Rotating beacon fuse...

SPAJC

SPAJC

Pre-takeoff checklist
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Spartanburg, South Carolina
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Jeff
Ok so, next problem...I noticed a while back that my rotating beacon, which is actually a strobe now, wasn't working. Checked the fuse and it was blown. I replaced it and it worked fine. Checked it after flying and it was blown again. I've tried treating it like you would the avionics, off until after start and off before shutdown...thought that was working, but it's not. I believe the plane was originally equipped with a generator but it now has an alternator. The strobe is on a 10A fuse. Any thoughts as to what would cause this other than a short? Is it possible that the 10A fuse is not sufficient and if so, would it cause further damage to try a 15A?

The plane is a 1967 Cherokee 140. Its an older Whelen strobe but I can't read the model number on it.

Any thoughts appreciated as always!


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Changing the fuse without knowing the cause of the over-current is ill-advised. You don't need a short to have a faulty unit drawing too much current. Busted wiring, bad connections, etc.
 
denverpilot said:
Changing the fuse without knowing the cause of the over-current is ill-advised. You don't need a short to have a faulty unit drawing too much current. Busted wiring, bad connections, etc.
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A bad ground will cause all kinds of strange things including high current draw.

As denverpilot says, broken wires ( only one or two strands actually allowing current to flow), and corroded or bad connections will increase the draw also.
 
AKBill said:
A bad ground will cause all kinds of strange things including high current draw.

As denverpilot says, broken wires ( only one or two strands actually allowing current to flow), and corroded or bad connections will increase the draw also.
Click to expand...

Another way to say things is if a fuse burns or breaker trips, maybe try replacing the fuse or resetting the breaker after inspecting the circuit. If the fuse burns again don't put a new fuse in until repairs are made.
 
AKBill said:
A bad ground will cause all kinds of strange things including high current draw.

As denverpilot says, broken wires ( only one or two strands actually allowing current to flow), and corroded or bad connections will increase the draw also.
Click to expand...
How would increasing the resistance of a circuit increase the current flow if the voltage supplied doesn't change?

Recall: I = E/R
 
Capt. Geoffrey Thorpe said:
How would increasing the resistance of a circuit increase the current flow if the voltage supplied doesn't change?

Recall: I = E/R
Click to expand...

I was thinking the same thing. To increase current there have to be more electrons (or holes, take your pick) flowing.

I'm speculating here, but if the strobe is mechanical (i.e. a motor rotates the light) increasing drag could cause an overload. DC motors draw more and more current up to lock rotor amps. (So do AC motors but it's a little more complicated.)

I'd expect bad connections to maybe cause heat. Frayed wires (inside the insulation) would probably have little effect on current. If the insulation is frayed then you could have an intermittent short.

I'm not an aircraft mechanic. I have done a significant amount of wiring in various types of transportation, however...

John
 
jsstevens said:
I was thinking the same thing. To increase current there have to be more electrons (or holes, take your pick) flowing.

I'm speculating here, but if the strobe is mechanical (i.e. a motor rotates the light) increasing drag could cause an overload. DC motors draw more and more current up to lock rotor amps. (So do AC motors but it's a little more complicated.)
Click to expand...

You missed the part where he said the beacon is a strobe...
 
Clark1961 said:
You missed the part where he said the beacon is a strobe...
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I read it, but I wasn't sure exactly what he meant. If it just flashes, no motor of course.

John
 
I would do two things.

1. Give the wiring a thorough checkout to find any problems. This means both visually and with a meter.

2. Find out the part number of the strobe. If someone installed it to replace the beacon, there is a logbook entry with the part number. Well, there should be. Then you can determine the size of fuse it should have.

My thought is that the blowing of fuses is probably a recent thing so a problem has been introduced into the system and needs to be fixed. It could be wiring or even the strobe power supply.

What I would NOT do is to replace the fuse again and fly it without being certain the problem is fixed.
 
AKBill said:
A bad ground will cause all kinds of strange things including high current draw.

As denverpilot says, broken wires ( only one or two strands actually allowing current to flow), and corroded or bad connections will increase the draw also.
Click to expand...

You need to take my circuits class.

Bad.


Jim


.
 
I don't have experience with the workings of strobes. So, the thought hit me that maybe since it isn't the original equipment, then the original type fuse just might not be sufficient. The strobe isn't all that bright and I was also thinking, again, as a strobe light in-experienced person, that that would either mean that the bulb itself was going bad or the power supply was going bad and causing a problem in the current flow.

I appreciate the input and will investigate further before doing anything else or replacing.


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Just a thought... May be overly obvious, but, if you can get (or know) the model/part number, or if there is a label on the unit, you may be able to find what amps are spec'd for the unit. Then you can safely judge if a more tolerant fuse is needed...
 
The old style rotating beacons with incandescent lamps sucked power.

I would be very surprised if a strobe needed more than 10 amps.

My money is on a harness that has chafed through.

But I ain't no A&P so of course I know nothing.
 
I found in the logbook where the strobe was installed in 1999 as part of a complete restoration. It gives no further details about the strobe.

I have looked on the strobe housing and can't read any of what is on it other than it is a Whelen strobe. I haven't actually pulled the strobe assembly from the tail to see if there is a sticker or otherwise on the part of the housing that is not visible as installed. Planning to do that today if I can get down there.

Incandescents generally suck power as noted by Mr. Thorpe...but, given the high voltage nature of a strobe, I had the thought that they might suck more...but thats talking voltage vs. Ampres in which case the voltage is really of no consequence here, I think...which means that I agree with Mr. Thorpe....

I'll post the model numbers and such when I figure it out...hopefully later today.

Thanks all!


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Last edited:
So as a side question, I've always noticed that it wasn't very bright. I've already replaced the lens as the original one that was all hazed up was relieved from me during a flight. Its still not very bright. So the question is: could this be symptomatic of the power supply failing, or the bulb failing? Or is it one of those if it goes bad, its bad and doesnt work at all kinda deals?
 
SPAJC said:
So as a side question, I've always noticed that it wasn't very bright. I've already replaced the lens as the original one that was all hazed up was relieved from me during a flight. Its still not very bright. So the question is: could this be symptomatic of the power supply failing, or the bulb failing? Or is it one of those if it goes bad, its bad and doesnt work at all kinda deals?
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iss

The more info you give the more I think this is a power supply issue. your issue is very symptomatic of a shorted transformer or capacitor.
 
Yep. I've been suspecting the power supply was going bad for a while, but, I'm no expert here so thought i'd ask around. Thanks for the input. More troubleshooting to be done....


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weirdjim said:
You need to take my circuits class.

Bad.


Jim


.
Click to expand...


Heh. I'd like it noted for the record that my two sentences were separate. Other folks put them together.

That he *had* high current flow to blow the fuse, and that there may be busted wires, bad connections, etc.

They weren't meant to be related statements. :)

Typed poorly at what was it, 3AM or something?

(Usually high current flow busts the wires for you if Mr. Fuse doesn't blow first. Grin... Since all Mr. Fuse is, is an barely rated wire for said current...)

The main point was NOT to up the size of the fuse. Find the problem.

Around my shack I'm usually blowing things up with arcing, so Mr Ohm and his Law is having a field day with all that popping and cracking and light show going on. Haha. (Not really. I haven't blown anything up since about four years ago. Trying to remember what it was. Wasn't too expensive. :)

Side note: If you want to watch someone be stupid with electricity, look up "Electroboom" on YouTube. Funny stuff.
 
denverpilot said:
Around my shack I'm usually blowing things up with arcing, so Mr Ohm and his Law is having a field day with all that popping and cracking and light show going on. Haha. (Not really. I haven't blown anything up since about four years ago. Trying to remember what it was. Wasn't too expensive. :)
Click to expand...

I get that pleasure every semester with one student or another forgetting that we number things FROM left TO right when facing the component. And that the little black minus sign in the envelope (-) really means to connect that lead to the most negative point in the circuit. And that the black stripe is the CATHODE stripe, not the anode stripe. And that it's really counterproductive to connect both transformer leads to the same point. ... ... ...
 
A Whelen single strobe will draw about two amps. "Strobe" meaning the xenon flash tube. Very bright.

The Aeroflash flashing beacon that replaced a lot of rotating beacons has an incandescent bulb that isn't so bright and draws about ten amps.

Upping the fuse size without making sure the existing wiring can carry the current is a crazy thing to do. The fuse is there to protect the wire, not the component, since too much current heats the wire and tends to cause fires. AC43.13-1B gives wire sizes necessary for defined current flows, wire lengths, whether in free air or bundles, and whether continuous or intermittent.

Does the OP actually have a strobe as opposed to a flashing beacon?
 
Yes it is a strobe. And I appreciate the info there. I guess I was always under the impression that it was more to protect the component. I have no intention of upping the fuse. Was just wondering if that would be something worth trying and after reading responses here decided quickly that it wasn't a good idea. This is why I ask the question first. Much more knowledge from you all on here on such things than what I possess. Thanks again.


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https://vimeo.com/137031647

Here it is after another fuse change. The video makes it look brighter than it actually is. It seems to work fine other than its not very bright and keeps blowing the fuse. This one would certainly blow during a flight. Just to illustrate. I'll post pics when I can get back out to take the lens off and such. This was best I could do while at work. Thanks all!!!


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SPAJC said:
https://vimeo.com/137031647

Here it is after another fuse change. The video makes it look brighter than it actually is. It seems to work fine other than its not very bright and keeps blowing the fuse. This one would certainly blow during a flight.
Click to expand...

Whether a fuse or breaker, old stuff tends to become oxidized and resistance builds. Contacts in breakers oxidize and the resulting resistance generates heat, fooling the breaker into thinking that too much current is flowing. Oxidized terminals in fuseholder will generate heat that can melt the fusible strip in the fuse. Besides all that, the resistance causes a voltage drop at the component, though with a strobe I'd expect slower or intermittent flashing rather than a dim flash.

Might be a good idea to look at the strobe power supply and see what it's supposed to draw, then measure it. The other obvious thing to look for is a short somewhere along the wire from the breaker to the switch and from there to the power supply. Might be chafing on something, worn through the insulation, and shorting when vibrating.
 
Dan Thomas said:
Whether a fuse or breaker, old stuff tends to become oxidized and resistance builds. Contacts in breakers oxidize and the resulting resistance generates heat, fooling the breaker into thinking that too much current is flowing. Oxidized terminals in fuseholder will generate heat that can melt the fusible strip in the fuse. Besides all that, the resistance causes a voltage drop at the component, though with a strobe I'd expect slower or intermittent flashing rather than a dim flash.

Might be a good idea to look at the strobe power supply and see what it's supposed to draw, then measure it. The other obvious thing to look for is a short somewhere along the wire from the breaker to the switch and from there to the power supply. Might be chafing on something, worn through the insulation, and shorting when vibrating.
Click to expand...


Will do. Thanks!


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Is it my imagination or is your strobe flashing at erratic intervals? If it is, this usually means a bad power supply or low line voltage.
 
SkyDog58 said:
Is it my imagination or is your strobe flashing at erratic intervals? If it is, this usually means a bad power supply or low line voltage.
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"Shutter" effects can cause a camera to miss some flashes.

If it runs for a long time with not problems while sitting on the ground but blows quickly while in the air, you most likely have a harness problem.

Unplug the power at the strobe and taxi around for a while. If the fuse blows, then the problem isn't the strobe.
 
Capt. Geoffrey Thorpe said:
"Shutter" effects can cause a camera to miss some flashes.

If it runs for a long time with not problems while sitting on the ground but blows quickly while in the air, you most likely have a harness problem.

Unplug the power at the strobe and taxi around for a while. If the fuse blows, then the problem isn't the strobe.
Click to expand...


Great idea! I'll do that. Thanks!


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