Cold Power

Jason Greenlow

Issue 3, September 2017

Every time the power goes out, we all think "I should really build something to provide backup power". Jason did just that.

Jason created his own Lithium Ion powered portable power supply. Using old laptop Lithium Ion (Li-ion) batteries and some Aussie ingenuity, he’s created a portable power bank in an ESKY, which arguably is better than having a few cold beers inside!

We’ve seen cooler boxes converted to powered cooling units, but haven’t seen too many power banks! What was the lightbulb moment that made you start this project?

It was a mixture of things. I had about 300 Li-ion cells lying around from old laptop batteries which I had stripped and tested each cell. One day there was a power cut, which lasted for a few hours, I thought I’ll give the generator a run but then on the other hand, it’s loud and I like my neighbours. So then I thought, wouldn’t it be great to have a mobile power supply?

inverter powering a lamp
The inverter provides plenty of mains power.
12V outlets provided too
12V outlets provided too.

Oh yes - the dreaded extended power outage. We’ve experienced a few of those ourselves. Did you set about designing it first, or wing it and see where you ended up?

I’m normally a rush to the finish line sort of fella. I want my project done now or yesterday, but I actually took my time with this one. I looked at the cost of all my parts first, to find the cheapest options available, knowing that the most expensive part would be finding a cheap pure sine wave 24V-240V inverter. I built my Li-ion battery pack to be 24V with a BMS (battery monitoring system).

Being a mobile device I wanted to get as much punch out of the battery pack without getting too heavy; this also meant that I could get more time out of the inverter. Well, the theory was: the less load on the battery pack from the inverter, the more battery time I would get. I built my own DC-DC converter to run the 12V system because I couldn’t find a 24-12V 30A converter anywhere; but it was also nice knowing that 70% of the project was built by me.

Low current DC-DC converters are readily available, but high current converters are hard to come by. We wondered if the conversion to 12V for low-voltage devices would offset any improvement from a 24V system, but there are many variables. What made you decide to build it into an ESKY?

I used an ESKY for a few reasons. The first was because it provided an insulator around the electrical components, so it meant there were two layers to get through in order for anything to be damaged due to impact. The second was the cost of an ESKY; compared to a typical junction box of the same size, the price difference was huge! And the ESKY comes with a free handle!

To be able to use a 12V solar panel or to charge the battery pack via 12V anything, I've used a 12V-24V boost converter to charge, and to create a stable charging input. The boost converter is set to boost to 25V and the BMS manages a balance charge.

Inside power supply
It might not be pretty, but it's highly functional.

Integrating battery management for flexible recharging is a great idea. How fast can you recharge the battery?

The BMS controls a balance charge, cuts the power off at 22.5V minimum voltage output, cuts charging off at 24.4V, and has an output current rating of 50A. It also has overload protection. So far a full charge takes about 1.5 hours.

That’s VERY fast recharging! If you had your time again, would you change anything?

If I was to change anything, I would find or make my own storage unit instead of an ESKY. One extra component I’d like to install is a battery bar meter, so I can easily see the battery’s state of charge.

Well, it would save you buying another ESKY for beers, but it did turn out really well! What are you working on now?

Currently I am thinking about building a device for drivers that prevents falling asleep at the wheel. I’ve not started anything yet; it’s more of a brainwave at the moment but the device involves blue light theory.

Sounds great! Be sure to update us when you get that one in the works!

Jason Greenlow

Jason Greenlow

Mechanic and lifelong gadget enthusiast living in Perth, from Christchurch, NZ.