Jabiru trouble shooting

[deadstick]

Well noting there isn't a thread that helps members troubleshoot faults I thought I would start one.

 

Probably a bit long winded this one but you will get the picture.

 

I experienced the strangest fault recently, upon pressing the start button in one of my jabs it would throw the solenoid but with a delay, so to prevent it failing when I least wanted it too I replaced the solenoid with a new item supplied by jab. Well it would not work at all so I rang Jabiru to discuss the issue and they stated that the aircraft being a 2006 model might have a previous version of the solenoidand that an extra earth may be required, so to trouble shoot I checked all the terminals to ensure they were receiving the correct output and they were, from previous experience I thought I might just give the new solenoid a light tap to free anything that may be stuck internally and it worked the start system was fine.

 

So the aircraft hadn't flown and I received a call from the CFI stating that he had started the aircraft and then witnessed the battery voltage drain to zero over a 3 minute period (battery dead as a door nail) so I proceeded on out to check the problem! on cowl removal I tested the Battery which was dead not even a spark if you bridge the poles, so I removed a serviceable battery from my other Jab and installed it, prior to connecting the Positive lead I asked a couple of people that had turned up to watch whilst waiting to go fly to get out of the prop arc, thank god I did!!!!

 

After connecting the + lead and tightening the nut the solenoid took on a life of its own, the starter engaged and the prop was spinning, even though the master was off ,so I had to remove the lead.

 

A few things to note

 

1.Big reminder to me to ensure people treat that prop arc with respect especially on jabiru's.

 

2.Solonoids are just a piece of machinery and in this wiring configuration if they fail the only way to stop the prop is to remove the positive lead, un achievable if the cowls on due to the front two cam locks.

 

3 If you start your jab and the battery runs to a dead condition real fast (3 minutes)suspect the starter has remained engaged. No starter light engaged indication was present on the panel..

 

 

[motzartmerv]

Yes. The sound of the starter engaging was closely followed by the clapping sound as but cheeks tightened and puckered.

 

 

[Gentreau]

........from previous experience I thought I might just give the new solenoid a light tap to free anything that may be stuck internally and it worked the start system was fine.........

That would bother me on a brand-new solenoid. Doesn't sound like terribly good quality control by whoever made it.

 

.

 

 

[frank marriott]

Point 2. You seem to be suggesting that there is something wrong with the wiring configuration of the solenoid? Could you explain what you are suggesting please?

 

Sounds like a stuck solenoid in which case master or exciter wire would have no input?

 

Frank

 

 

[jakej]

Anyone know why the solenoids usedn on the Jabby don't have a diode fitted to prevent switch contacts from welding closed ?

 

 

[deadstick]

Hi frank, the implication is that the solonoid is always live ie it always has power to one pole and in this instance that configuration almost spelt injury due to an internal fault. Some other aircraft wiring config's have an interlock that prevent power to the solonoid pole without master on. I would never have beleived it if I hadnt seen it myself and in essence has heightened my respect for that prop arc.

 

 

[frank marriott]

Thanks,

 

I was not aware of the interlock with the master on other aircraft. The live pole was normal to me (like cars) thus missed your point.

 

The always treat prop live is a must - I have had the prop swing when working on the back of the engine by resting my arm with a metal watch band across the solenoid. Certainly wakes you up.

 

 

[Jabiru7252]

"not even a spark if you bridge the poles". Never short a car battery out, even if it's dead! Why?, because if the battery had an intermittent fault (like in my car) it could appear dead one second (zero volts across the terminals) then after a bump, it could easily crank the engine. Sounds to me like the solenoid had welded itself in the on position. I have heard of this before. Google 'stuck solenoid' and you will get some pretty good articles.

 

 

[JEM]

I once had a similar sounding problem with a Jab with a progressive voltage drop during a short flight following a stay at a dusty breezy airport. After landing I found that the starter button had jammed in on start up. The starter motor had apparently been operating without load and drawing down the battery reserve. The post flight shut down was normal. I popped out the button, cleaned the button slide and could not replicate the fault. System checked by electrician then restarted with jumper leads. Battery charged normally. Starter motor checked OK by L2 . The starter system has since always worked normally and the fault has not reappeared. Now I include the starter button in my pre takeoff instrument scans.

 

 

[Guest Andys@coffs]

Anyone know why the solenoids usedn on the Jabby don't have a diode fitted to prevent switch contacts from welding closed ?

Jake

 

As I recall the diode if fitted is normally reverse polarity across the energising coil and is there so that when the field collapses because power has been removed, the diode then limits the reverse voltage to the diode junction voltage (0.6v or thereabouts). The reverse voltage being induced as the magnetised bar that the relay switch contacts (as distinct from the activation coil contacts) are attached to moves back to its normal unenergised position.....

 

Normally such a diode is fitted if the driver circuitry for the relay is sensitive integrated circuitry where reverse polarity will cause Death and destruction..... When the driver circuitry is a bloody great "start" push button there isnt really anything much to protect and the battery itself acts as bloody good regulator for the rest of the aircraft circuitry....

 

Now, all that said Arc suppresion is required if you intend your relay to last a long time, and you can use a diode in parallel across the load as one form of arc suppression but generally its more complicated than that and requires the addition of capacitors to the load such that any inductive charcteristics are removed by the added capacitor and your left with a resistive load.... In our config a relay that needds to last in excess of 1000000 cycles in a jab is purely optimistic I think.......

 

Andy

 

 

[jakej]

Andy

 

We both know that & having diodes fitted is the norm for GA aircraft etc too but specifically the question is why Jabiru doesn't USE one on the starter solenoid & also why no battery master solenoid for that matter too ?

 

JakeJ

 

 

[Old Koreelah]

All this electrical jargon makes my head spin. The simpler the better for me. I replaced the Jab solenoid with a better one, and installed an automatic battery isolator. A heavy landing or prang throws a weighted swing arm which disconnects the earth terminal. The lever is easily accessible so the battery is isolated whenever the aircraft is not running.

 

 

[Jabiru7252]

All this electrical jargon makes my head spin. The simpler the better for me. I replaced the Jab solenoid with a better one, and installed an automatic battery isolator. A heavy landing or prang throws a weighted swing arm which disconnects the earth terminal. The lever is easily accessible so the battery is isolated whenever the aircraft is not running.

Can you post a photo as I am interested.

 

 

[Jabiru7252]

AndyWe both know that & having diodes fitted is the norm for GA aircraft etc too but specifically the question is why Jabiru doesn't USE one on the starter solenoid & also why no battery master solenoid for that matter too ?

JakeJ

Jabiru aircraft are great value for money, a J170 for $80,000 - if they started adding all this other crud, up goes the price. What do you mean by 'battery master solenoid'.

 

 

[fly_tornado]

Its a solenoid that acts as a battery isolator

 

 

[Old Koreelah]

Can you post a photo as I am interested.

Sorry about the wait, Jab7252, had to get access and take to following pix:

1. The arm pulled back, which pushes a wooden rod forward...

 

2. until the aluminium socket engages with the aluminium knob (the tip off a Speedwell brake lever).

 

This is clamped on the end of one engine mounting bolt, which is earthed to the starter and the rest of the wiring harness.

 

3. The lever is easily released, which pulls the rod back,

 

4. separating the alloy contacts, isolating the battery.

 

Very little pressure keeps the contacts together, yet they carry enough current to crank the engine.

 

 

 

 

 

 

[facthunter]

I think every plane needs a method of isolating the battery in flight. It must be of such a design that it doesn't add unreliability to the system. It also has to be close to the battery to be effective. I think in a U/L it should be mechanical rather than a solenoid. Nev

 

 

[jakej]

Two things can feed a fire in an aircraft, fuel & battery ( electrical issues can cause one too) most aircraft (all ?) have a fuel tap but most rec aircraft don't have a battery switch ( master solenoid) at the best location, ie within 6-8 inches from battery. On the panel is not good enough IMO as any shorting of wires caused by say rubbing on a sharp edge of firewall pass through could cause an electrical fire that can't be stopped except by disconnection of the battery - a battery master cutoff very close to the battery would stop a fire in this situation .

 

 

[geoffreywh]

Just look at aircraft spruce's website. There is a whole selection of them. Certified if you like...Quite reasonably priced (but watch out for the postage!) A battery isolator has to be essential equipment I would think. So when you throw the off switch everything is really off.......

 

 

[Old Koreelah]

Just look at aircraft spruce's website. There is a whole selection of them. Certified if you like...Quite reasonably priced (but watch out for the postage!) A battery isolator has to be essential equipment I would think. So when you throw the off switch everything is really off.......

Beware. A popular automotive battery isolator need to have the red plastic key fully removed for safety. Just turning it to the off position isn't enough; if you press it lightly it reconnects.

 

 

[geoffreywh]

I really don't think that type of isolator should be used. I would stay right away from the caravan type of isolator, just get the correct thing from the US !

 

 

[Jabiru7252]

Anyone know why the solenoids usedn on the Jabby don't have a diode fitted to prevent switch contacts from welding closed ?

The diode would not help. A diode across solenoids and relays is to prevent back voltage killing any semiconductor/low voltage circuit attached to it. The solenoid contacts weld when a heavy current flows through a less than perfect connection between contacts causing heating that melts the contacts together. Hope that explains things.

 

 

[cooperplace]

Just look at aircraft spruce's website. There is a whole selection of them. Certified if you like...Quite reasonably priced (but watch out for the postage!) A battery isolator has to be essential equipment I would think. So when you throw the off switch everything is really off.......

they do? Can you post a link please? I can't seem to find it there......

 

 

[geoffreywh]

I dont know how to link a page. But I used this one.......................LAMAR SOLENOID 12 VOLT (X61-0028)......

 

 

[facthunter]

Why not just use a mechanical switch. What are you going to power your solenoid with? nev