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Amperage question.

Old 12-14-2008, 04:45 PM
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Snaut Rocket
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Default Amperage question.

How come you don't need really big gauge wire for these brushless applications.
My dad is so confused on this subject.
He dosent understand why the house setup is 100 amps but requires 0 gauge wire.
And my brushless motor can take up to 115 amps and its using 10 gauge wire.
Is it cause of the Ac and Dc thing. Why is it that much of a difference.
Old 12-14-2008, 04:49 PM
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HandyRacing
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Default RE: Amperage question.

Bigger wire has less resistance. Bigger is better to a point, I would think regardless of brushed or brushless.
Old 12-14-2008, 04:50 PM
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Access
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Default RE: Amperage question.

It's since the distances involved are really short, so resistance isn't as much of a factor as when you are wiring your house or with power lines. You typically only have to worry about saturation current.
Old 12-14-2008, 04:56 PM
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Default RE: Amperage question.

Interesting:

http://en.wikipedia.org/wiki/Saturation_current

We've seen 1/8 scale buggies that have the power leads coming off the ESC (Mamba Max typically) get so hot the solder wicks up the motor wires (ESC power output) to the point the wires get stiff and snap off about a quarter or half inch up from the solder connections.

I wonder if this is related to what you speak of?
Old 12-14-2008, 06:24 PM
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Default RE: Amperage question.

ORIGINAL: Access

It's since the distances involved are really short, so resistance isn't as much of a factor as when you are wiring your house or with power lines. You typically only have to worry about saturation current.
+1 and to handyracing it is. The more resistance the more heat. So if they are running to high of a guage the resistence will be great and it can get extrememly hot. Thats why birds sit on powerlines in the winter. They are warm due to resistance.
Old 12-14-2008, 07:34 PM
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Default RE: Amperage question.

Maybe it has to do with the voltage also. A house is 120 volts and our little trucks are anywhere from 7.2 to 22.2 volts. It might not be though, i dont know but it could be.
Old 12-14-2008, 08:19 PM
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Default RE: Amperage question.

It's mainly due to what Access said.

For short distances you can get away with higher gauge wire generally.

Also, home wiring is overbuilt generally due to electric codes. It's so that if later on you upgrade to a 200 or more amp system you may not have to replace internal wiring.
Old 12-14-2008, 08:27 PM
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Default RE: Amperage question.

Something not mentioned yet is / are the various styles and choices of connectors......

(often singly accounting for more resistance than the wiring)

If one talks to the racers from the old days (well prior to the days of the "Deans" connector)....

Performance oriented folks would ALWAYS hard solder the battery and the motor leads, AND run with as short a length of wire as needed to get there, but no more. They would un-solder after each race in order to re-charge the battery, then re-solder for the next race.

Like everything else, its all relative.

(Edited as my original sentence didn't make sense)
Old 12-14-2008, 08:30 PM
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Default RE: Amperage question.

The main thing is that the R/C system only reaches that high of amperage for short bursts and only runs for the length of the battery life. Despite this, in high draw applications the wires often get very hot. So hot sometimes that connectors melt, wire insulation melts, solder joints come undone, etc.

In your home the current can be sustained for hours on end during periods of high use (not to mention the wires are in walls, insulation, conduit, etc. and heat cannot escape). While a 10AWG wire might carry the current temporarily, you wouldn't want the wires in your house getting hot under any circumstances.
Old 12-14-2008, 08:34 PM
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Default RE: Amperage question.


ORIGINAL: BigTb17

The main thing is that the R/C system only reaches that high of amperage for short bursts and only runs for the length of the battery life. Despite this, in high draw applications the wires often get very hot. So hot sometimes that connectors melt, wire insulation melts, solder joints come undone, etc.

In your home the current can be sustained for hours on end during periods of high use (not to mention the wires are in walls, insulation, conduit, etc. and heat cannot escape). While a 10AWG wire might carry the current temporarily, you wouldn't want the wires in your house getting hot under any circumstances.
Anyone want to do the math for 120 volts at 20 amps

- compared to -

14.8 volts at 150 amps

?
Old 12-14-2008, 08:44 PM
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Default RE: Amperage question.

ORIGINAL: HandyRacing


Anyone want to do the math for 120 volts at 20 amps

- compared to -

14.8 volts at 150 amps

?
What math?

Wattage (therefore total power) is higher on the 120v circuit.

120 volts at 20 amps is 2400 watts. 14.8 volts at 150 amps is 2220 watts. If you had 150 amps at 120 volts it would be 18,000 watts. This is a much higher total power level. Amperage (more accurately, resistance to its flow) is what causes heat, and therefore determines wire size. But the total power level of the 120v circuit is much higher.
Old 12-14-2008, 08:55 PM
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Default RE: Amperage question.


ORIGINAL: BigTb17

ORIGINAL: HandyRacing


Anyone want to do the math for 120 volts at 20 amps

- compared to -

14.8 volts at 150 amps

?
What math?

Wattage (therefore total power) is higher on the 120v circuit.

120 volts at 20 amps is 2400 watts. 14.8 volts at 150 amps is 2220 watts. If you had 150 amps at 120 volts it would be 18,000 watts. This is a much higher total power level. Amperage (more accurately, resistance to its flow) is what causes heat, and therefore determines wire size. But the total power level of the 120v circuit is much higher.
I was letting you (anyone) demonstrate that folks are more or less playing with the same amount of power, be it by plugging something into an outlet (for example an electric appliance), or tinkering with an RC toy.

Thank you.
Old 12-14-2008, 09:42 PM
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Default RE: Amperage question.

Thanks guys all valid points, so maybe this will shut him up.

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