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Unread 01-03-2019, 09:02 PM   #1
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Default 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 537289mm,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 3.700.03V, Delay 1.00.5S, Dismiss 3.400.03V
Single cell over-discharge protection Voltage 2.700.05V, Delay 1.00.5S, Dismiss 3.100.05V, Charging
Discharge over-current protection First rank 1105A, Delay ≤2500mS, Second rank 1305A, Delay ≤10mS
Charging over-current protection 60A5A, Short circuit, Current 18010A Load short, circuit Delay ≤800μS
Short circuit protection dismiss Charging cut off or disconnect the load
Charge High temperature protection 653℃, Recover 553℃
Low temperature protection -103℃, recover -13℃
Discharge High temperature protection 753℃, Recover 653℃
Low temperature protection -303℃, Recover -203℃
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Unread 01-05-2019, 12:58 AM   #2
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Default Re: Lifepo4 Pack Specificatons

Peak discharge of 250a is really pushing those batteries in a Rxv.
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Unread 01-05-2019, 07:03 AM   #3
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Default Re: Lifepo4 Pack Specificatons

Quote:
Originally Posted by cramermy View Post
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 537289mm,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 3.700.03V, Delay 1.00.5S, Dismiss 3.400.03V
• Single cell over-discharge protection Voltage 2.700.05V, Delay 1.00.5S, Dismiss 3.100.05V, Charging
• Discharge over-current protection First rank 1105A, Delay ≤2500mS, Second rank 1305A, Delay ≤10mS
• Charging over-current protection 60A5A, Short circuit, Current 18010A Load short, circuit Delay ≤800μS
• Short circuit protection dismiss Charging cut off or disconnect the load
• Charge High temperature protection 653℃, Recover 553℃
• Low temperature protection -103℃, recover -13℃
• Discharge High temperature protection 753℃, Recover 653℃
• Low temperature protection -303℃, Recover -203℃
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
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Unread 01-05-2019, 07:11 AM   #4
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Default 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."
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Unread 01-05-2019, 07:50 AM   #5
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Default 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.
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Unread 01-05-2019, 09:03 AM   #6
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Default Re: Lifepo4 Pack Specificatons

Quote:
Originally Posted by cramermy View Post
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.
The RXV is an AC drive cart. The controller takes the nominal 48V DC and inverts it into 48 Volts 3 phase AC. The current rating is the per phase current (X3) for a total of 3 times that rating. The factory programming limits motor current to 62% of that rating, which is where the 3 phase maximum of 437.1 Amps figure comes from. It's more complex than that, but it is simpler to keep in mind that the DC current can be 1/2 to 2/3 of the 3 phase AC value. There are many variable involved, such as current required to maintain rotor lock over the RPM range (allowed amount of slip to maintain torque demanded) that you are operating. The more torque demanded, the higher the current required to maintain that torque. So when climbing hills, max current is demanded. Speed is regulated by motor RPM, so when you reach speed, current required drops off and just enough rotor lock current is applied to maintain the speed regulation. The controller functions required are quite complicated, and there are a lot of calibration values stored in the controller to allow it to work with the AC motor. When you turn it off, the controller must write values to controller memory, which it reloads the next time it is started. Normally, the power is not cut until after this write is finished. If power drops suddenly, like when a BMS shuts down, the controller loses power in the middle of this memory write operation, which will corrupt the memory.

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
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Unread 01-05-2019, 01:41 PM   #7
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Default 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:
  • I don't screw up my controller by shutting it off before it writes to its internal memory
  • Have a way to gently bring the cart to a stop if i have a cell or BMS fault condition (as noted in one of the other threads that an abrupt stop at 20mph would be a big problem)
  • Build a manual override like BobBoyce did for his 2008 RXV
  • Adjust the BMS specs to handle the required motor amps. I don't want this awesome battery pack to under perform

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
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Unread 01-05-2019, 06:16 PM   #8
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Default Re: Lifepo4 Pack Specificatons

Quote:
Originally Posted by cramermy View Post
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:
  • I don't screw up my controller by shutting it off before it writes to its internal memory
  • Have a way to gently bring the cart to a stop if i have a cell or BMS fault condition (as noted in one of the other threads that an abrupt stop at 20mph would be a big problem)
  • Build a manual override like BobBoyce did for his 2008 RXV
  • Adjust the BMS specs to handle the required motor amps. I don't want this awesome battery pack to under perform

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
If I remember right, the peak rating at 5C has a much longer runtime vs the 5 second peak rating at 10C. The pack capacity at the continuous 3C rating would be desired to accomodate your hill climb times, if any.

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
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Unread 01-06-2019, 12:37 PM   #9
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Default Re: Lifepo4 Pack Specificatons

Quote:
Originally Posted by BobBoyce View Post
If I remember right, the peak rating at 5C has a much longer runtime vs the 5 second peak rating at 10C. The pack capacity at the continuous 3C rating would be desired to accomodate your hill climb times, if any.

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
Hi Bob, thanks again for the continued support/guidance for a newbie like myself. I have more questions... I hope you don't mind.

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
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Unread 01-06-2019, 02:58 PM   #10
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Default Re: Lifepo4 Pack Specificatons

Quote:
Originally Posted by cramermy View Post
Hi Bob, thanks again for the continued support/guidance for a newbie like myself. I have more questions... I hope you don't mind.

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
I prefer a LVCO alarm, so it warns the driver to get out of traffic and head for a safe location. You could set up a low voltage alarm that will sound off before the pack reaches the BMS LVCO setpoint. Solves your concern.

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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