gbee), NON-rechargeable Lithiums should indeed have a very good shelf (and low drain) life, but so should Alkalines. Most Alkalines have a "sell by" or "best by" date at least 5 years ahead, even the cheap "heavy duty" cells should be good on the shelf for a few years. It's the rechargeable NiMH and NiCd (and to a lesser extent Lithium Ion, etc.) that have a terrible "shelf" life, typically losing up to 10% each month.

Sorry Alan,
My brain was not completely in gear.. When I said "Alkaline" I meant zinc carbon, which has a lower 3 sigma of 1 year. The zinc Cloride (heavy duty) should last about twice that long, and alkalines even longer. I can't find my notes right now, but I believe that 5 years on an alkaline is an UPPER 3 sigma number, with a lower being closer to 3, but I'm fuzzy on that one.
Not fuzzy on the lithiums, however, which had a lower 3 sigma shelf life of 9 years when I studied the problem.
All batteries produce energy through a chemical process which does not stop completely if they are not connected to anything. Some technologies use themselves up faster on the shelf than others, that's all. The clock obviously starts at manufacture.