FatBoy Mini Sparky Switch 50A - 200A 100V PreCharged Anti-Spark Switch

Hi guys, today I would like to announce a smaller more universal and better anti-spark switch

After doing a lot of research of making switching least painful in our cases and minimizing the switch to small 2 x 18650 size (36mm x 65mm) Also much cheaper for simple projects from 50A to 200A on paper with bit tinkering could do much more :slight_smile:


  • High Side Switching (Switches positive wires)
  • Push button (hold 0.5s to turn on / 3s to turn off)
  • Output for power indicator (will require resistor according to your selected led specs)
  • Multiple IRF DirectFet mosfets (N+1 for PreCharge)
  • Pre-Charge circuit before turning on main MOSFET’s to charge capacitors via a resistor to limit inrush current.


  • Up to 100V (23S)
  • 1 to 4 MOSFET’s
  • In rush current limited to (V/2 A) (for e.g. 50/2 = 25A max inrush current)
  • Dimensions would be 36mm x 65mm (2 x 18650)

It will have a small aluminum plate under it to cool down the MOSFET’s a bit.

Here is simulation I have done with this style design, as you can see no inrush current higher than 50A @ 100V.

Without inrush limiting:


With pre-charge:






You make some cool shit dude! I’m so glad you came to this forum. When will you hopefully be selling these?

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also interested

Oh I’d be interested in picking up a few of these! I’ve been looking for an eswitch that can reliably handle 13S

We will be ordering PCB’s today for all the projects and doing some testings with it after everything works I guess maybe in the first weeks of July or something similar.

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Nice ! :fist_right: How thick will these be with alu heatsink ?

This is AWESOME. Any way to lower the turn-on hold to like 100ms?

I really like how flying road debris can’t shut your board down…


At the moment I can’t tell but definitely not thicker than 10mm or for 100% sure not thicker than 18mm (18650 thickness)

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Awesome! Any idea on price range of this one compared to the non mini version?

Heatsink really shouldnt be needed. If there is a need for a heatsink, you got the wrong mosfets or too few in parallell

Awesome! I’m in for a set!

36mm by 65mm is like half the size of a Focbox (=64 by 64mm with case) - just for switching it on/off. Is there a possibility that you really make a mini version? My Lou needs a switch but space is very limited :frowning:

There will be multiple options (price levels) so for all of them there will be heatsink included as even on lowest level you could still pull more than 50A but heatsink will be required same as Focbox and etc :wink:

If you take off heatsink, remove button connector you should end up with like 3-5mm height so you can put it on top of your batteries… I will think about smaller version but I don’t think it wil be anything soon as I have other projects which needs to be finished for Evo project :stuck_out_tongue:

I’m in for one :slight_smile:

The battery compartment in the Lou is exactly the height of the battery inside the hardcase - no way to fit even a 1mm switch on top. But to put it somewhere else it needs to have a smaller footprint. Well i guess my search continues.

What current ratings you are looking into?

Well the battery is 10S1P so even if i upgrade the cells to VTC6 I am looking at a max of 30A for short bursts (10s-30s otherwise voltage sag will probably cause an undervoltage error in the focbox anyway). I guess we are rather looking at 5A continuous or something like that. The original battery has XT30 connectors - that says it all :smiley:

I will try to think of something but no promises :slight_smile:

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Today parts and PCB arrived, will be assembling several units and doing some basic testings