[Duncan]

Anywhere where the "metric-sytem" is used; there is no use of the word Horse Power, it is a forbidden-word in the Euro-Union,

COBBLERS!

The demon word - Horsepower - is frequently used - the only problem is that there are lots of different -horsepowers-, SAE, DIN, PS

I have taken numerous European technical papers - and set a few - and I have never heard of anybody being penalized for using the word - horsepower

Mind you if you tried to answer a technical question in horsepower instead of Kw I would have marked it wrong - just as I would have if you answered a distance question in Roman miles

Have you ever tried to do any serious engineering work in the Imperial system?
It's bloody hard - Rotary Slugs for example

during the "changeover" to metric.

I remember the UK as the last country in Europe to "changeover" - but that was over forty years ago!!

 

[Duncan]

Hi Electro

In a lot of calculations it is easier to use metric, but that is the only advantage I can see.

Just try to calculate driveshaft resonant frequencies in Imperial! - nevermind anything difficult

The real advantage is that SI is a designed set of measurements so that everything keys together

This is a major advantage when you are trying to understand what is going wrong

Imperial is a set of almost random units related to the size of somebodies foot and the width of a horses arse thousands of years ago

 

[Duncan]

A query I have is finding a source for a forklift motor. Other than purchasing a wrecked forklift I have seen information about picking them up from servicing and repair places. However if a motor is being thrown out then surely it is not going to be worth salvaging for using in an electric car conversion. If it won't work in a forklift any more then to me it follows that it is only suitable as scrap. Please any advice gratefully received.

Hi Weenam
Forklifts can live for a very long time - long enough to outlive their spare parts supply

There are lots of parts on a forklift from the batteries to the hydraulics to the controllers - any one of them dying on a ten year old machine can make it not economical to repair
This results in a lot of forklifts being scrapped - the motors are still fine
Some of these are kept as spare parts - but forklift motors are robust - spares are not needed very often
So forklift motors become scrap metal

I got real lucky on mine, it had just been refurbished when the forklift was scrapped
$100 - its bigger than I would have chosen but more torque is good!

 

[Duncan]

"Traditional" is not too bad for simple stuff

But it's truly awful if you have to do anything remotely complicated!

 

[Duncan]

Hi
An industrial motor at 90 -100Kw will be HUGE - 300Kg or more

About the only source of AC motors of that sort of power level and a decent weight is Electric Cars

The motor from a crashed Nissan Leaf or something

 

[Duncan]

My opinion is that they're charging 4x what it's worth.

Go to, or call up a local forklift repair yard and ask for old DC motors they may have sitting around. You'll get something better for closer to $200.

I sort of agree BUT - it's not as simple as that!
I finally tracked down our local elephant's graveyard - but it was not easy or fast

 

[Duncan]

I have been struggling to find a forklift yard locally. That's the only reason I'm looking online. I'll keep checking, and I agree the price is high. Just trying to get a better idea. Thanks!

Sent from my SM-N960U using Tapatalk

Hi
the way I found mine was by asking at a furniture place that had an electric forklift who looked after it!

You want "industrial concerns" that require cleanliness - so no exhaust soot from their forklifts

 

[Duncan]

The mast and forks are worth something in an agricultural area - you can attach them to the back of a tractor for a useful forklift thing

 

[Duncan]

Lead is dead - with lead actual ranges were less than 20 miles and 2 years for life
For your needs a Chevy Volt pack would be great - I paid $1800US for mine

Motors - most here are 48v
But you will be running them higher
I'm running 340 volt - but that is excessive - 150v is OK - much below and your top speed will suffer

This is my "Device"

https://www.diyelectriccar.com/foru...dubious-device-44370p15.html?highlight=duncan

 

[Duncan]

Thank you.
I see a few hybrid battery packs from Prius and Camry available. So, those would be suitable? And I'm looking for around 8kWh?
Looks like Prius Gen 1 is only 1.6kWh and Gen 2 is 4.4Kwh.
And are controllers and BMS hard to find/match for those?

P.S. Please let me know if I should start a thread in the battery section instead of here.

I would be looking at more than 8 kWh

I have 14 kWh in an 800 kg car - and that gives me a 50 km range at 100 kph

Admittedly my car is aerodynamically challenged!

 

[Duncan]

Hi. What car do you have? 800kg it's so light

This is my "Device"

https://www.diyelectriccar.com/foru...dubious-device-44370p15.html?highlight=duncan

And 800 kg represents at least 150 kg more than it should have been - I overbuilt it a bit

 

[Duncan]

Hi Major,
One thing that I have a hard time to understand. Many folks on this site are suggesting to use a forklift DC motor to replace the original combustion engine. But as you say, an electrical motor HP and a combustion engine HP is the same... So, if I want for instance replace a 100 HP combustion engine and look at the 100 HP electrical motors outthere, they are a lot bigger than the typical forklift DC motors. And for some reason, these forklift motors are not showing the amount of HP they are providing on any nameplates that I looked at. So, how can you size a "good" forklift DC motor to fit your expected output power?

Thanks,
eSharo

The motor is a device to convert electrical power into mechanical power
The more power you "feed" it the more mechanical power is produced

So the power that can be produced is determined by the controller - not the motor

A motor can produce a LOT of power if its only for a short period

Additionally

Power = Torque x Speed

Torque is (roughly) proportional to Current - as is HEAT

So if you are going at twice the rpm THEN you can produce double the power for the same amount of heat
AND if the motor is cooled by a fan on the motor shaft - THEN you can cool and remove more heat

The result is that a Fork lift motor with a 10 kW "rating" at 1400 rpm will have about the same heat buildup at
4,000 rpm and 50 kW
That would be the "1 hour rating"
Most cars will "do the speed limit" at about half of that (25 kW) - so they can't pull 50 kW continuously anyway

Short term power - for acceleration - can be much higher!

I am feeding my 10 kW Hitachi motor with 400 kW for a short period

 

[Duncan]

Thanks a lot guys.

Waiting for your replies, I educated myself in parallel and found out many interesting things on the subject on this forum and on the net.

What I understand better now is that the required starting torque for a DC motor is not an issue since the lower the RPM, the higher the torque for a DC electrical motor.

My main concern now is the higher speed torque peaks required for say hill climbing or higher speed acceleration. For a given voltage supply, the generated HP will be the same so that for higher RPM, I will get a lower available torque. But on the other hand, I can configure the controller to supply higher voltage to generate higher HPs (raise the "speed-torque curve") therefore, higher torque for a given RPM. But in this situation, the dissipated heat may be a problem but as Ducan said, a fan installed on the motor shaft would help a lot.

I figure out that I will not be able to anticipate completely the behavior of a given DC motor to replace my current engine while designing my system but as a general rule, I will choose the highest possible HP rated motor available with the ability to install a fan on its shaft if not already equipped as such. I will also plan for a controller that will allow to supply higher voltages (higher than the nominal voltage of the motor) at higher RPMs. Since I will keep the current transmission in the vehicle, my sweet spot RPM for a 100 KMH speed will be around 2000 RPM as it is now. So, I'll have to keep a fairly good acceleration (torque) beyond this RPM until say about 2500 RPM. The rest of the story will be a try and "error" workbench test plan making sure that I will not let the motor to overheat not to damage it.

Any other comment from the community would be welcome!

Thanks!
eSharo.

Kind of!!
But its better if you think about Current = Torque
Your controller will alter the Voltage it feeds to the motor in order to deliver the demanded current - up until 100% when the Motor voltage = Battery voltage

Rather than
the lower the RPM, the higher the torque for a DC electrical motor
In most cases you have the same torque up until you don't have enough voltage to sustain that current THEN as rpms rise the current and the torque both drop

Most motors will survive a lot more than 2500 rpm - and its better to operate at higher rpms - also gearing for 100 kph and 2000rpm is difficult!!!

 

[Duncan]

Thanks again Duncan. I got you... But regarding the 100 KMH at 2000 RPM, there is nothing I can do since it is the current built in mechanism characteristics. But I will try to find a controller to have the ability to cope with it and, as I said before, provide a battery pack that will supply higher voltage than the nominal voltage of the motor. This will leave the controller to adjust the voltage to cope with the torque (current) demand at higher RPMs. Sounds good?

If you are keeping the transmission simply use a lower gear
Top gear may be 2000 rpm for 100 kph - but lower gears will be more revs - first gear is usually three or four to one
So in first it will be 6,000 to 8,000 rpm at 100 kph

Keeping the revs up will reduce the heat as the motor will be spinning faster and you will require less current

You may well find that you never use "top gear"

 

[Duncan]

thanks, that was a mouth full. i thinking seriously converting my 1971 MG BGT 1800cc. it's got great power and tuned per MG spec. I could sell the original motor and keep the tranny for the conversion. do you know where to get the adapter plate to mate the E-motor to the MGB tranny or make an aluminum for light weignt? what is the best and high effeciency lithium ion phosphate battery, the cost, number of cell per pack? i'm just tire of paying high gas price. what would be an ideal budget for this venture?

First and most important with any conversion - what range do you need?

Range - and hence battery size required sets the rest of the needs