Dead battery, tech support needed :)

[lockeed]

I have an O-360 in my RV-6. Yesterday after my flight, I somehow forgot to turn off the Master. When I got the the hangar today, I had obviously no power.

We started the engine manually and I still didn't had any electrical power.

I let it run at idle for 5-10 minute (increasing/decreasing RPM regularely) as I though that after a couple minutes running, the ALT would pump enough juice into the system for it to kick in. Didn’t worked.

Any of you guys have experienced a dead battery before? Did it had the same symptoms?

 

[bbchien]

If you have a dead battery, there is no field voltage, so there is no electrical field from which to generate current.

I have seen one homebuilt intallation in whcih a Diac connected the main battery to a backup, keeping it charged. The operator, however, had to prop the a/c as teh Diac obviously can't transmit starting power, but it seemed to be designed just for this situation.

 

[RJM62]

If you have a dead battery, there is no field voltage, so there is no electrical field from which to generate current.

I have seen one homebuilt intallation in whcih a Diac connected the main battery to a backup, keeping it charged. The operator, however, had to prop the a/c as teh Diac obviously can't transmit starting power, but it seemed to be designed just for this situation.

Jeez, Doc, is there anything you don't know?

I was going to say either charge it on a charger, or parallel it to a charged battery for a few minutes to goose the field.

-Rich

 

[lockeed]

Makes sense. I will definately charge it before next flight...

A friend suggested someting too: "I suspect your voltage was so low on what was left of your battery, the alternator field circuit couldn't excite your alternator. Your alternator is not a permanent magnet and therefore requires voltage to "get it going".

 

[Graueradler]

I would have expected the alternator to have enough residual magnetism, even though it doesn't have a permanent magnet, to boot strap itself. Probably the battery was so dead that the semiconductors in the voltage regulator wouldn't pass any current to the field.

 

[RJM62]

Makes sense. I will definately charge it before next flight...

A friend suggested someting too: "I suspect your voltage was so low on what was left of your battery, the alternator field circuit couldn't excite your alternator. Your alternator is not a permanent magnet and therefore requires voltage to "get it going".

That's right. You have to get an alternator excited before it puts out.

[ hides ]

EDIT: R.I.P. Tony L. Your one liners live on!

 

[Dan Thomas]

I would have expected the alternator to have enough residual magnetism, even though it doesn't have a permanent magnet, to boot strap itself. Probably the battery was so dead that the semiconductors in the voltage regulator wouldn't pass any current to the field.

The old DC generators would bootstrap themselves, since the iron field pole shoes held some residual magnetism that would generate a bit of armature voltage, and that would be fed through the regulator to the field in an ever-increasing flow.

The modern alternator also has a bit of residual magnetism in the rotor, which is the field in an alternator, but the tiny voltage generated in the stator isn't enough to overcome the six diodes that rectify the AC output to DC. They require a couple of volts to start conducting. The battery needs charging, or the system needs boosting.

Dan

 

[jpower]

Exact same thing happened to me one morning on a rental plane. The renter the night before had forgotten to turn off the master, and it was dead as dead could be. We jumped it, but the alternator wouldn't give us anything, so we switched airplanes. They replaced the battery in that one while we were out, and I think they put the dead one on a charger in the shop, but I'm not sure.

 

[MAKG1]

The old DC generators would bootstrap themselves, since the iron field pole shoes held some residual magnetism that would generate a bit of armature voltage, and that would be fed through the regulator to the field in an ever-increasing flow.

The modern alternator also has a bit of residual magnetism in the rotor, which is the field in an alternator, but the tiny voltage generated in the stator isn't enough to overcome the six diodes that rectify the AC output to DC. They require a couple of volts to start conducting. The battery needs charging, or the system needs boosting.

Dan

The generator/alternator is an issue, due to diode activation energy of 0.7V in the rectifier diodes. But it's not the only issue.

A bimetal voltage regulator will conduct with tiny voltages, but a solid state VR won't, due to the same diode drop. Solid state is otherwise substantially more reliable, so they are quite common these days. They require periodic adjustments, as they work by heat opening a gap.

 

[Capt. Geoffrey Thorpe]

I assume the battery is connected to the rest of the electrical system through a master solenoid per typical aircraft practice. So, if you left the master on long enough to run down the battery, it probably ran down enough that it doesn't have enough power to close the solenoid (the solenoid coil typically gets it's power from the battery). And with the solenoid open, you got nothing.

Even if the alternator / generator were kicking out amps, it wouldn't charge the battery because the solenoid is isolating the battery via the open master solenoid, so you got nothing.

It doesn't take much at all to get an alternator / generator to kick something out, but until you close the master solenoid, you got nothing.

If you were to jump the master solenoid with a bit of wire once the engine is started, you will have enough juice to start the alternator / generator working and that (at least after a very short time) will be enough to hold the master solenoid closed while the battery charges.

But, since you ran the battery down to the point that the master solenoid opened on it's own, you don't have enough to close it (duh). So you got nothing.

Options:
Jump start.
Charge the battery a bit.
Hand start and bypass the master solenoid until the battery charges enough to hold it closed.

 

[jesse]

If you ran the battery that low you might as well junk it. I simply do not trust batteries that have been drained anywhere near that far. If there wasn't even enough left to let the alternator do it's thing..that's no good.

Throw a volt meter on the battery and see waht you've got. I bet it's crazy low.

Seriously. I'd dispose of the battery and buy a new one. Everytime I've ever had a battery go that low then just charged it and moved on with life it's bit me in the ass in short time.

 

[Silvaire]

Here's another tip - leave either the strobe or rotating beacon switch ON at all times. That way you will notice if you have left the master on as you walk away.

 

[Capt. Geoffrey Thorpe]

If you ran the battery that low you might as well junk it. I simply do not trust batteries that have been drained anywhere near that far. If there wasn't even enough left to let the alternator do it's thing..that's no good.

Throw a volt meter on the battery and see waht you've got. I bet it's crazy low.

Seriously. I'd dispose of the battery and buy a new one. Everytime I've ever had a battery go that low then just charged it and moved on with life it's bit me in the ass in short time.

You can get away with it a few times, but you do greatly reduce the life and will kill it dead if you do it more than a very few times. Personally, I wouldn't replace it without at least giving it a chance.

Besides, it only discharged enough to open the master solenoid (assuming he has one) so it wasn't totally flat.

 

[jesse]

You can get away with it a few times, but you do greatly reduce the life and will kill it dead if you do it more than a very few times. Personally, I wouldn't replace it without at least giving it a chance.

Besides, it only discharged enough to open the master solenoid (assuming he has one) so it wasn't totally flat.

You can sometimes get away with it a few times and sometimes you can't. I've had too many batteries strand me after one discharge incident a month or so before they give up the ghost. It's just not worth it to me, if a battery gets majory discharges like his did I replace it.

 

[Old Geek]

My rule for car battery lifetime is 5 years, minus one year for every jumpstart. I suspect it would hold true for aircraft as well.

 

[dell30rb]

I'm with jesse, you need a new battery

 

[Dan Thomas]

You can sometimes get away with it a few times and sometimes you can't. I've had too many batteries strand me after one discharge incident a month or so before they give up the ghost. It's just not worth it to me, if a battery gets majory discharges like his did I replace it.

Twice seems to be about the limit. That's what my flight-school maintenance experience tells me. A deep, slow discharge causes such severe sulfation of the lead plates that recharging isn't able to completely drive the sulfate back into solution again. Sulfation is a normal process during discharge, but only a deep-cycle battery has the necessary magic to tolerate total rundown and still desulfate during recharge, and I have never seen them in use except as the power sources for electric trolling motors on boats. They're expensive. I had one in my 13-foot cracker box runabout, powered by a Chev 283. Can't hand-start that engine if a cheap battery decides to go south when you're deep into deserted, remote lake country, 30 miles from the nearest road.

Dan

 

[gismo]

If you have a dead battery, there is no field voltage, so there is no electrical field from which to generate current.

I have seen one homebuilt intallation in whcih a Diac connected the main battery to a backup, keeping it charged. The operator, however, had to prop the a/c as teh Diac obviously can't transmit starting power, but it seemed to be designed just for this situation.

Diac??? I can't imagine what use a diac would be when connected between a backup battery and the main battery. Did you misspell diode?

Starting an airplane with a dead battery has some serious downsides, whether accomplished by hand propping or using a GPU. First and foremost is the inability to energize the alternator but a secondary issue is the fact that unless you load the alternator significantly or keep the RPMs down around idle for an hour, you will be charging the battery at a rate far in excess of what it's designed to handle and are likely to take a big bite out of the battery's life every time you do this.

Finally, even if you do get the alternator online (see below for methods) there's a risk that a heavy load (landing gear motor, landing lights, etc) will drop the battery voltage enough to open the master contactor at which point there's no way to get the alternator online again.

But if given all that you still want to get that alternator online after starting with a dead battery, there are a couple options. One is to connect a small battery to the main bus through a diode with everything turned off except the alternator. As little as 1.5 volts is often sufficient, a 6v lantern battery should always work and I've heard of success using an alkaline or nicad 9v battery, either of which is capable of delivering a could amps briefly.

 

[Dan Thomas]

The generator/alternator is an issue, due to diode activation energy of 0.7V in the rectifier diodes.

Sounds about right. Each stator winding has to deal with two diodes in its series, so the total would be 1.4 volts required for flow.

Edit: found a better diagram.

Dan