Building a Festival Ready 12 Volt Rechargeable Power System Part 2: Putting It All TogetherFollow article
A weatherproof case to house everything, featuring connectors for solar/mains charger plus the Red Tin and PA, ready to provide off-grid power at festivals and outdoor events.
Having done the research on solar chargers and batteries in Part One of this blog post series it was now time to put the system together.
The container for the system needed to be as weatherproof as possible. However, given that it needed to house a lead acid battery it could not be completely airtight and would need venting, but as long as it could withstand a good bit of wet and dust, that would be good enough. The Facom TOUGHSYSTEM boxes looked like a good option
I had an old Radio Flyer trolley that would provide the wheels once it had been cleaned up; it had a proven track record, having withstood various festival adventures including a couple of very wet and muddy Glastonbury outings.
Unfortunately, it has been sitting in storage for a couple of years so the tyres are flat and the paintwork has seen better days, but nothing that can not be fixed.
Selecting a suitable battery and other components
After my research outlined in Part 1, I looked at batteries that offered between 15Ah and 30Ah and ultimately went for something in the middle of that range that provided 24Ah. At just over 7kg it was not light, but it would be fine on the trolley and could be carried if necessary.
To make the system as weatherproof as possible I selected IP65 or better-rated components wherever I could.
Bill of materials:
- Facom TOUGHSYSTEM Structural Foam Tool Box
- Binder 720 Series, 3 Pole Panel Mount Miniature Connector Socket, Female Contacts
- Binder 720 Series, 3 Pole Cable Mount Miniature Connector Socket, Male Contacts
- Binder waterproof connectors series 693, 4 Pole Panel Mount Socket, Female Contacts
- Binder series 693, 4 Pole Cable Mount Connector, Male Contacts
- Bulgin FX0462 Series 10A Manual, Slotted Cap Panel Mount Fuse Holder
- Littelfuse Inline Fuse Holder for ATO Blade Fuse
- Murata Power Solutions Digital Voltmeter DC, LED Display
- Single Pole Double Throw (SPDT) Latching Push Button Switch
- HellermannTyton NGM M16 Cable Gland With Locknut, Red Nylon
- RS Pro Lead Acid Battery Charger
- Euromas ABS Enclosure
- Air Vent
- Lead Acid Battery 12V, 24Ah
Adapting the case
I wanted to keep as many of the connectors, buttons etc. inside the box as possible, since the fewer holes I put in the box, the more weather resistant if would remain. In the end, the only holes I put in it were for the charging connector and a vent for the battery.
I decided to construct a compartment inside the box to keep the battery secure so it did not shift about in transit and to support the internal electrics.
After making some prototype panels — first in cardboard using good old-fashioned scissors and then in laser cut MDF — I cut the final version in acrylic. I ended up with the battery standing on a sheet of laser cut acrylic that was in turn supported by a stack of MDF sheets. I am hoping the MDF will not get damp in the box and turn to pulp, but it can be replaced if it is not up to the job. The battery is held in place by another stack of MDF finished off with a sheet of acrylic for appearance sake.
A vertical panel keys into the base and again restrains the battery as well as supporting the top panel where the power button, voltmeter, fuses and outgoing 12V connectors are situated.
A box is attached below the top panel to provide some protection for the electronics. Its IP66 rating is lost as it is installed without its lid but a deep etch on the underside of the top panel for the edge of the box to key into should mean it provides reasonable protection from moisture ingress.
Although I had sourced a power button with an LED, I decided not to connect this so as to save a little power. The voltmeter lights up nicely and, when tested, only used about 5 mA at 12 volts, so it would also serve nicely as a power indicator.
Each of the 12v output sockets is fused and two in-line blade fuses are also installed on the cable running from the battery positive terminal, to power distribution and the charging socket.
I replaced the plugs that were on the solar panel and the battery charger with the large waterproof Binder series 639 onesto provide a weatherproof connection.
The remaining space in the box provides useful storage for the mains charger and assorted cables.
Once again it has been a steep learning curve trying to work out all the variables of solar charging, power consumption and battery amp/hours, but I think it has really paid off. I have ended up with a practical and good looking system that should keep the music rocking for a good few hours after the sun has gone down. I am now eager to put it through its paces.