By Craig Van Batenburg
Let’s explore the ins and outs of hybrids systems and how they mix with scopes, digital volt-ohm meters, and insulation testers.
First, a look back. A micro-hybrid is usually a stop-and-start system that may have a small amount of boost to the internal combustion engine (ICE). An example is GM’s 2007–2010 Malibu, Saturn Aura and Vue. The GM system is known as a belt alternator starter system or BAS. Micro-hybrids used a 36-volt battery. Under 60 volts DC is not considered a high-voltage system. This article is about high voltage.
It is important to note that all hybrids use a 12-volt battery that allow the high-voltage battery to be turned on and off for safety reasons.
Why do you need to know about the BAS system and other medium-voltage (32 to 48 volts) systems? The higher voltage (over 60 volts) systems require Category Three (CAT III)-rated equipment before you work on a hybrid to perform any tests. What is CAT III? Look around your shop and you will most likely see a CAT II environment, and the office is a CAT I. These categories describe the risk factor for electrical shock. There are CAT IV and CAT V environments as well. When you start to work on a hybrids and electric cars, trucks and motorcycles, you open yourself up to a CAT III situation. There are high-voltage cables, motors, batteries and capacitors, and you are just a “one wrong hand” placement away from trouble. It is dangerous, plain and simple. Not only must you know what to do, you must wear safety gloves, and have hands-on experience before you try this on your own. The equipment you buy must be safe. A CAT III meter or scope must also include CAT III cables and ends.
What makes a CAT III meter safer than a CAT I or II? When a meter or scope is designed, the placement of the components inside the meter must have a certain distance between them so in the event that a lot of energy is introduced into the meter, there will not be an arc of electricity. CAT III meters are designed to have the necessary spacing between the internal parts so that the digital volt-ohm meter can withstand the amount of voltage and current found in the hybrid systems.
When using the meter or scope, here are a few precautions. Don’t hold it in your hand just in case it explodes. Rest it somewhere you can see it, but on an angle. Staring directly at the meter screen is another unnecessary step that you should eliminate. Again, if something goes wrong, don’t be in the line of fire.
Micro hybrids use a maximum of 48 volts, well below the 60 volts that is the amount of voltage required to penetrate your skin. Many studies have been done to study electrocution of humans. One such study was shown to me by a company not based in the USA. They used 150-pound pigs to study the amount of voltage, current and time that it took to kill a pig. It can be as little as an eighth of an amp at 50 volts for 15 seconds. You are dead if it is a direct hit to your heart. That is high voltage from one hand to the other hand. The good news is no one in America has ever done this! It would take one hand on positive and other hand on negative of the high-voltage system in order to have the above scenario happen to you. That’s unlikely, but a severe burn is possible if you carelessly lay your bare arm across the orange bars of a half-dismantled battery removed from many hybrid models. So awareness of the potential is a must. Don’t even think of servicing a hybrid without the required safety equipment and hands-on training.
Insulation testers for testing high-voltage insulation are not new, but they are new to our industry. Some call them “MegOhm meters” or “Megers.” Chrysler, before they canceled their hybrid Durango 10 years ago, required the Fluke 1587 in their shops. My old shop always used Fluke products, so when we needed hybrid equipment, we went looking at the Fluke 1587 “insulation” tester in 1999. (Yes, hybrids go back that far.) Much like an ohm meter test, if the insulation tests bad, it is bad, but if it tests good, it is a maybe. Still, I highly recommend this tool (or equivalent) as it is also a CAT III meter and is important for hybrid testing.
How many volts are the maximum that a hybrid can produce? My company owns a fleet of 14 hybrids and plug-ins, from Ford, Toyota, GM, Nissan and Honda. Under normal conditions, hybrids from Toyota can produce 650 volts when driving hard, but when the system is in “idle stop” the voltage is no higher than 288 volts. In the case of Ford HEVs, the Escape is the biggest at 330 volts. Generally speaking HEV battery packs are from 100 to 330 volts. Plug-ins are usually at 400 volts. The new Porsche Taycan has a 800-volt pack. So your equipment should be rated CAT III at 1,000 volts to be safe.
Let’s talk about using a Fluke 1587/1507 insulation tester (or equivalent). This type of tester will produce 50 to 1,000 DC volts to test the insulation of the cables or high-voltage circuits. The current produced is milli-amps for safety reasons. The manuals are easy to understand but the difficulty is knowing where to connect the leads.
Understanding the “construction and function” of all the parts that make up a hybrid system is what is required to know where to test. Make sure you carefully examine the cross section of high-voltage cables. If you have access to a high-voltage orange cables, cut them in half and then use a belt sander to make it easier to see the layers of the cables. Note the shielding, and when and where it is used. Note the grounding of the shielding both in external cables and those used inside a HV components. When using an “insulation tester,” be sure the capacitors have been discharged and the high-voltage battery pack is off. Safety is always number one.
The second issue is finding a specification for what is an acceptable amount of leakage. Here is a test tip:
1. Set your “insulation tester” at the level of the high-voltage battery at rest voltage (or slightly higher).
2. Hold the insulation test meter leads apart and press the test button.
3. Depending on the voltage setting, you will see a number on your screen that represents the best insulation value. For example; if you set the tester to 1,000 volts, the best result will be 2.2 gig ohms.
4. As you test at a lower test voltage, the best result will be less ohms.
Practice using the insulation test meter until you have mastered its operation. Take some time to look up the specifications for the components you are working on, and then measure with the insulation tester.
Note: Most insulation testers are battery operated and will consume a lot of energy when used, so keep extra batteries on hand. If you can use rechargeable batteries, all the better. These “insulation tester” meters can shock you so wear your high-voltage safety gloves when using them. •
Craig Van Batenburg is a former repair shop owner who is the CEO of Automotive Career Development Center (www.fixhybrid.com), which offers training and consulting related to electric and hybrid vehicles; he can be reached at Craig@fixhybrid.com.
