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7-Plus-NGM Digest September 2011

Date: Fri, 09 Sep 2011 17:15:43 -0000
From: "The Dragon"

Subject: need advise on choosing electric motor

It is evident that I need to replace a 12/24 volt 3HP Leesen perm. magnet traction motor. {It was cooked'/overheated by the previous owner... the coils are possibly shorted/the varnish is cooked off, and the magnets are very weak.}

Thus my problem is:
What sort of motor should I look for?

What are the advantages and disadvantages of 'shunt wound' compared to 'series wound' motors?

How do they stack up against PM motors in a battery powered, 'traction' application?

Any suggestions/opinions would be helpfull.

The Dragon
PS: I am on disability, so I'll be doing this as cheaply as possible.

Date: Fri, 09 Sep 2011 22:26:52 -0000
From: "derek"

Subject: Re: need advise on choosing electric motor

hi there

personal choice here

use a 1 kw ish motor and controler straigh out of a pedestrian operated fork truck. series traction motor will overload very well and stand all sorts of abuse.

will push a 500 kg loco with ease pulling 17 adults round 40ft rad curves on 1 in 20 grades does it all day every day or on a flat land railway will pull most anything you can put behind it.#

if you are located close by have some second hand ones at 75.

thanks derek!!!!!!!

Date: Sun, 11 Sep 2011 14:32:28 -0000
From: "The Dragon"

Subject: Re: need advise on choosing electric motor

It sounds like you might be in another country, I am in Pennsylvania, in the USA...
Also...am I understanding you correctly?
That I should down-size from 3 HP down to 1KW or so?
OR do you just mean I should switch to a series wound motor?
The Dragon

Date: Sun, 11 Sep 2011 19:01:00 +0000
From: Roy Stevens

Subject: RE: need advise on choosing electric motor

Before I can recommend a replacement, perhaps it's best to explore why your leeson motor burnt up the first place. What motor controller are you using, what voltage, what kind of battery pack, what drivetrain reduction ratio are you using, how heavy is your loco, and what exactly is in the drivetrain?
My gut feeling is that you are using either the incorrect motor controller, or incorrect gearing, or both. It may also be possible that you have something in the drivetrain or axles that is binding, causing the motor overload. Because with the correct setup that motor should have lasted forever in anything weighing less than 1200lbs. Leeson are industrial rated, which means it takes a LOT of abuse to kill it.
Shunt and series wound motors use coils to create the static magnetic field. Series wound motors tend to be less efficient and have speed control issues, but have higher starup torque. Shunt wound are better explained as 'parallel wound' motors. They are more efficient and have better speed control, but have low starup torque because at zero RPM all the amperage is going through the commutator, starving the field.
Permanent magnet motors have come a long way in the past few years with dropping price of rare earth magnets. The best choice in motors in my opinion are sepex motors, or permanent magnet. They offer low speed torque, excellent speed control, regenerative braking, and efficiency.


Date: Sun, 11 Sep 2011 21:46:06 -0000
From: "derek"

Subject: Re: need advise on choosing electric motor

hi there

i made 1 or 2 asumptions based on use of that type of series motor.

the loco transmision is in the order of 90% efficent from motor shaft to the wheels.

the explanation of the power rating of a 1 kw traction rated motor is very complicated.

in short it can be used for 1 hour at 1 kw or untill it reaches is maximum temp if it does not reach its max temp you can keep using it.

i push proably beyond 4 kw through mine climbing banks but it has never reached even warm on a hot day because the load is transient.
and the loco coasts down hills thus cooling the motor but even using pluging braking does not warm it up to much in use.

not that i recoment this sort of abuse you could push it up beyond 10 kw without damage if it was very transient and you did not allow the motor to over heat.

the leason motor you used i am not familar with but it may be peak rated at 3 hp not constant rated.

there is no peak rating on a seres wound traction motor just a curve that is advisable to keep it below.

i have used all the basic type of motors out there for traction.

three phase

but for all out grunt and pulling ablity there is no substitue for a good series motor.

sepex and three phase are good but wont keep going with a series motor.

once too far overloaded a three phase motor goes into slip and stops.

sepex are beter but controling them is more complicated and the controlers cost more. and at a push you can use a series motor on a pm controler where that wont work with a sepex motor.

if the loco is set up like the usual american layout with cardan shafts and gearboxes to the axles then you will have to use a bigger motor proably in the region of 2kw motor due to the inoridinate losses in the transmision.

thanks derek!!!!!!!