MakerX simple Anti-spark switch

[b264]

The post you’re referring to, I think, is

Vedder antispark, design problem or implementation problem?

They blow because they are operating in linear mode during inrush. It’s a design limitation on every one I’ve seen so far except one.

Imagine a FET is a resistor with a variable resistance. When it’s “off” the resistance is [nearly] infinity and when it’s “on” the resistance is [nearly] zero. That’s all fine and dandy until you add capacitors to the load, like the filter capacitors on VESC and other ESCs. Right when it turns on, it’s effectively a momentary short circuit with [not really…] infinite current because the capacitors are empty. So what the antisparks do is they limit inrush current by turning on not from zero to full blast, but gradually over several milliseconds they ramp from [nearly] infinity to [nearly] zero ohms. It’s this period during the ramp that is the problem, the FET itself is taking almost the entire load due to Ohm’s law because the capacitors have effectively zero resistance to inrush. It’s said to be operating in “linear” or analog mode at this point, as opposed to “digital” mode where everything is either on or off with no in-between. This is extremely stressful to the junctions inside the FET and technically exceeding the design limitations for a very brief period of time. Each time it’s powered-on, it’s taking a tiny bit of damage.

The way to ameliorate this is much the same way a loopkey works – you have a “precharge” circuit where the nonzero inrush-limiting resistance is provided by an actual discrete resistor instead of the FET junction itself. So you have one FET with a resistor in series, typically a 5.6 ohm resistor, that is separate from the one or more FETs on the main power switch.

So in order of operation, you’d have a single FET turn fully on [nearly] instantaneously (digitally) with a resistor in series to charge the filter capacitors, then once the output voltage approached the supply voltage (meaning the capacitors are nearing full charge) then the main FET(s) turn on [nearly] instantaneously (digitally) to supply high-current power to the system. This is never operating in “linear” mode but is “fully digital” and will not suffer the incessant failures that plague the inrush-limiting Vedder design. The power limiting and heating is moved to a discrete resistor instead of burning off the energy inside the FET junction itself, which stays cool during inrush.

There isn’t a magic trick to make it work without a precharge, if you turn it on slowly enough it can prolong the life of the FETs. But ideally a precharge (all-digital) is better.

[Gamer43]

LTC7004.pdf

Page 11 :). I learned first hand that precharge circuits actually cause RESISTORS to fail.

Also, to all antispark designers, please for THE LOVE OF GOD use high side switching.

So many f—ing fires have happened because of that lowside switch garbage.
It one of the many reasons why CAN bus explodes.

[tomiboi]

@b264 Yes, that’s exactly it. Thank you.
Also, another thing that I notice about these switches is that they are double stacked PCB. Maybe the secret sauce is sandwiched in the middle.

[b264]

It can’t be, because it would get hot and need to radiate heat.

[Dareno]

they are double stacked PCB.

What do you mean by double stacked?

[Zach]

You seem very educated in the subject , why not make one yourself?

[Gamer43]

New Open Source Antispark Switch

also this https://easyeda.com/editor#id=|602dc2b7711e4c16b88d2f5de19e1ff6|42d88dfcf3ce4bfd8d401d1ee3b6d229|0de2667950c84b919473f754356c5827

Smart switch is in the pipeline.

[mishrasubhransu]

So did you update the PCB to allow for a higher wattage smd resistor? BTW, please consider creating a thread here on it. Would be nice for this forum.

[Gamer43]

Use through hole resistors.

I will update the PCB accordingly.

Actually, if you’re going to have PCBs made, just use the high side switch.

Less headache.

[tomiboi]

@Dareno It’s thick. Look’s like two pieces of G10 glued together. I was looking at this one next to the Flispky and that was just a difference that I noticed. It’s probably nothing. Also, there isn’t a heatsink and the thing never seems to get hot. Baffling.

[ARetardedPillow]

I don’t know about you guys but I’ve been using and making my own switches and I run it at 13s and go over 100A all the time, 4-5k+ miles and still going strong.

Sent one to @Skunk but if anyone else wants to try to kill one I’d be happy to share

[b264]

The thing that kills antispark switches usually isn’t voltage or continuous current, it’s the amount of capacitance on the load.

[ARetardedPillow]

Well then, I’ve got 3x 2200 uf capacitors and whatever is on 2 focboxes on that build, I don’t know whats keeping my antispark alive but it works

[YUTW123]

https://www.ebmakers.com/

welcome!

[Gamer43]

Send be one, let me know what I owe you. I usually kill an AS switch in a few days

Can I send you my new smart antispark for product verification :p.

[mmaner]

You can, I’ll do my best to kill it

[Gamer43]

Just don’t hook up more than 15mF of capacitance to the output :p.

Also it doesn’t have a push button is that ok.

[mmaner]

I have a board that is for testing. I swap stuff in and out all the time. Currently I have a FS 420 plus with 12s4p.

[Gamer43]

Ah ok.

The dimensions of the first prototype are 51mm x 38mm. Would that be too big?

Do you need a pushbutton? If so I can bodgewire in one.

When I did my tests I didnt bother with a pushbutton.

Also, did you bypass the antispark on the 4.20 plus?

[mmaner]

I have room for that. I can wire in a switch, just include the schematic please. I’ll bypass the internal AS or I’ll swap in a couple of FocBox’s. I’m happy to test within your criteria.