20S antispark ? - AS150 gets blown

[Battery_Mooch]

@frame

omfg, thank u for the tldr

LOL…yea, I went deep on that one. Decided that posting the two pages of calculations might be a little too much though.
Perishable skill, that type of analysis is. I needed to flex the neurons a bit.

[frame]

we all appreciate the knowledge u bring, just that my dumb brain can’t process all these info at once

[Battery_Mooch]

Here’s a “fun” fact…
At the 150A continuous rating of that switch just those four 12AWG wires alone will generate at least 70W of heat. If you can imagine placing your hand on a 60W light bulb you can get an idea of how silly that rating is.

[frame]

@Battery_Mooch

continuous rating

i thought all the cont. rating is always “as long as u don’t exceed XX°C” kinda rating

[Battery_Mooch]

There can be a “do not use above xx°C” ambient temp rating.
If the continuous current rating is ambient or component temperature-limited then they need to say that. Otherwise we have to assume they are claiming a true continuous rating.

This device has a preposterous 300A “max” rating that would be the one we could possibly consider as being temp-limited. But this is a beyond silly rating since 12AWG wire melts…literally melts…after a few seconds at about “only” 220A.

Since we have no way of knowing the temps inside the case, and how close different components are to their max temp, we need to trust the manufacturer’s current rating. A temp-limited rating would place all the work on us the find out how hard a device can actually be used. Different setups would results in different current ratings.

A manufacturer’s current rating, IMO, needs to be set for the worst case which can be reasonably expected for the intended use. If the current rating is somehow limited then we need to be told. That way we don’t need to measure temps to know which current rating to use and we can trust that the manufacturer is actually selling a product we can use the way they say it can.

Otherwise the product can burn out…oh…wait…

[b264]

I explained one of those phenomena (number 8) in a little more detail over here:

Tackling the anti-spark problem (Title by a good friend)

Most “inrush limiter circuits” fail because they are operating in linear mode during inrush. It’s a design limitation on almost every 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…]…

[Battery_Mooch]

@b264

I explained one of those phenomena (number 8) in a little more detail over here:

That’s it.
The particular characteristic I was talking about though is a (seemingly) little-known aspect of operating FETs in this linear region. I don’t want to mention it here as will be taken into account with my AS switch (when I dive back into it) and can help to differentiate it from other designs that don’t do this.

[Battery_Mooch]

@mr.shiteside

Righto this is a very preliminary look at the FlipSky 20S Anti Spark but I thought I’d share some pictures because I could take ages to give much else

Sorry, forgot to mention this…
It’s a really not good thing to have bits of metal bouncing around inside an AS switch case.

I don’t know what kind of QC checks are done before putting the board in its case but, at least for this unit, the QC was…umm…inadequate. Where it is in this photo is no problem but that bit-o-metal will not sit there when the switch is being bounced around.

[frame]

@Battery_Mooch

I don’t know what kind of QC checks are done

No one knows because there probably isn’t any

[BenjaminF]

@Battery_Mooch

It’s a really not good thing to have bits of metal bouncing around inside an AS switch case.

ESPECIALLY when the bits of metal look like dicks.

[tech.shit]

thanks I can’t un-see that now

[glyphiks]

Those pesky dick-shaped solder balls

[mr.shiteside]

@BenjaminF

ESPECIALLY when the bits of metal look like dicks

I’m so glad someone else beat me to this

[Gamer43]

I wonder who picked those components

(I didn’t pick the MOSFET)

Well nice to know that flipsky’s QC is nonexistent.

@Battery_Mooch

It appears that this switch uses the FETs themselves for the pre-charge instead of a separate resistor (with its own smaller on/off FET) to slowly let the current through to the ESC. This is perfectly acceptable for an AS switch but when used this way there is a certain FET operating characteristic that can cause big problems and can easily lead to FET overheating. This can lead to FET failure if the switch manufacturer does not take it into account. I have met power electronics product designers who were not aware of this operating characteristic so it’s certainly a possible failure mechanism.

It’s a fixed dV/dt rise time, so the capacitance determines the inrush current. Following MOSFET SOA tells you maximum rated capacitance the switch will work with.

[Battery_Mooch]

@Gamer43

It’s a fixed dV/dt rise time, so the capacitance determines the inrush current. Following MOSFET SOA tells you maximum rated capacitance the switch will work with.

There’s another issue to deal with though for any higher power AS switch. That’s the one many engineers don’t know about and the one I’m convinced leads to some of the failures.

[mr.shiteside]

Hahahaha I was gonna tag you in and ask if you were involved in this one as well, that’s cool

[Gamer43]

Its the same as the smart antispark, the gate driver, mosfets, diodes, and input capacitor are all scaled up from 12s to 24s.

[hummieee]

Wish I’d found this thread sooner and I see the Jeti has a decent resistor, but in the meantime got the QS8 manufacturer to make some QS8 plugs with a 15ohm resistor (5w). Surprised they would do a small batch of 20.

[zero_ads]

So trying to understand the benefits of these Flipsky and Maytech antisparks. Once the connection from the battery is made to the ESC all is good right (as in antisparks won’t matter at this point)? And when you turn on and off the ESC (maybe via a switch connected to the ESC) there cannot be a rush of current because it’s already connected, right? It’s when we connect and disconnect the battery to the ESC that the rush can happen and damage the ESC? Or am I missing an important step here?

[fessyfoo]

going through this same experiment.

got a AS150, measures 5.7Ω from tip to sleeve. feeds two little focers. at 20s.
it sparks every time, from female connector to the tip of the male connector. ie with the resistor in the path.

so. i think it’s spark from inrush without the resistor blown.

will need to iimplment alternate solution. either parallel AS path or Jeti