This project started a couple of years back based on nervousness over charging lithium batteries at home. This write-up has also been in the works for a while . . but its completion triggered by recent events. In its current form it likely does a reasonable job, but also has some shortfalls based on what we have learnt (see notes at the end). As with all this site, this is not a recommendation – just an idea being shared as part of the wider discussion.
Context
With all the warnings and nervousness, I had a go at building an enclosed charging station for the collection of batteries in my workshop – covering hobbies, cordless tools, and larger storage batteries (lithium iron based chemistry). In retrospect my charging set up failed the secondary fire audit test badly with chargers and batteries mingled with all sorts of flammable stuff.
I spent a while searching Dr Google for battery charging boxes and found little beyond charging bags and some specialist charging boxes that would take one set of batteries in a tightly closed container. What I did find is the consistent reminders that lithium batteries burn at very high temperatures (> 1,000 deg C) and do not require oxygen to burn – so starving them of air doesn’t help. So I set about contemplating a charging box that could house a variety of DC and AC powered chargers and allow charging of multiple sizes and types of batteries.
As a result I now have a quite large box that lives on a cheap kitchen trolley near the door of my workshop so it can easily move outside for charging. It houses a 24 Volt and 12 Volt power supply, along with multiple charging bays.
I opted to put all the power supplies and the chargers in the same box as the batteries being charged. If it goes up it will take all the electronics with it but hopefully contain the fire. It is much more convenient to use that way and swap across a range of batteries and charger types. I also have no idea how effective it will be in the event of an incident and whether the materials have any hope of containing a fire – and I hope not to find out. At minimum it forces a discipline of isolating and containing the batteries being charged.
Design Summary
The box is built from readily available steel angle welded together into the basic shape and supporting 6mm cement sheet panels to make the sealed enclosure. The angled front lid is hinged at the top and held down firmly with retaining clips when in use.
The DC power supplies live in a sealed section at the base of the cabinet at the rear, vented by computer case fans. The chargers sit on top of the power supply enclosure and the batteries being charged either attached directly to the chargers (typical for cordless tools) or sitting in ceramic containers (flower pots!) held in the partition in front of that. In turn I put cement sheet lids on the containers when charging. Overall it makes for a very usable space.
Build Pictures
End frames welded. They are made of 25mm x 25mm x3mm steel angle.
Core frame structure welded. It is 500mm high, 500mm deep and 750mm wide
Finished and primed frame with door hinges attached. The hinges are mid-sized gate hinges welded on.
Cement sheet attached and sealed with flame resistant adhesive called Selleys Flameflex fire and acoustic sealant in Australia. It is also used for the door seal.
Location of DC power supplies wired to terminals in shelf. The AC input power leads come out the bottom to a power board.
Computer case fans at each end connected to 12 volt supply
DC power supply area closed in and charging bays roughly in place (ceramic flowerpots and cement sheet)
A selection of chargers and batteries in place – plenty of flexibility.
Addition of covers over charging batteries helps with containment; I now put weights on them as well
Finished charging box – lid closed and secured as it would be during charging.
Brackets on top are supports for open lid.
Outside, roller door gets closed behind it.
As next steps the tree will go, the fence will get some cement sheet on it, and a chimney to be added to take smoke above the roof line (see Footnotes)
Footnotes
Discussions around this first attempt been raised a few new considerations.
- It was designed to be outside while charging. This influenced:
- Materials, priming and painting
- DC power supplies inside – allowing for a single extension lead connection to power the whole box, rather than DC wiring and somewhere to put power supplies in the workshop.
- Lid design so a light can easily be mounted on the inside top of the box and it acts as some kind of shelter if you need to open in the rain. And if my seal is good enough it should be somewhat water-proof (but is not currently water proof enough to live outside).
- While it should help constrain the fire from a lithium battery event the area of concern is the combination of heat and pressure leading the walls to fail. The flower pots and cement sheet should handle the temperature (welding steel on them doesn’t seem to do damage) but pressure is untested. And add to that that the box as is does nothing to manage the smoke. We sense both are alleviated by addition of a chimney, likely steel downpipe, to manage smoke out the top of the box and relieve the pressure.
- It needs a light and a smoke and particle detector inside the enclosure.
- While the fans and vents are necessary for cooling the power supplies, reality is they will also ensure any smoke will certainly get dragged in unless the chimney box seals work and the chimney takes it a long way away.
Note the simple act of putting it outside and closing the door behind it helps with isolation from secondary ignition sources. The two layers of protection (flowerpots with lids, then the box chamber itself) should help contain flames for some period. Addition of a chimney makes sense.