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Battery power and power consumption help! Answered

I have a geocache project and need help with the power supply and power consumptin inside it.

The basics of the project:

It is a large wooden box.
The box has a on/off switch.
It also has various various coin slots.
Flip the switch, turning it on, to supply power to the solenoid inside.
Dropping a coin through the correct slot will trigger a momentary micro switch which activates the solenoid and springs out the drawer of treasures.
Take your loot.
Close the drawer.
Turn off the switch and leave it for the next adventurer.

And it works! Yay!

Commoonents the question: 

The solenoid is a 12v  door latch solenoid.
https://www.adafruit.com/products/1512

The battery is a 12v 5ah sealed lead acid battery. 

The coin micro switch is:
https://www.adafruit.com/products/820


My question.
This geocache that lives, protected, about 3 blocks from my house. I obviously won't be charging the 12v battery very often.

Since this setup only has momentary power draw once in a while. Say once a week. Maaaaaaybe. Does anyone have any alternate power recommendations? I am okay with changing out the batteries once in a while. But I'm hoping for a once every few months.

I originally used a new lead acid battery but it seems to have died. Possibly from letting the charge fall to low and then sulfation occured.

I'm considering using a 11.1V Lipo Rc battery instead so I can recharge it at various levels of depletion.

Thing is I need it to last a worth while amount of time without loosing power but also killling the battery from just sitting there. 

Thoughs woukd be GREATLY appreciated. 

-McG

Discussions

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iceng

4 years ago

I'm a Geocacher and while the box works collecting coin, I think it is highly illegal.

Setting that aside, how is it hidden, can you plaster some solar cells to trickle charge the batteries because the use of the box will be rare compared to the waiting time.

Also I would loose the on/off sw and have an ON button on a time latch to avoid the casher forgetting to turn the sw off.

Let the unit turn itself off and save a lot of discharged battery.

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McgCacheiceng

Answer 4 years ago

Hello cachetr. It seems I need to clarify something. The box has a coin return slot on the front. Everything that goes in, comes riiiiiiiight back out. :)

Solar is an interesting idea I'd previously thought of it but am unfamiliar with how I'd set that up. I'm sure my googling will land me some where, but, is there a kit you recommended? And what type of battery would be best suited if I tried that route?

Thanks for all the help and I assure you, if you ever found my cache... you'd get your quarter back.;)

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icengMcgCache

Answer 4 years ago

Great the coin is a trip wire only. Notice I moved on.

When you select a battery, then select a solar cell group that is 3 or 5 volts more then the battery at full sun add a diode to prevent discharging at night and you have a simple charger.

SolarLipoCharge.bmp
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McgCacheiceng

Answer 4 years ago

quick follow up question:

With the solar setup idea... Is there any worry about over charging?

Also under the current setup I described, (I.e. swapping out batteries once in a while. It only being triggered once a week under a very small load. Etc.) Using a 12v 2000mah LiPo battery, how long do you think it could stay out there before I need to swap it for fear of harmful under charge?

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icengMcgCache

Answer 4 years ago

Trickle charge only under 20ma average over a day maybe a peak of 50ma, from a $20 Harbor Freight 12v solar array with the diode inside, you can always put a 100 ohm series resistor. I don't think it will overcharge.

Not sure about how many ma hours your system actually uses, to predict how the battery will do.

As a startup you may want to try using eight low cost rechargeable 1.5v cells.

.

BTW I did a geocache that had people stand in a stone circle and call out or clap their hands and a very very low power audio amp (change_battery_every_year) that would ring a bell in an other tree above a plastic pipe going deep down and a long string with a magnet on the other side of same tree which would allow to pull up a metal capped bottle from the plastic pipe.

Unfortunately all but one never found the string and one actually climbed the tree to take apart the doorbell receiver circuit.

Point being be ready for difficulties :-P

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McgCacheiceng

Answer 4 years ago

Fantastic! Thank you for the schematic too! I will start brainstorming where this could go. :)

Also, I did notice you moved on. :) I appreciated your comment. A Geocache piggy bank theif would certainly go against the "code". Just wanted to clarifying for you and all the millions who will read this post. ;)

Thank you again for your ideas. :)

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FarmerKJS

4 years ago

You could put a small solar panel to charge it.

If you put it near a tree you could hide a panel in the top of the tree

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McgCacheFarmerKJS

Answer 4 years ago

Thanks for the the thoughts Rocks! The tree would absolutely be the best place for a solar setup. Now..... how do I do it so it doesn't get stolen? hmmmmm thinks cap on.

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FarmerKJSMcgCache

Answer 4 years ago

Tamper Proof screws all the way

plus if you somewhat hide it and the wires it wouldnt be easily seen

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icengFarmerKJS

Answer 4 years ago

Ahem so what did i say .... that

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FarmerKJSiceng

Answer 4 years ago

I understand that but it seems you said to put them on the box

I was saying make them external so you have more freedom in cache location

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icengFarmerKJS

Answer 4 years ago

Yea you did say that :-o

I live in a desert, just sagebrush, sand and rocks unlike your area where crops and trees can grow :-)

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McgCache

4 years ago

here are a few pictures of the cache and where I put it. I did add swivel covers for the coin slots as well. Ah weather protection. :)

image.jpgimage.jpgimage.jpg
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steveastrouk

4 years ago

Lipo is a good choice, they hold their charge better than most other technologies. SLA don't like getting too cold, and self discharge pretty rapidly