# Wiring a SepEx motor and controller



## alxpril (Dec 21, 2008)

SepEx motors and controllers have smaller connectors for the field windings than the armature windings. How do I size the wires for the field coils? They are going to be smaller than the armature windings but how much smaller? I found one example of a SepEx motor with 500amp armature/20 amp field rating...is this 25:1 ratio typical?

Thanks!


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## major (Apr 4, 2008)

alxpril said:


> SepEx motors and controllers have smaller connectors for the field windings than the armature windings. How do I size the wires for the field coils? They are going to be smaller than the armature windings but how much smaller? I found one example of a SepEx motor with 500amp armature/20 amp field rating...is this 25:1 ratio typical?
> 
> Thanks!


Hi alx,

Depends on the particular sepex control you have. Realize the 500 amps armature rating is likely the current limit or max. The 20 amp field rating may be the continuous.

I use a 48 volt sepex system where the armature limit is 500. Field max is 50. Average for the two systems is closer to 1/10th the max. I use #4 for the battery and armature circuits and #12 for the field. Haven't had any problems, knock-on-wood.

Hope that helps,

major


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## engineer_Bill (Jun 24, 2008)

It doesn't hurt to size both conservatively. I'm using a 72volt system with 400amps top speed I use 2/0 guage on the armature, and 8 guage on the field. I could of used 6 guage or 4 guage on the field, remember the bigger the wire the less voltage drop under load and the less losses to heat.


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## alxpril (Dec 21, 2008)

Ok, Thanks for the input guys. Any advice on where to buy cables from? I was looking at http://www.cloudelectric.com/category_s/55.htm. I'm hoping its similar to Vu-Tron welding cable I've used before.


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## engineer_Bill (Jun 24, 2008)

I would buy the larger guage from a welding shop, cheaper by far for good quality 2/0 cable. Smaller guages "Home Depot" thhn stranded.


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## Guest (Apr 4, 2009)

The field is a low amperage circuit compared to the armature. Here is a little vid from my SepEx starter/generator test. The sound quality is garbage and has loads of feedback. Hey, what do you expect from a phone video. It shows the field wire and the main wires are 2/0 welding cable. It is a pretty stout wire but handled the power with no problem. When it was installed in the car and driven on the street the wires never got hot. Ever. 

Was a 72 volt system. 

http://www.youtube.com/watch?v=RYkkCZI2k3Y

Pete : )


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## Telco (Jun 28, 2008)

engineer_Bill said:


> I would buy the larger guage from a welding shop, cheaper by far for good quality 2/0 cable. Smaller guages "Home Depot" thhn stranded.


X3, you can get welding cable for pennies to the foot as opposed to ten dollar bills to the foot as some of the high end heavy gauge wiring. This wiring is made up of thousands of thin strands of wire which is going to be a lot more flexible, and welding wire is designed to live for years in industrial environments where high heat and nasty chemicals are used without degrading. I've been using welding wire for my high amp needs for years in my vehicles with zero problems.


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## Guest (Apr 4, 2009)

Main Armature Cabling should be 2/0 fine strand welding cable. The field wire should be fine strand but far smaller. I am not sure of the gauge but it is not huge. It is more than ample sized for the amps.

Pete : )

Do you happen to have some good close up photos of your SepEx (shunt wound) Motor so we can see how your motor is setup?


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## Guest (Apr 4, 2009)

4 gauge should be fine for the field winding cable. : )


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