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Melted 60 Amp Shunt on RV 4

riobison

Well Known Member
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Would anyone have any idea on what would cause a 60 amp shunt to fail? Melted or fractured and then melted.

8 years ago I replaced the Amp meter for a Volt meter due to preference and in 1000 hours on my RV 4 and never had an electrical issue.

Run up was good 14.3 volts and everything worked. 10 mins into the flight and total electrical failure.

Back on the ground this is all I could find. Battery still has 12.9 volts and no other signs of arcing.

Trying to insert the foto, so here goes...............

:confused:

Thanks

Tim
 
About 80-90 amps will do it. Now you gotta figure out what caused THAT.
 
A loose connection on a high current path might do it. It does look like there is a little discoloration on the lower part of the right hand screw terminal. Hard to tell if that is partially a shadow. Or it might have had a crack in the shunt resistor. There was some uneven current flow based on only part of the element remaining.
 
Shunt short

If the shunt is mounted on the firewall and exposed, I would look for indication on the firewall of a particle that could have caused a short to ground. There should be a burn mark on the firewall (or wherever the short was) if 90A went thru it.

Also check to make sure the shunt sense wires to the instrument have fuses in line. I used a fusible link.

lastly, if these things do crack, then resistance will build up and then cause a failure. If you were seeing higher and higher current readings, that could be an indication of a pending shunt failure due to cracking.

I plane to make a simple fiberglass cover for my firewall shunt.
 
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Alternator side

Alternator side. I can turn the master on and activate the solenoid with 12.9 volts still there. So power from the battery to the one side of the shunt is ok.

All of the cables are tight and no signs of any arcing that I can see.

There is or was nothing floating around behind the panel that could have touched it. Its been 9 months and 40 hours since I've even been in behind the panel.

Never noticed any change on the voltage readings.

Is there a chance that the voltage regulator failed and sent a big spike to cause the failure of the shunt?

Thanks
Tim
 
Lowmresistance

Shunts are very low resistance, so unlikely enough current can pass to cause damage. I suspect a cracked shunt that finally broke, or a short, but the shunt should take more current then the wire since it is low resistance by design. So it could be a crack propagation without any real resistance change until the very end. Is the whole break burnt and melted, or just the last little bit?
Sure looks like a short to the mounting screw.
 
Question for my benefit

Does the shape of the "fracture" surface mean anything to those experienced in this art? I have no experience with such. The large amp fuses I've seen blow tended to melt/vaporize the conductor fairly uniformly but these were much higher/medium voltage devices. Would the non-uniform shape of the formerly single conductor make anyone think FOD was involved?
 
Only two possibilities, too many amps or material fault.

Given you find nothing to suggest a battery short to ground, I'll speculate the second, based on the picture. Note how the blocks have rotated slightly in the holder, and that the lower edges of the bridge are not aligned. The components rotated when the nuts were removed from the cable ends. It suggests they could have also rotated the other way when someone tightened those nuts without a holding wrench on the blocks, cracking the bridge.
 

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Only two possibilities, too many amps or material fault.

Given you find nothing to suggest a battery short to ground, I'll speculate the second, based on the picture. Note how the blocks have rotated slightly in the holder, and that the lower edges of the bridge are not aligned. The components rotated when the nuts were removed from the cable ends. It suggests they could have also rotated the other way when someone tightened those nuts without a holding wrench on the blocks, cracking the bridge.

This would be my guess as well. Nut tightening or loosening put stress on the copper bar and over the years of vibration, a crack developed from the bottom up. Once the crack was large enough, there was not enough surface area to pass the current and the remaining material melted, just like a fuse.

Larry
 
Shunt failure

To me it looks like an RC Allen shunt made by Kelly.
If so it should have part nr: 12-902-3 if it's a 60A shunt.
The bridging element usually has a U-shaped cut out that provides for
a 50 mV drop at 60A.
No other part of the shunt looks over heated or burnt.
If there is nothing that is wrong in the electric system I would suspect that
it was a crack that eventually broke.
When replacing it, I would sugest a rubber gasket under it.
If the surface isn't flat this might create a stress to the bridge on the shunt.

Good Luck
 
Only two possibilities, too many amps or material fault.

Given you find nothing to suggest a battery short to ground, I'll speculate the second, based on the picture. Note how the blocks have rotated slightly in the holder, and that the lower edges of the bridge are not aligned. The components rotated when the nuts were removed from the cable ends. It suggests they could have also rotated the other way when someone tightened those nuts without a holding wrench on the blocks, cracking the bridge.

I wouldn't have thought of that but certainly will back up the blocks when tightening in the cables.

From what I'm seeing when doing my searches, this not a normal failure?

Thanks
Tim
 
0 to 300 ohms

I’ve checked continuity thinking if there was a short between the wire and it was grounding on the plane I would find it. With an open circuit there was no buzz on any of the wires so that made me feel better.

I did check for resistance on the wires and a couple of the wires were zero. But a couple of the wires that I believe go back to the alternator had readings that floated from 0 to 300 ohm.

Now I’m confused.:confused:
 
Dan has a good point. If you look at the lower edge of the sense element the two sides are not aligned. I'm not sure how accurately the terminal blocks would be aligned in the mfg process, but the element would certainly be aligned.

Its also a good comment that these terminal blocks need to be supported with a wrench when installing those cable lugs. I'm not sure that would necessarily be obvious to the installer.

I wonder if you recently had an annual or if you could have touched these lugs recently. Otherwise I guess it could be stress over time that finally broke under the aircraft vibration.
 
Back up block

No, 9 months ago and 40 hours. I do all of the work and have never come close to touching it or even leaving anything under the panel.

I agree when doing the install that a guy might be tempted to not back up the block and could potentially initiate a hair line crack.

I'll be backing it up.

Those shunts are over $150.00 cdn for probably a $10 item and nothing in Canada available at the moment that I can find.

So special order out of the US will probably be north of $225 with shipping by the time it gets here.

Any suggestions on my testing the wires or am I over analyzing this worrying about the alternator or regulator?

Thanks

Tim
 
Tim,

Just curious. Did you back it up when you did the install then?

This got me thinking because I'm not sure I would have done that before reading this thread. I do always use a torque wrench so that might lessen the chance of causing a potential future failure, but then again maybe not.
 
Mooney

I didn't build the plane so I don't know. It was by a respectable builder but again it would be an easy mistake for anyone to make.

Until I have actually held a new one in my hand it might it might be obvious that its a delicate piece. Then again maybe not.

This type of failure doesn't appear common. I think I found a Mooney that had a similar failure 2016 but the thread died off and I don't know what they found as a cause or if they did.
 
I would suggest you get the 100amp shunt to replace it, a 60 seems marginal anyway and the 100 is more robust.
I have one available if you want to stop by and pick it up :eek:
 
Fuse of circuit breaker

Tim

A quick question is there a fuse or circuit breaker on the alternator lead?

Regards

Peter
 
Im just heading out to the hanger again. I didn't see one between the alt and the shunt. Its time to start cutting tie wraps and seeing what I'm missing.

Thanks
Tim
 
Tim

Convention is to use a circuit breaker or ANL fuse on the alternator output lead. It’s a heavy wire that needs protection in the event of a short circuit.
On my aircraft I’ve used ANL fuses as I don’t plan resetting high amp circuits if there’s a problem when I’m airborne.

Regards

Peter
 
could a mounting screw fastener come in contact with the shunt? the lower hole looks rough.
 
Shunt

Tim,

If it helps why couldn’t one of us purchase the shunt you need here in the States and send it to you in Canada? Would that save you any money? I’d be happy to help.
 
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An ammeter is not a necessity. My plane does not have one. Jumper the shunt until it can be economically replaced. A voltmeter is all you need to verify charging system health.
 
I suspect some more experienced Sparky's to chime in. Here is my rudimentary understanding. I'm ME not EE.

A volt meter tells you bus voltage; no more, no less. It's an indirect measurement but decent indication of the Alternator and related VR health.

An amp meter can be a pretty good, indirect indication of battery health. A good way to spread out the costs of a new battery and a new alt and/or VR if you have a bad cell and related constant high amp draw.

Stating an amp meter isn't an necessity when the pilot mission and related fuel, ignition, and electrical architectures aren't known seems a bit cavalier to me.
 
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I suspect some more experienced Sparky's to chime in. Here is my rudimentary understanding. I'm ME not EE.

A volt meter tells you bus voltage; no more, no less. It's an indirect measurement but decent indication of the Alternator and related VR health.

An amp meter can be a pretty good, indirect indication of battery health. A good way to spread out the costs of a new battery and a new alt and/or VR if you have a bad cell and related constant high amp draw.

Stating an amp meter isn't an necessity when the pilot mission and related fuel, ignition, and electrical architectures aren't known seems a bit cavalier to me.

This suggests that we cannot safely fly without an ammeter. I disagree. I point out that all cars had ammeters at one time - but for the sole reason that they were cheap to make compared to reliable voltmeters of the day. I’d guess this carried over to the GA aircraft - and still lingers in the “always had this” category.

Personally I did not install an ammeter on any of my projects as voltage tells me what I need to know. If I ever decide to add one however, I will use a pick up coil, not the clunky shunt on the firewall.

For those wanting to know what their power consumption is in various configurations, I suggest a one time data run in the hangar using a regulated power supply with both a output voltage and amp readings. While there is value in the data (such as determining electrical power reserve), it is not something I need to watch when flying. The EMS will tell me if the alternator goes south, and if the backup alternator has picked up the load when it does. Additionally, buss voltages before engine start tells me the health of each battery.

Note - I’d temper this for anyone using an EarthX type battery as having the EMS trigger an alarm on abnormal high current flow is desirable as an early warning for it going south.

But - build what you want. Just know why you want it.

Carl
 
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I would say an ammeter isn't required, but I would say it is needed. Many folks I hear on this site have said an ammeter isn't needed and that a voltmeter is sufficient. I wouldn't agree, but everyone is welcome to their opinion. A voltmeter cannot tell you of pending problems while an ammeter can. Yes a voltmeter can tell you if your alternator has stopped outputting since the voltage will be lower. However an ammeter can tell you what your actual current draw is. If for example you have figured out ahead of time how long you can live on your battery with a specific current draw which is a good thing to do BTW then having the actual current draw from the ammeter could help you make a quick prediction of how long you have before the lights go out. You can shed loads until you get to the current you have previously decided is your target low power current. On the other hand having a specific voltage won't be able to tell you that. You can only see the voltage going down as the battery looses its charge. I don't think anyone can tell how long a battery will last by looking at the voltage.

Also per Steve's comment. It looks like the lower mounting screw has some residue in the area of the screw head. I'll assume that lower hole was also the lower hole when mounted. That residue seems to be molten metal of some sort. I'm not sure how that would have gotten under the head of the screw if it were completely tightened down. The upper hole area looks completely clean in comparison. It is difficult to tell specifics from the pic though.
 
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Uh oh

Uh oh. I'm disagreeing with Carl Froehlich on an electrical issue. This can only go bad for me.

I mentioned, the pilot's mission and other system architecture isn't known.

Most people aren't Carl Froehlich. They haven't conceptualized electron flow and the devices that control/condition them. They aren't intuitive when electrical things become off nominal. They need to trust the condition their related gages are telling them is true to stay safe.

In the simplest aircraft, a prolonged high amp flow indication can help prevent flying/landing a blacked-out aircraft . On an electrically dependent aircraft, this condition is worse or better depending on the system architecture and the pilot's understanding of those systems (e.g. turning on a cross feed could make things worse, not better). The shunt is a pseudo "last chance" safety device which conveniently can indicate amp draw due to it's known resistance. Flying without it's primary functionality (via whatever means) or unsystematically jumpering the terminals is dangerous IMO. The current measurement functionality is there via the aforementioned. Understand it's meaning and use it, IMO. For the record, I'm not saying there's a single way or mine is the more correct way for monitoring electrical system health.

@Carl. If I haven't p!&^%d you off, I'm still wondering about in-rush current capabilities for the power supply you recommended.
 
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No, 9 months ago and 40 hours. I do all of the work and have never come close to touching it or even leaving anything under the panel.

I agree when doing the install that a guy might be tempted to not back up the block and could potentially initiate a hair line crack.

I'll be backing it up.

Those shunts are over $150.00 cdn for probably a $10 item and nothing in Canada available at the moment that I can find.

So special order out of the US will probably be north of $225 with shipping by the time it gets here.

Any suggestions on my testing the wires or am I over analyzing this worrying about the alternator or regulator?

Thanks

Tim

Hey Tim ,

Check Stein Air.....a 100 amp shunt is 41.00 and a 60 amp is 20.00 maybe it will work you.
Shipping is insane to Canada...I feel your pain every time I hit confirm you order.
Keith
 
Uh oh. I'm disagreeing with Carl Froehlich on an electrical issue. This can only go bad for me.

I think I'm going to join you about disagreeing with Carl, mostly. An ammeter may not be required, but it certainly is good to have.

Let me tell you of an incident where the ammeter was indispensable in isolating a problem. I have no engine-driven fuel pump, but rather dual electric pumps. Those dual electric pumps nominally draw about 5-5.5 amps of power each during normal use. I have them individually breakered at 10 amps each.

One day I was cranking up to go play in the wild blue yonder, and before I started to taxi my engine died - just up and quit, cold - and in my headset the Dynon Skyview is warning me of low fuel pressure as the prop spins down. I had one of the two pumps turned on at the time, the switch was still on, the fuel pressure was zero - then I saw the breaker had tripped. Hmmm, ok, that's odd. Reset the breaker, try the same pump again, fuel pressure comes up, restart the engine, watch it for a bit - BAM the breaker trips again.

Ok, simple enough, I've got a bad pump, right? I've still got one other pump but I'm not flying on just one. I'm grounded until I solve the problem. I reset the breaker but switch the other pump, crank up again, and run for about 2 minutes when THAT breaker trips. Hmmm - two bad pumps? What are the odds? Something else is going on here. Possibly a breaker issue? Voltage was completely normal for all this.

So sitting there without cranking the engine again, I looked at my ammeter while running one pump, then the other. I saw a delta of 9 amps on one side, 10 amps on the other, and tripped the breaker again. The pumps were BOTH pulling nearly twice their normal amperage, the breakers were fine. Again, the odds of losing BOTH pumps at the same time are quite long, but the ammeter confirmed they were both pulling too much current, and the fuel pressure was bang-on normal at 44 psi the whole time (sensor is FWF at the injector rail). What gives?

At that time I had the dual output of the two pumps Tee'd together into a single output, then a final filter assembly before sending the fuel FWF. Turns out I had gotten a load of what looked like mud-dauber nest (mud) into my left fuel tank, which was fine enough to make it through the pre-filter and pump but plugged that final fuel filter, causing both pumps to push against a much larger than normal backpressure, drawing more amps and finally tripping their breakers. (The mud originated from my fuel tank/pump in the hangar, I found the remains of the nest inside the fueling nozzle.)

So knowing the data above, I deduced the fuel filter blockage and it became a very simple fix - but I want you to think for a minute about how many hours, and how many dollars spent replacing/checking components, were saved by the presence of the ammeter in that case. Would that total cost offset the value of installing the ammeter, do you think?

Which parts would you replace first - the pumps? Then the breakers? And when the problem persisted, what next?
 
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View attachment 19305

Would anyone have any idea on what would cause a 60 amp shunt to fail? Melted or fractured and then melted.

8 years ago I replaced the Amp meter for a Volt meter due to preference and in 1000 hours on my RV 4 and never had an electrical issue.

Run up was good 14.3 volts and everything worked. 10 mins into the flight and total electrical failure.

Back on the ground this is all I could find. Battery still has 12.9 volts and no other signs of arcing.

Trying to insert the foto, so here goes...............

:confused:

Thanks

Tim

Do you have the ANL inline fuse? And what is the condition of the fuse?
 
If you are to the point of desperation, suggest checking the marine industry.
Simular shunts are used in fishing boats and should be available locally in Vancouver.
 
Yes, an ammeter is useful for troubleshooting when safely on the ground.
A handheld meter will do just fine. When in the air, fly the plane. Save troubleshooting for later.
If the alternator quits while airborne, the pilot should already know which loads to shut off to conserve the battery.
Who is going to fly the plane while the pilot is flipping switches and watching the ammeter?
 
@Airguy. That's a bit scary if you think that one through. I'm sure you've replayed the potential consequences in your mind if the FOD hadn't completely migrated when it did, if you'd started on the other tank (a quick selector cycle may not have found this), etc. I'm planning for oversized (surface area wise) pre and final filters. Now I'm wondering if I should have redundant finals. Your situation would have become worse when the second pump was switched on for TO or landing. Before anyone interjects; no, a legacy fuel system would not have been a savior as the mech pump is limited by the spring force and vapor lock would have gotten it anyway. Scary.

Yes, an ammeter is useful for troubleshooting when safely on the ground.
A handheld meter will do just fine. When in the air, fly the plane. Save troubleshooting for later.
If the alternator quits while airborne, the pilot should already know which loads to shut off to conserve the battery.
Who is going to fly the plane while the pilot is flipping switches and watching the ammeter?

To each his own but similarly, one size doesn't fit all. It's not just about troubleshooting. If I'm flying (especially at night or in weather) and I see an unexpectedly high current, regardless of any other system related pilot procedures I'll be looking for a place to land. Minutes or seconds can count. What if a lithium battery was used which have a much flatter voltage curve before they collapse?

On another (humorous?) note, I've disagreed with Ross on the contributions of instantaneous torque versus engine HP. Now I've disagreed with Carl on this electrical discussion. Maybe I'll save time in my trifecta pursuit and just insult the great state of Alabama for DanH.

Cheers boys.
 
In my setup, the connections from the shunt to the EMS are protected with 1amp fuse as required by the Dynon EMS device. The circuit is also protected by a 60A ANL fuse. The Dynon shunt provided in the kit can handle a lot more current than the ANL fuse. Regarding the fuse protection of the shunt to the EMS, I know of one RV owner who discovered the shunt sensor wire was destroyed by an overload condition, and losing the voltage monitoring capability while the plane was in flight. Fortunately, the small wire guage was destroyed without causing any fire hazard.
 
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Shunt location

Can an expert please advise which is the best location for the current sensing shunt? Dynon installation manual offers three options:
1) Battery output/input
2) Alternator output
3) Aircraft equipment input

It appears that ideally there should really be two ammeters to give a complete picture. My current aircraft is fitted per #1 but that only indicates what is happening at the battery and it doesn't really give complete insight for the load to the aircraft equipment or whether the alternator may be failing, I believe?
 
best location for the current sensing shunt?

It is a matter of personal choice. I prefer alternator output.
Others prefer battery in or out. Equipment input is not very common.
Wherever the shunt location, it is important that the pilot understand its function.
If the pilot observes normal current flow when the shunt is located in position 3,
but fails to notice low voltage, he will be alarmed when the battery dies.
 
Can an expert please advise which is the best location for the current sensing shunt? Dynon installation manual offers three options:
1) Battery output/input
2) Alternator output
3) Aircraft equipment input

It appears that ideally there should really be two ammeters to give a complete picture. My current aircraft is fitted per #1 but that only indicates what is happening at the battery and it doesn't really give complete insight for the load to the aircraft equipment or whether the alternator may be failing, I believe?

Alternator output is the most common and most useful IMO.
 
Bob Nuckolls located the shunt in series with the alternator output on most, if not all, of his architectures.
Vansaircraft prefers to monitor current into and out of the battery on the RV-12.
I agree with Walt.
 
I can see the utility both ways, I personally have it set to monitor battery in/out amperage. I have EFIS alarms set for high/low voltage and high amperage.
 
Just Me

Can an expert please advise which is the best location for the current sensing shunt? Dynon installation manual offers three options:
1) Battery output/input
2) Alternator output
3) Aircraft equipment input

It appears that ideally there should really be two ammeters to give a complete picture. My current aircraft is fitted per #1 but that only indicates what is happening at the battery and it doesn't really give complete insight for the load to the aircraft equipment or whether the alternator may be failing, I believe?

I think knowing the battery current DOES give an indication of the alternator health. If the battery current shows that the battery is charging or neutral current (battery is charged), then the alternator is doing its job by putting out enough energy to keep from discharging the battery. As soon as the battery current goes neg (battery being discharged), then I know there is a problem, and I can calculate the time remaining since I know the capacity and the amount being drawn. Also in an emergency, the battery current will give me an indication of how much stuff I need to turn off to get the battery discharge current lower. Having the alternator current just tells me if it is working; i dont know if it is going into the battery or the plane. Unless I am trying to measure the plane’s power consumption during my test flights, I really don't care to know how much current is flowing thru the plane. Lastly, if I see the battery (bus) voltage dropping, with only a small current draw, then I know the battery is taking a dump and needs to be replaced.
 
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One question. If this is the fuse protecting the B lead from the alternator, why would a break in this circuit cause a total electrical failure? Shouldn't you just have lost alternator function?
 
why would a break in this circuit cause a total electrical failure?

A fuse should be installed in the alternator "B" lead to protect the battery and
electrical system from a shorted "B" lead or shorted alternator. That fuse
should be located at the battery end of the "B" lead, NOT at the alternator end.
Usually the aircraft main power bus is not protected by a fuse because it is an
unnecessary failure point. Instead, the battery contactor can be shut off in
case of smoke in the cockpit. Some builders do install an ANL fuse to protect
the main power bus. And some those builders might decide to use just one
fuse to protect both the main power bus and the alternator "B" lead. So they
connect the alternator output directly to the main power bus. In that case,
when the alternator or its "B" shorts out, the ANL fuse blows and main bus
loses all power. The best electrical architecture is the simplest one.
 
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