# newby question, need help



## Woodsmith (Jun 5, 2008)

I wondered this when I started looking and found that it all seemed to depend on length and diameter as the main starting point.

Round about 9" diameter and about 17" in length.

A grown up will come along and explain further.

Anyway, I posted in your other thread about volts and amps and watts. There are 746 Watts = 1 HP.


----------



## marc1337 (Aug 11, 2009)

wow i didnt even see the size you are talking about when i was looking for used electric motor in quebec.

In which on my threads did you post the stuff about volts and amps? because i only have 2 threads...this one and the other one is the EV i want to make...


----------



## Woodsmith (Jun 5, 2008)

Ahhh, sorry, two of you have asked the same question on volts and amps and I answered in the other one. Will resolve that now.

Well, amps and volts go together to make power.

Volts x amps = Watts (power)

The more Watts you have the more powerful your motor will be, in a very simplified way as there are other factors involved.

However, you would have a preference towards more volts as for the same power you will use less amps.

The reason for using less amps is because lots of amps need bigger cables to flow through, if the cables are too small for the amps then they will get hot and melt. That is the way fuses work. Too many amps and the fuse wire melts.

So for more power the Volts go up.

Range is another matter.
If you want to go further you will need more amp hours (Ah) of capacity in your batteries, like having a bigger fuel tank in your ICE car. How many amps, at rated battery voltage, the battery can provide in an hour.

10 Ah means 10 amps in one hour or 20 amps in half an hour or 5 amps in 2 hours. Again this is simplified as there are other factors.

As you can see the more Ah you have the further you can go, or the quicker you could set off to get there, depending on these other factors again.

However, range is also affected by the rolling resistence of your vehicle, how hard it is to roll it along the ground, and air resistence, how hard it is to push through the air.

Now rolling resistence is pretty much consistent(ish) for your vehicle but air resistance increases as you go faster. It is a square factor, as you double your speed you quadruple your air resistance.

So for range you want to keep your speed low to reduce the resistance that your motor will have to work against. The harder the motor works the more amps it wants to draw with the given battery pack voltage to achieve the power it needs to keep working that fast.

And back to the top.


----------



## marc1337 (Aug 11, 2009)

edit: nvm i saw your msg on my last thread


----------



## marc1337 (Aug 11, 2009)

look this website: http://www.electricmotorwarehouse.com/close_couple/leeson3p__close_coupled_pump_OPDP.htm
idk if u saw this before...
Would the motor #*801057 work?
it's 166 lb and has 25hp....
*


----------



## Georgia Tech (Dec 5, 2008)

There is a whole science in choosing a motor for an ev.
Things in the "Motor World" are different from the engine world. In theory size matters in how much Power the motor can "take" before it burns up! In the case of an Engine , size plays the role in how much Power it can produce! A small motor can theoretically make as much power as a big motor but it will not sustain it very long without getting hot, as the previous post alluded to, Power equals volts times amps. The power "producer" if you would is in the batteries and the controller. Now a smaller motor will make that power at a different rpm band than a bigger motor will.

This is a start, if you have more question please feel free to ask and I will answer them.


----------



## vpoppv (Jul 27, 2009)

Georgia Tech said:


> There is a whole science in choosing a motor for an ev.
> Things in the "Motor World" are different from the engine world. In theory size matters in how much Power the motor can "take" before it burns up! In the case of an Engine , size plays the role in how much Power it can produce! A small motor can theoretically make as much power as a big motor but it will not sustain it very long without getting hot, as the previous post alluded to, Power equals volts times amps. The power "producer" if you would is in the batteries and the controller. Now a smaller motor will make that power at a different rpm band than a bigger motor will.
> 
> This is a start, if you have more question please feel free to ask and I will answer them.


 You know, I was wondering about that because I have this motor that weighs 45 pounds, close to 7" diameter, 9" long, and yet is only rated 2 horsepower??


----------

