Even when the damage is minor, the HV system should be de-energized. Ford's Hybrid Vehicle Operation and Diagnosis Training Manual FCS-21020-REF states: "Most electrical accidents are the result of incorrect or careless action, not faulty equipment. Follow procedures exactly." That is, all recommended safety precautions must be followed to avoid injury and damage.
After a collision, the primary disconnect breaker (Fig. 1) may not be accessible, in which case an alternative should be sought. Though the HV batteries – nickel metal hydrate (NiMH) or lithium – are located intentionally in one of the least likely areas where damage occurs, they still may become damaged in a collision; and they pose safety concerns different than the lead acid batteries used in the past. Even pushing a disconnected disabled vehicle potentially can injure or harm a technician. HV batteries and force drying also can harm the vehicle. Special HV tools must be used when checking capacitors to be assured the system is completely discharged. With new second generation HEV and EV may have multiple electrical and electronic systems, such as low voltage (less than 30 volts DC), intermediate voltages to power electric air conditioning and power steering (30 to 60 volts DC), and high (over 60 volts DC) for vehicle power.Disconnecting HV batteries
First, a collision repair technician must disconnect the HV battery. But before disconnecting the vehicle, you should remove all rings, watches and other metal objects (including keys and metal belt buckles). Also, never work around high voltage with wet clothing. Even polyester clothing will melt with an electrical arc, so natural fibers, such as cotton, should be worn when working around high voltage. Safety glasses and face shield for face protection in case of a HV arc are also a must (Fig. 2).
Unfortunately, different makes and models may have a different type and/or location for the disconnect. Honda has an unassuming on/off switch in the trunk (Fig. 3), while the Ford Escape's is a round switch (Fig. 4) under the cargo mat, and the Fusion is completely different (Fig. 5). The type and location of a vehicle's HV disconnect breaker can be found in its service manual.A secondary location that will disconnect the HV power supply sometimes can be found in the vehicle service manual, or through varied online searches. The secondary location for some HV disconnect is often in the fuse box in the engine bay (Fig. 6). Never assume the vehicle is disconnected until you verify it is and the capacitors (Fig. 7) have discharged. You'll need a high-voltage digital volt and OHM meter (DVOM) to check that all the charge has had time to drain from the capacitors.
To ensure accidental shock doesn't happen when disconnecting the breaker, high-voltage lineman's gloves should be worn (Fig. 8). Additionally, while skin isn't a good conductor, moisture, in the form of sweat, is. Therefore, the gloves should be tested for leaks before each use. To do this, roll up the open end of the glove, inflating the fingers (Fig. 9), to see if there's any leak. Even a pinhole will let moisture out, thus allowing accidental conduction. For better protection, especially if there is torn metal or glass shards, a pair of leather work gloves (Fig. 10) should be slipped on over the lineman's gloves to protect the rubber gloves.
If a technician is shocked by HV electricity and you try to help, never touch the person. Use a nonconductive safety hook (Fig. 11) to pull him away from the contact. In case of a fire, use a carbon dioxide (CO2) gas extinguisher because water can conduct electricity and should be avoided always.
Battery life and paint curing
High-voltage batteries, which could be NiMH or lithium, are sensitive to heat and must be kept cool. Though the HV battery is placed in a relatively protected area and encased in a protective box (Fig. 12), cooling still is a concern. Some systems use vents and fans, which bring in air from the passenger cabin (Fig. 13) around the battery, then out of the vehicle (Fig. 14). Some have dedicated air-conditioning units designed for HV battery cooling (Fig. 15). Ford says temperatures hotter than 140 degrees F will damage a battery. When their hybrid vehicles first came out, Ford recommended removing the high-voltage battery before applying heat for curing. Now it recommends leaving the battery in but not heating hotter than 140 degrees F and not for more than 40 minutes. Not heat curing the paint on hybrid vehicles might be a good safety policy for all hybrid vehicles.Battery NiMH and lithium
Though a leaking lead acid battery is corrosive and dangerous because of its acid content, NiMH batteries are alkaline, and when leaked onto aluminum, they produce hydrogen gas, which can explode easily. The area should be ventilated, and all electrical sources – the HV and 12-volt battery – should be disconnected to avoid accidental arc.
A battery suspected to be leaking fluid first should be tested with litmus paper to determine if it is acid from the low-voltage system (lead acid battery) or alkaline from the UV battery (NiMH battery). Synthetic rubber boots, coveralls, gloves, as well a face shield, safety glasses and respirator all should be worn to protect a technician until the liquid can be neutralized. Acid is treated with baking soda or ammonia, and NiMH battery leaks can be neutralized with boric acid and water solution, or with vinegar. After cleanup, retest the liquid to be sure it is a ph of 7 before removing the protective clothing.
Regenerative braking
Hybrid and full electric vehicles use regenerative braking to help charge the HV batteries through inertia. As the vehicle is coasting or braking, electricity is generated at each wheel, helping to recharge the HV system. Because of this, hybrid and EV vehicles shouldn't be moved with their wheels on the ground. As the wheels move, the vehicle will charge the capacitors in the inverter/converter and cause the HV system to be charged, which can cause arc or accidental shock.
Multiple voltages
Hybrid and EV may have multiple voltages to power the standard 12 system with a smaller 12-volt battery used for fans, turn signals and other accessory systems. The wires have nonspecific color coding, but generally are in black conduit covering the harness. The high-volt systems (60 volts and higher) have bright orange conduits (Fig. 16). Intermediate voltages (30 to 60 volts) often are covered with bright blue conduits. This helps identify the needed safety equipment and tools to perform the repair.
Consequences
In a related article, "Hybrid Safety" on this issue, the consequences of accidental electrical shock are outlined, explaining that as little as 1 mA (milliamp or 1/1,000th ampere) can cause a tingle and 50 mA can cause severe muscle contraction and may stop breathing.
There are considerable risks involved in the repair of HEV and EV that have been damaged in a collision, including additional risks that haven't been seen in the service industry previously. However, if all the recommended precautions and procedures are followed, these risks can be minimized. So find, read, understand and follow the manufacturer's recommendations to establish a safe work environment for hybrid and electric vehicle repair.
