Experimental Aircraft Ground Power Supply

[timotb]

I'm looking for an inexpensive, safe and reliable method to power an experimental aircraft avionics/computers using 120volt ground power with the engine off.

My thoughts so far are to bypass the battery with a switch and install a 12 volt regulated power supply. Ive read about converting an ATX computer power supply to a 12 volt power source. Sounds simple, but is it safe? Ideas?

Tim

 

[MikeMl]

During day VFR, the avionics and engine instruments in my C182 draw ~12A from the alternator after the battery is recharged. If I turn on nav lights, the beacon, the pitot/stall switch heaters, the load increases to ~35A.

I'm thinking that the 12V output from an ATX supply is too whimpy. I use a MeanWell SE600-15 (similar to **broken link removed**), set to 14.25V. I bought mine on EBay for ~$35. It had a bad fan and I changed it. Works great, and can charge the battery, too.

 

[Sceadwian]

The 350watt ATX I have for my bench supply will do 16 amps on the 12 volt line. I checked Newegg real quick, the most expensive supply they have is a 750watt ATX that will do 60amps on the 12 volt line. Any power supply made for a modern machine over about 500 watts should supply plenty of 12 volt current, modern PCS have switched to higher current 12 volt rails because more devices now days use 12 volts directly and buck it down locally to their needed voltage, although Mike's power supply sounds nice as well as it has only the 12V line that's required not the additional 5 3 etc.. that an ATX has.

As long as you pick one that meets your load requirements they're incredibly safe and easy to use, you don't even need to disassemble the power supply to do the 'conversion' all the wiring can be done on a panel externally. All that's needed is a on/off switch and a power resistor to draw an amp or two from the 5 volt line, the 5volt power resistor is needed to help maintain regulation on the 12V line.

 

[timotb]

I expect to use less than 5 amps while setting up the EFIS (Electronic Flight Information System made by Advanced flight System-3500) and Garmin GNS430 GPS. Transmitting on a comm can draw 10 amps. No intention to transmit.

Knowing how to pick an ATX that will supply 5 amps safely and reliably is my problem. Most that Ive seen already have a power on/off switch. I know an ATX needs a power draw to start. I was thinking of a simple light bulb for the power resistor.

"all the wiring can be done on a panel externally." <<<Not sure what you mean.

Im a pilot/aircraft builder not a electronic expert. Was hoping to hear some electronic expert thoughts....I did. Thanks

 

[Sceadwian]

If you pick an ATX supply that can't provide 5 amps on the 12 volt line something is very wrong =P The 350 I have can put out 16. To get less than 5 I think you'd have to have an ATX supply less than 100watts and they just don't make them that low. I had a 250 previously that was around 10 or so. So that'll give you something to go with. It's pretty easy though there's a sticker on the side of every ATX supply that tells you exactly how much current each rail is rated for.

ATX's do not need a power draw to start, then need a small load on the 5V line to properly regulate though. Only the most poorly designed ATX supplies will not start even if there's no load.

All the wiring can be done externally means just that, you don't have to open the supply at all, so it's very safe. All you need to do to turn the supply on is short the green wire to ground, just about any low current low voltage flip switch will work fine. There's a purple wire that will provide a 5V sidebus that is always on if the power supply is plugged in, some ATXs have a seperate power switch on the back that actually hard turns the supply off, meaning even the 5V sidebus will go dead. Just tie a few red wires together and attach them to binding posts or the outlet that you decide to use and you're all set.