running brushless esc slow information?

[gasayers]

I've been told often that a brushless esc will fail if the boat is run slowly. yet in aircraft we run esc's slow for hours without failure.

This leads me to believe it is to do with the loading of boats at low speed and the consequential current draw through the fets.

Is there an article explaining this phenomena? yes I have tried to search.

I'm running a Pursuit on it's original setup. 5000mah battery, 180amp esc. battery currently lasts about 12-14 minutes of fooling around (not hard out running)

That would indicate the esc isn't working very hard. Should I expect it to fail? I have a young daughter who likes to play with the boat.

At what point of unloading the motor by propping would problems dissipate?

This isn't a high performance setup that can flatten a battery in 4 minutes.

Cheers

http://www.hobbyking.com/hobbyking/s...dProduct=44649

[Fluid]

From a Castle Creations tech:

"A speed controller controls power to the motor by turning full throttle current on and off really fast, 11 to 13 thousand times per second (Pulse Width Modulation or PWM). The percentage of each on/off pulse that is off compared to the part that is on determines how much power the motor sees. I.E. With a pulse that is 50% off and 50% on the motor will see 50% power*. Because each on pulse is 100% of full throttle current, a system set to pull 20 amps at full throttle through a Phoenix 10 will not last if you are throttled back to the point where you only see 10 amps on a wattmeter. The ESC in this case is still switching 20 amps, which it can’t do for long. Actually it is worse than the simple example above. Because an electric motor will always to try to pull as much power as is available to get to its rpm (volts times Kv), when you are running the motor below its Kv speed by switching power on an off, each on pulse will actually be way over the full throttle amp draw. That is why ESCs work harder at partial throttle than full throttle and why we underrate our ESCs. We underrate not so they can handle more current than their rating at full throttle, but so they can handle extended partial throttle operation with no problems.

* Actually, electric power is not linear as in this example, but you get the idea."


From actual testing (not mine):

ESC: Castle Creations Phoenix 10
Motor: AX-2208C-1080Kv
Prop: GWS EP9050
Battery: Bench Power Supply

ESC was attached to the back of my thrust stand, shielded from propwash. Temperature readings were taken with an Extech Infrared thermometer.

Full throttle for 1 minute:-
Wattmeter readings: 10.6V, 8.1A, 7620rpm
Start ESC temperature: 29ºC
End ESC temperature: 45ºC

75% throttle for 1 minute:-
Wattmeter readings: 10.6V, 4.0A, 5895rpm
Start ESC temperature: 29ºC
End ESC temperature: 75ºC

.

[gasayers]

From a Castle Creations tech:

[I] and why we underrate our ESCs[/B]. We underrate not so they can handle more current than their rating at full throttle, but so they can handle extended partial throttle operation with no problems.

[/B]

.

Thanks for that.

Ok, well I kind of figure I bought the boat to use how I want and if it doesn't work then I'll have to look at some kind of alternate.

so

I'll avoid high loading of the motor by not running it at speeds where it is pushing water. other than that I will run it at very low idle, where there is no real load on the prop (yes I read the article) and at a variety of planing speeds, checking for cooling water and see how it lasts.

Worst case scenario is a retrieve and new esc. Not really the end of the world.

[RandyatBBY]

You can put a "Cap Bank" on the system and be quite a bit more reliable. I have raced Aquacraft UL-1 systems with a good cap bank for 5 to 7 years with out failure.