After 3 iterations and far too many dud pcbs, here’s a new antispark i hope the community will appreciate.
This started with @b264 and his excellent explanation on why the vedder switch blows.
In designing this, I had a couple goals:
overbuilt current and voltage ratings for eskate
as small as possible
momentary button
To satisfy goal 1:
this design uses 175A midi fuse blocks I saw on the DieBieMS.
The midi fuse standard allows for much higher currents than the old blade fuses.
The mosfets chosen are rated for 100V and 260A, doubled up for a theoretical 520A continuous.
You’ll never be able to get that much current through this design but this removes the mosfets from being a bottleneck in either voltage or current.
Traces are beefed up with solder to improved current capability across them.
The 5v regulator is rated for 150V.
To handle the issue of precharge, the design uses a 10ohm resistor and a small 10A continuous mosfet.
This combo is enough for precharging even at 100V.
For goal 2:
the pcb is shrunk down to a 23mm by 40mm size, restricted by the size of the midi fuse
If you don’t mind forgoing the fuse, the design can be even thinner.
The 2 power mosfets are mounted on opposite sides of the pcb to further minimize the size of the pcb.
With goal 3, I personally couldn’t come up with a solution that didn’t require a microcontroller, so I ended up with an attiny85 running the show. Honestly could’ve gone even smaller, but this works great. But as many people have found out, these momentary button designs incur a cost of power drain while off. Luckily @Blasto made a post with an excellent design to disable the 5v regulator while off to minimize power. The 5v regulator used sips 1uA while disabled, which results in less battery degradation than the battery would see just sitting on its own. I didn’t have equipment sensitive enough to measure that little of current draw, but I imagine its effectively 0.
@Winfly gonna be testing this on the road, so we’ll see if anything funny happens
What a wonderful piece of engineering, I need exactly this. Can you please confirm that it can use a momentary push button and is auto reset to off position when you plug the batteries ?
Yup, uses a momentary push button, no latch required. The switch remains off with or without a battery, until you hold the push button for a set amount of time. I personally selected a 1 second on, and a 1.5 second off, but technically it could be personalized.
Honestly don’t know if I’ll sell much of these, which is why the design is released. Its a bit of a pain in the ass to put together due to the smallness. But the bom cost is around $18 without fuse, and $25 with fuse related parts.
