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HelicopterMain Discussion › Question for the E guru's
06-19-2015 01:36 AM  35 months agoPost 1
Dan Minick

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Columbus, WI

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I made a custom diode to drop the voltage coming off one my BEC leads from 7 to 5 volts. When I hook it directly to a 2s pack it works great. When I wire it into my helicopter I can only get 1.5 volts from a 7 volt feed through it. What gives?

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06-19-2015 01:51 AM  35 months agoPost 2
EEngineer

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TX

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Did you plug it in backwards to the BEC?

The cathode/s should be oriented "away" from both the BEC and the battery.

Do you have the part # of the diode or diodes used?

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06-19-2015 01:54 AM  35 months agoPost 3
EEngineer

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TX

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When I wire it into my helicopter I can only get 1.5 volts from a 7 volt feed through it.
Is that the "open circuit" voltage?(measured with the BEC powered but not connected to anything but your volt meter)

Or, is that when power is applied to the FBL/servos, etc.?

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06-19-2015 02:03 AM  35 months agoPost 4
Dan Minick

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They are 1N5408. This is with everything powered up.

I marked the cathode when I built it, so I though it was funny this was happening. Took it back out to confirm its correct.

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06-19-2015 02:07 AM  35 months agoPost 5
Dan Minick

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I suppose I tested this on a BEC that had no load. Maybe I do not need as many in a series to drop the V with load? This doesn't see correct to me

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06-19-2015 02:11 AM  35 months agoPost 6
EEngineer

rrProfessor

TX

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That's a 3A diode with a max. forward voltage of typically 1.2V at 3A.

https://www.fairchildsemi.com/datasheets/1N/1N5404.pdf

Looks like with the BEC it's doing it's job properly.

The 5400 - 5408 series just varies with the amount of reverse voltage that can be applied.

Is this for use with just one tail servo? Worried about the max current this diode assy. has to carry.

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06-19-2015 02:13 AM  35 months agoPost 7
EEngineer

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TX

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I suppose I tested this on a BEC that had no load.
With no load, there will be little drop.

But, at 3A, the spec sheet lists 1.2V.

If you used 2 in series you would have more voltage drop.

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06-19-2015 02:19 AM  35 months agoPost 8
Dan Minick

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OK, so my Vbar control can monitor HS with my Jive controller and a Phase sensor. But the kicker is the input from the sensor can only be 5v into the Vbar. I run my servo's at 7 volts, so I need to drop the voltage just to the phase sensor lead. I had to use 12 to get the voltage to drop my 2 volts no load. That is the problem. How many would you recommend?

I am guessing I will still need at least 3 with such little current

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06-19-2015 02:24 AM  35 months agoPost 9
EEngineer

rrProfessor

TX

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need to drop the voltage just to the phase sensor lead
the phase sensor won't get near 3A....do you know how much current the sensor wants?

12 diodes in series?.....

2 would do....but you want precisely 5V?...what are your tolerances?

5V +/- 10%...+/- 5%.

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06-19-2015 02:27 AM  35 months agoPost 10
Dan Minick

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4-5v would be good just not much over 5v. The sensor can operate down to 3.5v. Hobby wing sensor

I am told the last port on my mini Vbar can only handle 5v

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06-19-2015 02:34 AM  35 months agoPost 11
EEngineer

rrProfessor

TX

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The diode series(5400 - 5800) are used for a "full wave rectifier" circuit, for example, used to convert 120 VAC to some DC voltage.

I think what you need is a "fast Schottky" diode.....less current but the voltage drops of each diode are slightly smaller....which get's you closer to 5V without exceeding 5V.

Do you use DigiKey?

Have to run an errand right now...back in about 1.5 hours.

Will spec(Digikey) this type of diode for your app.

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06-19-2015 02:48 AM  35 months agoPost 12
WessCo

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Summerville, GA USA

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The last port on a Mini Vbar don't use any voltage. You'll need to use the white wire on the top pin and the red and black in another port. Do you have any more ports open? If not, you'll need to y off of any other port.

MikadoUSA
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06-19-2015 02:51 AM  35 months agoPost 13
WessCo

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http://www.vstabi.info/en/node/442

MikadoUSA
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06-19-2015 02:56 AM  35 months agoPost 14
Dan Minick

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Columbus, WI

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I understand that, but the signal wire still carries voltage. I located my diode down near the battery tray.

I did figure it out for now. 6 in a series drops to 4.4v consistantly on a load and the Head speed popped right up on the V-Control. Just what I was looking for. I would still be interested if there is a better option as I plan on doing this on all my Jive helis.

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06-19-2015 02:57 AM  35 months agoPost 15
WessCo

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Summerville, GA USA

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Should be ok with 7v.

MikadoUSA
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06-19-2015 03:01 AM  35 months agoPost 16
Dan Minick

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Columbus, WI

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Its not the sensor that is limiting. Its the Vbar. Only 5V max is allowed from a signal wire on the RX A port

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06-19-2015 03:05 AM  35 months agoPost 17
WessCo

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I'll bow out. You've thoroughly lost me. Never heard of anyone putting anything on the signal wire of an RPM sensor, except a servo connector.

MikadoUSA
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06-19-2015 03:14 AM  35 months agoPost 18
Dan Minick

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Columbus, WI

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You are correct on the signal wire going into the top of RX A. But I can not pull voltage directly from another port because I use 7V to the servo's. RX A is only allowed to have 5V, even though I am not connecting a power wire to RX A voltage is still fed through the signal wire. So I need a way to drop just the line voltage to the Hobbywing sensor.

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06-19-2015 03:33 AM  35 months agoPost 19
WessCo

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Summerville, GA USA

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I understand now. . .though I've never worried about it.

MikadoUSA
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OptipowerUSA

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06-19-2015 03:54 AM  35 months agoPost 20
EEngineer

rrProfessor

TX

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I did figure it out for now. 6 in a series drops to 4.4v consistantly on a load and the Head speed popped right up on the V-Control. Just what I was looking for.
So, it took four....1N5480's to drop the voltage from 7V to ~4.4V...and it works?....5480's right?

That's great....
I would still be interested if there is a better option as I plan on doing this on all my Jive helis.
And, I think there is indeed a better and cheaper way....which involves using simple resistors rather than diodes(diodes are non-linear...resistors are linear).

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HelicopterMain Discussion › Question for the E guru's
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