How do you power your smart caches?

[+BunHeads]

Smart cache owners what type of power supply do you use to power your caches?

Thanks! 

[+Ragnemalm]

1 hour ago, BunHeads said:

Smart cache owners what type of power supply do you use to power your caches?

Thanks! 

You mean electronics caches, obviously. I have used three different methods:

 

Fixed battery, 9V or 18650. Can last for a long time if the container is well built so it doesn't take in moisture. Should be in placed where the maintenance is reasonably easy since you need to check it fairly often.

 

Visitors bring their own 9V. Bad, positively needs a proper protection diode to protect the circuitry from getting the power in the wrong direction. Also, the connector is likely to rust if it sticks out (I have a friend who did this and it didn't last well).

 

Visitors bring their own power banks. This has worked very well. I have used this for four builds. A slight risk that the connector will wear out if visitors are careless but that has not happened yet.

 

A fourth method is to use a solar cell. I have seen one that used that to charge a battery, which has worked remarkably well. I never used that myself. However, I made one that was powered by a solar cell directly to drive a motor. I can't really recommend that since the power was too low and it broke down multiple times.

[+BunHeads]

Thanks for your info!

[+barefootjeff]

I have a cache hidden in a dark place inside a cave. It's based around a halloween toy I bought that does spooky sound effects that are triggered by the searcher's flashlight. I'd have liked to have made it solar powered from a small panel outside the cave but couldn't see a way of concealing the power cable, so it's simply powered by AAA lithium batteries which give me about an eight or nine month life. I replace them every six months, which is a bit expensive, but for now I'm happy to keep doing that.

[+Ragnemalm]

16 minutes ago, barefootjeff said:

I have a cache hidden in a dark place inside a cave. It's based around a halloween toy I bought that does spooky sound effects that are triggered by the searcher's flashlight. I'd have liked to have made it solar powered from a small panel outside the cave but couldn't see a way of concealing the power cable, so it's simply powered by AAA lithium batteries which give me about an eight or nine month life. I replace them every six months, which is a bit expensive, but for now I'm happy to keep doing that.

How about using rechargeable batteries?

[+barefootjeff]

7 minutes ago, Ragnemalm said:

How about using rechargeable batteries?

 

The 1.2V cell voltage of rechargables isn't enough for the device and, even if it was, I'd probably have to visit the cache more frequently to do the recharging.

[+arisoft]

2 hours ago, barefootjeff said:

it's simply powered by AAA lithium batteries which give me about an eight or nine month life

 

I put a single CR123A lithium battery to my gadget cache ten years ago and it is still running.

[+Ragnemalm]

On 12/18/2021 at 10:15 AM, arisoft said:

I put a single CR123A lithium battery to my gadget cache ten years ago and it is still running.

Indeed, a battery can last a long time if it the contaner is well built.

 

I made one with a 9V in 2016 and expected it to last, maybe a few weeks since the insulation was very improvised, mostly a matter of wrapping some plastic around the electronics. I might have changed the battery once, not more. It just keeps running.

[+Wet Pancake Touring Club]

WVTim had a Gadget Cache, I think it was called something like the "Well Prepared Driver". It had two bolts sticking out of it, and was designed to use 12v from a car battery with jumper cables. It used an electric antenna motor to raise/lower the log container. Reverse the cables to lower the container. He had it at a Library (I think), at the end of a parking place. Looked like a small house, and the container came up through the chimney.

[+fizzymagic]

USB power banks have become so ubiquitous that I ask for those, and specify that I provide a micro USB connector.  When USB-C becomes the standard, I will ask for that.   It's also not hard to include a set of adapters if the environment is OK for them.

 

I usually use a female pug in the cache itself; ideally, the electronics are contained within an ammo can.  I have never tried using a rubber cover to protect it from the elements.

[+lee737]

On 12/18/2021 at 5:49 PM, Ragnemalm said:

How about using rechargeable batteries?

The self-discharge rate of rechargeables is pretty high generally, and primary batteries are cheaper anyway - I've used 6xAA's in a bank as a big 9V battery, one has 8xAA - this powers a DC-DC converter to output 5V, and is stable until the AA's are down to 8V at least, so makes the most of their capacity....

[+cerberus1]

On 12/17/2021 at 10:48 PM, BunHeads said:

Smart cache owners what type of power supply do you use to power your caches?

 

Guessing you're talking about "gadget" caches, and most we've found required one or two AAs, or one 9v, but the battery was supplied by us.

That's where writing a good description comes in handy, so everyone brings a battery, rather than attempting to disassemble your work for a smiley.

[+lee737]

As important is preventing battery drain between visits. I don't trust people to switch things off, so use a momentary switch that fires the microcontroller up, then it kills its own power automatically after a defined interval, so it is impossible to have a cache left 'on' by a finder.....

[+fizzymagic]

5 hours ago, lee737 said:

As important is preventing battery drain between visits. I don't trust people to switch things off, so use a momentary switch that fires the microcontroller up, then it kills its own power automatically after a defined interval, so it is impossible to have a cache left 'on' by a finder.....

 

Yes.  Pololu makes nice pushbutton power switches with which a microcontroller can turn its power off.  Highly recommended.

[+lee737]

6 minutes ago, fizzymagic said:

 

Yes.  Pololu makes nice pushbutton power switches with which a microcontroller can turn its power off.  Highly recommended.

I just assemble my own little circuit from a pair of MOSFETs.... found the schematic online...
 

[+Capt. Bob]

To prolong the usable life of the battery it should be completely disconnected from the circuitry when not in use. A simple on/off switch would suffice but this requires humans to switch it off when finished (I find nothing destroys a cache quicker than humans). The method I use is with a normally closed reed switch with a magnet embedded in the lid and the reed switch mounted in the body of the cache. (Mouser Electronics, Part #934-MDRR-DT20-30F @ $2.50 ea.)

[+lee737]

1 hour ago, Capt. Bob said:

To prolong the usable life of the battery it should be completely disconnected from the circuitry when not in use. A simple on/off switch would suffice but this requires humans to switch it off when finished (I find nothing destroys a cache quicker than humans). The method I use is with a normally closed reed switch with a magnet embedded in the lid and the reed switch mounted in the body of the cache. (Mouser Electronics, Part #934-MDRR-DT20-30F @ $2.50 ea.)

I've done this too, and bonnet/door switches from cars.... the leakage current through a MOSFET transistor though is an order of magnitude or two lower than the spontaneous discharge of the batteries in any case....

[+arisoft]

3 hours ago, lee737 said:

I've done this too, and bonnet/door switches from cars.... the leakage current through a MOSFET transistor though is an order of magnitude or two lower than the spontaneous discharge of the batteries in any case....

 

Gadgets I made 10 years ago are using a single CR123A battery as I told earlier. These gadgets have no power switch and the microcontroller is powered 24/7. Leakage current of transistors is not a problem unless there is some design problems. To get the longest life for the battery, I sealed the electronics into a PET-preform topped with silica gel to prevent any moisture. Operating voltage is low (3V) to keep leakage currents in the minimum. Microcontroller is sleeping most of the time. It is woken up by the watchdog timer.

Edited December 26, 2021 by arisoft

[+lee737]

Just now, arisoft said:

 

Gadgets I made 10 years ago are using a single CR123A battery as I told earlier. These gadgets have no power switch and the microcontroller is powered 24/7. Leakage current of transistors is not a problem unless there is some design problems. To get the longest life for the battery, I sealed the electronics into a PET-preform toped with silica gel to prevent any moisture. Operating voltage is low (3V) to keep leakage currents in minimum. Microcontroller is sleeping most of the time. It is woken up by watchdog timer.

I've got a little gadget on my bench, a prototype for one never sent out (maybe we should get a wriggle on) - it uses a ATtiny85, asleep on the bench the past 2yr, with a bunch of activations as I remember, its still going strong on a single CR2032.... I've measured its sleep current with my meter - 0.1uA....

[Johannis10]

On 12/18/2021 at 7:49 AM, Ragnemalm said:

How about using rechargeable batteries?

I once used 3 Eneloop AA cells, but a few months later a hero replaced them with disposable batteries. I don't know if he knew what he was doing and if he threw it away, or if he could use it himself.

Greetings Johannis10