Power for an outdoor project

I’m working on an electronic bench (lights, sounds, etc.) that will be outside. Going in position was there would be an outlet. No go, so it’s battery power. Solar charging was an option, but after looking at the location, sunlight hours, etc. it’s a non starter.

I’m now looking at using the battery packs for portable drills/saws/etc. One pack will run the unit for a few days (depending on use, etc.) Plan A is to hit the local flea market and buy a defunct drill, take it apart and harvest the battery connection. I’d mount it under the bench, most likely so the battery hangs down to keep rain/snow/birds /etc. from filling the cavity.

I’d pick up a pair of battery packs and a charger (one on the bench, one on the charger) to allow for a busy day of use.

Peak load is about 2.5 amps and that’s only for 500ms to do full on all three RGB LED’s as a quick surprise flash. Normal load would be ~1 amp with a 20% duty cycle. So I’m expecting a full day use, but there is the second battery pack.

Flaws in my plan? Tips for mounting the battery holder on the bench?


I am fascinated by a bench that will have lights, sounds, and surprises.

I think your idea should work. What is the voltage of your electronics? If 5V, you could also consider a beefy portable power bank. They’re making 'em pretty big these days - 32AH and up to 2.4A per port.

You should also consider having a generator. Depending on where it is relative to the possible battery charging locations, it may wind up being less work. We’ve gone with solar for our trailer power (which mostly runs lights and charges batteries), but then we have ten to eleven hours of daylight at our latitude during build season; your latitude may vary.

Edit, after re-reading OP and response:

**Under **the bench, for the charger/regulator/inverter as well as the batteries. Out of the way and (even more importantly) out of the weather.

Cranky! :smiley:

Edit 2:

+1, or perhaps +1k… What free energy is available in your outdoor environment?

Need 12 volts for doing the LED strips, but the power packs would be a great choice for a 5 volt only project.

The office staff next to the bench need to be able to manage the recharging. A generator would make them cranky.

Is wind power an option? If it’s near moving water, that could be an option as well. I think there are thermoelectric generators, so maybe you could use heat or cold to charge it? Though I think solar would be more efficient…what type of battery do you need to charge?

1A @ 20% = 0.2 Ah, x24 = 4.8 Ah per day. That’s close to the 20 hour setup they use to measure Ah capacity, so it’s close to a real number. That discharges the battery 100% though. An FRC battery would do well. YMMV especially if your numbers are off.

Is theft a consideration? If so, lock the whole thing in an ammo case, chained to the bench. Worst case they cut your wires and steal the LEDs. Think water-tight though.

Solar: a 2A panel for 6 hours = 12 Ah.

So are you going to give us any more details about what this is for? Inquiring minds and all… :smiley:

Fully agree - if the posts above appear to be spit-balling, it’s probably because no one quite understands what you’re trying to do. That’s definitely the reason in the case of my earlier post. By sounds, do you mean providing tunes to people working tools, or something else? By lights, do you mean status lights, or enough light to work an hour (or two, or six) after sunset (or before sunrise)? What tools do you want to run, and for how many hours per day, and how many days per week? Do you want to charge robot batteries out there, too (if so, how many)?

Ahh the joys of being nose deep in a project and seeing only leaves and not the forest. :rolleyes:

Picture your favorite art place. Out front is a comfy looking wooden bench. You sit down and rest your arm. The bench lights up and plays a comforting series of tones. But it startled you and you move your arm and the lights dim and the tones stops. You put your arm back down, in a slightly different place and a different tones play and you think a slightly different color light glows. As you move your arm up and down the bench, the lights change and so does the sound.

Your friend sits next to you and starts moving their hands along the arm rest, also playing tones and changing the light show. After a few minutes of fun you both get up, the lights dim and go out.

So it’s not a robot, more of an art installation.

Hardware is an Ardunio (maybe a Mega if we feature creep on the number of imputs), midi-sound shield, speaker with 9 watt amp and about 6’ of addressable RGB LED strip that has been imbedded in the sides of the arms and across the back. Copper strips in the arms generate the inputs for lights and sound. Electronics are in a small waterproof box under the bench held on with security screws. Cables are in routed channels under the bench, wires secured with 3M 5200 marine adhesive sealant. (If you are a boater you are nodding, once the 5200 dries it’s not coming off the bench).

Plan 1 was to just plug the bench in but there isn’t an outside outlet. So the search started on alternative energy sources

Solar power ended up being a non starter due to trees and the street direction. Wind power is out, since it would need to be mounted high enough so people standing on the back of the bench could not touch the spinning blades. Gas/propane/coal/etc generators are out since the noise would make the art staff cranky with it running all day. So some type of battery power was the end result.

Because the bench is outside of the gallery, the people inside will keep an eye on it. At night it gets moved to the side lockable space. The staff will be responsible for keeping the battery set up working.

So the battery requirements are:

  1. Easy to change on the bench, no tools
  2. Daily load is about 6AH
    2A) minimal battery changes (so packs of AA batteries are out)
    2B) be able to manage a higher load (summer evening hours, festivals, etc.) with a second battery change.
  3. Waterproof or be mountable in a waterproof container
  4. Inside recharging should be simple, no tools

I was thinking of using the battery from portable tools. (You have them, you take the battery off the charger, snick it into the drill, saw, etc. do the job and then put the battery back on the charger). I was going to get a broken tool, take the battery holder off of it and use that. The tool locks the battery in place, so I could mount the handle under the bench (keeping it out of the direct rain) and it would stay in place. I could use a charger base and rip the charging circuit out, but most bases I’ve seen / used, the battery is held in via gravity. So when the battery isn’t in place and it’s inclement the cavity would fill with water/snow.

LED strips want 12 volts (so getting 12v tool battery makes that easy), but I did find some strips that will work on 5 volts, so the GreyingJay idea of the USB 5v recharge packs are on the table for discussion. (I’d mount a plastic “ammo” box from HF @ $8.99, waterproof and locking and put the battery pack in there)

I led with the portable tool recharge packs since the gallery has power drills and sort of understands that technology.

Hope this helps.

Sounds awesome! I’d like to see the finished product. Maybe you could use the same battery they use for the tools at the gallery? Most cordless tool batteries are < 6 Ah, especially the 12 volts. Maybe the battery could stay in the bench and it could just be plugged in with an extension cord to charge? I think it could work by using the charger/battery holder/output from a tool like this

Oh - a sitting bench, not a work bench. That’s a horse of a different color.

Have you considered burying wires (suitably deep and moisture resistant) from “the gallery” to “the bench” to carry the electricity? This would open up a wide variety of options, from solar to a wall-wart.

Your power needs may even be small enough to pull a trick out of Tesla’s bag and transmit the power wirelessly from the gallery to an antenna above the bench but below the canopy of the tree.

Edit: Overhead wires (routed mostly along a branch headed toward the gallery and down the trunk) are also worth considering.

I was thinking the same, but the 12 volt variety of wires. Go to Home Depot or Lowe’s and look at their wired lighting section: It’s junk but you’ll get the idea.

Run some #12 wire underground from a convenient window to the bench area. Put a waterproof electrical box (the kind for outdoor receptacles) on a pipe sunk a little into the ground, and a set of Powerpoles inside. Unplug to move the bench, plug in in the morning. Leave extra wire so you can replace the powerpoles once a year…

Batteries are a last resort, if there is AC power within 100 feet of the bench, run low voltage out to it. Very small likelihood someone’s gonna mess with the wires.

Arm detection: Maybe some ultrasonics too, maybe for leg position?

I’m pretty good with the feature creep on ultrasonics, but not on now needing to get a building permit, digging around in walls and maybe a short trench to run wires. The building is commercial space, so it’s conduit for the AC. Low voltage is easier, but will need plastic flex to meet local code.

But I’m sensing a clue train (*) here, I had come trying to get some ideas on best practices on battery power for an outdoor project. but I’m getting lots of cycle back to AC power. Should I go back and say “Sorry, this isn’t going to fly since I don’t have a reliable power source. Battery is a short term, you’ll get bored with changing the battery packs and the bench will die.”? I’d like the project to fly, but don’t want to see hours sunk into something that isn’t going to be really viable.


(*) Clue train reference is from a person that used to walk up to me and go “Clue train now departing to Smartville. All Aboard” and hand me what ever document she had to prove that I was being stupid. :rolleyes:

So if your power usage is 6a/h per day ( at 12V) and you are wanting minimum battery changes/maintenance surely larger batteries would be better.

Is there anything which makes large lead-acid batteries unsuitable for this purpose?

A large sealed lead acid battery/marine battery ( let’s say 60a/h) should be able to power the bench for more than a week before needing a battery change.

Because of the relatively high weight of the battery (probably 20kg) you could have a high-amperage battery charger already attached to the battery and simply need to run a power cord to the bench to plug in and charge with when possible or when the gallery is closed etc. You could even use two batteries in parallel if you have the space. Although the battery(s) would be bulky and heavy this has benefits, if you attach it to the bench securely enough (in a nice looking weather-proof enclosure) the 20-40kg of battery weight, is going to make someone seriously reconsider trying to steal or move the bench.

If you have battery charger permanently attached to the battery the people at the gallery would simply have to run an AC power cable to it occasionally, and potentially click a switch to change it from operation to charging.

Take a look at PowerFilm Solar. They might have something for you and their cells are supposedly better than others. If you’re a ham radio operator, you can get a discount as well on factory seconds.

I am surprised you’d need a permit to run low-voltage DC. Even commercial space. But OK.