wiring meltdown

turbo36 · Jan 7, 2006

Actually the reason is as easy as PIE /forums/images/graemlins/smirk.gif as in P=IxE.
Power (watts or P) = amps (I) x volts (V). Since the solenoid requires a specific amount of power to operate, if the voltage drops the amperage must increase to maintain the same power. Now if we think of the flow of the electrons through the wire in terms of water through a hose then the voltage is like the pressure, and the amps are the amount of flow. The wire has resistance (measured in Ohms) to that flow that cause heat to be produced, so if the flow (amps) increases then the resistance to the flow increases causing the amount of heat to increase faster then the wire can dissipate the heat thus leading to melt down. :shocked
I left out a few things like the design of the coil voltage, temp rating of the wire etc. etc. so all you EE's can fill in the gaps if you must.But remember I'm just a dumb Mfg. Engineer /forums/images/graemlins/wink.gif so give me a break.

TMcD_in_MI · Jan 7, 2006

( Actually the reason is as easy as PIE /forums/images/graemlins/smirk.gif as in P=IxE.
Power (watts or P) = amps (I) x volts (V). Since the solenoid requires a specific amount of power to operate, if the voltage drops the amperage must increase to maintain the same power. )

Turbo - Thanks for jumping in here, and the power equation does sound pretty good at first. But ... /forums/images/graemlins/confused.gif there's something I don't understand (big surprise) about what you just said. You said the solenoid requires a specific amount of power to operate. Fair enough, but why would there be any guarantee that the solenoid will always get that amount of power? According to that reasoning, if the battery was fried and went down to 1 volt, the current to the solenoid would automatically ramp up and the tractor would still start. That would be cool, 'cuz we wouldn't ever have to worry about dead batteries. See my problem?

I think Jim is maybe taking a principle from AC motor theory, and applying it to a DC circuit. I'm sticking with Ohm's Law and the idea that a lower DC voltage can't result in higher current through the solenoid.

I appreciate your throwing in your thoughts. /forums/images/graemlins/smile.gif

Tom

turbo36 · Jan 7, 2006

Hey teach, I think you are right on this, I overlooked the fact that the resistance is a constant and therefore the amperage is directly proportional to the voltage, now it the resistance changes then it is a different story. I hope you don't send a note home to my parents /forums/images/graemlins/laugh.gif
Here is a link to trouble shooting a 12 volt automative circuit.
Link

turbo36 · Jan 7, 2006

Now you really have me thinking /forums/images/graemlins/confused.gif What happens if the voltage is so low that the solenoid does not close thus the iron core does not enter the magnetic field and satisfy the designed circuit loss, doesn't that in a sense raise the resistance??? Now we really do need the Double E -how about it any electrical engineers in thehouse?

gates · Jan 14, 2006

Turbo,

With out getting to technical I will try to help. There have been two equations talked about in this thread, p=iv & v=ir. The problem is that they must be applied together, not seperately. I believe you figured this out when you stated that the resistance was constant. If you apply the given numbers in the equations simultaneously you will find that some of the statements made above are incorrect.

RRacing,

The only way, with a drop in the voltage, that the current could increase is if the resistance of the solenoid changed. Once again both formulas need to be applied simultaneously.

Fladeere,

I believe what happened in your situation is the sol. shorted to ground, thus lowering the resistance, increasing the current and ultimately putting the wires in an over current situation.

Tom,

If you can come up with that battery where as voltage goes down the current increases we could immediately put MR. in front of your name. /forums/images/graemlins/grin.gif

Ron

CAL123 · Feb 6, 2006

ok...just to follow up since I finally fixed the problem...here's the story on the wiring meltdown...

There is/was a defective "module" which failed, that did not cut off the higher voltage to the fuel solenoid once the solenoid opens (apparently the higher voltage opens the solenoid then converts to low voltage to keep it open). The module/fuse did not shut off the greater current which overheated the solenoid. There were no fuses in between the solenoid and the return wiring - so it heated up and melted the wiring all the way to the dash. Fortunately when I got in there the wiring finally burned through leaving enough ground to attach onto just behind the fusebox. In the repair I also wired in 2 in-line fuses after the solenoid so it doesn't repeat. What a mess. I ran a google search and apparently it's a known problem. I'm not sure all the models with the issue, but I would strongly consider putting in an in-line fuse or see which solenoid you have in your machine. BTW, I was quoted $800 for the repair, but was able to complete it with the help of a friend. /forums/images/graemlins/cool.gif

thanks to the posters for the input...frustrating to have a major repair at 125 hrs!

hawk7 · Feb 7, 2006

OK Just some Info to freshen up every one from there school days. I've been an industrial Electrician for 10 years working on CNC equipment, 3Phase, single Phase, conduit, low and high DC circuits and so on. But we all tend to forget some of the basics from time to time. Remember one thing. If some one ever tells you their an expert, Get away from them as they will get killed or somthing. But this is the purpose of this forum, To learn from each other and this is why I joined. Anyway here is the theory. /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif
 OHM'S LAW
Ohm's Law says: The current in a circuit is directly proportional to the applied voltage and inversely proportional to the amount of resistance. This means that if the voltage goes up, the current flow will go up, and vice versa. Also, as the resistance goes up, the current goes down, and vice versa. Ohm's Law can be put to good use in electrical troubleshooting. But calculating precise values for voltage, current, and resistance is not always practical ... nor, really needed. A more practical, less time-consuming use of Ohm's Law would be to simply apply the concepts involved:

SOURCE VOLTAGE is not affected by either current or resistance. It is either too low, normal, or too high. If it is too low, current will be low. If it is normal, current will be high if resistance is low, or current will be low if resistance is high. If voltage is too high, current will be high.

CURRENT is affected by either voltage or resistance. If the voltage is high or the resistance is low, current will be high. If the voltage is low or the resistance is high, current will be low.

RESISTANCE is not affected by either voltage or current. It is either too low, okay, or too high. If resistance is too low, current will be high at any voltage. If resistance is too high, current will be low if voltage is okay.

NOTE: When the voltage stays the same, such as in an Automotive Circuit... current goes up as resistance goes down, and current goes down as resistance goes up. Bypassed devices reduce resistance, causing high current. Loose connections increase resistance, causing low current.