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Rotax PM regulator

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yellowduckduo(at)gmail.co
Guest

Posted: Fri Jan 02, 2015 9:52 am Post subject: Rotax PM regulator

There are a couple of interesting quotes from Hawker (on the 

www.aero-hesbaye site) saying their Battery life is shortened by 

charging ripple. The link below seems to validate the statement.

http://www.cdtechno.com/pdf/ref/41_2131_0212.pdf

Makes me curious whether a large capacitor in the PM charging circuit 

might increase battery life a bit.

Ken



"The power being transmitted per burst, voltage ripples are more 

important. This can affect all powered systems and instruments but it is 

the battery that will suffer the most. To avoid premature aging, Hawker 

advocates RMS voltage ripple of less than 1% (battery not connected) ..."



On 01/01/2015 3:38 PM, D L Josephson wrote:

 	  Quote: 	
		   

 <dlj04(at)josephson.com>



 It looks like an alternator regulator because that's what it is. The 

 output from the stator coils is single phase AC.



 There are many attempts online at drawing out the schematic of the 

 existing unit (it helps to search with the correct spelling of Ducati) 

 but I think the most complete one is in Gilles Thesee's 

 http://contrails.free.fr/elec_ducati_en.php. There is another website 

 in Belgium that has some of Gilles' earlier work, with some SPICE 

 simulations of the waveforms at 

 http://www.aero-hesbaye.be/circuit_elec.htm. Google Translate does a 

 good enough job if you don't have any French.

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nuckolls.bob(at)aeroelect
Guest

Posted: Sat Jan 03, 2015 5:23 am Post subject: Rotax PM regulator

 	  Quote: 	
		  "The power being transmitted per burst, voltage ripples are more 

important. This can affect all powered systems and instruments but 

it is the battery that will suffer the most. To avoid premature 

aging, Hawker advocates RMS voltage ripple of less than 1% (battery 

not connected) ..."


	


   I've reviewed several papers on the topic of

   charger ripple.  While technically accurate

   I'm not seeing much significance with respect

   to how we use the SLVA battery.



   Here are two exemplar documents . . .



http://tinyurl.com/pprktbt



http://tinyurl.com/lkfrwzy



   It's clear that these papers speak to

   SLVA batteries as standby power where they

   are 'floated' on a charger set for the

   system operating voltage. I.e.

   well above the open circuit voltage for

   the cells. It's also clear that the

   effects of poorly filtered charger output

   are continuous and potentially deleterious

   to battery performance when the stresses are

   being impressed 24/7/365 by a 'charger'

   that is also the ac mains power source

   for the system.



   Batteries on storage in the OBAM aviation

   community should be "maintained" in a

   fully charged state just above open

   circuit voltage for the battery. The

   maintainer is not an power source for

   anything beyond simple offset of leakage

   currents in the battery.



   The conditions more nearly approximating those

   explored in these papers are present during

   normal operations where the engine drive

   power sources are both CHARGERS and ENERGY

   suppliers to the ship's systems. The duty

   cycle for ripple stresses is exceedingly

   low. A few hours per week for a total of

   perhaps 100/year. A tiny fraction of that

   imposed by un-interruptible power systems

   in terrestrial, ac mains powered applications.



   I'm skeptical of the notion that adding capacitance

   across the output of the Ducati-style PM rectifier/

   regulator will produce any observable improvement

   in battery life. I'm acquiring test equipment

   to quantify and qualify the performance

   of PM R/R and will have some better ripple/

   noise numbers to offer on the topic later his year.

   Bob . . .

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jimkale(at)roadrunner.com
Guest

Posted: Sat Jan 03, 2015 7:43 am Post subject: Rotax PM regulator

I have also studied batteries for many years, although, I am not a battery

engineer.    I too feel that ripple current has no effect on battery life.

It could affect avionics a lot though.  On simple systems, the battery is

often used as the only device to reduce ripple current, and it does a fair

job at that.  I have never seen any sign of short battery life, where ripple

current is high.

Jim



--

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yellowduckduo(at)gmail.co
Guest

Posted: Sat Jan 03, 2015 9:22 am Post subject: Rotax PM regulator

The references to "with the battery disconnected" threw me as then any 

charging source with a diode in it will "ideally" prevent any discharge 

at the low point of the ripple.

I believe I have a decent grasp of charging voltage constraints and 

system voltage ripple but never really thought much about battery 

charging current ripple from AC chargers or my single phase PM alternator.

Seems I don't need to give it much more thought either 

As I recall, common large capacitors alone do next to nothing for 

smoothing ripple on AC chargers and presumably my relatively low 

frequency single phase PM alternator anyway. Perhaps less true of modern 

AC chargers that use high frequency transformers.  And then there are 

the desulphaters that intentionally add ripple (spikes actually)... 

thanks

Ken

On 03/01/2015 10:42 AM, Jim Kale wrote:

[quote] 



 I have also studied batteries for many years, although, I am not a battery

 engineer.    I too feel that ripple current has no effect on battery life.

 It could affect avionics a lot though.  On simple systems, the battery is

 often used as the only device to reduce ripple current, and it does a fair

 job at that.  I have never seen any sign of short battery life, where ripple

 current is high.

 Jim



 --

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nuckolls.bob(at)aeroelect
Guest

Posted: Sat Jan 03, 2015 9:28 am Post subject: Rotax PM regulator

At 09:42 2015-01-03, you wrote:




I have also studied batteries for many years, although, I am not a battery

engineer.    I too feel that ripple current has no effect on battery life.

It could affect avionics a lot though.  On simple systems, the battery is

often used as the only device to reduce ripple current, and it does a fair

job at that.  I have never seen any sign of short battery life, where ripple

current is high.



   One of the difficulties we face with making

   such determinations is data . . . laboratory

   data in particular. The ripple vs. service life

   effects are going to be bounded by the single

   digit percentages . . . in an operational

   environment where the effects of other variables

   are several times greater thus smothering any

   ripple/life studies in 'noise'.



   We used to teach that the battery was the ship's

   best filter for small perturbations in bus

   voltage . . . it was taught to me and I repeated

   it faithfully until I began to study system

   integration and design regulators.



   Numbers refuting the 'best filter' assertions

   were laying out on the table in profusion but

   there was a predominant notion that batteries,

   like capacitors, were these huge energy storage

   devices with similar characteristics. But aside

   from being able to store energy, similarities

   end there . . .



   An SVLA battery delivers energy at 12.5 and below.

   It gets charged at 13.8 and above. In that gray

   area between deliverance and acceptance of Joules,

   the SVLA becomes 'soggy' as mitigator of

   noise. Unlike the capacitor that presents a

   relatively constant reactance at any voltage,

   reactance of the battery rises sharply in the

   gray area between charge and discharge voltages.



   This means that batteries are not good 'filters'

   of small (+/-5%) excursions in bus voltage. This

   is why DO160 suggests that we expect and plan

   to deal with certain noises on the DC bus. See:



http://tinyurl.com/pt36wsb



   They tend to be a little better at the top

   end of the gray area (at nominal bus voltage)

   but in no instance does any salt-worthy

   system integrator rely on battery presence

   for anything but energy storage.



   During the planned studies for this year,

   I'll gather and publish data that supports

   these notions . . .



   Bob . . .

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raymondj(at)frontiernet.n
Guest

Posted: Sat Jan 03, 2015 9:48 am Post subject: Rotax PM regulator

Kinda sounds like: Be given a fair trial, and then executed. :>)



Raymond Julian

Kettle River, MN



The things we admire in men, kindness and generosity, openness, honesty, 

understanding and feeling are the concomitants of failure in our system. 

And those traits we detest, sharpness, greed, acquisitiveness, meanness, 

egotism and self-interest are the traits of success. And while men 

admire the quality of the first they love the produce of the second. 

-John Steinbeck, novelist, Nobel laureate (1902-1968)



On 01/03/2015 11:26 AM, Robert L. Nuckolls, III wrote:

-------------------SNIP--------------------------

 	  Quote: 	
		  

    During the planned studies for this year,

    I'll gather and publish data that supports

    these notions . . .



    Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Sat Jan 03, 2015 3:04 pm Post subject: Rotax PM regulator

 	  Quote: 	
		  As I recall, common large capacitors alone do next to nothing for 

smoothing ripple on AC chargers and presumably my relatively low 

frequency single phase PM alternator anyway.


	


   Even the smallest capacitor will do something . . . albeit

   tiny. One way to put a sanity check on any recommended

   capacitor is to consider the rate-of-change for voltage

   across a capacitor based on current being drawn out of or

   pumped into it.



   A good estimation can be made by calculating

   the drop between half-cycles of the full wave rectified

   ac. Assume 200 Hz alternator. Assume capacitor gets

   charged to 10V at top of each half-cycle. Let's say

   we want the capacitor to hold the output at no less than

   9.5 volts between half-cycle periods of 2.5mS.



   1 Amp impressed on 1 Farad will change its voltage

   by 1 Volt every Second or 2.5mV every 2.5mS. We're

   trying to stay in a 500mV window so the CURRENT

   can go up 200 times or 200A. To support 20A we can

   cut it to 0.1F (100K uF).



   This ball-parking exercise suggests that a 20A alternator

   would have to be 'smoothed' with 100,000mF at 200Hz

   operation to keep the ripple under 5% peak-to-peak. Of

   course, a higher frequency of operation helps as does

   a lower operating current. But that 0.1F capacitor

   estimation illustrates your assertion nicely . . .

   10 or 22KuF on a 20A Rotax alternator is not going

   to be a robust 'smoother'.

   Bob . . .

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