I've noticed the same thing on my car, CAC is 149.2 but only get just over 180Kw on full power. Considering checking the cable contacts are tight enough and not getting loose
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Losing maximum power in Roadster Sport - due to battery aging?
- Thread starter Marius
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- Performance Roadster
I've noticed the same thing on my car, CAC is 149.2 but only get just over 180Kw on full power. Considering checking the cable contacts are tight enough and not getting loose
Mine was a flase alarm. I had low tyre pressures. Pumped them up and it's the full 200 again. Maybe the system was detecting too much slip or poor rolling resistance. Who knows. All good now.
Kerios
Member
My CAC sitting at 135, with almost 73k (miles) on the clock. Still getting full 200kw delivery abet the PEM is new as of Sept 2016 (or re manufactured, hard to tell). Actually CAC improved over the summer which was interesting, went up from 134.5 to 135.7, maybe an error.
CAC will vary over the course of the year, due to temperature and other effects. It's only an estimate, too, so will drift a bit over time. Most accurate estimate will be after a full range charge after a nearly-complete discharge, but since that's a bit of a stress on the battery, it's best not to get too fixated on the exact number.
I have a 1.5, CAC 135, 37,516 miles. With the Motor and PEM on the 3rd blue bar, and the battery on the 2nd blue bar, I get 185 kw. I didn't think to use OVMS to get the exact temps. D'oh! However, my tires are each about 4 lbs low. I did several 0 to 60 sprints and the logs show each one was between 4 and 5 seconds depending on when during the second the throttle hit 100%.
Strange deduction as the bms would not be limiting the wattage, the PEM would be incharge of supplying the motor with power, even a pack with 50% charge theoretically can still produce 200Kw. The only thing limiting the power is the PEM surely?
I think the power limit is due to the battery - the PEM will not allow the voltage to drop below a certain voltage per cell to prevent damage.
How much current can be drawn (so hence the power) before that limit is hit depends on state of charge, temperature and internal resistance of the cell (which may rise with cell age).
The difference in voltage in cellular level will only be .4 at worst though?
If they were SLA’s then possible due to the Peukert effect, or cells being drawn at 5+ C but the some fact is the cell draw is much lower, the next comparable cell with a ton of data is arguably the NCR18650B which I built many battery packs for EV’s with. The ability to draw 10 C at the lower voltages (3.6V) was comparable to fully charged (4.15V) the resistance could be going up but then your creating a toast rack in your batterypack and temps would get very hot, very fast. Are the temps climbing dramatically in the battery packs? No one has reported that, just a lower power delivery from the motor which is controlled via the PEM. If however a sheet is dead lowering the available amount of parallel groups that would show a significant power drop across the entire voltage range.
If they were SLA’s then possible due to the Peukert effect, or cells being drawn at 5+ C but the some fact is the cell draw is much lower, the next comparable cell with a ton of data is arguably the NCR18650B which I built many battery packs for EV’s with. The ability to draw 10 C at the lower voltages (3.6V) was comparable to fully charged (4.15V) the resistance could be going up but then your creating a toast rack in your batterypack and temps would get very hot, very fast. Are the temps climbing dramatically in the battery packs? No one has reported that, just a lower power delivery from the motor which is controlled via the PEM. If however a sheet is dead lowering the available amount of parallel groups that would show a significant power drop across the entire voltage range.
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Also, It was only the 2.5 sport drawing over 185 kW suggesting the power is limited by the PEM as there was no battery change or cell change.
How much data is available from the logs, does it give you data to brick level or sheet level? That would answer a lot of the questions.
then you need to see if you have all parallel groups working evenly by pulling the logs straight after a charge and again once you run down to 40-50%. If a brick is discharging quickly then you need to replace it as the available capacity of the battery is only as good as a each parallel group. Even a low capacity battery should reach full output unless there is a brick/sheet out or the PEM is restricting due internal breakdown.
Peter.h
Since 2017
I know this thread has been quiet for a while ... But recently I have noticed the same on my roadster. @Marius - did you get to the bottom of this?
It's a 2.5 Sport with 20k miles and CAC of 146 (ideal range 171-174). I can tell from the logs the SOC hit zero a couple of times (once for almost 2 weeks) while the car with with the dealer before I bought it. So there may be some battery degradation from that beyond what the miles would suggest.
Recently I noticed that the wattage gauge only gets up about 180kW on full acceleration.
I will do a run after a full charge and check the max amp reading and the HP/Torque screen. Temps are in the 70s here in LA today so should be perfect conditions.
It's a 2.5 Sport with 20k miles and CAC of 146 (ideal range 171-174). I can tell from the logs the SOC hit zero a couple of times (once for almost 2 weeks) while the car with with the dealer before I bought it. So there may be some battery degradation from that beyond what the miles would suggest.
Recently I noticed that the wattage gauge only gets up about 180kW on full acceleration.
I will do a run after a full charge and check the max amp reading and the HP/Torque screen. Temps are in the 70s here in LA today so should be perfect conditions.
dhrivnak
Active Member
On my Roadster both my HP and 1/4 mile times dropped a bit after 8 years with the original batteries. I got all that back plus some
with the 3.0 upgrade. So it may be a "feature" of lithium batteries and aging.
My CAC is now on 114, so I have difficulty to reach more than 150 kW.
I think explanation is just the fact that due to aging voltage drops more when hitting the throttle.
Power is current multiplied with voltage. So dropping voltage makes a drop in power.
Peter.h
Since 2017
Thank you Marius and dhrivnak for the insights - that makes sense.
Fortunately it seems my pack hasn't degraded as much. I experimented yesterday (roughly 70% SOC) and got the full 200kW (620-650 Amps during acceleration - which would give nominally 234kW = 625 A x 375 V)
I saw around 240 HP around 293 ftlb (397 Nm) in the VDS
I believe torque is pretty much spot on, power is a bit below spec but I assume that's because I kept it at relatively low RPM (below 60 mph)
Temps all went up a little bit stayed in the blue.
I wonder whether power stays being throttled around 50% SOC ... That seems consistent with my experience?
dhrivnak
Active Member
For some detailed numbers in the 1/4 mile when my car was relatively new I ran 13.1 and 101 mph. My CAC had dropped to 141 after 6 years and I was running 13.3 and 98 mph. With the 3.0 battery I now run 13.0 and 105 mph. So yes I think performance drops as CAC drops.
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