Great Question!!!!!!!!!!!!!!!
jamiller said:
This brings up a question. I have an RV wired pretty much according to Van's plans - thus a separate switch for the alternator field. I've been starting the engine and THEN switching on the alt field. Is this harmful to the Van's internally regulated 60 amp alternator? Or should one turn on the alt. before you start cranking?
Thanks,
John Miller
YES YES YES turn it on BEFORE cranking. BAD BAD BAD idea to do it after engine is running, in my opinion. This is why I take the time to write this and hope it helps you.
How does it work in a Cessna or Piper? We have all flown them right. Do you turn alternators ON and OFF separately? NO you usually turn the ALT ON with the master, before engine start and OFF with the master, after you shut the engine down.
In a car how do you start the engine and turn the alternator ON? You put the key in and turn it, first you get ignition than start. When you turn your car off you turn the key to off. As the engine revs up the alternator comes on line. When you turn the key to turn your car off, the alternator goes "off line" when it sense the IGN signal or no longer can maintain internal voltage as RPM decays. Don't get fancy with switch throwing. LET IT DO IT OWN THING, WHICH IS A SOFT START AND SOFT SHUT DOWN.
INTERNAL REGULATED ALTERNATORS are differnt than external regulated ones. They are really more sophisticated and designed to be ON at all times. The start up and shut down are automatic.
Internal VR's know how to handle coming ON line at certain voltages and off at certain voltage as RPM builds or drops off. Some have time delays and soft start (ramp voltage slowly). Not all are the same, and differnt ND alterantors have differnt characteristics. Now if the alternator is at high RPM and you tell it to "come alive" what will happen? It may deal with it. It may surge. It may just sacrifice itself to avoid a large volt/amp overshoot, burning out a component. There's NO advantage doing the extra (abrupt) step of cycling the alternator switch, none. The alternator takes so little HP to turn it is nil.
So don't turn the ALT on after start, turn it ON before cranking and leave it ON until the engine is shut down.
Anecdotal evidence/case studies: I have talked to two guys (one directly and another second hand) who had problems with their ND alterantor.
The common thread was they turned there alterantors ON and OFF under load while the engine was still spinning.
In the first case the builder / pilot liked to throw switches and turned his 55 amp ND on after start and before shut down. The alternator was fine for awhile, but voltage started to become unstable. The voltage varied and dropped with load, which was above 14.5 volts (but below 16-17 volts). He also could NOT turn the alternator off using his panel switch for the ALT (IGN) as he had before. ****
****( The IGN wire on a ND alternator is NOT a FIELD wire. THE IMPORTANT POINT IS if the alternator regulator fails, the IGN wire may no longer control the VR, so you may not be able to shut it down? THE ONLY SURE METHOD TO ISOLATE THE ALTERNATOR IS TO PULL THE B-LEAD (CB). This definitively and without question will protect the aircraft and isolate the alternator, independent of anything. Some are using fuses on the B-lead and no CB as aeroelectrics suggest. I think its a bad idea. You loose a manual way to isolate the alternator.)
Also Van suggest not using an OV modules because they tend to damage alterantors. Since internal voltage regulators have OV protection already (internally, Yes they do), its not necessary in my opinion. Add on OV protection to an internally regulated alternator is a Rube Goldberg contraption, it adds weight, cost, parts and potential for nuisance trips. Again internal and external voltage regulation are different concepts, don't mix and match.
The second case the guy was flying and for some reason with all his electrics on he wanted to turn the alternator off to see if the battery would work? Really. Well when he turned the alternator back on the voltage spiked and weird things happened. He was able to turn it off again by turning the ALT switch off. The alternator was fried. What fried I don't know. I would love to get one of these abused alternators and see whats what.
What is happening? There is a big demand for power, the voltage is down to 12.6 volts or less, the alternator is spinning (fast) and has a large potential to produce lots of power, the alternator switch is thrown and the alternator surges and tries to ramp up the voltage fast. I have no exact failure mode since most guys do NOT do an analysis.
Its only a theory on my part. Its based on the knowledge of the original intended application and the fact when you throw switches against how they where intended, they fail. People who leave them alone, have no problem. 1 + 1 = 2. (Note: If you get 1 + 1 = chair; stop reading).
HERE IS MY OFFER TO THE GROUP: IF THIS EVER HAPPENS TO YOU (regulator failure) PLEASE SEND YOUR REGULATOR TO ME. I HAVE CONTACTS AT A MAJOR AUTO ELECTRONICS COMPANY WHO MAKES VOLTAGE REGULATORS, AND THEY WILL DO A FAILURE ANALYSIS AND TEST IT USING SOPHISTICATED EQUIPMENT, X-RAY AND DISASSEMBLE THE REGULATOR TO SUB COMPONENTS TO FIND WHAT FAILED. Drop me a note and send me your damaged regulator. (There will be no charge to analyze your failed regulator, but you will have to pay to ship and will not get your damaged regulator back.)
HOW TO WIRE THE ND ALTERNATOR WITH INTERNAL REGULATION
Here is the way to wire it. When the master is ON, the ALT is ON. When the master is OFF, the ALT is OFF. For NON-normal conditions in the event of a failure of some kind, you should provide a way to turn the ALT off while the master is still on. This can be done with a pull-able circuit breaker (CB) or a "Cessna Style" split master switch. I don't don't like the Cessna switch, because its possible (easy) to turn the master ON without the ALT unknowingly.** At least you can't turn the ALT ON with BAT OFF which is Bad news.
I prefer a Double Poll Single Throw (DPST) toggle or Rocker switch that handles both the Master (BAT) and ALT; you know they will always be On or OFF together. In the event you need to shut the ALT lead OFF, use a pull-able CB for emergency ALT shut down. NEVER have the alternator on with the battery OFF. The DPST or Cessna Master will prevent this, and separate independent toggles or switches for the BAT and ALT are not a good idea at all, for this reason.
** (Always have a Hi/Lo volt indication (idiot light) if not the internal warning light provided by the alternator an after market warning device. Many engine monitors provide hi/lo volt warning. A volt meter is great if you check it all the time.)
Van does not recommend or show the use of the warning light (from what I hear). WHY NOT USE THIS GREAT FEATURE???? They just don't connect it to anything. That is a mistake in my opinion. Its also a fault indication, as well as high and low voltage indication. That was the way it was meant to be wired, wire it that way.
Most ND's have a plug with 2 or 3 wires: They all have IG or IGN, for ignition. The next common connection is "L" for light. This is the warning / fault light, which has varying functions between models. The next connector is "S", for remote voltage SENSE. The other wire is the large gage wire to the post, that is the output or B-lead.
Van also does not use the remote voltage sense (from what I hear). Some ND alterantors do not have remote voltage sense and use the b-lead or IGN wire to sense buss voltage. Van recommends you just tie the IGN wire and the S wire (sense wire) together (if you have a S wire, some don't). If you have a "S" wire and tie it to the IG wire, it works, but its not how it was designed.
The remote Volt-"S"ense goes direct to the battery and not the main buss. To be honest the "S" lead is more for cars that have long wire runs between the alternator, battery and fuse box. However its an input to the logic of the IC, and it uses that input to determine if things are OK. One big thing its checking for, is that the output (b-lead) is not shorted or disconnected, and it keeps the voltage at the battery more accurately controlled (as designed).
Pictures below: One is an alternator wired and another is expanded to show my
no relay concept. Why have a BIG fat master relay sucking 3/4th amps of wasted power. Also most modern starters have their own relay. Why have two start relays? Some say you don't want the big battery cable HOT all the time. I think the risk is low, especially if you put a fuse on it (see my diagram). The other thing is starters with solenoids don't stick engaged like the old Bendix drive, so isolating the started is not critical.
One way to wire a ND alternator (error IGN wire should be 1 amp CB, 5 amps is not needed.) (Click to enlarge):
Here is an expanded diagram with the NO REALY concept. The master relay is a small solid state relay that only needs to handle 40 amps for example VS 400 amps. The emergency battery isolate is optional.
Even SkyTec Starters has Certified installations without a firewall Relay.