# Choosing a motor/hp



## Frank (Dec 6, 2008)

Motors are typically rated for constant, steady state output. Because these motors are air cooled this controls that number. With the right controller and batteries, that Warp 9 can make hundreds of HP short - term. 

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## Duncan (Dec 8, 2008)

An electric motor is a converter - it converts the electrical power from the battery into mechanical power
The limiting factor is the temperature
So a Warp 9 - which is truthfully a forklift motor with a nice paint job can handle 32 hp - continuously
But for a short period it can handle a LOT more

I'm using the next size up - a 11 inch Hitachi forklift motor - this is rated at 13 hp!! - but I'm feeding it about 400 kw - and I blow away almost all of the supercharged V8's at our local drag races

A 9 inch or 11 inch forklift motor will give you more than enough performance


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## Antoine (Nov 2, 2020)

Okay thanks! So I could go to a junk yard and pickup pretty much any 6-11 inch motor?!


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## Frank (Dec 6, 2008)

Smaller diameter motors will run hotter so I would think at least 8" diameter. Note: we are talking series DC brushed motors which use mechanical commutation. It all depends on your goals. A lot of folks are adopting OEM drivetrains from wrecked vehicles but I think it takes more skill to make them work. There seems to be various hacks used in order to adapt OEM controllers, for example.


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## Antoine (Nov 2, 2020)

Okay I'll aim for 9-11 then! 
Thanks!!!


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## brian_ (Feb 7, 2017)

Antoine said:


> Okay thanks! So I could go to a junk yard and pickup pretty much any 6-11 inch motor?!


Sure... except that many recent posts suggest that there are none of these motors in junkyards any more. After all, they're long-obsolete technology.


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## Tremelune (Dec 8, 2009)

What are your power/speed/range goals? What kind of car are you converting (and is it manual)?


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## Antoine (Nov 2, 2020)

I am converting a 6speed mini cooper that originally had around 120hp engine. I want to have a good acceleration and a top speed of around 100-120mph. This means that the motor has to spin (in 6th gear) between 2080 and 2500rpm. According to the other answers, I think a 9inch motor would be enough, but a 11 would probably be better. What is your opinion?


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## Tremelune (Dec 8, 2009)

Interesting. How do you plan to drive the wheels? Do you know what you'll use for batteries?

Don't be fooled by the horsepower numbers...Electric motors can run out of steam at higher RPM, but your car is likely to be _much_ quicker to 60mph with even a modest electric motor in place of a 120hp ICE.


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## Antoine (Nov 2, 2020)

I was thinking of making a battery pack out of multiple modules made out of Boston power swing 5300 cells. They have a very good energy density and the price is also very good. I am still trying to figure out what voltage I want for my total pack thought.
About the lack of juice at high rpm, I don't actually care if it goes faster than 100 mph. I just want to be able to pass cars on the hwy. Do you think this will be an issue?


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## Antoine (Nov 2, 2020)

Would it be worth it to change the final drive ratio, to get better torque at higher speeds?


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## Duncan (Dec 8, 2008)

Re - motors from scrapyards
We are talking forklifts here - so car scrapyards are useless
Find out who repairs/rebuilds electric forklifts in your city - then visit them with a case of beer and some folding money

They may have a couple of motors as "just in case" spares - but they won't have lots as the damn things are so reliable and the rest of the motors will have gone straight to the scrap metal man - an 11 inch motor is worth about $100 in scrap


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## Antoine (Nov 2, 2020)

Thanks for the suggestion! I was going to go my local electric motor store/repair shop tomorrow! I'll see what they have there...


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## Tremelune (Dec 8, 2009)

Have you looked around for a wrecked EV you can salvage the battery pack from, or buy one partially. I've seen a worn-out but usable Leaf pack for sale for $1,000 on eBay. The _most_ I've seen a 24kWh Leaf pack go for was $4k, which is under $200/kWh. There are a few different ways you could use the Leaf motor, too.

I'm not sure I see a reason to build your own pack in 2020.


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