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Discussion Starter · #1 ·
Some of you E.E.s out there help me on this....

Here's the scenario:

The battery alone can supply approx 400hp (less losses) to the wheels. In sport mode, this is increased somewhat.

The Karma drops out of Stealth and auto-starts the generator when the battery is depleted to approx 15%. This extended range mode attempts to recharge the battery to approximately half charge while still supplying max (batt) power on demand.

Now, we know the engine alone can not supply all the power the Karma uses at max output. At max output, the generator has (I believe) about 1/2 the power output of a charged battery.

Presumably, the engineers at Fisker figured that the 15% cut in for the generator would provide enough of a buffer in **ordinary circumstances** (where max battery output is not being called for most of the time) to, on average, allow for recharging to occur.

But, what about extraordinary circumstances, say high performance driving up a long high-grade hill? It would seem to me that it would indeed be possible to completely exhaust the battery under this scenario (and let's hope that Fisker built a protection circuit in so we don't hear about Tesla style "bricking"), in which case the maximum electrical power being supplied would be from the generator alone.

Or, about "half a Karma"....

Do I have this right? Anyone know what would happen?

Here in the flatlands of Florida, I can't imagine this ever occurring but in certain mountainous areas, with spirited driving, it seems entirely possible to me....
 

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Those of us who plan to drive the car to Tahoe (in the summer, not the winter!) are most interested in the answer....
 

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FredFriendly said:
Some of you E.E.s out there help me on this....
I am not an EE, but I think I may be able handle this one.

Here's the scenario:

The battery alone can supply approx 400hp (less losses) to the wheels. In sport mode, this is increased somewhat.
That's not correct. The battery can supply about 200 HP. You need both the battery AND the generator working together to get to the 400HP total.

The Karma drops out of Stealth and auto-starts the generator when the battery is depleted to approx 15%. This extended range mode attempts to recharge the battery to approximately half charge while still supplying max (batt) power on demand.
Also not correct. In Stealth mode, when the generator comes on, the generator is only replenishing the amount of power used to move the car from the battery. In other words, the generator keeps the battery at 15% but does not charge it beyond that. It only supplies up to 200HP to move the car.

Now, we know the engine alone can not supply all the power the Karma uses at max output. At max output, the generator has (I believe) about 1/2 the power output of a charged battery.
If by "all the power Karma uses at max output" you mean the full 403HP peak rating of the inverters and the motors, you are correct. The engine can provide approximately 200 HP equivalent of electric power.

Presumably, the engineers at Fisker figured that the 15% cut in for the generator would provide enough of a buffer in **ordinary circumstances** (where max battery output is not being called for most of the time) to, on average, allow for recharging to occur.
I am not sure what you mean here exactly, but to be precise, the car is not diverting 15% power to the battery. The power to drive the car comes out of the battery and then the generator recharges the battery back up to 15%. You can think of it as borrowing power to move the car out of the battery and then paying it back with the generator.

But, what about extraordinary circumstances, say high performance driving up a long high-grade hill? It would seem to me that it would indeed be possible to completely exhaust the battery under this scenario (and let's hope that Fisker built a protection circuit in so we don't hear about Tesla style "bricking"), in which case the maximum electrical power being supplied would be from the generator alone.
Or, about "half a Karma"....
The Karma does not allow you to completely exhaust the battery below 15% under any kind of driving conditions. As we discussed above, when the battery is down to 15%, the only power you have available to you is what the generator can supply, which is around 200HP. This is going to limit how high your "high performance" driving would be, but the battery reserve will stay constant until you plug the car in and charge it back up again.

Do I have this right? Anyone know what would happen?

Here in the flatlands of Florida, I can't imagine this ever occurring but in certain mountainous areas, with spirited driving, it seems entirely possible to me....
So here we get to the heart of the question. I live in San Francisco and I climb up steep hills in the city all the time. In fact, my house is located about 500 Feet above sea level half way up one of the highest peaks in the city, and I have to climb up a fairly steep grade every day to come home. The Karma has absolutely no problem climbing the grade on battery alone, or on generator alone. I have not tried doing it at highway speeds, obviously, but at fast city speeds, around 40-45 MPH, the Karma climbs like an electric mountain goat without missing a beat. Admittedly, I have not tried to climb up I-80 to Tahoe in the Karma, but our other car, MB ML-350 Blue Tech weighs about as much as the Karma and has a 220 HP Diesel Engine, and when we drive up to Tahoe in that car, we get nowhere near redlining the engine. I would expect the Karma to behave similarly under those conditions.

Hope this helped.
 

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Skibum said:
Those of us who plan to drive the car to Tahoe (in the summer, not the winter!) are most interested in the answer....
I have a timeshare at the Ridge at Lake Tahoe and I was planning on taking my Karma there this summer and maybe even continuing on down to Reno, NV. Should be interesting to see what Hill mode can do on my return to the Bay Area. Obviously I will be on mostly engine power on the way up.
 

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Discussion Starter · #5 ·
I'm finding it hard to believe that Stealth mode is supplying a maximum of 200 hp to those rear wheels.

According to Motor Trend, the 2012 Camry Hybrid, a car weighing 40% less than our Karma, with a 200hp powerplant, accelerates 0-60 in 7.2 seconds, not much faster than our Karma's in Stealth mode. If I remember my physics correctly, acceleration (leaving aside aerodynamics, rolling efficiency, etc.) for a given power input, is linear to mass. The Camry, at 60% of the weight of the Karma, should accelerate nearly twice as fast. Clearly it doesn't.

I can't find any sources stating maximum battery only power output. Can you point me to this?
 

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FredFriendly said:
I'm finding it hard to believe that Stealth mode is supplying a maximum of 200 hp to those rear wheels.

According to Motor Trend, the 2012 Camry Hybrid, a car weighing 40% less than our Karma, with a 200hp powerplant, accelerates 0-60 in 7.2 seconds, not much faster than our Karma's in Stealth mode. If I remember my physics correctly, acceleration (leaving aside aerodynamics, rolling efficiency, etc.) for a given power input, is linear to mass. The Camry, at 60% of the weight of the Karma, should accelerate nearly twice as fast. Clearly it doesn't.

I can't find any sources stating maximum battery only power output. Can you point me to this?
You can't just use raw horsepower numbers, because a motor (especially a traditional gasoline engine) does not put out its maximum power at all speeds. There is a tradeoff of torque and power curves, and for gasoline engines it tends to be pretty terrible (hence the need for many gears in the transmission).

Electric motors are much better. An ideal electric motor has infinite torque at zero RPM, and zero torque at infinite RPM, and hence a totally flat power "curve". Of course ideal electric motors do not exist but you're still way better off with electric than gasoline, hence the Karma's relative-better performance (after adjusting for weight).
 

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I have to climb two mountain passes to make it home from Denver, both peak at around 11,000 feet, and Karma has had no issues whatsoever. In fact, coming down each pass I gain about 7-8 miles of battery range using Hill 2. I keep her in sport mode both ways, but next time I'll try putting her into stealth on the way down and see what happens.
 

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In theory, YES it is possible to wind up in a power limited mode. Heres how:

the rear electric motors are 150kw each, and in stealth mode max power is 200kw. The ICE generator is 175kw output, and sport mode delivers 300kw max. HOWEVER max is not the same as sustained, and in order to maintane the battery health, it will only allow so much to be drawn out at maximum rate, before cutting it back. Suffice to say, your probably using not much more than 50kw or so to maintane speed on flat ground, so if on a hill the car dips below 15%, the generator has reserve capacity.

now there is only one car on the market with a setup similar to the Karma, and thats the Volt. In the volt, you have a 111kw traction motor and a 55kw generator, and GM has found that certain grades (CO's I70 being the most difficult) if entered in range extended mode will drop the battery below their safe threshold of 35kw. the solution was a mountain mode that if activated 20-25 minutes in advance could bring the battery charge level upto 40% before climbing the grade. If this was not used, and the battery fell below 35kw, the driver gets a warning message and the output drops, effectivly limiting the car to about 45mph while the generator brings the battery back upto 35kw.

Now the Karma is only about 1000lbs heavier than the Volt, but it's generator is three times the size, i think it will be less likley to run into the situation, but doing 125mph up a long grade could very well drop the car below its safe threshold and trigger a power limiting mode.
 

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This may be slightly off topic but a question of extended performance. I am considering entering the Karma in the Silver State Classic (see SSCC.US) in May. It is a 90 mile timed event on public HY318 in Nevada.
I've entered ICE cars in the 150 mph class several times but would enter the Karma most likely in the 110 or 120 mph class.
Question: is the Karma capable of sustained running in 110 - 120 mph range for 90 miles?
 

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110mph may be a doable thing, though i am not positive. if i get the opertunity to ask, i will. my concern for the event however though is your 15mph buffer in the top speed to work with to bring the average speed inline however.
 

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I know this is an old thread, but I've had a lot of mountain driving experience back up and down the various Tahoe mountain roads.

On a recent drive, I saw a red karma in reno last week, near Mt Rose Highway, and was wondering if it was marswill.

I have taken the Fisker up from Reno to Incline Village on Mt Rose Highway (http://en.wikipedia.org/wiki/Nevada_State_Route_431) . This road goes from about 4500 feet elevation up the 8900 in about 20 miles. In other words, a pretty serious grade for a pronounced period of time. Going down the grade, I pick up about 10 miles of range alternating between light breaking and Hill modes.

I have had no problem in stealth mode, with or without battery. The best part is how well the car handles on the hairpin turns.

Coming from El Dorado Hills, up to Tahoe, on 1-80, I would deplete my electric range by the time I got to Auburn, and would be on generator/ICE for an hour or so, and have had no problem sustaining 60-75mph up the hill. The main issue is not zipping along too fast.

Since I am used to being in stealth with battery power 75% of the time, the only issue I have is I dislike the sound of the ICE & turbo. But, turning up the satellite radio seems to solve that issue.

There is a clipper plug in in Truckee, near a park, and in walking distance to some restaurants. When I came back after an hour, I saw a Tesla driver reading his book and patiently waiting. I felt both good & bad. Good that I got a few more miles of range, that pretty much let me get over the peak to where I could coast using almost no gas... but bad because I really didn't need the charge with the onboard ICE+Generator... the Tesla guy had no choice... He had to wait to get a charge, because he couldn't make it without it. (Which is why I like the Fisker better than Tesla).
 

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There is a clipper plug in in Truckee, near a park, and in walking distance to some restaurants. When I came back after an hour, I saw a Tesla driver reading his book and patiently waiting. I felt both good & bad. Good that I got a few more miles of range, that pretty much let me get over the peak to where I could coast using almost no gas... but bad because I really didn't need the charge with the onboard ICE+Generator... the Tesla guy had no choice... He had to wait to get a charge, because he couldn't make it without it. (Which is why I like the Fisker better than Tesla).
The Model S driver was most likely trying to add enough range to get to the Folsom supercharger for his return to the Bay Area. While the supercharger network is great, they can't put them at destinations/cities because they will be tied up by locals getting free charges. So Model S owners have to find other (slower) places to charge for local driving at their destination or getting enough range to reach the first supercharger on their return trip.
 

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I know this is an old thread, but I've had a lot of mountain driving experience back up and down the various Tahoe mountain roads.

On a recent drive, I saw a red karma in reno last week, near Mt Rose Highway, and was wondering if it was marswill.
It wasn't me this time on the Mt Rose Highway although I have done that route in the past. So far I have covered these Sierra passes with my Karma:

Pass Name Highway Elevation
Carson Pass SR 88 8,650
Daggett Pass/Kingsbury SR 207 7,334
Donner Pass I-80 7,085
Ebbetts Pass SR 4 8,730
Echo Summit I-50 7,382
Luther Pass SR 89 7,735
Mount Rose Summit SR 431 8,911
Pacific Grade Summit SR 4 8,050
Sonora Pass SR 108 9,624
Spooner Summit I-50 7,150
Tioga Pass SR 120 9,943

In addition I have been to Lick Observatory on top of Mt Hamilton.
 

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Now is a good time to repost this photo...
 
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