REFLECTOR:Panel Switches

[Scott]

The reason why some AC switches are not as long as long lasting as DC 
switches has nothing to do with the rating.

A 24 volt switch wether DC or AC will handle the same load of what ever it 
is rated at.  It don't care if its AC or DC current flowing.

The problem is when you turn the switch off or disconnect the circuit.  AC 
helps out by cycling through the zero potential point 60 or 400 times a 
sec, or whatever HZ your AC is running at.  When the switch is opening as 
the potential(voltage) swings by zero the current stops for a very short 
time,  when it resumes flowing the switch has opened further and it can't 
jump across the air so the switch is off as is the current.  It takes more 
current to initiate a spark gap than to sustain one.

DC however keeps trying to cross the gap as the switch opens, causing an 
arc every time you open the switch.  There are different methods 
manufacturers use to  sneak around DC reluctance(another story) to stop 
conducting.

That being the case there are DC, AC, and DC/AC rated switches.  Some over 
rate an AC switch to use as a DC switch, this kinduv works.  A case in 
point is house circuit breakers.  I have both DC and AC breakers in my 
house, I use SquareD breakers because below 240 volts they are equally 
rated(amperage) for AC and DC usage. Above 240 volts they are not approved 
for DC.  Not all breakers are rated for both DC and AC, most aren't.

Scott

At 11:04 AM 11/29/2003, you wrote:
>This may be obvious to many ... but it is important enough to emphasize:
>
>It is very important to pay attention to the ratings on the switches.
>So many switch makers boast of 200+ voltage capacity ... but it is for
>AC current.  If you use AC switches in DC circuits, they will not last
>long because DC current is much more load than AC.
>
>It is very difficult to find adequate DC switches.  They should be rated
>as 12VDC along with the amperage rating you need.  I also suggest silver
>contacts.
>
>
>
>-----Original Message-----
>From: Glenn Babcock [mailto:gbabcock@tampabay.rr.com]
>Sent: Friday, November 28, 2003 5:12 PM
>To: reflector@tvbf.org
>Subject: REFLECTOR:Panel Switches
>
>I'm wiring up my panel, and I'm looking for recommendations on power
>switches.  I don't plan to use a prefab switch/power unit, and have
>already
>completed my breaker panel.
>
>I want to install rocker switches for various lights (NAV, landing,
>etc.) on
>the main panel, and rockers for engine functions (mags, starter, fuel
>pump,
>etc.) on the overhead panel.  I would like the switches to have a
>lighted
>label and a power indicator light.
>
>I also need push buttons for the stick and panel mounted switches such
>as
>PTT, autopilot, COM flip, etc.
>
>I did find an interesting looking item by Carling Technologies
>(www.carlingtech.com) called the Contura.  This is an attractive, sealed
>switch with LED lighting for both label and status.  It's rated 20A at
>12VDC.  DigiKey has it available.
>
>Should I stick with sealed switches (marine type)?
>
>Besides obvious sources like Spruce and Chief, any tips on sources?
>
>Regards,
>Glenn
>N697RG
>http://web.tampabay.rr.com/gbabcock
>
>_______________________________________________
>To change your email address, visit
>http://www.tvbf.org/mailman/listinfo/reflector
>
>Visit the gallery!  www.tvbf.org/gallery
>user:pw = tvbf:jamaicangoose
>Check new archives: www.tvbf.org/pipermail
>Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
>
>
>_______________________________________________
>To change your email address, visit 
>http://www.tvbf.org/mailman/listinfo/reflector
>
>Visit the gallery!  www.tvbf.org/gallery
>user:pw = tvbf:jamaicangoose
>Check new archives: www.tvbf.org/pipermail
>Check old archives: http://www.tvbf.org/archives/velocity/maillist.html