[NSRCA-discussion] Plettenberg 30-10 evo and Jeti ESC

[James Oddino]

No the peak current will be lower at low rpm.  The motor is an inductor that resists current flow especially at high frequency.  Low duty cycle means very short pulses that so the current doesn't build up to its potential peak before the FETs open up and turn off the current from the battery.  However, the ESC has a free-weeling diode that takes the energy stored in the motor to supply current during the time the switch is off so the current doesn't drop to zero.  The motor/diode circuit has a kind of flywheel action.  Give it short input pulses and it goes slow and long ones and it goes fast.

Jim O


On Mar 15, 2012, at 10:52 PM, Ed Alt wrote:

> Jim:
>  
> I was thinking along the same lines, but maybe what Peter is driving at is that current peaks will be greater at lower RPMs.  I think that might be true, not entirely sure though.
>  
> Ed
>  
> From: James Oddino
> Sent: Friday, March 16, 2012 1:15 AM
> To: General pattern discussion
> Subject: Re: [NSRCA-discussion] Plettenberg 30-10 evo and Jeti ESC
>  
> Let's look at this from a logic standpoint.  
> 1) We limit the duty cycle to decrease the rpm.  Lower duty cycle means lower average voltage, therefore lower rpm.  RPM= Kv*V
> 2) Let's say we cut the voltage and therefore the rpm in half.  The power to turn the prop required would be much less than half because power varies with the cube of rpm.
> 3) Therefore, if power is reduced by more than half the current will be reduced as well as the voltage.
>  
> In our modern day speed controllers the current through the motor does not go full on/full off with the duty cycle but remains relatively constant through the cycle due to the ESC design and motor characteristics.  The peak current during the on portion of the cycle is lower than the current at 100% duty cycle.  Limiting duty cycle does reduce the current and the power consumption.  Does it limit power dissipation in the ESC?  That is another question.
>  
> Jim O
>  
> On Mar 14, 2012, at 9:59 PM, Peter Vogel wrote:
> 
>> potentially, yes.  The most efficient running of the ESC is WOT.   An electric motor is a constant speed system, it will draw whatever amps it needs in order to spin at the speed defined by the kV * received voltage for however long it receives voltage.  The motor will pull the amps it wants to during each pulse from the ESC.  That'll obviously depend on all kinds of factors including the weight + size of the prop, whether you are in an up or downline, etc.
>>  
>> Peter+
>>  
>> On Wed, Mar 14, 2012 at 9:45 PM, James Oddino <joddino at socal.rr.com> wrote:
>> Can you elaborate?  Are you saying more current flows at lower duty cycle than it does when the FETs are full on at high throttle?
>> 
>> Jim O
>> 
>> 
>> On Mar 14, 2012, at 9:15 PM, Peter Vogel wrote:
>> 
>> > Limiting throttle does NOT limit current to the motor, in fact, it can cause higher current draw.  All throttle does is vary the on vs off cycle during which voltage is sent to the motor.
>> >
>> > Peter+
>> >
>> > Sent from my iPhone4S
>> >
>> >
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>> 
>>  
>> -- 
>> Director, Fixed Wing Flight Training
>> Santa Clara County Model Aircraft Skypark
>> 
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> 
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