Blackouts and batteries

Cyclone Kirrily’s brief visit last Thursday (January 25) left about a third of Townsville without power for a few days, throwing us on whatever off-grid resources we had. Here at Green Path HQ we put Off-grid but not by choice into practice. I’m happy to report that it worked pretty well, but we were very glad to get power (and air-con!) back after only 36 hours.

We shared that blog post on social media in the hope that it would help others and received useful tips in return. Here I want to share and expand upon a comment from Michael Crozier, “Cordless tool companies are just starting to bring out 18V-DC to 240V-AC inverters. Not as powerful as your power station, but great if you already have lithium-ion power tools anyway.”

It was a good thought and prompted me, with his collaboration, to take it further.

As I said when I described my own set-up, every reader will have different needs so I will focus on general approaches rather than identifying particular models. All my figures will be approximate and links to commercial sites are purely for illustration – they are not recommendations.

What can you do with batteries in a blackout?

Going out and buying a power station in case of another blackout is unlikely to be worthwhile but most of us have other batteries which are powerful enough to be useful. Capacity is critical, so I will look at that before looking at how we might use them.

Capacity

The physical size of Li-ion batteries is a fairly good indication of their capacity but we need to look at the label. It usually states Voltage and Amp hours, e.g. 12V 3 Ah, but the better measurement of capacity (how much electricity it holds) is Watt hours, Wh, which is calculated by multiplying those two figures together, i.e. 12V x 3 Ah = 36Wh. (See this page for more about electrical units.)

Typical figures are:

• Small power tools, e.g. drills: 12 or 18V, 3 – 12 Ah, i.e. 36 – 216Wh
• Large power tools, e.g. electric mowers: 36 – 60V, 2.5 – 6Ah, 180 Wh or more
• e-scooters or e-bikes: 12 – 48V, 7 – 20 Ah, 70 – 960 Wh

And we shouldn’t forget the old-style lead-acid batteries we might still have. The one in your ICE vehicle is likely to by 12V and up to 1200 Wh, and you may have a smaller one in your ride-on mower.

By way of comparison, my power station is 580 Wh.

Getting useful power out of them

How might we use them to supplement a Li-ion power station or petrol generator when the mains power goes off? Or get by if we have no other power at all?

36 Wh is enough to run LED lights for hours, or recharge phones, or run a laptop for a while, so even the smallest tool batteries are useful. Bigger ones will do it for longer, and the biggest ones may run a camping fridge or a small air-con for a while; so would an e-scooter battery, if we could get the power out of it.

Getting the power out of any of them, in fact, is the first difficulty. Let’s look at off-the shelf options:

• Most power tool makers offer USB power stations which clip straight on to the battery.
• Most also include clip-on portable fans and working lights.
• Some brands (not many, so far) offer battery-top inverters with 240 V outlets.
• There are some after-market adapters designed to let people use a battery from one maker with a tool from another (which may be useful in itself) and some of them have USB outlets built in.

All of these are quite cheap and would be useful in normal life so they are worth thinking about. Also:

• Some e-scooters and e-bikes have built-in USB outlets.
• Lead-acid batteries are easy to work with. All you need are crocodile clips on the terminals and you have a 6V or 12V supply. (If you want to use one regularly, consider getting a battery box, $50 – 80, with built-in USB and cigarette-lighter sockets.)

Bear in mind that USB power was designed for low-power applications (15W or less, at 5V) so a large battery may run one or two lights for a long time through a USB port but never be able to power a large device.

Getting more power into them

Recharging your Li-ion batteries might be difficult, because most of them need to be charged from a 240V supply.

• A simple solution is to plug their standard charger into a power station with a 240V outlet. That only shifts the problem from one battery to another, but it might be worthwhile if you need power in two locations. There’s a cost, though: neither inverters nor battery chargers are 100% efficient so some power is wasted in the conversion. (Inverter efficiency is usually around 90%; I have no figures for battery chargers.)
• Charging them from a petrol generator, if you have one, is no problem at all.
• If the cause of your blackout (e.g. a cyclone) hasn’t blacked out your whole region or blocked your roads, you may be able to put your batteries in your car and take them somewhere you can recharge them.

We may have to settle for using each battery until it runs flat, hoping that mains power is restored before we end up sitting in the dark.

Lead-acid batteries can be charged directly from solar panels, which is fine if you have enough spare panel capacity, or (again) from a generator or power station.

Safety

Li-ion batteries do burst into flame if mistreated but everything I have described so far should be perfectly safe. It all uses standard components and doesn’t require any technical expertise. Be sensible, though – keep electrical gear away from water, keep it in good condition, etc.

There is a loose community of DIY people and hard-core hackers out there on the internet. Some of their ideas are good but please proceed with caution if you are tempted to join them.

• Thanks again to Michael for the initial comment which sparked this article and for supplementary technical advice which improved it considerably.