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Serious electrical problem

T

tullow

Member
Hello to all,
Ready to start engine for the first time and had removed the battery for a final charging.( an Odyssey 680 ).I asked a friend to reinstall the battery when it was ready as I had to leave for a few hours. When I came back I did a quick check and everything looked normal so I switched on the master/battery switch to check cockpit lights and indications. I was suprised to see that the instrument panel warning lights were quite dim and indicated voltage was only about 12.5 V , the ammeter on the other hand indicated +30 A and the alternator breaker (60A) had tripped !!.
I immediately switched the battery switch off and checked the engine and battery -- I found the battery connections reversed !!.
As you can imagine my first engine run will not take place today.
Does anybody know what damage has been done to my electrical system in general and my instruments in particular.?
I have a basic Vans electrical system with Vans "steam " instruments. Radios etc. are on an avionics switched supply,which was off at the time. Alternator is an ND 35A model.
How could the master relay close with reversed polarity and allow power to trip the 60A alternator breaker?

Any help and information would be much appreciated

Mike
 
tullow said:
Hello to all,
Ready to start engine for the first time and had removed the battery for a final charging.( an Odyssey 680 ).I asked a friend to reinstall the battery when it was ready as I had to leave for a few hours. When I came back I did a quick check and everything looked normal so I switched on the master/battery switch to check cockpit lights and indications. I was suprised to see that the instrument panel warning lights were quite dim and indicated voltage was only about 12.5 V , the ammeter on the other hand indicated +30 A and the alternator breaker (60A) had tripped !!.
I immediately switched the battery switch off and checked the engine and battery -- I found the battery connections reversed !!.
As you can imagine my first engine run will not take place today.
Does anybody know what damage has been done to my electrical system in general and my instruments in particular.?
I have a basic Vans electrical system with Vans "steam " instruments. Radios etc. are on an avionics switched supply,which was off at the time. Alternator is an ND 35A model.
How could the master relay close with reversed polarity and allow power to trip the 60A alternator breaker?

Any help and information would be much appreciated

Mike
Click to expand...

Hi Mike,
The master relay is pulled closed with a small wire wound electro-magnet. Any current flowing through it (forwards or backwards) will generate a magnetic field and pull it closed. Without looking at all of your instrument schematics, it's hard to say whether they're damaged, but some should have some type of circuit protection for this kind of thing. Even if they didn't, I'm not sure any damage would occur.

If it were my airplane, I would reconnect the battery properly and turn everything on one at a time. If it works, then move on. I would perform an electrical system check if everything works and call it good. Just my 2 cents.
 
You'll just have to hook it up correctly and start checking things. I can almost assure you all the Van's gauges are toast as they have no polarity protection. The alt "may" be ok, other things like spike diodes across relays (like the master contactor) will also be fried. Master contactors don't care about polarity so they will pull hooked up either way. I would call it a "minor" setback since the avionics (expensive) stuff is ok :eek:
 
Consider yourself very luck that your avionics were all isolated. A few of them probably would not have lived to tell the tale.

As an electrical engineer, I second the idea of just fixing the polarity and turning it back on in a progressive fashion. Thats probably the best way to discover any problems, and its unlikely you'll cause any further damage. If everything seems to still work --- fire it up!

-DC
 
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Well thanks for your advice,
I've just spent the last couple of hours at the hangar ( it's now past midnight here) and as you suggested I connected the battery correctly and find that my ammeter,voltmeter,manifold pressure and fuel guages work normally,so my fingers are crossed for the other Vans instruments on the panel. The avionics are all ok as they are on a separate switched power supply.
So not as bad as I initially feared, must get some sleep now and up to the hangar tomorrow to check out the rest,
Thanks again to those of you who replied to my question

best regards

Mike
 
A couple of ways to prevent a reoccurance....Make the battery leads short enough that if the battery is installed in the box backwards they won't reach the terminals. Has anyone installed a diode in series with the master switch to prevent the master relay from energizing if the battery is backasward?
 
replacement guages

I'm pulling my Vans engine guages out to put in an EIS-4000. Let me know if you need a replacement!
 
Alternator toast?

The Vans (Ispro) gauges have a reverse polarity protection diode inside so they should be OK. While not all of the current paths are after the diode, they are through resistors which should make it OK.

On an alternator, reverse polarity will usually toast the diode packs, opening one or more diodes. When this happens, one or more of the 3 phazes will be inoperative. This condition can be misleading as under light loads the alternator can appear to carry the load with a phaze missing but not for long. If it seems that the alt survived, you should do a load test. Also, some outfits sell a cigarette lighter affair that looks for missing phazes in the alternator output (looks at the ripple voltage) as well as low volts etc. but if it were my plane, I'd pull it off and replace it (or have it rebuilt with new diode packs). The breaker popped because some of the diodes carried essentially everything the battery had to offer for as long as the breaker took to open.

Personally, I'd also replace any other diodes across solenoids etc. You could do a detailed analysis but those are cheap.

Glad you didn't have the avionics on.
 
Or at least some...

CESSNADON said:
A couple of ways to prevent a reoccurance....Make the battery leads short enough that if the battery is installed in the box backwards they won't reach the terminals. ....
Click to expand...

....RED and BLACK heat shrink to color code the battery wires.
 
Not as bad as I thought

I've just come back on here and I have read all of your helpful hints and information.
John, thanks for the details re Vans instruments and the alternator, I most likely will change it or have it checked out in a specialist shop.
Seth, the guy who reversed the connections is , as you can imagine, a little down in the mouth, but as they say , there are those that you have made and those that you will make, - I'm talking about mistakes here.
The law of Murphy being what it is, it's certainly best to modify the leads or circuit so that it's not possible to reverse the connections.

Moral of the whole story -- check and check again , don't take anything for granted

once again many thanks to all,

great to be part of the RV builders/flyers community

Mike
 
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Engine run

All is well that ends well,-well almost !!

After having checked all the Vans instruments individually, the only one which seems to have a serious problem is the ammeter, I disconnected the alternator and ammeter and then started the engine yesterday,everything indicating in the green .
It really is something to turn that ignition key for the first time and have your pride and joy come to life for the first time.
I'll order a new ammeter and check that there isn't a serious mismatch between it and the shunt which would explain some of it's abnormal indications.

Best regards to all

Mike
 
tullow said:
All is well that ends well,-well almost !!

After having checked all the Vans instruments individually, the only one which seems to have a serious problem is the ammeter, I disconnected the alternator and ammeter and then started the engine yesterday,everything indicating in the green .
It really is something to turn that ignition key for the first time and have your pride and joy come to life for the first time.
I'll order a new ammeter and check that there isn't a serious mismatch between it and the shunt which would explain some of it's abnormal indications.

Best regards to all

Mike
Click to expand...

Depending on what the abnormal indications are, it is possible that it is simply connected backwards a crossed the shunt.
 
rvbuilder2002 said:
Depending on what the abnormal indications are, it is possible that it is simply connected backwards a crossed the shunt.
Click to expand...

Scott, the abnormal indications are as follows --
With everything connected up,when I select the battery switch On , the ammeter indicates +35amps. !! ie a charge of 35 amps even though the engine and alternator are stopped. I reversed the wires at the shunt but the indication remains the same.
Yesterday I ran the engine with the alternator connected and its output seemed normal ie 14.8 V .

I am now awaiting the new ammeter from Vans to see if that solves the amps indicating problem.

All in all I think I got off very lightly for what was potentially a very big mistake

all the best

Mike
 
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