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SELF EXCITING DUAL POWER SUPPLY WITH OCM

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Peter H

Joined: 20 Mar 2007
Posts: 197

Posted: Sat Apr 28, 2007 11:41 pm Post subject: SELF EXCITING DUAL POWER SUPPLY WITH OCM

Hi again, more questions,  

As a newbie I get to make my share of mistakes. I have taken the liberty to modify Z-25 to show an over current module and a dual power outlet for the essential bus and I would welcome some guidance along the following lines:  

<![if !supportLists]>1.                   <![endif]>The OCM item A I inherited from another project, a Norton rotary engine install with 3 phase solid state regulator rectifier. It is supposed to protect against over current from a short in the alternator or on the battery side. Question : Should I keep it ? Is it in the right place ?  

<![if !supportLists]>2.                   <![endif]> Is the dual alternate feed path for the dual supply to eBus OK ?  It should supply from the self excited PM alternator/regulator, or from the battery, or both (normally both) Should those two switches be protected ? How ?  

<![if !supportLists]>3.                   <![endif]>Should I consider a switching sequence for start up and shut down ? Details?  

   

If you read this far you will know that I have just enough knowhow to get into trouble and I would appreciate any comments. If the html diagram does not post below I will set it up in the pictures section.  

Thanks  

Peter                [img]cid:image001.jpg(at)01C78A84.B656DA90[/img]

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Gilles.Thesee(at)ac-greno
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Posted: Sun Apr 29, 2007 1:36 am Post subject: SELF EXCITING DUAL POWER SUPPLY WITH OCM

Peter,



 	  Quote: 	
		   1.                   The OCM item A I inherited from another project, 

 a Norton rotary engine install with 3 phase solid state regulator 

 rectifier. It is supposed to protect against over current from a short 

 in the alternator or on the battery side. Question : Should I keep it ?




	


Your diagram already shows a fuselink. With your setup I would install 

it direct at the battery positive post. I always choose the simplest, 

lightest, least expensive device.

This module seems to include a 30 amp CB. This means running a fat wire 

from the battery + to the intended location.



 	  Quote: 	
		   2.                    Is the dual alternate feed path for the dual 

 supply to eBus OK ? It should supply from the self excited PM 

 alternator/regulator, or from the battery, or both (normally both)




	


That's a lot of switches to manage. What purpose did you say the dual 

E-bus supply was for ?



 	  Quote: 	
		   Should those two switches be protected ? How ?




	


I would protect the E-bus alt feed with a fuselink or something direct 

at the battery.



 	  Quote: 	
		   3.                   Should I consider a switching sequence for start 

 up and shut down ? Details?



Since those switches are "alternate feedpath", I would leave them always 
	


open except in case of alternator loss (real or simulated). In that 

case, I'm trying to figure out why you would need the "direct from 

alternator" path ?

Especially if you decide not to (or forget to) close the alternator switch.

Please note that the OV module will only work when the alternator switch 

is closed. In a worst case situation, you may well fry your avionics 

while attempting to sort out an OV event and closing the wrong switch. 

Better leave this "alternate alternate" out.



The Jabiru is a simple engine. If it were up to me, I'd control the 

alternator through the master switch, a' la figure Z16.



Best regards,

Gilles

http://contrails.free.fr



 	  Quote:

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Peter H

Joined: 20 Mar 2007
Posts: 197

Posted: Sun Apr 29, 2007 1:53 pm Post subject: SELF EXCITING DUAL POWER SUPPLY WITH OCM

Thanks Gilles,

The principle is to make use of the self excitation feature to make a dual

power supply that would work either from the battery or from the alternator

or both. I am planning to fit EFI to the Jabiru 3300.



Re 1. Suppose I would quit the fuse link in favour of the OCM which

automatically resets. ? It could be relocated closer to the battery.



2.	The dual ebus is for the EFI covering an ECU and a fuel pump. It

could also supply a single electronic ignition module and I would plan for

say 8A I was planning to leave those switches normally closed and opened

only if for some reason I wanted to isolate from either the battery or the

alternator. Ie that is not an alternative path it is for the sole supply for

the EFI.



3.    I overlooked the need for the alt relay to be closed. I would want to

connect that line to the alternator side of the alt relay and protect it?



What do you think?

Thanks for the help.

Peter 



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Gilles.Thesee(at)ac-greno
Guest

Posted: Mon Apr 30, 2007 10:35 am Post subject: SELF EXCITING DUAL POWER SUPPLY WITH OCM

Hi Peter,

 	  Quote: 	
		   Re 1. Suppose I would quit the fuse link in favour of the OCM which

 automatically resets. ? It could be relocated closer to the battery.

   


	


I would be wary of any system automatically resetting without me being 

in the loop.



 	  Quote: 	
		   2.	The dual ebus is for the EFI covering an ECU and a fuel pump. It

 could also supply a single electronic ignition module and I would plan for

 say 8A I was planning to leave those switches normally closed and opened

 only if for some reason I wanted to isolate from either the battery or the

 alternator. Ie that is not an alternative path it is for the sole supply for

 the EFI.



   


	


I understand your engine setup is to be electrically dependent.

I had the same problem and solved it with figure Z16 and an auxiliary 

battery to feed the fuel pump as a last resort. The aux battery only 

connects when the bus voltage is above 13 volts, and automatically 

disconnects when bus voltage falls below 13V (dead alternator/regulator, 

flat main battery, etc.).

According to the Jabiru engine groups, the Jabiru voltage regulator has 

a less-than-stellar service reliability. The safest current source in 

your airplane is a well charged battery.



 	  Quote: 	
		   3.    I overlooked the need for the alt relay to be closed. I would want to

 connect that line to the alternator side of the alt relay and protect it?

   


	


Not sure to clearly see what circumstances would lead to the necessity 

to use the alternator and not the battery ?

Rememeber that the more switches you have to manage, the more likely 

pilot errors.



Best regards,

Gilles

http://contrails.free.fr

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Peter H

Joined: 20 Mar 2007
Posts: 197

Posted: Mon Apr 30, 2007 4:09 pm Post subject: SELF EXCITING DUAL POWER SUPPLY WITH OCM

I have just realized that the alternator disconnect relay in Z25 is wired to

trip by the OVM and isolate the alternator if there is a spike but I am

thinking that I would not want to disconnect for the sake of a transient

which could be taken by the OVM safely to earth .

But does the OVM have sufficient current capacity to carry for a failed

regulator? Can we assume that the PM alternator will be saturated at about

20A ?

( I will run out of questions soon I promise)

Peter

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klehman(at)albedo.net
Guest

Posted: Tue May 01, 2007 5:36 am Post subject: SELF EXCITING DUAL POWER SUPPLY WITH OCM

Peter



Yes we like to use diodes or something to recycle the inductive energy 

when things like contactor coils are de-energised. However for practical 

purposes, spikes or "transients" capable of doing damage don't really 

exist in our systems.



An OVM tripping event is not instantaneous. If the overvoltage lasts 

long enough to trip the OVM, then it is about long enough to fry most 

devices (such as transorbs) designed to limit/absorb excess 

voltage/energy. Further, if the overvoltage is that long, it is most 

certainly coming from an out of control alternator and you want that 

disconnected before it can damage other electronics such as your EFI. 

 Yes the OVM can limit the voltage for the few tens of milliseconds that 

it will take for the relay to open.



For a more direct answer to your question:

A 20 amp PM alternator won't put out much more than 20 amps under any 

circumstances but little solid state protective devices can only absorb 

that kind of power for a few millecseconds, thus the need to disconnect.



I have never had a false OVM trip with either of my OVM's that are of 

the current design. I have had real trips when my PM regulator failed. 

Nothing else was damaged. If it trips you can always turn it back on and 

watch it trip again if the voltage still rises too high.



You definately want notification of low voltage to warn you of a trip or 

alternator failure. My Grand Rapids EIS with the Big Red flashing Light 

is effective for that.



Ken



PS-Being on a dial up connection, I have not looked at your diagrams.



Peter Harris wrote:



 	  Quote: 	
		  



I have just realized that the alternator disconnect relay in Z25 is wired to

trip by the OVM and isolate the alternator if there is a spike but I am

thinking that I would not want to disconnect for the sake of a transient

which could be taken by the OVM safely to earth .

But does the OVM have sufficient current capacity to carry for a failed

regulator? Can we assume that the PM alternator will be saturated at about

20A ?

( I will run out of questions soon I promise)

Peter

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Peter H

Joined: 20 Mar 2007
Posts: 197

Posted: Tue May 01, 2007 1:53 pm Post subject: SELF EXCITING DUAL POWER SUPPLY WITH OCM

Thanks Ken that clears it for me and now I know with certainty to use the

alternator contactor relay/OVM .

I understand that the OVM will trip before damage to the remainder of the

circuit.

Peter



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