formula

[TONE]

hi

is there an approx formula for working out the
motor size
motor voltage
battery capacity

if vehicle is 700kg
maximum speed 120kph
distance on a charge 100km

or say you have an idea is there a simple formula where you can put in say motor size and vehicle weight and come up with the max speed etc.

and how is wind and friction losses calculated in simple terms

cheers
tone

[antiscab]

hi Tone,

what vehicle are you planning on converting?
here are a few shortcuts to wokring some things out:
battery capacity: you need 2kwh for every L per 100km the car used when it ran on petrol.
battery voltage: use 144v, unless you have access to a higher voltage controller, or are going AC.
motor voltage, ditto.
motor size: make sure the motor can put out in kw, the kwh need/100km continuously at 100kmh at least one gear.

max speed is where wind resistance = developed power.
wind loss = drag coefficient (look this up) * frontal area (car width * height) * speed^3 (in ms-1) * air density (just use 1.225).

have a look through both this forum archives, the EVDL archives, and the EVALBUM for more ideas.

Matt

PS welcome to the forum

[Richo]

Hi Tone,

Welocme.
If you are in WA the next AEVA meeting is this Wed night.
See the Perth section for more details.

A 700kg vehicle is quite light.
There are many motors with different sizes and different outputs.
So just selecting a motor size is not much help.
It also makes it harder as there are AC motors, DC motors and permanent magnet motors.

You could try an on-line calculator such as this.

Typically a car may use say 150Wh/km.
So if you wanted 100km range it is 100km x 150Wh/km = 1500Wh useable battery capacity.
But depending on what battery you use the actual capacity will be different as you should not use the entire capacity as it can damage them.

The top speed and overall performance is determined by the size of the motor.
Typically you may need 10-15kW of mechnical power to stay at 120km/hr.

For existing cars the aerodynamics is sometimes published and so can be dropped into formulas to show the forces on a car at a given speed.

So it's not so simple and takes multiple formulas to work it out.

You could give us more info and let the AVEA members help you work it out.

[TONE]

hi

thanks for the replies.
i have been to a couple of the meetings and will be going to the next one .
i would like to build a three wheeled car (2 at front 1 rear)from scratch .i would like to run ac but pricey.
would like to run two dc brushless motors (mars)but i think these would be to small .
would like to keep the voltage has low has possible but still have reasonable acceleration

cheers

[Richo]

Just remember that the range is determined by total Wh.
So it doesn't matter too much if you have high voltage/low current or low voltage/high current.
As long as you can get the appropriate sized battery to get the total Wh.


MMMmmm.
two mars on 700kg may be a bit light.
We were looking at BLDC motors from China in a different post.
These might be more the size you need.

Industrial AC you would need prob 11kW motor.

[TONE]

thanks

neat pic
bldc from china how much more info

cheers
tone

[Richo]

viewtopic.php?t=505&start=3
read pages 3-5 I think has most of the info.

[Richo]

What do you think is reasonable acceleration?
Do you have a 0-100km/hr goal you would like to achieve?

[TONE]

0-100 10sec

[Richo]

Had a quick look for Industrial motors.
Western Electric have 11kW in Cast iron and Ali in a 132 frame.
That would pump out about 200Nm peak.

If you want too keep voltage low then the Series DC motors would be suitable as well.

[TONE]

i will check it out
sounds like bldc is the way i would like to go, can regen too

cheers

[Richo]

For 0-100 in 10 sec 11kW industrial may not quite make it but would be close.
Hard to say without the aerodynamic data.
The 15kW motors are usually in a 160 frame and are quite a bit heavier.

Probably a bit of a catch 22.
You want to design the whole car before building.
But can't determine motor size properly until the car is built.
Computer simulated aerodynamic modelling is out of my scope.

The BLDC on the other thread a BLT15/37-2500/216 would be close but after asking prices they may not be available yet.
The BLT22/55-2500/312 should do it.

Matt any suggestions on an appropriate sized series DC?

[antiscab]

hi Tone,

is the 700kg the final weight?
or the weight of the vehicle without any EV components in it?
or the weight without any ICE components removed.

what is your definition of low voltage?
what is the reasoning behind it? i normally suggest DC conversions to be no lower than 144v.
Its not that lower voltages wouldn't work, the performance just wouldn't be as good at speed, even if the max power of the 144v setup was the same as that of a lower voltage setup.
If you intend to go to AC at a later date and want to invest in lithium now, i would suggest 300v.
If you intend to go AC now, i would suggest 600v.

100kmh for 700kg is 270kj.
to get there from 0 in 10 sec requires an average of 27kw.
from here you calculate the wind resistance at 100, and add that to the 27kw. (actually thats wrong, but its wrong in the conservative direction, mathematicaly far simpler than doing it properly, and gives a decent degree of error margin).

so you need 37kw at the wheels (since 10kw is around the going rate).
that means you need batteries and a controller that can put out around 50kw, average.

now a few more questions before i go ahead and suggest a motor:
do you already have a gearbox? if yes, a warp 9 would probably be fine.
we would need to know its gear ratios, and your wheel sizes though.

If not, then you could consider a direct drive setup (you need a more powerful, more expensive controller for this) but if you don't already have a gearbox it should work out the same cost wise, unless you get a good deal on a gear box.
again, we would need to know the ratio on your differential.

luckily you are in Perth, theres a rumour floating around that a good chunk of the last zilla controllers are heading this way:)

Matt

[TONE]

hi

thanks for your info

700kg is the flnal weight of car complete
no gearbox ,chain drive to rear wheel ,ratio adjustable (2.5:1-3.5:1 sprockets) size of wheel not determined yet (215-60-15)

if you use high voltage don't you need more batteries, more weight ,more expense, more expense on battery control

cheers

[antiscab]

Hi Tone,

the weight in batteries is proportional to energy stored.
20kwh at 144v will weigh the same as 20kwh at 600v.
The total weight in copper needed for the wiring is also related to the amount of power you need to transmit.
halving the voltage will need half the interconnects, and thus half the wire by length.
however, to retain the same power through-put you need twice the wire size, and thus the same weight.

battery control also doesn't come any cheaper. Larger cells need more powerful balancing units than smaller ones.

again, its not that a lower voltage setup wouldn't work, its just we need to make sure the assumptions behind your decisions are accurate.

a thought does occur however, perhaps Ian could answer this one:
whats the max speed an mars brushless can do?

you might be able to use a 72v system and 3xmars motors, one for each wheel, and 3 kelly brushless contollers. combined system output would be around 60hp peak.

Matt

[TONE]

hi

i was originally going to use two mars motors on the rear wheel

i would love to have 3 wheel drive but this would be to had to set up a much more expensive.

cheers

[Gow864]

The nars brushless does 70rpm/VDC, not sure what the motor maxes out at though

[Gow864]

TONE

Do you have pics of your trike? I've been dreaming of a "can-am" style trike (two seat wide) and would love to know either where you got yours from, or how you're going to build it.

Cheers,
Gow.

[Richo]

I was just in Freo and saw one of those 3-wheel trikes for hire.
Although it would be scary doing 100km/hr in one of those!

[TONE]

two seater side by side
double a arm front suspension
4130 cds frame ,rollcage
swingarm rear susp
fibre glass body

[bga]

I've been doing a small survey-

Western Electric has the best torque (226Nm) of my set in the 11KW range.
The aluminuim version is relatively heavy at 107Kg compared to A similar, but less torquey 11KW Crompton Parkinson.

I note that the CP motors have a very efficient range (92%+) and have
more torque in the larger sizes than do WE or ABB:
11kW   160 short frame 85Kg, 207Nm
15kW   160 Long frame   95Kg, 384Nm (Very good, but am I correct?)
18.5kW 180 Short frame 118Kg, 414Nm (Not so good)
22kW   180 Long frame 126Kg, 548Nm (should be able to break something)

The next questions:
Can we get them and, whats's the damage?

[TONE]

thanks for your comments

they are heavy
a warp9 weighs 70kg i thought that was heavy
an advance 7" weighs 40kg 70hp peak

cheers

[Richo]

Most people won't sell ali above a 132 frame.

I have asked WE about the 11kW Ali and they don't sell it anymore even though it is still on their website.(MEPS regulation)

Do you have a link for the CP motors?

The 548Nm ABB they won't sell (MEPS again)

Here are some typical prices:
7.5kW Ali $1200
11kW Cast Iron $900
22kW Cast Iron $1800
22kW Ali $3000

[a4x4kiwi]

If you are looking for an aluminium framed motor, you could try a used ASEA one. Mine was $400 from M&E equipment in Sydney.

They had a few 15kw units when I was there.

Here are the specs of the relevant 4 pole units.



Also see my blog for the name plate data.

[acmotor]

Hey that 11kW ASEA is the one in red suzi. Note 3.2 Tb/Tn.
1980's ASEA made in Melbourne. Works fine.