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Discussion Starter #1
i found a company that sells forklift parts, including motors.
How do i know what motor will be strong enough to power my car?

car is 800kilo, must be able to do 80km/hr.

only thing i can find on the internet is 9" 11" etc, but all these motors have kW's on their ID tags.
so, can i choose an engine based on the kW's it has/can take/produces?
 

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The physical size is a good indicator.

The forklift motor will generally be rated in kW running continuously for 60 minutes. That usually means that it can run in excess of that for short bursts when accelerating a car from stationary.

There are aspects of the motor that you can also look at, the size of the brushes and the commutator bars, the number of commutator bars, the size of the copper used in the coil winding, the amount of air cooling that the motor allows.

There are two sticky threads at the top of this forum page that will give a lot of information but it can be a lot of posts to trawl through.

However, in general, you could loosely assume that a 9" motor will be lighter then an 11", and it will spin faster when over volted. An 11" motor will produce more torque then a 9" but that comes with a weight and maximum speed penalty.

It depends a great deal on how you want to use it and what sort of driving you do.

major, on this forum, is one of the knowledgeable and experienced motor gurus who can advise if photos are posted of the motor.
 

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Hi Eric

My car is 710Kg and I am using an 11 inch forklift motor - I have had it up to 108Kph

Does 0 - 100Kph in ~ 8 seconds

I am using direct drive to the diff

A 9 inch motor would probably have been even better (lighter, higher rev limit)
 

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Discussion Starter #4 (Edited)
thanks for the replies, i read through the entire two topics. It was a lot of reading i can tell you :)
But i didnt really got the answer i was looking for so thats why i started another topic, what i'd like to know is how many kW is the average 9" or 11" motor?
Because measuring up motors that are still in forklifts showed on pictures on the internet makes it hard for me to decide if that could be a good motor for my car. But i can see tag plates on the motors most of the time that tell me the kW's of the motor.

So if the tag plate says 6kW and most 6kW engines are not strong enough for powering an 800 kilo car i will know i dont have to look at 6kW engines anymore.

http://www.ebay.de/itm/BalkanCar-Stapler-Elektro-Motor-mit-Hydraulikpumpe-DDR-/230979365120?pt=LH_DefaultDomain_77&hash=item35c7716900

like this
 

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Hi Eric

My motor was rated at 10Kw - that is it's one hour rating
That gives sporty performance in a similar weight car

6Kw would give adequate performance - especially if used with a gearbox

The motor you link to is a pump motor
- possible problems
It may have an internal spline driveshaft making it difficult to mate with the gearbox

The 6Kw is probably a 15 minute rating - meaning that it's one hour rating may be only 4Kw
 

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I haven't done a build yet so I can't speak with authority, but I am wanting to do a forklift based EV conversion as well and have asked myself this very question, many times. I hope someone will correct me if I steer you wrong. It will help me too if they do.
First, I don't think there is a simple answer to your question. There are too many variables that you haven't answered, and those will change the final answer.
Before you start looking for a motor(designing your whole build for that matter), you need to identify exactly what your needs are. It's not just weight of the car and max speed. Acceleration is the biggest power draw, how fast do you want to get to your 80 kph? That will determine peak power, amperage(motor torque) and voltage(Motor Speed) requirements. There are calculators that can help with all this here and on the web, but I think you need to do the math first. Here are the list of questions I've come up with in my search, including the ones you've already answered, hope they help.
What is/are:
the primary purpose of the vehicle?

the weight of the vehicle, including passengers?

max. speed and max distance?

max acceleration? See above

avg. speed and trip length? You may be able to push a small motor harder if you never will be driving it very far. According to Major, the continuous power rating of the motor can't be increased much. If that is true, then your continuous power needs should match the kw rating on the motor.

the terrain, hilly or flat?

the gear ratios available in the donor and will they work with the motor? You need to match the motor somewhat with the car. Speed and torque of the motor should be compatible to the donor car.

the type of motor? As was said, series wound is best and easiest. Sepex could work, but good controllers are hard to find.

the size and configuration of the motor? Will it fit in the car? Too big can cause problems, too small and you might not have enough power. Does it have an adaptable shaft? Can it be made to spin the right direction? (pump motors usually spin one way only)

Once you've figured all that out, then you will know what size motor to look for.

So, to all of you who know more than me, did I get it about right?
 

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Discussion Starter #7
I know what i want to use the car for and what kind of car it will be.
It will be a Nissan Micra, already own it, and i want to drive it to work and back on a daily basis.
to get it roadlegal it must be able to do 80km/ph, my trip is about 25 km, so a 50km round trip.
all of it is flat roads, 5 km of town traffic rest of it is freeway, i dont want it to be any slower than it is now, but it now has a 1.0l engine, so that wont be a problem i guess.

the engine bay is pretty spacey, so engine size wont be a problem. i can choose for a fe types of gearbox from other Micras which have different gear ratios.
 

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I would suggest that you measure the clearence between the bellhousing face and the side of the engine bay for the maximum length of motor. Possibly stick with a 9" motor to ensure it clears the drive shaft.

Look for a motor from a truck that is at least 48v, higher would be good. Also make sure it is a DC series wound drive motor. It should have a built in fan, but if not then it should have vent holes at both ends so you can force ventillate it.
 

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I'm guessing you will want a 8-10kw motor for highway speeds
Probably a bit higher. Highway speed (100 Km/h) is greatly influenced by the aerodynamic of a car.

Reference for you Eric:

My Smart Fortwo (865 Kg) with a 9'' motor need between 8-12 Kw to maintain 80 km/h and 13-20 Kw to maintain 100 km/h on flat terrain (more on slopes)
Weather influenced a lot the power requirement (wind, cold, etc.).
 

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Further from your post in the other thread....

One of the issues is going to be that the motor you get from the forklift truck is going to be run at increased voltage, increased power (for short bursts), and probably increased speed.

The manufacturers data plate is there for information on its OEM use. So a 6kw motor will run at no more then 6kw continuous for an hour and never get too hot nor fail within that spec in its truck use.

You will be possibly doubling (or more) the voltage, demanding more power and possibly spinning it faster, then the manufacturer will ever warranty, so the data plate needs to be taken with a pinch of salt.

The physical size of the motor will allow it to have heavier duty windings and commutator bars, as well as bigger brushes. It will be able to dissipate more heat (that will be one of the killers) and withstand the high demands with less risk of failing.
Look for big brushes on a long comm and lots of ventilation.

You could use a small motor but it will most likely burn out. You could use a very big motor but it will have a lower speed and it will be excess weight, unless you are really going to push it hard.

It comes down to a compromise based partly on what you can find within your price range and locality, and what would be ideal.


The other aspect is it isn't so much down to the number of kw on the motor plate.
It has often been said as an analogy, on this forum, that you should look at the motor as the transmission in the car and the controller as the engine.
The controller, along with a suitable sized battery pack, will deliver the power. The motor just has to convert that electrical power to mechanical power to the wheels, with or without a mechanical transmission.

So the motor only needs to be physically strong enough to do that, electrically robust enough to not melt its windings, and the right size to fit in the car.

A golf buggy or lawn tractor can manage with a 6-7" motor easily. A road car will usually need around 9-11", a race car 11-13" or twin motors.

My tractor ran a 7" motor and exploded the axle. I then fitted a 9" and a bigger axle and it exploded the axle, I may next fit an 11" and a bigger axle...:rolleyes:
The 9" motor might find its way into my EVan-Tricycle that the 11" motor was destined for. However, it lacks ventilation and large brushes.
I also have a 12" motor.:D

I am only using the motors I found or were given to me and that 9" is rated at 24v and around 110A, that is only 2.64kw. That is currently running at 48v with a 350A controller, that means a peak of 16.8kw. The tractor's axle gave up before the motor did!:eek::D
 

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Discussion Starter #13
Thanks, your post and the link to the other topic is very helpfull to understand how this motor thing should be looked at.
 

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So to move a 3800 lbs total to a speed of 38 mph With 48 volts , how many amps would you use to leave a stop light (not fast) at a good speed if a cop car is beside you ?
 

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Further from your post in the other thread....

One of the issues is going to be that the motor you get from the forklift truck is going to be run at increased voltage, increased power (for short bursts), and probably increased speed.

The manufacturers data plate is there for information on its OEM use. So a 6kw motor will run at no more then 6kw continuous for an hour and never get too hot nor fail within that spec in its truck use.

You will be possibly doubling (or more) the voltage, demanding more power and possibly spinning it faster, then the manufacturer will ever warranty, so the data plate needs to be taken with a pinch of salt.

The physical size of the motor will allow it to have heavier duty windings and commutator bars, as well as bigger brushes. It will be able to dissipate more heat (that will be one of the killers) and withstand the high demands with less risk of failing.
Look for big brushes on a long comm and lots of ventilation.

You could use a small motor but it will most likely burn out. You could use a very big motor but it will have a lower speed and it will be excess weight, unless you are really going to push it hard.

It comes down to a compromise based partly on what you can find within your price range and locality, and what would be ideal.


The other aspect is it isn't so much down to the number of kw on the motor plate.
It has often been said as an analogy, on this forum, that you should look at the motor as the transmission in the car and the controller as the engine.
The controller, along with a suitable sized battery pack, will deliver the power. The motor just has to convert that electrical power to mechanical power to the wheels, with or without a mechanical transmission.

So the motor only needs to be physically strong enough to do that, electrically robust enough to not melt its windings, and the right size to fit in the car.

A golf buggy or lawn tractor can manage with a 6-7" motor easily. A road car will usually need around 9-11", a race car 11-13" or twin motors.

My tractor ran a 7" motor and exploded the axle. I then fitted a 9" and a bigger axle and it exploded the axle, I may next fit an 11" and a bigger axle...:rolleyes:
The 9" motor might find its way into my EVan-Tricycle that the 11" motor was destined for. However, it lacks ventilation and large brushes.
I also have a 12" motor.:D

I am only using the motors I found or were given to me and that 9" is rated at 24v and around 110A, that is only 2.64kw. That is currently running at 48v with a 350A controller, that means a peak of 16.8kw. The tractor's axle gave up before the motor did!:eek::D
What kind of 9" motor did you have?
 

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Hi, I am a complete newbie here and have a few questions for the brain boys out there.
Why does one need to use batteries - can one not use a smallish generator 4.5kva x 220 v and step down the voltage to make it compatible with the electric drive? Secondly can one not use a belt drive off the motor to a variable speed pully drive on the drive shaft to regulate speed, etc.
I am not sure any of this is sensible or even on track, but I have this rolling over and over in my stupid head and need clarity - please someone put me out of my misery
 

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If the generator is that small, you'll still need batteries if you want to drive faster than a golf cart.

And if you're going to be burning fuel, what's the point of the conversion?
 
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