2023-11-21 ASC Regs Review

Owned by Jonathan Xie
Last updated: Nov 22, 2023
3 min read

 

Solar relays cant be behind relay

  • Batteries are rly sensitive to current, so any mA of current can make it go boom

 

‘Power switch includes all switches that isolate all devices’

  • when power switch is open, it opens all devices from each other

 

‘nothing can be behind the power switch. Does that include BMS?’

  • no, BMS is allowed to be behind power switch, but…. see BMS section below

 

Precharge:

  • precharge ‘behind’ main power switch on positive side; is this ok?

    • forest: 'its the equivalent

    • him: every time u add relays in parallel, you double the effect of reliability

    • you are not allowed to have more than 2 relays that protect the battery pack

  • precharge is only needed for motors, not solar or other things

    • steve: “if you put precharge with the motor switch, you’ve done both in one go”

    • you do need to have a dedicated switch for the motor (and ‘anything else that's needed’ like MOV stuff but doesn’t apply to us)

  • forest: ‘if we put precharge somewhere else (e.g. isolated DCDC), then can we avoid putting in a relay?’

    • e.g. on industry EVs, LV

    • you can’t pre-charge with AUX

      • in sec 8.2.C.3, it says that ‘supplemental battery cannot provide motive power to the vehicle’

      • fsfs

  • ‘I haven't seen a car with less than 4 relays’

    • 2 for batt, 1 for solar, 1 for motor

    • so you can’t have a pre-charge on the main relay, cuz then that reduces reliability of

  • ‘you can’t put pre-charge on the main contactor'

    • why?

      • diode could fail

      • precharge could short out

      • ‘at least doubles the unreliability of the relay you’re working around, because you’ve added a second device that is supposed to be carrying much less current, but is capable of failing'

    • ‘how does adding a second relay in series make anything worse'

      • steve: 'you can figure that out

 

BPS:

  • ‘the battery protection system shouldn’t be dissipating any power from the battery pack'

  • ‘if your BPS isn’t powered off DCDC or AUX that’s a problem'

 

Power path:

  • easiest way to select between DCDC and AUX is to just have DCDC be higher voltage than AUX and use a diode

    • ICs and stuff is ok, but

 

Voltage Taps

  • “8.5.c: any battery measurement tap shall be less than 10mA”

    • forest: ‘if the IC consumes less than 10mA, is this ok'

    • steve: ‘but what happens if it does exceed 10mA tho’

  • Need to hard limit all voltage taps to less than 10mA

    • current limiting resistors

    • current limiting small wire (e.g. 32 awg wire)

  • The 10mA applies only to the current being drawn from the battery thru taps, NOT for the BMS board itself

 

AUX Batt Monitoring

  • forest: ‘is it ok to just have a voltage monitoring pin for passive protection’

    • him: ‘yeah voltage monitoring is all you need’

  • steve: ‘What’s the concern on NiMH?'

    • steve: ”low voltage, ofc that’s the issue cuz then ur relay will fail”

    • ^ that’s the only thing you need to monitor

 

BMS location:

  • AFEs are allowed to be before main switch

  • current sense should be after main power switch

    • current IC on current sense determines SOC through current & voltage, so we’ll need a voltage tap pin that goes to the battery too

    • ‘you can have that voltage tap going straight to the pack, it just needs to be 10mA limited’

 

Battery Box Cooling:

  • for battery box cooling, are u allowed to have intake and exhaust fans?

  • ‘let’s say you’re driving a car, you see smoke under you, what do you do' → you stop and get out

    • ‘the reason we don’t allow 2 fans is because 1 pan will pressurize the back, so smoke will go to the back through exhaust and not the driver'