1992 EZ GO Marathon

[mike71]

Talk about sticker shock!! I just priced a Curtis like the one that is on the cart now and it was around $485.

I definitely would like to make sure that it is the controller before dropping that kind of $$.

[72volt_ezgo]

They are sure proud of that one!

Advertisement or not,I just looked at the alltrax series controllers at evdrives web site and you can have an AXE 4834 new $268 and used for $225 and you could even go to 48 volts with it if you like.Also it is a 300A rated controller.

Testing!

Cart on jackstand! - Jump M- and B- terminals on controller. Be careful! That will bypass controller and and send full battery power down the line!

F&R will obviously have to be in either F or R for anything to happen!

( I don't know if I said the above to you before or not! If I did,ignore me.)

Barna

[fishb8]

As 72 said be careful and don't let the motor run for long like this. All you need to know is will the motor run.

72, good info on the controllers thanks.

[mike71]

Hey Guys I really appreciate it.

I will jump between (B-) and (M-) this morning and see what happens. Will the pedal need to be pressed or will I be bypassing that also?

I tested between (B+) and (M-) yesterday and only got (7) volts. Is that a typical reading for a bad controller? I'm pretty sure that I checked it correctly.

I found a schematic which shows that (B+) goes from the Controller to the (-) side of the solenoid and (M-) goes to (C) on the F-N-R switch. It also shows (B-) going to one of the small posts on the solenoid. Does that seem right?

[72volt_ezgo]

As long as your solenoid is activated (closed/jumped if you have to)during the test,the pedal input does not matter!

I never had to test this before between B+ and M- on a controller but depending on conditions (load) you would want to see more than 7V because that little potential will not move the motor.
Imagine the B+ and M- is the operating voltage going to your motor! (of course it has to loop through a buch of other things before it makes it there) So like I said I've never checked this for myself but I imagine you would want to see a "little" more than 7V across there! (a "little" closer to battery pack voltage).

There is no -side of solenoid (only activation) the solenoid is a switch that brakes the flow of current on the large cables when in the off state, or allows current to flow through (across it's two large posts) when the contacts are closed! And they are closed when it gets a + and a - on the small connections!(across it's coil that will power the electro magnet inside and closes the contacts)(the coil inside the solenoid IS the electro magnet that pulls a ferrous plunger into position to close the big contacts)
So both sides of the solenoid is +!
The rest seem right!

Barna

[JohnnieB]

Originally Posted by 72volt_ezgo

................ I never had to test this before between B+ and M- on a controller but depending on conditions (load) you would want to see more than 7V because that little potential will not move the motor.
Imagine the B+ and M- is the operating voltage going to your motor! (of course it has to loop through a buch of other things before it makes it there) So like I said I've never checked this for myself but I imagine you would want to see a "little" more than 7V across there! (a "little" closer to battery pack voltage).

Sorry to nitpick, but what you are measuring across B+ to M- is PWM (Pulse Width Modulation). The DC voltage is actually the full battery voltage (or close to it), but it only occurs in short pulses and voltmeters typically read average or RMS (Root Mean Square) rather than peak, so the displayed reading will get higher and lower as the pulse width increase and decrease.

That said, using a typical DVM, the voltage measured there should vary from something around Zero to something close to the full battery pack voltage.
If the 7 Volts being measured was PWM DC, it would equate to about about a 20% throttle, which should move the cart, or at least make the motor wheels spin if they were lifted off the ground.

Therefore, I suspect the 7V is actually a DC voltage measurement and is most likely random leakage through a dozen or so blown MOSFETs and their associated components. (Bad controller in other words)

FWIW: The output stage of the electronic speed controllers used in most golf carts and similar applications is a dozen or two MOSFETs in parallel. The MOSFETs are either fully on or fully off and they are switched on/off at about 15 to 20 Khz. How long they stay on each time they are switched on (Duty Cycle) determines how much current is allowed to be sent to the motor.

The MOSFETs are typically located between the B- and M- terminals on the controller, so shorting (aka jumper or bypass) B- to M- is effectively turning the MOSFETs on all the time. At best, this is dangerous to both you and the cart, and should be avoided.

An ohmmeter from B+ to M- (disconnect wires from controller and attach ohmmeter to B+ and M- wires) will tell if you have continuity through the armature, brushes, f/R switch and stator.
Pushing the cart by hand will tell you if the motor/differential/axle/brakes are seized.
Gives you about the same information and is a lot less dangerous.

[72volt_ezgo]

@JohnnieB!
I agree 100% but we are dealing with someone who just want to determine what is going on with his cart and the information he is absorbing probably already getting over his head as it is!
Therfore I try to keep it cut and dry.

I'm also sure that he is depressing the pedal all the way when he sees that 7V on his meter!

The reason I was only hinting that the voltage is too low to move the drivetrain at 7V is because I never personally measured voltage across B+ and M- (Have you?) and if the circuit is complete with the armature and the field windings loading across B+ and M- it will sure to be less than an open circuit voltage reading! But how much less? I don't know until I check one for myself. (or someone who did the test on a working cart can chime in)

Barna

[simple man]

Batt. Pack voltage with pedal pressed= 35.9 That's quite a voltage drop for freewheeling! Disconnect your ( M - ) at the controller and test between ( B+ ) and ( M- ) on the controller, pedal up and pedal down. If you have pack voltage with pedal down and zero voltage with pedal up, your motor could be shorted internally. Do the 12V test on the motor as previously described. It is also possible to have a dead cell in one of the batteries. If you can get a load tester ( automotive one will work fine ), test each battery. One bad cell in any battery can down your cart!

[JohnnieB]

Wow, I missed that completely and he said it in two different posts.

As an alternative to using a load tester, you could measure each battery separately with a DVM. Pedal up and pedal down with wheels off ground.
If they all drop about the same, something somewhere is drawing a significant amount of current.
If one (or more) battery(ies) drops more than the rest, that's the problem (or at least one of them)

Do you have the model number of the controller? (IE: Curtis PMC 120x-xxx)

Added: On further reflection, the motor still should be turning unless the battery drops below the controller cutoff voltage (about 25V ???)
But it would be good to find out if there is a weak battery or batteries.

[mike71]

Ok here is the results from the tests that I have performed this morning

The system voltage is 38.10vdc and with pedal pressed it drops about 2vdc.

Voltage from B+ to M- +6.8(vdc)

Continuity of wires(disconnected) between M- and B+(to motor)= Rings
Continuity of wires(disconnected) between M- and B+(to solenoid)= Rings

Ohm test: M- to B+(to motor) = 0.7
M- to B+(to sol.) = OL

With M- disconnected at controller, I checked between it and and B+(while still attached to the controller) and got 38.10vdc with pedal pressed(which matched the system voltage) and 0 vdc without pedal pressed.

I will go check the model number of the controller and check the ind. batt. voltages with pedal pressed and reply back shortly.