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Raise internal reg. Alternator voltage

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Tim Olson

Joined: 25 Jan 2007
Posts: 2872

Posted: Fri Feb 13, 2015 9:09 am Post subject: Raise internal reg. Alternator voltage

I've got an oddball question that I've been pondering

for a while.



I have an older Plane Power 70A internal regulated alternator.

The output voltage is always 13.9V at least as detected by

my engine monitor



Since it's internally regulated, and has it's own overvoltage

module, and ties to the bus through I think a 5A

breaker, I'm not sure what I would be able to do to

raise the output voltage.  They told me that

the regulator is fixed and non-adjustable, so on the

alternator end I'm sure there's not much I could do.



Now I've flown with it for almost 1,100 hours now and

it's never been an issue, but I do use an Odyssey battery

as my primary and some AGM batteries in my aux bus.

So I think ideally I'd raise the voltage up to

something just slightly higher if I wanted to optimize

my battery charge state.



Is there any simple way of tricking the alternator

into thinking the bus voltage is slightly lower than it

is so that it raises the output slightly?

I envision some way to drop voltage on the sense line

so that it jacks it up another .5V or so.



Just wondering what kinds of ideas anyone has, or if

maybe anyone else has done it and knows what would work.



Tim

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rene(at)felker.com
Guest

Posted: Fri Feb 13, 2015 11:57 am Post subject: Raise internal reg. Alternator voltage

Tim, depending on if you have an e-bus.



I see the same thing on my GRT EIS.  It is on my e-bus.  If I look at the power bus, then it is 14.2.  Just recently I added a GRT Sport (long story) as my backup and it is NOT on my ebus and it showed 14.2 all the way to Vegas and back this week (first real flight with it).  I never tried to measure my power bus before and my other EFIS is on the e-bus.  I had the same concern as you until this week.



One way to check, is to turn on your e-bus and see what happens.  When I did, my EIS and EFIS (SPORT) voltage reading was the same.  Only 500 hours...not a 1000 like you....and I finally figured it out.



I did not think the diode was supposed to drop the voltage that much.....but it sure appears to.  My normal full power voltage reading on the EIS is 13.9 or sometimes 14.0.



Rene'

801-721-6080



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nuckolls.bob(at)aeroelect
Guest

Posted: Fri Feb 13, 2015 12:46 pm Post subject: Raise internal reg. Alternator voltage

Is there any simple way of tricking the alternator

into thinking the bus voltage is slightly lower than it

is so that it raises the output slightly?

I envision some way to drop voltage on the sense line

so that it jacks it up another .5V or so.



Just wondering what kinds of ideas anyone has, or if

maybe anyone else has done it and knows what would work.



    It depends on where the internal regulator senses

    bus voltage. If it gets data from the b-lead terminal,

    there's nothing you can do but swap out the regulator

    and hope the new one is more SVLA-friendly.



    Try putting a 1N540x diode in series with the

    control wire off the 5A breaker. If it senses

    voltage through this lead, then the approx 0.5

    volt drop in the diode will spoof the regulator

    into boosting output voltage at the b-lead.

   Bob . . .

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nuckolls.bob(at)aeroelect
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Posted: Fri Feb 13, 2015 12:54 pm Post subject: Raise internal reg. Alternator voltage

At 13:55 2015-02-13, you wrote:




Tim, depending on if you have an e-bus.



I see the same thing on my GRT EIS.  It is on my e-bus.  If I look at 

the power bus, then it is 14.2.  Just recently I added a GRT Sport 

(long story) as my backup and it is NOT on my ebus and it showed 14.2 

all the way to Vegas and back this week (first real flight with 

it).  I never tried to measure my power bus before and my other EFIS 

is on the e-bus.  I had the same concern as you until this week.



    Ah . . . . but of course. It didn't occur to me that

    his voltage sample was coming off a diode-isolated

    e-bus.



One way to check, is to turn on your e-bus and see what 

happens.  When I did, my EIS and EFIS (SPORT) voltage reading was the 

same.  Only 500 hours...not a 1000 like you....and I finally figured it out.



I did not think the diode was supposed to drop the voltage that 

much.....but it sure appears to.  My normal full power voltage 

reading on the EIS is 13.9 or sometimes 14.0.



    The typical drop across a silicon rectifier is

    0.6 to 0.7 volts. A Schottky rectifier will be

    a little less. Rene's suggestion to close the

    e-bus alternate feed will, of course, bypass

    the normal feed path diode and raise the e-bus

    voltage.



    If this describes your situation, then all

    is right with the universe and the 13.9 volt

    reading is predictable and acceptable.



   Bob . . .

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yellowduckduo(at)gmail.co
Guest

Posted: Fri Feb 13, 2015 1:23 pm Post subject: Raise internal reg. Alternator voltage

If this is not simply an e-buss issue, how much capacity and life is 

actually being lost?

There is likely some temperature compensation in the regulator if it is 

running hot.  Is the EIS accurate? I know mine (different model) is off 

by a couple of tenths.



I would be happy with 13.9 volts  on an AGM battery in hot conditions as 

there is no need for a fast charge in my aircraft. Different story today 

with subzero temperatures here. Admittedly I don't worry much about my 

batteries with Z14 architecture.

Ken



On 13/02/2015 3:45 PM, Robert L. Nuckolls, III wrote:

 	  Quote: 	
		   

 <nuckolls.bob(at)aeroelectric.com>



         Is there any simple way of tricking the alternator

 into thinking the bus voltage is slightly lower than it

 is so that it raises the output slightly?

 I envision some way to drop voltage on the sense line

 so that it jacks it up another .5V or so.



 Just wondering what kinds of ideas anyone has, or if

 maybe anyone else has done it and knows what would work.



    It depends on where the internal regulator senses

    bus voltage. If it gets data from the b-lead terminal,

    there's nothing you can do but swap out the regulator

    and hope the new one is more SVLA-friendly.



    Try putting a 1N540x diode in series with the

    control wire off the 5A breaker. If it senses

    voltage through this lead, then the approx 0.5

    volt drop in the diode will spoof the regulator

    into boosting output voltage at the b-lead.

   Bob . . .

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Tim Olson

Joined: 25 Jan 2007
Posts: 2872

Posted: Sat Feb 14, 2015 8:32 am Post subject: Raise internal reg. Alternator voltage

Hi Rene',



That is a good idea, and one I've come across before.  I haven't

really explored watching the difference between switch on and switch

off for a long time, so I'll have to do that on my next flight and

see how much change it is.  I seem to remember it being .1V or so is

all.



The switch positions are definitely important. The alternator

field is connected to the MAIN bus.

But, in normal flight operation, the MAIN bus and E-Bus are

directly connected with no diode voltage drops in the path.



Now there is a little more complexity in the switching than that,

because I do have a schottky diode path to the e-bus (and aux batt)

when the switch is on to the e-BUS.  So my aux batt will always

be charged via schottky.  But the actual BUS the avionics are

on would only read that lowered voltage when the e-bus switch

is turned on.  It's harder to follow without a diagram because

there is a bit more to the system for brownout prevention

and such, but the important part is that in the position the

switches are all in for standard ops, the main bus and

"critical systems bus" as I call it, are actually at the same

voltage potential.  I actually feed that bus via 2 diodes from

both the MAIN bus and "Avionics" bus, which allows for

switching the e-bus feed without losing any power to that bus.

So the e-bus switch is always on during engine start but

then is turned off for normal operation, which keeps the bus

tied directly to the MAIN bus.  It is not an exact copy of

any z-diagram, but incorporates many features plus some

brownout protection.



I did think of the idea that Bob provided about putting a

1N540x diode in line with the alternator feed.  The worry I

had about doing that was that perhaps this extension of

the internal circuitry would have some unintended

consequence.  I couldn't think of any, but just wondered if I

may be missing something.  It's probably worth a shot some

day when it bugs me enough to dig into it.  I think before

I do that though, I should get a good independent volt meter

in the plane during a flight and actually test what that

reads for main bus voltage.  It could be that the EIS

has error, or by testing directly the various BUS voltages

I find what the real differences are.



For today, I was just putting the question out as a sounding

board to see if anyone else ever noticed the same thing and

what ideas everyone had.  I'm not too worried about actually

fixing it, because I don't really consider it "broken".

But I am building my 2nd plane which is going to be largely

identical to the first, and thought it a good time to start

thinking of this topic.  I'll probably go schottky diode

again on that plane too, just to keep the drop low where there

is a drop.



Tim





On 2/13/2015 1:55 PM, Rene wrote:

[quote] 



 Tim, depending on if you have an e-bus.



 I see the same thing on my GRT EIS.  It is on my e-bus.  If I look at

 the power bus, then it is 14.2.  Just recently I added a GRT Sport

 (long story) as my backup and it is NOT on my ebus and it showed 14.2

 all the way to Vegas and back this week (first real flight with it).

 I never tried to measure my power bus before and my other EFIS is on

 the e-bus.  I had the same concern as you until this week.



 One way to check, is to turn on your e-bus and see what happens.

 When I did, my EIS and EFIS (SPORT) voltage reading was the same.

 Only 500 hours...not a 1000 like you....and I finally figured it

 out.



 I did not think the diode was supposed to drop the voltage that

 much.....but it sure appears to.  My normal full power voltage

 reading on the EIS is 13.9 or sometimes 14.0.



 Rene' 801-721-6080



 --

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nuckolls.bob(at)aeroelect
Guest

Posted: Sun Feb 15, 2015 7:14 pm Post subject: Raise internal reg. Alternator voltage

 	  Quote: 	
		  I did think of the idea that Bob provided about putting a

1N540x diode in line with the alternator feed.  The worry I

had about doing that was that perhaps this extension of

the internal circuitry would have some unintended

consequence.


	




   No . . . been there . . . done that. BUT it ONLY works

   if the diode is in the regulator's voltage sense lead.

   It is unlikely that any commercial-off-the-shelf alternator

   with an internal regulator will sense through the control

   lead . . . all schematics I've had the privilege of viewing

   sensed the alternator's B-terminal.

 	  Quote: 	
		  For today, I was just putting the question out as a sounding

board to see if anyone else ever noticed the same thing and

what ideas everyone had.


	


    I'm not 100% sure that my mental image of your

    descriptions match the physical reality. How about

    sketching, scanning and then sharing an architecture

    drawing?  The SCHEMATIC is the universal language

    readable by any and all.

   Bob . . .

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