12V 50Ah portable battery bank

batt bank and light bar

Here’s a portable battery bank I put together for camping and power outage use. Rated capacity is 12V 50Ah (via 3 x 12V 12Ah batteries and 2 x 12V 7Ah batteries wired in parallel). These are used freebies which are sitting at between 60 – 90% so capacity will be a bit less than rated, but for the price I can’t complain. Weight is 18kg.

The case is a Supercheap Auto safe case (found here). Cost $35, which I think is an absolute bargain, as these cases are well designed, if sometimes a little iffy on the quality control of assembly. I also bought myself one of the smaller $18 ones, which is also great value.

Batteries are a bit snug, but this also servers to hold them in place well. They are held down using lengths of 25mm nylon webbing. Small slots were cut in the sides of the case to allow the webbing to wrap around fully. Much simpler than affixing internal brackets to hold. Waterproofing is compromised, however I don’t mind this, as I would prefer the case to have some capacity for ventilation in case of hydrogen build up.

Batteries are wired using 6mm and 4mm automotive wire (what I had lying around) and insulated crimp connectors. There’s a mini blade fuse inline with the output, and a 2 pin JST SM 2.5 connector as the main output. This connector isn’t high capacity (3A max), but I will primarily be using this to run LED lighting, charge USB devices and to power ELV devices (eg plugpack replacement).

The light strips I have pictured above are simply a set of these LED light strips screwed to short sections of PVC pipe with hanging loops. Some twin core figure 8 speaker wire is used for power leads. each tube, which consists of six modules, draws around 250mA at 12V.

Another shot of the side, showing the battery straps:

 

batt bank

 

Things to improve/add:

  • 4.65mm^2 wiring and higher quality brass female spade connectors for batteries, with PVC covers
  • multiple JST SM 2.5 outputs (collectively fused at 5A) for running ELV devices and also for charging input
  • small solar panel and charge regulator, probably in a separate case
  • main isolator switch
  • terminal block / busbar to neaten up wiring
  • 50Amp anderson plug (fused separately) for heavy loads (eg inverter)
  • power switches on each light module

Once some bits and pieces arrive from ebay for the above improvements I’ll update.

 

 

Gas cartridge converters – review

I recently bought some adapters off ebay to convert the screw mount adapter of lightweight hiking stoves which run off the squat butane mix cannisters to the butane cartridge gas canisters used by cheap portable stoves. Turns out it is workable, but probably not the most practical.

gas cartridge adapters

The idea is that butane cartridges cost around AU$6 for a pack of 4 250g cartridges, while the squat butane mix cannisters cost around AU$10 for a single 220g cannister.

The two applications I had in mind were a lightweight kovea stove, and a small gas mantle lantern. The lantern is more intended for car-camping use, but the stove is a for hiking. Whenever I’m car camping I’ll bring the big cartridge stove along as it’s easier to cook on.

Before getting into the adapters themselves, it is worth noting the differences between the cheap gas cartridges and the more expensive hiking cannisters. The cheap cartridges usually contain 100% butane, while the cannisters usually contain something like 80% butane, 20% propane. The key difference here is the 20% propane in the more expensive squat cannisters. Butane, it seems, boils at -0.5 degrees Celsius. Fine if you live in Queensland (which I do), however if you’re in in a cooler climate (or up a mountain or somewhere it gets to close to zero degrees Celsius) you’ll run into problems. This is the same reason cheap butane cigarette lighters won’t work if it’s too cold. The more expensive squat cannisters address this by containing 20% propane, which happens to have a boiling point of around -42.09 degrees Celsius. Why not just use 100% propane? Well, seems as it has a lower boiling point, the vapour pressures in a container of 100% propane can get much higher than that of butane. This is why butane cartridges are essentially aerosol cans, whereas BBQ gas cylinder are heavy steel. I guess the manufacturers worked out that 20% propane, 80% butane was a sweet spot in terms of boiling point and container weight/cost.

So, the moral of this is that at low temperatures, the cheaper cartridges won’t perform as well/at all compared with the more expensive butane/propane mix cannisters.

I bought two different adapters to trial. The first is a small cylindrical adapter that sits directly on top of a cartridge and couples to the screw mount.

I’ve found this one works really well for the lantern. As the lantern isn’t top heavy there’s no worry of tipping, and the lantern can even be hung from its chain quite nicely. It works well for the stove, but is a little unstable since you’ve got your cooking pot/cup up so high on a cylinder with such a narrow base. The cartridge coupling is a plastic job, with an expanding collar to secure it to the cartridge.

The second adapter has the screw coupling on a wide tripod base, and a hose running off to the cartridge coupling This coupling is a simple pressed steel job, which is functional, but it can be a bit difficult to get on and off. I much prefer the expanding collar design of the smaller adapter. I noticed that using the stove on this (which is the logical option, since it provides a nice stable base) give a bit of an uneven flame. It kind of pulsates in size. In addition, it does not pack down very small unless you unscrew the steel adapter plate – kind of irritating.

So for me, the compact inline converter is a winner for use with the gas lantern, which i’ll use when car camping. As for stoves, if I’m car camping then I’m going to be using a bigger stove which uses the cartridges directly anyway. If i’m hiking, then i don’t want the extra weight and space of a converter, and the gas issue clinches it.

Some background reading on gas mixtures and stoves:

http://www.bushwalking.org.au/FAQ/FAQ_Mixtures.htm

http://www.backpackinglight.com/cgi-bin/backpackinglight/canister_stove_faq.html