Series Wound DC Motor, HP, Controller?

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dereckbc

dereckbc

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Plano, TX
OK here is the deal guys, I am having a hard time wrapping my head around Series Wound DC Motors, Pulse Width Modulation Controllers, Horse Power, and Current. I think the manufactures are playing games with numbers.

Let; say I have a series wound DC motor rated at 10 HP continuous/16 peak , @ 6500 RPM @ 48 Volts DC. Why would I need anymore than a 250 amp PWM controller?

Here is where my brain is twisted. It is for a golf cart. The manufactures recommend a 400 amp controller and I cannot figure out why. If you take the peak HP of 16 and factor in 75% efficiency, I see no reason for anything more than 250 to 300 amps controller.

What am I missing? Or is it manufacture trying to up-sale? What I am stuck at is if I were to connect a 48 volt battery to the motor, the most current I would expect is 250 to 300 amps for a very short brief period of time like a few seconds then back off to 160 or so, assuming there is a load?
 
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R

rattus

Senior Member
Derek,

Perhaps they are considering locked rotor or other overload conditions. Also, the motor might not be as efficient as you think with a high torque, low RPM load.
 
Besoeker

Besoeker

Senior Member
Location
UK
dereckbc said:
OK here is the deal guys, I am having a hard time wrapping my head around Series Wound DC Motors, Pulse Width Modulation Controllers, Horse Power, and Current. I think the manufactures are playing games with numbers.

Let; say I have a series wound DC motor rated at 10 HP continuous/16 peak , @ 6500 RPM @ 48 Volts DC. Why would I need anymore than a 250 amp PWM controller?

Here is where my brain is twisted. It is for a golf cart. The manufactures recommend a 400 amp controller and I cannot figure out why. If you take the peak HP of 16 and factor in 75% efficiency, I see no reason for anything more than 250 to 300 amps controller.

What am I missing? Or is it manufacture trying to up-sale? What I am stuck at is if I were to connect a 48 volt battery to the motor, the most current I would expect is 250 to 300 amps for a very short brief period of time like a few seconds then back off to 160 or so, assuming there is a load?
Click to expand...

16 HP at 48V and 75% efficiency is about 332A.
Maybe a 400A unit is the next available standard unit?
 
H

hillbilly

Senior Member
Using your numbers for a simple calculation.

16HP x 746 watts/HP x 1.33 (75% efficiency) = 15,875 watts.

15875/48V = 330A

steve
 
drbond24

drbond24

Senior Member
Location
Barboursville, West Virginia
rattus said:
Derek,

Perhaps they are considering locked rotor or other overload conditions. Also, the motor might not be as efficient as you think with a high torque, low RPM load.
Click to expand...

I'm with rattus. I live on a country club course, and as you can imagine, there is no such thing as a flat golf course in the Mountain State.

Anyway, there are a surprising number of overweight golfers (probably from the amount of beer they consume while playing) and they are pretty rough on their carts. The cart has to drag two fat guys, their clubs, coolers and other accessories up every hill on the course. Sometimes, you could walk heel-to-toe next to the cart and keep up with it going up the hills. I'm sure that is putting quite a strain on the motor.
 
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