Dead Electrical System (was Need Help, Please)

[Paul Sharp]

I have a problem and would appreciate help: Flew to West Yellowstone, was struck by a fit of stupid, and left the master and mags on. Next day when I returned to the apt to fly home, naturally the system was dead. I had the service there give me a jump start, and after the front engine got going I told him to disconnect and back away. I noted that the rear engine wouldn't turn over and their was significant discharge when I tried to crank it. I shut down the front, had him reonect the external cable, and started both engines this time. I noted, however, that there was no reading on any gage. I couldn't get the electrical system to work. Switched votlage regulators, shut the master on and off, etc. I shutdown the engines, pulled the front cowling, and looked at the "gen" fuse, but it looked OK and I don't think it has anything to do with no electrical andyway although I don't know for sure.

Model: 1967 Turbo.

What could be wrong? Could both voltage regs be shot? What else could be wrong? I have to make some intelligent guesses and then steer A&P unfamiliar with Skymasters around the troubleshooting via phone, remote as it were, since I won't be there. I'd like to have him get to the bottom of things with the best guidelines.

Appreciate help from this always knowledgable group ASAP. Thanks.

[MikeZ]

Paul, I believe that the alternators need a minimal line voltage fro the batteries to kick in. There is in "exciter" inside the alternator that must be energized. The engines will start and run on a jump due to the magnetos but the alternators won't kick in. This would not happen if there was at least some juice in the battery. You need a new battery.

Someone correct me if I'm wrong.
Mike

[kevin]

Any A&P should be able to troubleshoot this one, it is not really Skymaster specific. I am not an A&P, but the things I would check first are:

1.) Is the battery holding a god charge? Can it be charged? Running it dead like that may have ruined the battery, you may need a new one. I would not necessarily replace the battery immediately, I would have them test it first. If you have no indication at all on your alternator guage, no lights, no fuel guages, etc. it almost (but not quite) has to be the battery, the alternators are not an issue yet.

2.) If the battery is good, I think other possible culprits are the battery contactor, and the battery (master) switch itself. But leaving the master on is not likely to hurt either of these, and would hurt the battery, so I still suspect that.

As you probably know, if the battery is completely dead, or failed, the alternators will not charge the battery (or power your electrical system) because there is no field current to get them started. I think your airplane is old enough to have a RUN/STANDBY switch (I think that is what it was called) that, when placed in the standby position, will power the alternator fields from dry cell batteries. You could try this. If it works, you've isolated the problem to the battery. If you go back to the RUN position after a couple of minutes and the electrical system dies again, it probably means the battery won't hold a charge.

However, if the RUN/STANDBY switch has no effect, it does not necessarily mean anything, because often the dry cell batteries are dead or sometimes completely missing in these airplanes. That should not be the case, they should be checked during the annual, but it gets missed frequently.

As always, I am sure the A&P's in the crowd can provide more knowledgeable input.

Kevin

[Paul Sharp]

(Thanks for the input.) The particular model I have doesn't have the "DC" field current backup system - it never did have, best I could research - even talking to Cessna's multiengine service department.

Meanwhile, neither the "Standby" or any other switch I tried would make any difference.

The reason I think something must be blown is because I was getting a working electrical system after the first jumpstart. It was only after the second that everything went dead.

[Pete Somers]

Hi
The second item that Kevin has posted is your problem.
If you start the airplane with external power with a flat battery, the battery will not charge because the battery contactor is not pulled in. Unfortunatly the external power socket is not across the battery.

If you had jumpered directly across the battery you would have had no problem in bringing the alternator on line.

This is a reason for having the alternator restart system on the newer models.

Pete

[Mark Hislop]

Try taking the battery out, servicing it, and charging it. If, as other posters have mentioned, your problem is no exciter voltage, this should take cre of your problem. At the very least, if the battery will take a charge, you will have eleminated one variable.

Mark

[Paul Sharp]

Wow - that is encouraging because if all I need is a new battery I can get one locally, run back up there, switch it out myself, and fly home (having delivered the rental car back to the same place, etc. and everything in one shot).

Thanks to all for their input. I'll be planning my return trip ASAP.

[Paul Sharp]

Happy to report that you were all correct - replaced the battery, and everything worked as designed. Problem solved, plane back home, etc.

Thanks for the help. It was much appreciated.

[kevin]

Hurrah! Glad to hear you are airborne again Paul...

Kevin

[Paul Sharp]

Thanks to you and the board, and all those who helped. Nice place to know one can find friends.

[sunnysky]

You replaced the battery when that was not the problem. If you had done as Pete Somers indicated and jumped directly accross the battery, this would have brought the alternators on line and the battery would have charged up. Or you could have just recharged the battery. The initial problem was caused by leaving the master on and flattening the battery. Sunny sky.

[Jim Rainer]

Sunny Sky, I diasgree and think you are wrong. In over more than 50 years of flying, 90% of the time replacing the battery will solve all sorts of electrical problems (excepting CBs that continue to blow.) It can be done very quickly and cheaply (under $300) and at the most one might have to wait one night to get a new one by overnight delivery.

Many years ago, I was in the FBO busniess. Often customers would come in reporting various electrical problems. Our standing solution was to put in a new battery. If it worked, we charged only for the battery and no labor. If it didn't work (maybe 20% of the time) we removed it and started troubleshooting. With maintenance rates up in the $75 hour range, batteries are really cheap. One can keep the old one and if it's still good keep it as a spare. BTW, we got quite a few new customers that way.

You might ask Paul Sharp if he wishes that's what he had done.

[Ernie Martin]

I wonder if Pete Somers can expand a bit on jumping across the battery, rather than through the external power socket. The way I read it, you're suggesting doing it as in a car, where you use a pair of jumper cables to go from one 24V external battery (or two 12V batteries in series, for people like me in-out islands where there are no 24V batteries) directly to the posts of the aircraft's battery. In Paul's case, would a desirable prior step might have been to check water level in the cells and add distilled water first?

The way I read this, if you do it Pete's way, and keep the external battery on for a few moments after both engines have started, both alternators will start because they are seeing a healthy 24V (from the external battery). I assume that the real value of this procedure is when you have a totally dead battery (if you have a battery which is too weak to start the engines but still has some juice in it, I think the alternators will start, right?)

We would be grateful, Pete, for your comments and suggested procedure. For instance, do you remove the jumper cables and external battery, and replace the battery cover and front-engine cowlings with the front engine running? Or -- for safety -- do you shut off the front engine and, with the rear engine running to charge the battery, clean up the front-engine area? My concern with the safer approach, for a totally dead battery like Pauls', is that the 10-15 minutes of charging with the rear alternator may not put enough energy into the battery to start the front engine.

Thanks in advance for your views.

Ernie
(Hadn't lost interest in Skymasters, just been away for two months)

[Pete Somers]

Ok Ernie and all.

If the ships battery is flat, ie you put on the master switch and nothing.
You go for the power cart and plug it into the external power socket, hey presto you have power (but the master is not on).
You carry out a start of both engines and disconnect the power cart, go to switch on the master and nothing, because the battery is flat.

However if you jumpered the battery and started the rear engine, disconnect and run the engine to enable the front to be started, the system would be online and charging the battery (at a high rate).

1. Some of the bus services are isolated with the external power connected including avionics.
2. The master relay and switch control the alternator field.
3. the 337G and above have ALT restart which (if the restart batteries are ok) should start up the alternators after start and bring the systems on line.

So the only way to get your Skymaster back into the air is to jumper the battery.

BTW, there is such a thing as removing the battery and charging up rather than replacing it due to it being flat.

Hope this answers your questions
Like to hear your comments?

Pete

ps Piper a/c external power sockets connect across the battery thru a contactor for starting, do'nt know why Cessna did not do this???.

Cheers

[Pete Somers]

I would be happy to explain this further thru the wiring diagrams, however there are alot of variation to the Skymaster electrical systems thru it's days.
Please let me know if i can help.

Have a good day