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Plane Power IR Alternator Implementation in Z-13/8

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nuckolls.bob(at)aeroelect
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Posted: Fri Aug 20, 2010 11:03 am Post subject: Plane Power IR Alternator Implementation in Z-13/8

At 10:27 AM 8/20/2010, you wrote:

I'm thinking about using one of these as the belt driven alternator in Z-13/8:



http://www.plane-power.com/AL12-EI60.htm



It's their experimental, internally regulated alternator that also 

comes with built in crowbar over voltage protection.  I'm not sure 

that I have a full understanding of the OV protection and control 

issues of IR alternators and how they pertain to this unit.



I have 3 primary questions- one for the AEC and two for Plane Power, 

though I welcome any insight about all three from the AEC readers.



So first, is it correct to say that Z24, Z24A, and the associated 

text on page Z-5 apply to IR alternators as they come off of the auto 

parts shelf, and not really to this unit?



    Correct . . . The P-P devices are not off-the-shelf

    automotive.

Based on their conceptual wiring picture here:

http://www.plane-power.com/images/AL12_EI60%20Installation.pdf



Primary Question 1: How would I make the wiring connections in Z13/8 

with this unit?  Should their field enable lead go to the 2-3 DC 

Power Master Switch with the 5A crowbar in the same place as Z13/8 

depicts it?  Also, what about that other optional alternator off lead 

(see 3 below)?



I think I understand that the battery dump issue (described at 

http://www.aeroelectric.com/articles/Adapting_IR_Alternators_to_Aircraft.pdf) 

is a problem in Z13/8 because we would like to occasionally 

(preflight, first flight of the day, etc?) turn the primary 

alternator and master off, and turn the ebus alternate feed on to 

test those associated switching systems.  Is that correct?



    No. "Battery Dump" is defined as the sudden reduction

    of heavy alternator loads wherein the major portion

    of that load included battery recharge current and

    it's the BATTERY that's being disconnected. There

    are no operational procedures that call for such

    a "test". Further, the way the Z-figures are drawn,

    such a test could not be conducted for the battery

    is always disconnected AFTER the alternator is shut down.

Primary Question 2: Will it do any physical damage to anything to 

turn off the 2-3 DC Power Master Switch while the engine is running 

(assuming that I need to)?



    It has been a legacy design goal for all TC aircraft

    to configure the system such that an alternator (or

    generator) may be turned on or off at any time under

    any conditions without hazard to other components

    in the system. An alternator that is controlled

    by breaking the field lead without breaking the

    b-lead MEETS this design goal. So, no . . . the P-P

    alternator may be turned on or off at anytime without

    concern for hazard to any compoent.

Primary Question 3: Does opening their Alternator Field Enable Switch 

fully shut down the alternator field?

    Yes



If the crowbar protection circuit pops that 5A CB, I should hope that 

opening that switch



    "switch"??? Do you mean "breaker"?  Yes, opening that

    breaker offers a quiet, orderly and benign disabling

    of the alternator.



. . . would completely shut down the alternator field too.  If so, 

then what does that other "optional alternator off" lead do?



    That's not a control, it's an indicator light which

    has some limited ability to annunciate alternator failure

    and has been used in cars for decades. However, active

    notification of low voltage by an independent sensing

    system is the legacy approach to watching for and

    announcing alternator failure.

   Would I need to hook it up at all, and/or would I need to still 

hook it up with a switch in the line?  Is there a failure mode in the 

other circuit that would require me to turn off a switch in the 

second line to shut the alternator off?



    You can drop the P-P product directly into any

    of the z-figures by simply eliminating any illustrated

    external regulators and/or crowbar ov protection

    modules.



I was going to call plane power to ask them a few of these questions 

but I need to make sure that I know what to ask about.  Thanks in advance.



   I've discussed Plane-Power design philosophy with

   them at length. It's a certainty that their answers

   will be along the same lines as that which I've offered

   above.



    Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Sat Aug 21, 2010 7:51 am Post subject: Plane Power IR Alternator Implementation in Z-13/8

At 09:02 AM 8/21/2010, you wrote:

 	  Quote: 	
		  Bob, thanks for your help!  Your answer clarifies many of my 

questions.  I was surprised by your answer about the test.  Did I 

understand correctly that there is never a time to intentionally 

turn off the primary alternator and battery for the purpose of 

testing the SD-8 and it's associated circuitry's ability to supply the Ebus?


	


    Sure, you can do that. BATTERY DUMP is dependent upon

    sequences of events. First you have to have a heavily

    loaded alternator (engine rpm high, discharged battery

    that is demanding and receiving most of the alternator's

    output). Then you unhook the battery while leaving the

    alternator on line. The effect is much like the tug of

    war game where one of the opposing sides suddenly releases

    their grip on the rope when the other side is concentrating

    on a max effort. There's no way that the other side can

    keep from falling on their butts.



    The folks who design regulators must strive for a magic

    compromise between stability (SLOW response) and

    and accuracy (HIGH gain). In engineering-speak this

    is often referred to as "damping ratio". See:



http://www.aeroelectric.com/Pictures/Curves/damping_ratio.gif



    Here you see the time versus temperature plots for

    various servo-systems tailored to hold a mass at

    some constant temperature. Raising the temperature

    of a large mass takes a lot of watts. But the device

    controlling the heater has to be fitted with some

    anticipatory features. If you're pouting out kilojoules

    of heat into kilograms of mass, you'd better start

    throttling things back as the system approaches

    the desired temperature.



    You can slow things way down and have an "over damped"

    system that is free of oscillations and overshoot.

    On the other hand, a high gain/ fast response characteristic

    may bring the temperature to the set point faster

    and with more accuracy, but tendency to overshoot

    and "wiggle" about the set-point is greater.  This

    system is said to be "under damped".



    Now, imagine a controller that is optimally damped

    (middle curve). Consider what happens if the heater

    is turned on but sometime along the temperature rise

    cycle, you suddenly reduce the mass being heated

    by say 90%. What's a poor controller to do? Now

    unable to detect the loss of mass, the probability

    for overshoot and oscillation is huge.



    The battery is electrical "mass" which your

    regulator expects to be in place all the time.

    Hence the design goal that calls for alternators

    not to be switched on/off without a battery being

    on line too.



    If you study what happens while sitting at

    the controls and flipping switches, there's no

    way you can produce that sudden reduction of "mass".

    Alternators are never switched on/off without

    a battery being tied to the bus.



    Hence the design goals are satisfied and risks

    to the system are reduced to insignificance.



   Bob . . .

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