RXV Leaf Conversion Brake Lock on Regen

[dangme55]

Sorry everyone if this is a question that has already been answered.

I did not find it on search. I do think I remember seeing a similar question but darned if I can find.

So I put the Leaf conversion in 14s with Chinese BMS # 70 amps. Took a test ride and everything seemed okay.

Let the wife use it for a real round today and she said it locked up twice when going at speed downhill. Almost caused a rear ender.

So I am not sure what the exact problem is but I am guessing the BMS is shutting off for some reason not sure which of these:

1. Throttle position is closed
2. Regen voltage is too high (seem to remember a brake controller parameter reference in some install)
3. Cell voltage too high - this happened after some use so not sure that could be it

This is obviously a safety issue so any help/links much appreciated.

Thanks in advance.

Jim

[Sergio]

When your BMS triggers on a LV or HV condition, how do you have it setup to stop the cart?

[Volt_Ampere]

If your BMS is set to open at 70 amps that is WAY too little. I have my current limit set to 400 amps on my Altrax controller. I do not use my BMS to shut my battery down ever. I have a very obnoxious alarm setup to warn me if any cells are getting near low voltage cutoff. I don't want my battery open circuiting when I am driving ever!

[dangme55]

Sergio,
Thanks for the reply. I looked at your circuit. I have not implemented it. I am not sure if I need the whole circuit or just the K1 leg.

Reading the EZGO documentation is like reading IBM documentation. :(

Right now everything goes through the ground leg of the BMS with the bms inserted in that leg. The battery is around 56V right now so I am not sure why the BMS would cut off the power.

This happened while coasting downhill so I am 'guessing' the BMS saw an overvoltage not at the cell but at the battery level? Can't find in the documentation what voltage the motor puts out in regen?

I am using a 70 AMP BMS and that was because I figured 3.3 kw motor = 70 amps.

I have a 150 continuous / 250 peak BMS on the way (stock 235A controller 2013 RXV)

Not sure I need a BMS for the current limiting. 3.3KW is only 1C on a 66AH and I believe leaf cells are rated at 2C continuous.

I am thinking that I really only need the BMS for protection on the charging side for HV and balancing?

If I remember correctly somewhere in 'EZGO sh-- for documentation' that the bus and controller drop offline at 42V. If true that would protect the battery since that would be 3V per cell?

Anyway you are the acknowledged genius here so HELP! ;)

Do I just need the top half of your circuit or can I get away with something else.

Thanks in advance

Jim

[dangme55]

Thanks for the help. See my reply to Sergio your wisdom solicited and welcome.

As I understand it the stock solenoid is only 150 Continuous and 200A briefly. So that is why I settled on the 150/250 BMS that is on the way.

All insights appreciated! Jim

[Sergio]

The only issue with your calculations is that the motor current is not a constant and it varies a lot depending on load and/or speed.

The current can get pretty high when first starting and that can trigger the BMS current limit.

During Regen, depending on how full the pack is and how much current is being allowed by the Controller, the BMS could trigger on a cell high voltage.

Keep in mind the job of the BMS is to monitor the cells, not the pack by itself.

If You don't care about disabling the cart during charge and want to pass the charging current through the BMS, all you need is the K1 relay, D1 diode and the P1 led/resistor.

The negative side of K1 gets connected directly to the P1 (+).

That way the BMS controls the charging (no controller lockout) and the BMS interrupts the pedal signal if any cell goes overvoltage during Regen or low voltage while driving.

How much you charge the batteries will affect how much Regen it can take on a full charge. if Your Controller allows you to limit the "Maximum Voltage" the pack can reach during Regen (like the Alltrax XCT Controller), that would be ideal.


Just wire K1 according to this drawing by molfpedal:

https://www.buggiesgonewild.com/show...95#post1711595

[baward]

Thanks so much for posting this. I'm having the exact same problem. I installed a voltage meter on my dash to monitor this, but still have problems with lock up during coasting as the voltage can climb pretty rapidly when coasting.