Question

[Bob-0]

I have a quick question for the electric car gurus.

I have a lifted 36v DCS that was converted to a 48v system and an AllTrax controller. Had to rewire the batteries and motor as they were all snafued.

It has a 400amp HD solenoid with a diode on the primary terminals (small) and it appears to have both a precharge resistor and a 6A6 diode on the secondary terminals (large). When you press the accelerator pedal it keeps popping the 6A6 diode on the controller side. The blink code on the controller says precharge resistor failure, but everything on the solinoid test fine.

The car will run a short distance before it pops the diode, but it does it every time. I’ve gone through 3 diodes testing it out, lol.

[JohnnieB]

Which Alltrax controller, DCX or XCT? The DCX uses a pre-charge resistor while the XCT uses a regen diode, but neither uses both.

Schematic for both types attached.

---------------
The 6A7 diode popping sounds like it is being installed backwards. Banded end should be connected to the battery side large terminal.

[Bob-0]

Originally Posted by JohnnieB

Which Alltrax controller, DCX or XCT? The DCX uses a pre-charge resistor while the XCT uses a regen diode, but neither uses both.

Schematic for both types attached.

---------------
The 6A7 diode popping sounds like it is being installed backwards. Banded end should be connected to the battery side large terminal.

It’s the XCT controller. It came in with both on, but I’m not an electric guy at all. I looked at the diagram and saw it said it wasn’t required but the seller promised that’s how he’d been driving the car.

Would the precharge resistor cause the diode to pop? The car won’t run after it does. The 6A6 (6a 600v) diodes i got were a little to short to span the secondary terminals so I added a 10ga wire to the “negative”’end of the diode (controller side of solenoid) so I could get it to run to try and do the tests that I know of. The original diode that was in the car melted in two.

[JohnnieB]

The purpose of the pre-charge resistor is to keep the filter capacitors inside the controller charged so the solenoid contacts don't arc as much while the bounce to a close. It is a preventative device rather than an operational one, so the cart will run with or without it, but the solenoid contacts will last longer with it.

The diodes (both of them) are preventative devices also.

The smaller one on the solenoid coil suppresses the voltage spike generated when the coil de-energizes, protecting the pedal switch contacts from arcing as much while opening.

The bigger diode (6A6) protects the controller from the higher than normal voltage that can be generated if the solenoid contacts open while in regen braking. (A very rare, if ever, occurrence with most carts)

For troubleshooting purposes, the resistors and diodes can be disconnected, but should be installed before cart is returned to normal use.

Sounds like there is two problems.
1. Precharge error
2. Diodes popping.

1. That error means the voltage between the controller's B- and B+ terminals and the KSI (Key Switch Interlock) voltage on pin-6 differ by more than 5V. Measure those voltages and find out which isn't right. Both ought too be the same as the battery pack voltage. The filter capacitors in XCT48xxx-DCS are kept charged via Pin-10, so check voltage on it also. (Check pin-9 voltage as well)

2. The banded end (cathode) should face the cable connected to the battery pack. The diode blocks current flow from battery pack to controller, so if it is popping, it is installed backwards.

[Bob-0]

Originally Posted by JohnnieB

The purpose of the pre-charge resistor is to keep the filter capacitors inside the controller charged so the solenoid contacts don't arc as much while the bounce to a close. It is a preventative device rather than an operational one, so the cart will run with or without it, but the solenoid contacts will last longer with it.

The diodes (both of them) are preventative devices also.

The smaller one on the solenoid coil suppresses the voltage spike generated when the coil de-energizes, protecting the pedal switch contacts from arcing as much while opening.

The bigger diode (6A6) protects the controller from the higher than normal voltage that can be generated if the solenoid contacts open while in regen braking. (A very rare, if ever, occurrence with most carts)

For troubleshooting purposes, the resistors and diodes can be disconnected, but should be installed before cart is returned to normal use.

Sounds like there is two problems.
1. Precharge error
2. Diodes popping.

1. That error means the voltage between the controller's B- and B+ terminals and the KSI (Key Switch Interlock) voltage on pin-6 differ by more than 5V. Measure those voltages and find out which isn't right. Both ought too be the same as the battery pack voltage. The filter capacitors in XCT48xxx-DCS are kept charged via Pin-10, so check voltage on it also. (Check pin-9 voltage as well)

2. The banded end (cathode) should face the cable connected to the battery pack. The diode blocks current flow from battery pack to controller, so if it is popping, it is installed backwards.

I’ll run the tests on Tuesday and find out how they are.

With the diode, the car won’t run without it, and if installed backwards it doesn’t run. When the silver banded side is on he batter pack side, the diode will pop and the car will stop working?

[Cartmaster]

To be honest, and I am not expert with electric carts and probably completely wrong but it sounds like the solenoid switch (large posts) are not making a good connection and all the current may be bypassing the solenoid via the diode and/or resistor causing it to pop but my understanding is that the diode correctly orientated should not pass current ? JohnnieB, you suggested taking both diode and resistor off to test, so this would confirm if the solenoid is good or bad if my theory is correct.

[Bob-0]

Originally Posted by Cartmaster

To be honest, and I am not expert with electric carts and probably completely wrong but it sounds like the solenoid switch (large posts) are not making a good connection and all the current may be bypassing the solenoid via the diode and/or resistor causing it to pop but my understanding is that the diode correctly orientated should not pass current ? JohnnieB, you suggested taking both diode and resistor off to test, so this would confirm if the solenoid is good or bad if my theory is correct.

That makes sense to simpleton me. That would definitely mean some kind of problem then as it has a brand new HD 400am solenoid on it. It won’t run without the diode on he secondary posts... so it must be popping the diode because the car is trying to run off of the diode.

I will run those tests and find out what’s happening at the pins and I will get it on the lift and double check all the wiring as well. I haven’t confirmed all of it, we have an awesome guy who is going to be the head tech when I leave, but he’s new to golf cars. I’m sure he has it all wires right but I will double check it. I do remember that they had the B+ wire on the solenoid and the wiring diagram shows solenoid to B+ then B+ to motor and it was wired B+ to motor on solenoid and solenoid wire to B+ so that the motor wire was going straight to the motor from the solenoid instead of from the controller. I did fix that, but she wants to run but isn’t happy about it, lol.

Back in the day, Leon Smith would come and help us out with electrics, but he unfortunately passed away a few years ago. He was one of the last true field techs EZGO had before they got rid of them and made the field techs a part of the privately owned branches.

[Cartmaster]

Bob, I could well be wrong, but might be worth pulling both the diode and resistor to test the solenoid. In a different application, I see burned up resistors due to high resistance in burned solenoid contacts on grass machinery controls. JohnnieB will know for sure I hope.
Don't forget my years old promise if you fly to the UK, pop round for a cuppa lol.

[JohnnieB]

Originally Posted by Bob-0

I’ll run the tests on Tuesday and find out how they are.

With the diode, the car won’t run without it, and if installed backwards it doesn’t run. When the silver banded side is on he batter pack side, the diode will pop and the car will stop working?

The solenoid contacts are not making good contact. The cart will run without any diodes or resistors on the solenoid.

Does the solenoid click when pedal is pushed?
If not, troubleshoot the solenoid activation circuit.

If it does click, it is bad, replace it.

[JohnnieB]

Originally Posted by Cartmaster

Bob, I could well be wrong, but might be worth pulling both the diode and resistor to test the solenoid. In a different application, I see burned up resistors due to high resistance in burned solenoid contacts on grass machinery controls. JohnnieB will know for sure I hope.
Don't forget my years old promise if you fly to the UK, pop round for a cuppa lol.

Solenoid contacts eventually burn out. Here are pictures of a stock EZGO solenoid that a forum member cut open.

First one shows the stationary contacts and the second show the moveable contact inverted on the stationary ones.

---------------
When a solenoid is energized, its contacts bounce several times before they stay closed and arcing occurs as they make and break contact. The controller contains upward of a Farad of capacitance and if the solenoid is energized while they are discharged, the inrush of amps is huge,as is the arcing that results from the contact bounce.

Keeping the filter capacitors charged to somewhere near the battery pack voltage reduces the number of amps flowing when the solenoid contacts bounce to a close, thereby reducing the intensity of the arcing and prolonging contact life. But, some arcing still occurs and the contact do eventually wear out.

--------------------
FWIW: I spent several years at RAF Chicksands in the early 70's and learned to enjoy a cuppa as well as a pint.