There’s no chassis but there is definitely a “common” connection in a board, the negative, and all of the non-isolated devices are referenced to this point. If this was not done then each device would have no way of knowing what the signal or power they are receiving are referenced to, they would have no idea what the voltage was for any signal or power they received.
It’s often via a long, convoluted path (causing all sorts of signal and power integrity issues) but all of the Negative or Ground connections in a board are electrically connected unless an isolated power supply or comms chip is used.
If the negative side is fused, and the fuse is blown, then this reference point/voltage is lost. Some devices might not care but others, that might still be receiving signals or power from another source, can misbehave quite badly if the ground is disconnected (“lifted”).
I recommend fusing the positive, just in case something might be sensitive to losing its ground connection.
I’m certainly not any kind of expert on automotive electrical stuff but I don’t believe there is an earth ground for any vehicle. All grounding is done within the vehicle and not to a true earth ground since the current is created within the vehicle and so only needs to return to that same source.
There is a “common”, often using the chassis on older vehicles, but that is just where all the negative connections are made so individual wires aren’t needed (to save money).
I second @Battery_Mooch
In the good old times when we made single motor builds without any electronics other than the ESC, fusing the positive or negative side didn’t really matter.
But nowadays, we have a lot more devices and cutting the ground path isn’t a good idea.
After doing some dumb things, I now fuse the balance wires.
And the main discharge [positive] with a fuse soldered into the xt90s loop key, but its NOT to protect the esc’s, its to prevent thermal runaway of the main pack if a dead short happens from being dumb or bad crash. So its rated to about double my expected peak battery load, and the hope is it would still blow in a dead short. Its not without the downside of potentially loosing breaks while ridding, but with appropriately sized fuse I hope that would be low chance of happening.
For people with really high power systems, the size of the fuse would probably not be very practical.
I still wouldn’t recommend to anyone, you would need a good level of electronics experience and willingness to accept the possible increased risk.
Sorry I didn’t realize you were referring to the rheo brake. I never tested disconnecting the battery and only leaving the rheo brake installed. I did test full charge downhill braking and found it worked as expected.
I’m not sure that the esc would be awake with the battery disconnected if you have a roll to start feature enabled and were rolling down hill. I don’t feel like that would be a steady enough supply of power for it to work right but I’m no esc expert.
i think from what i’ve read about the bms/breaks issue (but i’m not an expert at all and this is just elucubrations) that the esc would work without the battery with only the motors as a source of power,
but it doesn’t breaks because of a safety measures preventing it to push power down the battery if it doens’t detect a voltage input there
if i’m not crazy and it is so, it could be that it would work with the reho brakes (but haven’t had one at hand so no idea really)
I’m building a pack for a friend soon and he’s extremely paranoid and wants a fused charge port, discharge BMS, and fused discharge port. How can i convince him that just a fused charge port and bypass BMS is good enough?
