Salvage Wire

Salvage Wire
Helping Automotive recyclers become leaders in their industry

Thursday, 22 February 2018

Performing the “Universal” HEV/EV Power Down Procedure

Helping vehicle recyclers become leaders in their industry

Salvage Wire are pleased to produce a generic power down process for high voltage electric and hybrid vehicles.
It’s always best to follow the OEM’s unique power down procedure when working on the HV system on any HEV or EV. However, below is a very thorough and safe method that will work with most HEV/EV vehicles.

1. Turn off ignition/press “Power” ignition button.
This will of course turn off vehicle and make the IP’s instrumentation go dark.

2. Remove the 12-volt (auxiliary) battery ground cable.
This will keep the vehicle’s low voltage system from powering back up. It is important to do this AFTER the ignition has been switched off. The DC-DC converter (doing the job of a conventional alternator to supply 14 volts) will work to power all the 12-volt components on the vehicle including the Hybrid ECUs that control HV operations such as keeping HV battery pack main relays closed. Even if the I.C.E. is not running, a powered up HEV will produce 14 volts with or without a 12-volt battery connected.
Wait for at least 10 minutes to allow various capacitors and other components to fully discharge.

3. While wearing class 0/1,000 volt safety gloves, remove the vehicle’s HV battery pack service plug.
On Honda and GM intermediate voltage B.A.S. systems, a switch must be turned to the “OFF” position to achieve the same condition as removing the service plug on other HEVs/EVs.

4. Wait 10 Minutes Before Proceeding with R&R.
The 10 minute wait is for the vehicle’s HV capacitors to bleed down in case the normal capacitor discharge circuits are not functional. 
HEV High voltage capacitors can have enough current to cause injury or death should they discharge while you are servicing a Hybrid. The capacitors are connected in parallel and typically are located in the area of the power inverter. NEVER attempt to discharge one of these capacitors in the service bay. Electrical shock and burns may result.

5. While wearing class 0/1,000 volt safety gloves check for High Voltage.
Remove any cover/panel required to access the HV electrical component (i.e. the HV battery pack) connections. Using a CAT III/1,000 volt meter, test for any DC voltage between the two orange HV DC cables.

Note: Automotive HV systems DO NOT use a chassis ground or earth ground as with residential/industrial electrical systems. Place your digital multimeter’s (a.k.a. voltmeter or DMM) leads across each of the 2 high voltage DC cables. Any voltage less than 12 volts is considered safe. On the battery itself, perform the voltage test between the positive and negative orange cables on BOTH sides of the battery pack’s main relays. The side of the relays that connects to the orange cables that exit the HV battery pack should have no voltage if the main relays are not stuck shut. The other side of the main relays should also
be dead IF the service plug/switch was successfully removed/switched off.
HV battery packs, regardless of their design and construction with their HV service plugs removed/switches turn to “OFF” will STILL contain high enough voltages within them to cause serious injury or death. Service plugs/switches ONLY cut the internal voltage of a HV battery pack in half. This means on most HEVs/EVs half of their normal voltage (330, 300, 271, 201, 144, etc.) is STILL over the 60 volt spec. for an electrical safety concern.

6. Perform required removal/replacement of HV components being salvaged or serviced.
Note: With the exception of the HV battery pack, hot and cumbersome class 0 safety gloves do NOT have to be worn at this time. Regular mechanic’s gloves (or bare hands) may be used to perform the remaining procedures of part removal. However, if the battery pack is being serviced/removed from the vehicle, class 0/1,000 volt gloves are still recommended due to the electrical energy still remaining in the HV battery pack.

After a HV service plug is removed, place it in a secure place to prevent someone from reinserting it into the HV battery pack. After the HV battery pack has been removed from the vehicle to be stored — made available for resale or remanufactured by a rebuilder — apply heavy duty tape across the service plug’s connector opening and tape/tie the service plug to the other end of the battery pack. These steps will help prevent the plug from being reinserted into the connection by an untrained person and help prevent the service plug from being lost or damaged during shipping.

Service plugs can be very expensive on certain HEVs/EVs.

For more details, or to book a place on our WAMITAB accredited Safe Handling of Electric and Hybrid Vehicle training course that has been specifically designed for the vehicle recycling industry then please contact Salvage Wire via the website

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