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europa(at)pstewart.f2s.co
Guest

Posted: Wed Jul 26, 2006 8:00 am Post subject: wiring

I have another couple of questions relating to wiring:



1. The wiring diagram in the build manual has a alternator output  

switch (capable of taking 25A). Does the OV crowbar mod take the  

place of this switch?



2. In a 914 fit, one of the fuel pumps is wired directly to the  

alternator/regulator output. In the event of a regulator failure, the  

OV mod prevents the runaway voltage frying electrics/battery. Why  

would it not fry the fuel pump and if it would,  why not wire the  

essential fuel pump directly off the battery - would you not then  

have  a working pump to get the aircraft down.



Or have I got this all mixed up again



Paul

G-GIDY

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davidjoyce(at)doctors.org
Guest

Posted: Wed Jul 26, 2006 9:58 am Post subject: wiring

Paul & Gilles, I missed the beginning of this thread, but I am impressed

that if you wire your 914 fuel pumps according to the diagram that came from

Europa with mine, then you can switch off main switch and alternator switch

and one pump carries on - supplied directly from the alternator. It wouldn't

matter if the rest of your electrics were totally fried. Alternatively you

could have a blown alternator and power the other from the battery with the

alternator switched off, and inessential electrics switched off.

          I went some way to proving the former point when I managed to

switch both Main & alternator switches off with my left trouser leg (having

lifted my leg to replace my pee bottle under the L thigh support!), over

rather inhospitable countryside near the German/Czech border - nothing but

forest. All the dials were blank but the plane went merrily on while I

sorted it out.

         The latter situation is a bit like that I found myself in having

just departed the Belgian coast for Dover, and the regulator packed up

completely. The essentials (a radio and a fuel pump) took very few amps and

I readily persuaded myself that my 16 amp/hr battery would get me to the

other side, which it did and more. So you do have electrical redundancy in

the sense that you only need either the alternator or the battery to be up

and running.

  Regards, David Joyce, G-XSDJ

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nwcmc(at)tiscali.co.uk
Guest

Posted: Wed Jul 26, 2006 10:11 am Post subject: wiring

 	  Quote: 	
		  I have another couple of questions relating to wiring:


	


 	  Quote: 	
		  1. The wiring diagram in the build manual has a alternator output  

switch (capable of taking 25A). Does the OV crowbar mod take the  

place of this switch?


	


Effectively yes. The main purpose of the switch is to be able to isolate

the PM generator (alternator) from the rest of the system in case of a

problem. It should normally be left connected to ensure that some load

is created as no load can apparently cause a problem for the regulator.



 	  Quote: 	
		  2. In a 914 fit, one of the fuel pumps is wired directly to the  

alternator/regulator output. In the event of a regulator failure, the  

OV mod prevents the runaway voltage frying electrics/battery. Why  

would it not fry the fuel pump and if it would,  why not wire the  

essential fuel pump directly off the battery - would you not then  

have  a working pump to get the aircraft down.


	


The fuel pump load is normally sufficient to keep the regulator output

within limits. If the regulator goes totally out of control it needs

isolating from the rest of the system. Although this would mean one of

the electrical pumps going off line the other will still provide

pressure. Conversely should the battery or associated switches or

busbars go offline the generator will always have a direct connection to

one of the pumps. Thus any one failure should mean that either the

battery or the generator should be able to power at least one pump. Your

suggestion does not cover the case of total battery failure. 



Nigel Charles

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m.j.gregory(at)talk21.com
Guest

Posted: Wed Jul 26, 2006 11:14 am Post subject: wiring

Paul,



While I agree that the principal reason you might wish to switch off the

alternator is because of an overvoltage malfunction, which would be taken

care of by the crowbar circuit if you fit this, it does serve also to

isolate the fuel pump that is supplied from the alternator circuit when you

put the battery master on.  This means that you are not driving this pump

when the engine is not running, e.g. during pre-start checks, programming

the GPS, etc.  It also provides an easy means of checking that the

battery-supplied pump provides pressure prior to starting.



I note that the latest Z-16 diagram for a Rotax 912/91 circuit from Bob

Nuckolls AeroElectric Connection shows his crowbar circuit driving a relay

to disconnect one of the yellow leads connecting the raw alternator output

to the regulator.  The purpose of this may be to stop the alternator from

frying a faulty regulator.



Mike Gregory

Europa Club Safety Officer



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paul.mcallister

Joined: 09 Jan 2006
Posts: 177
Location: Waukesha, WI USA

Posted: Wed Jul 26, 2006 11:52 am Post subject: wiring

Paul,



I am with Nigel and Jos on this one.  The circuit proposed by Europa (in my

analysis) falls in the category of "crude but effective".  I can't recall if

the circuit shows a CB or not, but I have a pull able circuit breaker on the

panel in case I do need to shut all fuel pumps down.



I have tested this out by disconnecting / disabling the battery/main

contactor  just to prove to myself that the pump will continue to run.



I did get a real world test when I was hit by lightning, my Kilovolt main

contactor was destroyed and for a while the only power to the pump that was

being supplied was via the direct connection of the alternator to regulator.



I heaved a big sign of relief when I turned on the secondary Ebuss and it

actually worked, actually I heaved a big sigh of relief for a lot of

reasons.



Paul

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rparigor(at)suffolk.lib.n
Guest

Posted: Wed Jul 26, 2006 11:52 am Post subject: wiring

Hello Paul



To answer your 2 questions:



1) See page #4 of the Europa Club Over-voltage Crowbar Unit Installation. 

Figure #2 is for Permanent Magnet which is what you want. The OV crowbar

mod does not take the place of the alternator output switch. It essential

puts a relay in series before the 30 amp slow blow fuse. If over-voltage

is detected, the crowbar unit will crowbar (create a short)  placed on the

5 amp circuit breaker and pop and take the Rotax Alternator (really a

generator) off line.



I chose to use Eric Jones solid state OV protection on my Rotax generator:

http://www.periheliondesign.com./lovm.htm



2) I don't absolute agree with Gilles, if wired as per Europa, if for any

reason battery is not putting out, 1 pump will run off of generator

(provided it is excited, which would have happened upon start up), that is

why there is no switch to turn it off?? If generator fails, you can run

the other pump off of battery. As far as turning off fuel flow in event of

emergency, turn off the fuel selector (not good practice to run a pump dry

if you can avoid).



Gilles has 2 batteries on his 914 install which in my opinion is better

than Europas redundancy. That said I think if you are only going to have 1

battery and only internal generator, following Europa is not such a bad

way to go. I personal would put a switch on pump #1 and some sort of light

or warn to show it is off, that way you can test output of pump #2 more

easily.



I went with on my 914 with a SD20S as primary alternator with LR3C

regulator with built in OVP and Rotax internal generator as second or

standby with Eric's solid state OVP. Schematic loose based on Bobs Z13 /

8. 1 pump main bus and 1 on endurance bus. I also have a total loss 13

cell 2200mA NiMh battery pack in the starboard headrest, in under 10

seconds can run a pump on it (redundant wires to this connector), or if

lost main battery and main alternator, can excite internal rotax, or run

endurance bus from it. Very light, yet can probably output enough to start

the 914! Model guys draw 150 amps plus from these cells.  When soaring,

and main battery fails open upon restart, in 10 seconds and can run prop

off this battery to air-start after I take main alternator off line, if no

time to cycle prop and not enough altitude to dive can probably restart

form it, then put rotax internal on line (Rotax is much happier than SD20S

ND with no battery.



More than you asked for.



Ron Parigoris

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europa flugzeug fabrik

Joined: 13 Feb 2006
Posts: 65
Location: North Coast, USA

Posted: Wed Jul 26, 2006 3:01 pm Post subject: Re: wiring

 	  europa(at)pstewart.f2s.co wrote: 	
		  In the event of a regulator failure, the OV mod prevents the runaway voltage frying electrics/battery. Why would it not fry the fuel pump... 	


I rather believe we will have a dangerous situation if OV protection removes all load, and thus sends full, high-voltage regulator output to one of the 914’s fuel pumps.



Better to let the OV condition exist, and warn with an aural or visual alarm, plus a voltmeter.  If we have say 10A load on the bus, I doubt the system could supply more than 3-4 extra volts, which isn’t going to hurt anything if for not too long. Just turn everything on and reduce RPM until volts fall to a level the battery can tolerate for a while, like 14.7V.



Unless we’re too lightly loaded on the bus (few goodies), OV protection won’t do  much.  The AC wiring from the engine is also the place to install the OV relay, but simpler than that is just a switch next to our voltmeter and warning lamp.  If lightly loaded, and we want to just cut back alternator output, a pair of 50W resistors in parallel, value selected to douse the watts we need to pull the volts down, should work.  Switch “unbypasses” the resistors in the AC circuit.  This would not require us to have only battery keeping the pump running.



Fred F.

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europa(at)pstewart.f2s.co
Guest

Posted: Thu Jul 27, 2006 12:31 am Post subject: wiring

Thanks all for the discussion.



As a follow up.  What sort of switch have folk used to switch the  

alternator/regulator  output?



Paul

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ami(at)mcfadyean.freeserv
Guest

Posted: Thu Jul 27, 2006 2:21 pm Post subject: wiring

Honeywell locking toggle (i.e. the type where the toggle has to be pulled 

out against a spring before moving).



Duncan McF.



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