What voltage does a gen 2 inverter send to the HV battery

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by ilbdarned5, Aug 2, 2026 at 7:15 PM.

  1. ilbdarned5

    ilbdarned5 Junior Member

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    I am having charging issues. I have re conditioned my battery pack so it is good. I know what I am doing working around high voltage DC to be safe as I work with solar DC voltages in the high range.

    I really hate digital meters because if the voltage fluctuates at all, the meter is all over the place with readings, If the inverter does not put a steady voltage charge because of the electronics, it is hard to know what is normal.

    When I try and read the voltage at the battery side of the HV relays with the car off I get a steady voltage, but when I turn the car on, and it starts charging, the meter jumps all around and then maxes out and it is a 750v dc meter. I get the same situation when I set my meter to AC voltage, the meter is all over the place.

    I am aware I should not get any ac reading at the HV battery terminals with the car running and charging, but since the digital meter is all over the place on the ac setting just like with the dc setting, I can't tell if it is a slight ac leak from the inverter to the battery like a false voltage, or if it is sending ac with dc through my battery due to a shorted diode in the inverter. I would think if it was an insignificant ac leak like a false voltage my meter was reading, the battery in the circuit would eliminate it.

    I tried 2 different meters thinking my meter was bad, and both meters did the same thing. I am thinking my inverter is trash. When I shut off the car, the battery voltage starts dropping back down to normal so it seems like it is overcharging. My bars on my display will sometimes stick at 1 bar when the battery has a full charge at around 219 volts and the engine normally shuts off
    Then sometimes when I turn the car off and back on, the bars jump up to the number of bars the car shuts off at when the reading isn't stuck at 1 bar.

    The display shows the charging arrow, but the battery level sticks on the display at 1 bar although the battery is fully charged and the engine shuts off.

    I know this is TMI, but I am wondering if someone ever checked the voltage at the battery HV terminals with the car running and charging and if so what voltage did you get.

    I always disconnect the orange plug before hooking up my meter leads alligator clips to the HV battery relay Posts and turn my meter on, before replacing the plug, and I stay away from my meter while testing the high voltage. Everything is sitting on metal so the worst that could happen is my meter leads could get fried.

    I am thinking maybe my HV battery is being overcharged or getting some ac current from the inverter and the BMS is trying to protect it as best it can. My car is not acting normal, mileage is bad and seems to not maintain the bars it used to have , and no longer reaches green bars during regeneration.

    Any info from someone who knows the normal voltage at the HV battery during charging would be helpful. I wish I had a working Prius for comparison to troubleshoot.
    Think I will hook my meter to one of the 28 cells and see if it is overcharging the cell, At least my voltage reading will be lower and my meter will not peak if I am reading the voltage in series across one cell
     
    #1 ilbdarned5, Aug 2, 2026 at 7:15 PM
  2. Hammersmith

    Hammersmith Senior Member

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    You're in the Gen 5(2023-27) section of the messageboard. You'll have more luck getting an answer to your question in the Gen 2(2004-09) section.
     
    #2 Hammersmith, Aug 3, 2026 at 8:02 AM
  3. hill

    hill High Fiber Member

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    That said - is the inquiry about power at the boost converter? (~500v) or nominal SOC at the pack (~200v dc)
    at the cell (when new - not 16 to 20yrs old) they're 1.45v ±. 05v) fully charged vs 1v when the pack reads empty)
    Prius fun facts at the fingertips. What "she-who-must-be-obeyed" said, just 5 minutes ago? I got nothin'
     
    #3 hill, Aug 3, 2026 at 8:44 AM
    Last edited: Aug 3, 2026 at 8:56 AM
  4. pasadena_commut

    pasadena_commut Senior Member

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    Hmm.

    I'm thinking that the output stage of the inverter that goes to the HV battery may resemble a switching power supply, with a "high" frequency oscillation, some electronic power switches, and some capacitors to smooth it out to something resembling DC. If one or more of the smoothing capacitors is weak it would leak the high frequency signal onto those lines, and that would most likely confuse a voltmeter in DC mode.

    Another possibility is that it doesn't have those smoothing capacitors and uses the pack itself for that function. The circuitry could adjust very rapidly, once again producing a signal that your voltmeter could not interpret. (On a related note, I used to charge a Honda IMA pack with a Biorad model 200 power supply. When attached directly to the pack the supply was unstable, with the voltage and current rapidly varying. To tamp that down I had to add a large enough drop resistor, which turned out to be one which had about a 10V drop. The power supply was perfectly stable with a purely resistive load, like a light bulb or other big resistor, but the pack had too much capacitance or inductance for the supply and that caused it to oscillate.)

    Can you get your hands on an oscilloscope? This seems like a case where you really need to visualize the voltage, which is clearly varying much to fast for your voltmeter to interpret.
     
    #4 pasadena_commut, Aug 3, 2026 at 1:38 PM
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