2017 RXV Issue with New Lithium upgrade

[Cwad8505]

New user here and need a little help. I recently purchased the bigbattery.com BDGR 48 V 3 battery system. The project went well until I went into a hard braking scenario. After missing my garage door frame by about 6 inches, I had to regroup and figure out what just happened. I took it to the road and got to full speed (approx 22 mph) and slammed the brakes. I lost my stereo for about 3 seconds and then it came back. I quickly realized what was happening. These batteries have a full state of charge at 50.4v. I’m not sure what voltage is produced during a hard brake, but it is apparently enough for the BMS on these batteries to go into protect mode and temporarily shut them down. I’ve spoken with big battery and their answer twice now has been to disengage the brake solenoid, of which I responded that I don’t believe this model has that. Any suggestions on my next move? Can the regen voltage be adjusted with programming software? Can it otherwise be disabled? I appreciate any input as currently have a cart that I don’t feel comfortable letting my wife or daughter drive.
Thank you!
Chris

[Cwad8505]

Bumpage… anyone?

[PingEye3]

Originally Posted by Cwad8505

New user here and need a little help. I recently purchased the bigbattery.com BDGR 48 V 3 battery system. The project went well until I went into a hard braking scenario. After missing my garage door frame by about 6 inches, I had to regroup and figure out what just happened. I took it to the road and got to full speed (approx 22 mph) and slammed the brakes. I lost my stereo for about 3 seconds and then it came back. I quickly realized what was happening. These batteries have a full state of charge at 50.4v. I’m not sure what voltage is produced during a hard brake, but it is apparently enough for the BMS on these batteries to go into protect mode and temporarily shut them down. I’ve spoken with big battery and their answer twice now has been to disengage the brake solenoid, of which I responded that I don’t believe this model has that. Any suggestions on my next move? Can the regen voltage be adjusted with programming software? Can it otherwise be disabled? I appreciate any input as currently have a cart that I don’t feel comfortable letting my wife or daughter drive.
Thank you!
Chris

There is no brake solenoid on an RXV. Main solenoid only. When I first read 'slammed on brakes' I thought you meant the battery tripped and with all power turned off. The brakes will lock up in that scenario, as designed. But, I think you are saying that YOU slammed on the brakes. If so, the brakes worked like they are supposed to. When stomping the brake pedal, for a panic stop, once the brake limit switch activates with full pedal travel, they will lock up. Most people driving the RXV rarely use the brake pedal as the brakes are regen only to stop the cart under normal driving. Unless slamming the brakes, when they lock up. Regen can be adjusted with the handheld programmer., but it cannot be disabled as that is your only braking system on an RXV. You cannot adjust regen to a current or voltage value. You are adjusting it for brake feel only, ie, how much braking you feel when letting off throttle.

If you are saying the cart, while driving at full throttle and fully charged, then it locked up when you let off the pedal. Then it is possible that the BMS shut off the pack due to high regen voltage while braking. If it tripped the main contactor because of that, your brakes would have locked up. You can make regen adjustments to soften the affect.

[Cwad8505]

Originally Posted by PingEye3

There is no brake solenoid on an RXV. Main solenoid only. When I first read 'slammed on brakes' I thought you meant the battery tripped and with all power turned off. The brakes will lock up in that scenario, as designed. But, I think you are saying that YOU slammed on the brakes. If so, the brakes worked like they are supposed to. When stomping the brake pedal, for a panic stop, once the brake limit switch activates with full pedal travel, they will lock up. Most people driving the RXV rarely use the brake pedal as the brakes are regen only to stop the cart under normal driving. Unless slamming the brakes, when they lock up. Regen can be adjusted with the handheld programmer., but it cannot be disabled as that is your only braking system on an RXV. You cannot adjust regen to a current or voltage value. You are adjusting it for brake feel only, ie, how much braking you feel when letting off throttle.

If you are saying the cart, while driving at full throttle and fully charged, then it locked up when you let off the pedal. Then it is possible that the BMS shut off the pack due to high regen voltage while braking. If it tripped the main contactor because of that, your brakes would have locked up. You can make regen adjustments to soften the affect.

Thank you for the reply. I meant that when I apply the brakes forcefully, the BMS on the lithiums shut them down, due to an over voltage to the BMS (my assumption), and I have ZERO brakes. The brakes do not lock up (perhaps they should?). The condition usually only lasts 1-2 seconds, but that’s a lot if you’re moving pretty good.
Thank you!

[Imapled]

Originally Posted by Cwad8505

Thank you for the reply. I meant that when I apply the brakes forcefully, the BMS on the lithiums shut them down, due to an over voltage to the BMS (my assumption), and I have ZERO brakes. The brakes do not lock up (perhaps they should?). The condition usually only lasts 1-2 seconds, but that’s a lot if you’re moving pretty good.
Thank you!

Double up or triple up the capacity of the resistor coil on your cart. If you are running around at full state of charge the BMS will indeed shut down if you try to pass it more current than the batteries can hold. The BMS is doing exactly what is should do to protect the batteries.

If you provide additional space in the resistor coil that burns off excessive current from regen that the batteries cannot accept it "may" solve your problem.

Over charging lithium batteries is where bad things happen. If you over current them beyond their top capacity that is when you damage them and could find yourself with bulging batteries, fires, etc...

There is a reason that in the new RXV setups the controller and BMS are CAN bus connected.

The other option if you can is to reduce the full state of charge on the batteries to leave enough room in the cells to deal with the current generation from regenerative braking. Not sure what BMS your battery uses but, some you can configure the SoC levels etc...

[Cwad8505]

Thank you for the advice. I’ll search for additional resistors to start. I haven’t checked the situation with the batteries down a bit to see if it does it then. I’ll also check that out. Thank you!

[Imapled]

Originally Posted by Cwad8505

Thank you for the advice. I’ll search for additional resistors to start. I haven’t checked the situation with the batteries down a bit to see if it does it then. I’ll also check that out. Thank you!

Personally, I would really rethink that battery choice. I am always SUS of batteries that pose as traction capable and solar wall capable. The two things are not the same. Traction batteries require significant design over a solar wall. Traction batteries go into moving vehicles that shake, rattle and roll. It takes significant design to hold the cells in place to insure that shock impacts of a traction application do not cause significant damage to the cells inside.

I would recommend a setup that is indeed 100% designed for traction applications with a proper BMS that is designed for traction applications. Framing batteries for traction applications requires significant design considerations.

Also, not a fan of NCM as an application in traction applications myself. I typically don't like sitting on cells that burn as hot as NCMs do.

[Cwad8505]

Originally Posted by Imapled

Personally, I would really rethink that battery choice. I am always SUS of batteries that pose as traction capable and solar wall capable. The two things are not the same. Traction batteries require significant design over a solar wall. Traction batteries go into moving vehicles that shake, rattle and roll. It takes significant design to hold the cells in place to insure that shock impacts of a traction application do not cause significant damage to the cells inside.

I would recommend a setup that is indeed 100% designed for traction applications with a proper BMS that is designed for traction applications. Framing batteries for traction applications requires significant design considerations.

Also, not a fan of NCM as an application in traction applications myself. I typically don't like sitting on cells that burn as hot as NCMs do.

They actually are marketing these as golf cart batteries. I had purchased a different model from them 2 years back for another RXV and they worked great. Difference being, they were 58.8v instead of the 50.4. Of course, they don’t sell those anymore. These are the “new and improved “. Their customer service had been good, but they seem to be lost on this issue. Seeing as I’m around $2300 invested in these, I’m trying to make it work.
Thx again

[Cwad8505]

Would going with a 600A Navitas controller with the OTF regen lowered help me in this situation?

[jjordan32875]

Hi all...new to this forum but been reading a lot on lithium conversions for an RXV. Could someone recommend a lithium solution that actually does work when converting from lead acid? I can't seem to find a lithium battery that allows for enough peak amperage draw for an RXV based on what I've read on the forum. My cart is in an area with steep hills and therefore assume I would be demanding max amp draw often. Should I stay with lead acid or is there a lithium pack that works without complicated modifications? I have a 2018 RXV with 6" lift. Everything else is stock. Thank you!