nah is ugly. actually all topmount boxes are ugly. very practical. but ugly. its a lump on a very nice flowing line → ugly.
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for an “AUX pack” like exway does, like a secondary topmount battery pack for underslung battery boards… how should I go about connecting it?
my initial instinct was to just run a parallel port in my underslung enclosure and parallel the batteries when both were at a similar SOC
then I thought of running it into the charge port, but more questions came up, like would that work with the underslung BMS? how would charging need to work?
Assuming that this is how you would be connecting the groups, you’d be looking at a piece of nickel that would be ~120mm wide. At 0.2mm, you’d be good for around 300 amps continuous with a single sheet. If this is for an esk8, you’ll never pull even close to that. If it’s for another application (Surron for e.g.) I’m not sure what the current draw would be like even if the controller is capable of a 400 amp draw. You’ll have to sus that out.
In any case, p42a’s in a 12p arrangement would only be good for about 300 amps continuous. The 45 amp rating that Moli gave these cells does not hold up irl. Mooch rated these at 30 amps cont but I personally try to run them at 25 amps per cell to avoid sag. So:
12 x 25 = 300 amps cont.
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Best idea imo is just using it as a swap-pack. Store it on the board, charge it separately, and use a swap cable to switch between the internal pack and the top mount
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I want the underslung enclosure to be self-contained and semi-permanent. Would this mean I need to fit a second loopkey port to disconnect the internal pack and connect the external one? Or rather, I guess I’d just run it into the parallel port, and have the loopkey disconnected while using the swap pack, having the loopkey port between the internal battery and the parallel port.
Now the question is, what port to use for the external pack? It’s gotta be different to my charge port and I don’t like the idea of XT90E-M.
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There are a couple ways you can do it, I would probably put a mounted connector into the side of my underslung and just have an external cable that runs between the two. You could do it internally in the top mount with a switcher plug as well
XT90 or XT60
I don’t use either of those for charge, they’re a bit clunky for that
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Should this connection have antispark? Would having the female side mounted on board be okay?
I would make it so the cable that connects between the two IS an antispark, so when you switch the plug from one pack to the other, you won’t have to worry about it
You could alternatively have one lead (negative) permanently connected, and then have an AS150 as the other lead that you connect to one pack or the other
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I run a parallel pack in tandem with an underslung enclosure and use the first method. The charge port with a BMS on the other side will probably create issues as the current will be much higher than it’s rated for. I run a dedicated cable to it, but a panel mount XT90 would be a cleaner way to go
I don’t think an XT90s is necessary. The packs should be less than a volt apart, so the added resistance of an XT90s over an XT90 doesn’t seem to make sense. It’s basically the same thing as plugging a charger in, they are at similar voltages so there shouldn’t be a spark. Frankly an XT60 would probably work too. If you look at logs on an esk8, the battery current is rarely high enough for long enough to matter. Plus with parallel packs, the current the XT60 sees will be roughly half provided the two batteries are of similar specs.
I also like the parallel idea over separate packs because the total amp draw per cell will be less so the batteries should both provide more range, and last more cycles. Just important to check voltages before connecting. Really important.
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so taking into consideration both of your methods this is the schematic I’ve come up with, charging not included as that’ll be handled by each battery’s BMS individually.
Loop key should be closer to the ESC so it shuts off both batteries. As it is, it will not shut off the top mounted battery to the ESC.
I figured the method for shutting off the topmount battery was to unplug the cable, acting as a loopkey.
alternatively, I could have a loopkey mounted into the topmount battery as a separate shutoff.
It will spark then. The capacitors in the ESC is what makes it spark.
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so would I need a double loopkey setup? just needing to swap a single loopkey between 2 ports to switch between 2 batteries? or 2 loopkeys?
Just one loop key
This is how I have mine
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so this just means I can only connect the packs when the voltage is close, say within 100mV?
The math has been done somewhere, but even at 1v it’s only about 10A charging or something like that in my experience. It drops pretty fast as the voltages equalize. I use a DC clamp meter sometimes when connecting if I’m not sure.
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if my pack can handle up to 24A charging current can I connect them with a larger delta?
theoretically, I don’t intend to do it if I can help it
What added resistance?
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“technically” the contact area inside an XT90s is smaller than a normal XT90, since part of it is taken up by the resistor loop
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