[PerfTech]

...We had as it turned out, a small problem while returning from a $100 hamburger trip today. I decided to post it here to see if I were the only one or if others have seen this. It was very hot here in southern California today and upon returning to my plane the inside temperature of the cockpit was upwards of 140 degrees. We lifted off for the return trip home and immediately detected a new, unfamiliar smell resembling that of ethylene glycol that proceeded to get worse rapidly. My friend Bill noticed the voltage meter was falling and at that point we equated the smell with an electrical short and begun to fear fire and shut down all electrical via the master. The smell quickly dissipated. After landing I started searching for the problem and isolated it to the volt meter itself. When you show it 12 volts, it reads only ten and after 20 seconds it falls off to read zero. At that point it becomes so hot on the back of the gauge that you can't touch it and it begins to smoke and stink. I am relatively sure, if left with power applied it would soon burst into flames, and most certainly ruin my day. This is one of the $36 Vans 2 1/4" steam gauges and the cost isn't a problem but the potential for disaster is. This didn't pop a breaker or set off a warning of any type, and is most likely an isolated incident. At least I hope this is the case! If others have seen this please let me know. Thanks, Allan...

 

[Vlad]

I had similar experience with Lucas voltmeter during Phase One. The same symptoms but without melting the gage. After dissassembling I found a burnt part then ordered new gage. Still working.

 

[az_gila]

...We had as it turned out, a small problem while returning from a $100 hamburger trip today. I decided to post it here to see if I were the only one or if others have seen this. It was very hot here in southern California today and upon returning to my plane the inside temperature of the cockpit was upwards of 140 degrees. We lifted off for the return trip home and immediately detected a new, unfamiliar smell resembling that of ethylene glycol that proceeded to get worse rapidly. My friend Bill noticed the voltage meter was falling and at that point we equated the smell with an electrical short and begun to fear fire and shut down all electrical via the master. The smell quickly dissipated. After landing I started searching for the problem and isolated it to the volt meter itself. When you show it 12 volts, it reads only ten and after 20 seconds it falls off to read zero. At that point it becomes so hot on the back of the gauge that you can't touch it and it begins to smoke and stink. I am relatively sure, if left with power applied it would soon burst into flames, and most certainly ruin my day. This is one of the $36 Vans 2 1/4" steam gauges and the cost isn't a problem but the potential for disaster is. This didn't pop a breaker or set off a warning of any type, and is most likely an isolated incident. At least I hope this is the case! If others have seen this please let me know. Thanks, Allan...

What size fuse/breaker did you have installed in the instrument supply line?

This should have blown if the current drawn was large enough to generate that much heat.

Van recommends a fuse/breaker in the supply, but I'm not sure if he gives a value...

http://www.vansaircraft.com/pdf/Gauge_Install.pdf

 

[Captain Avgas]

My friend Bill noticed the voltage meter was falling and at that point we equated the smell with an electrical short and begun to fear fire and shut down all electrical via the master.

Allan, Vans cheap chinese steam gauges are notoriously shonky. You might have been a bit lucky that things did not get worse.

If you haven't got one, I highly recommend a small Halon fire extinguisher for the cockpit. A quick squirt up behind the panel in flight if required could stop a very small electrical fire from rapidly growing into a catastrophe. Once a flame has developed, cutting power will invariably not stop it spreading.

 

[PerfTech]

What size fuse/breaker did you have installed in the instrument supply line?

This should have blown if the current drawn was large enough to generate that much heat.

Van recommends a fuse/breaker in the supply, but I'm not sure if he gives a value...

http://www.vansaircraft.com/pdf/Gauge_Install.pdf

...I have one of the ceramic so called smart power panels that should have shut down this circuit at 3.5 amps. I wish it had individual breakers and old school switches instead. Allan...

 

[PerfTech]

Allan, Vans cheap chinese steam guages are notoriously shonky. You might have been a bit lucky that things did not get worse.

If you haven't got one, I highly recommend a small Halon fire extinguisher for the cockpit. A quick squirt up behind the panel in flight if required could stop a very small electrical fire from rapidly growing into a catastrophe. Once a flame has developed, cutting power will invariably not stop it spreading.

...I will get one this week. Thanks, Allan...

 

[L.Adamson]

If you haven't got one, I highly recommend a small Halon fire extinguisher for the cockpit. A quick squirt up behind the panel in flight if required could stop a very small electrical fire from rapidly growing into a catastrophe. Once a flame has developed, cutting power will invariably not stop it spreading.

Happily, the aircraft wire that most of us use, has insulation, that will just melt off a red hot wire. And if other components of the panel aren't too prone, to easily igniting, you'll have a good chance of no farther damage.

I actually tested this out (not by choice)............before the plane ever flew. I had installed a heavy duty relay, intended to cut power from the alternator B-lead, in cause of a runaway alternator. This particular circuit, was later scrapped by the designer. What I didn't know, is that the relay contained several diodes, that were supposed to be removed for this application. As I sat in the cockpit, and turned on the power.........there was a big puff of smoke, followed by hot melting insulation falling on my trousers, just above the knees. I actually had a direct short, to the main ground wire, which is a #4, as I remember. It was bundled with many others, but the others were not effected. This is aircraft wire, with the white insulation. I no longer know the particulars, & name of insulation. The wire itself, was nearly melted through.

Note: I suppose we could conduct a flame test on Van's instruments, to see how well the support combustion, or not.

L.Adamson

 

[gasman]

Allan, Vans cheap chinese steam guages are notoriously shonky. You might have been a bit lucky that things did not get worse.

If you haven't got one, I highly recommend a small Halon fire extinguisher for the cockpit. A quick squirt up behind the panel in flight if required could stop a very small electrical fire from rapidly growing into a catastrophe. Once a flame has developed, cutting power will invariably not stop it spreading.

There you go Allen...... we need a source for an honest priced small (one hand) Halon extinguisher.

You can do this........................

 

[rockwoodrv9]

Allen, you have to do a cool video showing how to use it - then I will buy!

 

[Flying Scotsman]

Like this?

 

[Brantel]

...I have one of the ceramic so called smart power panels that should have shut down this circuit at 3.5 amps. I wish it had individual breakers and old school switches instead. Allan...

Allan,

Tons of electronic devices can smoke with way less current than 3.5 amps. Depending on how the device failed, it is very much possible that you got smoke out of it without ever reaching 3.5 amps.

Fuses and breakers are intended to protect the wire not the device.

 

[John R. Graham]

An analog volt meter itself shouldn't draw more than a few hundred microamps. A 3.5a circuit will carry probably in excess of a thousand times more current than the gauge needs. This thread has me thinking about my (admittedly still far off) panel design in a slightly new way.

- John

 

[PerfTech]

Allan,

Tons of electronic devices can smoke with way less current than 3.5 amps. Depending on how the device failed, it is very much possible that you got smoke out of it without ever reaching 3.5 amps.

Fuses and breakers are intended to protect the wire not the device.

...The instruments are all wired from one lead like specified by Vans and apparently the 3.5 amp load in what they figure is needed collectively. No wires were compromised just the gauge internals. It just makes you a little nervous when you let the smoke out. Thanks all, Allan...

 

[az_gila]

Allan,

Tons of electronic devices can smoke with way less current than 3.5 amps. Depending on how the device failed, it is very much possible that you got smoke out of it without ever reaching 3.5 amps.

Fuses and breakers are intended to protect the wire not the device.

Well, not exactly.

Even if the wiring was 22g, a fuse/breaker of less than 5 amps (the approx. wire rating) would be quite acceptable and could protect a low power device as well as the actual wire.

I think the generic rule to use is never to have a fuse/breaker of a rating higher than the wire rating....

Does Van give a fuse rating (or even a current draw) for a set of his instruments? I couldn't find it on the data sheet.

 

[Brantel]

Well, not exactly.

Even if the wiring was 22g, a fuse/breaker of less than 5 amps (the approx. wire rating) would be quite acceptable and could protect a low power device as well as the actual wire.

I think the generic rule to use is never to have a fuse/breaker of a rating higher than the wire rating....

Does Van give a fuse rating (or even a current draw) for a set of his instruments? I couldn't find it on the data sheet.

Sure you can come up with a fuse that is rated low enough to barely drive the device but in most cases that is not practical.

I stand behind my comment...Fuses and breakers are intended to protect the wire, not the device. That's not to say you can't come up with a combination that achieves both though but it would take very specific knowledge of the internal design of the device and it's failure modes to guarantee you don't let the magic smoke out.

 

[celstar]

I had the same problem

http://www.vansairforce.com/community/showthread.php?t=71594&highlight=melting

 

[n82rb]

a note about halon, be sure to read all you can about halon before putting it in your aircraft. There have been computer operators nearly killed when the auto halon system went off in the computer room. Don't get me wrong, a fire is really bad, and having a defense against it is a very good idea but just make sure you learn all about the extinguishing agent and the proper use before mounting it in the aircraft.

bob burns

 

[az_gila]

Sure you can come up with a fuse that is rated low enough to barely drive the device but in most cases that is not practical.

I stand behind my comment...Fuses and breakers are intended to protect the wire, not the device. That's not to say you can't come up with a combination that achieves both though but it would take very specific knowledge of the internal design of the device and it's failure modes to guarantee you don't let the magic smoke out.

No, just a look at the device specification sheet or the sample wiring diagram for most avionics...

I never used the word "barely".... I stand by my comment too....

Just for an example - 1 amp fuse recommended for 24g (approx 4 amp) wire -

http://www.ps-engineering.com/docs/PM1000II Install Manual.pdf

A good avionics install manual will give a fuse rating, and usually a wire size greater than it's rating.

Protect the device first, and then the wire....

 

[JonJay]

Protect the device first, and then the wire....

That just does not work when you are cascading multiple devices off a single protection.

In the commercial construction world, we have standards like UL that could care less about protecting the device as long as when the device goes "boom", it does not cause a fire. You size the wire to the load and protection in kind. Many devices are hung off of one protection.

Not sure this exists in our experimental, aviation world.
So, if we are going to protect each device, we need an individual fuse or other protection sized for each component and should not cascade any devices off or one fuse or breaker. That means each and every post light, individually fused, as an example. I don't usually see this in aircraft.

Am I understanding this correctly?

 

[Brantel]

No, just a look at the device specification sheet or the sample wiring diagram for most avionics...

I never used the word "barely".... I stand by my comment too....

Just for an example - 1 amp fuse recommended for 24g (approx 4 amp) wire -

http://www.ps-engineering.com/docs/PM1000II Install Manual.pdf

A good avionics install manual will give a fuse rating, and usually a wire size greater than it's rating.

Protect the device first, and then the wire....

There are tons of components in that device that will smoke at less than 1 amp.

Not trying to be argumentative, but everyone from high school electronics to MIT teach that the fuse or breaker is there to protect the wire not the device.

I just don't want to give someone the false impression that they can somehow guarantee that some component in one of their devices cannot smoke because they have the proper fuse and wire feeding power to it. It can and does happen all the time.....

 

[Brantel]

That just does not work when you are cascading multiple devices off a single protection.

In the commercial construction world, we have standards like UL that could care less about protecting the device as long as when the device goes "boom", it does not cause a fire. You size the wire to the load and protection in kind. Many devices are hung off of one protection.

Not sure this exists in our experimental, aviation world.
So, if we are going to protect each device, we need an individual fuse or other protection sized for each component and should not cascade any devices off or one fuse or breaker. That means each and every post light, individually fused, as an example. I don't usually see this in aircraft.

Am I understanding this correctly?

Most electronic devices are just exactly what you speak of only all contained into one box. When the current paths are analyzed, that is all they are, a network of multiple devices cascaded off of one common power source. The NEC requires coordinated overcurrent protection for branch circuits but most modern electronics do not have anything of the sort built into their designs once you are inside the box.

 

[erich weaver]

1 Determine the normal electrical load of the device from the manual or the manufacturer

2 Size the wire based on the normal load

3 Size the fuse based on the wire rating

All critical devices should have their own dedicated power circuit so that the failure of one does not take out others.

erich

 

[az_gila]

1 Determine the normal electrical load of the device from the manual or the manufacturer

2 Size the wire based on the normal load

3 Size the fuse based on the wire rating

All critical devices should have their own dedicated power circuit so that the failure of one does not take out others.

erich

No, because the #2 step wire size may be based on length and voltage drop. If you increase the wire size to reduce the voltage drop down a long wire, you don't increase the size of the fuse/breaker.

I would use -

1 Determine the normal electrical load of the device from the manual or the manufacturer.

2 Size the wire based on the normal load, length and voltage drop required, or oversize it for practical handling. I personally don't like using wire below 20g.

3 Size the fuse based on the value found in step 1
- go to the next higher value, not lower... -- or use the value of fuse/breaker given in the installation manual (best idea).

A possible #0

0. Don't use any devices in your aircraft that do not have specifications giving current draw - such as Vans cheap gauges...

 

[az_gila]

There are tons of components in that device that will smoke at less than 1 amp.

Not trying to be argumentative, but everyone from high school electronics to MIT teach that the fuse or breaker is there to protect the wire not the device.

I just don't want to give someone the false impression that they can somehow guarantee that some component in one of their devices cannot smoke because they have the proper fuse and wire feeding power to it. It can and does happen all the time.....

Yes, but why allow extra current - the wire rating - when you don't need it?

Set the value on the device and make the wire large enough.

3.5 amps will usually make more smoke than 1 amp. It will certainly make more heat....

 

[DanBaier]

...I have one of the ceramic so called smart power panels that should have shut down this circuit at 3.5 amps. I wish it had individual breakers and old school switches instead.

What about making a fuseable link for that circuit as well as any others that might be of concern?

Dan

 

[Captain Avgas]

There have been computer operators nearly killed when the auto halon system went off in the computer room. bob burns

Is that so. Please refer us to any reputable source or report that substantiates such a claim. Otherwise we should all discard it into the Old Wives Tale bin.

Halon has extremely low toxicity and does not function by depleting the oxygen level. In the past it has been used in literally thousands of server rooms without any problems. You might in fact be referring to problems that have arisen by the use of Carbon Dioxide extinguishers in server rooms. Computer geeks know a lot about computers but often nothing about fire suppression agents... and that can lead to all sorts of misinformation. But let's not let that misinformation spread to this forum.

Halon is still the only agent that the military will use in confined spaces occupied by personnel (eg. aircraft, tanks, submarines) where highly effective fire suppression is required over a wide range of fire types .

Those who want further data can read this information from H3R:

http://www.h3raviation.com/support_faq.htm

 

[Brantel]

Yes, but why allow extra current - the wire rating - when you don't need it?

Set the value on the device and make the wire large enough.

3.5 amps will usually make more smoke than 1 amp. It will certainly make more heat....

On this we agree, I am not saying that just because a wire is rated for 10 amps that you should use a 10 amp fuse by default. I am sorry if I did not make this clear.

Any fuse up to the max current capability of the wire is fine but like you say there is no reason to do that when you have a device that uses much less.

In the case of the OP, I suspect 3.5 amp was the smallest he had available in that load center.

The only point I am trying to make is that fuses and breakers are there to protect the wire not the device and that just because there is a properly sized fuse and wire feeding a device (even a minimal 1 amp one), it does not guarantee that there can never be any magic smoke released....

 

[roee]

[snip]If you increase the wire size to reduce the voltage drop down a long wire, you don't increase the size of the fuse/breaker.[snip]

You wouldn't necessarily, but you could, and there wouldn't really be anything wrong with doing that. There are secondary considerations and trade-offs either way... but, either way the required relationship is preserved:

(max normal load current) < (circuit breaker current rating) < (wire current carrying capacity)
​

And just adding one more voice to what's already been said, but yes, the circuit breaker is there to protect the wire, not the load device.

Now, I'm not really an electrical engineer, but I did stay at the Holiday Inn last night. Oh, wait, I am really an electrical engineer

 

[az_gila]

You wouldn't necessarily, but you could, and there wouldn't really be anything wrong with doing that. There are secondary considerations and trade-offs either way... but, either way the required relationship is preserved:

(max normal load current) < (circuit breaker current rating) < (wire current carrying capacity)
​

.....

Give one good reason to do that, other than rounding up to the next higher fuse/breaker size...

I actually was in a Motel 6 the other night, does that count....

 

[roee]

Other forms of circuit protection

Now let's have some good clean educational fun! Since the great circuit breaker debate is cooling off, and everybody already knows all about fuses, I'll throw another alternative into the mix. For some very small loads, you can use just a simple resistor for circuit protection. Doesn't get any more cheap and simple than that. But you'd have to understand the basic math and physics involved to get it right (mainly just Ohm's Law), and understand that a resistor only acts as a current limiter and does not actually open the circuit, and what that means.

An example:

Note: This is just a general hypothetical example for educational purposes. Not a design recommendation for this voltmeter, which I haven't ever looked at!

Let's say we have a load device that draws only 100 uA (microamps). Note: I have no idea what Van's crappy voltmeter actually draws, and I wouldn't just assume that it's that little!

We could use a very small wire, let's say 22 AWG, which still has a relatively hefty current carrying capacity of 3 A. Obviously way more than enough for this tiny load.

Now, rather than using a circuit breaker, we could protect that wire with a 1 K ohm 1/4 W resistor. Huh? Sure! With a 1 K ohm resistor, a hard short downstream of it will be current limited to 14 V / 1 K ohm = 14 mA. That's less than the wire's 3 A carrying capacity, so the wire is well protected.

Now, we must ensure that the resistor itself can take it too. So, with a hard short we have 14 V x 14 mA = 196 mW being dissipated in the resistor. So with a 1/4 W resistor, we're A-OK.

And what about the extra resistance causing a voltage drop during normal operation? Well, that's why this solution only works for very small loads. In our example, the normal load current of 100 uA passing through the 1 K ohm resistor makes us incur a voltage drop of 100 uA x 1 K ohm = 100 mV. We can accept that.

Note that there is a minor shortcoming to this approach that must be understood. That if you do have a short or some other fault, then you don't get as obvious an indication of it after the fact like you do with a popped breaker or a blown fuse. So if your load stops working, you do have to be a little more knowledgeable to troubleshoot the fault (later on the ground, not in the air!). So that's a shortcoming. But in many cases it's a fair trade-off.

Enjoy!

 

[roee]

Give one good reason to do that, other than rounding up to the next higher fuse/breaker size...

One reason could be to maximize tolerances. For example, if the rating of the smaller breaker is pretty close to the max normal load current, then going to the bigger breaker will give more headroom and reduce the probability of nuisance tripping.

The tolerances on all these numbers tend to be pretty sloppy. Depending on what the load device is, it may have short transient currents that far exceed its normal steady state current (inrush currents are common for incandescent bulbs, motors, electronics with large capacitance in the power supplies...). And sometimes the manufacturers' published specs just aren't that accurate to begin with. And as for sloppy tolerances, same goes for the tripping currents of the circuit breakers themselves. So, with sloppy numbers abound, it's nice to be able to take the total tolerance window that you have available and spread it around as evenly as possible.

That's one good reason in some cases. And there are surely other reasons that deserve consideration on a case-by-case basis.

I actually was in a Motel 6 the other night, does that count....