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Old 06-29-2021, 07:22 AM   #21
egad
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Default Re: Melex 252 Curtis controller 1204 bad?

Ah, ok. That one measured 47.8k ohms
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Old 07-13-2021, 06:39 AM   #22
egad
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Default Re: Melex 252 Curtis controller 1204 bad?

Hi again. I have now soldered the Curtis controller. I put everything back together.
When i put it in reverse it ”hops” backwards. When i put it in forward and push the throttle the first time it put the cart in full accelleration. When I released the throttle it continued going full throttle. I turned off the cart with the key, and it kept going full throttle. I had to take off the cable to the battery to get the cart to stop going. Now if i put the positive cable to the battery+ the cart starts going full throttle. Even if the negative cable is off the negative pole on the battery. Could a bad solder cause These problems?
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Old 07-13-2021, 10:53 AM   #23
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Default Re: Melex 252 Curtis controller 1204 bad?

Wow! So many issues...where to begin? If you remove the negative (B-) cable from the battery it should be impossible for the cart to run. No controller issue can make the cart run with the B- cable disconnected. Also, it should be impossible for the cart to run until the solenoid is closed. The controller has no bearing on the operation of the solenoid. The solenoid should not close until you step on the pedal however you may have welded the solenoid closed by drawing a very large current when you first stepped on the pedal. Either that or you have somehow bypassed the solenoid.

You will need to restore the proper operation of the solenoid. Verify that it is not welded by removing all connections from both the LARGE terminals and also at least one of the SMALL terminals. Read the resistance between the large terminals. It should be an open circuit.

I suspect you have a wiring error somewhere. Please verify that that you do not have B- and B+ reversed. The B- cable from the battery should connect directly to the B- terminal on the controller (verify that it is not connected to M- or B+).

The B+ cable from the battery should connect to one of the large terminals on the solenoid. The other large terminal on the solenoid should connect to the B+ blade on the controller.
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Old 07-13-2021, 11:00 AM   #24
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Default Re: Melex 252 Curtis controller 1204 bad?

With regard to the controller, please verify that the replacement capacitor is installed with the correct polarity. Refer to your original pictures to identify the correct polarity. the negative (banded) side of the capacitor should be oriented upward toward the connections where the logic board attaches to the power board.
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Old 07-14-2021, 02:41 PM   #25
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Default Re: Melex 252 Curtis controller 1204 bad?

Capacitor is installed with the correct polarity. I removed everything from the two big terminals, and one small. Measured between the to large terminals and there is no connection. I guess it should read 0 Ohm?
When i first started it it took me a while to shut the cart down, and smoke came from the cart. Also the ground connection melted. Maybe the solenoid now is broken.

I also found What probably caused the problem. There is a small black cable going from the solenoid to the controller. I had it connected to B+ on the controller. Today i discovered that i should be connected to B-. I changed this, but the cart still goes full speed when i connect the +cable to battery. Even though the -cable is not connected to battery.
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Old 07-14-2021, 03:14 PM   #26
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Default Re: Melex 252 Curtis controller 1204 bad?

I have now completely removed the solenoid. If i measure between two large terminals the ohm-meter says the same, OL or ”open-lead”. Between the two small terminals there is 200ohm if I have the multimeter set to 2000.
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Old 07-15-2021, 08:47 AM   #27
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Default Re: Melex 252 Curtis controller 1204 bad?

1. The solenoid should show an open circuit between the large terminals when it is not energized so your reading appears to be correct. Also, 200 ohms between the small terminals is correct as well. if you put 36 volts across the small terminals the solenoid should click and the resistance between the large terminals should go to zero ohms. The cart cannot run if the solenoid is open because all current to the motor and the controller must first pass through the solenoid.

2. As I stated in a previous message:

"The B+ cable from the battery should connect to one of the LARGE terminals on the solenoid. The other LARGE terminal on the solenoid should connect to the B+ blade on the controller"

When you say that you found a "small black cable going from the solenoid to the controller" that was on B+ and you moved it to B- are you referring to a small wire that goes from one of the SMALL terminals on the solenoid to B- on the controller OR are you referring to a heavy duty cable from a LARGE terminal on the solenoid to the controller?

3. It is impossible for the motor to run if the solenoid is not closed. Also, it is impossible for current to flow if there is no return circuit to the B- terminal of the battery pack. I do not understand how you can say that you remove the connection to B- at the battery and the motor still runs. That is not possible, there must be some return to B- or you are getting free energy from somewhere.
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Old 07-15-2021, 09:37 AM   #28
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Default Re: Melex 252 Curtis controller 1204 bad?

SERIESCART.pdf

Here is a "typical" schematic.
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Old 07-17-2021, 04:58 AM   #29
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Default Re: Melex 252 Curtis controller 1204 bad?

The small black cable went from small terminal om solenoid
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Old 07-17-2021, 07:20 AM   #30
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Default Re: Melex 252 Curtis controller 1204 bad?

When you reassembled your controller, were you careful to restore the internal insulator between the aluminum heat sink and the box. The heat sink is connected to the M- blade and it is supposed to be isolated from the golf car chassis by an insulator. If somehow your chassis is connected to B-, you could be effectively shorting M- to B- if that insulator is missing or improperly installed. The six screws securing the heat sink to the box are also connected to M- so they must be insulated from the box and the chassis mounting surface. Shorting M- to B- effectively bypasses the controller and will cause the cart to run uncontrollably at max speed. Remove the controller and test to see if there is a short between the M- blade and the box.

You could try running the cart temporarily with the controller box isolated from the mounting surface to see if the cart runs properly. You should be able to stop a runaway cart by putting it in neutral. Of course, you should always test the cart with the rear wheels off the ground.
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