Basic Nissan Leaf 7 module Lithium setup with Generic Chinese BMS

[DaveTM]

Originally Posted by BLK MAJK

...I'm a moron. .

Nah.....we've all done things that are just plain stupid upon hindsight!!

We should have a thread......the "dumbest" things I've done with\to my cart!!

[Pat911]

Hi Sergio,

I’m about to commence a very similar project and have a question for you. I haven’t read the whole thread (it’s 38 pages long) so sorry if you’ve already answered it. You purchased a 20A BMS and are relying on it to both balance and protect your battery array. Current passes through the BMS and it can isolate the battery on HV or LV conditions, both at a complete pack and individual cell level. How can a 20A BMS pass the 100A+ drawn by the motor during discharge? What am I missing here?

Cheers,
Pat.

Edit....
I may have an answer to my own question, is the motor connected directly to the battery and a low current control line, say to the motor controller is disabled under an LV condition? This could also result in the motor being disabled.

[Sergio]

Correct, I don't think isolating the pack either by using an internal BMS FET or external solenoid is a good idea, specially in controllers that do regenerative brake.

The LV relay in my circuit is used to just disable the controller, in my Alltrax XCT I interrupt the KSI line to the controller.

The charger should run through the BMS for cell HV protection.

[Pat911]

Thanks Sergio, your answer confirms my thoughts.

I’m quite knowledgeable in electrical systems, electronics, lithium batteries etc. I know nothing about carts as this is my first one. Trying to read up as much about carts and their drive systems as I can so that I can adapt that knowledge to them.

Cheers
Pat.

[jhornbr225]

Anybody who has one of these China BMS's, do you have any information on how to hook to these with a PC?

I know that there are Bluetooth modules, and phone apps. Currently the BMS that Battery Hookup sells, they are out of stock on the Bluetooth modules. And they claim the Android app does not work.

There is a Youtuber, David Poz, he's got the same BMS as I do, and a Bluetooth module, but he uses his wife's iPhone to talk to it.

I believe that the interface is just a serial out of the module to the Bluetooth unit, along with power for the Bluetooth unit.

I've got PC's that have a serial plug, and I have a USB to serial converter, so that's not the issue, just the software.

There are no iPhone's in my family, so I need to either find an Android app that works, or a PC program.

[Sergio]

I have used several versions on my Android phone (Android 10 and 11) and never had an issue with the Bluetooth connection, perhaps they have some old phone.

The board also supports UART connection from a PC, You can download either software (IOS, Android or PC) from this link:

https://www.lithiumbatterypcb.com/sm...ware-download/

While there are some different implementations of the common Xiaoxiang BMS hardware/software, I would recommend you do not try to use your own interface.

As I recall the UART port on the Xiaoxiang BMS does not provide 3.3V or 5V on VCC, It is instead approximately 10V!.

Connecting VDD to a serial to USB adapter may fry the adapter and/or damage your computer's USB port, so leave the VDD unconnected if you try.

[Drumstick]

Sergio, thanks for the detail of this leaf conversion!
I do have one question I do not see an answer for - if not using the cart for a prolonged period of time (a few weeks maybe) should the BMS be unhooked to prevent it from drawing the batteries down since there is no sleep mode? And, if unhooked do you know if it retain the settings?

[Sergio]

As far as the settings it will be fine since they get stored in non volatile flash memory.

I would say most of the drain would come from other cart components like a voltage converter (remember even the 5-wire converters are always ON), voltage meter directly connected to battery, Controller capacitors etc.

If You disconnect the main battery cable from the cart so nothing else is connected, You will reduce the significant source of current drain.

I have never monitored the idle/quiescent consumption on my BMS but since it is powered from the entire pack, the drain is likely minuscule.

If You are planning in leaving the pack disconnected for more than a couple of months, it would be a good idea for the first time to have the voltage checked after a couple of months to get an idea of the drain.

[outdoorjunke]

Question. Would using a led with the below specs not allow K1 to close?
If - Forward Current: 20 mA
Vf - Forward Voltage: 2.1 V

[Sergio]

Originally Posted by outdoorjunke

Question. Would using a led with the below specs not allow K1 to close?
If - Forward Current: 20 mA
Vf - Forward Voltage: 2.1 V

It should work fine since the T9AP1D52-48 coil only needs a maximum of 20mA to operate.

The design assumes you are using a 14S Leaf setup, if your pack voltage is lower you need to make adjustments accordingly.