My airplane electrical system is based closely on Bob Nuckoll's Z-11 plan. I have a GRT EIS 4000 that gives me voltage. This voltage reading has always been lower than I think it should be but I've never had a problem starting the plane (odyssey PC-625 battery) or running the full set of avionics and lights. My alternator is Van's 60 amp internally regulated.
The other day during a 2+ hour flight the EIS gave me a low voltage warning a couple of times, just briefly. So I decided to finally find out what's going on. The first thing I did was measure the resting battery voltage - 12.6, pretty good.
I then decided to test the 15+ year old alternator. Took it to O'Reilly and they said everything is fine.
Then I started measuring voltage at various points with the engine running. The battery was 14+ volts and so was the reading at the main buss, right at the terminal feeding the fuse block. With no load other than strobes, the EIS voltage matched the buss voltage within .1 or .2 volts.
When I started adding load the EIS voltage went steadily down to around 13.2 volts but the buss voltage remained steady at 14+ volts.
I then measured the voltage at the EIS panel switch. It matched the reading at the buss but also went down when I started adding load.
So what I don't understand is why the voltage drops so much for a relatively short run. couldn't be more than 18-20 inches. Is it something to do with the fuse block? How can the buss voltage remain steady but what the EIS is seeing drop so much?
I'm really not sure where to measure next but am sure open to suggestions. I guess I could measure out to other switches. Or maybe just to where the wire leaves the fuse block - just thought of that. That would tell me if the drop was across the block.
Sorry to make this so long but I'm just trying to anticipate questions.
thanks,
rd
The other day during a 2+ hour flight the EIS gave me a low voltage warning a couple of times, just briefly. So I decided to finally find out what's going on. The first thing I did was measure the resting battery voltage - 12.6, pretty good.
I then decided to test the 15+ year old alternator. Took it to O'Reilly and they said everything is fine.
Then I started measuring voltage at various points with the engine running. The battery was 14+ volts and so was the reading at the main buss, right at the terminal feeding the fuse block. With no load other than strobes, the EIS voltage matched the buss voltage within .1 or .2 volts.
When I started adding load the EIS voltage went steadily down to around 13.2 volts but the buss voltage remained steady at 14+ volts.
I then measured the voltage at the EIS panel switch. It matched the reading at the buss but also went down when I started adding load.
So what I don't understand is why the voltage drops so much for a relatively short run. couldn't be more than 18-20 inches. Is it something to do with the fuse block? How can the buss voltage remain steady but what the EIS is seeing drop so much?
I'm really not sure where to measure next but am sure open to suggestions. I guess I could measure out to other switches. Or maybe just to where the wire leaves the fuse block - just thought of that. That would tell me if the drop was across the block.
Sorry to make this so long but I'm just trying to anticipate questions.
thanks,
rd