Battery/electrical problem...

tawood

tawood

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Tim
So last night I tried to go for a flight in my Cessna 150. When I started the plane, the prop turned very slow, and I attributed it to the cold (10F OAT), even though I preheat everything under the cowl.
Once the engine was running, I started turning on the Nav/dash lights, radios, and other electrical equipment. Over about 30 seconds, things started showing problems: first the radios seemed to shut off on their own, then the transponder quit, then the lights went out, all while the engine was running. The Ammeter showed a negative charge (obviously). I shut off everything electrical, checked the fuses (which were fine) and let the engine run for about 5 minutes, but never saw a positive charge. Finally when I shut it down, the battery was completely dead.
Seems weird that the battery would start the plane, but then die, while the alternator can't maintain the electrical accessories.
Dead battery? Bad alternator? Both?
 
From what I understand, most starters pull a heavy load from the battery to get going hence the slow prop you saw. If the alternator did not contribute to the load and the battery was already low on juice, it sounds like you would get what you saw.

Probably not a bad idea to get all the contacts checked/cleaned and the battery looked at to see if it's ACTUALLY dead. Start the cheap route before you go replacing an alternator.

I had an alternator fail (or appear to fail) on me in flight. Turns out it was just a wire that came loose. I had recently replaced the battery so I wasn't in danger there, but it's a lot cheaper to fix a wire then replace an entire alternator.
 
If the alternator were not charging, the battery going from low to flat would allow the master solenoid to open and everything goes off. Once the master opens, the alternator will never charge.

Two possibilities:Issue with the alternator / regulator and the battery isn't charging. Or the battery was just that close to the edge. Given that everything pooped out while you had it running, I would look at the charging system first (after putting some charge in the battery).

But I ain't no A&P and it appears that the laws of physics for a type certificated airplane are fundamentally different than anywhere else in the world, so I could be wrong.
 
tawood said:
So last night I tried to go for a flight in my Cessna 150. When I started the plane, the prop turned very slow, and I attributed it to the cold (10F OAT), even though I preheat everything under the cowl.
Once the engine was running, I started turning on the Nav/dash lights, radios, and other electrical equipment. Over about 30 seconds, things started showing problems: first the radios seemed to shut off on their own, then the transponder quit, then the lights went out, all while the engine was running. The Ammeter showed a negative charge (obviously). I shut off everything electrical, checked the fuses (which were fine) and let the engine run for about 5 minutes, but never saw a positive charge. Finally when I shut it down, the battery was completely dead.
Seems weird that the battery would start the plane, but then die, while the alternator can't maintain the electrical accessories.
Dead battery? Bad alternator? Both?
Click to expand...

For what ever reason, your charging system is not working; alternator/voltage regulator. Once you started the engine the alternator should be supporting your entire electrical load, plus recharging the battery. If it is not then then battery is trying to support the entire load.

Consider this: normally your battery will not be ever fully charged. To fully charge a 12 Volt lead acid battery it needs to be charged to 14.7 volts. Once it reaches 14.7 volts the charging system needs to back off to less then 14. However the voltage regulators in our aircraft are not very smart, they can only be set at one voltage and if they were set at 14.7 it would cook the battery. So they are typically set around 13.5 or so. So on the best day you will only have about 80-85% of the batteries rated capacity. Now you are at 10 deg. Major hit do to cold take half or the 80%. You are down to 40% and you used most of that to start the engine.

I hope you put the battery on a charger. A fully charged battery can tolerate cold well below zero. All of the liquid is acid and has a low freezing temperature. A DISCHARGED battery has basically water and will freeze in the mid to high twenties. If your battery freezes, you are done.
 
It's really simple to check and see if your alternator is charging. Take a reading at your battery with the engine off or shut down. Now start the engine. The reading should be above 13 volts. Anything below 13 volts or no difference at all you have a charging system problem.

Now lets say your battery goes dead over night. After charging th battery. Unhook your positive cable. Take the positive lead of your multi meter and touch the positive terminal. Now take the negative lead and touch the positive battery cable. If you see an draw you have an open circuit somewhere. Start pulling fuses one at a time until the draw goes away. Now you find what circuit the draw is in and can locate it by doing a very good inspection of the system.

A voltage regulator will only supply the amount of needed current. If your battery is fully charged you may see a very low reading of 13. 5 - 13.7 volts. Turn the lights on and leave them on for an hr. Now take a reading and see what the regulator is supplying. It will be over 14 volts. As the battery charges the regulator reduces this current. The regulator only supplies the voltage needed. If it supplied more the battery would boil.
 
Update:
Ok, just got off the phone with my mechanic...he thinks that my 2 1/2 year old battery was not producing enough voltage, so the master solenoid would not complete the circuit to the alternator. Hopefully a new battery will do the trick.
 
magicj said:
Consider this: normally your battery will not be ever fully charged. To fully charge a 12 Volt lead acid battery it needs to be charged to 14.7 volts. Once it reaches 14.7 volts the charging system needs to back off to less then 14. However the voltage regulators in our aircraft are not very smart, they can only be set at one voltage and if they were set at 14.7 it would cook the battery. So they are typically set around 13.5 or so. So on the best day you will only have about 80-85% of the batteries rated capacity. Now you are at 10 deg. Major hit do to cold take half or the 80%. You are down to 40% and you used most of that to start the engine.
Click to expand...

I wonder where those numbers come from. The Cessna alternator manual has these:

Ambient Air temp / Voltage setting
50 (F) / 14.1 to 14.8
75 /13.9 to 14.6
100 / 13.8 to 14.5
125 / 13.6 to 14.3
150/ 13.4 to 14.1
175 /13.3 to 14.1

The ambient temperature affects the electromechanical regulator so that it needs adjustment according to what it usually sees where it's mounted.

The usual alternator failures have to do with worn brushes inside the alternator, or a broken field wire between the regulator and alternator. Brushes should be checked every 500 hours but 98% of airplanes don't get that. Many owners are cheap and some are uninformed. They run things until they quit, which is not aircraft maintenance. That's automobile maintenance.
 
tawood said:
Update:
Ok, just got off the phone with my mechanic...he thinks that my 2 1/2 year old battery was not producing enough voltage, so the master solenoid would not complete the circuit to the alternator. Hopefully a new battery will do the trick.
Click to expand...

You are wasting your money and your mechanic is doing what is called a shotgun repair. Throw enough parts at a problem and somewhere along the line the problem will disappear.


Jim
 
I have my doubts as well. I've had lots of battery and alternator failures over the years, but I've never had a battery contactor open after engine start and the alternator on. Sure I've head times I've jumped the plane and the contactor was closed (and remained closed).

Further, the diagnosis doesn't match the symptoms. If the battery contactor never opened, it should have been trivial to get even a partially working alternator to indicate a charge (refilling the battery after engine start is a BIG load). The failure to show anything near a positive charge (especially after shedding all the load) indicates something wrong with the charging system.

Is this a belt-driven alternator? It's possible the belt is slipping (exacerbated by the cold weather). I'd check that for tightness/glazing. A belt is a whole lot cheaper than a battery.

Do you have an alternator at all? A lot of the Cessna 150s came with a generator, though Jasco and others have popular alternator conversions. I don't think the 150 got an alternator from the factory until the G (1967) model.
 
When I had my electrical failure in flight, it was due to a broken exciter wire to the alternator. The alternator is fine but needed a current to produce the magnetic field to then produce current when spinning. It cost me $20 to have that fixed as opposed to getting a new battery.
Also, unless you fly everyday, your battery should be on some form of maintainer.
 
flyingron said:
I have my doubts as well. I've had lots of battery and alternator failures over the years, but I've never had a battery contactor open after engine start and the alternator on. Sure I've head times I've jumped the plane and the contactor was closed (and remained closed).

Further, the diagnosis doesn't match the symptoms. If the battery contactor never opened, it should have been trivial to get even a partially working alternator to indicate a charge (refilling the battery after engine start is a BIG load). The failure to show anything near a positive charge (especially after shedding all the load) indicates something wrong with the charging system.

Is this a belt-driven alternator? It's possible the belt is slipping (exacerbated by the cold weather). I'd check that for tightness/glazing. A belt is a whole lot cheaper than a battery.

Do you have an alternator at all? A lot of the Cessna 150s came with a generator, though Jasco and others have popular alternator conversions. I don't think the 150 got an alternator from the factory until the G (1967) model.
Click to expand...

I think most have a vibrating type voltage regular too. I've had both really good ones and bad ones.
 
weirdjim said:
You are wasting your money and your mechanic is doing what is called a shotgun repair. Throw enough parts at a problem and somewhere along the line the problem will disappear.


Jim
Click to expand...
Indeed.

Yes, your battery was not producing enough voltage to keep the solenoid closed. But, is that because the battery is shot, or because the alternator was not charging it?

What are you going to do when your new battery goes flat in a couple hours because it isn't getting charged?

Charge the battery and do some diagnostics. It ain't effing rocket science. Get the diagnostics chart for a 1962 Chevy (or anything else this side of the '50s) and have at it.
 
weirdjim said:
You are wasting your money and your mechanic is doing what is called a shotgun repair. Throw enough parts at a problem and somewhere along the line the problem will disappear.


Jim
Click to expand...

The mechanic can't borrow a good battery and run the plane himself to see what happens...:mad2:
 
bnt83 said:
The mechanic can't borrow a good battery and run the plane himself to see what happens...:mad2:
Click to expand...

I don't know why not, but he certainly also could pull the battery and test it on the bench before declaring it dead. He could also start the airplane and check the alternator output.

This mechanic is the kind who has to replace all four tires on his car before he fixes the flat.
 
You all are funny...


Do I expect the new battery to "guarantee a fix"? No! But I also don't consider replacing a 2 1/2 year old POS Gill battery with a nice new sealed Concord a waste of money, either.
I'll replace the battery, check the voltage output of the alternator once it's installed, and report back with what I find...the new battery will supposedly be here by Friday.
 
tawood said:
You all are funny...


Do I expect the new battery to "guarantee a fix"? No! But I also don't consider replacing a 2 1/2 year old POS Gill battery with a nice new sealed Concord a waste of money, either.
I'll replace the battery, check the voltage output of the alternator once it's installed, and report back with what I find...the new battery will supposedly be here by Friday.
Click to expand...
Can I have your old one?
 
Welcome to the forum. Always nice to have another Tim around.

You'll get lots of opinions on this forum and they're all right. :wink2:

I had the same problem, ended up being a field wire connection to the alternator. The connector was too large for the size wire. It was installed before I bought the plane and lasted almost 50 hours before it let go. To combat the problem ever happening again I'm installing an ammeter that warns me of on overcharge or a discharge. Notice I didn't say "solve" the problem.

Tim
 
tawood said:
But I also don't consider replacing a 2 1/2 year old POS Gill battery
Click to expand...

Eh? There's nothing wrong with the flood cell Gills. I've been using them for years with my plane. But if you want to spend $225 or whatever on a new battery when there's nothing wrong with your old one, have at it.

Then when you find out that battery was NOT the problem and you have to work on the alternator, you can spend more.

This will absolutely kill your financial situation if the mechanic persists on poking at problems with a stick rather than properly diagnosing this. I learned this the hard way the first year I had my plane and used the rather quick and apparently inexpensive Appalachian-american mechanics.
 
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flyingron said:
I don't know why not, but he certainly also could pull the battery and test it on the bench before declaring it dead. He could also start the airplane and check the alternator output.

This mechanic is the kind who has to replace all four tires on his car before he fixes the flat.
Click to expand...
That won't work if the flat was on the spare
 
It's not hard to troubleshoot, but too many mechanics are weak on electrical systems.

Charge the bateery and put it back in.

Turn the master on. Use a voltmeter to see if there's voltage at the field terminal on the alternator. If not, check the "F" terminal on the regulator and see if there's voltage there. If so, the wire is busted. If not, see if there's voltage at the "A" terminal. If not, there's a busted sense wire between the alternator's "A" terminal and the regulator, or the big output wire is busted, or the noise filter is bad, or the alternator output breaker/fuse is bad. If there's voltage, measure the voltage at the "S" terminal. If so, the regulator is shot. If not, see if the alternator field fuse or breaker is bad. Some fuses (and 150s have fuses) corrode inside the end caps and still look good. See if the ALT side of the master is bad.

If it all checks out, measure the battery voltage before and after starting the engine. It should be a couple of volts higher when running than when not. If it's no higher, the alternator needs work.

Edit: there's one more real quick and easy check. Disconnect the plug at the regulator and connect an ohmmeter between ground and the "F" wire in that harness plug. (Look at the regulator for the I-A-S-F terminal idents.) You should see between 3 and 5 ohms. If it's open, the wire is broken or the brushes are totally shot. If you get some reading other than 3-5 ohms, move the prop back and forth a bit (watch those mags!) and see what the resistance does. If it's high and/or jumps around, the brushes and slip rings need work, a very common problem when some rebuilder puts way too much grease in the rear bearing or oil gets into the alternator.
 
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Just another good reason to run a One Wire Alternator.....

BUT....... You have to fly an experimental.....:rolleyes:;)
 
you need to find a new mechanic. if the battery had enough power to crank the engine it had enough to excite the alternator.

what most likely happened has been described. the battery started the engine, the charging system did not come on line and the load drained the battery down to the point where the radios went off line and then the master could not stay closed and everything shut down.
the proper diagnoses is to charge that battery, and load test it, if it passed that, reinstall it and start the engine and check the output of the alternator. i will bet it is the charging system.

bob
 
unsafervguy said:
you need to find a new mechanic. if the battery had enough power to crank the engine it had enough to excite the alternator.

what most likely happened has been described. the battery started the engine, the charging system did not come on line and the load drained the battery down to the point where the radios went off line and then the master could not stay closed and everything shut down.
the proper diagnoses is to charge that battery, and load test it, if it passed that, reinstall it and start the engine and check the output of the alternator. i will bet it is the charging system.

bob
Click to expand...

Agreed.... I would do the exact same thing.. Quick and easy...
 
flyingron said:
Then when you find out that battery was NOT the problem and you have to work on the alternator, you can spend more.
Click to expand...

Actually this approach is good for the economy.......just keep replacing components.....that will fix any problem.....except broken/intermittent wires, corroded connectors, blown fuses, intermittent grounds, slipping belts....and a host of other problems.

now how about a diagram.....not sure what system you have, but here's one I found.
 

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Oops, got busy at work, and forgot to post an update: got the new battery, installed it and started her up...checked the voltage: 13.7 with lights/radio on, etc. My mechanic said this is fine.


Guess my mechanic "got lucky" with the guess that it was the battery. Funny thing is, he always "gets lucky", every single dang time! Lol
 
Oh, I also checked for any drain on the system before starting (and with everything off), and there was none, btw.
 
resting voltage of the battery is 13.7. the charging voltage should be higher. you still have a problem. I bet it dies on the first flight.

bob
 
unsafervguy said:
resting voltage of the battery is 13.7. the charging voltage should be higher. you still have a problem. I bet it dies on the first flight.

bob
Click to expand...



My brand new "fully charged on delivery" battery showed 12.7 right before installation.
 
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Oh, and I've also flown on it now for about 4 hours...


Again, I'll keep trusting my mechanic until otherwise...
 
weirdjim said:
Come back in a couple of months and tell us how lucky he got.

Jim
Click to expand...
Cleaning the battery posts can do wonders for charging system efficiency. Particularly if they were installed without a layer of grease on the terminals in the first place.
 
Ok, you guys got me thinking...I'm gonna try my own load test on the old battery. I just downloaded the Gil pdf so that I can properly charge it...then I've got a 30-15-5 amp (on high-medium-low) trolling motor mounted to my workshop bench that I could hook to the old battery, and see how long it runs...although I think I'll need to submerge the motor to keep it from overheating.
 
tawood said:
Ok, you guys got me thinking...I'm gonna try my own load test on the old battery. I just downloaded the Gil pdf so that I can properly charge it...then I've got a 30-15-5 amp (on high-medium-low) trolling motor mounted to my workshop bench that I could hook to the old battery, and see how long it runs...although I think I'll need to submerge the motor to keep it from overheating.
Click to expand...

And.....

Put a load on it to duplicate rated amp draws...:yes:
 
N801BH said:
And.....

Put a load on it to duplicate rated amp draws...:yes:
Click to expand...

The easy way to do both is to submerge the prop in a LARGE bucket of water. I'm presuming the motor has a cooling line running into the water fed by suction.

Low speed will give you the most accurate results. Don't forget to top the battery liquid off with water before doing the charge & tests.

Jim
 
You may need to recondition the 'old' battery a few times. This is done by trickle charging it for about 24 hrs...and then you pull a know load with a current draw of say 10 amps until the voltage drops to the test bottom. All of these numbers I'm citing are in the ICA for your particular battery. But why bother? Bringing this battery back to life doesn't really help prove out your current situation. All we were saying before is that you needed a diagnosis done with equipment on site...such as a voltmeter, ammeter, resistance measurement.

The nice thing about a new battery (if the battery was not the only culprit) is that it will mask the real problem for a few days or even weeks....but it's still guesswork.

Maybe your 'guy' guessed right. If so, can you ask him for some Powerball numbers?
 
Submerging the trolling motor is necessary so you draw some amps, i.e. power.....or have a 'load'......spinning it in the air won't pull much current. Cooling the motor is something you already must know how to do.....
 
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