Electrical issue M20J - Need Help Please

[N177MC]

Both the Master switch and the Avionics switch went off line on take -off just as the gear was finishing retracting. The INST LTST breaker also popped .

 

This is a '76  M20J and it's the 3rd time - on all three occasions  the battery had been very low and the plane was started with an auxiliary external battery.

 

I'm thinking it might be a gear up limit switch out of adjustment but don't understand the correlation between that and the low battery/high charge situation not the INST LTST breaker blowing.

 

Any trouble-shooting help much appreciated !

 

 

 

 

[Hank]

My first guess is that your battery was still not charged, and the alternator was running hard to charge it. The gear motor also puts a large load on your electrical system.

 

The combination of charging the battery and running the gear motor tripped the master switch.

 

Next time you have to jump the plane, don't take off until the ammeter is showing low current. Then radio, lights and gear won't try to pull too much from the system. In the meantime, I wouldn't touch the gear limit switches.

[N177MC]

Thanks hank for the speedy reply !

 

So if the voltage dropped from landing gear motor pulling it down, could that potentially 'trip' the main relay ?  

 

Is that the general idea ?

 

ps: disregard the INST breaker - it was already pulled due to a faulty dimmer

[duke]

I agree with Hank. When batt voltage is low amp draw increases when a load is applied, especially elect motor load(gear actuator) This is because it takes a certain amount of power to do job (retract gear) and the only way is by amp draw increase. eg--12 v starter takes twice as many amps as a 24v starter. Thisis is why with batt low it is harder on all associated components.

[N201MKTurbo]

The gear motor takes about 30 amps if everything is working well. A discharged battery will draw about 30 amps of charging current. With a dead battery the alternator is supplying all the current. The 30+30 amps is right at the current limit for the breaker. it sounds like everything is working correctly.

[Marauder]

Duke's explanation is spot on. And a place to start when trouble shooting (battery). The amount of power drawn is relative to the voltage. If I had a 14V component draw 10 amps, it would draw 5 at 28V. If your battery is low, more amps would be required.

[Marauder]

The gear motor takes about 30 amps if everything is working well. A discharged battery will draw about 30 amps of charging current. With a dead battery the alternator is supplying all the current. The 30+30 amps is right at the current limit for the breaker. it sounds like everything is working correctly.

And that is an even better explanation!

[KSMooniac]

Sounds like it is time for some battery and charging system trouble-shooting if this has been on-going.  At the very least, you should charge the battery with a smart charger (like the Battery MINDer) for a couple of days before flying again, and ensure it passes a load test.  What kind of battery do you have?

[N177MC]

What a team !!!  

 

You are guys are great - and fast !

 

Okay, so sounds like the master is dropping off line due to voltage drop - makes perfect sense - I was not aware the gear motor pulls that much - I'm a Cessna guy and the powerpack on the Centurion and Cardinal RG pulls just 8 amp @24V.  

 

I agree we need to figure out why the battery is getting discharged in such little time, this was a 4 or 5 week spell .

 

Unfortunantly, a battery tender is not practical due to were in a "gang" hangar .

 

Thanks for the help !

[OR75]

IMHO, when a battery goes down, recharging it just kicks the can a bit down the road. You get back a fraction of the capacity only.    

[N177MC]

No doubt, putting 60Amps to a flat battery does no good at all ...

[N177MC]

KSMooniac - Agreed, need to look more closely at the battery issue(s) - it's Gill 35 .

[KSMooniac]

Ah, we might've found the problem!  Gill has been making excrement masquerading as aviation batteries for a few years now, and I'd start your troubleshooting there.  Take it home for a long trickle/smart charge, and then do a capacity test on it and be prepared to buy a sealed Concord RG-35 or -35AXC. 

[N177MC]

No kidding ?  

 

That sucks, but it also would explain why I'm getting the same sh!tty battery performance out of the Gill 35 in my Cardinal RG !

[Hank]

Go Concord! I put in whichever one has more cranking amps, since it gets cold around here. Been two years now, and it got me through starting problems related to the carb not sending fuel to the cylinders [sporadic issue for several months]. Still cranks great, at least through last Saturday.

[Hank]

 I was not aware the gear motor pulls that much - I'm a Cessna guy and the powerpack on the Centurion and Cardinal RG pulls just 8 amp @24V.  

 

In our Mooneys, the electric motor drives a four-bar linkage that moves all three wheels at once. Impossible to only move two, they are physically linked to the motor. We don't have a power pack--the motor turns, and the reduction gears slow it down so that the metal rods move slower. It's the same unit that the manual gear Mooneys have, except the electric motor is hooked up to a shorter Johnson bar.

 

I "think" Cessna's just use an electric motor to run a hydraulic pump or pumps, and each gear leg has it's own hydraulic cylinder and lines to the pump(s). Much easier for the motor, and probably a smaller one, too. Here at work, we get >100 tons of force using a 50-hp electric motor; one machine is all-electric, and it has multiple, larger motors to do the same thing. 480V, 3-phase, and really fat power cables coming out of the floor.

[SheryLoewen]

Starting with a jump start and taking off is a NO No. Your Battery is your Emergency back up.

 Often when jumping then disconnecting looses the battery relay that make the battery stay on line.The battery has to have enough power to keep that relay closed or your alternator putting out enough at disconnect to keep it closed without interruption. There is no way in flight to close that Master relay, so you are just running on your alternator alone and unable to charge the battery.

 

From Paul not Shery

.

 

[duke]

right on Paul. I would never fly after jump starting. Too many things in our birds depend on proper batt voltage--expensive garmins, auto pilots etc.

[testwest]

Hi 7MC

 

Welcome to the forum. Scott is right on that Gill, we have not used them in years. The Concorde 35AXC will help.....however, make sure you are charging correctly and that there is no drain on the electrical system when the master is off.

 

Try to figure out how to get that batteryMINDer on your plane when it is parked. It is a great device, we have one on both our planes, the Aerostar really likes it since we have to start 2 turbo-Lyc 6 bangers in a row on the same small(ish) battery.

[N177MC]

Totally agree that jump starting on a flat battery and going straight out is a no-no and the partner will be advised !

 

Also agree that a trickle charger battery minder is a must failing flying every single week.

 

How are you guys "hard wiring" the battery minders .?  (me lazy - I 'll bet a search will turn-up lot's of discussion on this!)

 

Sounds like it's time to switch from brand "G" to "C"  :-)

[carusoam]

N177C,

You may find that G batteries have a history of going only two years. Check the age of your battery...

Search this site for comparisons. There isn't a single post supporting brand G. Nobody has taken that side of the argument in years...

Best regards,

-a-

[KSMooniac]

The Battery MINDer comes with a harness that is not considered permanently attached and doesn't even need a logbook entry.  I connected mine to the battery and routed it through an existing hole in the baggage area bulkhead and had it come out from behind the interior panel.  I connect to it through the baggage door, which can be closed and locked carefully if you wish.

[N177MC]

Thanks - Sounds like that's the way to go !

[DonMuncy]

I leave my Battery Minder plugged into an outlet in the hangar. I wired a "two prong plug" on the Battery Minder cord and a like plug was wired onto the battery by my hangar elf. The plug from the battery is run over to the Oxygen "door" on my 231. I have heard that some people without oxygen run the plug up into the hat rack.  

[N177MC]

plug was wired onto the battery by my hangar elf

 

hangar elf ???