Left the master on...questions

[jesse]

Maybe this was already covered but im a little late to this thread, but if everything else is turned off, whats left to pull a current from the battery?

With the master on? The biggie would generally be the turn coordinator.

 

[gismo]

Why? Can you explain?

The primary issue is the charging current. With a dead battery the current can be quite high, limited only by the alternator's ability minus whatever loads are on. The effect on the battery of high current charging varies with battery type. AGM (e.g. Concord RG) types are hardly affected but a flooded cell design is subject to plate warping and uneven surface lead formation, both of which can significantly reduce capacity or longevity.

 

[ajstoner21]

Ahh I forgot about the turn coordinator.....

 

[Dan Thomas]

I've been guilty of leaving the master on before, it didn't kill the battery, but I worried about overheating the gyros.

If the alternator switch is left on as well, the alternator's field is being fed maximum current by the regulator, which is sensing an undervolt condition. In a 14-volt system and with a 60-amp alternator, this is around three amps. It's enough that the alternator's field coil can get pretty hot, since the thing isn't turning and the fan isn't drawing cooling air through it. I have seen a burned field coil from leaving the master/alt switch on.

Dan

 

[gprellwitz]

Slightly off topic, but not much. Is 90 minutes with the master on enough to completely discharge the battery? I know that it's enough to discharge it enough that the engine won't start (at least in the instance I'm thinking of). The solution used was to use a couple of car batteries to jump the plane with a 28V system, and I didn't hear of any ill effects. Not that I would have expected to be told. (And no, we weren't the ones who left the master on; not that we couldn't make such a mistake.)

 

[jesse]

Slightly off topic, but not much. Is 90 minutes with the master on enough to completely discharge the battery? I know that it's enough to discharge it enough that the engine won't start (at least in the instance I'm thinking of). The solution used was to use a couple of car batteries to jump the plane with a 28V system, and I didn't hear of any ill effects. Not that I would have expected to be told. (And no, we weren't the ones who left the master on; not that we couldn't make such a mistake.)

Hard to say really depends what was all powered up, without being there to see, who knows. Since they forgot the master on they may have forgotten other things on, also varies from aircraft to aircraft.

The turn coordinator by itself would take quite awhile to discharge it since they draw about .4 amps at the most.

 

[gprellwitz]

Hard to say really depends what was all powered up, without being there to see, who knows. Since they forgot the master on they may have forgotten other things on, also varies from aircraft to aircraft.

The turn coordinator by itself would take quite awhile to discharge it since they draw about .4 amps at the most.

It was a steam gauge restart 182. I don't know what else may have been left on, though I would expect that the avionics switch was off, as that's usually done before engine shutdown. We tried jumping from the 182 I was flying, but that was unsuccessful. Probably because of an imperfect connection in the two sets of jumper cables we needed to span the distance between the two planes.

 

[gismo]

It was a steam gauge restart 182. I don't know what else may have been left on, though I would expect that the avionics switch was off, as that's usually done before engine shutdown. We tried jumping from the 182 I was flying, but that was unsuccessful. Probably because of an imperfect connection in the two sets of jumper cables we needed to span the distance between the two planes.

Potential loads with master on and avionics off in a 14v airplane:

Master relay 1-2 amp
Turn Coordinator 0.5 amp
Instrument/panel lights 0.5-2 amp
Fuel and (some) engine gauges 0.5 amp
Alternator field and regulator 2-4 amp

Total 4.5- 9 amp (probably 2.5-5 amp in a 28v airplane)

I'd expect that kind of load to deplete the battery sufficiently to prevent starting in 5-10 hours depending on the battery's condition and capacity along with the actual current flow. Double that to total

BTW, besides being hard on the battery (unless it's a AGM type), jumping an airplane with a totally dead battery is that until the battery is almost fully charged you have little or no backup power to operate radios etc if the alternator dies and for the first 10-15 minutes you are likely to lose the alternator if a big load like landing lights or gear motor is added and you won't be able to get the alternator back online.

 

[jesse]

Potential loads with master on and avionics off in a 14v airplane:

Master relay 1-2 amp
Turn Coordinator 0.5 amp
Instrument/panel lights 0.5-2 amp
Fuel and (some) engine gauges 0.5 amp
Alternator field and regulator 2-4 amp

Total 4.5- 9 amp (probably 2.5-5 amp in a 28v airplane)

I'd expect that kind of load to deplete the battery sufficiently to prevent starting in 5-10 hours depending on the battery's condition and capacity along with the actual current flow. Double that to total

BTW, besides being hard on the battery (unless it's a AGM type), jumping an airplane with a totally dead battery is that until the battery is almost fully charged you have little or no backup power to operate radios etc if the alternator dies and for the first 10-15 minutes you are likely to lose the alternator if a big load like landing lights or gear motor is added and you won't be able to get the alternator back online.

Based on your load numbers above and the fact that a 172 has like a 22-25 amp hour battery it's going to deplete it enough to be unable to start in far less time than 5-10 hours. It's going to be totally dead in 2-5 hours.

 

[Unregistered]

Thanks again for all the replies. I've asked to see a copy of the invoices and am still waiting. We'll see what happens. I'll be sure to let you know.

 

[Dan Thomas]

Based on your load numbers above and the fact that a 172 has like a 22-25 amp hour battery it's going to deplete it enough to be unable to start in far less time than 5-10 hours. It's going to be totally dead in 2-5 hours.

It won't get totally dead. The master will open when the voltage gets too low to hold it shut.

But it will be far too dead to be of any use.

Dan

 

[Dan Thomas]

From: http://en.wikipedia.org/wiki/Lead–acid_battery

We read:

"Lead acid batteries designed for starting automotive engines are not designed for deep discharge. They have a large number of thin plates designed for maximum surface area, and therefore maximum current output, but which can easily be damaged by deep discharge. Repeated deep discharges will result in capacity loss and ultimately in premature failure, as the electrodes disintegrate due to mechanical stresses that arise from cycling. Starting batteries kept on continuous float charge will have corrosion in the electrodes which will result in premature failure. Starting batteries should be kept open circuit but charged regularly (at least once every two weeks) to prevent sulfation."

More reading on the difference between regular and deep-cycle batteries:

http://en.wikipedia.org/wiki/Deep_cycle_battery

Just for the guys who think that killing it dead doesn't really hurt it. They're talking automotive batteries here, and aircraft batteries, being made lighter, might be even more susceptible to damage through deep-discharging.

Dan

 

[Silvaire]

The Gil G-25 in my Champ finally died, it was 4 years old. I did leave the master on once and although it powers nothing but the relay it will run the battery dead if you leave it on for a week.

I'm replacing it with a Odyssey SBS-J15 which I've heard good things about. It's an AGM-VRLA, completely sealed and about half the size of the G-25 I'm replacing. You don't have to keep checking the electrolyte levels and it doesn't require a sealed container with external vent. Decent price too with free shipping.

 

[CApilot55]

At the flight school I fly out of it is written in a contract $125 for leaving the master on that is it, but good checklist usage is important.. Complacency kills

 

[Doggtyred]

So I walked into the rental outfit a couple of days ago, and I was informed that I left the master on in one of the planes about a month and a half ago, depleting the battery overnight. I of course felt (and still feel) terrible, because I know how frustrating it is to have to scrub a flight because of the stupidity of another renter. In fact, I've gotten into a plane (at another flight school) where the previous renter forgot to shut off the master. Very frustrating. Also, more personally, this sort of forgetting to do something trivial like turning the master off makes me feel like a blithering idiot.

Anyway, they jumped it and thought all was well (the plane went out for that flight without a hitch), but apparently the next two renters couldn't fly it because even after running the plane, the battery wouldn't "hold its power." They grounded the plane and ordered a new battery, displacing a couple of other renters. From what I've been told so far, they're looking for me to "offset some of the cost" of the maintenance issue.

This is the first time anything like this has come up for me, so I'm turning to the wisdom of PoA for thoughts. Would it be normal for them to ask me to cover some or all of the lost rental costs from the other renters? Lost instruction time too? A percentage of it? Also, roughly how much money are we looking at maintenance-wise for parts and labor? Would they normally ask for me to cover all of it? Part of it? And then, is this what renter's insurance is for? Would I see my rates go up for filing a claim for this? I'm not excited to pay for this out of pocket, but if it would mean that my rates go skyrocketing, it might be a good idea?

They've just now started the conversation with me, so I don't have any cold hard numbers. I know that some of those questions might require more information, and I'm happy to provide what I know. I don't have any dollar values from them yet, because they still need to pull the invoices from the shop they use. Part of me says "yeah, of course I should be liable for everything. It only makes sense." But another part of me says that it took them well over a month to get back to me...surely it can't be THAT important to them. It doesn't seem all that fair for them to wait a month and a half and then gouge me...right? After all, the least they could do is let me know right away. Also, are there any questions I should be sure to ask them?

I'm not looking to pick a fight with them at all--I've been very happy with them so far, a very good outfit--but I just want to be sure it's fair to both of us. So I'm basically just looking for initial thoughts and words of advice at this point. I'll update as I know more.

Mighty nice of them to let you know a month and a half later. Offer to cover part of the battery cost. Anything else is unreasonable. If their loss of income is so significant they can take it up with their insurer.

Hint: they aren't going to take it up with their insurer.

 

[MAKG1]

At the flight school I fly out of it is written in a contract $125 for leaving the master on that is it, but good checklist usage is important.. Complacency kills

The highest I've seen is $50, and even that's unusual. Which outfit is that, so I can avoid renting there?

I wonder how much they charge for leaving the fuel selector on "both." That often results in fuel spills if the tanks are full.

 

[asechrest]

Here's my school's policy, as written on their website:

Master Switch Left ON (if battery does not recharge, customer will be responsible for replacement costs): $65 per occurrence​

 

[Ghery]

Ahh I forgot about the turn coordinator.....

The sound of the TC running slower after only a minute or so was my indication of a bad battery on Father's Day. Hit the master, checked the gas gauges, turned on the lights. Quick walk around, came back and heard the pitch of the gyro was distinctly lower than a moment before. Looked at the gas gauges and they now read 1/2 tank (full when I started). Shut off the master, canceled the reservation, called the maintenance officer and grabbed a different plane. That change in speed in the TC really set up a string of events.

 

[Tom-D]

If the alternator switch is left on as well, the alternator's field is being fed maximum current by the regulator, which is sensing an undervolt condition. In a 14-volt system and with a 60-amp alternator, this is around three amps. It's enough that the alternator's field coil can get pretty hot, since the thing isn't turning and the fan isn't drawing cooling air through it. I have seen a burned field coil from leaving the master/alt switch on.

Dan

Not in the new era systems, with the single wire and electronic regulators.