Hey Everyone,
I did a 96v lithium swap last year from @lithiumgods and everything has been working great but I was never able to fully figure out the -77 error code that occurs when the batteries are fully charged. I either have to stop the charging before the batteries get to 96.75v or if it goes over I have to keep the head lights on until the voltage drops to 96.75v, (which can take forever). I was hoping that someone could shed some light on what I might be able to do to be able to fully charge the batteries without having this error Occur. I bought the Sentry software, so I am able to make adjustments to the controller if needed. Wasnāt sure if a more aggressive spoof would help or maybe adjusting function 14 and 15 to higher voltage would work. Cart is a 2002, E4 with a T2, 350 amp controller. Thank you for any help.
Some of this forum details pushing the limits of components beyond normal design limits.
From what I have seen there seems to be a 50/50 chance a T2 will handle voltages higher than 96v. Some just donāt like going that high and produce questionable and confusing results.
In your case it is actually a proper error -
-77 Capacitor (1C) voltage too high during motoring.
This status code will be displayed when the voltage at 1C exceeds 96 volts during motoring.
I personally have not seen a T2 that can handle voltage above 96v.
Your spoof is on Pin1 and that make the T2 see less than 86v on that pin and will allow the car to run.
However there is something in the T2 that does not allow it to function above 96v period. We have not been able to find a way around this limitation.
I have been out of the loop for awhile so maybe someone else has found a way.
Hey guys, Iām not trying to be argumentative but I have been driving this setup for a year and itās definitely 96v with a T2 controller.
We arenāt saying itās a specific number. Only that its about 4v less than t4 which we run at 99 volts.
And thats the reason we recommend a 22 or 23 cell limit.
You posted about a problem. Thatās the answer. 
Ps.
Spoof is not for -77 run error. Spoof is only used to allow starting.
Gotcha. Ok, well that kinda stinks. Thanks for the help. It drives great and is super quick but I was just hoping to be able to fully charge the batteries.
Dave we have dozens of T2 Gems running @96v. maybe one out of 10 fault with that voltage. A rebuild from flight systems has fixed them every time. Your T2 is going over 96v to 96.75v which is fine. All you have to do is limit it to 96v(4v per cell) and your good. 4.0v to 4.05v is target range. For longevity cells shouldnāt be charged higher than thatā¦Simple parameter change in the bms will do it. T4 and 5 will go a few volts higher but we limit them to 97v, 96v for a T2 is great.
For reference, it is recommended to operate an NMC lithium cell between 10-90% SOC. On a Samsung sdi cell that is 3.49v-4.01v. According to battery university limiting max charge voltage to 4.0v instead 4.1v doubles the battery life.
Also have 96V batter in T2 controller. Things were just working fine for the past month or so but today after charging I got a -77 code. checked the battery and it seems to be right at the targeted voltage (95.8v), which based on the thread above should not be triggering the error. Iāll let the battery drain overnight and check again tomorrow, but in the meantime is there possibly something else I should be checking? I thought I saw on a different thread that connectors should be cleaned and lubricated. Maybe something is getting corroded and causing a faulty voltage measurement?
The -77 fault is hard coded to B+ and B- controller cap volts. It will vary from controller to controller, but it is what it is. Find the limit and set charger or bms to keep battery below the limit.
Regen can still fault -77.
Overnight the battery dropped from 95.9V to 95.1V and the -77 fault is gone! Looks like Iām just right on the edge of the top voltage for my controller. I would like to change the max cell voltage to target 95.5V at max charge vs 96V to ensure I stay below this limit and avoid the -77 fault in the future. Current cell OVP in the BMS is set at 4.2V, so since Iām landing at just under 96V Iām guessing my pack is slightly less than 24 cells. Is setting the OVP in the BMS to something slightly less than 4.2V the best way to ensure my max charge is 95.5V or lower, or is there some other setting I should look to adjust?
4.2 x 24 = 100.8. ā This shows the BMS is currently not set to control your charge.
Hopefully you are not 22s. >92v is going to be a little hot for NMC.
Are you thinking 23s? Look in your BMS app. It should give you that info.
Which battery are you running again?
Verify how many cells and chemistry.
Your BMS looks like it is not set up correctly. - or - it has been accidentally reset to a default that may not be protecting it.
But yes, You can configure your OVP to shut down your charge so it does not go over a target V. Start low, then sneak it up.
Consider this:
Do you really need to run with such a full battery? I get it if you need the range, but the general consensus is that there are advantages to not running so hot.
Battery life (long term)
Room at the top to pack in some regen and live around hills.
I was curious and you made me go look.
At that time it looks like you built your own pack from some ID3/4 bricks. Are you still running these?
Your past topic/thread from 2023 shows you were going through the same thing. (code -77)
You had to knock down the charge via OVP to 3.95 x 24 = 94.8 to clear the -77 error.
If you say your OVP is currently set to 4.2 ā your settings have been reset and in need of a review.
(Reset is a stupid/easy thing to do. One accidental tap in the app while in admin mode and ALL of the custom settings get wiped. No warning. New app should fix this)
your memory is better than mine as I donāt recall ever having the -77 error before, but that is my post above, and that is my setup (confirmed 24P), so looks like I need to go reset the OVP setting to 3.95V. Thanks for helping with my poor memory!
just tried updating OVP and when i hit āOKā in the app i got the message āsending failureā and the setting reverted back. Iām using the JK BMS app and on version C5.11.0. Any known workarounds?
The ovp reset, ovpr, must be below ovp, so set ovpr first. You may run into some other do-funnies as well, but try that.