Can you find my missing 9 volts?
 

My Whelen strobe pack quit working last week, so I checked voltage at the pack; 12.5v (battery voltage). Sent the pack to Whelen and it bench tested OK.

Further testing last night finally revealed that I had 12.5v at the switch output, and ~3.5v at the pack (unloaded, not connected to a borrowed pack). A bypass wire from the buss to the pack was used; strobes worked fine, all good.

Voltage (3.5v) was tested with voltmeter 'red' on the positive strobe wire (at the pack), 'black' grounded to the aircraft (Note: ground wire from the panel buzzed out OK).

I'm yet to buzz the positive wire from the panel switch to the pack, so in the mean time....where is my missing 9v? :confused: Rosie

These things usually happen at connection points. I'd give the 2ends a good tug

Switches do go bad. It is easy when they fail in an always open or closed condition. Sometimes, they fail with burned internal contacts which causes a high internal resistance and a consequent voltage drop.

Do you have inline splices or terminal strips in the strobe wire power feed? These are additional areas to look.

Connectivity
 

Bad switch? Are you sure you were on the switch output (with the switch in the on position) when you measured the 12.5v at the switch?

My guess is either a bad switch or a bad ground.

Bevan

I'll second what Noel said. A Whelen power supply with three strobes pulls at least 7 amps in my airplane. That's a lot of current going through the switch. It will eventually wear out. Mine did, and the way I found it was I just happened to touch the switch and it was VERY hot. After I landed, I noticed my strobes were out. Changed the switch, all OK.

Another reason to upgrade to LEDs!

Common occurrence, especially with Carling switches. Strobe power packs are hard on switches and terminals.

Let me expand on the switch test (I'm testing at the correct switch)....I disconnected the strobe wire at the switch and measured the voltage at the switch output: 12.5v

I reconnected the wire and measured again at the:
**switch output: 12.5v
**Other end of the wire (no splices, not connected to strobe pack): ~3.5 v

I was tired, it was last and didn't get a chance to buzz the wire from the switch to the pack...will do that tonight, Rosie

Do you have a pullable breaker in the mix? If so, try resetting it 30 or 40 times. That may help.

No load?
 

A no current load drop of 9v is hard to do. Put a 1K load resistor across that meter and see if it's not really 0v

Rosie,
I don't think buzzing the wire will help.
It sounds like you have continuity that will buzz the test but not enough conductor to carry the large current. Somewhere in the circuit is getting hot.