The shit it tells my boss to comfort him at night is scary…
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Hell yeah. MPPT is the way for sure. Used some different search terms this evening and there are definitely products out there to suit my needs 
This is the first one i’ve found and looks like it ticks all the boxes, has customisable battery profiles and is a very reasonable price!
I do wonder about low voltage cutoff though. Because these devices are specifically made for solar panels as the source voltage, it doesn’t make a lot of sense that you could set a voltage where the MPPT stops drawing power, as the goal is to maximise power output no matter what the input voltage is…
So i’d really just be relying on a discharge bms on the trailer battery to shut down at LVC.
There seems to be several different options available on aliexpress, and most of them have wifi, but I can’t find one that communicates just with bluetooth…
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Ok so inductance issues on setups are on the phase conductors right? Like the limits of conductor length are for the phase wires and not the length of the battery output so im not seeing why you would need to do anything on the trailer’s battery if you were planning on having it run in parallel.
As i understand vfd’s and vesc/esc is they take battery voltage or source voltage and turn it into a dc buss that is then used via high speed switching to create an ac 3 phase output to the motors. This ac waveform can be sensitive to inductance if the phase conductors are over a certain length because it has to compensate for the amperage naturally lagging the voltage and have to correct it via caps and will have a sort of operational window of maximum or at least ideal inductance in the motor and phase wire circuit.
The battery input is dc - therefore any inductance or capacitance causing the amperage to lag the voltage isn’t really an issue pulling voltage and current from the dc bus.
Are you putting an esc in the trailer? Because that’s the only way i could see inductance becoming an issue on the trailer setup. Using a trailer as a charger would mean use a buck or mppt to charge the board battery from it but if just using it in parallel shouldn’t introduce inductance on the phase conductors
You’ve got that backwards. The general wisdom in this forum is that long battery wires cause inductance issues which blow up ESCs, long phase wires don’t seem to matter.
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Oversize the battery cables or double them up to minimize inductance issues and don’t loop them around and you should be fiiiiine
I understand wanting a secondary battery that you could drop into the main board and wanting redundancy. But a well built battery shouldn’t have issues over the few hundred miles you’ll be riding on a trip? What’s fun about diy is you get to call the shots and make the decisions you deem good.
But the way I would approach this. I’d build a large 10s pack to go in the trailer then you can draw off that as you need through the day.
Can confirm these are great units I’ve used them a decent amount and never had them blow. I’ve used them to boost up to 13-20s voltage and charged up to I think 10amps.
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I swear AI is just another tool to help brainwash the population.
Am I Strong/smart/attractive enough?
Am I a victim who can then do no wrong?
Never Fear AI is here, to boost your confidence, tell you are indeed smart enough, that you are attractive insightful and strong, and have been wronged, you are a victim of that other side, and here is a summary as to why……
It seems to go and figure out every word you have typed on the internet, and feed your opinions back to you.
I have a sibling who is not very smart, but you’d never know it by the tone of her voice. She has it all figured out. Complete confidence in stuff she knows nothing about. She loves AI. It always tells her not only what she wants to hear, but has been conditioned to NEED to hear/read.
She loves her some Antivax opinions, and faithfully repeats the Propoganda she deep throats and gargles, and unfortunately for the US and the world at large, She and her like minded below average intelligence individuals, vote.
So like All tools, AI can be a wonderful Aid, or if wrongly used it can kill you, or someone else.
That Said, I didn’t and Don’t understand inductance and how long battery wires can fry ESC’s.
Gemini seemed to come into this forum and read that high power builds need the battery close to the ESC and to use long Phase wires, rather than long battery wires and short phase wires and told me what I had already read. Aren’t I smart?!, Tell me I’m pretty too.
I asked about an external 18S battery physically 2 meters away and a ESC pulling 120 amps over 8awg cables and it threw up red flags and a bunch of numbers and formulas I scrolled past.
I asked about the capacitors needed to prevent the ESC frying voltage spike it guaranteed would happen if 120 amps were flowing and suddenly stopped. What I got out of the reply was that a Capacitor bank would be required and it was likely nearly as large as the ESC itself, and it should be wired as closely as possible to the Input of the ESC.
It would need a QS8 antispark, or that huge capacitor bank would destroy the connector.
It said the battery cables should be twisted tightly, 2 turns per 3cm or so and battery wires shold come off the battery as close together as possible, rather than at opposite ends.
I asked when the biggest inductive voltage spikes would happen and it claimed it would be at half throttle rather than full throttle, but I did not understand the logic behind that. something Mosfet switching duty cycle at 50%…. I don’t know.
I then asked more specific questions about my own system as I do occasionally use an external battery in parallel , and it had me believing it was amazing that my system didn’t blow up every time I let off the throttle, and I needed to start ordering capacitors and figuring how to attach them as close as possible to the PCB inputs
. Then I said I measured My ESC max amp draw at 27.1 amps and I am only using 10S and it Said to never reveal this to the skilled DIY Esk8ers or you will be mocked mercilessly and completely dismissed.
Not really, but it said the Input capacitors on my ESC had enough overhead to handle the inductive spikes in my low power build, but that the theoretical 2 meter away 18s battery on 8awg cabling would almost certainly cause ESC damaging voltage spikes on a higher power build.
I then asked about a 4 wheel drive set up with essentially 4 ESC’s drawing power, communicating via Canbus or split PPM, and I think it blew its own mosfets in its haste to throw up red flags.
But the inductance there is easy overcome by matching up and or twisting the power cables - by having the pos and neg cables tied together for the majority of their length it will couple and therefore cancel the induced magnetic field. If you have coils on one conductor isolated from the other it could be an issue but i don’t understand how long cable can CREATE an increase in inductance. If we assume that the battery current will always be the same on bothers the pos and negative - physically coupling them together will negate any inductance
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Yeah everything you’re saying makes sense, it just doesn’t seem to line up with the various anecdotes we’ve seen on this forum over the years. That said, who the hell actually knows what caused all the failures from those anecdotes? It’s not like we’re doing actual post-failure-analysis or anything.
I don’t really understand inductance well enough to say one way or the other. I just know the general wisdom which gets passed around.
Adding more copper reduces resistance, not inductance. Inductance is determined by the amount of area between the two wires that are sending power. As in, if you imagine the two wires to be the perimeter of a shape. If you pull your positive and negative wires apart into a big rectangle or circle or whatever, it will massively increase the inductance. You reduce inductance by having shorter wire runs of course, but also keeping the wires as close together as possible and preferably twisted.
An extra long twisted pair of cables that have been coiled up in a storage loop, would probably have less inductance than if you ran your positive and negative wires across opposite sides of the enclosure, for example.
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Long before the introduction of AI we discussed things with each other, rather than with the robots.
A quick search pulled up this thread, and concerns about inductance on long battery wires were raised by none other than @Battery_Mooch himself.
Things that we’ve discussed in my thread here have been confirmed there, to reduce inductance we keep the battery wires as short as possible, close together (preferably twisted) and if concerned still, add a cap bank (preferably several smaller caps rather than one big one)
As i’ve already mentioned, i’m far too illiterate around inductance and it’s effects to confidently implement something that I deem safe enough to protect thousands of dollars worth of parts.
I do not need the power advantage of a parallel battery, only the energy and redundancy of a spare battery. I am far more comfortable using a purpose built dc-dc charger (like the mppt controller I linked above) to drip feed (20a charge) extra energy from the trailer to the board.
I’ve built a couple of packs in my time. I’m not concerned about the quality of the build more than unforeseen disaster type events.
I’m curious why all of a sudden there are people spruiking the idea that long phase wires are more of an issue than long battery wires. It’s always been the general consensus around here that long battery wires are more of a concern.
I appreciate the discussion but I worry about misinformation and when ideas suddenly start going against the status quo, I do wonder what is driving that.
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That RCgroups article linked by @iamasalmon in that other thread is awesome.
I’m gonna direct link it here.
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I thought I learned (many moons ago, so I could be wrong) the inductance equation and it had wire length in numerator and radius in denominator. Maybe that’s just for single wire inductance and not the effect between the two
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Sounds like it, yeah. The inductance of a single wire is small compared to the interaction effect, so you can ignore the single wire stuff
You also may have been looking at magnetic field strength, which decreases with distance (usually labelled as r). The inductance formula apparently looks like this
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Clearly we need a coaxial power cable
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How about we just run the positive cable through a big metal pipe and ground the pipe? That’s basically a coaxial cable!
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Omg please no 
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Should be easy to stuff some round wire inside a flat braid cable, and heat shrink the whole thing.
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No moe of these bad ideas
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Thats it, you’re grounded.
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