How did you get radium Jk esc. Can’t find it on radium website?
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You can do 4kw with a modified Huawei R4875 from alibaba. I recommend going that route and designing for 4kw. You’ll probably also want a level 2 car charger adapter
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Something like this that @Pecos linked above
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I spoke with Liam directly.
I also reached out to Propel and Exway about potentially using their escs but they were not interested in selling the escs seperately
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On the topic of redundancy, what is the plan if the MPPT decides that it does not like one 18S battery as the input, and another 18s battery, at the output, or road vibrations, or life on its back?
Testing the function of the MPPT throughout the full range of input and output voltages it will encounter, will require a lot of time riding, and it wont be easy to have a quick look and see if it is still outputting 20 amps while rolling and with 8p of battery on both sides the expected voltage gains or losses at 20 amps will not be dramatic on shorter test rolls.
When the MPPT algorithm is sweeping for the Voltage max power to extract as much power as it can from a solar panel, Is this not pretty much a direct short?
Directly shorting a single solar panel , a current limited device, is pretty inconsequential, but directly shorting an 18S8P tabless 21700 battery will certainly not be.
I am having difficulty wrapping my head around how the MPPT solar controller is going to act as a 18s battery to 18s battery charger.
I see that @Goride65 has boosted from lower to higher voltages with a MPPT solar charge controller, found it less than ideal and went with a CCCV voltage booster, and @DerelictRobot has dabbled as well, but I have not found examples of an MPPT solar controller working as a battery to battery charger when input battery and output battery are the same nominal voltage.
I am not saying it cannot be done, just that I don’t understand how.
And if it does not work, or just works until you reach the NSW border, what is the plan?
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That’s a brutal price. Can it run motor detection? Or calibrate itself to the motor in some way?
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I’ve done it, it worked fine. It was a long ass time ago with a cheapo Amazon special mppt, and i don’t remember all the details. But it worked 
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Can you remember the source and destination battery voltages and the max potential output of the source battery?
No snarky tone intended.
There’s gonna need to be a lot of trial work before any real start to the big trip. If it doesn’t work as intended, thats a bridge i’ll cross when i get to it.
In any case, i’ll be in the van as well. It’s not like i’ll be stranded… well not much further than 100kms from the van anyway 
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I have thought about this. I will have a smart bms on both batteries, but the trailer battery will need to be set up to discharge through the bms, for the LVC protection.
I’ll be able to connect to the trailer battery via bluetooth to monitor whether it is still outputting, or the board battery to see if it is still receiving input.
I’m not sure exactly how the MPPT sweeps for the optimal voltage, but my understanding is that it’s intended use is for multiple solar panels, to harvest the maximum voltage for each panel. When solar panels are connected in parallel, their collective voltage is lowered to the lowest voltage panel and so a lot of power is wasted as heat for the panels in the higher voltage panel. The MPPT solves this by taking each panel input at it’s full voltage and doing it’s thing from there to convert whatever voltage it is receiving to the desired output voltage.
A small amount of googling tells me that it extracts the maximum power by modifying resistance on the input, nothing about shorting. BUT! As there is no easy way to limit the current coming from the battery, the trailer battery would likely just be dumping power into the mppt so i suppose that kind of is a short?
The bms would provide overcurrent protection, but this isn’t a suitable as a current ‘limiting’ device as it would just cut all power completely once over currenting.
The MPPT should provide a certain amount of resistance to limit current for optimal output voltage but it’s likely not going to be capable of handling an immediate inrush of current when the battery is first connected… we’ve come full circle
There are several threads on reddit and solar forums saying that using an mppt as a battery to battery charger is a bad idea because of this exact reason and i’m not exactly fucking around with small batteries here…
Back to the drawing board i guess, this presents enough doubt in my mind that this is perhaps NOT the best solution.
If the charging method from trailer to board does fail, its not the end of the world, it just shortens my range to whatever the board battery can do until such time as I either replace the charging solution or come up with a viable alternative.
The plan for the big trip is to complete it completely solo but have the van as a ‘support vehicle’. There’s no way I’m gonna complete this trip like @Mikes_Esk8 sprinted marathon, as i’ll likely want many days off to recharge (body and board), explore, learn about the areas i’m in, experience the areas i’m in and likely try and find bits and pieces of work along the way to compensate the trip financially.
In order to do this and still ‘skate the entire coast’, i’m gonna need to travel X distance in the van, park up and then skate a loop back to the last place i reached on the skate, then back to the van. By the time i reach the final destination I would have effectively skated up AND back down the entire coast.
Doing it this way allows me to pause or even defer the remainder of the trip if something comes up. It also allows the comfort of the van, the ability to charge while driving, I won’t have to carry extensive amounts of ‘living’ gear on the skate (although i will probably carry a very minimal hiking tent and a tarp in case of getting caught out in heavy rain). It’ll be much like a skating safari.
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This buck converter reckons it can do 4000w which is plenty of overhead for my intended 2000w charging. It is capable of the voltages i need. Its CHEAP!
There is a disadvantage to a buck only converter though as it can only output 0.945 x input (voltage).
It has backflow protection, so I imagine it would just shut down once that threshold was reached and i would manually have to turn down the output voltage to milk the most out of both batteries, gradually stepping down the voltage output to be lower than the trailer but higher than the board.
It has 10 storage settings though, so I could easily dial it down during the course of the ride.
This seems much safer although not super convenient.
A dc to ac inverter is starting to look far more appealling.
I feel like this is getting into a lot of extra components and systems vs just having an extra battery (or 3) in the trailer with leads ready to plug out and in as needed. A clean battery swap has to be better for the system longterm compared to constant discharging and recharging while discharging. Did you already mention why this isn’t an option? Tail mounted esc wouldn’t be a terribly long run from a trailer.
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4wd. Def want center mounted escs, tail box will likely exist but contain bms and power components
An inverter would be cool as it would allow the board and the trailer to be used as power banks to charge pretty much whatever i wanted.
As far as i’m aware, there shouldn’t really be any extra stress on the batteries being charged/discharged at the same time?
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Run hotter maybe? I’m no mooch but energy transfer is typically known associated with heat generation
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I definitely want center mounted escs so I really can’t make plug and play batteries work without a cap bank.
I’ve never done a proper charge and ride dealio before, i’ve always just paralleled packs but the longest wire run i’ve ever done was less than a meter with a MUCH smaller pack.
Right now an inverter is looking like the safest option. It also offers a lot of versatility so I’m pretty down with that. Looking at a couple of options on aliexpress they also seem a lot smaller than i expected, so that is a bonus too
Curious as to how that energy transfer will actually work.. wonder if it’ll fuck with the escs having power coming in from a charger at the same time…
This is fucked.
I could end up with the same problem of noise and voltage spikes interfering with the escs.
I think i’m just gonna do a cap bank and parallel the packs
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Center top mount Dual Escs with two cap banks each the size of a stick of butter, between and the antisparkus robusticus connectors is ultimately the simplest, imo.
Seems if ESC physical size and antispark were not a factor the input caps would be larger from factory. Less ripple, less mosfet stress, cooler caps better longevity.
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Figure out the inductance on the long power lines, and add the caps.
I believe that’s a buck converter only.
MPPT, just means solar charger.. which usually means one of boost or buck, not usually both.
the MPPT bit is just extra algorithm to vary the charge for maximum wattage.
bucks can only charge something with lower voltage. (with a couple volts minimum delta required)
boosts can only charge sometthing with higher voltage.
so if you want a charge and ride. you woul want a boost from a charger battery who’s max voltage is lower than your main battery’s low voltage.
buck boost is the handle everythign tool. but they are hard to find, even by combining in the voltages ranges you’d want.
Figure out the inductance on the long power lines, and add the caps.
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