TOPIC:

Ok guys, I am an electronic technician by trade, so I will try to clear up the heat verses resistance thing.

First of all, plain and simple, the higher the resistance, the more heat is generated. That is simple electronics. And of course this is at the same voltage and current source. The higher the resistor value, the more voltage it will drop, and that energy has to go somewhere, and it results in heat dissipation.

And loudhvx, your example with the light bulb is off too. The higher the wattage bult, the longer the filament is. And of course the longer the filiment, the higher the resistance. A 60W bulb has about 6 feet of tungsten wire, and a 100W will be even longer.

The only reason a wire will get hot if you short it across a battery, is because of the amount of current that the battery can produce is more that that wire is rated to take. If you stuck a huge peice of solid copper wire across a battery, it would not get hot at all. You would just be at risk of blowing up the battery. But you put a 10m Ohm reisiter in the middle, that resistor will certanly start getting hot, and the wire will not.

I hope this makes it easy for everyone to undersand.

750LTDRider wrote:

Ok guys, I am an electronic technician by trade, so I will try to clear up the heat verses resistance thing.

First of all, plain and simple, the higher the resistance, the more heat is generated. That is simple electronics. And of course this is at the same voltage and current source. The higher the resistor value, the more voltage it will drop, and that energy has to go somewhere, and it results in heat dissipation.

And loudhvx, your example with the light bulb is off too. The higher the wattage bult, the longer the filament is. And of course the longer the filiment, the higher the resistance. A 60W bulb has about 6 feet of tungsten wire, and a 100W will be even longer.
The only reason a wire will get hot if you short it across a battery, is because of the amount of current that the battery can produce is more that that wire is rated to take. If you stuck a huge peice of solid copper wire across a battery, it would not get hot at all. You would just be at risk of blowing up the battery. But you put a 10m Ohm reisiter in the middle, that resistor will certanly start getting hot, and the wire will not.

I hope this makes it easy for everyone to undersand.

im a retired licensed electrical and plumbing contractor and ive changed a bulb or 2 in my day.but i dont remember ever seeing a bulb with 6'of tungsten wire,i could be wrong but i tend to notice those things. a wire will also get hot from an amp draw higher than wire is rated for,a long wire is also more likely to get hot than a short wire of same size carrying same load.

750LTDRider, when you say :"but if you put a 10m Ohm resistor in the middle..."are you referring to a 10 milliohm resistor? Or do you mean a 10 Megohm resistor? I'm a little confused here because as you know, m ohm is the abbreviation for milliohm{1 milliohm = 1 part in 1000 of one ohm] whereas 1 Megohm = 1 million ohms. Just curious thanks.

Post edited by: tellietubbie, at: 2006/10/09 11:47

750LTDRider wrote:

Ok guys, I am an electronic technician by trade, so I will try to clear up the heat verses resistance thing.

First of all, plain and simple, the higher the resistance, the more heat is generated. That is simple electronics.

Sorry, but that is simply wrong, as the math shows clearly.
Same voltage applied to different resistances, the higher resistance dissipates less heat. (Heat dissipation and power are the same thing in a resistor.).
Here's the math:
Another formula for power is V squared over R.
P=(V^2)/R says it all.
V is constant (as we agree).
P is inverse proportional to R.
More resistance = less heat.
There can be nothing more simple or succinct than that.

I see what the big problem is.
You guys are confusing load behavior with transmission line behavior. They are not the same.

When a piece of wire is shorted, and has the full voltage drop on it, it becomes the load, and will heat up as such, and acts just like a resistor.

When in normal use, the wire is not the load, and does not have the bulk of the voltage drop on it, so it's resistance is negligible (and is considered 0 for practical purposes). The reason a transmission line heats up when overloaded with current, is because it is converting from a line to a load. This is because the resistance in the wire is no longer negligible when compared to the resistance of the actual load. As a result, the voltage drop on the wire increases and thus you get more heat. If the transmission wire's resistance is lowered by making it thicker, it converts back to a transmission wire instead of a load and will cool down. But don't confuse the action of converting from line to load with a correlation between resistance and heat. They are two seperate concepts.


750LTDRider wrote:

And of course this is at the same voltage and current source. The higher the resistor value, the more voltage it will drop, and that energy has to go somewhere, and it results in heat dissipation.

Your second sentence violates the first sentence of this quote. If the voltage is constant, then the resistor value will not affect the voltage drop, because it is constant.

750LTDRider wrote:

And loudhvx, your example with the light bulb is off too. The higher the wattage bult, the longer the filament is. And of course the longer the filiment, the higher the resistance. A 60W bulb has about 6 feet of tungsten wire, and a 100W will be even longer.

Not sure what to say. I would recommend measuring the resistance of a small 12 volt bulb and a big 12 volt headlamp. The problem is that they are all very near 0 and meters have trouble being accurate there. However, I have measured many bulbs and so I know what you will find. But different types of bulbs behave differently as in how their resistance changes as they heat up, so it's not such a good experiment.


750LTDRider wrote:

The only reason a wire will get hot if you short it across a battery, is because of the amount of current that the battery can produce is more that that wire is rated to take. If you stuck a huge peice of solid copper wire across a battery, it would not get hot at all. You would just be at risk of blowing up the battery. But you put a 10m Ohm reisiter in the middle, that resistor will certanly start getting hot, and the wire will not.

Another mixup between transmission wires and loads, but I can certainly tell you the 10Mega Ohm, 1/4W resistor won't get hot. It will dissipate .0000012watt and is rated for .25 watt... not enough to get much hotter than room temperature.

Why don't you hook up a 100 ohm, 1/4w resistor and then hook up a 10K ohm, 1/4w resistor. Be careful, don't burn your hand on the 100 ohm it will get hot!

In case you guys are still holding onto your premise...
Air is an insulator with very high resistance, how come the air around a battery is not on fire?

Post edited by: loudhvx, at: 2006/10/09 13:02

I deleted this for the time being. Got to run and want to rewrite later.

.

Post edited by: 750LTDRider, at: 2006/10/09 13:14

Sorry, I edited my post about the joking.

Post edited by: loudhvx, at: 2006/10/09 19:18

I have a website with some more recent stuff.
www.geocities.com/loudgpz

Post edited by: loudhvx, at: 2006/10/09 19:20

Loudhvx: ok, I think I get it now... a large value resistor, 10mega ohm, will not allow enough current flow to get hot...

And a 100 ohm resistor will allow a lot of current to flow and will get really hot.

So how come a 3 ohm or 5 ohm coil (without a ballast resistor) don't get hot as hell since they allow a lot of current to flow as the above examples show.

But if you put a 2 ohm resistor in the line then the coils don't get hot? Very confusing!!

But it's all good info you guys have been giving us and I now know that I can try different coils without to much worry.

I know most of you guys shop at the Accel or Dyna store, but me, I shop a Wal-Mart. I like to save a buck and maybe beat the establishment out of a sale. And the motorcycle salvage yard has a couple hundred coils and I'm gonna try them all if I have to.

I'm a bit fuzzy when it comes to ohms and watts, but I think I know enough now to go forward with my project.

I sure hope the GM coil experiment works out. That would sure go a long way towards making my point that there's gotta be a cheaper way (sometimes) to do things.

Thanks again,
Bob

Loudhvx: ok, I think I get it now... a large value resistor, 10mega ohm, will not allow enough current flow to get hot...

And a 100 ohm resistor will allow a lot of current to flow and will get really hot.

So how come a 3 ohm or 5 ohm coil (without a ballast resistor) don't get hot as hell since they allow a lot of current to flow as the above examples show.

But if you put a 2 ohm resistor in the line then the coils don't get hot? Very confusing!!

But it's all good info you guys have been giving us and I now know that I can try different coils without to much worry.

I know most of you guys shop at the Accel or Dyna store, but me, I shop a Wal-Mart. I like to save a buck and maybe beat the establishment out of a sale. And the motorcycle salvage yard has a couple hundred coils and I'm gonna try them all if I have to.

I'm a bit fuzzy when it comes to ohms and watts, but I think I know enough now to go forward with my project.

I sure hope the GM coil experiment works out. That would sure go a long way towards making my point that there's gotta be a cheaper way (sometimes) to do things.

Thanks again,
Bob

Bob_79KZ wrote:

Loudhvx: ok, I think I get it now... a large value resistor, 10mega ohm, will not allow enough current flow to get hot...

And a 100 ohm resistor will allow a lot of current to flow and will get really hot.

Right on. But resistors are rated for wattage (sometime they are rated for voltage or current but for the same reason of heat dissipation). A really big 100 ohm, 10 watt resistor won't get hot, but a small 100 ohm, 1/4 watt resistor will get hot. It's all because of size. They are dissipating the same amount of energy, but the 1/4 watt resistor is so small (about the size of a meduim ant), it only has a tiny surface to dissipate the same amount of energy, so it gets hot.

Bob_79KZ wrote:

So how come a 3 ohm or 5 ohm coil (without a ballast resistor) don't get hot as hell since they allow a lot of current to flow as the above examples show.

But if you put a 2 ohm resistor in the line then the coils don't get hot? Very confusing!!

They don't get hot as hell, because they are pretty big overall. Putting the 2-ohm ballast reduces the current in the coils so they run even cooler. The resistor doesn't get hot as hell because the coils are reducing the current as well.

You can also look at it as the ballast is reducing the voltage to the coils. With a 2-ohm ballast, 12-volt battery, and 4-ohm coil, the coil only gets 8 volts, and the resistor gets 4 volts, because they are all in series and you only have 12 volts to work with.

Voltage, resistance, and current are all directly related. You can't change the resistance without changing the current. On bikes, there is a brain controlling the voltage independent of the load. That is the regulator's job. So the bike's voltage is artificially constant by the regulator.

Anytime you put a load on a plain battery, it's voltage drops slightly. The regulator corrects this.


Bob_79KZ wrote:

But it's all good info you guys have been giving us and I now know that I can try different coils without to much worry.

I know most of you guys shop at the Accel or Dyna store, but me, I shop a Wal-Mart. I like to save a buck and maybe beat the establishment out of a sale. And the motorcycle salvage yard has a couple hundred coils and I'm gonna try them all if I have to.

I'm a bit fuzzy when it comes to ohms and watts, but I think I know enough now to go forward with my project.

I sure hope the GM coil experiment works out. That would sure go a long way towards making my point that there's gotta be a cheaper way (sometimes) to do things.

Thanks again,
Bob

Steell posted a link earlier which would be a good place to start. But nothing teaches you faster than doing, and blowing up resistors is fun.

I agree, there's always a cheaper way! It's going to be awhile before I can get to the GM coils, though.

Used coils have stranded me. The cost of driving a truck 150 miles to pick up a bike ends up costing more than what you'd save on used coils, so no more used coils for me.

Post edited by: loudhvx, at: 2006/10/09 15:04

Ok Loudhvx, I need to apologize to you. I got myself all twisted up. I started second guessing myself and that is why I deleted my other post. For some reason I had it in my head that I was right and when I asked to tech next to me he agreed with me. I really can not imagine what both of us were thinking. If you use PIE to figure it, of course your power(watts) will be lower as the resistance goes up. Thus less heat.

I think what threw me was the light bulb example, which I know is not right, the only difference in different wattage bulbs of the same V (your right cant compare differenct V) is higher wattage bulbs have longer filament, but Im pretty sure that has more to do with surface area than resistance.

So I think I will exit this conversation now, and sorry to Bob_79Kz also for possibly confusing you more than you already were.

No apology necessary. I get turned around on stuff from time to time as well.

We all learned some things. I never dealt with the transmission line confusion before and it was good to run through my head a couple times.

I'm glad people are at least talking some theory so I can brush the dust off of the math.