Probably one of the least understood devices we encounter in this hobby is the Electronic Speed Control.
How many of us think that when we reduce our throttle we reduce the maximum value of amperage through the ESC....WRONG..!
What we reduce is the TIME that the ESC is turned on and current is flowing through it.
This may help to explain why some ESC's fail, when it appears they should not have failed.
Check out this link from CASTLE...and review question #6.
http://www.castlecreations.com/support/ ... .html#gen6
Question:
6. Can I control how much current passes through my speed controller by limiting full throttle travel on my transmitter with endpoint adjustments/trim? In other words can I use a 25 amp speed controller with a motor that will pull 45 amps but lower my top throttle endpoint on my transmitter so my watt meter only shows 25 amps at full throttle? Will this be OK?
Answer:
NO!!! 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 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 and 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
..take note of the underlined sentence. When you are lumbering across the field at half throtlle...the ESC is working harder..!
Bill
ESC theory revisited..!
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retiredVTT
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ESC theory revisited..!
Bill
HEFA #5
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HEFA #5
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Rob
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Re: ESC theory revisited..!
This is a nice article on speed controllers.
http://www.stefanv.com/electronics/escprimer.html
Some of the older speed controllers may have had more losses, (more internal heat) at lower throttle settings. Most (almost all) speed controllers (ESCs) we use today in the sport today generate much less heat and have lower losses at low throttle setting than at full throttle.
Running an ESC at low throttle settings will barely warm up most ESCs now days do to improved design and higher switching frequencies. Since heat equals damage, you are very unlikely to damage your ESC buy running it at less than full throttle for an ESC that is properly matched to the load.
Basically heat generated in the ESC equals current x internal resistance x the time the pulse is on. For low throttle settings the pulse "on" time is very short compared to the pulse "off" time so there is less heat generated for a given period of time, and more time for the motor and esc to dissipate that heat.
To verify for yourself try running your motor at 1/2 throttle or less under load and check the temp of your ESC. Now run it full throttle under the same load and you'll find it's much warmer at full throttle.
http://www.stefanv.com/electronics/escprimer.html
Some of the older speed controllers may have had more losses, (more internal heat) at lower throttle settings. Most (almost all) speed controllers (ESCs) we use today in the sport today generate much less heat and have lower losses at low throttle setting than at full throttle.
Running an ESC at low throttle settings will barely warm up most ESCs now days do to improved design and higher switching frequencies. Since heat equals damage, you are very unlikely to damage your ESC buy running it at less than full throttle for an ESC that is properly matched to the load.
Basically heat generated in the ESC equals current x internal resistance x the time the pulse is on. For low throttle settings the pulse "on" time is very short compared to the pulse "off" time so there is less heat generated for a given period of time, and more time for the motor and esc to dissipate that heat.
To verify for yourself try running your motor at 1/2 throttle or less under load and check the temp of your ESC. Now run it full throttle under the same load and you'll find it's much warmer at full throttle.