# Voltage regulator options

Discussion in 'Instruments / Avionics / Electrical System' started by Dana, Oct 13, 2009.

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1. Oct 13, 2009

### Dana

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Looking at options to get DC power from the Cuyuna engine in my UltraStar. It has, of course, a lighting coil but no regulator. I don't want or need the weight of a battery.

All I really need to run is a strobe that draws 200mA, but it'd also be nice to power my handheld GPS (not sure of the draw but it runs a long time on two AA batteries) and my Icom A24 radio (which needsd 11V, not 12V).

The "standard" approach would be the Key West voltage regulator for about $80. No battery required, produces clean DC power, some people have had trouble with them exploding, or frying the lighting coil (though that just takes a fuse to prevent). Could go with a cheap ($20-30) motorcycle or snowmobile regulator. These require a battery or oher load; some bikers use a large capacitor for this. I believe the single phase Rotax regulator is similar?

The cheapest and lightest option is a basic 7812 voltage regulator and a bridge rectifier from Radio Shack... if the lighting coil puts out 35VAC it can barely handle the power dissapation for .25A if I put it on a heat sink, but that's enough for the strobe... I could add another one for the other stuff if necessary.

-Dana

What has four legs and an arm? A happy pit bull.

2. Oct 13, 2009

### Dan Thomas

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Use an LM317 chip (same case as 7812) and a couple of resistors to get what you need. See this, or Google some other sources:

Dan

3. Oct 13, 2009

### Dana

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Yes, the LM317 is what I had in mind for the 11V if I decide to go that route... no advantage for the primary regulator, though, since I imagine it's power dissapation capability is the same as the 7812. I probably won't bother, though, as the Icom's batteries last a long time; I take it home and charge it maybe once a month, or before a long flight... and it probably draws more current while transmitting than those tiny regulators can handle. The GPS is another matter; it's a lot easier to read the screen, even in the sunlight, when the backlight is on, and that sucks down the batteries.

-Dana

Hard work has a future payoff. Laziness pays off now.

4. Oct 13, 2009

### Dan Thomas

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I use an LM317 to drive my Icom and have no trouble. They'll handle 1.5 amps with adequate heat sinking. But then, I have a small sealed lead-acid battery that the generator feeds via the regulator, and the battery acts as a current buffer. It's a surplus unit from an emergency light and is about 6" long, less than 2" tall and maybe an inch think. Weighs a half pound or so.

Dan

5. Oct 13, 2009

### Dana

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You're using the LM317 to drop the generator's output to 12V? I wouldn't think it can handle that much current with that much voltage drop. What 's your generator voltage? Or are you using the LM317 to drop the already regulated output further down to 11V?

-Dana

A goverment that fears arms in the hands of its people should also fear ROPE!

6. Oct 14, 2009

### Dan Thomas

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The 317 will take up to 35V on its input. The little generator puts out around 32 in cruise. It's the little doodad under the belly of my airplane in the avatar and is driven by a tiny propeller. It was a ball-bearing DC motor from a photocopier in an earlier life. The Continental A-65 has no provision for an alternator or generator.

Dan

7. Oct 14, 2009

### needswings

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What you are after is probably something like the circuit shown on this page:
Power sourse circuits page
entitled LM317T Voltage Regulator with Pass Transistor (its a bit over half way down). Leave the transformer out but keep everything else. You can adjust the voltage output to whatever you want by changing R1 and R2.

Should be relatively low noise, but if you do get a lot of interferance you can try adding an inductor in series on the input line.

You can use the same series pass transistor method to boost the current with the LM7812 as well - check the datasheets for info/maths etc http://www.fairchildsemi.com/ds/LM/LM7812.pdf (see page 24 on that sheet).

Note that different models of the regulators have different current capabilities... the 78L12 for example can only handle 100mA - you'll definately need a pass transistor for that one.

Last edited: Oct 14, 2009
8. Oct 16, 2009

### Dana

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At this point what I expect to do is to use a 7812 to power this strobe. I haven't seen it yet so I don't know how bright it is but for the price there's little risk.

If I decide to power my radio as well I'll use a separate LM317 with the pass transistor to get 11V... accord to Icom it takes 12V to charge the battery but it must be turned off as 12V will fry it... 11V will run the radio if there's enough current but won't charge the battery. Or I could use the LM317 to get 24V and use Icom's power adapter to power the radio from the 24V and also run my GPS on the 24V... less voltage drop in the regulator means it can handle more current.

-Dana

I love my country, but I fear my government.

9. Oct 19, 2009

### needswings

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Interesting strobe... the max current draw you can expect from that is 240mA, which is well within the specification for a standard 7812, but not for a 78L12.

Strobes have a pretty bad reputation for electrical/RF noise - you may want to run some tests before finalising your circuit. That way if there is a problem you can deal with it before everything is committed.

10. Oct 19, 2009

### Dana

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Yes, noise could be an issue as it's not designed for aircraft. I figure on adding a couple of largish capacitors on both sides of the regulator anyway, which should help.

-Dana

Aviation has made the world a lot smaller, but it's still hard to miss it if you fall.

11. Oct 28, 2009

### needswings

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I noticed from your other thread that you've got the strobe installed now - did you have any issues or was it all pretty straightforward?

Did you wind up having any noise problems?

12. Oct 28, 2009

### Dana

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No radio interference whatsoever, if that's what you mean... though remember that at this point I'm running it from a separate battery pack, nothing in common with the radio.

-Dana

Daddy, why doesn't this magnet pick up this floppy disk?

13. Oct 30, 2009

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