Where to look for source of temporary electrical system failure?

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rv7charlie

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Hi Jim,

I won't pretend to be an expert, but I did have several careers in electronics, and I've been doing electrical/electronic maintenance on my homebuilts since 1994.
My reasons for separating the engine electrics are twofold. One is the obvious one you've just discovered. The other is simply pilot 'muscle memory'. We've trained and flown our our entire lives with mag switches and mixture controls being completely separate from all airframe electrics. If we don't continue that philosophy, the old 'smoke in the cockpit' scenario could easily cause an unnecessary engine shutdown, along with the master switch.

If the hydraulic pump did cause your issue, you have other serious problems with wiring architecture. Every flight-critical device should have its own protection, and there's no way a hydraulic pump should be able to overload a master contactor. Barring a dead short (which should just trip the pump wire's protection circuit), the worst the pump should be able to do is show up as a higher than normal current load on the system. Even a dead short should have melted any unprotected feeder to the pump, long before the contactor saw any distress, and if the contactor was that stressed, the damage would almost certainly be permanent. If the alternator was off-line, a pump could run the battery down fairly quickly, but that should be the only effect, and that wouldn't be temporary. The pump causing a complete *and purely temporary* shutdown of the entire electrical system should not be possible, if the plane is wired correctly.

If you don't have a wiring diagram, you really need to either get it or have someone knowledgeable help you create one.

I'd strongly suggest joining the Aeroelectric list, and getting a copy of the Aeroelectric Connection book. It's a great educational tool for learning about avionics, and studying the various wiring architecture drawings while asking questions on that list will bring you up to speed faster than a general purpose forum like this one. The author of the book and 'patriarch' of the list is Bob Nuckolls, who spent decades working for the aircraft 'big boys' and still consults. He applied what he learned over the years in certified and military stuff to come up with ideas that can be even better for us, with freedom to innovate with our homebuilts.

Sidebar: you don't have some kind of electronic electrical power distribution/control box in the plane, do you?
 
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TFF

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Hopefully the airplane is wired in stages. One failure can take everything out, but you want that to be a specific failure. Random failure should be segregated. On a plane like yours, engine electronics is primary. It should be wired so it take precedence. Radio or lights or whatever should never interfere with the engine, even if they are on fire. Something that complicated needs an emergency buss. Flip a switch and it’s all by it’s self. That needs to be looked at.
 

Dan Thomas

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A breaker that won't reset until cool after the load has been removed is also suspect.
Aircraft breakers are thermal devices and they require a bit of cooldown time before they can be reset. That's fine for a landing light, not so fine for ignition and fuel pumps. So the system needs two supply feeds through separate breakers and preferably from separate batteries. The second system would be off until the first fails, similar to an electric fuel boost pump that is switched on if the engine-driven pump fails.

A second battery needs to be charged through a diode so it doesn't discharge through a short in the primary system.
 

dog

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Here is a hypothetical circuit for keeping an electric dependent motor running with a loss
of power.Power from main battety to,1 a battery isolator,2 a voltage regualator(charge controller) 3 a second small battery (nickle metal hydride),4 master switch with this circuit where a second mag would be,5 a diode
6 plugs in parallel with power to ignition.
 

rv7charlie

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Small batteries won't cut it (for very long) on engines with automotive style fuel injection. Typical fuel pump draw is 4 to over 10 amps (likely nearer the high end for an LS motor). Then you need to power the cpu & ignition coils, which together will probably be 2-4 amps. Additionally, it's better for the engine & airframe to not share the same power 'path', so neither can take out the other. Studying the 'philosophy' of traditional airframe/engine separation and understanding the 'whys' is a good idea, so that when we do deviate, we'll have a better grasp of the ramifications.

Something the really smart people recommend is to draw the wiring diagram, and then make a spreadsheet with every wire identified. With each wire on the diagram, pretend it gets cut, and ask what happens. Then pretend it gets shorted to ground, and ask what happens. Document each condition for each wire, and the record the results. Then in the next column, describe what you would do to work around the failure. If it's non-critical (say, courtesy light power), then you can acceptably do nothing. If it's fuel pump power (obviously critical), do you have a backup pump on a separate circuit? If not, there's a problem that can be addressed (before flying). If power to an EFIS disappears, is there a backup on another circuit? Or legacy steam gauges you can reference? If not... If the engine monitor goes dark, that probably isn't a big deal if you know the airplane, but you need to know. If it is a big deal... Etc Etc.

Some things just can't be backed up easily in the electrical system, just like we can't have a backup wing spar. But by the same token, the hard-to-back-up stuff, like main battery cables and their terminations, should get special attention during manufacturing/installation and should be rugged enough, and installed with enough care, that they are as reliable as the wing spar. (And inspected with as much care.) BTW, the main battery negative cable, and its terminations, can have the most far reaching effects on the electrical system of any single component (it can potentially take down everything), and typically gets the least attention.

The whole electrically dependent engine thing has been hashed out pretty extensively on the AEC list. The diagrams there really are a good starting point for a new system. That doesn't fix Pantdino's current (pardon the pun) problem, but I do think it would be an excellent starting point for a path forward.

Pantdino, I wish you were a bit closer, but from your signature, you're almost as far from me as you could get and still be in the US. If you ask on the AEC list, there may be someone who's closer to you that can help you troubleshoot.

Charlie
 

gtae07

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I had a post typed up but @rv7charlie pretty much said it all already. There are a bunch of reasonable ways to skin the electrically-dependent-engine cat, but none of them say "run everything through a single breaker". Put each component on separate breakers/fuses (so failure of one won't take down the others), have redundant power for your engine, and separate engine power from the rest of the electrical system as best you can.
 

Dan Thomas

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Small batteries won't cut it (for very long) on engines with automotive style fuel injection. Typical fuel pump draw is 4 to over 10 amps (likely nearer the high end for an LS motor). Then you need to power the cpu & ignition coils, which together will probably be 2-4 amps.

BTW, the main battery negative cable, and its terminations, can have the most far reaching effects on the electrical system of any single component (it can potentially take down everything), and typically gets the least attention.
The UL Power engine needs 20 amps for its EFI and EI. Greedy stuff. Good thing we have alternators instead of generators now.

Yes, a lot of stuff gets little or no inspection at annuals. I have found some shocking stuff, and have fixed a lot of stuff that was due entirely to shoddy inspections letting things deteriorate too far. And I've seen some folks replace battery after battery, starter after starter, maybe even the alternator and regulator, simply because the starter won't crank well and they blame the big stuff and just start throwing money at the problem instead of troubleshooting intelligently and finding that it's the $30 master and/or starter contactors that are old and have oxidized or pitted or burned contacts. Thirty bucks that could have saved thousands. It's sad. A multimeter and some knowledge in its use can get one a lot of business from owners that are fed up with the costs of the shotgun approach and just want it fixed right the first time.

The tiniest resistance in contactor contacts can drop the voltage right off the meter scale if enough current is demanded. Ohm's Law.
 

Hot Wings

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Aircraft breakers are thermal devices and they require a bit of cooldown time before they can be reset.
Yes, they are thermal devices, but not like Polyfuses. Once tripped the breaker should cool down quickly enough to be reset just as soon as the offending load is removed.
I, maybe incorrectly, infered from the OP that the time between loss of power and the reset was on the order of several minutes.
 

Derswede

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Listen to RV7 Charlie. All circuits should be run so that one failure does not cascade into multiple failures, esp one causing the Pilot Cooling fan to stop. A hard look at the wiring diagram is needed at this point. There are ways of compounding problems. One of those is multiple vital circuits on one voltage bus. A short can cause a " Houston, we have a problem" failure. Such wiring will eventually cause sufficient problems that you will be forced to rewire anyway. Every critical system should be separate. One thing I saw and am incorporating on my little cheap Hawk, is a set of LEDs that I can glance at to confirm power on and flowing to each system. Tho it is orders less complex than your bird, still nice to get " power on all systems" at a glance.
 

BBerson

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The purpose of the fuse or circuit breaker is to protect the wire. The fuse should blow before the wire gets hot and burns up and starts a fire. So the breaker is matched to the wire.
That's how it works in homes.
 

Daleandee

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If a battery failed, the alternator becomes unstable and the electrical system should have been acting up well before it failed altogether. In this case, the lights just went out, indicating a sudden, total shutdown, which implies the master contactor opening for some reason. Bad battery terminal connections or grounds should show up as hard starting, erratic charging rates, flickering lights or whatever.

Without the wiring diagram it's all just guessing, and simply suggesting a bad battery or some other major component makes no sense. "Bad ground" covers a lot of territory, too. Every component in the primary electrical system has ground connections, so there are lots of them. Some will cause erratic performance, and a few will cause total shutdown.
My comment regarding batteries that shut themselves off was not my analysis of what went wrong but just an observation concerning some of the new battery technology being used. That fact, if it even happened, might contribute to finding an explanation of what did go wrong.

I agree and posted earlier that without a wiring diagram everyone posting here is just shooting in the dark ...
 

rv7charlie

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We're getting a bit far afield from the original question, but with typical automotive style alternators (with either external and internal regulators), they will not become unstable when the battery is removed from the system. I don't know where this legend originated; perhaps the old generators really would be unstable without a battery. Some older certified a/c can be observed with 'pulsing' voltmeters or ammeters; that's typically caused by resistance in the 'sense' path back to the regulator. If you look at how an alternator works, as long as there's current to excite the field winding, the regulator will keep voltage stable. The alternator can't 'start' without the battery to supply initial field current, but once everything is spinning and working, the alternator is actually supplying its own field current, via its output. (No, it's not a perpetual motion thing; we're still putting energy in via the pulley, spinning the armature.) I, and quite a few others, have demonstrated the process with internally regulators when we've inadvertently turned off the master after the engine was running. If there's no disconnect relay in the alternator's B lead (output), it continues to happily produce output and the bus stays lit up.

With 'dynamo' style alternators, you may get relatively high voltage 'ripple', but that amounts to noise; not actual instability.

BBerson is absolutely correct about circuit protection being for the wire and not the device itself. I didn't mention it because I was trying to stay out of the weeds for this thread.... ;-)

Charlie
 

Dan Thomas

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The purpose of the fuse or circuit breaker is to protect the wire. The fuse should blow before the wire gets hot and burns up and starts a fire. So the breaker is matched to the wire.
That's how it works in homes.
That's how it works in airplanes, too. AC43.13-1B lays that out nicely.
 

Dan Thomas

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We're getting a bit far afield from the original question, but with typical automotive style alternators (with either external and internal regulators), they will not become unstable when the battery is removed from the system. I don't know where this legend originated; perhaps the old generators really would be unstable without a battery.
I demonstrated that instability using the big circuit boards I had the students wire up at the college as part of their Aircraft Systems training. It's real. The boards had a motor-driven alternator, and when the battery was disconnected with the alternator running, the voltage went wild, surging up and down. This was with the electromechanical regulators; perhaps the electronic regulators respond much faster and don't permit that.

Some Harley hog (chopper) guys would take the battery out and replace it with a big capacitor that smoothed things out again. The system needs some low-resistance buffer to keep things sane.
 

rv7charlie

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The Harley alts I'm aware of are 'dynamos'; permanent magnet alternators. (Link chosen to make it look like I can do math stuff.) Instead of a field winding powered by the regulator supplying the magnetic field, there's a permanent magnet. A lot of the 2 stroke (& most of the small 4 stroke, like VW derivatives) stuff for a/c using dynamos recommend the capacitor even with a battery, but the cap and the battery are basically doing the same thing in smoothing the dynamo's output. But with solid state regulators, the output is still usable by most non-audio, non-digital accessories. Think 'lighting coil' on a Rotax; same tech.

The old contactor style regulators are basically 'prehistoric digital'; they're either on or off (in a couple of stages), pulsing all the time. Since I haven't worked on anything certified since a Swift back around 1994, I haven't even thought about one in a while. Probably explains the 'galloping current' syndrome in many certified planes that I mentioned earlier. Did you have any load on the alternator when you ran your tests? I can see lack of load making voltage excursions really wild with a contactor style regulator. Not an issue with solid state stuff. There is a bit more ripple in the voltage level due to the missing filter effect of the battery, but you often don't even know that the battery is offline unless you see the switch.
 

BBerson

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That's how it works in airplanes, too. AC43.13-1B lays that out nicely.
So in post 19 he said the main switch/breaker cut all power. Seems the pump should have thrown a dedicated breaker. It may not have a breaker on the pump.
I looked at the Cherokee electrical diagram. Can't see any breaker in the master circuit. Does the Master have a high amp main breaker?
 

rv7charlie

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The main contactor is 'manually activated circuit protection'. The size/weight/complexity of a protection device big enough to handle hundreds of amps (to the starter) just isn't practical for small a/c.
 

BBerson

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AC 43.13-1B shows automatic reset breakers are not recommended for aircraft. So if no auto breakers are installed then that isn't the issue.
On my infrequently used tractor the battery connection gets corroded and hitting the start switch frequently kills the connection completly. I get off wiggle the connection and then it works. It never fixes itself an hour later.
 

BBerson

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The main contactor is 'manually activated circuit protection'. The size/weight/complexity of a protection device big enough to handle hundreds of amps (to the starter) just isn't practical for small a/c.
Yes, the starter is direct. What about circuit protection of the main bus?
 
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