EZGO TXT Non-PDS Help/Questions

[yurtle]

Oops, I got leap-frogged.

[JoeBleaux]

Originally Posted by JohnnieB

You said the solenoid clicks, so the problem is in the high current circuit.

Jack rear wheel off ground and put on jackstands so the half ton cart doesn't take off unexpectedly and run over someone or something.

Connect your DVM between the B- and M- terminals on controller.
Press pedal just far enough to make solenoid click and you should read FULL battery pack voltage.

If you don't there is an open or excessive resistance somewhere in the high current circuit, which is highlighted on the attached schematic.

Go looking for the battery pack voltage and when you find it, the problem is between there and last place that didn't have it.
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If you do get full pack voltage, press pedal to floor slowly and voltage between B- and M- should smoothly decrease to zero or near zero.

If it doesn't either controller or throttle input to controller is bad.

To all attempting to help me out: thanks! Sorry I forgot to mention that it is a "series" cart as far as I can tell - is that right? I thought the A1, A2, S1, S2 connections on the motor and the 3 lug/"5 pin" controller only went in series carts, but ??? I also forgot to mention that all my testing has been done with the rear on stands.

JohnnieB: I have read several of your replies to others, and I have done those tests. Here''s what I've found: when the solenoid clicks with the controller and resistor disconnected, the solenoid is sending the pack voltage "down the cable" (IOW, it seems the controller is getting <nominally> pack voltage - I haven't checked amps, but...). I have only tested for voltage with the cable from the solenoid connected to the controller with the resistor connected as well (I figured it is there for a reason, so I have not attempted connecting to the controller without the resistor in place), so I get nearly pack voltage there even with the pedal untouched through the resistor. I have a DC capable ammeter, so I could check current (not tonight, though) and really, I don't THINK that low amperage is the issue, but ??? I do not get anything close to pack voltage at M-, pedal up or down. From what I can tell, when the pedal is pressed and solenoid engages, the controller gets pack voltage over cables that could handle the current, but the controller just doesn't react properly.

One more bit of potential info - the guy I got the cart from (the 2nd owner after the original owner golf course) said it had intermittent "solenoid clicks, no go" issues until it finally just started "click, no go." He was forthcoming about that, but he didn't attempt any troubleshooting.

I'm leaning toward a bad controller, but obviously, I'd rather it be a 15.00 solenoid than the more expensive controller.

Anyway, thanks to all for the help!

[JoeBleaux]

Originally Posted by JohnnieB

If you don't there is an open or excessive resistance somewhere in the high current circuit, which is highlighted on the attached schematic.

PS - that is the closest thing I've seen to my wiring - thanks! - except that this cart doesn't _seem_ to have ever had the reed switch in the charger input connector on the cart.

[yurtle]

Originally Posted by JoeBleaux

I have a DC capable ammeter, so I could check current (not tonight, though) ...

DO NOT use a DC ammeter, unless it is capable of reading 100s of amps, AND has cables as thick as your battery cables.

[JoeBleaux]

Originally Posted by yurtle

DO NOT use a DC ammeter, unless it is capable of reading 100s of amps, AND has cables as thick as your battery cables.

Thanks for the caution but it is a commercial true RMS capable of reading 200 amps plus, AC or DC. I'm not sure what you mean about cable size - it is a clamp-on.

[yurtle]

Clamp on is usually AC only, but not knowing what you have....

FWIW, a controller puts out PWM DC, so it's pulsed DC.

[yurtle]

Originally Posted by JoeBleaux

Thanks for the caution but it is a commercial true RMS capable of reading 200 amps plus, AC or DC. I'm not sure what you mean about cable size - it is a clamp-on.

RMS is AC, not DC.

[JohnnieB]

@yurtle:
I have a clamp-on amp probe that measures 10A to 600A AC or DC.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
Uses a Hall Effect sensor, powered by a 9V battery, puts out either 0.001V/A or 0.01V/A (user selectable) and can be coupled to any DVM or Scope.


@Joe:
Since Ammeters are seldom used in troubleshooting. (Same with Ohmmeters) Once a problem has been localized with a Voltmeter, they can be used to further verify a component the voltage readings say is bad, is in fact bad, but Amps, Ohms and Volts are all tied together by the laws of physics, so doing so is often a redundancy. On the other hand, there are times when invasive meters are needed, but for the most part a voltmeter is used to troubleshoot electric golf cart issues.

The purpose of the resistor across the solenoid's large terminals is to keep the filter capacitors inside the controller close to fully charged so the solenoid's contacts don't arc as much when they close. If completely discharged, the filter capacitors would try to draw infinite amps while the contacts were still bouncing. For safety reasons, the filter capacitors have bleed resistors to discharge them within a few minutes after the controller is disconnected from the cart wiring. The net result is that the voltage between the B+ and B- terminal is a few volts (3V to 5V or so) less than full battery pack voltage.


The B+ terminal connects directly to the motor's field (typically called the stator in series wound motors) winding, either S1 or S2 depending on which direction is selected. The speed control element (a dozen or so MOSFETs in parallel) is located between the B- and M- terminals and the M- terminal connects directly to the Motor's A1 terminal.

The MOSFETs (Metal Oxide Semiconductor Field Effect Transistor) are turned off and on about 18,000 times a second and how long the stay on during each cycle is called the duty cycle. The output of the controller to the motor is PWM DC (Pulse Width Modulated) and its duty cycle varies from 0% to 100% based on the throttle input to the controller.

I prefer measuring between the B- and M- terminals because they span a single variable. When the MOSFETs are at 0% duty cycle they are effectively an open and no current will being flowing, so all the voltage applied to the entire high current circuit will be dropped between those two points. If it isn't, there is an undesired open (or high resistance) somewhere in the circuit.

Since you are not getting any voltage between B- and M- with the pedal up or down, you have an open someplace in the high current cables (13 of them), connections (26 of them) F/R switch contacts (4 stationary, 4 moveable), motor (brushes and studs) or solenoid contacts. There are dozens of possibilities, but the most likely suspect is the F/R switch.

Should be voltage on all 4 of the studs the 4 high current cable connect to.

[JoeBleaux]

Originally Posted by yurtle

RMS is AC, not DC.

Just indicating that it is not a Harbor Freight freebie, but a commercial meter capable of reading the cart's amps, and it does do DC amps as well (AW Sperry, 600V/1000A, AC or DC).

[JoeBleaux]

UPDATE - Here are the actual readings from the cart:

Meter leads on B- and M-, key on, F-R in F, pedal pressed just to solenoid clicking on, voltage jumping around under 1 volt, pressing the pedal further decreases the voltage and seems to stabilize it a bit at full-down. When the pedal is allowed to return to full up, the voltage stabilizes at about .33 volts, within .05 volts (slightly different voltage with multiple readings) and starts to drop off in .01 volt increments - like a cap discharging???

It seems the last place I have pack voltage is inside the controller - is there any way to check it? I found nothing on the guts of the controller, so I am assuming that this isn't a fuse inside - correct?

Bottom line is that it would seem the controller isn't working properly - correct?