Wire size for 1200W?

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mf70
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Wire size for 1200W?

I've been looking at my well-mauled Yonkang Crown scoot "Hummer". I've got about 3000Km on it; the odo went out at 2400K.

It has a nominal 700W brushed motor that actually draws about 20A measured at full throttle, or about 1200W. The odd thing is that the wire from the controller to the hub is 14GA! In fact, after pulling up a long hill, the wires will be detectably warm.

Would upping the connection to 10GA, say, increase efficiency and potentially range, or would it open the door to melting the windings? (I.E. is the 3 feet of 14ga wire acting as a current limiter?) According to a DC motor rebuilder, the discoloration on the comm that I'm seeing is from overloading it already.

I had a look at the wire resistance table linked in the "Wiring brushless Etek, cable guage?" thread, but they don't go small enough for me.

MF

strawhistle
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Re: Wire size for 1200W?

:?
For wire sizes , it goes by AMPS at any voltage !! 14g = 15A 12g =20A 10g = 30a 8g =40A 6g =55 to 75 depending on the type of outer insulation If the max Amps to the motor is 20A then 20g wire with thhn coating (90degree ) will work for you , 10g would be called monster cable

thank GOD I wake up above ground !!!!

LinkOfHyrule
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Re: Wire size for 1200W?

Hmm, lets see:

14AWG wire has a resistance of 0.00297Ω/ft. You say there is 3 feet of wire between the batts and the motor, so I'm assuming a 6ft round trip. Since heat = current^2 * resistance, then you're losing 20A^2 * 0.00297Ω(6ft) = 7.128W of power to heating in the wire. A paltry amount. You're probably losing more in the contacts and controller workings.

For 10AWG it's 20A^2 * 0.00118Ω(6ft) = 2.832W of heat. Not worth spending the money on barely 4W of difference, unless you plan on upgrading to a much more powerful motor (like 40+A).

Now that I think of it, I wonder what I'm losing to heat? 33^2A * 0.00187Ω(8ft) = 16.29144W of heat. Had I went with 14, I would have been losing 25.87464W of heat. Still a small amount compared to the 1300W I'm running. The motor itself is probably losing dozens if not hundreds of watts to inefficiencies.

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andrew
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Re: Wire size for 1200W?

What system voltage does the scooter run at?

[url=/forum-topic/motorcycles-and-large-scooters/587-my-kz750-electric-motorcycle-project]KZ750 Motorcycle Conversion[/url]
[url=/forum-topic/motorcycles-and-large-scooters/588-fixing-my-chinese-scooter]900 watt scooter[/url]
Pic from http://www.electri

LinkOfHyrule
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Re: Wire size for 1200W?

What system voltage does the scooter run at?

1200W / 20A = 60V. :P

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mf70
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Re: Wire size for 1200W?

OK, thanks for the feedback. I guess I won't worry about it 'till I wire up the series-parallel plug so I can charge it with a single 12V charger.

It is a 48V system. The current draw may not be exactly 20A max, but it is WAY beyond the 14A I expected from a 700W nominal motor.

Mark

PJD
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Re: Wire size for 1200W?

It is a 48V system. The current draw may not be exactly 20A max, but it is WAY beyond the 14A I expected from a 700W nominal motor.

Motor wattage ratings are usually conservative, continuous-duty ratings and have nothing to do with the power the motor is capable of safely producing for shorter (but still minutes-long) periods of time.

My "2000 watt" e-max scooter motors have been run, even in hot weather, at 5000 watts, for 2-3 minutes, without problems.

BTW, I use 8AWG wiring. Never noticed any heating at the wires or connectors.

LinkOfHyrule
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Re: Wire size for 1200W?

My "2000 watt" e-max scooter motors have been run, even in hot weather, at 5000 watts, for 2-3 minutes, without problems.

My G1 skateboard's 200W motor has been run at 48V and 33A. In other words, over 700% of it's rating. Didn't take it on a very long ride, but it barely got warm 8).

I was using crappy 16AWG wiring, but it didn't get very warm.

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