Briggs and Stratton Instart Battery adaptor

So if I had my time again I wouldn't bother doing this - I'd just pay the money for the stupid proprietary Briggs and Stratton Instart battery. But once I started I was kinda committed…

This project is probably of quite niche appeal, even if you have a Instart lawnmower you might not have Makita batteries, but you could probably adapt these parts to suit other 18v battery systems. Hopefully the information here is of some use to people at least.

You will need a 40 amp 24→12V converter. A 15 amp one is not enough - the starter motor draws a suprising amount of current for a tiny little motor.

I also used an ‘engine start’ switch from Jaycar - it seems like the original battery has some sort of internal relay, and the original start switch on the handlebar of the mower closes the relay and the battery powers the starter. Makita batteries do not have this function so I just ditched the relay idea and used a switch rated for enough current to handle starting duties. To be honest I wished I just bought a relay and did it properly - a momentary on switch that can handle this much current isn't exactly cheap.

You'll also need a Makita 18v terminal block - these are easily available on ebay and other places.

The Makita battery plate is a remix of https://www.printables.com/model/187090-makita-lxt-18v-battery-mount-v4

The Instart battery adaptor plate is a remix of: https://www.thingiverse.com/thing:4565535

(apologies to the makers above, I don't know how to tag multiple items as remixes in this description)

The voltage reducer plate is my own design.

The various parts are held together with M3 and M4 screws and nuts.

I've included an F360 file if you should want to remix these parts to suit your own application.