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Old Jan 23, 2005, 10:20 PM
gasless
Seattle area
Joined Jun 2004
631 Posts
Low cost home-brew UBEC

I thought I would share a recent discovery at Radio Shack: 273-1863 9-Volt Vehicle DC-to-DC Adapter. Good for 1000mA, and 12-24 volt input. http://www.radioshack.com/product.as...%5Fid=273-1863

My 1oz wireless video camera needs 9V @ 270mA, and running off of 3 lipo cells means I need a regulator for the camera. KoolFlightSystems will do custom voltages of their UBEC, but they have a two week turn around, and the 2.5A capacity is overkill just for the 0.27A camera.

The RS 273-1863 is based on the MC34063A switching voltage regulator, so it should be much more efficient than a simple custom solution based on the 78xx series regulator (of which 9V is not a standard part). The adapter can handle up to 7S lipo too, maybe more as the MC part is actually rated around 30V. The board is single sided, with some surface mount components on the bottom/copper side, but quite easy to adjust for other voltages once someone reverses the circuit. Also, I tested (no load) down to 9V input. From 9.4 to 24 volts it has a constant 9.35V output. Below 9.4 volts, it tracks to the input voltage -0.1.

The board removed from lighter plug case and without cables weighs only 11 grams. After cables and heatshrink wrap it will be about 21 grams. Compare to a 9.6V 170mAH square battery and connector at 49 grams and only 15 minutes of video.

One thing I have not tested yet is the effect on the video signal with a switcher supply, but don't expect any adverse noise from it - if so it is an easy fix. I will test that tomorrow.

-Gerry
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Old Jan 23, 2005, 10:35 PM
Got shenpa?
flieslikeabeagle's Avatar
Los Angeles
Joined May 2004
10,940 Posts
gfcermak, that's an interesting find. I recently found very similar cellphone "quick chargers" for 99 cents at a local "99 cents only" store. They too are based on the 34063 switching regulator IC, and the one I measued put out about 4.7 V as designed, and was also rated for 1 amp, IIRC. Maybe it would be useable as a UBEC to power micro servos and a receiver.

The output voltage on these designs is set by a pair of feedback resistors, and changing one of them would be all that is needed to alter the voltage to 5V or 6V for the servos, if 4.7V is considered inadequate.

-Flieslikeabeagle
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Old Jan 23, 2005, 11:05 PM
gasless
Seattle area
Joined Jun 2004
631 Posts
That's even cheaper! $0.99! Where?

Yes, the standard 34063 circuit does just take a pair of resistor changes to change the step-down voltage, and no architecture changes like the 723 linear regulator for low vs. high input voltages.

I just tested with the video camera and a fresh 3S lipo pack, it does add a very slight amount of noise compared to the 9.6 NiMH square battery. It is probably switching somewhere near the camera's 15.734kHz horizontal scan frequency. Certainly not enough to effect servos if revoltaged at 5.0V. I'll add another LC stage on the output to get it clean for the video.

-Gerry
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Old Jan 23, 2005, 11:53 PM
Use the 4S Luke
feathermerchant's Avatar
USA, TX, Euless
Joined Aug 2003
9,341 Posts
Since your load is fixed, you could extend the input voltage range by using a zener or resistor in series with the lead from the LiPo.
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Old Jan 24, 2005, 01:21 AM
gasless
Seattle area
Joined Jun 2004
631 Posts
This is true, and also very inexpensive. But zeners don't have great regulation and work like linear regulators by bleeding off excess voltage as heat. I would prefer the efficiency of switching regulators.

I have wired in an extra LC (?100mH & 470uF) filter on the output, and all remnants of the switcher noise artifacts have disappeared. I will scope it sometime later to see the improvement.

Strangely the power analyzer plus could not see the current pulses from the switcher and began reading 0.00 or 0.05 A (down from 0.20-0.25A without LC). But the Whattmeter reads 0.2A stable with the LC in place. They must have much different AC conversion cut-off frequencies. Note to self, high speed sampling and cpu time weighted integration would be more accurate for switched loads.

-Gerry
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Old Jan 24, 2005, 01:51 AM
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flieslikeabeagle's Avatar
Los Angeles
Joined May 2004
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Quote:
That's even cheaper! $0.99! Where?
The "99 cents only" stores are a chain, fairly common here in Southern California. Not sure if they have any stores in Seattle...but take a look anyway: http://www.99only.com/

I found Qualcomm "Rapid Charger" cellphone chargers at one of these stores, and similar Belkin and Samsung chargers at another. Your mileage may vary...these stores sell surplus and discount merchandise, and stocks vary constantly.

-Flieslikeabeagle
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Old Jan 24, 2005, 06:50 AM
Use the 4S Luke
feathermerchant's Avatar
USA, TX, Euless
Joined Aug 2003
9,341 Posts
gfcermark - I was just suggesting a cheap way to allow you to use this switcher on higher voltage packs. I was not advocating replacement. With the zener in series in the input circuit you could use your camera in planes with higher voltage battery packs. The regulator would still do it's job.
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Old Jan 24, 2005, 12:18 PM
gasless
Seattle area
Joined Jun 2004
631 Posts
feathermercharnt, I get it now.

This specific adapter is already rated for 24V, and from the 34063 spec sheet I think it will go 30V (need to check the input cap). None of my planes go beyond 6S currently, as the controllers suddenly get much more expensive above "16 cells". So this item will do fine.
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Old Jan 24, 2005, 12:20 PM
gasless
Seattle area
Joined Jun 2004
631 Posts
flyslikeabeagl, nope, no "99 stores" chain hear in Washington. But I'm sure there are competitors that may have them.

I'm not sure what to think of their website:

Open 8am to 9pm - 9 Days a Week

-Gerry
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Old Jan 24, 2005, 07:13 PM
Mad Max meets the Thinker
Cyberman's Avatar
Pittsburgh, PA
Joined Apr 2004
569 Posts
Not to be a pesimist...

I always thought home brew involved making it yourself?

Perhaps more aptly put low cost 'requisitioned BEC'?

Although it's much easier and cheaper to requisition the parts that way

Do you know how efficient the convertor setup as is, is? (wow double your is!) You don't want to waste power

I've been looking at making a high voltage one myself from some of National Semi's line of convertors. Although what is the commonly desired output voltage? It seems to be 5 or 6V isn't 9.3V a bit high for that need?

Cyb
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Old Jan 24, 2005, 07:49 PM
gasless
Seattle area
Joined Jun 2004
631 Posts
Cyb, it easily adapts to 5V with just a resistor pair swap. See the MC34063A data sheet such as here: http://www.ortodoxism.ro/datasheets/aic/MC34063ACN.pdf

"Home-brew" didn't intend to mean all custom - sometimes goal is to spend a few $ to save many hours of time. Certainly I could have done a custom schematic/layout/board for this. But having done this a lot in the distant past I would have learned little. Yes, often times, single unit retail electronics parts are pricey. I think of it as object oriented construction.

I have been using KoolFlightSystems UBECs in my 6S EDF planes with great success. However the onboard 2.5 GHz wireless video camera needs 9V at 270mA.

Efficiency: at 9.3V, 0.27A (2.51W) output load, it was drawing 0.20A +/-0.05 @12.1V, which seems fine with me. As long as it won't be 0.27A at 20V as with a linear solution.

-Gerry
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Old Jan 24, 2005, 08:25 PM
Mad Max meets the Thinker
Cyberman's Avatar
Pittsburgh, PA
Joined Apr 2004
569 Posts
Quote:
Originally Posted by gfcermak
"Home-brew" didn't intend to mean all custom - sometimes goal is to spend a few $ to save many hours of time. Certainly I could have done a custom schematic/layout/board for this. But having done this a lot in the distant past I would have learned little. Yes, often times, single unit retail electronics parts are pricey. I think of it as object oriented construction.
Ahh OOC hehehehe

Quote:
Originally Posted by gfcermak
I have been using KoolFlightSystems UBECs in my 6S EDF planes with great success. However the onboard 2.5 GHz wireless video camera needs 9V at 270mA.
Now that could be a little problem.

Quote:
Originally Posted by gfcermak
Efficiency: at 9.3V, 0.27A (2.51W) output load, it was drawing 0.20A +/-0.05 @12.1V, which seems fine with me. As long as it won't be 0.27A at 20V as with a linear solution.
that puts it around 80-85% efficiency. Good enough. National makes the LM5010 which will get you 1A at various voltages at upto 75V input. Not cheap nor is it through hole (AKA perfboardable). End user cost to make something like that (getting boards done comercially etc.) Roughly 2.50 for each PCB and $5 to $7 for components. That's about 200 units so about 1500 to 1900 dollars worth. For multi voltage output the price goes up (of course), but with a jumper and a pot to set the other output voltage (the jumper turns off or on the second output). Nothing is free is it?

Cyb
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Old Jan 25, 2005, 11:54 AM
Got shenpa?
flieslikeabeagle's Avatar
Los Angeles
Joined May 2004
10,940 Posts
gfcermak wrote:
Quote:
I'm not sure what to think of their website:

Open 8am to 9pm - 9 Days a Week
Inflation?

After all, the Beatles had "Eight days a week" back in the 1960's!
http://www.beatlefans.com/lyrics/eight_days_a_week.htm

-Flieslikeabeagle
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Old Jan 25, 2005, 01:46 PM
MRI
Engineered RC Products
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Joined Jul 2004
466 Posts
Gerry and others,
We have a 9V, 1.7A BEC designed for powering cameras, lights, and other accessories. Ours is smaller and probably lighter than the Radio Shack unit you have, and it was designed with model aircraft in mind. The details for the 9V BEC are here:

http://www.medusaproducts.com/Other/...-BEC-35020.htm

Regards,

MRI
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Old Jan 25, 2005, 08:18 PM
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flieslikeabeagle's Avatar
Los Angeles
Joined May 2004
10,940 Posts
MRI, a little off topic, but when do you think the Medusa brushless IPS motor replacement will be available, and do you have an estimated price?

-Flieslikeabeagle
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