Replies to This Discussion

ModeratorPermalink Reply by Dean Wynton on May 18, 2012 at 4:13pm

The esc should keep a constant voltage throughout, if you are worried that it is too high your best option would be to add a diode on the positive. That will create a voltage drop of about 0.7 volts depending on the diode

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Permalink Reply by Rick Eis on May 18, 2012 at 4:37pm

Thanks Dean,

I have some cheap speed controls....

http://www.hobbyking.com/hobbyking/store/__11615__Turnigy_AE_20A_Br...

I am concerned about hooking them up to a new $200 APM2.

It seems like the voltage regulator would provide a bit of insurance against any weird voltage spikes these ESC's might spit out.

Would a diode do the same thing?  

Maybe I should just get some nicer ESC's   :)   !!

Thanks again,

Rick

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ModeratorPermalink Reply by Dean Wynton on May 18, 2012 at 5:08pm

All the diode would do is drop the voltage a few points
 to bring it closer to 5v I have cheap esc also but do not use
 the built in bec as it is not efficient and  heats up the esc with the wasted energy
Instead I have done what Wesley has suggested and I use a separate ubec
To power the board

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Permalink Reply by Wesley Chuen on May 18, 2012 at 4:54pm

I would recommend investing in an better ESC for your entire aircraft or a separate BEC to supply dedicated 5V just for the APM.  For ESC, I use Phoenix ICE LITE 50 Brushless ESC.  For BEC, I use the phoenix Castle Creations CC BEC.

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Permalink Reply by Rick Eis on May 18, 2012 at 8:07pm

Wesley,

So are you talking these ? 

http://www.amazon.com/Castle-Creations-Switching-Regulator-Pack/dp/...

http://www.amazon.com/Phoenix-ICE-LITE-Brushless-ESC/dp/B002NGORN0/...

Thanks for your help,  Rick

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Permalink Reply by Wesley Chuen on May 18, 2012 at 8:35pm

Yes.  I have both and I love them both.  You can precisely control what the voltage output.  The ESC also has build in logging for various parameters.  Good stuff.

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DeveloperPermalink Reply by R_Lefebvre on May 18, 2012 at 9:08pm

For what it's worth, I supply the APM with 5V via an LM7805 powered directly from a 3S lipo.  No problems, works well.

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Permalink Reply by Rick Eis on May 18, 2012 at 9:59pm

R_Lefebvre,

Ha...Yes!!       It is worth a lot....:)     This is exactly the kind of info I was looking for. :)

So we go from a slightly variable 11.1 volts to a constant 5 volts for a few bucks :)  

Tell me more if you can. Does the little guy get hot?  Did you add a heat sink etc?  How long have you been doing this? Do you know... are others using the little LM7805 on their APM2?

Thanks so much.

Rick

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ModeratorPermalink Reply by Dean Wynton on May 19, 2012 at 12:37am

Yes this will work and not be any problems but this is a linear regulator, so not as effiecient as a switching regulator, and the wasted energy will be converted to heat, and the hotter it gets the more is wasted.. Perhaps this wastage is very slight it depends on whats going in and whats being used?

Perhaps I am being a bit anal about it? I will run some tests and find out how many mah are wasted using a linear regulator in comparison to a switched one.. :)

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ModeratorPermalink Reply by Dean Wynton on May 19, 2012 at 1:03am

O.K using a regulator such as the 7805 on a 3s lipo, with 1amp draw, which 1 servo could use on its own without anything else would waste 7.6w of energy if you are only powering the board and nothing else you would waste 1.52w of energy.. So in terms we all understand drawing 1amp would cost you around 603mah and just powering the board will cost you around 121mah.

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Permalink Reply by Rick Eis on May 19, 2012 at 1:20am

Hey Dean, thanks for your time :)  

What is a switching regulator that you are talking about....can you give a link to one.  Then can you  show the calcs you used above and did you calculate what the switching regulator costs us in mah to power the board? :)

Thanks again,

Rick

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Permalink Reply by Wesley Chuen on May 19, 2012 at 1:26am

The 5-6V output from your ESC and the BEC that I was talking about are all switching regulators.

To calc the power draw, just connect an Amp meter in series to the 3s to the 7805 and check the current.  The (actual) W1=V1 * A1 that you measure is the total power being used.  Then you can check the actual current on the APM.  The actual W2=V2 * A2 on this side of the ESC/BEC would be the power actually delivered to the device.

Power wasted is W1-W2.  And the wasted mA is (W1-W2)/V1*1000

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