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Old Koreelah

Intermittent electrical power loss

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Maybe someone here can explan why my plane regularly loses electrical power. It always occurs after takeoff, about the time I reach cruising level. There is a total loss of electrical power- instruments go dead, then a partial recovery for a few minutes as the voltage and ammeter needles wildly swing in regular pulses. About five minutes after it fails, full power is mysteriously restored for the remainder of the flight.

 

This has happened on each of my last half-dozen flights. No amount of fiddling with wiring on the ground can replicate the issue.

 

It doesn't seem to be altitude-related, because it's started at levels from 2500 to 4500'. It seems to be more dependent on temperature, as if an electrical component goes thru a crazy phase as it heats up.

 

I doubt the battery (LiFePO4) has anything to do with it. The engine is a standard Jab with standard charging system. 

 

Any suggestions welcome.

 

 

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Thanks for the suggestion Don, but I've wasted the last hour trying to join that forum and send an abbreviated version of my problem. How can I explain it in less than 120 characters?

 

 

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To have total electrical failure in a system with an alternator and a regulator, I would think it would be a connection fault.

 

The next question is: How is the main current carried from the charging/storage system to the instruments? Is it a heavy duty battery isolator switch or a relay/solenoid? Obviously your engine is not losing power, so is the ignition electronic as in the Rotax engines or magnetos as in Lyc/ Cont engines? Next question: Have you tried extending the flaps to takeoff position, then putting some pressure on the flaps about equivalent to the aerodynamic pressure of takeoff?

 

I think even if the alternator stopped charging, you would still get power from the battery. Even if the battery was going open circuit you should still get power from the alternator.

 

I don't know specifics of JAB engines nor the setup in your plane and these are just some general troubleshooting techniques. HTH

 

 

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Thanks CS. 

 

I know enough to have designed and installed the whole electrical system downstream of the engine/alternator/regulator

 

(but that doesn't mean I know how it works!)

 

I initially suspected my battery isolator, but fiddling with it in flight doesn't replicate the symptoms.

 

As with all Jabs, the engine ignition system is independent of the battery. 

 

My flaps have no connection to the electrical system, so I can't see why they'd be involved.

 

Could some electrical component be chucking a hissy fit as it warms up?

 

 

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I would replace the regulator/rectifier. 

 

The Jabiru ones have caused lots of problems at my airport with electrical issues when they are under heavy load and lots of demand. They overheat and when the cool down they behave again. 

 

Note:  This is just a comment from an observer at the local airport. I am not an expert.

 

 

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Thanks for the suggestion Don, but I've wasted the last hour trying to join that forum and send an abbreviated version of my problem. How can I explain it in less than 120 characters?

 

  • G'day O.K. I managed to join without a great deal of effort and usually IT rejects my efforts out of hand. I am going to replace the Jab Kubota style reg/rectifier with a Powermate. Have found them to be without issues on my Thruster and the Kitfox. A friend has one on each of his 2 Jabs. Are you restricted in the number of characters you can send or just a bit economical. I understand that you don't want to rabbit on.
     

 

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Thanks CS. 

 

I know enough to have designed and installed the whole electrical system downstream of the engine/alternator/regulator

 

(but that doesn't mean I know how it works!)

 

I initially suspected my battery isolator, but fiddling with it in flight doesn't replicate the symptoms.

 

As with all Jabs, the engine ignition system is independent of the battery. 

 

My flaps have no connection to the electrical system, so I can't see why they'd be involved.

 

Could some electrical component be chucking a hissy fit as it warms up?

 

OK:

 

For the flap involvement, I was wondering if the mechanical movement of the flaps and linkage could be causing interference with the electrical system by disturbing nearby wiring or plugs etc.

 

Another area to look at: with Rotax systems, there is a large electrolytic capacitor that is wired across + and - downstream of the regulator. This is to act as a load for the regulator should the connection to the rest of the electrical system be lost downstream. Some Rotax systems don't have this cap, but Rotax recommend it. Does the Jab setup have something similar? If a big cap like that was shorting internally, it might cause something like you describe. But I think if that happened, the cap would most likely smoke or possibly even explode. That might be the component chucking a hissy. Also, capacitors are notorious components in electrocal circuits for causing problems. Most electronic faults are cause by ageing caps and when we used to have mechanical points in car ignitions, the "condenser" (which is another name for a capacitor) across the distributor points was a common source of engine problems.

 

 

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I would be surprised if it is a regulator as the battery should supply voltage even if that goes offline for some reason.

 

Could it be as simple as the connections in the Master switch or Avionics Switch, assuming it is standard Jabiru Wiring. The other option would be a faulty avionics or master Circuit breaker.

 

just thinking about it as I type I am leaning toward the circuit breaker as an option.

 

Mike

 

 

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Are you able and confident to set up a temporary feed to piggy back from the terminals on the rect/reg that supplies the aircraft's positive buss bar, go for a fly and repeat on another flight connecting to the rect/reg terminal that supplies to the battery pos terminal.   Connecting the temp feed to a multi-meter so you can see if when the panel mounted voltmeter is doing its erratic thing that the regulator is giving a constant ideal voltage; say 13.6 etc.  If reading is constantly good then you have a fault in the wiring, breakers etc.

 

 

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Can the LiFePo4 battery system tolerate the jabiru / Kubota pulse type rectifier / regulator?

 

The behaviour you are describing is typical of an overvoltage cutout system operating when it thinks the 20V or 40V spikes put out by the Jabiru dynamo (PMA) occur, which will be most prominent after the battery has been topped off from the starting and ground idle discharge period.

 

With a standard Jabiru wiring and lead acid battery this is not a problem. The Lithium Ion battery usually has management circuitry built in. I think Powermate and / or the regulators sold by B+C  Specialty for the homebuilt market are linear regulators and might be better suited. 

 

The later Jabiru PMA is rewound with double the output voltage of the original, in an effort to please the US market where they hang lots of extra avionics and the charging system doesnt work enough at idle. I dont think that is a good idea. 

 

Ralph

 

 

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Thanks for your thoughts, people. I'll narrow my investigation to the regulator and the battery.

 

I had intended to do Jabiru's alternator wiring modification to increase charge during idle, but that is no longer necessary because the Li battery can easily cope with loads from radio, strobes and lights during extended periods of idling.

 

Maybe the business I bought the LiFePO4 from can provide more details of its internal management system.

 

 

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The jabiru and rotax charging systems are not suitable for liFePo4 batteries  to many spikes as Ralph said the powermate regulator cures the problem ,charge rate must not exceed 14.6 volts 

 

Mick

 

 

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Do you have a schematic drawn up? It can help with faultfinding by allowing you to see the areas that are common and those that aren't.

 

A total electrical power loss I would think points to a master switch or breaker or connection/solenoid in that system. If the regulator fails the battery should still supply and if the battery fails, the alternator should still supply.

 

I had a brand new good quality key switch (the master controlling the master solenoid) a while ago that failed intermittently because of a poor swage on the back of it. I could reproduce the fault by jiggling the key or moving the harness attached to it.

 

As your aircraft is wood, Check the earth side if you haven't already done so, losing an earth could easily open circuit everything.

 

 

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I'd be closely examining the earth path all the way from engine to battery to load. Maybe the torque from the engine at max power is moving a part of the cabling, and when you ease back on power it flexes part part of wiring a little less.  I've experienced that sort of problem in a motor vehicle. Very intermittent and mostly when the motor was under heavy load.

 

 

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I think after reading all the above that nomadpete could have the answer. In my experience if there is ever an unusual fault in a 12V DC system, there is a good chance that there is a poor ground connection somewhere. 

 

 

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First thing that jumped out at me was the non-standard battery. Jabiru use Oddysey.

 

"Shouldn't make any difference."

 

What if it does? Simple solution to a complex problem - try something that cannot possibly make any difference - because it just might!

 

Borrow another battery and just try it. Nothing to lose, everything to gain.

 

 

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I'd be closely examining the earth path all the way from engine to battery to load.......................

 

I learnt a long time ago that 12V automotive systems are VERY dependent on a good earth return. There is not much cost involved, just an obsessively meticulous installation of a dedicated earth ring wire making sure all systems are connected directly back to the battery. Chassis/body/fuselage returns just dont "cut the mustard"

 

 

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Good point, Skip. All my earth wires converge onto a single stitching screw driven into the plywood under my panel.

 

All positive wires meet at a similar screw about 200mm away. That whole setup is easy to get to when the aircraft is folded onto the carrier. I just lay on the wing and slide in under the fuselage to work on the panel from underneath. 

 

I have a few of weeks of good flying weather before I put it on the carrier and bring it home. I can give it a thorough inspection then, just before I go to Newcastle for a month of grandkids- sitting.

 

 

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Good luck with the grand kids (future pilots) .

 

I have found that stacking ring terminals can result in a poor connection. Sometimes this is the only way to achieve the desired (cost effective)  outcome - when this is the situation I take pains to polish (with sandpaper or similar) the rings and then use an electrical paste  (as the jam) between each ring . I secure the sandwich by using a  plain SS washer top & bottom (to reduce distortion) with an SS lock nut/bolt (you could also use a brass nut.bolt) . 

 

 

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Good point, Skip. I might replace my timber screw with proper bolts so I can put a decent amount of pressure on the accumulation of wires to ensure good contact. By paste, do you mean conductive grease?

 

 

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............................By paste, do you mean conductive grease?

 

Yep! combination conductive/anti oxidisation is the ultimate goal but even petroleum jelly/grease will do the job - the aim is to preserve  a good connection for as long as possible..

 

 

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Never rely on a wood screw to hold terminals together.

 

 

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Before you replace the screw, just give all the wires a bit of a twist, so that the joint is disturbed, then see if you still have the problem. No problem means that there was corrosion, causing a poor connection. That cold tell you if you have solved it and you can then go about putting in a  better connection.

 

 

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The better your connections the further you go in life. Nev

 

 

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