Pre-buy inspection

[15384]

Kris: I'm only saying this because after 33 years of working on ships generators, switchboards etc.. There may be some terminology differences between what we say. But this I know. Two alternators genertors or what ever do not need to putting out the exact voltage or one will be doing all the work. The unit with the higher voltage will be taking more of the load proportional to the difference in voltage between the two. Until it becomes to a point that the difference between the properly functioning unit and the one putting out less then the properly functioning one does take all the load and after that begins to motor the other one. Sorry I don't have the exact voltage where this would happen. This is what I do for a living. There is no way in Hadies that this could ever be true. Other wise ever since the invention of a twin engine aircraft with each engine having a generator or alternator or when ever they put two generators or alternators on a single engine that the voltages could be exactly the same for the life of the units. Otherwise 90 percent of these situations would be only working on one generator or alternator. There are tolerances that change. There are degrees of magnetism that change. This stuff is not is not that critical that it needs to be exact voltages or one will do all the work. When paralleling different KW generators this is one of the ways in which we are able to have two different size generators share a load. Excite one more or less than the other that way it will be either a few volts higher or lower hence one will take more or less than the other. Or you run one engine at tad slower that the other. Voltage is a product of 2 things excitation and speed.
Yes it is dumb to have one voltage regulator for 2 alternators or generators. Would love to know the FAA inspector that approved that install.

John

[Charlie Tripp]

The Shadin will start blinking should a low voltage occur. The JPI will actually be the first to flash low voltage.

I know of a facility that has converted a twin Comanche to paralleling alternator systems. In conversation earlier this week he said he was thinking about getting an STC for the conversion however he did not know if there may be a demand for such.

[Jay]

Kristin, John:

Do you guys know how the PlanePower conversion is set up?

While I understand (I think) the advantage of a paralleling relay, I think that's a somewhat marginal improvement. As long as both generators (or alternators) are feeding one buss we have a common point of failure.

Having an actual primary and alternate buss (or like a twin Cessna, left and right) would be a big step up, but I suspect that it would also be tough to certify.

Best,

Jay

[15384]

Jay: Don't know any details about Plane Power. But if there is another relay involved or other component other than 2 alternators I'm not aware. It is something else to go wrong and it maybe something else to help. Alternators have voltage regulators built inside them. At least all I have seen on the DC systems on the Diesel Gen Sets I work on. They also have protective diodes built into them to prevent the alternator from being back fed from either another alternator should it fail or when sitting idle and you have a battery charger charging the battery. All this is happening on the DC systems for the diesel engines I work on that spin the generators which in turn provide ships power. And you will probably find the same on your car. You bring in a refrence voltage for excitation and the thing puts out.

As I said before. A DC motor can be a DC generator and visa versa. They are interchangable. This is why a DC generator does not have a voltage regulator built inside of it.

Reality is either you have a functioning alternator or generator or you don't is what I've seen. Every component, every connection every wire must be secure and working for all to work right. If not the alternator or generator will not work. The only time I have seen this not be true is when an alternator which has 6 diodes looses a couple. The alternator has the ability to produce voltage under no load but once load is applied voltage takes a dive and the alternator output goes to zero or close to it. Remove the load and the voltage comes back to rated voltage.

Within reason there is no problem if one alternator is providing more or less of the current for a common bus when in parallel with another until one unit fails while still connected to the bus and the other still producing power. At that point there better be protective diodes to protect the dead alternator or generator or some other device which maybe what this Paralleling relay is for.

Personally I would opt for protective diodes instead of another moving component with contacts that eventually fail or a coil that will sooner or later fail.

John

[Kristin Winter]

John,

I can't tell if we agree or disagree, as I don't really understand your point. I don't know nothing about boats. I am only talking about my experience with Piper alternator systems, not generators.

Pre-1972, when using alternators, Piper used one voltage regulator to drive both alternators. If you don't believe me, check the SM. During the 1972 model year, they phased in using one voltage regulator for each alternator. In this system, there was a circuit between the two voltage regulators to keep each alternator running at the same voltage. I do not know how close this kept the differences in output voltage. When I said "exact", I didn't mean to the nanovolt. Sheesh!

[15384]

Kris: Electricity does not act any different whether it is on a boat, airplane, refrigeration system, hydrauic system, in a house, lawn mower or whether it is AC or DC, or whether it is an alternator or generator, it doesn't care what vehicle is utilizing it. Voltage on planes is not somehow special and because so someone can use a source other than an airplane to explain a point about electricity. Sorry if I confused you by using examples of electricty characteristics from something other than an airplane.

I'm not challenging your resources. Your resources are not in question. I'm sure that they are good resources. If you tell me you read them in a SB then I'll believe you. I did not challenge your statement about the use of 1,2 or 47 voltage regulators for 2 alternators. I challenged the sanity of th FAA approving one voltage regulator for 2 alternators. Even with a back up voltage regulator.

Your statement to people that unless the voltages produced by two different sources are not exact then the one putting out the higher voltage will be doing all the work is false and misleading except in the most extreme situation. Is my point. I tried pointing this out to you using examples based on what I do with electricity to make my point. I'll take the blame for not making it easy enough for you to understand. Maybe others got something out of it. Sorry you took offense at being corrected.


John

[Kristin Winter]

>>Your statement to people that unless the voltages produced by two different sources are not exact then the one putting out the higher voltage will be doing all the work is false and misleading except in the most extreme situation.<<

You are reading more into my use of the word "exact" than was mean or warranted. I am sorry that I did not define my terms with more mathematically precision. The truth is, I have never flown an aircraft that is instrumented well enough to tell how close the paralleling circuit keeps the voltages of the alternators, relative to each other.

I can say that when the paralleing system isn't working, I have seen one alternator putting out 60 amps and the other putting out less than 20 amps. When I switched the high output alternator off, the output of the other jumped up. When I adjusted the voltage regulator on each separately so that they were within .2 volts of each other, then the both alternators would read a bit over 30 amps. This is how the system works, according to my experience and training.

[15384]

Kris: This is how electricity (magnetism) works. The unit with the higher output voltage will attract more of the load. It won't be doing all of the work until you cross a certain threshold but will doing more proportional to the difference between the refrence voltages. If you read back to one of my other posts you will see this is what I told you happens. This is not in itself a bad thing. Under certain situations in fact it is what is needed. Such as when you have two different size generators or alternators providing electricity to the same load. Or maybe you're in a Twin and have one engine that is running slower than the other becasue of some mechanical problem but you're still producing power you don't want to shut that engine down cause you want the additional power and need all the electronics cause it's night and you've got alternators. Yes an alternator can put out at low RPM's. BUT. You are working the voltage regulator to death when you do this for an extended period of time which in turn will burn it up. So it would be prudent to maintain the slower engine since it is still producing power and if you have the capability which you had to lighten the electrical load on that engine by adjusting the remote voltage adjust rheostats you could then shift most of the load to the good engine alternator thus easing the work load of the slower running alternator possibly extending the life of its voltage regulator which in turn could make the difference whether you maintain the critical electronics as you're heading down the glide slope or you go black.

I deal in mathematical precision. When I ask one of my workers to go and turn off a circuit breaker whether it be a 120V or 480V 3 phase breaker before working on a circuit and he disappears and returns and I ask him did you do exactly as I asked I expect "exact" to mean "exact". It sometimes means I live another day.



John

[Kristin Winter]

Flipping off a circuit breaker does not have a mathematical component. Either it is on or off. "Exactly" doesn't really factor in.

[15384]

You know this is pointless. You are not going to get this. I'm starting to believe the woman who interviewed you for a pilots job knew what she was doing.

For the benefit of the ICS members I point out that you made a false and misleading statement. I detail and explain the hows and why your statement is false and your responce is that I am at fault because I accept that "exact" means "the same" and somehow I'm wrong for doing so.

Take note of this people. This is what awaits members should you point out to Kris that if the technical information she answers questions with is wrong and you point this out to her, her tactics will be to shoot the messager.

If you can prove any of the information I have used to show why your statement was false I will graciously accept that I errored verses trying to shift the blame to you.

I'm done with this, hopefully if my explanations of electricity and some of its characteristics will or might help a member better understand or help with troubleshooting a problem then your attempt to shame me will have been worth it.

John

[Tom Corell]

Are you two married ?