LifePo4 Vs Lipo 48v packs in electric racing kart setup

U

userix

10 mW
Joined
Jan 4, 2011
Messages
34
I currently run a 48V 300A BMS lifepo4 70Ah battery pack on my electric racing kart setup. Overall, the performance of the pack is good, but I do notice that as the voltage drops (further into the discharge cycle), the power is weaker (ie, acceleration/torque is weaker, top speed is lower). I was wondering if I used a lipo pack, such as a custom built 40C from maxamps, of the same voltage and 22Ah, will it perform better over the whole discharge cycle? I believe Lipo can hold higher voltage under load, but will it provide consistent, strong power throughout the discharge cycle? Ie. will it pull just as hard and have the same top speed as it does at 100% SOC and at 40% SOC?

Will a lipo pack provide even more power(torque) than a lifepo4 of similar spec?

I'm still learning the ins and outs of lithium battery tech. I know lifepo4 is the far safer chemistry, but I see a lot of electric karts using lipo packs, as they seems to pack more "punch." Thanks in advance!
 
What you are experiencing is sag due to a low C rating. I run LiFePo4 in my e-bike because it is a safe chemistry to charge over night. It, however sags under load. This is what is happening to you. RC Lipo will give you a higher discharge curve compared to LiFePo4 or just about any other battery chemistry under load. Google "battery C rating" and learn what it means and you will understand why the other go-cart guys are using lipo.

:D :bolt:
 
I see. The lifepo4 pack performs really well from 100% charge, no severe voltage sag. It's more a gradual decrease in maximum power as SoC decreases. As the SOC drops, that's when the power felt decreases too.


With Lipo packs, would the power at 40% SoC be just as strong as when at 100% SoC? Or is there an overall decrease in performance at lower SoCs?
 
this is natural and not easy fixed unless you have a controller that is a lot smarter, you get into the sevcon range, those are capable of controlling power based on watts instead of amps.

what you can to do minimize this behaviour is to reduce the amps so you dont get a big change during discharge as all controllers are amp limit based. going from 100A at 60V to 50V is a 1kW reduction while keeping the same current flow. if you incease the volts you can reduce the amps so you dont get such a huge swing in power during discharge due to less voltage losses.

so that means cranking up the voltage of the battery so you have less amps going into the controller for the same amount of power (watts).

doubling the voltage means halving the amps wich means you reduce the sag you experience by more then half as you also reduce voltage drop and lower the IR of the battery.
 
userix said:
I was wondering if I used a lipo pack, such as a custom built 40C from maxamps, of the same voltage and 22Ah, will it perform better over the whole discharge cycle? I believe Lipo can hold higher voltage under load, but will it provide consistent, strong power throughout the discharge cycle? Ie. will it pull just as hard and have the same top speed as it does at 100% SOC and at 40% SOC?
Click to expand...
simple answer is no.,, the lipo may not sag as much as the Lifepo4, but your speed is determined by the actual voltage and at 40% any pack will have less voltage than the same pack at 100% SOC.
As flippy said, if you want to controll the voltage, you will need a smart controller.
 
I'd imagine the weight savings of going to lipo would be of benefit for your application. That aside the amount of space they would take up would presumably be much less, so if you're able you could add more parallel packs to keep you in the high speed sweet spot for that much longer.
 
All else being equal, LiFePo4 operates over a narrower voltage range than LiPo, so you'll have a wider gap in top speed between full and dead.

My 16S LiFePo4 pack ranges from 58.4V to 48V, but spends most of the discharge between 56 and 50.

My 14S Li Ion pack goes from 58.8V to 42V, and goes down in a fairly linear fashion from charge to discharge.
 
RC Lipo performance is a lot more consistent over your cycle, yes. For an electric racing kart you certainly don't want LiFePO4 cuz the performance is much crap and packs weigh like twice what they would with high performance lithium ion.
 
It really depends on the racing class rules, if there's a minimum weight requirement then energy density might not matter at all.

A123 pouches have excellent power density, especially considering their lifespan.
 
flat tire said:
No it doesn't. Even the best lifepo4 has shitty energy density.
Click to expand...

Define shitty -

I have some 460 Ah LiFePO4 storage cells which have about 140 Wh/kg. 0.5C continuous, 1 C peak though.
I also have some 10 Ah, 40C LiPo pouch cells which are about 140 Wh/kg. 20C continuous and 40C peak.

If the goal is power, you choose a cell with more copper and aluminium than black stuff.
If the goal is energy density, choose a cell with more black stuff than copper and ali.

LiFePO4 can be crazy powerful like A123 20 Ah pouches, which themselves have an energy density of 110 Wh/kg.
 
140kw/kg is worse than high discharge rc lipo and way worse than less high discharge lithium ion. Lifepo4 has advantages in cycle life and safety, THAT'S IT. It is NOT a performance chemistry in any sense.
 
flat tire said:
140kw/kg is worse than high discharge rc lipo and way worse than less high discharge lithium ion. Lifepo4 has advantages in cycle life and safety, THAT'S IT. It is NOT a performance chemistry in any sense.
Click to expand...

I dunno, the 400A peak capable under 20lbs. pack on my rack might disagree.
 
Hillhater said:
jonescg said:
If the goal is power, you choose a cell with more copper and aluminium than black stuff.
If the goal is energy density, choose a cell with more black stuff than copper and ali.
........
Click to expand...
Sure, but where does Lifepo4 score in either of those ?
Click to expand...

Somewhere in the middle. If you are OK with the weight, energy, power and space occupied, you can choose a safer chemistry with long cycle life. It really depends on the application.

I wouldn't bother with LiFePO4 for a road going vehicle, or a racing vehicle, but if it was for an application where it was likely to cop abuse (hire karts) or the risk of a fire is too great (home storage) I would opt for the olivine cathode for sure.
 
Sorry, I am such a noob. Turns out I have regular li-ion high energy battery pack. I asked the company that made my battery pack. For some reason, I assumed it was a lifepo4 pack.

flippy said:
this is natural and not easy fixed unless you have a controller that is a lot smarter, you get into the sevcon range, those are capable of controlling power based on watts instead of amps.

what you can to do minimize this behaviour is to reduce the amps so you dont get a big change during discharge as all controllers are amp limit based. going from 100A at 60V to 50V is a 1kW reduction while keeping the same current flow. if you incease the volts you can reduce the amps so you dont get such a huge swing in power during discharge due to less voltage losses.

so that means cranking up the voltage of the battery so you have less amps going into the controller for the same amount of power (watts).

doubling the voltage means halving the amps wich means you reduce the sag you experience by more then half as you also reduce voltage drop and lower the IR of the battery.
Click to expand...

I am running a Sevcon millipak 4Q controller, but if I limit the current, wouldn't the torque/acceleration be weaker overall (if keeping voltage same). I do like how torquey it is at max 300 amps. I couldn't find any options in the programming manual to control power based on watts.

The millipak is a 48V controller and I am using a Motenergy Me0909 48V PMDC. Doubling or upping the voltage wouldn't be good for either component? But I see what you are getting at.
 
a millipack is direct brushless DC. that is basically useless if you want the control you seek.

you need sensored brushless (BLDC) and a sevcon gen4 if you want to go balls out.
that gives you perfect control over max power usage, voltage, amp and torque curves just to name a few. it can help a lot by preventing max torque at low speeds so you dont strip the tires when flooring it, something brushed motors are REALLY good at.
but it will be "cost prohibitve" to get such a controller if you are running cheap brushed motors now by comparison.(the motor is about the same cost but much simpler, no brushes) but the amount of added control and power increase due to the smaller motor (and silent!) will give you a much better experience.
if you are prepared to fork the 500 bucks it costs to get a sevcon programming cable you can do everything you can think of. you can even run controllers in tag team style so a dual motor setup becomes possible and it can even deliver torque steering to help you make turns if you mount a steering sensor.

despite the millipack doing a great job in making a brushed motor driveable its nothing compared to BLDC motors.

for a more budget oriented approach i would just grab a mid motor from QS and a big honking kelly controller and go to 72 or 96 volts. that makes the currents a lot more managable and will give a much more flatter performance curve when the battery drains then you have now.
 
999zip999 said:
Wait wait who says this is a racing go-kart ? This couldn't just be a Leisure go kart. Go Go baby go.
Click to expand...

Sorry, yeah It's more of a leisure go kart. For fun :D
 
flippy said:
a millipack is direct brushless DC. that is basically useless if you want the control you seek.

you need sensored brushless (BLDC) and a sevcon gen4 if you want to go balls out.
that gives you perfect control over max power usage, voltage, amp and torque curves just to name a few. it can help a lot by preventing max torque at low speeds so you dont strip the tires when flooring it, something brushed motors are REALLY good at.
but it will be "cost prohibitve" to get such a controller if you are running cheap brushed motors now by comparison.(the motor is about the same cost but much simpler, no brushes) but the amount of added control and power increase due to the smaller motor (and silent!) will give you a much better experience.
if you are prepared to fork the 500 bucks it costs to get a sevcon programming cable you can do everything you can think of. you can even run controllers in tag team style so a dual motor setup becomes possible and it can even deliver torque steering to help you make turns if you mount a steering sensor.

despite the millipack doing a great job in making a brushed motor driveable its nothing compared to BLDC motors.

for a more budget oriented approach i would just grab a mid motor from QS and a big honking kelly controller and go to 72 or 96 volts. that makes the currents a lot more managable and will give a much more flatter performance curve when the battery drains then you have now.
Click to expand...

With a Sevcon Gen4 controller, which motenergy bldc is good for it? I do like the high torque at low speeds. I want that crazy acceleration with a little loss of traction. The millipak 4q and me0909 brushed DC is pretty quick for what it is, but I can't peel out from a stand still.
 
motor wise its pretty simple: what you can fit/afford.
you might want to look at the midmotor from QS:
https://www.aliexpress.com/item/32956195974.html?spm=2114.12010612.8148356.14.6d882df3Ts9nWk

its cheaper, is known to handle 8.5kW peaks at 72V@150A.
with the proper reduction you can get yuge torque numbers down compared to brushed, especially at speed. low end pulling is a brushed motor party piece but its not really useful when accelerating out of corners. BLDC motors will keep their pulling power much better then a brushed motor. and you get a reverse.... :roll:

for the price of a simple sevcon and its programming cable you can buy this motor, matching kelly controller and have money left to buy a second one for 15kW peaks and then you can cut the rear shaft and have independant drives at each rear wheel. pretty sure you will gain some speed in the corners when you lose the fixed shaft at the back and gain basically a very loose diff.
should be able to strip tires bare pretty easy if you put 450A on each motor.
 
Doesnt the ME0909 support 15kW peak @48v (300A).. already ?
Do you have any way of knowing exactly what peak current your pack is producing at the moment ?
A split axle (diff’) may be useful playing in a car park, but it will not help on a race track.
 
Hillhater said:
Doesnt the ME0909 support 15kW peak @48v (300A).. already ?
Do you have any way of knowing exactly what peak current your pack is producing at the moment ?
A split axle (diff’) may be useful playing in a car park, but it will not help on a race track.
Click to expand...

flippy said:
motor wise its pretty simple: what you can fit/afford.
you might want to look at the midmotor from QS:
https://www.aliexpress.com/item/32956195974.html?spm=2114.12010612.8148356.14.6d882df3Ts9nWk

its cheaper, is known to handle 8.5kW peaks at 72V@150A.
with the proper reduction you can get yuge torque numbers down compared to brushed, especially at speed. low end pulling is a brushed motor party piece but its not really useful when accelerating out of corners. BLDC motors will keep their pulling power much better then a brushed motor. and you get a reverse.... :roll:

for the price of a simple sevcon and its programming cable you can buy this motor, matching kelly controller and have money left to buy a second one for 15kW peaks and then you can cut the rear shaft and have independant drives at each rear wheel. pretty sure you will gain some speed in the corners when you lose the fixed shaft at the back and gain basically a very loose diff.
should be able to strip tires bare pretty easy if you put 450A on each motor.
Click to expand...

I have the Sevcon calibrator hooked up to my millipak (it does have reverse and regen built in) and it shows it's pulling 300A (the max the controller can handle), yet I can't burn out from stand still. I have traction when flooring the pedal from still. Since a brushed motor should have the crazy low end torque, does that mean my pack has too low a C value and not dumping that high current the motor can take? So using a 40C 44Ah 48V lipo pack, I should be getting a true 300A to the brushed motor?
 
You must log in or register to reply here.

Similar threads

N
Replacing Sealed Lead Acid (SLA) battery with LifePo4 Battery in home computer UPS
Replies
4
Views
954
amberwolf
amberwolf
S
difference between standard vs max continous discharge vs peak how to establish what is needed for a motor's need
Replies
1
Views
536
neptronix
neptronix
M
3s3p Ridgid 18v Battery Packs for an E-Pocket Bike…safe?
Replies
10
Views
552
Michael86
M
riding_on
(Mis)using a Priority Current range extender: should I expect fire damage in my future?
Replies
12
Views
781
calab
C
c111jp
Samsung 50E vs LG M48 vs "Tesla" (help me choose new battery pack)
2
Replies
26
Views
3,197
c111jp
c111jp
Back
Top