# Confused on motors



## Bmmoffat (Nov 14, 2018)

Hey guys it seems the more I read the more confusing it is on motors. 

Like a smaller motor is better because it has a higher rpm? What affects the motors rpm? Like between a 9” and a 11” motor? Also are you exceeding the rpm rating? 


I saw this 15hp 230v 3phase ac motor at the scrapyard today. Says it says it’s rated for 1700rpm. This motor is massive, I would estimate 15” diameter and 20” long. 

How is this only rated at 15hp when it’s probably double the size of a 9” motor? And since I’m assuming this isn’t going to be a good canidate for an ev car, what should I be looking for in an ac motor that would make it a good canidate?


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## DrGee (Aug 22, 2018)

The first thread may help you understand the difference in characteristics between ac and dc motors. The second thread clarifies alot about motors in general and dc motors in particular. 
Hope they help you as much as they helped me. 
Cheers. 

AC Vs DC https://www.diyelectriccar.com/forums/showthread.php?t=198379

Using a forklift motor, and choosing a good one https://www.diyelectriccar.com/forums/showthread.php?t=7598


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## Bmmoffat (Nov 14, 2018)

Thanks I’ll give them a read, the more info the better. From what I’ve read ac motors are better because speed depends on frequency not voltage, so you aren’t limited like a brushed dc motor. I’m an electrician so I have a basic understanding of motors but we don’t repair them, it’s cheaper to throw them out and get a new one, so I’m trying to see if it’s worthwile to get a scrapped one and rebuild it for an ev car.


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