I am an idiot

[Hap Call]

Hap,

I believe you're incorrect.

Here's the equation:
Voltage = current x resistance

The resistance (the fuse) stays the same, so an increase in voltage will result in increased current, burning the fuse. That's why fuses are rated in amperage (a unit of current), because they can handle up until that amperage, not higher.
That's why electrocution with high voltage can kill someone. The person is a resistor. The high voltage results in high current, frying the person.

An easy way to test this idea out is to hook up three 12 volt batteries in series (not in parallel), thus tripling the voltage. Your bike's fuse will certainly burn at this voltage.

Actually the correct formula to use is:
Power = Voltage x current

If your starter motor pulls a 100 watts and you use 12 volts to turn it then you use 8.33 amps to turn it. If you have 20 volts, you use 5 amps to turn it. This is theory. Actually, it will turn faster but due to windings on the rotor (making it an inductive-resistive circuit) it will not pull as many amps as if it were at 12 volts.

What you say is true for a strickly resistive type circuit (i.e. your lighting circuits) so you are also correct but normal voltage on a motorcycle system can be as high as 14.8 to 15 volts and the fuses are rated at to operated at 200% over current (and that is a slow burn calculation). Even at 20 volts you should be okay. You will, however, burn out filiments in the lights due to excessive heat produced from the formula you mentioned earlier if you keep the voltage too high for an extended period of time.

Hap

[nabrams]

Actually the correct formula to use is:
Power = Voltage x current

If your starter motor pulls a 100 watts and you use 12 volts to turn it then you use 8.33 amps to turn it. If you have 20 volts, you use 5 amps to turn it. This is theory. Actually, it will turn faster but due to windings on the rotor (making it an inductive-resistive circuit) it will not pull as many amps as if it were at 12 volts.

What you say is true for a strickly resistive type circuit (i.e. your lighting circuits) so you are also correct but normal voltage on a motorcycle system can be as high as 14.8 to 15 volts and the fuses are rated at to operated at 200% over current (and that is a slow burn calculation). Even at 20 volts you should be okay. You will, however, burn out filiments in the lights due to excessive heat produced from the formula you mentioned earlier if you keep the voltage too high for an extended period of time.

Hap

Well, we're both in agreement on the fact that too much voltage will burn the main fuse, we just disagree on how much. An older, stressed fuse will have a lower tolerance and may burn more easily.

By the way, for your starter motor example: I think you're assuming that the wattage is a constant - it is not. The wattage rating for the motor is, once again, a "recommended maximum". If you apply more input voltage (resulting in more input current) then the motor will turn faster (more "power/wattage" - a Watt is a unit of "work per time"). The resultant wattage "stress" on the windings in the motor can burn the motor out. That's why there's a fuse in many household fans and such - to protect from over-voltage that will burn the motor out.

Definition of a Watt:
the SI unit of power. Power is the rate at which work is done, or (equivalently) the rate at which energy is expended. One watt is equal to a power rate of one joule of work per second of time. This unit is used both in mechanics and in electricity, so it links the mechanical and electrical units to one another. In mechanical terms, one watt equals about 0.001 341 02 horsepower (hp) or 0.737 562 foot-pound per second (lbf/s). In electrical terms, one watt is the power produced by a current of one ampere flowing through an electric potential of one volt. The name of the unit honors James Watt (1736-1819), the British engineer who built the first practical steam engines.

[Tervo]

Definition of a Watt:

Definition of an electric device: it works as long as you keep the smoke in, if you let the smoke out, it is not working anymore.:-D The fastest way of letting the smoke out is giving it too many volts.

[nabrams]

Definition of an electric device: it works as long as you keep the smoke in, if you let the smoke out, it is not working anymore.:-D The fastest way of letting the smoke out is giving it too many volts.

You said it a lot better than I did!!!!

[Hap Call]

Well, we're both in agreement on the fact that too much voltage will burn the main fuse, we just disagree on how much. An older, stressed fuse will have a lower tolerance and may burn more easily.

By the way, for your starter motor example: I think you're assuming that the wattage is a constant - it is not. The wattage rating for the motor is, once again, a "recommended maximum". If you apply more input voltage (resulting in more input current) then the motor will turn faster (more "power/wattage" - a Watt is a unit of "work per time"). The resultant wattage "stress" on the windings in the motor can burn the motor out. That's why there's a fuse in many household fans and such - to protect from over-voltage that will burn the motor out.

Definition of a Watt:
the SI unit of power. Power is the rate at which work is done, or (equivalently) the rate at which energy is expended. One watt is equal to a power rate of one joule of work per second of time. This unit is used both in mechanics and in electricity, so it links the mechanical and electrical units to one another. In mechanical terms, one watt equals about 0.001 341 02 horsepower (hp) or 0.737 562 foot-pound per second (lbf/s). In electrical terms, one watt is the power produced by a current of one ampere flowing through an electric potential of one volt. The name of the unit honors James Watt (1736-1819), the British engineer who built the first practical steam engines.

Yes, that is the definition of a watt. But voltage will not and has never burned open a fuse. Voltage does not produce heat. Only heat will burn open a fuse and heat is produced by current. I've never heard of the term wattage "stress". It is not the speed of a motor that causes it to "burn up" it is the load and/or lack of cooling of the motor that causes it. In house hold appliances, the thermal overloads located in the small motor windings or circuits are there to protect from over heating, not over-voltage.

In a permanent magnet DC motor the speed of the motor is determined by the voltage but the torque is determined by the current. Again, it is current that determines if a fuse blows or not. There are other factors such as back EMF and armature flux that determine speed and reaction to load. Again, this is a RLC circuit, not a strictly resistive circuit. You are thinking only in terms of resistance.

But then again, I don't know much about electricity

Hap

[nabrams]

Yes, that is the definition of a watt. But voltage will not and has never burned open a fuse. Voltage does not produce heat. Only heat will burn open a fuse and heat is produced by current. I've never heard of the term wattage "stress". It is not the speed of a motor that causes it to "burn up" it is the load and/or lack of cooling of the motor that causes it. In house hold appliances, the thermal overloads located in the small motor windings or circuits are there to protect from over heating, not over-voltage.

In a permanent magnet DC motor the speed of the motor is determined by the voltage but the torque is determined by the current. Again, it is current that determines if a fuse blows or not. There are other factors such as back EMF and armature flux that determine speed and reaction to load. Again, this is a RLC circuit, not a strictly resistive circuit. You are thinking only in terms of resistance.

But then again, I don't know much about electricity

Hap

Yes, of course, voltage doesn't burn anything - it's just potential. And of course current is what makes circuits heat up. Voltage defines how much current WILL flow for a given resistance WHEN you apply that voltage, regardless of the nature of the circuit. And the more voltage, the more current. So the voltage is the catalyst for the current.
The windings in a motor are the circuit through which the current flows. More current will make them hotter (unless they're made out of perfectly super-conductive material).
No matter what other factors are involved in a circuit (RLC, EMF or any other acronym) it's still a circuit and will heat up and burn when more current is flowing through it than it can handle - I think we both agree on that, right?

An electric motor's electro-motive-force (EMF) is a by-product of the magnetic field generated by the current flowing through the windings. That interacts with the permanent magnet and causes the motor to turn. The actual resultant speed that the motor turns at (RPM) is dependent on many other factors besides electrical input (friction, the load its turning). It may not turn at all if there's too much friction and/or load. That motor can be expending tons of energy even though its at a speed of zero. At a speed of zero, the current input will be converted to heat energy and that motor will radiate a lot of heat!

[bonanzadave]

Holy Crap, Now Im really con-fused (thats a pun). I always looked at it as the killer of electrics is heat. Heat is friction. If your wires are too small (High resistance) theres friction for current flow and a build up of heat. Thats why clean grounds and connectors are so important. If there dirty its a point of high resistance (friction) and heat will build and wires & insulation starts to melt. Fuses were designed as a calibrated point of friction to protect wires. When current flow exceeds the point of calabration of the fuse (in amps). The fuse burns opens, current flow stops and the wire has been protected.
As far as jumping a bike with a car I still see no problem with it electrically. 12vdc to 12vdc. The problem Ive had are that automotive jumpper cables are too big to get to the tight spots on a bike. And like someone else said. shorting or crossing polarity can cause problems with sensitive solid state devices.

[Steve]

BonanzaDave,

The problem with jump-starting a bike with a car that is running (as I see it, at least) is not the voltage, but the current (amperage). The regulator on your bike is rated to handle a nominal amount of current that is likely to be produced by your bike's charging system. I can not find charging specs for either my 650 or my 850, but I suspect that the system is rated for no more than 20-25 amps. When you connect the cables to the car, it is possible that the voltage regulator on the car is set just a bit higher than the one on your bike. If this is the case, your bike is now going to try to regulate the car's alternator output. Many of today's cars have alternators with a LARGE capacity. The alternator in my Toyota van is rated at 90 amps. There is no way the bike's regulator will be able to handle that much current.

For all those who say they have had no problem, consider yourselves lucky. Evidently the car's regulator was set lower than your bike's.

The safe way to jump start your bike is with the car's engine off. There is no way that will harm anything on your bike, it is the same voltage. There are some who will claim that the larger battery will push too many amps through the cables. Hogwash. Amps are pulled by the starter, not pushed by the battery. Same starter, same amps, but you can crank longer with a bigger battery.

Because of the regulator issue, I would not charge a bike battery in the bike by connecting jumper cables, but I have reversed the situation and used my bike to charge up a car's battery enough for them to start it. Disconnect the cables first, to protect the bike's battery and wiring. The car' starter will draw a LOT more than the bike's wiring was designed to handle.


.

[renobruce]

Amps kill fuses, not volts. Amps burn wires, blow fuses, and overheat motors.

[Hap Call]

Yes, of course, voltage doesn't burn anything - it's just potential. And of course current is what makes circuits heat up. Voltage defines how much current WILL flow for a given resistance WHEN you apply that voltage, regardless of the nature of the circuit. And the more voltage, the more current. So the voltage is the catalyst for the current.
The windings in a motor are the circuit through which the current flows. More current will make them hotter (unless they're made out of perfectly super-conductive material).
No matter what other factors are involved in a circuit (RLC, EMF or any other acronym) it's still a circuit and will heat up and burn when more current is flowing through it than it can handle - I think we both agree on that, right?

An electric motor's electro-motive-force (EMF) is a by-product of the magnetic field generated by the current flowing through the windings. That interacts with the permanent magnet and causes the motor to turn. The actual resultant speed that the motor turns at (RPM) is dependent on many other factors besides electrical input (friction, the load its turning). It may not turn at all if there's too much friction and/or load. That motor can be expending tons of energy even though its at a speed of zero. At a speed of zero, the current input will be converted to heat energy and that motor will radiate a lot of heat!

Alright, you know a lot more about electricity than me. I'll return my EE degree to the university and tell Reliance Electric I'm sorry I worked on motor design for them.

Hap

[bonanzadave]

BonanzaDave,
For all those who say they have had no problem, consider yourselves lucky. Evidently the car's regulator was set lower than your bike's.

Steve, Ill go with ya on the running car. It just seems safer. But to me the cars alternator is working to keep its battery charged. When you hook up the dead bike battery the cars alternator will work to charge both batteries. Once charged, the cars alternator goes off line. When you hit the bikes starter button there is a big draw on the battery but that shouldnt effect the bikes R/R. Should be no different than a big battery charger.

Oh ya, Hap....If you put batteries in a flashlight backwards does it suck up light ?

[Hap Call]

Oh ya, Hap....If you put batteries in a flashlight backwards does it suck up light ?

'Fraid to say...may be rong... I think it puts out dark energy.

[renobruce]

Yes, of course, voltage doesn't burn anything - it's just potential. And of course current is what makes circuits heat up. Voltage defines how much current WILL flow for a given resistance WHEN you apply that voltage, regardless of the nature of the circuit. And the more voltage, the more current. So the voltage is the catalyst for the current.
The windings in a motor are the circuit through which the current flows. More current will make them hotter (unless they're made out of perfectly super-conductive material).
No matter what other factors are involved in a circuit (RLC, EMF or any other acronym) it's still a circuit and will heat up and burn when more current is flowing through it than it can handle - I think we both agree on that, right?

An electric motor's electro-motive-force (EMF) is a by-product of the magnetic field generated by the current flowing through the windings. That interacts with the permanent magnet and causes the motor to turn. The actual resultant speed that the motor turns at (RPM) is dependent on many other factors besides electrical input (friction, the load its turning). It may not turn at all if there's too much friction and/or load. That motor can be expending tons of energy even though its at a speed of zero. At a speed of zero, the current input will be converted to heat energy and that motor will radiate a lot of heat!

Are you talking AC or DC? What about VFD? That will slow and speed up a motor. Sorry.... way off topic.

[Hap Call]

Are you talking AC or DC? What about VFD? That will slow and speed up a motor. Sorry.... way off topic.

Throw in vector control, IGBT, and PWM and call it a day!

Hap:-D

[Tom MLC]

What about VFD? Sorry.... way off topic.

Bruce, you're just a trouble maker. You threw that VFD stuff in on purpose, dintcha? 8-[

Seriously, back to the top. I wouldn't charge that battery in the house. It will off-gas hydrogen while charging. Very explosive. If you think you saw sparks before, stand back! Hope I'm not too late. I haven't heard of any houses blowing up in the Cambridge area in the last two days.

After you get your electrical woe's fixed, buy a battery tender. To keep a slow charge on the battery during the cold months.