Wiring diagram - For my first build

Hi to everyone, so after reading and researching I came with a diagram for my first build. It will be a 12s4p 30q dual focbox bms for charging and discharging and a e-switch. Any suggestions advices corrections comments will be appreciated. So this is it:

If I want to use a fuse, where it should go?

P.S: The battery diagram and balance wires will be another chapter.


Nice diagram. Fuse should run in series with the anti spark plug.

Edit - Or rather on the positive lead coming off the battery before anti spark, so that it protects from a short even on the charge plug.

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Nice man, Im doing the same except with a Supower BMS no e-switch (Antispark Loopkey is my switch). I would also suggest cell level fusing over the series fuse (Just cause thats what im doing on mine).

You will most likely want the HM-10 bluetooth module on the same VESC (the Primary VESC) as the RX). If you dont have one PM @GrecoMan, he makes and sells them cheap.

@Sebike is right. If you are going to use a XT90s loop key, you want it after the battery but before anything else. If you have a BMS with an E-Switch its unnecessary.

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You’ve got this wired like it’ll run in bypass but then also wired in discharge mode. You typically want one or the other.

You want either A) bypass mode

  • you need a loop key
  • don’t run the esc power through the BMS at all
  • no power switch needed

B) discharge mode

  • you need a power switch
  • run the esc power through the BMS (P-)
  • no loop key needed

Make sure you understand the pros and cons of each method

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I’m not sure I’m following here… The diagram looks like charge+discharge and is how it should be set up if discharging through BMS. It’s either charge only or charge+discharge. At least I haven’t seen anyone going discharge only and then charging pack without balance charging…?

Only thing that is not necessary is e-switch, since a loop key is being used.

This confused me. From the image I see the Battery negative connected to the BMS at B- and the BMS negative connected to the VESC’ at P- and the charge port negative connected to the BMS at C-. The E-switch should kill the negative flow of current when in the off position thereby isolating the battery from electronics down the chain. That’s textbook discharge mode right?

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pros of running bypassed:

  • smaller BMS requirements (charging/balancing only)
  • brakes won’t cut out if the battery is completely full
  • can be safer for humans, at the expense of possibly damaging batteries or electronics
  • BMS discharge current rating is irrelevant

pros of running through BMS discharge circuit:

  • will shut down if any P group runs down quicker
  • safer for electronics

cons of bypass:

  • if a parallel cell group gets weak it can get damaged
  • you can hit the brakes until your battery is destroyed, if you wanted to and had a big enough hill and had a completely full battery
  • need to carry a key for your skateboard and not lose it

cons of discharge:

  • you need a BMS rated at >= 50A (one motor) or >= 80A (two motors)
  • if you start braking on a full battery it can shut down, killing your braking ability
  • more expensive BMS
  • bigger BMS

yes, except with an extra loop key

Ahhhhh, I thought you meant the BMS was wired in discharge. I assume he just wants extra protection by using the XT90s loop key. Seems needless to me with a quality BMS, but I can understand wanting to protect a few hundred bucks worth of electronics :slight_smile:

looks like eswitch is permanently connected then loop key is master switch. this is exactly how I’ve got mine wired up right now, same bms and all that.

only thing, I stopped using xt90s because they’re bulky. and once wires are soldered up they’re pretty long/tall. and doing the split to dual focbox as in the diagram, you’ll be surprised how bulky that loom becomes. I’ve switched mostly to bullet connectors.

I’d prefer to protect the human at all costs, even if it means overcharging the battery while braking hard. But there are many pros and cons to sort through, all depending on your preferance. I also like the BMS being physically smaller and not needing heatsinks on it.

I’ve put the loop key for extra protection, not sure why So I moved the bluetooth to the main vesc, put a fuse and removed the loop key

Now what do you think?

Why would you need a power switch in discharge mode? You mean, in discharge mode you can either use a BMS e-switch or a loop key?

TBH I think dont use e-switch and use loop key :joy:

That’s the textbook discharge mode circuit.

I meant the BMS e-switch or a separate antispark e-switch

If you want the extra protection, use the loop key. When a fuse blows you will eat pavement, at least most people do as it will most likely blow under a heavy load meaning fast.

This is how I wire mine, maybe it will simplify the concept a bit…

But at the rate e-switches and separate power switches seems to be failing on peoples builds, and for the sake of better protection (like @mmaner already mentioned) I’d still vote for an XT90s ! :wink:

I haven’t noticed a failure in BMS E-switches, just Anti-Spark switches. That being said, an XT90’s loop key won’t hurt anything.

If you want to use a loop key instead of the eswitch, put the loop key on the BMS P- to XT90 run

Also, this. Consider soldering them together too, instead of bullet connectors or the XT90/XT60/XT60 harness unless you have tons of space in your enclosure. I wouldn’t solder them together unless you use a loopkey though