Makita 18V LXT Portable Power Station – howto
This is “work in progress” thing!
So recently I’ve switched to Makita 18V system. And I was a bit disappointed there was no something like DeWalt Power Station – that is 230V inverter powered with Makita batteries.
So like usually, I simply need to make one… cheap 😉
This gave me a bit of thinking, what voltage would be the best for this task. I’ve checked 12V and 24V, car inverters and sadly they all have over/under voltage protection that will not work with 18V Makita (that can be change from 20V to as low as 10V).
Then I’ve checked for 36V inverters, and there are some available, but the price is discouraging (like 300+ dollars) and they DIY would be very bulky, since it requires large transformer (all custom/DIY are base on customizable Pure Sine Wave EGS002 board – you can watch more about it on Great Scott channel, but beware, there are mistakes in this video – read comments).
So back to car inverters… that are cheaper (like 50$) and more useful (car/camping) then 36V solution.
I could step up voltage to 24V or step it down to around 12-13V (later I’ll write why). Since 12V inverter will be more useful to me, because I can also use it at my car, I’ve decided to go for step down.
I’ve ordered 800W pure sinewave inverter (peak power 1600W) for around 50 USD shipped. I don’t think anything more will be useful for this type of power source, even with the car battery.
If you would go with 24V and want to use inverter later on, for some kind of the off grid system – you could use more robust device – this won’t hurt batteries if you will limit power usage to something sensible.
800W inverter still requires at least 67Amps (more like 80A) for 12V and this is already a lot of current (twice at peak). For large car batteries it’s not something terrible (my 100Ah battery has peak current over 800A) – but it could drain it real fast, and four Makita batteries in a blink of an eye.
Actually let’s do some calculation here. Makita 5Ah battery will give us roughly 90Wh, times four it’s 360Wh. Assuming 85% (I’m guessing here – but based on some experience) step down efficiency. This will give us 360Wh*0,85 = 306Wh, I’ll make it 310Wh. Now again, assuming efficiency of the inverter at 80% (this is wild guess – I don’t know that). We have 248Wh. So finally for 800W load, we should get around 18minutes of run on four batteries, two will give us only 9 minutes – and this is still much more we will get, because of buck converter voltage drop limit (more – later).
Anyway, I assume Makita batteries (5Ah or more) can provide 20A current easily. I haven’t tested that, but quality 18650 cells are usually rated 20A-30A. There can be some limitation for electronics inside battery – so 20A is my limit.
I’ve ordered two DC-DC step down boards, that are rated for 300W (20A) – but it’s “Chinese” 300W, so more like 200W or even less. Judging by the components used, I was surprise it handled 10A that well 🙂
Recommended load is 15A (small print), so around 180W. I’ve prepared additional cooling, so I guess it should manage to go to 20A peak (240W-250W).
After some tests, I’ve ordered two more buck converters and prepared printable case for entire device. In general it’s large and quite powerful 12V power supply, that can be extended with 12V inverter (up to you if it’s going to be 230V or 110V).
Single battery – 15-20A, two batteries 30-40A, three 45-55A and four 60-80A.
Printable version of battery holder and the box itself I’ve put on Thigiverse.
- 1 or more step down (buck) converters to change 18V (20V) to 12V
- 1+ Makita battery connectors – you could also print it. I’ve manage to find genuine parts in Poland for 2EUR
- 1+ Schottky diode – 25V+ 20A+ (I’ve used 20SQ045 – 45V, 20A – bigger would be better, this is what I had at hand)
- 60x60mm 12V fan
- XT90 connector – to connected battery pack to inverter
- Optionally beaker box – but recommended