Right right thanks, yeah that just clicked a minute after I posted
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Well I’ll be damned, that’s perfect, thank you! I guess I should have searched for “48V inverter” rather than “50V inverter”, lol 
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An inverter isn’t fundamentally different from many other types of switching power supplies (for how it draws current in). It’s probably just DC (non-pulsed) current with some voltage ripple, most likely not an issue for a pack. Especially since there are untold numbers of inverters being used with batteries around the world.
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Well… anyone yet?
USB C PD is all the rage so AC is a little old fashioned.
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It’s simple
Buy 24v inverter.
Put your loopkey between groups 6 and 7 of a 12S battery.
Solder leads to the +/- of your 2 6S groups.
Pull loopkey.
Plug leads into inverter in parallel.
Problem solved
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Forcing group 7 into parallel with group 1, and 8 with 2, etc. will create a massive short through the balance wires unless those are disconnected first, unfortunately. JST-HX loopkey, maybe?
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I apologise for there is a decent chance I was being silly and just thinking of how I’m set up differently and already doing this. Also in hindsight I should have worded it as a question not a solution.
So I think the 12S load will be supplied by 6S but that’s ok, I know connecting 2 packs in parallel is bad practice even if they are really well balanced, and the balance lead isn’t doing anything while the battery is being discharged right?
I would guess the bms is just unhappy with the numbers but I’m not confident.
So has anyone found an inverter that takes 75VDC?
I think you want to be looking at solar inverters. Something like this:
All the 12vdc 120vac inverters I have used, cause a huge violent spark when I first connect the second ring terminal to the battery, or battery cable to inverter input, as they have physically huge capacitors.
I started using one 800 watt msw inverter with a 45 amp Anderson powerpole connector on 8awg , and a 22ah 12v AGM as a portable power station to power a vacuum, and pick up broken glass shards on the street where I was walking my dog.
The spark on hookup was largely contained within the connector. Then one day when several broken bottles threatened paw pads, It appeared the inverter fried, but it was the connector itself, damaged from the sparking, and not making proper contact anymore.
That was well prior to me getting into esk8.
I now have a XT90s antispark to anderson powerpole adapter I can use to prevent that spark on initial hookup.
I’d fear for the BMS, and the ESC, when hooking the correct input voltage inverter to an Esk8 battery because of that giant spark.
I grew to hate inverter fan, and electrical noise, and inverter inefficiency, in 12v vanlife duty, so whenever possible, used Dc to Dc converters instead.
I just did a short search for a 36v inverter, and got plenty of hits. My esk8 is only 10s.
The one 36v inverter I saw said its input voltage range was 30-45vdc.
So in theory I could hook my 10s2p battery’s XT90s to said inverter, and the inverter’s LVD should prevent overdischarge.
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I’m tempted to get this thing for science with the bezos warranty
Seems like anything with a higher input voltage than 48v gets crazy expensive. So I’ve got the ultimate 1st world problem of all my boards being too high voltage but vantablack lol
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Appropos of nothing I have a rule about buying from Amazon, if it’s got more than 10% 1 star reviews walk away. This one has 16%.
That said the inverter I did get works great except the fan is really noisy and doesn’t have thermostat control so it’s always noisy. Too annoying to have running in the back of my car charging the board which is what I bought it for 
Whoever said to stick with DCDC converters is probably on to something - I should try to find a 12V to 50.4V converter.
or is 56 too high for 12S?
If you are charging from a car, the 12v power port on dashboard and mating connector will not handle 100+ watts for very long, if at all, even if it says 150watts max.
I have 3 different DC boosters I can go into detail on later this evening. Proven reliable for me, boosting to 39.5 to 42.06vdc from 12,19, and 29.4vdc, upto 250 watts, and could push to 420 if I needed to.
Link?
on the DC-DC camp
I got this for bucking 12s voltage down to variable output voltage.
https://www.amazon.com/dp/B0B38GYF74
and got good usage out of the mpt-7210a as an adjustable output boost converter / charger up to 72v
https://www.aliexpress.us/item/2251832685277010.html
sometimes have to use them in combo.
done things like. charge lonestar (12s) from solar. charge proto (12s), srb v5 (8s), onewheel (15s) from lonestar. power hobby charger (6s) from lonestar. use hobby charger as usb charger.
juntek makes a bunch of other bucks. i thought about trying if i needed more power.
that said. it’s hard to find bucks that do higher DC voltages.
and it would be nice to have a handy adjustable buck/boost combo all in one package.
also non esk8 related was looking at LM2596 based bucks to maybe make a multi out DC buck box. 7v 9v 12v 19v (for home router, switches, modem, off custom battery DC ups )
Yes, I didn’t think that through.
It’s a cig lighter adapter in the cargo part of the car (Rav4). In the old days they were 10A so if I’m boosting 12V10A (120 Watts) to 50.4V I’m only going to get a little over 2A.
The irony is the car has a great big hybrid battery in it, but for some reason they don’t give us access to it 
I am going to look at that mpt-7210a though, it would be nice to dial in 50.4 to avoid big fires.
On a whim and because it was a pretty good deal (renewed) I ordered one of those Jackery power banks - 500W. I think I can probably trickle charge it from the car’s 12V and then use the AC port to charge the skateboard. We’ll see.
I hope this is kinda on-topic…
If you are running a VESC on your setup, you can use the controller/motor winding’s as a boost converter to charge the traction battery pack.
Write up I did on Endless Sphere:
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This one^, the voltage potentiometer is backwards. Ccw to raise. Current pot is CW to raise. No leds
This^ is my favorite for charging upto 150 watts. I put a 24vdc 50mm fan on heatsinks, wired to the input very quiet at 12vdc input and gets pretty warm at 150 watts. Pretty loud at 29.4v input, but unit stays cool at 150watts output.
Normal clockwise to raise voltage and amps. Has a third potentiometer to decide at what amperage that red LED light turns green. I set mine to 0.2 amps.
This one^ is CCW to raise both voltage and amperage. opposite. weird. unintuitive. It is limited to 10 amps output, so in my case 42 v, 10 amps, 420 watts. Attach it to larger heatsink.
I always run a wattmeter inline on the output, and initially on input as well.
Set output voltage unloaded then hook to battery, then dial amperage up or down as desired.
On initial powerup, dial output voltage, when output is not hooked to battery, set it to just above battery to be charged voltage so there is not a huge delta.
If you set it to 4.2 volts per p group, then hook it to depleted battery, the 20 turn current potentiometer might be cranked all the way up from the factory, and try to send amperage far beyond its rating and magic smoke might escape.
I bought all mine from ebay. sorry the middle link on 150 watter is currently unavailable. There are others that look similar, make sure it has 3 potentiometers and goes to 60vdc output, not the one which says 32v max output.
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update, this thing has arrived. As near as I can tell the discount was due to the following power cord anomaly which took all of 30 seconds to fix:
Everything else seems to work fine.
It will take an input and deliver an output at the same time (it even has MPPT for solar input). So here it is driving the Cycle Satiator.
Assuming I get the same 80 Watts in from the Cig Lighter adapter in the car that means my net loss to charge is ~120 Watts. at 500wH of capacity that means the batteries will run for 4 hours.
Unfortunately I don’t remember what the charge time is on my boards, but it’s certainly less than 4 hours.
So it will work - I will be able to charge my board while driving to the next destination
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10 years ago I made a huge heavy AF powerpack/jackery with a 125ah Lifeline GPL-31XT 12v AGM battery for a friend. Made a wooden box for it, and it had a 45 amp grid powered charger, a 400 watt pure sine wave inverter, and ability to easily hook to his alternator over 1 gauge cable.
Thing was able to charge at 100 amps from alternator.
Talked with him a few months ago, figuring the battery aged and cycled out by now.
He claims ‘strong like bull’ performance still, and still powers his ARB fridge without issue for as long as he needs.
Could stuff 304 amp hours of EVE Lifepo4 inside of it today, and it wouldn’t weigh 100lbs.
Probably fry the alternator though.
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