2009 TXT no go II - The Saga Returns

[Powder Burns]

OK I had a thread a couple of months back (2009 TXT no go) and got lots of help, mainly from JohnnieB. I diagnosed and fixed a couple of small problems, and things were OK - for a while.

Then I started getting periodic times where the solenoid would click, but the cart would not run. It seemed like a loose wire, as sometimes moving the F/R lever and/or turning on/off the key switch would get it to kick in. I checked a bunch of connections, but all seemed OK.

Then that all stopped working. The solenoid clicks, but no go.

Here are my present observations:

Switch on, pedal OFF, 37V battery voltage:
On controller
M- is 0V
B+ is 37V

Switch on, pedal ON, 37V battery voltage:
On controller
M- is 0V
B+ is 4.5V

Then I release the pedal, and B+ slowly climbs back to 37V.

My controller is Curtis, likely the stock one, P/N 25864G09.

I previously replaced the solenoid diode, and this one still checks out good.
The solenoid resistor checks out at 250ohms.

What should I check next? I'm concerned that my controller may be bad, but I don't know how to confirm if that is the case.

Thanks in advance for any advice.

[JohnnieB]

Appears the solenoid is clicking, but the contacts aren't making good contact.

Measure the voltage between the controller's B- and B+ terminals. If it drops down lower than what the pack voltage is at the time, the solenoid contacts are bad.

If it is a stock solenoid, the moveable contact is a ring of copper and it can rotate, so intermittent operation is possible. Attachments show fixed and moveable contacts of used stock solenoid.

It is only rated for 85A, so replace it with a higher ampacity solenoid. At least 100A for a stock (275A) series controller.

[Powder Burns]

Thanks JohnnieB.

I'll check that voltage next. I didn't think I could get inside of the solenoid to adjust the contacts, but I'll look closer when I go out and check it.

I'll report back ASAP.

Thanks again.

[JohnnieB]

Originally Posted by Powder Burns

Thanks JohnnieB.

I'll check that voltage next. I didn't think I could get inside of the solenoid to adjust the contacts, but I'll look closer when I go out and check it.

I'll report back ASAP.

Thanks again.

You can't. That was cut apart with a sawzall, or something similar.

[rockfordpi]

Originally Posted by Powder Burns

Thanks JohnnieB.

I'll check that voltage next. I didn't think I could get inside of the solenoid to adjust the contacts, but I'll look closer when I go out and check it.

I'll report back ASAP.

Thanks again.

Sometimes a wire or connection will read good voltage without a load and then fail when under load. As JB said, that can happen with Solenoid or other connections.

[Powder Burns]

OK for B+ and B- with a battery pack voltage of 37.4V

Pedal switch OFF
B+ = 36.7V
B- = 0V

Pedal switch ON
B+ to B- drops to about 6-7V, then if I fully depress the pedal it drops to about 0V with some noise

Release pedal switch, and B+ to B- slowly climbs back to 36.7V

[JohnnieB]

Originally Posted by Powder Burns

OK for B+ and B- with a battery pack voltage of 37.4V

Pedal switch OFF
B+ = 36.7V
B- = 0V

Pedal switch ON
B+ to B- drops to about 6-7V, then if I fully depress the pedal it drops to about 0V with some noise

Release pedal switch, and B+ to B- slowly climbs back to 36.7V

Solenoid contacts not making contact. Replace the solenoid and cart ought to run normally.

The precharge resistor charges up the filter capacitors inside the controller to a few volts less than pack voltage, so what you are seeing with pedal up is normal. The slight voltage difference is due to the amp flow through a bleeder network that continuously discharges the capacitors for safety reasons, being replenished via the 250Ω precharge resistor. If you do the math, you'll find the bleeder network is discharging the capacitors at about a 3ma rate.

When the pedal switch closes, the controller normally trys to draw more amps through the solenoid contacts, but they aren't making good contact and the only path is through the 250Ω resistor, dropping the voltage further.

When the pedal is pushed further, the controller tries to pass a lot amps to the motor and nearly the entire pack voltage is dropped across the 250Ω resistor. It only take about 150ma to drop 37.4V across 250Ω and the motor is trying to draw 150A or more.

[Powder Burns]

OK I will get another solenoid. This will be the third one....

Now, I have a White-Rogers 70-120224 model solenoid on it. That’s what was on it before as well.

I think the prior one died due to heat from the battery cable. In the prior round of diagnosis, I noticed that the cable from the positive terminal of my battery bank was a little tarnished/burned looking and had a few strands that were broken at the terminal where it attached to the solenoid. Thus I recently replaced that cable with a 2 gauge welding cable that I bought from AD/DC Wire and Supply.

I don’t see an amperage rating on the solenoid itself, or with the spec sheet that came with it. Is there another model I should use? If so, how can I tell the amperage rating?

Maybe I should be buying the solenoids by the dozen.....

Is there another problem that is causing me to burn up solenoids?

Thanks as always.

[JohnnieB]

The NO (Normally Open) contacts in a W-R 70-120224 are rated at 50A continuous (Spec sheet attached) and a stock series drive controller will pass up to 275A, so it is way too small for the application.

The motor in a completely stock series drive cart draws up to about 275A (max controller throughput) during max effort accelerations from a standstill and from about 50A to 75A while cruising at speed on level ground. A solenoid that will pass 100A (or more) continuously is needed. Personally, I have a 400A controller that will pass 460A in peak amp mode and a 400A continuous/1000A peak solenoid (MZJ400) that has been in service since 2011.

A SW180 is the smallest solenoid I'd use on any golf cart. https://www.cartsunlimited.net/solenoids.html

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Poorly installed cable lugs can also cause heat. Crimp and soldered is best. Excerpt from Trojan white paper on cables attached.

[Powder Burns]

That makes sense. Thanks for the additional information. It looks like for now I’ll order the SW180 as I can use it with the cables I just bought.

Thank you very much, JohnnieB!

I’ll report back when I make progress.