Electric Vehicle Frequently Asked Questions

SAFETY

What are the safety concerns for working with electric vehicles?

1. 1. Electrical Shock
2. 2. Electrical Fire (plasma fire)
3. 3. Chemical Burns
4. 4. Chemical Spills
5. 5. AC Electrical Safety (Charging Issues)

How do I avoid electrical shock?

When working with electrical components:

1. 1. Always assume every component is "hot" or "live"
2. 2. Wear rubber gloves UL listed for 600V isolation
3. 3. Work with one hand behind your back to avoid bridging between circuits
4. 4. Use tools designed or modified to avoid creating shorts when dropped (not "if," but "when" they are dropped - cynicism works in your favor where safety is concerned)
5. 5. Know where all safety devices are and how to use them
6. 6. Check cables and wires to see if they are "hot" before working on or around them. If they are hot, disconnect them. Even after you have disconnected them, remember no. 1 - work on it as though it were live.

What is a plasma fire and how do you put it out (also general fire safety)?

The following was found on the internet from Aaron J. Redd, Post-doc/Fellow, Plasma Physics and Controlled Nuclear Fusion, University of Washington, in response to a question about whether a spark can occur in a vacuum, and whether it is considered "fire" (emphasis added by FAQ editor):

"The short answers: yes, a spark can occur in a vacuum; and, no, the spark isn't really a "fire", but such a spark can start a fire. So it is still a safety hazard.

The spark or electrical arc is not a fire, in the sense that it is actually a superheated gas, also known as plasma. The plasma of the arc does not burn, in the sense that it is sustained by the electrical current traveling through the arc -- just as a wire will heat up when electrical current travels through it, the plasma stays hot because of the current in the arc. In theory, two metal surfaces with a vacuum gap between them can safely hold off an arbitrarily high voltage between them. In the real world, though, there are two important ways for the spark to happen: (1) No vacuum is perfect, so there will be some small amount of gas present. As shown by Paschen in the early 20th century, there is a maximum voltage that can be sustained between two (metal) electrodes, determined by the density of the trace gases in the area and (speaking loosely) the distance between the metal plates. If the voltage is above the so-called Paschen voltage, then there will be an arc between the metal surfaces. Also, the gas doesn't need to be air: helium, neon, hydrogen, carbon dioxide -- any of these will show the same Paschen breakdown. (2) Real surfaces (such as metal surfaces) aren't perfect either, and if the electric field at the surface is too high, then the material will sputter and/or vaporize, creating some gas which can then become an arc plasma.

Once the arc is occurring, more material can be sputtered off from the surface, adding more gas to the plasma arc and pitting the metal surface. This is part of the reason why electrical fires are so hard to fight: the spark that causes the fire won't stop until the electrical current stops, so whoever is fighting the fire first has to shut off the current, and then try to put out the fire.

As for this pitting on the electrode surfaces, it is quite noticeable -- electrodes tend to look very "beat up" after being exposed to arcs.

If your light switches (or any other switches!) generate visible sparks when they are switched on or off, then they need to be replaced immediately. Like I said above, the spark isn't a fire itself, but it can start a fire. "

This is very good information. To stop a plasma arc, you must first stop the current (you DID install a mid-pack service disconnect, didn't you?), and then extinguish anything that is burning. In the case of EV's, the only really flammable thing I can think of is the car interior. The plastic case of the battery may burn, but it is usually polypropylene or ABS, and these burn relatively slowly and in a controlled manner. Take note if using flooded batteries that a plasma event will likely melt holes in some batteries, which will spill acid, so have baking soda around to neutralize it so you can safely mop it up. Users of nickel chemistries should take note that your electrolyte is KOH, a basic electrolyte that may be neutralized with vinegar. A family safety website I found states that baking soda may be used to fight electrical fires (after turning off the current) by throwing handfuls at the base of the flames. This is good information for an emergency, since most of us have baking soda around for working with flooded lead-acid batteries, but it should only be used in an emergency. Really, a class C or ABC fire extinguisher would be quite a bit more effective, and you should have some in your house, anyway, at least in the garage and the kitchen. Fire extinguishers are available at home centers, hardware stores, and discount stores like wal-mart. Class A is for solid items on fire, class B is for liquids, and class C is for electrical. Multiple combinations of classes are available. Just make sure for fighting electrical fires that it is rated for a combination that includes class C.

It should be noted that electrical arcing from an AC power source is much easier to extinguish because it turns itself off 60 times every second. The DC power we deal with in EV's is continuous. The only way to stop it is to break a connection in the circuit somewhere away from the plasma. And if two or more batteries have become "fully involved" in a plasma ball, that may be all she wrote. Even without the voltage added by the other batteries in the string, once the plasma establishes itself between two power sources, it is pretty much self-sustaining until the power is gone. Theoretically, this type of plasma arc can be extinguished by placing an insulator (a darn good one!) between the arc points, if you can locate them. But the arc may be hot enough to simply melt away the insulator. Personally, I wouldn't try this unless someone's life depended on it, because of the risk of serious burns from being that close to the arc.

There's still one more thing to consider: If a plasma event happens, things get very hot. If you are using flooded batteries of any kind, some electrolyte will likely boil into vapor. If you suspect this is happening, then DO NOT APPROACH YOUR VEHICLE! You likely do not have a respirator that will filter sulfuric acid vapor or KOH vapor, and you do NOT want to breathe this stuff!!!

To sum up, plasma events are nasty. Our first response to a plasma event should be to pull every safety disconnect we have. If that does not extinguish the arc, then get everyone away from the vehicle and call 911. You may be tempted to try to move the EV out of any building it is in, so as to keep the building from catching fire. While I would want to do this, too, any safety-minded person would tell you to get out and get help instead. Personally, if it was relatively easy to move it out, and it was not a hazard to approach the car, I would try to push it out of the garage. If you cannot safely approach the car, however, then get everyone else out of the building and call 911.

How do I avoid chemical burns?

The electrolyte in the batteries of an EV is what can cause chemical burns. Wear chemical resistant gloves, long sleeves, and long pants when working with the batteries. Always have an appropriate neutralizing agent available (baking soda for acid, vinegar for KOH). An apron would be a good idea if you work with the electrolyte a lot. Most importantly, WEAR SAFETY GLASSES WITH SIDE SHIELDS

What do I do in case of a chemical spill?

The main chemical to be concerned with when dealing with an EV is the battery electrolyte. This is sulfuric acid (H2SO4) in lead-acid batteries, and Potassium Hydroxide (KOH), a base, in nickel based batteries such as Nickel-Cadmium, and Nickel-Iron. Use baking soda and water to neutralize acid. Vinegar can be used to neutralize KOH. After neutralization, the leftover constituents are harmless, and may be cleaned up with soap and water. KOH is more dangerous to deal with than the relatively weak H2SO4 solution used in lead acid batteries. Both will burn you if you touch them, however. Wear proper protective clothing, and safety glasses with side shields while working with electrolyte.

What is the maximum DC voltage that is considered safe to work around?

Although there is no cut and dried answer to this question, generally, a 36V max. battery or group thereof is considered safe by the auto industry. This is the basis of the 42V standard being discussed for ICE vehicles.

What are some tips on short-proofing tools?

Wrap exposed metal areas of tools electrical tape with a minimum 600V rating. Cover all exposed metal except what is needed for the tool to function at it's "business end." An alternative is to use a liquid vinyl dip such as those available under many brand names at hardware stores, to coat the handles. It dries to a conformal vinyl rubber coating. It's also good practice to use tools that are too short to bridge between terminals if dropped.

What are the guidelines for working around hydrogen?

So your charger didn't shut off all night and you can hear all the batteries gurgling merrily, and you want to know how to NOT blow up the garage.

The required concentration for an ignitable mixture is generally too high to generate from batteries charging in an open space in a garage, but the same might not be true for small spaces like battery boxes. Still, hydrogen is so combustible, that it behooves us to take every precaution.

For battery boxes that are sealed relatively well, draw air out of them with a brushless design fan to the outside of the car while charging. This is only necessary if your boxes are closed and sealed, of course. For the garage, install a CO detector. CO detectors are very sensitive to hydrogen as well as CO. Wire the output to a latching relay instead of to (or in addition to) the piezo speaker that comes with the alarms. Use the relay to trigger a brushless garage vent fan to draw air out of the garage to the outdoors. This would require a manual reset by the user when it triggers on, and the relay could also activate some sort of alarm or indicator inside the house. A bonus is that it also ventilates automatically if CO builds up in the garage.

What are the safety protocols for the AC side of the equation when I charge my EV?

First, grounding. The vehicle chassis should be connected to AC ground.

Second, GFI (ground fault interrupt) circuits should be employed. The NEC requires a Ground Fault Interrupt (GFI) device to be incorporated into the AC wiring used to charge any EV. A GFI (also called a GFCI for Ground Fault Circuit Interrupt) senses the difference in current between the hot and neutral AC lines. When there is a difference, the GFI shuts off the circuit. Some people have argued that a GFI is not required for "every" EV. C'mon folks. Regardless of whether it is or not, GFI breakers and outlets are so common and inexpensive that you really don't have an excuse to not use one. The most inexpensive chargers (K & W and Russco) have them built in, which is handy when opportunity charging.

Third, there is a form of protection called isolation. This is accomplished by running the AC through a transformer with a 1 to 1 ratio (called an isolation transformer) before it goes into the charger. This provides protection because on the secondary side, there is no path to ground, should you accidentally touch a wire. The secondary is floating, just as the traction pack in the EV is floating with respect to the 12V system. However, since it is floating, it can develop what is called a "common mode" voltage. That is, if you were to measure the voltage to ground from either of the secondary lines, it could be very high, though there is still only 120V between the two secondary wires. Theoretically, there is no danger in this, since any connection to ground (by a person accidentally bridging between the wire and ground) only adds a reference point, and the common mode voltage vanishes quickly through the bridge (the person) with little current.

Is it dangerous to have all those batteries in the car?

There are four areas of safety concern when dealing with batteries. Weight, acid, hydrogen, and electrical considerations.

1. Weight should not be a factor in an EV, because the EV is designed with the batteries in mind. Properly designed battery supports (see the appropriate section of this FAQ) withstand high loading and contain the batteries in an accident. Improved suspension components (again, see the appropriate section of this FAQ) restore vehicle handling and ride quality.

2. Battery acid is moderately dilute, but should still be treated with respect. Baking soda should be kept handy to neutralize any that spills while you are maintaining your batteries, and obviously, appropriate safety precautions should be followed (i.e. safety glasses or goggles, gloves, and an apron).

Acid is only a consideration for flooded lead-acid batteries. AGM and VRLA or gel-cell batteries have the acid immobilized and are spill-proof. Even with floodeds, acid is only a danger if a battery ruptures. In everyday use, well cared for flooded batteries do not vent or spill enough acid to be an immediate danger.

In an accident, a properly designed battery enclosure will prevent any acid from entering the passenger compartment.

3. Hydrogen: batteries generate hydrogen gas during charging. That is why battery boxes are ventilated to the outside. Normally there is only a small amount generated, and with a properly designed battery box, it is not a problem. Again, this is only a consideration for flooded batteries. AGM and VRLA types recombine the hydrogen and oxygen inside the battery, and will only vent if charged improperly. The small amount of electrolyte in these batteries further reduces the amount of hydrogen it is possible to vent.

4. Electrical considerations: Proper use of terminal covers and rubber battery terminal boots can help guard against accidental short circuits, as can tools with insulated handles and being very deliberate where you put your tools. Batteries are always "ON".

What about high voltages?

As far as operating an EV goes, the high voltage is transparent to the driver. All of the high voltage traction pack is isolated from the vehicle frame, and multiple safety devices are incorporated to break the circuit in an emergency and on demand. Example include multiple fuses, service disconnects, circuit breakers, and inertia switches. The main contactors also act as a cutoff point.

All of the normal precautions for dealing with high voltage electricity should be followed when working on an EV. These include insulated tools, personal protective equipment, and activating service disconnects before service. Remember: "batteries are always ON".

What is a GFCI circuit?

GFI stands for ground fault interrupt. These circuits measure the difference in current between the hot and neutral legs of an AC circuit. If there is a difference between the two that exceeds a certain current (5 to 15 mA, depending on the manufacturer), the GFI breaks the circuit. these devices may also be referred to as GFCI or ground fault circuit interrupt devices.

See question 9 for a discussion of AC protection, including GFI/GFCI.

Is splashing water into the engine compartment safe?

The motor, cables, and batteries don't mind too much, but some of the electronic components (contactor, heater relay, controller, charger, DC/DC converter) may not be environmentally sealed enough to withstand the automotive environment. Unless the component is listed as being splash-proof, then it should be enclosed or otherwise protected from water.

Is it safe to wash the engine compartment at a car wash?

As discussed in section 6.13, it is usually OK to get the cables and motor wet. The electronic components usually are not sealed enough to withstand this type of treatment, however. A small amount of water is all it takes to seep inside and ruin an expensive DC-DC converter or controller. Generally, EV's stay much cleaner than their ICE counterparts, so power washing the engine compartment will not usually be required. If it does get dirty from road grime, it can usually be easily hand cleaned with a mild soap and water solution.

How do I build a safe EV?

In an EV, the primary safety concerns are electrical safety and battery containment. Having a safe design is of paramount concern when building an EV. It is also fairly easy to do.

The most important thing is to read all you can on the subject. Bob Batson of Electric Vehicles of America produces a free technical paper "Safety First" which you can request by e-mail. The EVA website is at www.inc.com/users/evainc.html?111.

Battery containment techniques are an important part of EV design, as they restore the structural capacity of the car in areas cut out to make room for the batteries, as well as keeping the batteries from becoming projectiles in a crash. Battery box and restraint design is addressed elsewhere in this FAQ list.

Battery care is also addressed elsewhere, but it bears repeating to use appropriate personal protective gear (safety glasses, gloves, etc.) when working with flooded lead acid batteries. Also, keep a box of baking soda nearby to neutralize any spilled acid. These are just the same precautions you would take dealing with a battery in an ICE vehicle.

Leave all the safety devices which were already on the car as an ICE vehicle (like seatbelts and airbags) intact. If you got the donor vehicle from a salvage yard, have these items checked by a qualified mechanic before placing the vehicle into service.

Design your vehicle such that no single failure would be catastrophic. Specific items to pay attention to are as follows:
1) Each series battery string should incorporate a fuse.
2) Incorporate fuses between the front and rear portions of a battery pack.
3) Fuses should be incorporated between parallel packs.
4) Fuse both the positive and negative legs of auxilliary high voltage devices.
5) The main traction circuit should incorporate at least two devices besides fuses capable of interrupting the current from a shorted pack (i.e. a manually activated circuit breaker and a contactor).
6) Take great pains to electrically isolate the traction pack from the car's 12V system, which depends on a body ground. If any accidental contact occurs, it could lead to charging problems, damage 12V devices and/or deliver a nasty shock.
7) If you use an onboard charger, use at least a GFCI protected circuit breaker on the AC input line.

There are some items which are inexpensive to add, but which increase the safety of your EV.
1) An inertia switch is used to sense the accelerations of a crash and cut power to the main contactor. This switch is used in some ICE cars to shut off the electric fuel pump in an accident.
2) A circuit breaker with a remote handle for activation in the cabin is often used as a service disconnect to disconnect main battery power while servicing the car. Disconnecting the power during service should be like pulling the emergency brake - an automatic action that is always performed. It can also double as an emergency shutoff, although separate shutoffs can also be incorporated.
3) If using a DC motor controller, you should know that a failure mode for the power section is to fail shorted. That is, to apply full power to the motor. In this case, leaving the clutch in your conversion adds a safety measure, as anyone familiar with a manual transmission will instinctively depress the clutch and brake in the case of such a failure. This means you won't be careening down the road while fumbling for the disconnect.

Lastly, if you are in doubt about something, ask someone. The EV list is an excellent resource, and EV parts suppliers have extensive experience with EV conversions. They are a great source to ask.