Motor vermogen regeling vanuit de zender

[Jan Jaap]

Het klinkt wel logisch.

Ik was altijd van mening dat door sleepgas de regelaar warm zou worden omdat de elektronica aan het regelen is en het niet verbruikte deel in warmte wordt omgezet. Maar zo goed heb ik mij niet in de materie verdiept.

Of je nu iets over het hoofd ziet weet ik niet. Op het MBF zitten een paar elektronica nerds (Ernst Grundmann en Rick NL) die precies weten hoe het werkt. Er staat in onderstaande link ook nog een zeer uitgebreide uitleg in het engels van de werking van de regelaar.

http://www.modelbouwforum.nl/threads/mo ... st-3888980

[GVT]

Hier staat het mooi uitgelegd (Er van uitgaande dat het klopt wat Bruce Abbott zegt):

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You shouldn't try to limit ESC heating by simply using less throttle.

Reducing throttle may reduce ESC heating, but it might not. For example, let's say you have a 30A ESC but the motor draws 40A at full throttle. So you wind the throttle endpoint down to 89% and the ammeter now says 30A. It's all sweet, right?

Wrong! The ESC reduces throttle using PWM, ie. by pulsing the motor on and off rapidly. 89% duty cycle means that the battery is connected to the motor 89% of the time, and motor current is recirculated through the FET body diodes during the other 11%. The average motor current will be 30A/89% = 33.7A (peak current will be higher again). The FET body diodes drop about 0.7V (compared to about 0.1V when the FETs are turned on), and the high PWM frequency causes extra switching loss as the FETs are turned on and off more often. The high frequency battery current pulses also make the input voltage smoothing capacitors work harder. The result is even greater heating than would be expected from 33.7A at full throttle. If the ESC was designed to just manage 30A at full throttle, there's a good chance it will overheat when you try to make it pass that '30A' at 89% throttle.

Most ESCs are only designed to take their rated current at full throttle. To avoid overheating at part throttle, they rely on the fact that motor current will be less than at full throttle. You may get away with it, but using throttle limiting to get around the ESC's current rating is not good policy


ESC efficiency is expected to drop at part throttle due to several factors, including:-

1. FET switching losses. Each time a FET is turned on or off it looses a bit of energy. Part throttle applies PWM to lower the effective voltage, but the FETs are then switched on and off much more often, so their total switching losses are higher.

2. Driver switching losses. Drivers turn the FETs on and off by changing the voltage on their gates. But the gates have high capacitance, so a significant amount of electrical charge is required to change the voltage. Once again, losses are greater when switching at the higher PWM frequency.

3. FET Body Diodes. The body diodes are activated whenever power is disconnected from a motor winding. As the magnetic field in the coil collapses, it generates a voltage that tries to keep the current going. This 'BackEMF' current is routed through the FET body diodes. Unfortunately while conducting the diodes drop voltage (~0.8V at full rated current) which wastes power.

Some high-end controllers eliminate body diode loss by turning the FETs back on at appropriate times, thus bypassing their body diodes. This technique is called 'synchronous rectification' or 'active freewheeling'.

4. Higher peak currents due to insufficient motor inductance. Components affected include the FETs, filter capacitors and pcb tracks.

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[GVT]

Excuses dat het allemaal in het engels is.
Wil je een vertaling, dan geef ik die wel mondeling

Deze vond ik wel mooi simpel en duidelijk weergegeven:

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Your watt meter is showing the average currrent. The ESC throttle works by giving full voltage for x% of the time. So 50% throttle means 50% of the time on, and 50% of the time off.

If you are measuring 25 amps at 1/2 throttle, you are actually getting 50 amps half the time, and 0 amps the other half.

Since heating goes as the square of the current, 25 average amps at 1/2 throttle means the heat dumped in a resistance "R" is just R*[(50*50 *1/2 )+(0*0*1/2)]=1250*R watts. Notice that this is twice the heat if the current was really at 25 amps for the full period =25*25*R=625*R watts
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[GVT]

Deze vind ik ook wel mooi:

The 80% rule :

Batteries: Discharge rate and discharge capacity.
If you have a 35C battery, do not pull more than (35 x 0.8) 28C from it.
If you have a 4000mah battery, never pull more than (4000 x 0.8) 3200mah from it during a flight.

Motors: Max Power ratings and Max current ratings.
If you have a motor rated for 100 amps don't pull more than (100 x 0.8) 80 amps from it.
If it is rated for 2000 watts, don't run more than (2000 x 0.8) 1600 watts through it.

Speed Controllers: Current Rating.
If you have a speed controller rated for 90 amps, don't run more than (90 x 0.8) 72 amps through it.
Forget about "Burst Ratings" on speed controllers! If you are even considering that in your ESC calculations use a bigger speed controller!