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Andy7:
19 Aug 2019 09:14:20
Good for you!  ~~
DarkButterfly:
18 Aug 2019 19:13:57
Had another negative encounter, it's been a few years since the last one, just an uneducated ******, going on about drones being illegal yada yada yada.    :-/
Still that didn't spoil my flying time, had an absolute blast  ~~
Gaza07:
07 Aug 2019 19:52:01
ooooh mrs jones  :D
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30 Jul 2019 15:26:34
D.B. you tightwad.. :cool:
atomiclama:
29 Jul 2019 20:14:10
DB that just means you have shed loads of props in the first place ;-)
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29 Jul 2019 18:53:33
Just had a thought, even with all the crashing I've done, I haven't bought any replacement props in over a year ~~
ched:
09 Jul 2019 19:45:42
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09 Jul 2019 18:10:30
Hope you all have a great day  :beer2:
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09 Jul 2019 14:05:28
BFU#8 details locked in for this saturday - see the head of the forum thread for all details.
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05 Jul 2019 21:51:05
Good for genital warts as well......or so I'm told.. :hmm
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Printing 3d Forum

Make your own Linear 5 Volt BEC!

Started by teslahed, Wednesday,July 03, 2013, 21:54:32

Previous topic - Next topic

teslahed

Wednesday,July 03, 2013, 21:54:32 Last Edit: Wednesday,May 14, 2014, 15:10:04 by teslahed
In order to try and cut down on interference in my FPV system i thought i would use a linear BEC instead of a switching one. Linear BECs run constantly rather than at a high frequency so don';t produce interference which can cause your FPV system problems.

Unfortunately they are quite hard to find as ready made BECs on hobbyking or similar.


QuoteFirst of all, the 5 volt power supply, thats easy, simple and cheap as chips, all you need is a small 3 legged voltage regulator called the 7805, this is an analog voltage regulator and doesnt create noise, and costs about 50p or less, just add a small .1uF cap on the input and output pins. If whatever you want to power, uses less then 100ma, then you can use the smaller and lighter 78L05 here is more info... http://en.wikipedia.org/wiki/78xx


None of that sounded impossible so i though i would give it a go myself.

I got my 7805 voltage regulator from here;

http://www.bitsbox.co.uk/vregs.html
http://www.bitsbox.co.uk/data/vregs/78xx.pdf

And the 100nF (0.1uF) capacitors here;

http://www.bitsbox.co.uk/cercaps.html

I took the ferrite ring off an old ESC but you can buy them off ebay or giantshark if you need to.

This is the circuit;



And the chip itself looks like this;



And here are my results;





I will post up more information when i have had a chance to properly test it.
One circlip short of a quadcopter.
 1 lobe short of an antenna.

Gaza07

Nice job Chris might have a go at 1 of these to  ~~

Hands0n

That';s a really cool and simple circuit.  Amy thoughts on how much heatsink, if any, is required for 3S and 4S LiPo? Those analogue regulators will generate heat in the voltage conversion process, although I';d not imagine you';ll be pulling much current through the BEC

Sent from my Nexus 7 using Tapatalk 4 Beta

--
Danny
"Its better than bad, its good"

Current FCs: Pixhawk, APM 2.6, Naza M V2, Naze32, Flip32+ CC3D, KK2.1.5
Aircraft: miniMax Hex, DJI 550 (clone) TBS Disco, 450 Firefly, 250 Pro, ZMR250, Hubsan X4, Bixler 2

barneyg

Nice ... and for those of you with a Crius v2 ...could you not make it with a 7806 and then add a small potentiometer to act as a voltage divider ... something like :

http://www.maplin.co.uk/square-22-turn-cermet-preset-potentiometers-2202

powerlord

I think it';s the 7813 that is variable anyway.  You';ll need an big heatsink to pull an amp out these though - they are really for small currents.

Sent from my HTC One using Tapatalk 4 Beta


pheasant_plucker

I wouldn';t even bother with the Vero board. Just solder the capacitors directly to the legs.

Gerry
The man serving me in the canteen said "Look, You can see the face of Jesus in the Margarine" The Asian guy next to me replied "I can't believe it's not Budda"
http://www.namfc.co.uk/pictures/fly.gif

Hands0n

I';d start to worry about the mechanical strength of doing that :-) 

Sent from my Nexus 7 using Tapatalk 4 Beta

--
Danny
"Its better than bad, its good"

Current FCs: Pixhawk, APM 2.6, Naza M V2, Naze32, Flip32+ CC3D, KK2.1.5
Aircraft: miniMax Hex, DJI 550 (clone) TBS Disco, 450 Firefly, 250 Pro, ZMR250, Hubsan X4, Bixler 2

teslahed

Thursday,July 04, 2013, 17:38:03 #7 Last Edit: Tuesday,October 22, 2013, 18:39:17 by Jumpy07
I';ve made a second Linear BEC. I';ve added a heatsink this time and used a voltage regulator that';s rated to 2 amps.

I used veroboard to add mechanical strength. This will be powering my hexacopter, i don';t want to risk it failing in flight.



I';ve added 10nF capacitors between the inputs and outputs and the ground and a 470nF capacitor between the input and the ground to add extra filtering. The 10nF capacitors would be a good idea and i';ve noticed that most other BECs seem to use a 470nF capacitor as well so i thought this would help.

I will also add a ferrite ring on the input as well as the output.
One circlip short of a quadcopter.
 1 lobe short of an antenna.

powerlord

I';d advise testing it for heat on the ground,  especially if you haven';t matched the heatsink  to the ic heat dissipation requirements - they do get very hot. It';s far more likely to fail due to thermal shutdown than a broken connector.  Just my 2c. Something to consider is using more than one to dispute the heat (different circuut)

Sent from my HTC One using Tapatalk 4 Beta


teslahed

Friday,July 05, 2013, 12:36:12 #9 Last Edit: Friday,July 05, 2013, 12:52:08 by teslahed
Quote from: powerlord on Thursday,July 04, 2013, 18:58:40
I';d advise testing it for heat on the ground,  especially if you haven';t matched the heatsink  to the ic heat dissipation requirements - they do get very hot.


This might be a problem for me. I';ve had it flying and after landing the heatsink only felt moderately warm, but when i run it on the bench it gets to about 95 degrees C. Obviously the heatsink needs a bit of airflow to keep it cool enough.

What temperature do these things start to melt down at? Maybe i need a bigger heatsink.

edit - just read the specs; http://www.bitsbox.co.uk/data/78S15.pdf apparently the voltage regulator operates up to 150 degrees C so the fact it';s almost 100 C on the ground isn';t great but as long as it';s not getting much higher than that i should be ok - in theory. In flight it runs a lot cooler because i have the heatsink exposed and facing into the airflow.

If anyone with more experience than me with these thing can tell me if these temperatures are ok or not i';d appreciate it.

One circlip short of a quadcopter.
 1 lobe short of an antenna.

pheasant_plucker

If you use aluminium arms on your frame use one of those as a heat sink.

Gerry
The man serving me in the canteen said "Look, You can see the face of Jesus in the Margarine" The Asian guy next to me replied "I can't believe it's not Budda"
http://www.namfc.co.uk/pictures/fly.gif

teslahed

My frame is made of wood, fibreglass and carbon fibre, so i can';t really use it as a heatsink. That';s a really good idea for anyone who can though.

Here';s a photo showing the FPV Hexacopter and the Linear BEC. The Linear BEC is just to the right of the centre of the picture, the heatsink is positioned to clear the transparent heatshrink and face forwards into the air flow.

One circlip short of a quadcopter.
 1 lobe short of an antenna.

SimonS

I';m using a 7812 on my new quad to provide 12v for the camera from the 4S Lipo.  I';ve not used any capacitors and all seems ok.


SimonS

True. Next time I';m near Maplins I';ll get some.

Gav

Going to get a 7812 too now I';ve gone to 4s lipos. Next time in town will get a couple. Just for 12v supply for the accessories like gimbal controller board, leds and camera. Will save my quad carrying an extra lipo in flight albeit a small mah 3s.

SimonS

I';ve found that the AlexMos board actually works better with a 4s supply than 3s especially if you want to use something like a NEX-5.  3S is fine for a gopro but stability in agressive flying is improved on 4s.  The AlexMos is listed as 2-4S.  I';m not sure about the various open source bords (Brugi, RCTimer etc).