[Oatz328]

Hi all,
I am new to the forum and have a general question. I've searched this forum and found multiple discussions on specific projects regarding EV system Fuse sizing, but nothing that addresses a general rule of thumb. Is there a basic formula for determining adequate fuse protection for my wiring and battery pack? I have a system that was packaged for me through an EV parts distributer, and I want to determine how the fuse size was chosen.
I have a hyper9 LV motor, 108V battery pack, Orion2 BMS, Elcon 3.3KWh charger. My system has a gigavac maintenance switch, dual contactors (motor and BMS), and has a 600amp class T fuse (amongst other items of course).
Given that the low voltage hyper 9 can draw 750amps, and my batteries can deliver 3C at 900amps, i guess the fuse can pass higher than rated amperage for short durations. as you can see, i'm no electrical engineer, nor a particularly smart guy, so how did they figure out the fuse size would allow transient current above rating but still provide adequate protection for my wiring etc?🤯
cheers

 

[Oatz328]

The rule of thumb is your fuse should be the weakest link in the system, so it fails before any other component fails. I don't believe delay fuses are appropriate for the systems with programmable motor controllers - the motor controller should limit the current before a current spike exceeding the fuse's rating would be produced. Fuse in that context really is to account for a short circuit either in the wiring, or in the motor controller itself. Likewise there should be no need to account for inrush currents to the motor, motor controller should ramp it up slowly enough that there is no spike exceeding the ratings.

Either way, that's just my opinion. To sum it up: fuse size = min(Imax(controller), Imax(wiring), Imax(battery), Imax(contactor)) - 5%.

Perfect. That leads me to another question I had about precharge circuits. I dont have one, but there is a delay following my key switch activation before my main contactor closes. I assumed SME controller had some form or internal precharge circuit, as the KSI input wire delivers HV pack voltage through the harness. My kit didn't specify a precharge circuit. thoughts?

 

[Oatz328]

That sounds reasonable, but your motor controller vendor would be the ultimate authority on this. Is this what you got ? https://www.go-ev.com/PDFs/HyPer_9_IS_User_Manual_REV09.pdf

yup, that's the one. Vendor told me I was overthinking it...but this stuff isnt cheap and I would like to understand the logic behind the design of the protection system.

 

[Oatz328]

🍿

 

[Oatz328]

so, if Im following you guys, the fuse is for wire and connector protection. I have 2/0 cable throughout my truck. when I use online wire calculators, I keep getting warnings that my cable isn't thick enough. If I my motor can pull 750A, and my cells are 300Ah 1C and capable of 900Amps for short durations, im utterly confused and concerned that the 600 amp fuse and my 2/0 cables are inadequate.

 

[Oatz328]

That makes sense. The 750amps is definitely peak. I’m not sure what continuous rating is, as Netgain only publishes the 750amp rating. I think my confusion arises from the idea of peak vs. continuous current. Do I size my fuse based on the continuous current with a time delay fuse that can sustain short burst of increased amps during acceleration or the occasional hill? If that’s the case, then am i adequately protected with a 600amp time delay fuse?