Inside a solenoid

Part 1 The problem

Tech note from Carts Unlimited. 
It has come to my attention that a few users of the MZJ200 solenoid are experiencing failure. 
This solenoid was extensively tested under the harshest conditions possible with an engineer at the wheel. The solenoid met all requirements and was recommended for all Alltrax controls 400a and less. 

I spoke with the testing engineer today who explained how the installer may cause the solenoid to fail. This is what I want to share with you. 
The solenoid has side mount main terminals. these stud terminals are double nutted on the outside of the case. The nut against the case has 2 functions:
1. light tension against the case or housing holds the inside contact in place.
2. when held with 1 wrench a second wrench can be used to tighten the outward nut against the cable terminal without spinning the solenoid stud.

If 2 wrenches are not used when tightening the outer nuts, there is a risk the stud may turn. The slightest turning of the stud will greatly reduce the available contact surface. Reduced contact will cause solenoid failure.

Just like a motor stud, always use 2 wrenches when tightening solenoid nuts on solenoids with side mount studs. Top mount studs have round contacts and are not susceptible to the same problem. We no longer sell this solenoid

 Part 2 The test

I use a meter with large alligator clips set on continuity beep. Attach this to the large posts. A jump wire with alligator clips is attached from one small post to the battery main -. Another jump wire is attached to battery pack main + and touched to the nuts on the other small stud.(not the threads - the nuts)
Each time it is touched the meter beeps. Do this 50 times in a row. 50 Beeps? Ok, clip the + onto the solenoid so the beeper is on constantly. Disconnect the beeper and set your phone clock timer for 10 minutes. Go find you HF laser temp gun and come back in ten minutes - the solenoid should be 10-15 degrees above ambient temp and not much more.

Why do I need a resistor and diode on my solenoid and what size solenoid, resistor, and diode do I need for my cart?  See Alltrax link below

Solenoid and contactor are interchangeable terms for the main power disconnect device

The BEST solution is a NEW arrival

200 amp contactors with magnetic breakouts

Providing arc suppression 

for improved service and extended life

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Golf Cart Accessories

There are many choices when it comes to solenoid selection.

​The solenoid must be sized correctly to handle the amperage the controller is going to allow to pass to the motor. All of the amperage passing through the control comes through the main solenoid.

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Solenoid & Contactor 

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Arc suppression

Without adequate contact protection, the occurrence of electric current arcing causes significant degradation of the contacts, which suffer significant damage. An electrical arc occurs between the two contact points (electrodes) when they transition from a closed to an open (break arc) or from an open to a closed (make arc). The break arc is typically more energetic and thus more destructive.[3]

The heat developed by the resulting electrical arc is very high, ultimately causing the metal on the contact to migrate with the current. The extremely high temperature of the arc (tens of thousands of degrees Celsius) cracks the surrounding gas molecules creating ozone, carbon monoxide, and other compounds. The arc energy slowly destroys the contact metal, causing some material to escape into the air as fine particulate matter. This activity causes the material in the contacts to degrade over time, ultimately resulting in device failure. For example, a properly applied contactor will have a life span of 10,000 to 100,000 operations when run under power; which is significantly less than the mechanical (non-powered) life of the same device which can be in excess of 20million operations.

Each solenoid has a dual rating. These ratings are continuous and peak.

Our 200 amp continuous duty solenoid has a peak rating of 800 amps.

Our 400 amp continuous duty solenoid has a peak rating of 1000 amps.

Copper contacts are standard in regular and heavy duty solenoid's.

Larger silver oxide contacts are used in super duty contactors and solenoid's.

The higher-quality contacts resist pitting and give a longer service life.