Pulling strength of an 8274

[BogMonster]

Maybe they are - I've just googled and most industrial motors seem to be up around 90% efficiency which surprises me. No idea about winch motors though.... anybody know?

if about 90% also, then 6hp would need a bit over 400 amps at 12V

[Daan]

I don't doubt your maths is correct but there is no way any 8274 winch I have had experience with could exert anywhere near that kind of pulling power, safely or otherwise. That is why I use a mechanically driven power take off winch, which does what it says on the tin and more.

Bill.

[will_warne]

Maybe they are - I've just googled and most industrial motors seem to be up around 90% efficiency which surprises me. No idea about winch motors though.... anybody know?

if about 90% also, then 6hp would need a bit over 400 amps at 12V

Ah, but from what I've been told, series wound aren't that efficient: arround 60% is about the best you can expect.

[simonr]

90% is possible out of a permanent magnet motor.

95% is just about possible with brushless DC or polyphase induction motors.

Series wound motors are more difficult. 60% is a commonly quoted figure - but this is a peak efficiency.

Since the power is a product of torque and speed and the series wound motor produces max torque at zero rpm (where power output is zero and thus efficiency is zero) and max rpm at zero torque (where power output is also zero and thus efficiency is zero). The peak power and peak efficiency are somewhere inbetween. Trouble is, on a winch - you never really use it in the inbetween!

This is why the figures for series wound are quoted as max (stall) torque and max rpm. Under most circumstances, the power is meaningless.

In our case, I would be surprised if we were seeing more than 30% efficiency out of the motor.

My 4.5Hp motor draws 480A at stall. This is equivalent to 5760W or 7.7Hp

If the 4.5Hp figure is to be believed, the motor would have to be 60% (57.8%) efficient. It might have this as a peak efficiency - but not where we are using them!

This might lead one to believe that the 'power' of the motors has been calculated as 60% of the peak electrical power input.

Personally, if I were trying to select a motor, I would go for as high a stall torque as possible. The further away from this torque you are operating, the more efficient the motor will be.

Shame nobody makes a series wound pancake motor!

Si