-77 error on 96v Lithium setup

GEM Forum
23

You are correct, in part. The >+96V that is being detected that causes the controller to shutdown and throw the -77 code is being read at 1C (capacitor 1) inside the controller, this monitoring is constant / real-time, so the controller will throw different codes for the same high-voltage condition depending on what it is currently being requested to do, aka: “traction codes”. For example -76 is >96V on pedal up regen, -77 is pedal depressed / driving >96V detected.

There may be a way around this internal failsafe / voltage watchdog, but it’s there to protect the drive electronics that provide power to the motor, so you probably could pop open the controller and find the sensor circuit and add a component to make an overvoltage condition be read as 95V. And then your bank of FWD or REV mosfets burn up or your capacitors bulge and go kablooey, and you no longer have a controller or a complete / fully functional one because that mod let the magic blue smoke out.

Now, your idea about dropping the voltage at Pin-1 is valid, and it’s how anyone running a battery pack that’s above 88V dodges the code -16 bullet when the key is turned “on”. The moment the key switch closes at “ignition on, Major Tom”, the before the controller sends voltage to close the main contactor, it checks P1 which is, on paper, from BATT + and BATT- . If it’s over 88V, it throws a -16 code and it won’t energize the main contactor coil to send battery directly to the controller BATT connectors. -15 is low voltage 68V or less. Once the initial key on condition and voltage check on P1 have occured and the main contactor is energized, I don’t think it never looks at P1 again until you turn key off and try to key on again.

It’s been a few years, but I want to say that on my 2010 (T4 controller) running around 92V-something pack, at some point one day, I turned the key on, unhooked the alligator clip from wherever it was on the series string of diodes and clipped it back on itself, leaving P1 open 0V potential and just drove off,

And now, back to your regularly scheduled programming, made possible by a grant from the Lego corporation.

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24

Right. But you are missing a few key elements.

  1. What/where are you going to dial in the max of 95 to clear the 77?
    (Note that P1 is already dialed back since he has been running this car since 2023 on a 24s pack without a -16 over volt Startup error.)

Just give it a Max of 95 and the 77 code should go away

  1. This is actually what we did by setting OVP in the BMS which shuts down the charge a tad early. This is what he did to solve the problem back in 2023 and simply needed to be reminded.
25

Ok, I missed that. Just a thought. I’m just one of those people who hates to overthink stuff. My experience has been that simple is usually the right solution.