Switch on BMS - good or anti-spark better?

Howdy, quick question for you guys!

I have a Lipo battery connected to a BMS, and the BMS has a switch attached to it… But (I’m pretty sure) every wiring diagram I’ve seen so far has the switch attached to the main electrics… It’s fine but there’s no anti-spark so trying to figure that out.

So, should I keep the switch as is, or pull that out (is that possible?) and put in the anti-spark switch??

Well, an antispark switch is really just a electronic switch like the one already in the BMS, in terms of how they operate I mean. It’s going to have a transistor that gets turned on opening the circuit just like any antispark switch does. I think the confusion here is that the “antispark” component of the antispark switch comes from the fact that the current does not arc over a small distance when being connected because here we are always connected, but we have a “valve” on it.

I might be a little off in my interpretation if I am someone feel free to correct me, but i think your okay. Only thing I’d be concerned about is do you know how much current your onboard switch is rated for?

You are correct! Also BMS and Antispark mosfet switches alike use soft on to prevent peak current flow.

So if I have a switch on the bms there’s no need for another one?

Correct sir

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I concur. BMS switch is sufficient.

Anyone know if there’s generally any difference in reliability between a BMS with softswitch and a standalone mosfet switch?

The high voltage switching is achieved with the mosfets, like you’ve described. We stack multiple fets in parallel to achieve the necessary current rating. But the anti-spark function comes from the capacitor and resistor, which are connecting the gate to the drain. This slows the inrush of current to the caps on the ESC, arresting the spark. There is also a Zener diode from the source to the gate, which serves as a flyback diode

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I’ve had 2 stand alone anti-spark switches fail.(one of them in the first 5 min) The soft switch on my Bestech BMS has not failed yet.

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My Vedder Anti Spark switch failed today when i connected the Battery to it. It doesn’t switch off anymore and i get a spark. the good side is Esk8.de will take it back. Hopefully they will switch it because i kind of like it. I guess it would be better to use a additional xt-90 anti spark to close the connection between the Battery and the Anti Spark Switch. Eats some space but maybe this way they don’t brake anymore.

Yeah, hard to go wrong with a Bestech (kinda wish I had one). I’m using @chaka’s version of Vedder’s anti-spark switch (bought the board on oshpark and soldered it myself). No issues so far.