Working on Hybrids Safely
This article is part two in our series about the electrification of the auto industry. We’re talking about electric vehicles, their history, how they work, how to service them, and what the trend towards more electric vehicles means for our industry. Click here for the first article in this series. Click here for the third article in the series.
Seen any hybrids around lately? The ones with big old batteries in ‘em, don’t make the vroom vroom noises like a car should? Yes, you have. Hybrids are everywhere. Look out your window and you’d probably see a whole slew of them. There’s a Prius over there, an Escape hybrid there, a Leaf, a Volt, and a BMW I3. Nope, sorry, that’s a pack of AA batteries taped to a deck of cards…close enough. Hybrids, plug-in hybrids, and fully electric vehicles (EV) are here to stay and we need to accept that.
In 2017, nearly 3.8 million hybrid/EV vehicles were sold worldwide. Take a look at the chart below, which shows hybrid/EV vehicles sales across different countries for the last several years.
Domestically, hybrids and EVs are no slouch in the market either.
You may be asking, “Why should I care?”
Do you plan on wrenching for the foreseeable future? Do you like to have a heart that beats in the diastolic/systolic cardiac cycle? If you answered yes to either question, then it’s time to learn some of the basics of hybrids/EV vehicles to keep yourself safe and turn a buck while you’re at it.
Hybrid Vehicle Basics
Let’s start by talking about what a hybrid is; keep in mind that EVs are essentially the same, minus the gasoline engine. A hybrid vehicle consists of a large DC battery, a large 3-phase electric motor or two, an inverter, a DC-DC converter, and a gasoline engine which is usually referred to as an ICE (Internal Combustion Engine). For specific examples in this article, we’ll be referencing one of the most common hybrids, the Toyota Prius. Other hybrids have a very similar generic setup—consult service manuals when it’s time to put wrench to vehicle. See the example diagram here.
Let’s start from the back. Usually, hybrids keep their large batteries back there, which can range anywhere from 140-340 volts, depending on the vehicle. EV vehicles are going to have higher voltage, but rest assured, 140-340V is enough to stop anyone’s heart. EVs typically house their big batteries in the floor. The hybrid battery sends out DC voltage to a unit called the Inverter, but before it does this, there are several large relays called “Contactors” that must shut first. These Contactors are closed by a smaller 12v battery—this is how a hybrid uses low voltage to activate high voltage. The hybrid battery has a means of interrupting voltage flow for service, usually called the “Service Grip Plug” or “High Voltage Shut Off,” and can be in the form of a removable plug or a switch. Always check your service manual for the vehicle you’re working on.
When the high voltage leaves the battery, it does this on two large orange cables—orange because that’s the color that denotes lethal voltage. If you see orange on a hybrid, you know to be wary. One cable is positive, the other is negative. The high voltage system is totally enclosed and does not ground through the chassis. These two cables go into the Inverter, whose job it is to turn the DC voltage from the battery into AC voltage that the 3-phase hybrid motors can use.
From the Inverter, there are 3 cables leaving for each hybrid motor. A Honda Civic hybrid has one motor between the engine and the transmission. A Toyota Prius has a setup like the one in the diagram above, one motor (MG1) is attached to the ICE and the other motor (MG2) is attached to the wheels. They’re called MG1 and 2 because they’re actually Motor/Generators—they regenerate voltage when the vehicle is slowing down, a hallmark of hybrid vehicles. These two motors are connected in the middle with something called the Power Split Device (PSD), a small bit of engineering that puts the Prius head and shoulders above the competition, in my opinion. Other vehicles, like those made by GM and Hyundai, have motors that help run the engine via a very tight serpentine belt.
The hybrid motors themselves are just large electrical stators with permanent magnet rotors in the middle. Think of a huge alternator and you get the idea.
There are a couple more pieces to the hybrid puzzle that aren’t depicted in the diagram above. There’s a battery ECU, which watches the battery voltage and temperature; a cooling system to help cool off the battery, usually a very small cooling fan; a hybrid vehicle ECU, whose job it is to decide how much work each motor does and whether or not it should charge or discharge; there’s also a DC-DC converter. You have high voltage from the hybrid battery, and one or two very large motor/generators to charge it with, but what about the 12v battery? It would be an exercise in poor judgment to have an alternator on a vehicle like this. The DC-DC converter steps down the high voltage into something the 12v battery can use (think of the DC-DC converter as a high-low solid state alternator).
Hybrid Service Tools
Before you jump in, let’s cover the safety equipment you should invest in. Don’t skimp on this stuff! The human body ranges from about 1,230 ohms to 3,000 ohms, depending on how big you are and how much Gatorade you have in you. That means that if you close a 125V circuit with yourself, you can get anywhere from 42-102mA of current running through you. It might not sound like a lot, but respiratory paralysis occurs between 30-70mA. Since 125V is about the weakest hybrid you’re likely to encounter, I would keep safety equipment nearby.
We’ll start with gloves. Class 0 gloves are highly recommended and come with a 1000v rating. Over these, you’ll strap on another pair of leather gloves. The rubber protects you and the leather protects the rubber from all the sharp metal bits you might be working around. You can find them at most retail stores—we recommend the Salisbury gloves from Grainger. Your gloves must be inspected and certified for use every 6 months and you should also inspect them yourself when you use them: roll up the cuff to inflate the glove and look for leaks. If it leaks, get another set.
Next up, DMM. A digital volt/ohm meter has to be up to the challenge of potentially high voltage work. The recommended rating for meters and leads is CAT3 @1000V. If you’re in the market for a capable meter, we recommend you also get one that has the “Insulation Test” function, which we’ll cover later. Here is the one we use, the Fluke 1587 Multimeter and Insulation Tester.
Now on to hand tools. There are a lot of insulated hand tools—they look like regular tools that have been dipped in a rubberized coating. Beware: these tools are not cheap, but your life is not cheap either. Focus on collecting what you need—a ratchet, 10mm socket, 12mm socket, flat head, and Philips screwdriver should get you started.
Some more specialized diagnostic equipment you may consider would be the Milli-ohm meter. The stators for the hybrid motors on these vehicles are very precise, so precise that the ohm meter on your Fluke isn’t going to pass muster. Enter the Milli-ohm meter. This tool can tell you the resistance of the hybrid motor stators and can also tell you how long a wire is based on its resistance. For example, if you test between a wire and chassis ground and the reading indicates the wire length is 6 inches, then you know you’re looking for a short to ground approximately 6 inches from the connector. Very handy to have around.
Ready To Start
Now that you have an idea of what you’re looking at when one of these electric razors pulls into your stall, and you have all your safety equipment, you’re ready to start work right? Not yet. Always make sure you have verified that high voltage is gone before touching anything, and always assume anything orange on the vehicle has high voltage going through it. In order to start work, you must disconnect the 12v battery, then disable the high voltage system by either pulling the service plug or flipping a switch, put your DMM across the 12v battery to verify it works, then check across whatever component you’re working on to confirm it is inert. Finally, check across the 12v battery again to make sure your meter hasn’t died since you checked it last. This might seem tedious, but cardiac arrest is a much bigger hassle. Happy wrenching!