BMS and Charger Reccomendations

[Johnd]

I have no real knowledge on this, thus I need help.

I made the scooter below, designed for two lead acid batteries in series (24v). The lead acid batteries have low endurance, so I am trying to build my own LIPO4 battery. I am starting with eight 280ah Prismatic cells that I have already bought. They have a 1C rating for output current.

I need to buy the correct BMS and charger to protect my sizable battery investment. Searching online is confusing, and I am Leary about buying direct from China. You all have experimented with BMS brands, and I hope to learn from you.

I power the scooter with a golf cart motor and golf cart speed controller. Both work fine, no changes needed. For helping me choose a BMS, here’s what I know. The maximum peak current draw is 240 amps from a dead stop and applying full throttle. At cruise on pavement, the scooter varies between 45-60 amps. I like the Bluetooth and battery balancing features, but am confused about the limitations on current for balancing between cells.

For a charger, I am ok with charging overnight using an AC powered charger. My LIPO4 custom battery will be 24volt using eight 280ah Prismatic Cells. Should the charger be constant voltage, constant current, or smart enough to use both?

Please be specific on brand and part number on suggestions. I will be buying these two items based on your feedback.

 

[amberwolf]

A typical charger uses CC/CV, it just automatically happens during the charging process if the charger is designed as a lithium charger (or LED PSU like Meanwell, etc). So anything that provides a CC/CV output will work.

The cells are probably capable of 0.5C charging rate, but you'd have to check their specs. The lower the charging rate, the longer they usually last (but the longer it takes to charge).

Other than the 2415 Cycle Satiator from ebikes.ca, I don't have a specific charger recommendation, but it is probably insufficient current for your needs--it only goes up to about 10A at about 30v (300w total), so if you empty the 280Ah pack completely, it would take *at least* 280 / 10 = 28 hours to do most of the charge, but probably up to a day and a half or more in reality, including any balancing the BMS might have to do.

Another option if you are monitoring end-of-charge manually is to use the Meanwell HLG or ELG LED PSUs. The HLG-600H-30A should work, as it goes up to 30v, and up to 20A, cutting the charge time down some (but still a long time). You can parallel multiple PSUs to get more current and faster charging (just be sure you've adjusted them all to the same top voltage). (manual monitoring is needed because an actual charger will shut off output once current drops below some specific point, but the LED PSU does not have this since it is a PSU. I still use one built onto my SB Cruiser trike, the HLG-600H-54A.


Both of these options can be built into the scooter for opportunity charging if you like.


I don't know which specific model would work best, but the JBD BMS brand has been found to be good, and they make contactor-based units for high current (a FET model could be large and expensive to handle the peak system current reliably, and make a fair bit of heat). If you are already using a contactor for your controller, you can set up your system so that the BMS can also control the coil, to shut down the system safely the same way you already do.



Please note that prismatic cells need compression enclosures to provide a specific amount of pressure evenly across the faces of the cells so they don't outgas internally and swell up, which damages them and degrades their characteristics and capabilities. You can find out the specifics of what's needed for your cells from the manufacturer, if the seller doesn't have this info (most sellers don't have a clue). This post
https://endless-sphere.com/sphere/t...ver-low-voltage-ncm-cells.119878/post-1758895
has some pictures of compressing-containment boxes.

 

[Johnd]

A typical charger uses CC/CV, it just automatically happens during the charging process if the charger is designed as a lithium charger (or LED PSU like Meanwell, etc). So anything that provides a CC/CV output will work.

The cells are probably capable of 0.5C charging rate, but you'd have to check their specs. The lower the charging rate, the longer they usually last (but the longer it takes to charge).

Other than the 2415 Cycle Satiator from ebikes.ca, I don't have a specific charger recommendation, but it is probably insufficient current for your needs--it only goes up to about 10A at about 30v (300w total), so if you empty the 280Ah pack completely, it would take *at least* 280 / 10 = 28 hours to do most of the charge, but probably up to a day and a half or more in reality, including any balancing the BMS might have to do.

Another option if you are monitoring end-of-charge manually is to use the Meanwell HLG or ELG LED PSUs. The HLG-600H-30A should work, as it goes up to 30v, and up to 20A, cutting the charge time down some (but still a long time). You can parallel multiple PSUs to get more current and faster charging (just be sure you've adjusted them all to the same top voltage). (manual monitoring is needed because an actual charger will shut off output once current drops below some specific point, but the LED PSU does not have this since it is a PSU. I still use one built onto my SB Cruiser trike, the HLG-600H-54A.


Both of these options can be built into the scooter for opportunity charging if you like.


I don't know which specific model would work best, but the JBD BMS brand has been found to be good, and they make contactor-based units for high current (a FET model could be large and expensive to handle the peak system current reliably, and make a fair bit of heat). If you are already using a contactor for your controller, you can set up your system so that the BMS can also control the coil, to shut down the system safely the same way you already do.



Please note that prismatic cells need compression enclosures to provide a specific amount of pressure evenly across the faces of the cells so they don't outgas internally and swell up, which damages them and degrades their characteristics and capabilities. You can find out the specifics of what's needed for your cells from the manufacturer, if the seller doesn't have this info (most sellers don't have a clue). This post
https://endless-sphere.com/sphere/t...ver-low-voltage-ncm-cells.119878/post-1758895
has some pictures of compressing-containment boxes.

Amber wolf,

i visited the JBD website, but their products seem to be rated in amps. I do have a main on/off contractor operated by an ESTOP push button. I could easily use a relay style BMS where my existing contractor could be triggered by the BMS, but I have never seen a BMS that does that specifically. I guess I need a 300 amp BMS, but I haven’t been able to find one.

 

[amberwolf]

i visited the JBD website, but their products seem to be rated in amps.

Yes, all things that need to pass current will be. If they dont' have an amp rating, they would not be useful (you wouldn't be able to pick one that could handle the current required for an application).

I do have a main on/off contractor operated by an ESTOP push button. I could easily use a relay style BMS where my existing contractor could be triggered by the BMS, but I have never seen a BMS that does that specifically. I guess I need a 300 amp BMS, but I haven’t been able to find one.

They certainly exist; a google search for "300A bms" finds plenty for various voltages. They're just very large if they are FET or IGBT based.

It would be better to use the contactor style such as JBD makes (others do too). A quick google for "JBD Contactor BMS" pulls up this page as the second hit

JBD Smart BMS 7~21S 8S 16S 20S 200A 300A Communicate with UART, Bluetooth or RS485 Function freeshipping - Jiabaida BMS

Jiabaida BMS JBD Smart BMS 7~21S 8S 16S 20S 200A Communicate with UART, Bluetooth or RS485 Function. High quality better service and favorable price with free shipping. Battery Management System for NMC/Li-ion Lifepo4 battery, 10+business for the protection boards manufaturing experiences.

jiabaidabms.com

specs copied below and attached pdf. Unfortunately their wiring diagram is not at the linked location of their site, so you would have to ask them for that.

Since it's programmable, and operates a relay, you can set the current as high as your cells and contactor will handle.

They have others that are 200-250A continuous, with over 300A peak, if your system doesn't draw that max current long or often.

JBD Smart BMS 7~21S 8S 16S 20S 200A 300A Communicant PCB with Relay Support UART, Bluetooth or RS485 Function for Lithium Battery LiFePo4 Li-ion​

JBD-AP21S002 is a software protection board scheme specially designed for 7~21 strings of lithium battery packs. The product adopts architecture of front-end acquisition chip + MCU, and some parameters can be flexibly adjusted through the host computer according to customer needs.

PARAMETERS​

Cell specifications	7~21 strings of Lithium Iron Battery
Interface type	Charge and discharge are both at the same port
Charging voltage	3.6V*Number of strings
Cell voltage	2.2~3.75V
Continuous charging current	200A 300A
Continuous discharging current)	200A 300A
Consumption of running	≤300mA
Consumption of sleep	≤1000uA
Sleep conditions	Delay 65000s under no current \ communication \ protection state (settable)
Circuit resistance)	≤10mR
Operating temperature	-30℃~75℃
Size	200±2mm * 114.5±0.5mm * 51±1mm

Supplementary note:


Continuous standing for 65000s (settable) will automatically disconnect therelay and reduce the standby power consumption of BMS. A large charge discharge current will be identified through the pre charge discharge circuit, and then close the relay.

https://cdn.shopify.com/s/files/1/0606/5199/5298/files/JBD-AP21S002-_-A.0.pdf?v=1662621392

https://cdn.shopify.com/s/files/1/0606/5199/5298/files/AP21S002.rar?v=1668045488

 

[floydr]

7s-21s 300a Lithium Ion / Lifepo4 Smart BMS + Bluetooth JBD BMS doubtful you will find it cheaper in the US
another option ANT BMS come in many different amp ratings which can work for you.
Later floyd

 

[Johnd]

Update with new question:

I purchased and installed the Prismatic batteries, the BMS and the charger. I’m really happy with all so far. The batteries prove to last much longer than my original lead acid car batteries.

My scooter uses a shunt wound golf cart motor and an Alltrax programmable golf cart throttle. I have been tweaking the current limiting and throttle response settings on the throttle to balance performance versus maximizing miles between recharging, and to prevent the BMS from shutting down due to overcurrent.

I chose a Daly 300 amp smart BMS, and my charger is specifically made for my LIFPO4 battery system (8 prismatic in series) the charger is CC/CV with a final trickle charge to 29.2 volts (8 x 3.65 volts).

Here’s the question for you all:

Should I trust the charger or the BMS to stop the charging process? I like the trickle charge process as the batteries get close to full charge, but I also bought the BMS to protect the batteries from a possible overcharge. Or, does It really matter if the batteries don’t get to exactly 3.65 volts?