Quote:
Originally Posted by cramermy
Hi All, I have a late model year 2013 Ezgo RXV Fleet with stock Curtis 1206AC-5201 controller. I have the 4 @12v model. I hate my FLA batteries and they are just about shot so I want to upgrade to a nice 48V nominal Lifepo4 battery pack. I have been reading all the great info you have shared on lithium conversions, so thanks for all the great threads.
I've been communicating with a supplier in China who makes custom packs for lots of applications including golf cars. I'd love some advice on the suitability of the specs we have been discussing as outlined below for my specific cart model.
Thanks in advance for your comments.
• 48V 100Ah lifepo4 battery pack (Made by 32pcs 3.2V 50Ah lifepo4 in a 16s2p configuration) (single cell 3.2V 50Ah )
o Prismatic cells
o All wiring sized to handle peak discharge current
• BMS for the battery pack
o With LED display. The wire between the battery pack and LED display is about 8 feet
o Continuous discharging current 100A
o Peak discharging current (less than 5 seconds) 250A
o Discharging and charging port is the same port to accommodate the electric motor brake and regenerative braking
o Discharge voltage range 57.6V to 43.2V (2.7 v each cell)
o Discharge cutoff voltage 43.2
o Balancing voltage 3.5V difference of <=20mA
• Metal case(IP Rating--65) for the battery pack
o Maximum dimensions 333× 537×289mm,length,width,height.
• Charger for the battery pack with a charging current of 25A CC-CV
BMS (Battery management system specification) specification
• Single cell over-charge protection Voltage 3.70±0.03V, Delay 1.0±0.5S, Dismiss 3.40±0.03V
• Single cell over-discharge protection Voltage 2.70±0.05V, Delay 1.0±0.5S, Dismiss 3.10±0.05V, Charging
• Discharge over-current protection First rank 110±5A, Delay ≤2500mS, Second rank 130±5A, Delay ≤10mS
• Charging over-current protection 60A±5A, Short circuit, Current 180±10A Load short, circuit Delay ≤800μS
• Short circuit protection dismiss Charging cut off or disconnect the load
• Charge High temperature protection 65±3℃, Recover 55±3℃
• Low temperature protection -10±3℃, recover -1±3℃
• Discharge High temperature protection 75±3℃, Recover 65±3℃
• Low temperature protection -30±3℃, Recover -20±3℃
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As cgtech mentioned, peak current for an RXV at 250 Amps is simply not enough. That BMSs short circuit cutoff spec shows that it will detect the RXVs demand as a short, and cut out at 180 Amps +/-10 (170 to 190) Amps. Every stock RXV I've monitored current on draws over 200 Amps from the pack when you hit the go pedal on
flat level pavement! Having larger than stock tires, climbing hills, or going off-road requires a lot more.
Even a stock 235 Amp controller, with the factory E-Z-GO current cutback still in place, can deliver 437.1 Amps of 3 phase AC power to the RXV motor at wide open throttle on a hill steep enough that it is not regulating speed down. That works out to about 288.5 Amps from the battery pack. That is assuming 100% controller efficiency, actual efficiency ranges 91% to 96% on average. An RXV that has been performance tuned can demand a bit over 500 Amp peaks from the pack in similar conditions when 2 guage cables are installed.
So I would look for a pack rated for 400 to 500 Amp peaks. Those peaks can last for a minute or more when climbing hills, not just 5 seconds. Depending on the lithium cell design, that can dictate the cell type and BMS used. The BMS must be able to support the demand without going into shutdown, which will destroy/corrupt an RXV controller when the BMS goes open circuit!
My highest demand design is my Bandolero, which uses an RXV chassis and motor. That will be able to deliver long term 500 Amp peaks with no problem, and 2,000 Amp peaks for 5 seconds. That pack is using GBS 100 A/H cells in a 16S2P layout. The BMS for that has a 500 Amp shunt.
Bob