Power output question...

Website · Post by **htial** » Tue, 25 Nov 2008, 06:17

So I'm still learning and trying to work out what would be the best way to go with a project...

Most likely I'll be going with a Skyline as my base... ...As I'm a huge Skyline fan... ...('09 Nissan GT-R Electric? I WISH!

)...   ...I love the performance of my current Skyline and really think that besides getting the weight of the batteries placed right to keep it balanced...   ...acceleration would be the only other difference...   ...Oh...   ...and range (around 100km)...

I really don't know how power is measured for electric motors...   ...But I'm sure comparing Power Curves from a Dyno run at the wheels between a fuel car and an electric car would be a fair way of doing it...

So below is the dyno run that my Skyline did earlier this year...   ...it isn't much compared to other Skylines out there...   ...but it is my daily driver that I use for work and want to replace with an electric version...

I'd also be interested in seeing what people think about how I would go about reproducing a power curve like this for an electric Skyline...

I hope I don't sound like too much of a noob and haven't placed this in the wrong Forum area...

- - Laith...

Post by **woody** » Tue, 25 Nov 2008, 07:11

Hi Laith,

the peak kW of a petrol engine is the big number that people compare. Kind of like the megapixels in the camera world, or the GHz for computers.

As with computers and cameras, that number isn't the only important thing. It's kind of like comparing drinks by percentage alcohol - you end up deciding that metho is the way to go.

With electric motors, the kW rating is the all day, everyday, in a hot factory rating. i.e. an 11kW motor can do 11kW all day everyday for 40 years with only bearing grease + electrons.

For short periods, it will do 5 times that or more.

If you want an EV which has 148kW peak, you could get a danfoss 5152 110kW high overload AC VFD, an ABB 30kW HO induction motor, rewind it for 230V, and you're putting 158.7 kW on the road, doing 15 second quarters.

I guess you're looking at about $30-40K for new bits to do that

With the right contacts, or some luck on ebay, you might get that down to $10K.

The power curve looks a bit different, a dead straight line from zero at rest to 165 @ 2800rpm, then a shallow curve dropping off to 100kW at 4400 rpm.

There's probably a DC solution for about $10-15K too which someone else might detail for you, probably a Kostov + Zilla 2K or dual warp 9s.

White Zombie has Siamese warp 8s with a Zilla and does 11s quarters, which would mean 200kW + I'm guessing, but his car is about half the weight of an R33 skyline.

If you are on a budget, you could start with an R31 pintara, which are basically free, and don't weigh much

Add $50 for skyline tail lights, and you're away

You won't need 150kW to get a buzz from an R31, probably 90kW is heaps. You could get away with 18.5kW motor + a Danfoss 5102 (75kW) which puts 93kW on the ground on the way to 16.5sec quarter mile.

Anyway, I currently drive a '94 V6 commode which is faster than anyone could possibly need (0-100 in 9.3), but my favourite cortina is heaps of fun despite glacial performance (0-100 in 26) since I've put most of it together myself, which I think is most of the fun of an EV anyway.

cheers,
Woody

Post by **zeva** » Tue, 25 Nov 2008, 07:51

woody wrote: There's probably a DC solution for about $10-15K too which someone else might detail for you, probably a Kostov + Zilla 2K or dual warp 9s.

KOSTOV?! *cough splutter* nobody uses those anymore.. (Hi Rob

)

OK in all seriousness.. Dual Warp 9s is probably overkill for any sort of daily driver, here's an example: Mike Willmon's Crazy Horse. But you could look at a single Warp 11 with a 1000A controller & high power battery pack.. should give pretty comparable performance to your RB25.

Website · Post by **htial** » Wed, 26 Nov 2008, 06:35

Hay Woody...
Thanks for your reply...
I didn't fully understand how power was rated for electric motors...   ...but you've cleared that up heaps...
You've also given me a heap to think about...   ...and lots of new words to learn...   ...and a realisation that this isn't going to be cheep to start with...   ...But I know how much I spend on fuel each week driving from client to client each day...   ...and even if I spend $10,000 on batteries and they only last 5 years...   ...I'll be making a huge saving...

The R31 Pintara option sounds like a good idea...   ...Debadge it and most people would know the difference...

Post by **acmotor** » Wed, 26 Nov 2008, 17:54

I'd like to see that dyno graph done in 1st, second, third and fourth on the same chart to compare gearbox/diff efficiency at various speeds.
It would require a dyno that can handle high torque.
Are there any graphs of that sort out there ?

Website · Post by **htial** » Wed, 26 Nov 2008, 18:40

acmotor wrote: I'd like to see that dyno graph done in 1st, second, third and fourth on the same chart to compare gearbox/diff efficiency at various speeds.
It would require a dyno that can handle high torque.
Are there any graphs of that sort out there ?

I don't have any power graphs for any other gears at the moment... ...That one came from a Dyno Drag night where all cars had to run in 4th gear and only the boost pressure and air temp were recorded... ...All other details like tire pressure were assumed to be the same... ...And I think the ramp speed of the dyno was set flat... ...I really can't remember all the details...

As for the dyno being able to handle high torque... ...I'm sure the one that my car was done on could... ...it is a four wheel drive dyno... ...a lot of GT-Rs were getting big numbers that night... ...Highest was around 850kWs...

Post by **Richo** » Thu, 27 Nov 2008, 01:34

A 0-100kph time seems to be what most ppl are after.
This will determine your torque and peak power.
Your top cont speed (100-110kph right!) will determine the cont power from the electric motor.

Yeah I've never seen a dyno plot of other gears - just 4th.
Plus they have dodgey correction factors to get "Engine Power".
Most cars are 1:1 in 4th so there is no correction reqd for the gearbox...
Obviously nothing happens to the power going through the box in 4th...

Post by **acmotor** » Thu, 27 Nov 2008, 03:25

Why obviously ?
1:1 only specifies the gear ratio. The power is still traveling through typically 2 gear wheels in mesh. ????

Post by **Electrocycle** » Thu, 27 Nov 2008, 03:45

usually 4th gear has marginally less loss than the other gears - as the shaft is basically locked together from input to output. There is still parasitic loss from the other gears, but there's less loaded tooth loss.

I've seen dyno runs in multiple gears and the power figure is usually within a couple of percent.

Post by **Richo** » Thu, 27 Nov 2008, 03:58

sorry - the sarcasm is lost
Maybe they should just provide rear wheel power/torque.
Trying to fudge numbers to get "engine" power doesn't seem right.

Unless they tested the engine before hand and got flywheel data.
then everyone used the same petrol, oil, air temp/density, gearbox condition the numbers would be good.
Then you have to rely on the dyno being accurate - not fudged to talk your power up/down depending what they want to sell you.

Bah throw away the dyno plot.

Tell us what you want from the eV?

Post by **Electrocycle** » Thu, 27 Nov 2008, 05:05

most dynos give you power at the wheels, but there are compensations for inertia and air temp / density to improve repeatability of the figures.

The idea is that you could test the car on any day on the same type of dyno and it'll give the same figure.
Generally a dyno dynamics dyno with the right settings will give rear wheel power of exactly what you'd expect assuming 30% drive train loss.

Website · Post by **htial** » Thu, 27 Nov 2008, 06:03

Hay Richo...

I guess I just want to get out of it kinda the same as I do with my current car...   ...Just less carbons...

My current car is my daily driver for work...   ...anything between 50 to 100km a day...   ...sometimes more...   ...Club events...   ...track days...   ...drift and drag on occasion...   ...I guess a kind of all rounder...

But it is still early days...   ...I'm still learning and I think I'm just asking the questions that interest me the most first thing...   ...Then when there is something that puzzles me I'll go in search of that answer...

This time around it was about electric motor power and how it is rated...   ...I've been thinking that how Woody explained the power curve for an electric motor would be at the motor itself...   ...Where if you were to take the power at the wheels (rwkw - rear wheel kW) you'd get a not so straight line because of the gears and diff and so on...

I've had people look at the dyno sheet and tell me to go to this and that place because so and so dynos this way or that...   ...Then I get told by others that such and such is a "happy dyno"...

I by no means want to go straight for huge power numbers...   ...It was more just asking the question in a way that hopefully people could see where I was coming from with my current understanding of power output...

Post by **woody** » Thu, 27 Nov 2008, 07:24

A few late night thoughts from Woody:

1) I reckon diff + gearbox losses are proportional to power - so the lines would be about straight.
2) If I was dynoing my car, I'd be getting the wheel kW.
3) 400m is the great leveller. Everything can do 400m, not everything can do 0-60/100.
Women (47.6s)
Men (43.2s)
1962 Valiant (20s)
Lotus Cortina (17.5s)
VR Commodore V6 (16.8s)
Hotted up Ladas (14.5s)
1972 E49 Charger (14.4s)
New Monaro (13.5s)
White Zombie (11.4s)

cheers,
Woody

Post by **Johny** » Thu, 27 Nov 2008, 14:51

So White Zombie is only 4 times faster over 400m than a woman...

Post by **Goombi** » Thu, 27 Nov 2008, 20:08

Hi Htial,
When you stop stirring everyone with your Dyno stuff, look around for something more practical and achievable like 120volt 8.5 Kw Electric vehicle that will get you to the pub and back

Website · Post by **htial** » Thu, 27 Nov 2008, 21:43

Sorry Goombi,
I don't mean to stir anyone at all.
I guess I just have an idea of what I would like an electric car to do but don't know how to achieve it.
Also, when you say 8.5Kw, I kind of think that isn't enough power to get me out of the drive way. But that's because I'm coming from performance knowledge based on petrol motors.
I'm sure I'll ask more stupid questions in the future, which will get people going again. I just hope that I'll be pointed in the right direction if I do.

Post by **Richo** » Thu, 27 Nov 2008, 22:17

Is your car stock?
Or have you altered it someway to improve the performance?
I agree the 400m would also be a good measure.
I wouldn't mind seeing Zeva's MX5 on the dyno
just for comparison between ICE and eV.

Website · Post by **htial** » Thu, 27 Nov 2008, 22:26

Richo,
My car is stock apart from an exhaust that was done in Japan. The last owner also lowered it with some suspension mods and put a high flow kit in the turbo.
From the factory an R33 GTS25t should have around 130 to 140 rwkw.
I've been searching for an EV dyno run with no luck so far.

Post by **zeva** » Thu, 27 Nov 2008, 22:38

Yah I'll get the MX5 dyno'd sometime.. probably not until after the planned rebuild over summer though. (My last ICE-mobile was a 265rwkw Skyline, and I'm not going to be satisfied until the MX5 feels faster than that

)

It'll be pretty interesting to see what the electric power curve looks like.. I imagine it'll be very different to the typical dinoburner curve. (Probably sees peak power around 2500rpm instead of 5000rpm due to the lower RPM range and more low-end torque)

Website · Post by **htial** » Sat, 15 Aug 2009, 01:40

Sorry for digging up an old thread... ...but...

Zeva... ...Did you end up getting your MX5 dyno'd???...

Post by **EV2Go** » Sat, 15 Aug 2009, 19:15

Had to have a bit of a chuckle to myself people thinking 148rwkw figures are fudged, sorry htail no offence but I would nearly be embarrassed to post a dyno sheet making so little power.
Yeah I know Electrocycle will probably try dig up my bog stock 119rwkw 180sx dyno sheet with factory air cleaner and exhaust still on it, or my aborted on low boost run of 200rwkw (199.7) sheet.
While many on the guy forum think their EVs are quick, many haven’t driven in a seriously quick street car to compare. But having said that you need to compare apples with apples while an electric motor won’t produce the same numbers on the dyno it doesn’t really have to in order to provide the same result.
The massive off line torque compensates a lot while most turbo cars are still getting on boost the EV has already been there and done that. The power drops considerably at higher revs which will result in almost walking pace terminal speed over the quarter mile (100-110mph) as opposed to around 120mph for the same ET.
Zeva also very curious to see what your MX5 put out as it somewhat a template for quicker EVs.

Website · Post by **htial** » Sat, 15 Aug 2009, 19:38

Don't worry about it EV2Go... ...it's my daily and it does the job... ...I'm not that worried about big power with this car...

In the last year since I made this post I've got a bit of s clearer idea of what I want to do with an EV...

Post by **Andrew** » Sat, 15 Aug 2009, 20:06

KW's sells cars, but torque wins races

Post by **Richo** » Sat, 15 Aug 2009, 21:32

EV2Go wrote:While many on the guy forum think their EVs are quick, many haven’t driven in a seriously quick street car to compare

That's a bit of a broad statement.

Also I don't think ZEVA did a dyno before he started upgrades on the MX5.
So I doub't he will be doing one soon

Post by **acmotor** » Sat, 15 Aug 2009, 21:51

Hey, talking of dyno tests, has anyone come across a dyno test on a tesla roadster ?? That would be interesting to see.