Whelen Strobe Electrical Issue

I have an RV9a with Whelen model A650PG/PR wingtip and tail Anti-collision/Position Light assemblies powered by a Whelen model HDACF power supply. All has worked fine for several years until last week, the breaker for this circuit popped and would pop after re-setting, with the strobe toggle switch in both the on or off position.

My first thought was that the toggle switch had gone bad. Installed a new switch today and strobes worked as designed, except, wires at back of switch became extremely hot, too hot to touch, within 10 seconds. I disconnected the two wires from the switch and tested the strobes bypassing the switch by holding the two strobe wires that would normally attach to the switch, together. The strobes worked fine, but, the wires became hot again very quickly.

So, I have concluded that the original toggle switch had indeed failed, but, probably failed due to over heating and is thus not the source of the problem.

Before take the plane to someone who really knows what they are doing, I thought I'd solicit some thoughts as to what might be the problem from the forum brain trust first.

In summary, I don't think the issue is the toggle switch as the new switch is turning on and off normally. And, unlike the switch that it replaced, the circuit breaker does not pop if I leave the new switch in the off position.

The circuit breaker also does not pop with the new switch turned on but the two wires connected to the switch on the back become very hot within 10 to 15 seconds. I did not leave the strobe powered long enough to see if the breaker would pop, as the wires were too hot, but, during the 10 or 15 seconds, the breaker does not pop.

So, I don't think I have a short in the wiring, as the strobes function both when connected to the switch and when the wires are held together bypassing the switch. I'm thinking that a short in the circuit would not allow the strobes to flash but would pop the breaker immediately...but I am anything but certain of this theory.

Any thoughts would be appreciated.

Thanks,

Curt

How many terminals on the switch have wires attached to them, just 2? Or more? Can you feel the wires at the other end that is farthest from the switch to see if they are hot there? Can you feel the wires at any other intermediate points to see if they are hot? What happens if the wires are disconnected at the strobe end? Do they still get hot at the switch?

Two Wires Connected To Switch

Joe:

Two wires are connected to the switch. Not sure if the wires get hot anywhere else.

It would seem that a short circuit located some distance away from the switch that heats the entire length of wire would draw so much current that the circuit breaker would trip immediately. That scenario is unlikely. If the wires only get hot at the end, then there is a bad connection. If so, replace the wire terminals at the switch end.

With the power supply disconnected, check for continuity between each wire and a good ground. If all wires check good, the power supply is likely going bad.

Heat is caused by current and resistance. Either it's pulling to much current or has to much resistance. 1. Are the wires properly sized for current draw and length of run? 2. How much current is it really pulling? . What is the resistance of the switch and wiring?

Bob

Progress Report

The installation worked fine for the three years it was installed so something changed suddenly.

Checked continuity and ground today...all seems O.K.

Operated the strobe with only left wing, right wing, then rear, and wires overheated each time. Supplied current to the power supply with all strobes disconnected and wires did not overheat. We don't appear to have a short.

I don't have a meter that measures current draw but the problem seems to be excess current draw. Since operating only one strobe at a time gave the same overheating results as operating all three strobes, I'm guessing at this time that the power supply is faulty.

Ordered new power supply today. Will report out once installed.

Curt

RV9Otter said:

I don't have a meter that measures current draw ...

Click to expand...

Can you not use the ammeter on your panel?

snopercod said:

Can you not use the ammeter on your panel...

Click to expand...

...that Whelen power unit is rated at 7 amps @ 14volts D.C.

I'm concerned that your wiring could get "Too hot to touch" and not trip the breaker.

I'd take this time to verify wiring length, type, and size. Circuit breaker type and size. And switch amperage rating.

With best regards,

Tommycat said:

I'd take this time to verify wiring length, type, and size. Circuit breaker type and size. And switch amperage rating.

Click to expand...

Definitely. Personally, I decided to use fuses for most equipment. My rationale was that circuit breakers won't necessarily trip for minutes on a 200% overload. For that reason, I only used circuit breakers where I needed to be able to open them. In reality, CBs are only designed to protect the wiring from burning up, not to protect the equipment. The wiring to the Whelen should NOT be getting warm, no matter how long they are. This is a pretty good wire selection guide from Aeroelectric. Wire Size Selection. Looking at that, it seems like #14 or #16 would be the proper wire size.

Problem Solved

The overheating was caused by a poor connection on the lead that attaches to the switch from the wire that runs from the breaker.

I appreciate everyone's input. Always helpful.

Thanks,

Curt

RV9Otter said:

The overheating was caused by a poor connection on the lead that attaches to the switch from the wire that runs from the breaker.

Click to expand...

I'm not trying to embarrass you but would you mind explaining about the poor connection? I think you mentioned that you changed the switch, so was the problem a loose screw on the switch, a bad crimp on the ring tongue connector, something else? We're just trying to learn something...

It looks like Joe got it right in post #4, a bad connection.

A bad connection has resistance. When current flows through that resistance, heat is generated. That heat can damage whatever the terminal is connected to, like switches, circuit breakers or fuses.

#4 Had It Right

The crimp on the connector on the wire that connected to the terminal on the switch was poor, creating resistance and heat. The heat was sufficient to damage the switch. Putting a new connector on the wore solved the resistance/heat issue.

Curt

There is a historical discussion on VAF on this topic, however, the photos have been disappeared. I have the photos from my failed strobe switch.

Here's what happens: Switching power supplies, such as the strobe supply, exhibit a 'negative resistance', which means that if the input voltage drops, the load current increases in order to maintain the output (strobe) power.

This means that if you have resistance in the power feed due to a bad switch, failing crimps or a bad circuit breaker, the current will increase to compensate, resulting in thermal runaway, burnt terminals and fried switches.

A rule of thumb is to use a heavier gauge wire than nominal for the strobe supply.

I'd recommend replacing all of the crimp terminals, the switch and the fuse/breaker. Check the fuse socket as well.

I Think Your Assessment Is Exactly What Happened

Vern:

I think your explanation is dead on. The connection was poor on the terminal that attached to the switch on the power lead. I have repaired this lead, replaced the switch, checked the other lead connections, inspected the breaker, and tested the unit operating for an extended period of time with no observed heat build-up.

Thanks,

Curt