[Frank]

My main concern with using the BMS to open a contactor is that it might happen under load. You don't want to have the situation where a momentary dip below some LVC causes it to open. This might be in the middle of some acceleration event, example, passing a car. It could also damage the contacts which are impossible to inspect with an enclosed contactor. I have an "okay" green light wired to my Orion and I find sometimes it goes out for strange reasons which have nothing to do with protecting the pack. With a light you can always slow down and check things out in a secure setting.

 

[Frank]

You can get away with a single contactor with an A.C. motor but I would always use two contactors with a D.C. setup. DC controllers typically fail "on" and you need all the help you can get to open the circuit should this happen. First contactor turns on with keyswitch, second (typically) is activated by the controller. If not, then use a separate switch to "arm" the system.

 

[Frank]

It looks to me like your setup is fine. The throttle "cutoff" switch will probably never be used - but you never know. Two contactors is never a bad idea: first wired through ignition switch and second controlled by the controller. If you were racing, a switch to interrupt power to the contactor coils would be required.

Using the third contactor would be a personal choice I guess, but you could obtain the same functionality with two, depending how you wired them; ex. key switch to leave basic functionality "active", toggle switch to activate first contactor, then momentary push-button switch to "start" the system up.