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Old Mar 05, 2015, 11:23 AM
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Wire size and amp ability

hummm.. Looking on the web at amp ratings for different wire sizes it seems rc motors have thin phase wires.
What's exceptable for 12aug or 20aug?
Haven't seen real numbers on this site. People are saying if it gets hot its too small
It'd be good to know numbers
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Old Mar 05, 2015, 11:56 AM
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20awg can handle 11A and 12awg can handle 41A continuous, going by chassis ratings which is what we're looking at here. The lower figures for power transmission don't apply for our usage.
When the current rating charts say continuous, they mean continuous, as in 7/24. For the very short runs we use on our motors and the relatively short times we can run WOT, these ratings are very conservative.
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Old Mar 05, 2015, 12:02 PM
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Lots of motor manufacturers combine thin-gauge wires in place of using a single larger wire for motor windings. More wires are combined to handle larger currents.

A google search should find many wire-gauge tables which specify how much current a given wire size can safely conduct for AC and DC currents.
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Old Mar 05, 2015, 01:13 PM
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Things on the web differ widely
http://knowledge.sonicelectronix.com...re-gauge-size/

I've got a motor with what I think is 17aug wires d wondering what amps it could continuously do
I imagine the "enamel" would decide a lot
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Old Mar 05, 2015, 01:48 PM
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It gets very complicated to predict the exact number in a motor. Many start with the mass of the motor, to predict its amp rating. So yes, if the wire is too hot you have a problem.
This is a basic explanation of why the chart numbers are conservative.
http://www.powerstream.com/Wire_Size.htm
Quote:
Load Carrying Capacities (see table below)
The following chart is a guideline of ampacity or copper wire current carrying capacity following the Handbook of Electronic Tables and Formulas for American Wire Gauge. As you might guess, the rated ampacities are just a rule of thumb. In careful engineering the voltage drop, insulation temperature limit, thickness, thermal conductivity, and air convection and temperature should all be taken into account. The Maximum Amps for Power Transmission uses the 700 circular mils per amp rule, which is very very conservative. The Maximum Amps for Chassis Wiring is also a conservative rating, but is meant for wiring in air, and not in a bundle. For short lengths of wire, such as is used in battery packs you should trade off the resistance and load with size, weight, and flexibility. NOTE: For installations that need to conform to the National Electrical Code, you must use their guidelines. Contact your local electrician to find out what is legal!
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Old Mar 05, 2015, 02:37 PM
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Quote:
Originally Posted by Hummina View Post
hummm.. Looking on the web at amp ratings for different wire sizes it seems rc motors have thin phase wires.
What's exceptable for 12aug or 20aug?
Haven't seen real numbers on this site. People are saying if it gets hot its too small
It'd be good to know numbers
Depends, depends, depends. Depends if you are talking about magnet wire or lead wire. Depends on the type of insulation. Depends on the amount of air flow over the wires. Depends on the outside temperature. If you're talking lead wire, it depends on whether it is solid or stranded ... and it depends on the number of strands it has. You won't find anything that agrees on the web because everything on the web uses different assumptions.
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Old Mar 05, 2015, 02:52 PM
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As far as the motor leads go, the chassis ratings are a very good conservative rating.
The physical size of a motor and the desired Kv go a long way in determining the gauge of the wire to be used for the windings. In the end, it's the motors ability to carry heat away from the windings that determines how many Amps or Watts the motor can be run at.
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Old Mar 05, 2015, 03:52 PM
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Mr. Lucien Miller, Has a great table.

http://www.rcgroups.com/forums/showt...=565590&page=3
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Old Mar 05, 2015, 05:02 PM
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What about y vs delta? I read y can do as many amps as delta with much smaller wires. True?
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Old Mar 05, 2015, 08:02 PM
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Quote:
Originally Posted by Hummina View Post
What about y vs delta? I read y can do as many amps as delta with much smaller wires. True?
At the same turn count, changing from Delta to Wye drops the current by a factor of 0.58. But it also changes the Kv by that same factor. And it also raises the torque by 0.58 so even though it is drawing less current you seat of the pants impression may be that the Wye terminated motor has not lost any effectiveness in flight even though it might be flying at a lower input power.

You also have to look at the Kv when you consider your question. The image shows the ways to get a Kv around 750 with LRK, Half Parallel dLRK, and dLRK winds and, as you can see, when you go from Delta to Wye while also targeting a specific Kv, there are other considerations that can make one wind type and termination more attractive.

That motor was factory wound dLRK-Delta with 18 turns for a Kv of 750. If you wound it for that same Kv you could do 10 turns terminated Wye. And that implies bigger wire, less resistance, and a much higher current capacity.

For that particular motor, the Half Parallel dLRK-Wye wind has pretty well proved to be the wind that get the best power out of it s long as you want a Kv that is only little higher than the original Kv.

We sort of lose track of it sometimes, but the primary consideration in rewinding is to get a specific prop turning at range of RPM that makes the best thrust. So if you see a prop that you think you will use in the 5,000 to 7,000 RPM range you really have to decide a battery voltage and a Kv rating that will give you about 8,000 RPM at full throttle.

And then, to decide the best wind, you can try all the different winds and terminations that will give you that Kv and fly them and one of them will be the one you like the best. But two fliers may prefer different winds because they fly differently or are focused on different considerations as to which is best.

Jack
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Old Mar 06, 2015, 12:18 AM
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had to erase all my qeusitons
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Old Mar 06, 2015, 06:28 PM
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rediculous swamp I was writing.
one quesiton.
to be the strongest, most torque motor, it would need lots of poles, and the variables between thin wires for flux and fat wires for heat, you chose a balance. and strongest magnets. and smallest gap

what kv would you think they'd use for this:
https://www.kickstarter.com/projects...ref=nav_search
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Old Mar 06, 2015, 07:38 PM
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I don't think they will ever get that working as they show it there. There is simply no way to enough power into motors that small to move up to 250 pounds at up to MPH.

It is a scam or pipe dream or something...

Jack
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Old Mar 06, 2015, 09:33 PM
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they maybe exaggerate their numbers but it's a real vehicle and skateboard motor using a 1:1 drive has been done many times. I wanted to know your thoughts on how the design could be optimized but you think it's ...too inefficient to work at all? It uses what looks two 50mm motors while a typical board will have one or two motors and also use 2:1 or 3:1 gearing.

why do you think it's a problem?
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Old Mar 07, 2015, 07:00 AM
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It was just my guess, it may work OK if power is applied once the wheel is turning and modulated as it is applied.

If you have some weight on the board and it is not moving or moving very slowly, and you apply power to the motor, that will have the motor drawing a lot more current until it gets up to speed and relieves the load a little. You can really see the effect of that if you have a motor running slowly with a watt meter on it. If you use a gloved hand or leather strap around the magnet housing and restrain the housing a little, the input power goes up.

And if you apply enough restraint and keep jt there long enough the windings will start getting warm. My quitting point for a continuous load would be to not let the windings get them over 130F/54C or so . That is the point where I can't keep a finger on them.

Jack
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