Maximum power for Karma

3187 Views 7 Replies 4 Participants Last post by Fabulist, Jun 27, 2013

SoCalGuy

Discussion Starter · Jun 19, 2013

So we all know we're not getting the advertised 403 hp from our Karmas. I was trying to figure out/guess what is the max power we're getting in Sport mode (and Stealth).

Fact 1: We know the Ecotech 4-cyl range extender has been limited to peak power output of 170hp (Fisker press released this fact during the Texas fires), despite the rated maximum power output of the turbocharged Ecotec being 260hp.

Fact 2: The Tesla Model S Performance has a rated power output of 416hp, weighs 4700lbs and does 0-60mph in 3.8-3.9s (as tested, official rating is 4.2s). The Karma weighs just 600lbs more and has only 13 fewer horses, yet is rated at 6.3s and tested at about 5.9-6.0s. Surely those differences can't account for 2 full seconds of slower acceleration

Fact 3: In the power system screen, under hard acceleration, I think the most I've ever seen is 170 kw of consumption (which is about 228 hp).

Fact 4: A video on YouTube has a Karma hooked up to a dyno and it clocks in at 230 hp (

)

Could it be that even in Sport mode, we're only getting 230hp worth of power?

We know that the two electric motors in the RDM are rated for 300kw total (402 hp) and that the A123 battery allows for peak bursts of power of 50C and sustained power of 10C (1,333hp and 267 hp respectively). We also know that the current Sport mode operation combines power borrowed from battery reserves to supplement the 170hp it gets from the Ecotec genset. I just wonder why the engineers at FA don't use the battery as a buffer to unleash more power that the genset could pay back later so we could get more power/acceleration. Wonder if it has to do with cooling of the inverters/motors or battery. Curious if any ex-FA folks could shed light.

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ffcars

· #2 · Jun 19, 2013

Wow, that's disappointing. That's about 280HP at the "crank" which is far from the advertised 400HP.

If they were still going to be in business, that would be another bog lawsuit. Look how many companies have had to pay big bucks for over advertising HP. Ford Mustang Cobra's, Mazda had one,

Seeing motors and splines frying, I doubt the car can handle more power.

Bill

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Antonin

· #3 · Jun 19, 2013

I cannot imagine that FA has released figures that do not correlate with reality, more precisely are off by so much. In next two weeks I will put the car on the dyno and will post results. Does anybody know what is Karma's final gear ratio to wheel ratio? We need to match wheelspeed to theoretical engine speed... I think this is the tricky part where mistakes can be made... dynos calculate torque against engine rpm and power is just equation of torque and engine's rpm... since we are searching for "equivalency" with ICE engine, we probably need to make some assumptions about final gear ratio... another possibility is to measure torque at the wheel and compare it to another car's torque at the wheel, but that will not give us engine torque...

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SoCalGuy

Discussion Starter · #4 · Jun 19, 2013

Antonin said:
I cannot imagine that FA has released figures that do not correlate with reality, more precisely are off by so much. In next two weeks I will put the car on the dyno and will post results. Does anybody know what is Karma's final gear ratio to wheel ratio? We need to match wheelspeed to theoretical engine speed... I think this is the tricky part where mistakes can be made... dynos calculate torque against engine rpm and power is just equation of torque and engine's rpm... since we are searching for "equivalency" with ICE engine, we probably need to make some assumptions about final gear ratio... another possibility is to measure torque at the wheel and compare it to another car's torque at the wheel, but that will not give us engine torque...

That would be cool if you can test it out.

But the energy flow screen on the System tab on the Karma never shows anything even approaching 300kw of power consumption... like I said, max I've seen is around 160kw or so.

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Fabulist

· #5 · Jun 19, 2013

SoCalGuy said:
Could it be that even in Sport mode, we're only getting 230hp worth of power?

We know that the two electric motors in the RDM are rated for 300kw total (402 hp) and that the A123 battery allows for peak bursts of power of 50C and sustained power of 10C (1,333hp and 267 hp respectively). We also know that the current Sport mode operation combines power borrowed from battery reserves to supplement the 170hp it gets from the Ecotec genset. I just wonder why the engineers at FA don't use the battery as a buffer to unleash more power that the genset could pay back later so we could get more power/acceleration. Wonder if it has to do with cooling of the inverters/motors or battery. Curious if any ex-FA folks could shed light.

One major unknown in this case is the battery's SOC. As I understand it, the full battery+Genset power is only available in Sport mode when the battery has more than 50% charge (26+ Miles indicated range). If the battery is discharged more than 50%, Sport mode would just keep the battery at approximately the current level and would not use it for additional power so you will never get the full 300 KW.

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SoCalGuy

Discussion Starter · #6 · Jun 19, 2013

Fabulist said:
One major unknown in this case is the battery's SOC. As I understand it, the full battery+Genset power is only available in Sport mode when the battery has more than 50% charge (26+ Miles indicated range). If the battery is discharged more than 50%, Sport mode would just keep the battery at approximately the current level and would not use it for additional power so you will never get the full 300 KW.

I had suspected this as well but forgot to test this using the Energy Flow screen when I was last in my Karma - perhaps someone can try that today and see if that makes a difference. Funny that I asked this question of Fisker folks a few months ago and they maintained that Sport mode produces the same power regardless of the battery's SOC (provided there was at least the '15% reserve' avail i.e. 0 miles EV range).

Intuitively, a short burst of power for a few secs wouldn't require more than 0.5 kwh (300 kw x 6.0 secs = 0.5 kwh) which would be less than the 3 kwh 'reserve' power that the Karma maintains even when it has 0 miles of electric range.

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SoCalGuy

Discussion Starter · #7 · Jun 27, 2013

Some more info on A123 battery:

http://www.a123systems.com/lithium-iron-phosphate-battery.htm

anophosphate is a positive electrode material of remarkable rate capability, critical to high power systems. Our high power products are able to pulse at discharge rates as high as 100C and deliver superior power by weight or volume in a cost effective solution. With their low impedance and thermally conductive design, A123 high power cells can be continuously discharged at a 35C rate, a marked improvement over other rechargeable battery alternatives, and have consistent power over wide state of charge (SOC) range. - See more at: http://www.a123systems.com/lithium-iron-phosphate-battery.htm#sthash.pyzqAEni.dpuf

Also, looks like their next gen Nanophosphate EXT increases power output by 20-30% and can operate in much wider temperature band, leading to reduced thermal management systems (air cooling maybe?) and longer battery life. Would be cool to find out when A123 will be releasing a Karma format battery pack we can swap with our batts in a couple years...

http://www.a123systems.com/lithium-ion-battery-technology.htm

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Fabulist

· #8 · Jun 27, 2013

SoCalGuy said:
I had suspected this as well but forgot to test this using the Energy Flow screen when I was last in my Karma - perhaps someone can try that today and see if that makes a difference. Funny that I asked this question of Fisker folks a few months ago and they maintained that Sport mode produces the same power regardless of the battery's SOC (provided there was at least the '15% reserve' avail i.e. 0 miles EV range).

Intuitively, a short burst of power for a few secs wouldn't require more than 0.5 kwh (300 kw x 6.0 secs = 0.5 kwh) which would be less than the 3 kwh 'reserve' power that the Karma maintains even when it has 0 miles of electric range.

From my observation, the energy flow screen is not very helpful in this situation because it appears to show flow into, and out of, the battery, not the total energy flow in the system. I believe this is the case because when the ICE is running, I have observed the flow meter to go positive (recharge) even under heavy acceleration with the ICE running at higher RPMs. If the meter was showing total energy flow, it would have to show a lot of power coming from the Genset in that situation.

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