Can anyone tell me to what extent the HV battery is (or is not) electrically isolated from the car's chassis. From what I've read I think that when the Prius is off there are relays isolating both the +ive and -ive ends of the battery. Is that correct? What about when running. Is the battery negative electrically connected to the chassis, or does the entire HV system remain completely isolated from the body at all times?
Neither side of the high voltage is connected to body ground. Therefore when a high voltage ground fault occurs, this can be detected and a DTC is logged. 2G will refuse to become READY after the DTC has been logged (Classic can continue to be driven although doing so would be an unsafe practice). There are three system main relays. Two of the relays switch the positive and negative high voltage. The third relay shorts a current limiting resistor which initially is inline to allow the inverter capacitors to charge up gracefully without sucking excessive current.
Thanks Patrick. I knew about the relays, but I just wanted to make sure that both poles were isolated from the body at all times (regardless of the state of the relays). I'm glad that it's so, as obviously that makes it a lot safer to work on the battery while it's in the car. I'm planning to take the covers off and have a good look over my battery some time soon. Just a check over for dust and corrosion etc, but I'll probably make a few measurements too.
Yes, I agree and no this is not completely right. There is a high voltage connection between the battery and car body. It is through the battery computer. I know it is on the negative side of the sensing wire harness. I think it is the most negative sensing wire. I have measured this. It is easy to bleed off the voltage with a volt meter. I think there must be small capacitors in the circuit. This small reference to ground is needed to detect large ground faults. Brad
Thanks Brad. So what you're saying is that there's no direct (low impedance) connection between the two, but the HV battery isn't completely "floating" either. Any idea what type of impedance we're looking at here?
Halfway down this page is a diagram and test of the ground fault sensing circuit: Prius battery exploration
I had a pack open today. With all the modules disconnected I checked for continuity from the voltage sensing wires to ground. Only the most negative line showed continuity. I had to use the 200M ohm setting. The reading started at about 1 mega ohm and within 10 seconds exceeded the 200m limit of the meter. Brad
Here is the circuit diagram for the HV battery. The Smart Unit monitors a number of battery parameters, including resistance to ground, and will issue an error code if it gets below a safe level. I do not know what the alarm point is.
The system works because the capacitor will pass the AC source, and block DC current flow. The resistor shown as "vehicle insulation resistance" is not a physical resistor in the circuit, but the insulation between the high voltage + and - supplies through the various Prius systems, and motors to ground. This includes the air con motor and inverter. Leakage is detected as an AC current path. This then then shuts down the DC supplies. John (Britprius)
Hey everyone just an update.. I took the battery out, tested all cells, tested all cables and no leaks in the HV battery. I cleaned all of the bus terminals and replaced the cables with good used ones. Started the car and the code came back in about a minute. I'm 100% positive there's nothing wrong with the HV battery. I replaced the auxiliary battery as a precaution. I bought a mini vci however the drivers for it aren't working, I had to acquire a 32 bit computer because tech stream doesn't work on a 64 bit. More info... My sister advised me that this all occur led after she ran out of gas.. When I drove the car for the first time after confirming the HV battery went the issue the cluster was showing low/no gas and blinking with one bar on the gauge. I drove it to the gas station to fill it up and the car only took 1 gallon of gas before it started coming out the full tube. To my amazement the fuel gauge showed full after adding this gallon.... Is there a possibility the issue is the fuel pump if so what is the correlation with the code??? I'm so confused...
Would it help to briefly run the car with the battery isolated from body? maybe just put a rubber mat under it or something similar for a quick test. I wouldn't hit the streets like it! just run the car in your yard for a while see if it helps any
Did you try this test? It takes five minutes to know where the leak is coming from. The car will not start if the battery case is not grounded to the body. Brad
