First build - Xenith, LLT BMS how to bypass for discharge?

This is my first post, my apologies if this was already answered but I’ve already searched and while I found similar posts, different components were used and I’m still little bit confused.

This is my first ESK8 project, it’s actually an upgrade on exisiting Evolve GT Carbon. new components to be used :

  • 10S4P battery
  • Xenith V2 ESC
  • 20A LLT BMS
  • 2x 6374 170kv Maytech motors with 18T pulley
  • 2x Radium Performance 63xx motor mounts
  • 2x 415-15mm belts
  • VX2 Pro Remote & Receiver
  • existing 7" offroad tires/wheels with 66T pulley

My questions :

  1. is the wiring diagram (bellow) correct to bypass BMS for discharge ? I’m only not sure whether there needs to be an additional negative wire from the battery to the “B-” on the BMS, I’m thinking the battery is already connected via balance lead negative wire to the BMS, so do I still need to run an additional wire ?

  2. is the battery still getting charged with regenerative braking with this setup and if so how is battery protected when say fully charged and I start my ride downhill while braking, where is the excess charge going without overcharging the battery ?

  3. as the battery gets discharged while riding and then say I’m at 50% battery going downhill and assuming the battery is getting charged by regenerative braking, how do the cells get balanced or do they get balanced while on a ride ?

  4. the Xenith ESC comes with it’s own power switch wired straight to the unit, I note many people build their boards with anti-spark switches which I assume this one is not, is that a potential issue ?

  5. is the VESC Tool 3.0 for Mac all I ever need to configure the Xenith ESCs once installed ?

proposed wiring :

LLT BMS :

Xenith V2 ESC :

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Hey Booz! Welcome to the ESK8 forum. Wow I sure could use some booze, but its only monday. Gotta wait for the weekend. :crazy_face:

Pretty sure your battery negative needs to connect to the B- port on the BMS and the C- goes to the negative lead on your charging adaptor. I doubt it charges thru the small balance wires. And dont worry about regen overcharging you pack unless you’re always going downhill for some odd reason. It doesnt put that much energy back into the pack. Keep in mind that the BMS is still connected thru the balance leads even during discharge so it should burn off any excess charge as heat thru resistors.

For question #3 I’m not sure if that BMS is always balancing. I would guess that it isnt but it shouldnt be an issue. Most BMSs do top balancing where extra current is converted to heat to keep cells from overcharging. I’m not familiar with that particular unit though. And for #5 I dont have an answer either. Fairly new here myself.

Since that ESC has its own power switch, just look and listen for any sparks when you connect the battery and turn it on. If it does spark when you connect the battery or turn it on via the switch, then yes a loop key with an XT90 anti spark connector would be your best bet.

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@kavic5150 once I have the BMS in my hands I’m going to check with multimeter whether there is continuity between balance lead Battery cell 0 ground and the “B-” port, if not then I’ll just run the extra wire.

obviously I don’t travel downhill all the time, but first 100m out of my driveway it’s downhill about 30 degrees so I didn’t want the fully charged battery to explode before I even start my ride :slight_smile:

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Thats a good idea. Sounds like its time for a before and after check of your batteries. Charge all of your cells to a fixed amount, say 4.1v each then roll for that 100 meters with different levels of regen and see what your ending voltages are.

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@kavic5150 ok so my build is finished and I tested the downhill driveway getting out of the house, since I have that smart BMS I can monitor in realtime all cells. if I fully charge the battery previous evening, by next morning all cells start at around 4.17V, as I’m driving down the driveway while braking for the first 100m, by the time I get down my cells get to about 4.18V, so I think it’s fairly safe.

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just to conclude this topic, in the end I had to run the additional negative wire from the battery to the “B-” so the final corrected diagram is like so :

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