J1772 and Ground Faults

modular EV power LLC Back to Homepage

Ground Faults and J1772 Charging stations

As charging moves from NEMA14-50 receptacles powered by a standard circuit breaker to J1772 connectors with Ground Fault Interrupters some people may find their vehicle causes Ground Faults.

The Ground Fault Interrupter in the J1772 charging stations is just like the ones in your home protecting outlets in the wet rooms and outside your home. Just like those home units occasionally have a device you plug in that they refuse to work with, this can happen to an EV.

Ground Fault Interrupters are a great safety system that removes electrical power if it appears any of that electricity is leaking out of the system. The leaking electricity may be due to a component failure, wet parts, or a person touched an energized part and is at risk. The system is very sensitive so that power is removed before a person can be injured.

Simple electrical circuits have 2 wires, current flows out one wire, through the device, and back to the source through the other wire. In the alternating current system we use, the direction of these currents reverse 120 times a second here in North America. The alternating nature of the electricity is what makes transformers work. The GFI is simply a small transformer that both of the power wires pass through. One wire always has current going out and the other has the exact same current returning so they cancel exactly resulting in no output from the GFI transformer. If some of the current leaks to ground or some other place due to some fault, the two currents in the GFI transformer do not cancel perfectly and the imbalance is detected. When that imbalance reaches 5 milliamps, 5ma, 0.005Amp, the relay of circuit breaker in the GFI device is turned off and power is removed. It happens in a fraction of a second and everything is off and safe.

It seems that older devices are the ones that have the most problems with false GFI trips at home. The reality is these older devices were designed with some leakage allowed. It may have been a filter to stop electromagnetic or RF interference, or older materials that are not as good of an insulator as our modern plastics. Fact is these devices cause real ground faults that are annoying but the fault exists and the GFI trips.

We were contacted by a potential customer in Chicago who has access to J1772 charging but has had problems with his converted vehicle tripping GFI breakers and wanted to know what might happen with J1772 GFI. He has a conversion vehicle with a Manzanita PFC charger, lithium batteries and a battery management system. We Googled Manzanita PFC GFI and found this thread http://evdl.org/archive/#nabble-td2715788 . The thread begins with a long discussion about keeping lead acid batteries clean because small amounts of electrolyte can cause a leakage path to the grounded vehicle frame the will cause a ground fault during charging. Later it describes a method for using a voltmeter to find what parts of the vehicle are causing the leakage current. Basically you measure the voltage from the most positive battery pack terminal to the frame and from the most negative terminal to the frame. They should be isolated and there should be no voltage if the batteries and high voltage DC is isolated from the frame at every component. In the real world, there is always some leakage, so a small voltage may be seen. If the voltage is large, that same leakage path will cause the ground fault on a non-isolated charger like the Manzanita. If a problem is found it is a long a laborious method that involves in disconnecting parts and reconnecting them to find the source. With a battery pack of 144 volts, the 5ma of leakage that would trip the GFI is a resistance of 28,000 ohms to ground. Attention to detail and good insulation practices are needed in the vehicle assembly and all of the electrical parts used. In this case, the problem was tracked to the battery management system. At the time, battery management was more important than public J1772 charging for this person.

Another person who purchased an adapter wrote asking about ground faults stopping J1772 charging of a Tesla in San Francisco. Other Tesla owners have not complained and we wondered if it was an issue in the specific car of that model or vintage. We Googled Tesla car GFI and found this thread http://www.teslamotorsclub.com/archive/index.php?t-2875.html from a Tesla group about GFI problems in 2009 and software changes. We suggested they contact Tesla and see if they have any fix or advice. No response yet.

If you have a story or have had problems with GFI and your EV, with or without our adapter please share it with us. Many of conversions and early production vehicles may not be that GFI friendly and we all need to learn how to identify and resolve these problems. We are not experts but we want to help.

If you are concerned about your vehicle possibly not working what can you do? Ask others you may know or in your local EAA chapter who have a similar vehicle or similar parts about their experience. Find someone who has a GFI protected NEMA 14-50 outlet or who has an adapter you can try to prove everything works as expected. You could make the voltage measurements and if the voltages are near zero confidence should be high.

What if you buy an adapter and you end up with GFI problems when using public J1772 stations? We would hope you try to resolve the GFI issue by evaluating and taking measurements on your conversion or discussing the problem with your dealer. If the GFI problem cannot be resolved or outweighs the J1772 public charging benefits, we at modular EV power would hope you could sell the adapter to some other EV owner without GFI problems. If none of that is possible write us and we will negotiate a refund for GFI problems in the first 30 days even though this is entirely outside of our control and the scope of the adapter.

We are limiting this GFI window to 30 days because an adapter could work with your vehicle for weeks or, months and something changes in the vehicle causing a ground fault. The change causing the fault is entirely outside of our control and the scope of the adapter, further the adapter work as expected for a reasonable period and has no actual fault of its own. We will still try to help get these issues resolved.

e-mail: david@modularevpower.com