Solar Ammo Can Disconnect Switch

by admin on July 26, 2018

On the original Solar Ammo Can project, I got a few questions about a battery Disconnect Switch. “Don’t we need one?” Well, the answer is NO, but let’s discuss this deeper.

Many battery chargers can become a slow drain on a battery if they are left permanently connected, but are NOT powered up. That’s not a problem on a device which is regularly charged, but can be an issue on a device put into storage or otherwise not used in a while. In the case of the Solar Ammo Can, even the solar charge controller CAN become a drain on the battery.

So, how do we prevent the charge controller itself from becoming an unnecessary drain on the battery?

The easiest way is simply to unplug the main 12+ positive wire from the battery. I designed the project using Velcro, so that I could easily pull up the faceplate and unplug from the battery.

Alternatively, you could also remove the main automative-style 20A fuse. Either way completely disconnects everything from the battery, and prevents any accidental draining.

But what if you want it to be super-convenient and NOT have to pull up the faceplate?
Originally, I designed my project NOT to have a dedicated disconnect switch, as I liked the way everything laid out, and for me, it wasn’t inconvenient to pull up the faceplate and disconnect the main red wire or pull the fuse. I also liked having the switch on the quad-output turn on and off just those components.

But since people have asked, I’d like to show an alternative way of wiring things up where we repurpose that same switch to act as a main disconnect.

To start with, wire up the project as we’ve already shown in the original step-by-step project video, with the following changes:

  • Run the 12V Battery Terminal to the center terminal (+) of the switch
  • Run the Switched output of the switch to the BATTERY+ terminal of the solar charge controller
  • Run the LOAD+ output of the solar charge controller to the 12V cigarette lighter plug, USB ports, Secondary Voltmeter, and 12+ output banana jacks. (The change is that the +LOAD is NOT going to the switch anymore.)

When using the Solar Ammo Can, make sure to turn the switch to ON. The display on the solar charge controller will come on, as well as the lights on the quad-outputs. Turning the switch off will power down everything INCLUDING the charge controller. This prevents any battery discharge when storing the unit.

As a reminder, make sure to turn the switch ON while trying to CHARGE the Solar Ammo Can, otherwise no amount of sunlight will charge the battery!

If you are interested in purchasing a laser-cut faceplate, they are now available for sale.

I hope you’ve enjoyed this project, and that it helps you learn a little more about batteries, solar, 12V DC, and DIY projects.

If you have any questions or comments, please let us know!

Until next time, stay charged up!
-Ben Nelson

{ 13 comments… read them below or add one }

1 David Hosmer February 8, 2019 at 10:44 pm

Thanks very much for the spacers. The project was very fun. I am a fan of the channel. I enjoy all your videos, especially the “not a flamethrower”. You put a lot of personality into your work. That something the other channels seem to lack.


2 Paul Ebelmesser April 17, 2019 at 11:47 am

Ben, Am building this to power a Mobile Ham Radio station. Question. When at home, Can i just plug a A/C Battery charger into the Solar Port? Thank you.

3 admin April 17, 2019 at 1:48 pm

Hi Paul,
You can just use a plain small DC power supply straight into the Solar IN port. The Solar Charge Controller will make sure it doesn’t get overcharged. If you want to use a dedicated 12V battery charger, best to just flip up the cover and attach the charger connections straight to the battery. If you did plug a charger through the Solar In, it’s possible that your charger and the solar charge controller might conflict. It would probably be fine for bulk charging, but cause issues on the top end of completing a charge.

4 Peter November 3, 2019 at 4:48 pm

Hi Ben,
Thankyou very much for these 2 detailed videos on the ammo solar box. I will be making one. Continuing on from Pauls question, I would like to include some terminals on the board so tha i can use a battery charger when i get home from camping. I guess they would be connected directly to the battery(?). My question is, would i have to disconnect the existing red and black wires to the battery each time i want to use the charger (either physically or by some switch) so that i don’t damage the controller?

5 admin November 5, 2019 at 4:57 pm

I just used a simple 18V wall power supply for charging. I plug it in to the “Solar In”. That way, the solar charge controller prevents overcharging, and you simply reuse the ports already available.
Just unplugging at the battery would certainly be a simple way to do it. They are just spade connections on that style of battery and it’s easy to just plug and unplug.

The “12VDC OUT” goes to the battery, but through the controller from the LOAD side. I’d have to check of that has any reverse polarity protection (I don’t think it does.) That SHOULD also work as an input, as long as the controller is on, but I’d have to double-check that.

6 Chris Tozzi February 29, 2020 at 1:29 pm

Hi Benjamine, This was a great addition!

Two Questions:
1.) I also use a simple 18V, 1 amp wall power supply for charging. The instructions on the solar charge control (using the same one you do) discourage using a source other than solar panels. Last time I used it, the meter on the control registered 14.1 V when the cut-off was set to 13.7 V. Do you think this is a potential problem.
2.) Do you think the banana jack terminals can handle a load of 7 amps? I’m thinking about upgrading my solar panel to a DOKIO 100 Watts 12 Volts Monocrystalline Foldable Solar Panel. Just wondering if you think the terminals can handle it.
Thanks, Chris

7 admin March 1, 2020 at 2:31 pm

I don’t see any issue with using an 18V 1A power supply. The charge controller will just cut off power once it’s up at your cut-off point.

Banana jack terminals should be fine with 7A. They are nice and solid. 14 AGW wiring is generally used for 15A circuits. If your project is all wired up with 12 or 14 AWG wiring, that’s MORE than good enough.

8 valerie whitear January 2, 2021 at 11:06 pm

I had a friend help me to build your ammo Generator. However it will only work on 12 v low watts. How can I make it so it would be able to have power enough for a electric frying pan, or run a electric fan?

9 admin January 3, 2021 at 9:38 am

To upscale the Solar Ammo Can project, you will want to add a higher power inverter – one rated for enough power in watts to run your electric frying pan or other device.
Depending on how much power you want, you will also need a larger battery (or at least connect a second battery in parallel with the first) as the voltage drops quickly on small batteries when placed under a heavy load.

To run heavy power items on a regular basis, the ammo can format might not be right for you. Instead, you can connect all the same components to a deep cycle marine battery, and house them in something like a large plastic tool box.

10 Patti Whiffen February 12, 2022 at 10:46 pm

Hi Ben,

Do you/would you sell one completed?


11 Tim March 22, 2022 at 6:12 pm

Hi Ben
Got a quick question. I did the solar ammo can setup. When I plug in a portable 100 watt inverter into the 12v cigarette lighter plug the ammo can unit shuts off. All wiring is done right. Do you have any answers to this issue. Thank you.

12 Ben N March 23, 2022 at 7:35 am

Without knowing very specific details or seeing the unit itself, the one thing that immediately comes to mind is just that the 12V battery might be low. If it is, and you put a solid load on it (Which an inverter certainly can be) you may be dropping the battery voltage down low enough for the low voltage disconnect to activate.

13 Ben N March 23, 2022 at 7:40 am

The cost of materials PLUS the time I would have to put in to build one means I would have to charge the same price (or more!) as some commercially-produced units.
I designed this as a project for people to enjoy building themselves and learn about DC basics, batteries, and solar.
If you simply want to purchase a similar device take a look at some units available such as these:

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