- #1
thender
- 39
- 0
Hello, I am an automotive technician so I work with a lot of 12volt DC motors.
First, it seems to me that bad connections or wires can cause excessive voltage drops to motors, but I don't understand what the difference is between a good cable and a bad cable. Or what qualifies a good connection vs a bad one. It seems that corrosion develops in electrical connections but I have a hard time seeing how it could develop to a damaging extent inside a tightly bolted connector and metal frame piece. As for wires I don't understand why one battery cable would drop more voltage than another unless there were broken strands that reduced the current carrying capacity by converting the energy to heat at those points. Like a light bulb filament.
That's the other thing, if I am losing energy that should be delivered to a component it should be manifested in some form elsewhere.
To my knowledge there is no internal insulation to go bad in stranded wire, and as far as I know copper does not magically lose its ability to carry current over time. I can see that heat could cause increased resistive losses though.
My big question and current concern is the DC motors. I think that the voltage dropped on the way can cause any electrical component to not function properly but my suspicion is that a DC motor is affected more.
I don't know and can't find much information about DC motors - mainly AC motors are talked about, but I think DC motors are designed to run at a rated voltage(?) or wattage(?). By reducing the voltage I think the motor will take longer to build enough magnetic force to commutate. Which would lead to increases in current and heat and decreased life span.
But that brings me back to the question of what is the difference between good and bad components. In the case of motors there are some mechanical and environmental factors like bearings, lubrication, moisture, dust from brushes, and overloads, but what is the electrical wear?
Do brush springs not push as hard? Slip rings wear? does the commutator short or develop high resistance? Do the turns of copper wire short to each other?
What happens as it fails? Changes in speed? Current draw? Inductance of each rotor winding?
Most of my motors are permanent magnet type.
I don't consider myself a competent technician until I can identify the specific component and part that is faulty, identify the cause of the fault, know whether it was preventable and how, and verify with certainty that it was repaired.
My tools are oscilloscopes, amp meters, and multimeters.
Thanks for comments and advice.
-Andrew
First, it seems to me that bad connections or wires can cause excessive voltage drops to motors, but I don't understand what the difference is between a good cable and a bad cable. Or what qualifies a good connection vs a bad one. It seems that corrosion develops in electrical connections but I have a hard time seeing how it could develop to a damaging extent inside a tightly bolted connector and metal frame piece. As for wires I don't understand why one battery cable would drop more voltage than another unless there were broken strands that reduced the current carrying capacity by converting the energy to heat at those points. Like a light bulb filament.
That's the other thing, if I am losing energy that should be delivered to a component it should be manifested in some form elsewhere.
To my knowledge there is no internal insulation to go bad in stranded wire, and as far as I know copper does not magically lose its ability to carry current over time. I can see that heat could cause increased resistive losses though.
My big question and current concern is the DC motors. I think that the voltage dropped on the way can cause any electrical component to not function properly but my suspicion is that a DC motor is affected more.
I don't know and can't find much information about DC motors - mainly AC motors are talked about, but I think DC motors are designed to run at a rated voltage(?) or wattage(?). By reducing the voltage I think the motor will take longer to build enough magnetic force to commutate. Which would lead to increases in current and heat and decreased life span.
But that brings me back to the question of what is the difference between good and bad components. In the case of motors there are some mechanical and environmental factors like bearings, lubrication, moisture, dust from brushes, and overloads, but what is the electrical wear?
Do brush springs not push as hard? Slip rings wear? does the commutator short or develop high resistance? Do the turns of copper wire short to each other?
What happens as it fails? Changes in speed? Current draw? Inductance of each rotor winding?
Most of my motors are permanent magnet type.
I don't consider myself a competent technician until I can identify the specific component and part that is faulty, identify the cause of the fault, know whether it was preventable and how, and verify with certainty that it was repaired.
My tools are oscilloscopes, amp meters, and multimeters.
Thanks for comments and advice.
-Andrew