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Unread 10-16-2019, 11:02 AM   #1
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Question Mechanical Electrical Engineer Expertise Interpretation Please

I consider myself mechanically inclined and have the curse of being able to repair/rebuild/diagnose and just flat out tear things apart to see how they work mindset. Same as a good number of people on here probably, BUT I have had this 1987ish Melex 3 wheel cart for about 10 years now and I cannot comprehend how this speed controlled, Potentiometer, contactor, solenoid microswitch, A2, S1, diode, resistor, series motor monster actually works. My brother and I have studied these many, many different versions of wiring diagrams from multiple sources and manufacturers and electrical specifications including the original Melex manual (and even talked to the guys in Poland at Melex on multiple occasions and still cannot clearly say that we comprehend how this machine operates. Can somebody....anybody please give me a schooling on how the system operates based upon this drawing that I spent hours cleaning up and coloring and studying so I might be able to understand the components and flow of electricity in this cart. I have the battery power, key switch, throttle (potentiometer) and mechanical operation parts down but how the current flows through switches that are not even technically being energized and a speed controller that absorbs excess energy that is fed by a solenoid and protected by a diode and capacitor that somehow tells a motor which way to turn is not clear. Based on the interpretation of this wiring schematic one thing that confuses me is how the Forward micro switch appears to be directly connected to the Reverse Sensing Device and as well how there is No Direct Negative Connection from the batteries to the motor. In my experience you need positive and negative connection to operate a DC motor. The speed controller and the F/R switch is the difference I know. BUT I do not understand the M+ M- A2 S2 S1 Microswitch Solenoid Speed Controller, diode basic functionality. Sorry for the long ramble but this thing is really getting the best of us and currently we are dealing with an upgraded (rebuilt) speed controller to 400 amp from stock 275 amp with new 400-1000AMP Solenoid and 4 smoked microswitches (waiting on 2 more to arrive) right now and just want someone with some expertise to help make us feel smarter than a 5th grader right about now..!
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File Type: pdf Colored Electrical circuits.pdf (966.7 KB, 0 views)
File Type: pdf The Melex Bush Blind.pdf (103.0 KB, 0 views)
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Unread 10-16-2019, 03:17 PM   #2
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Default Re: Mechanical Electrical Engineer Expertise Interpretation Please

Quote:
Based on the interpretation of this wiring schematic one thing that confuses me is how the Forward micro switch appears to be directly connected to the Reverse Sensing Device and as well how there is No Direct Negative Connection from the batteries to the motor.
Changing rotation direction of a Series wind DC motor is done by changing polarity of the Field coils (labeled S1-S2 on motor). The FnR switch changes the polarity for the S1, S2 and A2 connections.
Your A1 connection on the motor is connected directly to the battery pack positive, so it has full voltage applied whenever the pack is connected.
Your power flow in Forward selection is:
Pack + to solenoid, Solenoid to Motor A1,
Motor A1 through the armature to Motor A2,
Motor A2 to FnR switch post A2,
Across FnR switch to S1 post, to motor S1
Motor S1 through the field coil to motor S2,
Motor S2 to the FnR switch S2,
across FnR switch to M terminal, then to M- on the controller.
The Controller handles current control on the Negative side of the circuit, by limiting current flow (amps) back to the Pack negative on B-.

Directional control is done by reversing the S1-S2 polarity at the FnR switch. This changes the direction of current through the S1-S2 connections of the motor.
The controller still limits current flow on the Negative side of the motor regardless of F or R selection.

Microswitches have nothing to do with directional control. The "reverse sensing device" is the buzzer that sounds to tell you the selector is in R. The buzzer is powered by the reverse microswitch, it has absolutely zero effect on the motor or controller. You can remove it, and the cart still operates the same.

The "forward" microswitch is merely an input to the controller to tell it to allow current to pass. It provides a low current, pack voltage signal to your controller KSI input pin when the FnR switch is in either F or R, but Not when in Neutral. This is the Key Switch Input (referred to as KSI by most manufacturers), and without it the controller simply does not allow current to pass. It is a logic circuit, which means it is very low current, usually less than 100mA. Think of it like the "Remote ON" for a car stereo amp.


Some people here who know this better than I will probably be along soon to point out anything I may have said wrong. I'm far from an expert. I don't know exactly how the A2 connection on the controller comes into play in this setup.
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Unread 10-16-2019, 04:10 PM   #3
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Default Re: Mechanical Electrical Engineer Expertise Interpretation Please

Well said FT.

Also, the diode has nothing to do with the functioning of the cart, but if installed backwards it will blow micro switches.
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Unread 10-16-2019, 04:38 PM   #4
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Default Re: Mechanical Electrical Engineer Expertise Interpretation Please

A+++ for the details!! Excellent job.....
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Unread 10-16-2019, 11:03 PM   #5
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Default Re: Mechanical Electrical Engineer Expertise Interpretation Please

I did make a mistake in my earlier post. I couldn’t see the diagram very well, for some reason the full resolution version would not load on my laptop, but it shows up just fine on my phone.
I also now see you added a drawing of your own, which I’ll give some attention.
And I also found an article that helped me understand the controller a bit better, and may help you as well.

1. Key Switch: The Microswitch on the FnR gets B+ power via the key switch. The Blue wire is spliced at the common terminal, so power is delivered through the switch, as well as being then directed to the controller ksi pin, so the KSI input is basically “hot” with the key On.
The microswitch also draws power from there to send to the microswitch inside the throttle box, and that switch then makes the connection to send power to the Positive terminal of the solenoid activation coil. This is so the solenoid does not power on (close the main contacts) until you have Key switch On, Forward or Reverse selected, And have pressed the throttle.

KSI being the same as mentioned above, is the Remote On for the controller, and is provided regardless of throttle or FnR position. It is only given if the Key switch is On.

2. Resistor and Diode function:
The Controller has several capacitors inside that provide power for various functions during moments of “surge” current such as sudden changes in throttle command, among a few other things. Since the solenoid main contacts are normally Open, this breaks the main power supply from Pack+ to the controller. The Resistor across the large posts of the solenoid allows a small current to pass by the solenoid to charge the capacitors inside the controller. This is quite often refered to as a “pre-charge resistor”, and serves a few important functions. One being that it allows the controller to stay powered when the solenoid contacts are open, and two it prevents arcing of the solenoid main contacts when they close as the capacitors inside the controller can pull quite a bit of energy when first connected to battery power. Arcing of the contacts will cause them to burn and create a poor connection of the battery supply voltage for the motor, and can result in the solenoid burning internally or even melting and catching fire.

The Diode is across the small terminals of the solenoid. This diode is to prevent voltage in the coil from holding the solenoid core in a partially closed position during disengagement of the solenoid. Partial disengagement can result in burned contacts. When the solenoid coil is powered it creates a magnetic field which forces the magnetic core of the solenoid to close the contacts. When the power to the solenoid coil is removed, the magnetic field collapses, and the core passes back through the coil. Both of these actions induce current flow inthe coil, which cause the magnetic field to remain active for a short period of time, a few hundred milliseconds maybe. This slows the disengagement of the main contacts of the solenoid, which can allow the contacts to arc and burn. Eventually causing damage to the solenoid. The diode provides a current path for the voltage in the coil to take as the field collapses, which prevents the coil holding the contacts open. It can also serve as a suppression diode to prevent a possible voltage surge from the field collapse from back-feeding to other components and causing arcing in other switches.

3. I noticed in your drawing that you have a microswitch on the right side which draws power from the B+ terminal at the solenoid via green wire. The switch then returns back to the negative of the coil side (Small solenoid terminal), which is connected to the B- at the controller, which is literally the pack main negative. That arrangement is a direct short from positive to negative, and will melt that switch and/or wiring when the switch is engaged. The Green wire according to the diagram is supposed to go to the reverse buzzer. If you do not have the reverse buzzer, or it does not work, then you need to disconnect the wires from that switch and tape them off. It would be best if you can remove the green wire from the solenoid entirely.

4. Controller A2 terminal:
When a series motor is being powered and is in operation the armature acts as a motor. If for some reason the rotation of the motor reverses while still being powered, such as the operator mistakenly changing the FnR switch from Forward to Reverse, this causes the motor armature to then act as a generator, and it can have disastrous consequences for the armature and the driveline of the cart. The A2 terminal of the controller is used to control “plug braking” which diverts current created by the motor armature through the controller to pack negative should the desired direction of the motor be changed while the cart is still in motion. It’s basically a safety release to prevent your motor armature from trying to rip itself apart or shredding the gears in the axle if you should ever accidentally (or on purpose) change F to R or vice versa while driving. This article by Alltrax goes into more detail: https://alltraxinc.com/wp-content/up...ug-Braking.pdf
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Unread 10-18-2019, 02:58 PM   #6
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Default Re: Mechanical Electrical Engineer Expertise Interpretation Please

That is great information and I thank you for taking the time to do so. It gets really frustration when you think that you have made all of the right connections and spent the time to draw it all out only to have something short out or not work correctly. It challenges your patience and makes you feel like an idiot when you don't see something obvious that is wrong. It is nice to have a resource to help give you some insight.
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Unread 10-18-2019, 03:35 PM   #7
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Default Re: Mechanical Electrical Engineer Expertise Interpretation Please

Again I am at the end of the rope of this one so I appreciate your information. In regard to the #3 response. This drawing that I have color coded to try and match the color of the wires on our cart is actually a schematic directly out of the Melex manual. I did not change or alter the drawing only cleaned it up and added the color. The GREEN wire was the wire for the reverse sensing device or back up beeper. I did remove the beeper itself and then just made it a direct connection basically to the smaller - post on the solenoid. You are exactly correct though. After we got the new microswitches installed on the F/R Switch and turned the Key switch ON nothing happened UNTIL we moved the Forward Reverse switch to FORWARD position and the Diode blew instantly. We have not done anything yet as it has been so frustrating with all of this we did not know what we damaged now. I have ordered two more microswitches not knowing if they were blown because we have our annual trip coming up next week that we have been doing for the last 30 years and I wanted to make sure I had replacement switches on the way. We have new diodes and pre-charged resistors as well. this will be the 4th set of microswitches on the F/R switch that we have had to replace. We are about at such a state of defeat to a point of giving up. We need the cart so I am hoping for the Hail Mary at this point. I am attaching a copy of the original drawing that came from Melex to show that we are basically connecting everything just as they have it on drawing. I am also attaching a drawing that we made where we think that the wires go based upon the Melex wiring diagram. I don't know if this will help or make things more confusing but I am throwing everything out there.
Attached Files
File Type: pdf Electrical Fig 11 1 7.pdf (212.7 KB, 0 views)
File Type: pdf Redrawing of Davids Hand Drawing.pdf (50.0 KB, 0 views)
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Unread 10-18-2019, 04:14 PM   #8
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Default Re: Mechanical Electrical Engineer Expertise Interpretation Please

thebonecollector A Melex is a copy of a ezgo marathon. You posted this in the Club Car forum. it should be in the ezgo forum. I will move this for you. OK
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Unread 10-18-2019, 05:05 PM   #9
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Default Re: Mechanical Electrical Engineer Expertise Interpretation Please

Ok Thank you. I am assuming that I will need to go into the EZ Go forum for responses now?
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Unread 10-18-2019, 05:11 PM   #10
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Default Re: Mechanical Electrical Engineer Expertise Interpretation Please

Yes you will need to go to the ezgo electric forum. All the guys helping you are from the club car forum.
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