The main contactor is a high-capacity relay-operated switch separating the battery's positive side from the bike's propulsion systems.
- It mutually protects the battery and the bike's systems from damaging each other, particularly for rush currents or overcurrent conditions.
- Contactors for the 2013+ years are GIGAVAC GX-series contactors.
- The 2013 year contactor is not identified, and some reported an occasional failure mode where "contactor welded shut" could occur.
- 2014+ years feature the GX11, which appears to fail safe open by design (SPST-NO) and has had no significant reported issues.
- The 2013+ power pack contactor is housed within the "dog house", an enclosed area extending from the main power pack enclosure top face at the rear.
- For the Power Tank accessory and bricks and long bricks, each enclosure has one contactor operated by the BMS within.
- Theory (ref)
- A contactor is a large relay: it allows a fairly small voltage/current signal to switch a much larger voltage/current.
- It has two sides:
- The drive/coil side (control).
- The load (contact) side.
- On the drive/coil side, there's a "kickback" diode which handles the inductive spike caused when the drive to the coil ceases.
- Without that diode, the energy represented in the magnetic field inside of the coil would have no place to go, so it would cause a voltage spike which can be damaging to components.
- The kickback diode gives that energy somewhere to go, allowing it to ramp down fairly slowly without a big voltage spike.
- Depending on how the coil side of the contactor is wound, it has a certain current requirement to pull the contactor shut, say 12V @ 100mA, which will be provided by the driving circuitry.
- There's not necessarily any relationship between the coil rating and contact rating, except that bigger (higher-current rated) contacts might be heavier and require higher coil current to get the armature to move.
- The kickback diode only needs to carry this amount of current, regardless of the contact side current.
- If a 3A kickback diode is specified for that contactor, it will be adequate for any contact side current.
- The make/break current is the rating for the contact side of the contactor.
- You won't actually want to make or break the contactor under the limiting conditions (you'll always want to both make and break the contactor at exactly 0 amps), but in an emergency, it's rated to do so without the contacts welding together -- and an emergency is what the contactor is there for.
- In automotive use, you often see the coil set up for 12V, drawing maybe 100mA (the current can vary widely though).
- That small current pulls the contacts together, which switches on the high-current side.
Zero's effective contactor limit for the charging rate is 95% of 1C rate.
The BMS will open the contactor for the following conditions:
- If the motorcycle is keyed off and not otherwise set in charging mode, the contactors will open after a few seconds.
- If the motorcycle is keyed on and not otherwise set in charging mode, and then 30 minutes pass without control input.
- Twisting the throttle is sufficient to reset this timer; otherwise restart charging once it happens.
- Voltage is too low or too high outside its safe operating range.
- If voltage is too high (117V):
- Confirm with the Zero mobile application
- Attempt to bring it back to normal range by discharging the battery:
- operating the motor (fastest but requires a closed contactor, and the Sevcon won't operate above 118V) or:
- turning on all available electrical loads.
- If voltage is too low, charge by any means necessary:
- Prefer the onboard charger or an equivalent rate source through the charging port.
- In an emergency, the regen feature can be used to charge the battery through the motor.
- Drive the motor by spinning the rear axle with a suitable power source, with the bike in Custom Mode with regen set to 100%.
- Incoming power exceeds 1C rate continuously for a minute. A 1C rate charges the battery fully in 1 hour.
- For a battery with 13 kWh max capacity, this value will be 11.4 kWh nominal / 102V = 110A (say).
- If the charge rate is too high for the battery, downgrade the charge rate manually and restart.
- Field testing indicates that the short time setting for the contactor opening is 30 seconds, and that a 20 second period under that limit will reset it.
- This may vary due to environmental conditions like ambient temperature.
- If the battery temperature (not ambient) is outside safe operating bounds:
|Cold Battery||Normal||Hot Battery|
|Range||operation prevented||charging prevented||charging tapered||operation prevented||damage likely|
|(F)||… -22F||-22F … 32F||32F … 110F||110F … 122F||122F … 140F||140F …|
|(C)||… -30C||-30C … 0C||0C … 43C||43C … 50C||50C … 60C||60C …|
- The Zero battery will emit heat while its charging rate exceeds 4 kW, and it will cool if under that threshold.
- If temperature is out of safe range, do whatever is appropriate to bring the temperature back in range.
- Calculating Contactor Limit Per Bike
Per Zero's specs pages:
- Maximum capacity (kWh) = COUNT(cells) × (cell capacity rating (Ah)) × MAX(cell rating (V))
- A 2015 SR w/ Power Tank has 15.3kWh max, 13.5 kWh nominal, with a 102V nominal voltage, so is nominally rated at 133 Ah.
- 1C rate means that it can charge at up to 133A.
- At 10% actual SOC (3.4 volts per cell), 1C = 3.4 volts per cell × 28 cells in series × 133 A = 12.7 kW.
- At 95% SOC (4.1 volts per cell), 1C = 4.1 volts per cell × 28 cells in series × 133 A = 15.3 kW.
- These are DC power ratings; AC input power will read 10 to 20% higher (due to conversion losses).
- Contactor Limit Per Power Tank or module
- The current capacity will be proportional to the number of bricks vs 4 providing a scaling factor.
- Or, more directly, the Ah rating on the label indicates the 1C rate.
|Capacity (kWh)||Voltage||Capacity||Contactor Limit|
|Year||Cell||# Bricks||Max||Nominal||Max||Nominal||(Ah or 1C amps)||A (95% assumed)|