# How to bench test a SEPEX motor?



## evcars (Mar 15, 2008)

How do you check a SEPEX motor using a 12 volt battery? I am able to make a series motor spin by connecting A1 to S1 together and attach jumper leads to A2, S2. The two SEPEX motors in question, however, will not spin when I do this. I know for sure one of the motors was working. I just mixed up the two and don't remember which is the good one. I want to make sure I pick the working motor. Thanks


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## DavidDymaxion (Dec 1, 2008)

Use an ohm meter. A pair of posts that has low resistance will be either the field or the armature. Use 2 sets of jumper cables, and jump the lower resistance pairs of posts.

On my sepex motor the field is about 1 Ohm, the armature is about 30 milliOhms, and going between a field post and an armature post gives something like megaOhms.

It is good practice to hook up the field first, and unhook it last. Probably not a problem at 12 V, but at higher voltages pulling the field off while the armature is still connected could cause the motor to overspeed or could fry your brushes.

Something I think is fun is to hook up a battery charger to the field, and a battery to the armature. Then switching the battery charger between 2 and 6 Amps, and 6 and 12 Volts changes the motor speed.


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## major (Apr 4, 2008)

xtreme cartz said:


> How do you check a SEPEX motor using a 12 volt battery? I am able to make a series motor spin by connecting A1 to S1 together and attach jumper leads to A2, S2.


Hi xtreme,

First off, you sure it is a SepEx motor? Usually SepEx motors have the field terminals labeled F1 and F2. S1 and S2 are common for series motors.

You don't give us a lot of info on the motors. Like the nameplate voltage. So let's assume it is a 36 volt rated motor. Then the field, if SepEx, may be nominally rated for 5 or 6 volts. You want to test using only a 12 volt battery. So you should connect it as a shunt motor. That is field in parallel with the armature. Or A1 to F1 to Bat Pos and A2 to F2 to Bat Neg. That might be too strong for the field current, but it would certainly be o.k. for a short test.

When you connected it in series as you say, it might not work well, or at all, depending on the particulars of the design. Say, for example, it was a 36 volt motor with a 12 volt field. When you connect it in series, and apply 12 volts to it, the field will drop 12 volts and leave little or no voltage for the armature. Like putting a 10 Ohm resistor in series with a 0.01 Ohm resistor and applying 10 volts to the series combination. The 10 Ohm resistor sees a 9.99 volt drop and the 0.01 Ohm resistor sees only 0.01 volts. But if you put the resistors in parallel, both would see 10 volts.

The best way to test a SepEx motor is to separately excite it. Always have the field on first and off last. Hook the F terminals to a power supply of the proper voltage range. A variable supply is nice because you can vary the field strength and see the effects on the motor speed. You use a separate power supply for the armature, rated voltage or less. It does not need to be variable. You can use a battery. Set the field voltage mid range and then apply voltage to the armature. Monitor RPM and armature current. When you raise the field voltage, field current increases and the RPM goes down. And visa versa. If you have a battery on the armature and an ammeter, when you quickly increase the field voltage, you see the armature current go negative as the RPM decrease. This is regeneration from the inertia of the armature slowing down. Kind of neat to actually see. Only last about a second, but you can definitely see it on an analog meter.

I've done this a few times. Hope my experience helps.

major


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## sammyleal (Aug 1, 2016)

Hey Major! Thanks for all advice about sepex motors.

Today I tested my sepex motor already connected to the transmission. 

I tested it like a series motor with 12V, using 2nd gear, and the wheels rotated backwards! 

Exciting it separately, or using the Curtis, can I change the direction of rotation? Or should I look for another motor? 

Thank you very much.

Greetings from Brazil!


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