Changing battery type and solar charging?

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GreginCO

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I am a complete Newbie, so simplicity is appreciated.

I use battery powered irrigation valve timers. They come set up to use 2 x AAA standard alkaline batteries. For reasons too lengthy to explain here, I converted the internal 2 x AAA power to an external 2 x AA standard alkaline battery source. Alkaline batteries do not last the entire watering season so the batteries have to be changed. However, because the timers are not digital, changing the batteries then also requires resetting each timer - a physical process of turning two knobs at exactly the time you want the valve to open.

I'd like to convert the 2 x AA alkaline battery source to a 2 x AA rechargeable battery source with an attached solar panel charging system so the batteries stay charged all season. I have scoured the internet looking for a simple plan (or kit) for accomplishing this but I can't seem to find anything. Can anyone here point me in the right direction?

(For reference, other than keeping the timer electronics active, when the timer calls for the valve to open, a 3v (geared) motor rotates and closes a switch and rotates a small ball valve 1/4 turn and then opens the switch - about 5 to10 seconds. In my case, this may happen a total of two times a day. Yes, these are clumsy timers, but they are one of only two timers that I found that do not require back-pressure to operate.)

Thank you in advance.
 
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Regards, Dana.
 
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You will need someone to get a lot of specs from you to design something to your budget.

V min, I pk, I avg, motor R. Temp, range. Battery life (days) Load Wh/ wk, Min Solarity Wh / wk ,

If this works from 2.5 to 3.7 then Li Ion or Eneloop Ni MH, what is the spec?

https://www.amazon.ca/Panasonic-BK-...ocphy=9000793&hvtargid=pla-348609717566&psc=1


I'd consider 2 D cell Alkalines to last at least 1 season and maybe a more reliable cost-effective solution.

good luck.
 
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It does not have to be complex!

NiMH batteries can be charged at up to 1/20th C rate for long periods without harm.

eg. If you had two 2.5AH AA NiMH cells, a solar panel that could give 50mA could be left connected, just with a diode to prevent discharge through the panel at night.

That's only 1/50th C rate so should be fine for years, especially as it's intermittent.
 
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Exactly - however, 'years' might be optimistic (or at least many of them), as NiCd and NiMh tend to be relatively short lived.
 
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Thank you, all, for your responses. I greatly appreciate the information.

On "Banggood" I found the NIUP11TA which seems like it might be a little excessive for my situation.

I had seen the "diode" solution online but it seemed overly simple and I didn't want to take a chance of killing the batteries by overcharging them. I think I'll look around to see what small (50mA) solar panels are available. (D batteries are also an option but I'd like to find a more environmentally friendly solution, if possible.)

(If anyone is interested, the reason I changed the original 2 x AAA internal batteries to 2 x AA external batteries is because the timers are sealed enough to make them waterproof and, in my case, they are in direct sunlight all day. The internal temperature in the sealed timers would get hot enough to make the small AAAs swell and press against each other and eventually disconnect themselves from the battery holder terminals which turned the timers off.)

Thank you all, again.
 
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Hi,

My recommendation is that you overestimate the required charging power by a few times or even more. That's because at night you get no power, and during the day if you get several days of cloudy weather the batteries deplete a lot more than usual.

I have had this experience with my solar charger and battery over some months. You will get some power during a cloudy day, but it may not be enough if the solar panel is too small.
You could also make room and plan for a second panel in case the first one is not powerful enough over the weeks you test it.
Aiming is important also if you do not use a mechanical tracker mechanism. If you aim due south in this area you get reasonable effectiveness. In your area it may be different though depending on where you live of course. Probably if you aim the panel at the mid travel of the path of the sun overhead you would get reasonable results.
 
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Thank you for your advice.

My newbie logic tells me that I don't need to completely recharge the batteries on a continuing basis because the single set of 2 x AA alkaline batteries I installed in April have adequately operated the timers until about the beginning of October. Now a couple of the timers seem to occasionally not have enough power to start the motor that opens the valve. At the end of October, in preparation for winter, I stop using the timers until the beginning of April when I will put them back online. So, what I'm seeking out of the small solar charging system is to keep 2 NiMH AA batteries alive about a month longer than I'm getting out of the alkaline batteries. Is my logic flawed?

As for my location, I'm in the high desert. It is rare to get 3 consecutive cloudy days any time between April and October. Generally, my timers are in full sunlight most of the day. My plan is to point the little solar panels south/southwest in a fixed position and I am hoping (guessing?) that whatever daily charge the batteries get will just about replenish their daily usage. I am interested in seeing what the voltage is for this year's alkaline batteries when they're shut down at the end of this month.
 
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Thank you all again for the responses.

At this point, I think I will be using a Sunyima 5v 60mA panel to charge 2 EBL NiMH AA rechargeable batteries. The EBLs are 1.2v 2800mA. What blocking diode should I use?

Thanks.
 
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Hi,

Sounds good.

You're lucky here in NJ we can get clouds for a week straight.
 
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