Honestly i had never read the specifics of avoiding inductance on the battery cables (until now) and have just leaned on my experience with vfd industrial controllers. All of the engineers I’ve worked with have always specified a maximum length of the phase wires but never dc inductance of the supply so i kinda hijacked the thread to dig into y’all’s collective knowledge. These are obviously not a direct apples to apples comparison so im learning here and not trying to mess up your build thread. Sorry if im coming off as demanding or derailing i just don’t understand the specifics well enough and was hoping for some better clarification of the concept and theory behind it. (Pretty sure im the only agitator )
Also i dont want to work on my projects so i figured id just mess with yours lol
One thing we mustn’t forget here is that, while we are dealing with DC, the VESC generates 3-phase AC; this results in intense switching—turning on and off—that closely resembles AC behavior. That’s why having capacitors on the input side is a good idea. I suspect that many of the VESCs people condemned would never have failed if they’d had them.
The Long battery wire inductance thing sent me down long deep twisting rabbitholes, for which I am grateful.
It seems that more capacitance at the input of the ESC is a very good thing when there is Antispark measures employed. Absorb the voltage spikes caused by long battery wire inductance, and reduce voltage ripple as the mosfets switch on and off.
Reducing Inductance which can cause the Water hammer like ESC damaging voltage spikes is something I had put no thought into when I built my batteries, nor did I managed its output wiring or the loopkey harness as well as I would today to reduce potential inductance.
On my future battery builds, My output wires are going to leave the battery in close proximity to each other, run in close as possible Physical parallel proximity for their complete distance to the ESC, while trying to minimize that distance. Reduce the loop area, reduce the inductance, reduce the size and speed of that voltage spiking electrical hammer, AND have some more capacitance at ESC input to soak up any which still does occur.
I intend to attach a capacitance ‘wart’ on my ESCs, even though Mine are low powered and I’ve yet to smoke an ESC. I like the idea of reduced stress on it and potential avoidance of the walk of shame. Or a smoke release event when emergency braking.
Reducing inductance potential with shorter runs of parallel battery to ESC wiring can likely also reduce EMI/RFI and perhaps those signal dropouts or general ESC whackadoodlery.
We’ve seen a not indiscriminate number of xt90s fail at higher voltages on this forum. I assume that adding in a cap bank would likely place even more stress on the antispark device.
Both of the links that you’ve posted talk about extending the length of the wires from the esc, but there has to be some length of wire from the battery, i wonder what the esc engineers would consider an ‘average’ battery cable length, as this would surely need to be considered when choosing the caps that are native to the esc.
Lol me neither, so i appreciate the conversation! No such thing as stupid questions, just stupid people i just still had a bee in my bonnet from the AI slop misinformation.
14S+ voltages and 500+ uf of capacitance are some AI slop numbers when I asked it at what voltages and capacitor capacitance does the resistor inside an XT90s fail.
I am totally clueless on how ESC with built in antispark works.
Are the Caps only eagerly sucking everything they can when the battery is plugged into the ESC that first time, or every time the ESC is powered up, and the ESC has to do some electrical mystery magic to prevent magic smoke every powerup?
Most modern VESCs just spark on the initial plugin and then turnoff is actually just “hibernation” or “low power sleep mode”. So inrush is only there once. I sometimes don’t even bother using XT90S anymore. Regular XT90 has longer contacts so should be lower resistance…
For setups that I do unplug often (like raceboard lipos) I use the Yeti 8mm antispark bullet plugs, they are the best antisparks I found so far and reliable at 20S voltage. XT90S resistor would fail in 1-5 plugins at 20S in my experience.
Does the amount of capacitance have an effect on the longevity/effectiveness of the antispark tho?
Like say you hade a HUUUUGE cap bank, surely the inrush current would be prolonged/maximised and the resistor in the antispark should be capable of handling that?
I’m sure there would be some kind of formula to figure that out?
$2868 shipped… the grand total is quickly adding up
Apart from the cells, this is pretty much the last significant ‘off the shelf’ purchase that i’ll need to get the board up and running. Once these parts arrive i’ll be able to start piecing things together and designing/producing all the other necessary components…
I was asking it for my own curiosity and potentially incurring the wrath of Bens Bees in bonnets, but I told it two Radium mach1s ESCs ( NON VESC) in a 4wheel drive set up, a 18S battery 2 meters away with 8awg tightly twisted, 100 battery amps
It said 2200 to 3000Uf of total capacitance at each ESC, assuming minimal loop area( space between the battery to ESC conductors)
Looks like the Jeti 8mm AS connector fits upto 4 SMD resistors?
It says total combined target resistance of 30 to 40 Ohms for antispark.
Select 1206 size (or larger, like 2512) if the physical collar has room
Pulse Withstanding Thick Film Resistors (such as the Panasonic ERJ-P series or Vishay CRCW-HP series)
I’ve No idea if the total capacitance or resistor values info is remotely accurate.
perhaps some EE’s can pick it apart, or maybe confirm.
I should be able to keep the wire length from battery to escs pretty minimal I reckon. I’ll configure the battery similarly to how I did in the Step Bro build, with the positive and negative terminating centrally from the battery, and running up through the center of the deck into the esc box.
I think using either those yeti connectors or Amass AS150 if I still have some will be sweet to come off the battery and then split to the 2 escs from there.
As i’ll be able to keep that battery wire length to what I would see as a reasonable minimum (less than 300mm from battery to esc connector) i don’t think i’m gonna need to fuck with additional caps.
I’ll see how things are looking once all the parts arrive. @Tony_Stark are you able to ask the esc engineers what an acceptable total length of wire from ESC to battery would be before requiring additional caps?
Yea, I was still thinking you maybe wanted an 18S trailer battery directly in parallel with the 18s enclosure battery feeding ESCs directly, without an MPPT converter in between 18S trailer battery and enclosure’s charge port.
Huge capacitance needed to be added at ESC input for that, it seems.
Interesting thought experiment though, I learned a lot, and also learned how little I know.
Somehow I have a bunch of low esr 63v 100uf capacitors ordered, and dreamt of electrified water hammers all night, while stressing about 10awg red and black wires not running right next to each other.
Woke up with a burnt loopkey pacifier in my mouth.
I’m super glad we’re having the conversation too and I believe that the cap bank is a totally doable and feasible solution, I just think that for my needs and peace of mind, the MPPT charge and ride solution is what I would prefer. It’s more versatile and the configurable MPPT can be a multi-use device, not just one purpose.
It could even be used to drain fully charged batteries into lesser charged batteries to bring things down/up to storage voltage.
The only caveat is that the input battery will need to be a higher voltage than the output battery in order for the MPPT to kick on, but I can deal with that.
The trailer battery will be built exactly the same as the board battery, so it’ll literally be a drop in replacement.
There’s no way i’ll be buying another enclosure so fuckin expensive and i have serious doubts about it’s design. If the board enclosure ever breaks, i’ll make my own to replace it.
I truly doubt i’ll ever need to put the trailer battery into the board but redundancy if i’m spending the time and money on making a battery of the same size, it may as well be identical.
I looked at a few different MPPTs but i think i’ll go with the one i linked on aliexpress a bunch of posts up
Just wondering, why not the top mounting enclosure? That way you could have battery and escs close to each other in the same enclosure. as well as quick battery change from the trailer?
I get that the battery would be smaller, but then you could have even 2 spare batteries in the trailer.
@SternWake
The resistors are populated already on the connector - haven’t measured what they are but they work wonderfully for 2x D100s
@glyphiks yes the amount of capacitance does influence how well the antispark holds up. Estimating the energy that heats up the resistors should be simple. You can then use that to estimate heat rise but you’d need to know how much copper is in the resistors exactly, and that probably won’t lead to very accurate results.
Haven’t put a lot of thought into that just yet but I think i’ve been persuaded into getting one or two of those adjustable voltage/current jobbies that do huge watts.
Still a long way off being ready for a battery, so plenty of time to think about charger
)
redundancy