you my friend should get the maytech 300A antispark, I have bought my second one after having one on my DIY fluxx board, never had a single issue, using the second one for the a DIY e-bike project.
Well I have had so far no issues with it during regenerative breaking, might just be a disclaimer.
56 volts, or 56 volts?
Always confusing whether theyâre using ebike jive or not.
Yeah. Whereâs those fucking standardsâŚ
What voltage you at?
I vote for Volt = kg¡m2¡sâ3¡Aâ1 but some people prefer otherwise. IDK
The exact same battery can be called 42V or 36V depending on who is typing. Idiotic.
I just want volts that taste like real volts.
66 volt 18s setup, never had any issues, maybe with high reflow amps it could be an issue frying the anti spark, but yet again never had a single issue so far, been reliable as all hell
18S is usually 75.6V
66V is ebike jive
Peak volt is 75.6V, I usually calculate with the average charge I have in real life.
But when it comes to what components can handle or actual design considerations, only actual battery voltage matters. The kg¡m2¡sâ3¡Aâ1 type of voltage.
An abstract âlead acid equivalencyâ or ânominal voltageâ or âmid-charge approximationâ is not useful for that, and seems to cause confusion.
Your antispark solution needs to be rated for and able to handle actual volts.
Yeah i agree. Nominal ratings are fucking useless.
Well it hasnât blow yet to this day
Posted in the wrong thread but moved back over here (soz)
Righto this is a very preliminary look at the FlipSky 20S Anti Spark but I thought Iâd share some pictures because I could take ages to give much else
Overview: (I like the bus bar for the negative)
Core power components:
MOSFETs
High Side Driver (bottom left)
Linear regulator for the circuit logic (top right-ish, square package below the bus bar and solder blob)
Disclaimer: This is only commenting on basic component choices and not the topology, and Iâm not an expert. With the exception of that diode I didnât check, they all seem to be 150V rated parts from big name manufacturers. The current ratings on the fets should be weeell within spec, if the traces are up to it they could theoretically do 676A continuous. 12AWG though lol.
If I get some inspiration Iâll check some less basic stuff like comparing it to application notes and see if that driver can match the gate charge of the 4 or whatever.
PCB:
I didnât do a great job capturing this (and forgot to measure) but it is as advertised a big chonky aluminium PCB. This pic might be useful?
Thank you so much for taking a look at this switch and posting your findings!
A few (very technical) thoughtsâŚ
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The continuous current rating of 169A in the datasheet is a theoretical number and canât be used here. Everyone uses the front page current rating (itâs incredibly convenient) but itâs listed for a case temp of 25°C and once current flows in the FET the case temp is no longer 25°C, no matter what kind of heat sink you have. The datasheet also mentions that the current rating is limited by the max junction temp rating and that will be reached very quickly at high current levels.
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Calculating the power each FET must dissipate at this switchâs continuous 150A rating (37.5A/FET) means that each FET creates more than 14W of heat! That would bring the FET temp to over 600°C, probably way over as I am being extremely generous with my calculations here.
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The wire-to-board and bus-bar-to-board connections each create heat too. The four wire connections could add about 3W more heat at 150A. The bus bars would add at least another 1W. That means the board is creating about 60W of heat at 150AâŚit would not survive.
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We need to use the on-state resistance and thermal resistance numbers to calculate how much current each FET can handle before reaching its limit of 175°C. If each FET was alone and on a square inch of 2oz copper that would be about 15A. But they are on tiny copper pads and each FET heats up its neighbor. That lowers the current rating considerably. Being on an aluminum PCB brings it back up a bit so letâs call it 10A per FETâŚabout 40A total.
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Adding up all the FET+connection+bus bar heating numbers for running at 40A continuous gives us about 7.5W of heat for that switch. In my opinion, based on my experience, that sounds about right for a normal board that size (with all the necessary compromises made to keep it that small). Using an aluminum PCB, thermal pad, and an aluminum case helps to raise the current rating some though. I canât say by how much. A lot depends on the desired life span for the FETs. Some companies are willing to run them at their max temp since it doesnât happen often during actual use. Other companies, for increased reliability, would lower the current rating so the FETs never exceed about 80% of their temp rating. For very high reliability designs the rating might be halved.
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The board traces are the equivalent of a wire much smaller than 12AWG. This combined with the 12AWG wiring and all that component and connection heat means that the 150A rating is absolutely preposterous. But since esk8 doesnât (typically) run continuously at high current levels this doesnât have to be a big concernâŚunless, like me, you hate seeing these kind of bs ratings games being played.
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Regarding the voltage ratingsâŚthe board layout looks to be pretty low inductance. As long as the FET driver was set up properly I donât think there will be a lot of extra board-created voltage spiking (need to use a scope to know for sure) but since they say 80V max then I would stick to that or lower as there are spikes everywhere in an esk8 setup.
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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 itâs certainly a possible failure mechanism.
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If the aluminum PCB is not grounded then it just becomes a big antenna, possibly making any voltage spiking worse and/or interfering with operation of the switch because of electrical noise. I do not know if they ground the PCB aluminum or not.
Thanks again for posting that info and the photos! I always enjoy teardowns.
I have no idea about most of what youâre talking about but i appreciate it.
no need to go into detail etc, would be a wasted effort for my monkey brain
TL;DR:
IMO the 150A continuous rating is ridiculous and if they did not take certain things into account in the design then the FETs can pop.
Hahahaha thanks for all that, muuuuch more detail than I was going to be able to add. Iâd like to add some basic calculations for thermal output in these things as practice, might try and update this over the weekend
omfg, thank u for the tldr