Re: How to determine Torque from these motor numbers?

Thanks for all the help and numbers so far yall. You dont know how
much the helps out! :)

these motors are around 4"D x 5"L in size.. I guess from what I'm
hearing is that they are actaully more powerful than I thought?

Lastly, Greg when you mention testing the motor for temperature
buildup, Is it OK to let the motor cook at locked shaft.. even at (a
low) 3.7A? just seems that cant be good on it for any length of
time... but if thats what it takes! :)

thanks again all-
Colin


--- In CAD_CAM_EDM_DRO@yahoogroups.com, Gregory Kamysz
<smsupply@a...> wrote:

> Ok, two people beat me to this while I was typing and calculating

so

> this might be redundant.
>
> Kv(rpm/volt)/1352=Kt (torque constant). This is valid for permanent
> magnet DC motors. So your motors have a torque constant of about

54

> oz-in/amp. Out of curiosity how big is your motor? These numbers
> describe a large motor.
>
> As far as how much current or power they can handle depends on a

few things.

>
> Heat that must be dissipated in the motor is found with
> Rm x amps^2
>
> 1.7 watts at 1A
> 6.8 watts at 2A
> 15.3 W at 3A and so on.
>
> If the motor is turning, it gets more complicated but for these

motors

> the heat due to current accounts for most of the heat generated.

The

> heat must be dissipated in some way. This will be mostly based on

the

> surface area of the motor and the airflow around the motor. At no

load

> it's just V x A. You can see that even at no load at 30V your motor

is

> generating 17.4W of heat but this isn't that important. To give

you an

> idea the motors I'll be using have a Kt of 14 oz-in/amp and spec

5.4A as

> max continuous current. Rm(motor resistance) is 1.0 Ohm. This is

29W.

> It is 3.5" in diameter and 4.8" long.
>
> Is it OK to run the motor over 30V? Well the manufacturer put the
> number there for a reason. It may be that the motor can not hold

itself

> together at over 720RPM. It may be that brush wear is not

acceptable

> above that RPM. Going to 45V would probably be OK but I would not

go

> much higher without fully inspecting the motor. Max RPM on my

motor is

> 5000 RPM which equates to 50V for my motor at no load. Max voltage

is

> specified at 80V Bus voltage and 104V Terminal voltage, though I'm

not

> sure what the difference in terms means.
>
> Like Jon said, I wouldn't be too concerned about the voltage. If I
> wanted to test the motor you have, I would lock the shaft and put

it on

> my power supply at fixed current while watching the temperature.

Start

> at Mariss' suggested 3.7A and see what temperature the motor

stabilizes

> at. If it's pretty low you can run more current if it hits 250-260
> Fahrenheit and keeps going up the continuous current will be lower

than

> that.
>
> Greg