stunt /go fast button

[Sergio]

Just be careful and if you notice the cart is starting to loose speed, release the button immediately at that point.

The ability of a series motor to produce torque with a shorted field if very limited, specially if not at full rpms.

Revolution: The math is not quite that simple, the field coil resistance is much less than the armature, but that would only apply on a motor that is not turning.
As soon as the motor starts to turn, the Back EMF produced reduces the voltage at the armature, and that is what causes the current to go down under speed.

[Revolution]

Originally Posted by Sergio

Just be careful and if you notice the cart is starting to loose speed, release the button immediately at that point.

The ability of a series motor to produce torque with a shorted field if very limited, specially if not at full rpms.

Revolution: The math is not quite that simple, the field coil resistance is much less than the armature, but that would only apply on a motor that is not turning.
As soon as the motor starts to turn, the Back EMF produced reduces the voltage at the armature, and that is what causes the current to go down under speed.

The back EMF is why I thought the crusing at speed current would increase once the field was shorted, since the field windings cause a large part of the back EMF on the rotor. Once that magnetic force is reduced the armature would allow more current through it. Add that to the reduced resistance from bypassing the field and you should see an increase in current.

I might just have to set this up temporarily to see the current difference with and without the field shorted.

[Sergio]

I definitely agree on that point, the motor will attempt to compensate for the lost flux (field shorted) by increasing the rotational speed (the theory behind field weakening).

The problem is that the rotor alone cannot make up the lost flux so if the motor gets subject to torque conditions, the speed will continue to decrease and the armature current will continue to increase.

That is a receipt for a core meltdown as you already experienced in your previous motor.

[paintdude96]

I only use the button when I get up to speed. not used for taking off or going up hills

[93yellowclubcar]

Tested out this mod for myself today on my old 3 wheel Marathon because, well, I've always wanted to. Threw it together from some 4 gauge cables that used to be in a CC wiring harness for the wires to short the field, a solenoid from an old Cushman, a cheapo momentary N.O. switch that I had lying around with my electrical stuff, and some 16 gauge wire and assorted ring terminals of the appropriate sizes for the batteries, solenoid posts, and switch. Cost me a grand total of $0.00 since I had all the stuff.

Results: When running wide open at speed down my flat gravel driveway I get 11-12 mph out of the old cart. With the shorting solenoid engaged I get 15 mph. Roughly a 25% speed increase by my math. After four or five runs the motor was still cool to the touch, solenoid was hot though - I am guessing it's a limiting factor here.

The gravel is a drag on the speed, could probably get 16 on pavement and 17 or 18 if the rear tires on the cart weren't so darn small. They're standard 18s, but they only measure about 17" tall. Plus, this is an old battery pack that is probably getting weak, and a stock motor running on the oddball 87 rear end that had slightly lower gearing.

Do I recommend this? No. Too easy for something to go amiss and fry an expensive motor. If I were to leave this on my cart and actually mount stuff right and put in a switch that wasn't just dangling by the wires, I'd hide an on/off toggle in the shorting solenoid activation circuit somewhere under the seat. That way the go faster button would only be active when I wanted it to, especially if kids were around.

[93yellowclubcar]

Had another thought on this this morning. I think that the "Caddy Shift" golf cart shift handle replacements have standard shift knob threads. If I was doing the setup permanately, I'd have one of those Go-Baby-Go shift knobs with the red button to activate the solenoid.

[paintdude96]

ok update ..... I had an old F&R switch took the bus bars out and added it to my F&R . then I got some extra wire and doubled up and went from my F&R to the motor. with 27" tall tires 500 amp axe controller full charge running on the button for a good distance I has hit 28-30mph going down a little hill going up the same hill on the button I was hitting 26-27 mph. so now we have been doing the street out law racing thing in our neighborhood in on the #1 spot . I was in the #8 spot now im on #1. so its working for me .

[paintdude96]

[Revolution]

Glad its working for you. Hows the motor temp after a speed run with the field shorted?

[paintdude96]

went riding 2 nights ago and I rode a good amount last night and went over a bridge 2 times and rode more around our neighborhood and hit the button for a good distance on and off . well I get home and I smell something so I lifted up the seat and I could feel a good amount o heat so I reached back to the motor and it was too hot to touch. I ran the cart hard this time but any other time I haven't I was just testing this out to see how hot it gets . but any ways the button is like NOS you only use it when needed .if u have NOS on your car your not going to use it the whole time your riding cause that will eat your motor up . so anyways its an old wear out motor if I burn it up they make replacement ones and so Im having fun while I can and if I need a motor ill check with people on here or check with my cart buddies here thanks