'84 Marathon resistor -- Ghost in the machine

[rlw]

It's been a long time since I last posted here, must mean my cart's been working well (up 'til now!).

Yesterday, my lovely wife came into the house after using the "buggly" and said it wouldn't stop. I asked her if she meant the brakes didn't work, and she said "No, when I went to park it, it kept moving forward, even with my foot off the accelerator". She said she turned the key to off, and when THAT didn't work, she put the FNR switch into neutral. That made the cart stop. This happened on flat ground.

I went out to check it, and sure enough, without pressing the accelerator and the cart in either F or R, AND the key either ON or OFF, the cart moved.

The first thing that popped into my mind was that I could sell the cart to Google as a "self-driving vehicle" and retire with untold riches.

Since that wasn't gonna happen, I thought it might be a possible short between the bottom (off) position on the wiper board and "first gear", but that didn't account for the key being off.

Another odd thing is that when the FNR switch is in the neutral position, I can hear the backup beeper faintly "chirping", about once a second. The ghost doesn't care if the key switch is off or on, he just keeps chirping.

So... I pulled the thing into the garage and proceeded to take things apart so I could take a look.

First, I took the back cover off so I could see the resistor. That looked OK, and my crimp and solder of the cable lugs looks like it's held up nicely. BTW, this is the "old" Marathon layout - motor juts into the battery compartment, resistor mounted between the rear differential and driver side rear wheel.

Next, I yanked out the two middle batteries so I could get a look at the wiper board and the FNR switch. Even after I took the cables off the passenger-side middle battery, the ghost (backup beeper) still chirped. It only stopped chirping once I removed the cable from the driver-side battery.

With the batteries out, I inspected the wiper board -- nothing obvious -- the bottom 4 contacts look pretty clean, and there's some pitting and carbon on the top contact. The microswitch engages when the accelerator is pressed (I can hear it click) and seems to disengage when the accelerator is resting.

Nothing obvious on the FNR switch, either - looks like the microswitches are microswitching at the proper time (when the FNR is in either "F" or "R").

So, I came back into the house and thought I'd start a post about my problem. While I was writing up this post, it occurred to me that it would help to review the wiring diagram. Looking at it, a light bulb popped on above my head, and I said to myself "SOLENOID!" "SHORTED/WELDED ON!".

I'm going to head back to the garage tomorrow and check to see if the solenoid is shorted (I bet it is). If so, I have a spare I can install.

I DO have a couple of questions for the BGW brain-trust, though:

• Why is the reverse beeper chirping? Could it be getting some kind of current loop through the voltmeter I have wired into the battery pack?
• Why is there a cable from the solenoid to the wiper board position 1 (See attached schematic)? Is it to keep the thing from arcing when the accelerator is pressed? It seems that, with this wire connected, and the solenoid shorted/welded in the ON position, it would guarantee that the cart would move forward. That seems like a safety issue, but maybe EZGO didn't care about that sort of thing in 1984.
• Is there any downside to removing that cable (like causing the thing to arc when the pedal is first depressed)?

Thanks in advance for any replies or advice.

RLW

[cgtech]

Solenoid "always stays on" is the place to start. Keyswitch, microswitch (that seems ok, but actually always stays on), welded solenoid. These are where i would start.

[rlw]

Today I pulled the solenoid, fully expecting it to be welded shut (ON). The coil side reads about 110 ohms, and the switch side reads open. I haven't hooked it up to 36V to test it yet (2 of the six batteries are sitting across the garage from the cart), but it ohms out just like a spare solenoid I have in my parts box.

It must have gotten pretty hot - the soldered lug on the cable that comes off the FNR switch to the solenoid got hot enough to melt the solder. I had to unscrew the cable from the copper threads on the solenoid.

Any suggestions would be appreciated (again!).

RLW

[rlw]

Bump! Anyone have any ideas?

[JohnnieB]

The easy one first.
The high current cable between the solenoid and position-1 is to minimize the arcing between the wiper and contact-1.
The 0V to 36V transition occurs across the solenoid contacts, which are better suited for the abuse since they are fully closed by an electromagnet while the wiper/stationary contacts can be partially closed by a slow or timid foot and the current density through a partial contact is huge compared to the current density of a fully engaged contact.
The cart will run without that cable, but contact-1 and the wiper will burn out faster.

It may be the reason the cart continues to move, but not the cause.

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The cable getting hot enough to melt solder indicates a connection with excessive resistance. Could be something like corrosion getting between the cable conductor and the solder & crimped ring terminal.

Cable getting hot is not causing cart to keep moving.

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The beeper sounding when it shouldn't be is weird, in fact just the way the beeper is turned on is weird.

The only time it should sound is when the key is ON, F/R is in R and the pedal not pushed. That is the only time B+ is applied to one side and B- to the other.

B+ is always applied to the Common of MS-3 (Pedal switch), so B+ is applied to one side of beeper whenever the pedal is not pushed, but when the F/R is in F, B+ is also applied to the other side so there should be a difference in potential across it and it should sound.

When the F/R is in R, the direction of current flow through the solenoid contact is the opposite, so the side of the beeper connected direct to the solenoid is more negative and the beeper sounds.

Basically a phantom current path could cause the beeper to beep. IE carbon dust buildup in motor, conductive paths on top of batteries putting voltage on frame and things like that. Possibly the 250Ω resister added to the schematic you posted is causing it, or contributing to the cause.

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The added diode is good, keep it. The added resistor is bad, get rid of it.
In fact, it may be what is causing the cart to creep with key off and pedal up.

It bypass the solenoid contacts and probably gets hot as hell when the cart sits.

I don't know if it could get hot enough to melt the solder out of the crimped/soldered cable end, but unlike the pre-charge resistor used on controller carts, it is actually passing current through the motor when the F/R is in either F or R and the solenoid contacts aren't closed.

Get rid of it. It serves no useful function on a resistor drive cart and may be the source of the problems you are experiencing.

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Remove the resistor and let us know how the cart works. If it still creeps, the solenoid contacts are not opening and we can troubleshoot why not.

[rlw]

JohnnieB,

Thanks for the help. Sorry for taking so long to get back on it, but today was the first day I had to really work on it.

Turned out that the wiper contact (the one that moves) was melted all to hell 'n' back. I couldn't see it, but I think there were a group of other problems. There must have been some molten copper between a couple of the stationary wiper contacts AND the solenoid was locked on. However, with the solenoid out of the circuit, it showed open. I haven't checked it yet, but I suspect the wiper board microswitch is the culprit (that'd keep the solenoid on, but not sure why if the key's off).

I ended up installing a new (to ME) wiper board, wiper arm, solenoid, and wiper board microswitch. I'll do a post-mortem on the parts I took out and see if I can figure out what happened.

As to the 250 Ohm resistor, that was just on the diagram, I didn't have one in my cart.

I put everything back together and took it for about a half mile drive -- all connections at the solenoid, wiper, FNR, and batteries were barely warm to the touch.

Looks like it's back on the air for now.

Thanks again for your help.

RLW

[rlw]

Oh yeah,

The ghost is gone. No more chirping.

RLW

[JohnnieB]

Originally Posted by rlw

Oh yeah,

The ghost is gone. No more chirping.

RLW

Halloween is just around the corner, it might be resting up for an all-nighter.

Glad to hear it is running right again.