External power plug wiring.

[Lood]

Last Saturday, I had to jumpstart my Mooney due to the battery not having enough power. My Mooney does have an external power receptor, but unfortunately, I didn't have a dedicated airplane jumper cable with the relevant plug. So, I just jumped it directly on the battery, vehicle style.

During the week, friend visited me and gave me an airplane jumper cable with the proper plug. So, this morning, my battery was too low, once again, to start the engine. No problem, I though and was rather excited to try out the new jumper cable.

Somehow, things don't make sense to me or the wiring is wrong, because this is what seems to happen:

With the jumper cable connected and the master OFF, the gear down and vacuum low lights come on, the turn co-ordinator starts to spin and my JPI EDM700 turns on, showing 14.3 volts.

As soon as I turn the master switch ON, it seems that the external power supply is isolated and the batt voltage on the JPI showed 12.8 and later 13.2 volts.

Turning the master OFF again, the JPI shows 14.3 volts.

When trying to start with the master ON, there still wasn't enough power due to the fact that the external power is now isolated and I have only the airplane battery as sole power source.

When trying to start the airplane with the master OFF, everything shuts down immediately when the key is turned. This happens with a very definite "clunk" sound. I'm not sure though if it is made by the relay back at the receptor plug.

In the end, I was once again forced to open the battery box and jumpstart with normal vehicle jumpers directly on the battery.

Is this the way it should work or is something wrong here. To me, it doesn't seem right the that external power suplly is cut off when the airplanes' master is turned on, nor when trying to start using external power with the master OFF.

I would appreciate any advice or explanation on this and in the mean time, I'll also have a look through the manuals.

[OR75]

if the battery does not have enough power ... most likely you need a new one.

how old is it ?

trying to re-charge it (by taking it out and using a charger) does not work.

[Lionudakis]

The powering up on external does usually bypass the master on anything I've ever worked on, but when you turn the master on it should stay energized on external power, unless Mooney wired it not too, (Never encountered, but curious now) Will it start with master still off though, so Its cranking on external power?

And careful jumping on the battery, my former plane partner assisted current plane partner with his previous mooney C on a jump direct to battery. Dropped + clamp when engine cranked and frightened him. Fried the Generator, regulator, starter relay, master switch, oil temp gauge and sender, amp gauge, transponder, audio panel. Fun stuff

[Lood]

It is obvious that the battery is in the process of dying and I am already getting prices on a new one. What bothers me though is that this battery was installed, brand new in November 2010. So, it didn't last 2 years. I will check the fluid levels tomorrow and if it needs to be topped up, I'll do so and then put it on a trickle charger and see what happens.

That's what I don't get. When the master is turned on, the supply from the external battery is definitely cut off and with the master turned off, the external power is cutt off as soon as the key is pushed and turned to the start position. So, before any cranking can happen, everything dies.

I'd certainly prefer not to jump start using the conventional way, but in some situations, there's no alternative.

[carusoam]

Lood,

As a friendly gesture, I went out to pick up my POH that was outside in my car...

Unfortunately, the electrical schematic does not indicate where the external plug is wired into the system.

When I first bought my plane, I had difficulty using ground power while at AAA (All American).

In short, it seems to require the master switch to be on to charge the battery. There is a relay that needs to close to make that happen.

Why the relay opens when you engage the switch....your voltage must drop out below what the relay requires. That's my best educated guess.

Gil makes a very nice "smart" charger that may revive your old battery, but it costs nearly as much as a new battery.

Let's get to the bottom of this so I can update my POH notes...

Good luck.

Best regards,

-a-

[Lionudakis]

The schematic shows that when gpu is connected, it should supply enough power to the battery side to keep the ext relay closed no matter what, but there is a diode on there that could be causing an issue with flow. I'll attach the pic I'm referring to. It is wired like all others, so something isn't quite right

Mooney Operator's Service & Maintenance manuals (1).pdf

[DrBill]

Based upon the schematic provided above, let me explain the operation and the purpose of the diode. Given Lood's symptoms, his airplane is defninitey NOT wired like this schematic.

External power enters via connector F. When the connector is inserted, the negative is connected to GROUND and the positive connects to both + terminals. The top terminal, is wired to the coil of the relay with the diode to ground. If the wiring of the external power was REVERSED, the relay would NOT be energized and no problems would occur. If the polaiity is correct, the relay is energixed and the + side of the external power is then connected to the battery.

Wired correctly, applying external power should have no change IN THE COCKPIT.

It is interesting to see that the Master switch provides the GROUND connection for the POWER relay which then directs the positive power to the main bus as well as to the starter solonoid.

I'd love to put an external power jack on my 63 E, does this require any unique parts or STC ?

BILL

[carusoam]

Dr. Bill,

Thanks for the explanation. That all makes sense now. I forgot how the polarity protection worked and that it was even there.

My 65 C had the external plug added as a factory option. It resides in the area near the battery. It should be a relatively simple, but expensive addition of sheet metal work and paint/parts/wire. It will be worth it on the day that you need it for sure.

Contact the factory/MSC to see what's involved for support.

Best regards,

-a-

[Lionudakis]

Good explanation ! I have installed some at shops on various airframes that installed them under the minor alteration mindset, using a factory, or a salvage plug off a same/similar airframe, same location etc. , the rest is minor work. A fed even pointed out, if it was an option, and in the parts book as an option, and installed in the same fashion, it's legal if done with acceptable methods. Everyone's interpretation is slightly different, including the feds I've dealt with. Lood's gpu is def wired differently. Most airframes use the ground to trip the master relay, as the relay is energized directly off its own power input via the jumper, I haven't messed with an airframe that wasn't this way including regional jets. No fuses or circuit protection needed on a grounding circuit. It sounds like the master is supplying ground to both relays, one at a time, though. No telling how it got hooked up without looking at it. Every gpu I've been into is wired this way except some pipers and a T34 Mentor.

Let us know if you find something out of the norm !

[butchgilbert]

I'm not an electrician, but I have had a bad battery relay before. I would take the time to check out the entire system before I applied external power again. A bad battery relay will also slowly deplete the battery without you being aware of it. This also might be part of the problem.

[Hank]

Carusoam--

You had an unusual C model. My battery is on the firewall inside the engine bay, in a wonderful box with a difficult-to-fit lid and two cotter keys holding it on. I'd love an external connection instead of having to either remove the cowl or work through the little access opening that is smaller than the battery box top. Needing to stand on something ~6" high to get the box top on through the opening doesn't help any, either, and I'm 5'11" in my socks.

[carusoam]

I hear ya Hank. I maxed out at 6.00'

My external plug was added on early in its working life.

My gill battery leaked and ruined my battery box in my M20C. rebuilding the box cost more than a battery.

One challenge in the C... The plug operator is stationed between the wing and the spinning propeller. One distraction away from serious injury. Same kind of distraction that leads to gear up landings....

Having the external connection is very helpful. Having it back in the tail cone is even better.

It is a better procedure to charge the battery, using the plug, than to jump start the plane.

Best regards,

-a-

[N601RX]

The reason the master grounds the relay is it is safer that way. Because it is just providing a ground if the wire that goes to the master rubs and shorts to the airframe it just turns the master on. If the same wire supplied the voltage to the master relay and rubbed and shorted it would trip the breaker and the master relay would drop out turning everything off. Not something you want to happen.

[Hank]

I've only jumped the plane once, didn't care for it. But sometimes I have to charge her up through that little opening, and it's frustrating. May have to look into a way to add a plug somewhere. I've seen some planes with the plug mounted in the ELT access panel, but that would be a hassle to disconnect and reconnect when removing the panel. And I'm allergic to sheet metal work except right before a paint job, hopefully many years in the future.

Since I put in a new Concorde dry-cell almost two years ago, I've not had to recharge and only open the little bitty access hole to peek inside on pre-flight. Love it, love it! Don't recall which Concorde, but discussed it with my A&P and bought the one with higher CCA since it does get cold here on the Ohio River.

[MARZ]

The reason the master grounds the relay is it is safer that way. Because it is just providing a ground if the wire that goes to the master rubs and shorts to the airframe it just turns the master on. If the same wire supplied the voltage to the master relay and rubbed and shorted it would trip the breaker and the master relay would drop out turning everything off. Not something you want to happen.

Not to mention that to have the master switch trip the relay with power would require power to the cabin in the first case.... pretty much defeating the purpose of the master switch.

Don't lose site of the simple things first - check and clean all of your connections positive and negative

[wsbuilder]

The schematic shows that when gpu is connected, it should supply enough power to the battery side to keep the ext relay closed no matter what, but there is a diode on there that could be causing an issue with flow. I'll attach the pic I'm referring to. It is wired like all others, so something isn't quite right

The schematic reflects my M20G. I'm getting no power from the external plug through the relay out to the battery terminal. The diode and ground are common. Seems the relay is bad? How to check? Anyone have a part number for the relay? What purpose does the diode perform?

[DrBill]

"What purpose does the diode perform?", The diode is there so that if the power on the external plug was reversed, the relay would not energize. This prevents an incorrectly wired plug from being connected to the battery and causing a high current short. The only way the relay will "pick" is if wire X1 is +12V relative to ground . This allows the diode to conduct and turn on the relay. If wire X1 is negative 12 V, then the diode will NOT conduct and the relay will not energizze.

With your external power connected, measure the voltage across the coil contacts of the relay. You should see +12V relative to chassis on wire X1 and 0.7V at the contact with the diode. If you read +12V at the contact with the diode, the diode is OPEN (bad).

BILL

[wsbuilder]

Makes perfect sense. thanks!

[AmigOne]

I stopped buy Gill batteries a long time ago. In my experience over many airplanes, Concorde is the way to go.

[DrBill]

got a quote of $295 form Wentworth for the entire APU. Can someone post a picture of the APU assembly so I can see what I'm buying ?

The hard to find part is the door covering the socket. All the other parts are easy to find.

BILL

[1001001]

On 10/14/2012 at 7:08 PM, DrBill said:

"What purpose does the diode perform?", The diode is there so that if the power on the external plug was reversed, the relay would not energize. This prevents an incorrectly wired plug from being connected to the battery and causing a high current short. The only way the relay will "pick" is if wire X1 is +12V relative to ground . This allows the diode to conduct and turn on the relay. If wire X1 is negative 12 V, then the diode will NOT conduct and the relay will not energizze.

With your external power connected, measure the voltage across the coil contacts of the relay. You should see +12V relative to chassis on wire X1 and 0.7V at the contact with the diode. If you read +12V at the contact with the diode, the diode is OPEN (bad).

BILL

I found out the hard way that another thing the diode does in this location is to prevent the battery from holding in the auxiliary power relay due to the two positive terminals on the aux power plug being connected together.  On my J model, either there is no diode or it is there and damaged (I haven't looked into it enough to know, yet).  But I ended up killing a battery because I left the aux power plug connected and turned off my external power supply.  Because of the lack of a diode, there was a current path from the battery through the aux power plug allowing the aux power relay to remain pulled in.  This caused the battery to drain itself completely.

[PT20J]

1 hour ago, 1001001 said:

I found out the hard way that another thing the diode does in this location is to prevent the battery from holding in the auxiliary power relay due to the two positive terminals on the aux power plug being connected together.  On my J model, either there is no diode or it is there and damaged (I haven't looked into it enough to know, yet).  But I ended up killing a battery because I left the aux power plug connected and turned off my external power supply.  Because of the lack of a diode, there was a current path from the battery through the aux power plug allowing the aux power relay to remain pulled in.  This caused the battery to drain itself completely.

The diode won’t help you there. If your ship’s battery isn’t completely dead and you plug in the external cable and apply external power, the relay will close and stay latched even if you remove external power since there is now a current path from the ship’s battery through the relay contacts and the external cable plug to the relay coil.

Always unplug the cable after use.

Skip

[1001001]

58 minutes ago, PT20J said:

The diode won’t help you there. If your ship’s battery isn’t completely dead and you plug in the external cable and apply external power, the relay will close and stay latched even if you remove external power since there is now a current path from the ship’s battery through the relay contacts and the external cable plug to the relay coil.

Always unplug the cable after use.

Skip

Maybe I misstated what I meant, which was there ought to be a diode installed in the external power connection system to prevent this.  I guess it would be a different diode (in a different location in the system).  I haven't dug into the electrical diagrams in depth enough to determine where this should be located and whether it would work.  It's on my list to see if such a modification would be possible.

[Yetti]

That's going to be a big ole diode.  The solenoid to your external power supply plug should shut down when it loses power (your diode solution)   Unless your solenoid is welded closed.

[carusoam]

+1 for the Yetti with drawings!

Thank you!

Best regards,

-a-

I’m still trying to figure out how the three prong plug checks polarity, before opening the relay though...