VAC to DC

[jlfernan]

How many amps 10a 250VAC or 15A 125VAC in DC. This is for a landing light switch and I want to know if it's enough for a standard PAR 36 GE light.

[DakotaHawk]

Switches have two different ratings - AC and DC. A switch may be rated for 25 amps AC, but only 5 amps DC. The ratings are based on the switch's ability to extinguish an electrical arc when the switch is opened(turned off).

Since AC voltage passes through zero volts 120 times pet second, AC ratings are generally pretty high. Zero volts = 0 amps = no arc to extinguish!

On the other hand, DC voltage never goes to zero, so an arc could leap across the switch contacts (inside the body of the switch), ionizing the air and creating a path for continued current flow.

DC rated switches have internal arc-quenching designs to prevent continuing arcs. If the specs for the switches that you're looking at don't include a DC spec, look somewhere else!

[jlfernan]

This switch is actually from and for a Cessna. The issue I have is that the original switch is a single. The new part number for the switch is for a single with a blank side (essentially a double switch). I have some single switches that are marked 5A 250v, 10A 125v, 1/2 HP 125-250v. Before I open up the hole in my panel, I would like to know if the smaller switches are sufficient for my landing light. I asked my local Cessna parts people, but they weren't much help.

[Walt]

Originally Posted by jlfernan

I have some single switches that are marked 5A 250v, 10A 125v, 1/2 HP 125-250v. Before I open up the hole in my panel, I would like to know if the smaller switches are sufficient for my landing light.

Those are AC ratings, but if they are good aircraft quality switches they should be ok. Personally I would prefer to see a DC rating on a switch but not all switches carry that rating. If you're talking about some of the mini switches available from places like radio shack I would avoid using those.

[jlfernan]

NEVER from the Shack! These are PMA'd parts approved by the FAA and Cessna. Those are the only markings on them. They are made by Carling and even their site doesn't offer mush insight.

[Walt]

A 100W par 36 will draw about 8 amps normally but these lamps have a high in-rush current so derating the switch is required, I would use a 15A switch in this case to be safe. Sounds like the switch you have should be ok.

[jmjula]

Just because a switch only lists an AC rating doesn't mean it has no DC spec, though it isn't necessarily easy to find. See Bob's article for more information: http://www.matronics.com/aeroelectri...ch_Ratings.pdf