# Mismatched controller Question



## Qmavam (Aug 17, 2008)

Hi All,
I'm building a go kart on a budget. I got a gokart for $100.00, a free 2hp shunt motor, batteries from a auto recycler, and a great price on an NPX4834 controller.
The controller is for a series wound motor, I want to make it work with the shunt motor.

Should I parallel the shunt with the armature and then PWM the combination with the controller?

Or should I control the shunt separately and PWM the just the armature.

Is it customary to put a reverse diode across the motor?

I'll add a solenoid (with reverse diode), fuse, throttle (pot box), and probably amp and volt meters, key switch, emergency OFF button.

Any hints or ideas you can give me?
Qmavam

PS. the motor is a Baldor 28v at 65 amp, 2600 rpm. I'll have a 36 volt system. A little high for the motor, just have to baby it till we see how hot it gets.


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## Johny (Jul 21, 2008)

This is all a bit dicey but it may work OK.
Use the controller to control power to the armature.

The 'shunt' you are talking about I assume is the field coils. Essentially you will get the most torque out of the motor with the fields connected straight to the battery BUT be careful. Start by connecting the field only and check how much current it draws. It should only be 1 or 2 amps or even less for a higher voltage motor. Ensure the motor doesn't get too hot with the fields connected.
Do you know the motor voltage? Stick this voltage on the fields.

If all goes well, use the controller on the armature. It should run. By weakening the current through the field the motor will go faster but have less torque. Since the field doesn't draw much current you can use a resistor or even lights to go in series with it. Make sure the field has current going through it or you will draw way too much current through the controller/armature.

Generally SepEx controllers control both armature and field. Maximum voltage on field at low revs, weakening current as more revs are wanted - but not too weak.
Hope this helps.


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## Qmavam (Aug 17, 2008)

Thanks for the response Johny,
The field (shunt) resistance is 40 ohms, so the current is less than an 1 amp.
I don't think that will get hot.
I like the light bulb idea, for top speed I could flip a switch and put 1 or 2 car tail lights in series, probably need to experiment a bit to get the right resistance. Hmm, maybe an rpm counter that opens a relay across the lights at a certain rpm. 
I tried to get info about the motor from Baldor, I got zero response. 
The motor voltage is 28v, I'm going to run it at 36v. I may need to limit the 
voltage to the field because of this, and maybe not allow the controller to go to 100% duty cycle to keep the heat low.
Thanks again for the info,
Qmavam


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## Johny (Jul 21, 2008)

No problems. For 1 Amp I would invest in a few 10 Watt resistors, as light bulbs may be a tad unreliable. If the field current stops then the motor will draw HEAPS of current. Edit. BTW The controller will already have a reverse diode but if you are going to introduce a switch into the field it would be wise to protect the switch with a reverse diode across the field.


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