Lifepo4 Pack Specificatons
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℃ |
Re: Lifepo4 Pack Specificatons
Peak discharge of 250a is really pushing those batteries in a Rxv.
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Re: Lifepo4 Pack Specificatons
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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 |
Re: Lifepo4 Pack Specificatons
These guys speak a wealth of information.
On my 48V series TXT the data I've recorded from my Alltrax controller shows that the demand and delivery of power is up to 400amps when I'm going up steep hills (woods). A 5 second max of 250amps at 5 seconds simply would not "cut it." |
Re: Lifepo4 Pack Specificatons
Thanks cgtech, BobBoyce, and DaveTM for your feedback. I wasn't aware that the stock 235 amp controller would allow the motor to draw more than 235 amps. I know the battery cells can handle more than 250A. I have to look back in some of my communications to find out what the max amps are that the cells can handle.
My understanding (please correct me) is that its the BMS that will need to be modified to allow for a peak amp rating of 500 amps for 1 min. Is 100 amp continuous ok for normal cruising on mostly flat ground? i'm mostly using my cart at a campground and around the house which is mostly flat with some small hills. |
Re: Lifepo4 Pack Specificatons
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Your pack is likely similar to the LiFePO4 GBS cells I bought, except they are half of the capacity. I would have gone with the 200 A/H cells, but I was able to buy the 100 A/H cells for a much better price. I bought 48 of those cells for about $100 each. In order to size the BMS, I needed to provide the specs required by the vehicle. Originally, it was for 200 Amps max, using a 100 Amp shunt. After discussing that with the seller, he realized that I needed better than 500 Amps, with peaks of just over 1000 Amps. So he included a 500 Amp shunt with the BMS package before shipping it. I had to double up on the buss bars between cells as well in order to carry the incrased load. Your next question is why I was able to get by with just doubling the buss bars... My continuous current requirements will be well under the peak demand, as it is for a road car to be driven on pavment. It has the peak capability for hard accell, as the Bandolero body I used is a race car, built for the track. But I intend to drive it on the street. So unless I'm climbing mountain roads, most of my power demands will be lowered. The controller I'm using is a Curtis RXV 350 Amp upgrade controller. While cruising, current should be well under 100 Amps most of the time. In your case, 50 to 60 Amps is going to be typical, once you are up to speed. I converted a 2008 RXV to lithium using a 7 Nissan Leaf module pack. Those modules are designed to deliver hundreds of peak amps, since they are in series and each module must deliver peak Amps for the car as it is driven upon the highways. Your BMS will have to meet your needs, both normal use, and max peak demands. Make sure that the BMS you get can handle the usage. You may have to get them to add an external shunt to the design. Most of those chinese BMS boards have the shunt built-in. My RXV lithium conversion uses one of those, and I modified the way I use it to allow it to control the current path external to the BMS board itself. It controls the solenoid of the cart. Pack voltage is never turned off to the BMS, and the controllers logic (Controller Pin 1) is manually turned off when I am done riding. I reprogram RXV controllers to deliver 100% of their rating. I know them well. Bob |
Re: Lifepo4 Pack Specificatons
I was able find the rating for the cells. The manufacturer says the cells are rated for 3C continuous and 5C~10C peak without the BMS.
BobBoyce, thanks again for the added information. Its very helpful. I definitely have some other things to consider before i pull the trigger and order these cells and the battery kit. I need to make sure:
Do you think i should have a BMS built state-side or via a well know BMS manufacturer rather than get through the chinese cell manufacturer? Any recommendations on a good BMS company to work with? thanks, Myles |
Re: Lifepo4 Pack Specificatons
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I would go with a chinese BMS board, and integrate it into your build. The member agpfl has found sources for programmable BMS boards that are relatively inexpensive. You would need one designed to work with a 16S pack. That way you can set your upper, lower, and charge limits. Otherwise you can buy a slightly lower cost ($35 - $40) preprogrammed BMS board that is already programmed with those settings for you. I went the preprogrammed route with my RXV, just shopped around until I found what I wanted. Since my Bandolero build is to be a much more sophisticated build, I chose a much more sophisticated BMS and charger with a control display that I will integrate into the dash of that vehicle. Bob |
Re: Lifepo4 Pack Specificatons
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Do you think the BMS manufacturer could program in a "soft stop" for any failures? So that the controller has time to save the settings to memory, and also if the amps were limited or ramped down maybe this would avoid the brake lock-up issue? Would love a "limp" mode or something too so that the cart isn't stranded in an out of the way area. I've read where some other EV's and even outboard boat motors have a "limp" mode. Any idea how much time the controller needs to write to memory? How about running a DC to DC converter off the whole pack? In some of the threads I see that guys are only using the lithium packs for traction and then have a separate 12v FLA or Lith battery for accessories. I'm only currently running my lights off 12V and don't have any immediate plans to add other accessories. When I bought my cart, it had the factory DC to DC converter wiring harness installed, but the converter is missing. I was planning to buy the EZGO OEM converter (CONVERTER ONLY) #632185 which is available on the EZGO site for $150. Seems expensive compared to the aftermarket converters I see online but I believe it will use the existing harness which would be simple/clean. thanks, Myles |
Re: Lifepo4 Pack Specificatons
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I bought a new factory E-Z-GO 12V converter for $25 from a seller on eBay. Just keep doing searches from time to time. I had no harness or connector for it at the time, so I bought the harness from the E-Z-GO site afterwards. Bob |
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