And if you were to add a on/off switch that should be turned on once all packs are plugged in, would this help in preventing the sudden changes in voltage?
Not a good idea to put a new group once the others have been subject to some degradation unless you have a good BMS for charge and discharge
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Ya. Replacing a pgroup isnt just pull the old one and slap in the new one. Need to have the volatages close.
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Well, a on/off switch would regulate the outgoing voltage, but wouldnt affect the balance leads iirc.
Ofcourse. Ideally voltages are the same, but, this is more giving that ability for waterproofing and modularity
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Im aware of the degradation bit, but coul you elaborate on the Charge/discharge BMS bit?
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What would cause this to happen in your design vs plugging a balance charger?
When using a balance charger, you plug in all of the balance leads at once, whereas in this design, you are effectively removing one wire from the balance lead and replacing it with another. Hope that makes sense lol
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So you would essentially need a way of cutting the balance circuit until everything is in place?
Ive thought about this in the past.
XT60 should be fine. Modular plugged modules would be great. Simple serial bus pcb (xt60) with balance connector, change(xt60) and discharge port(xt90).
If you wanted to you could have configurable charging for big backs - dual 4A charging for a split 12s8p for instance.
/edit
Keep in mind the pcb serial connections need to be augmented. Some copper bar soldered to the exposed bus should be enough.
That would be the less elegant solution, ideally the BMS would be able to cope and understand the removal and addition of a pack, without freaking out or throwing smoke
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In your opinion should I opt for dual XT60 over dual XT90? You’re not the first person to recommend it, and i dont want to be headstrong if those with experience are offering knowledge.
Look at the OG FocBox. XT60
XT90 is going to kill you on spacing and height.
You want a single connector to make these modules airplane safe. Multiple connectors means the possibility (however unlikely) of a short. Housing both terminals of the battery in a single connector is easier to make safe.
Less complexity = more predictable/safer
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Thats true. Although i know one of the rules is that the leads need to be isolated, which could equally be done with a 3D printed cover, which would end up appearing as though it was just one output.
Was the OG focbox alright with 150+amps?
No, but look at the unity. XT60 as well.
Is it possible to pull 150A from a 4p? If we’re going up to 8p then yeah, 150 is reasonable.
Id say design for a set of constraints and stick with that. Dont try to make the final revision the first time. For sure be smart about the design, but dont let the perfect be the enemy of the good.
Keep at it! Pushing forward with new ideas and bringing them to the community is always a welcome development!
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Of Molicell p48a? Hell yeah. In a 4p group theyre rated for 180a cont and 225 Burst.
I know the Focboxes and Unity have XT60’s, but i also know that many weren’t a fan of that, and even opted to change their leads.
Im just trying to be safe. With so much current, I’d rather be pushing things to 80% spec instead of 110% spec, especially if others are going to follow and do the same thing. All it takes is one fire to ruin yer day 
I appreciate the insight and support! I’ll look into the XT60’s since theyre more size friendly
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If you are using just the VESC low voltage cutoff and the different parallel groups have different capacities (the new one will have more), the others can go bellow the minimum per cell than what you had in mind
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Would this practically be an issue if you keep your low voltage cutoff above 3.2v per cell? Then theoretically you should never push it that far?
I would love to see a discharge only BMS with CAN capabilities that could communicate to the ESC to trigger low voltage cutoff if the BMS detects a cell at the desired voltage. Then the rest would just be above, but no cell would be damaged
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Depends on the relative strength of the new vs old pgroups.
Replacing a single pgroup isnt going to make huge differences, but you want to up the cutoff to be safe. The new pgroup will throw your average off.
Yes, a discharge bms with CAN that talks to the esc would be ideal. Right now its a guessing game.
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I think this is awesome, I have no advise at all other than please keep pushing on this!
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