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Which Motor?

Posted: Sun, 12 Aug 2018, 08:07
by Mawson
Hi Everyone. I'm converting a 1963 Renault Floride to electric. The car will weigh just under 1,000 kilograms with the battery pack.
I've looked at the HPEVS AC50 motor which they tell me will power the car up hills at highway speed with a 96 volt battery pack. I've also found a Chinese AC motor which is supposed to be equivalent. However, the performance graphs supplied by the manufacturers are presented quite differently and I don't have enough knowledge to make a decision. Can anybody have a look and give me any advise? I would be most grateful

Re: Which Motor?

Posted: Sun, 12 Aug 2018, 08:40
by brendon_m
I've noticed that a lot of Chinese motors use that style of graph and I assume it's done in order to make it harder to compare them to non Chinese "quality" units. I mean who cares about torque vs kW. Just give me the data vs rpm so I can read what's going on

Re: Which Motor?

Posted: Sun, 12 Aug 2018, 10:43
by jonescg
You will definitely need the gearbox - anything under 200 Nm is a bit weak for pushing 1000 kg of car around.

Re: Which Motor?

Posted: Mon, 13 Aug 2018, 13:19
by Richo
Mawson wrote:
Sun, 12 Aug 2018, 08:07
I've also found a Chinese AC motor which is supposed to be equivalent.
Firstly I notice the Chinese motor is a very high spinning motor.
More resembles a large outrunner?!?
At the nominal voltage tested is does 6400RPM!
So to get the claimed power it has to spin much faster.
I probably wouldn't suggest this motor.

Ignoring the high RPM it does have enough torque for a small car using a gearbox.
Do you know what voltage the test was performed at?
brendon_m wrote:
Sun, 12 Aug 2018, 08:40
...Just give me the data vs rpm so I can read what's going on
The graph is for the motor by itself.
The graph you want is for a complete system.
Unfortunately unless you are buying that compete system the data would be limited.
jonescg wrote:
Sun, 12 Aug 2018, 10:43
...anything under 200 Nm is a bit weak for pushing 1000 kg of car around.
So the 700kg Handi at 90Nm with a 2.5x for a 1-2 gear ratio is 225Nm.
So yep that does sound right 1000kg with 200Nm sounds weak.

Re: Which Motor?

Posted: Mon, 13 Aug 2018, 13:20
by Richo
Was there a suggestion that this was supposed to be direct drive?

Re: Which Motor?

Posted: Tue, 14 Aug 2018, 06:43
by Mawson
Thanks for your help guys.
It's difficult to get good information out of China. This motor and controller is only 1/3 the price of the HPEVS but it's not worth anything if it doesn't do the job.
I'll keep looking in the hope that something more suitable comes up. The HPEVS is not available in Perth but I'm sure there's one (or an equivalent) somewhere in Australia.
And yes, I'm keeping the original gearbox and assumed that it would run in 2nd or 3rd. It's very hilly here in Bridgetown and although the car is only going to be used locally I want to have highway speed capability just in case.

Re: Which Motor?

Posted: Tue, 14 Aug 2018, 12:50
by Richo
I Like Bridgetown!
So a motor that has 34kW@5,500RPM and 74Nm@3,500RPM.
Rod is just round the corner - can't you get a Motenergy system off him to do that?

Is the diff really 4.37:1?

Re: Which Motor?

Posted: Wed, 15 Aug 2018, 09:24
by Mawson
Yes, I contacted him. Their motor is too small for a car in a hilly area.
I'm still looking, so any suggestions for alternatives are much appreciated

Re: Which Motor?

Posted: Mon, 17 Sep 2018, 16:42
by francisco.shi
Generally you will have two parameters for a motor:
Torque and power/RPM
You can calculate the power as follows:
p= 2*pi*rpm*t/60
where:
p = power in watts
pi = 3.14...
rpm = motor speed in rpm
t = torque in Nm

Electric motors tend to be a torque machine meaning that the size of the motor depends on the torque they put out. Then the power will depend on how fast you spin them.
For a brushed motor (not a good idea for an electric car imo) the speed is limited by the brushes.
For an ac machine the speed is generally limited by how well balanced the rotor is and how fast it can spin before it flies apart and of course the speed rating of the bearings.
Within limits (under 60krpm for a 2pole motor) you can double the speed without significantly increasing the electrical loses.
The next consideration for how fast you can spin the motor is the back emf (for a permanent magnet motor) or the magnetising current for an induction motor.
So if a motor runs at say 3500rmp with a 100v supply you will need 200v to make it spin at 7000 rpm.

I am currently doing a conversion and I have bought some Chinese pm motors and I am in the process of building the inverter. The motors I have will do 260Nm at 5500 rpm from a 400v battery. If you are not in a big hurry I may be able to help you with the motor/inverter

Re: Which Motor?

Posted: Mon, 17 Sep 2018, 17:04
by francisco.shi
So for the graphs you have the Chinese graph is clear as to what you are getting. What it does not tell you is what voltage you need and you will need this info for choosing the inverter.
The HPEVS graph tells you it runs of 96v but the vertical scales are not clear so you really can not tell for sure what the value is.
For example on the right it says torque and power so not sure if 30 means 30kw or 30Nm.

Re: Which Motor?

Posted: Tue, 18 Sep 2018, 12:26
by Richo
francisco.shi wrote:
Mon, 17 Sep 2018, 17:04
For example on the right it says torque and power so not sure if 30 means 30kw or 30Nm.
Ah its both.
Only the colour of the line makes the distinction between kW and Nm.

Re: Which Motor?

Posted: Tue, 18 Sep 2018, 12:37
by Richo
francisco.shi wrote:
Mon, 17 Sep 2018, 16:42
The motors I have will do 260Nm at 5500 rpm from a 400v battery.
Well that would be enough for direct drive in this case - hills included.
400V maybe too high though for direct drive on something that only had 70kW.
200-300V would be ok.

Re: Which Motor?

Posted: Wed, 19 Sep 2018, 22:23
by francisco.shi
If you run the motor at lower voltage you will get less power. The torque will be the same but the max rpm will be less.
I have made a page that can help you to calculate the power of the motor you need depending on what you want the car to do.
It is a bit rough and I have not checked everything thoroughly but the numbers seem reasonable. The motor power and top speed calculations are correct. I just did not check the max slope thoroughly.
the address is http://www.becman.com/MotorSport/index. ... calculator
I hope it helps.
The motors I have will give you 150kw at 400v or 300kw after rewinding. After rewinding the torque will remain the same, just the rpm will be 11000 at 400v.
If you run it at 200v you will get 75kw or 150kw. The torque will remain the same but the rpm will be half so you will need higher gearing.

Re: Which Motor?

Posted: Thu, 20 Sep 2018, 08:08
by Richo
The car in question only had 34kW.
200V / 75kW would be plenty - no rewind and no gearbox.

How much does the motor weigh?

Re: Which Motor?

Posted: Thu, 20 Sep 2018, 13:23
by francisco.shi
The motor weighs 50kg and the inverter will probably add another 10kg. So I am expecting a total weight of about 60kg.

Re: Which Motor?

Posted: Tue, 25 Sep 2018, 13:14
by Richo
Well that is impressive.
That kind of performance is like a $10k motor...

Re: Which Motor?

Posted: Tue, 25 Sep 2018, 19:10
by francisco.shi
I am hoping I can make them for less than 10k for motor and inverter. I am still working on the system so I am still not sure how much it will cost to make but I am hoping it will be around 7k or maybe a little less.