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HomeAircraftHelicopterMain Discussion › Question for the E guru's
06-19-2015 04:27 AM  3 years agoPost 21
Aaron29

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USA

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Does this BEC not have a voltage that can be set?

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06-19-2015 04:29 AM  3 years agoPost 22
EEngineer

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TX

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dyecocker1, here goes...

Referring to the link to the spec. data of the 5400 series rectifier diodes...and your success using four 5480 3A diodes in series....resulting in a consistent 4.4V...from your BEC...and resulting in your VCntl "verification"...here's my suggestion:

The specs of the 5480 diode(pointing to Fig. #2 of the spec data), since it took 4 diodes to drop to 4.4V, your Hobby Wing sensor is drawing so little current that the diodes are being "biased" at close to 10mA of current...

So the voltage drop is ~.6V per diode.....4 x .6 = 2.4V

7V - 2.4V = 4.6V...consistently...right?

Your sensor is probably on drawing ~10mA...so there's a little more drop from it...making the voltage at 4.4V

Unlike a servo "drop down", the HW sensor also draws the same amount of current...and that current is very low.

A simpler way to achieve this....for your situation...is to use a resistor "combo"(rather than a non-linear diode "combo" to achieve this same goal.

So, what worked for you is a voltage drop of 2.6V from 7V...

V = R(res) x I(current)...so...R = V / I...

I = ~ .01A(by your measurements of what worked)
V = 2.6V

R = 2.6 / .01 = 260 ohms

The nearest standard value for a cheap 10% resistor is 270 ohms.

So, the resulting voltage will be slightly lower.

But, it's one 1/4 watt resistor that's so cheap...you'll want to buy two.....

That's my recommendation....

FWIW

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06-19-2015 04:31 AM  3 years agoPost 23
EEngineer

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Oh, crap.....so it was 6 diodes that dropped the voltage to 4.4V.

Let me re-work my math.....

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06-19-2015 04:37 AM  3 years agoPost 24
EEngineer

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TX

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dyecocker1, here goes...again....

Referring to the link to the spec. data of the 5400 series rectifier diodes...and your success using six 5480 3A diodes in series....resulting in a consistent 4.4V...from your BEC...and resulting in your VCntl "verification"...here's my suggestion:

The specs of the 5480 diode(pointing to Fig. #2 of the spec data), since it took 6 diodes to drop to 4.4V, your Hobby Wing sensor is drawing so little current that the diodes are being "biased" at so little current on the Fig 2 curve...it's off the chart.

So the voltage drop is <.6V per diode.....6 x it's off the chart = 2.6V

7V - 2.6V = 4.4V...consistently...right?

Your sensor is probably drawing very much less than 10mA...so there's little more drop from it...making the voltage at 4.4V

Unlike a servo "drop down", the HW sensor also draws the same amount of current...and that current is very low.

resistor method

A simpler way to achieve this....for your situation...is to use a resistor "combo"(rather than a non-linear diode "combo" to achieve this same goal.

So, what worked for you is a voltage drop of 2.6V from 7V = 4.4V...

V = R(res) x I(current)...so...R = V / I...
I = ~ .001A(by your measurements of what worked)

V = 2.6V
R = 2.6 / .001A = 2600 ohms
The nearest standard value for a cheap 10% resistor is 2700 ohms.
So, the resulting voltage will be slightly lower.
But, it's one 1/4 watt resistor that's so cheap...you'll want to buy two.....

That's my recommendation....

FWIW

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06-19-2015 05:19 AM  3 years agoPost 25
Aaron29

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USA

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..

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06-19-2015 05:26 AM  3 years agoPost 26
EEngineer

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TX

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The OP solved his problem, Aaron....

Asked if there was a better solution....

Even provided very good empirical data...

A resistor solution will not cause a fire.

You haven't tried to "port" an exhaust header...and now electronic theory?......

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06-19-2015 12:21 PM  3 years agoPost 27
Dan Minick

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Columbus, WI

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Does this BEC not have a voltage that can be set?
Absolutely, but then I would be running my nice HV servo's at 5v. Seems silly
But, it's one 1/4 watt resistor that's so cheap...you'll want to buy two.....
I think I actually have these. Used to make my own anti-spark connectors. Though the diodes were dirt cheap as well 5$ for 50

Team Synergy, Team FBL Rotors-------if its not broke...it will be!

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