Ed Anderson
Joined: 10 Jan 2006
Posts: 475
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 Posted: Mon Jun 29, 2009 1:48 pm Post subject: Time to Battery Exhaustion: RE: Lee KR-2 System Architecture |
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Having had some recent real-world experience with battery exhaustion, I
though some of you might be interested in actual flight duration with all
systems on - until the battery voltage dropped below that necessary to run
crucial flight systems.
Without going into the "why it happened - switch in wrong place, deficient
design" as that has already been posted to this forum, rather this is the
following systems I had on during the period of battery-only powered flight:
1. Engine started from battery (naturally) after refueling - no recharging
after start - due to switch in wrong position.
2. Two 50 watt Landing lights ON (my normal practice for take off and
landing)
3. Two High pressure EFI fuel pumps (probably drawing 4-5 amps each)
4. One 6 psi boost pump
5. 4 electronic fuel injectors
6. 2 ignition modules
7. 1 radio
8. 1 transponder
9. 1 Gps
10. 1 Strobe light on
I took off with a 1 1/2 year old PC 680 Odyssey battery (which as I
mentioned above did not get alternator recharge after engine start - so was
somewhat depleted).
I took off and flew for 45 minutes before (dropping battery voltage) started
to manifest itself in undesirable and very noticeable ways. Approx 50
minutes after take off I found the engine would no longer run - prop
stopped. Approx 54 minutes after take off while in engine-out glide to Craig
Field, Selma, Al. The master relay (held closed by battery voltage) gave up
and removed the alternator and therefore all power from the system. Dead
panel, dead engine - rather lonely. Did get one radio call off before panel
went dead.
No - low battery voltage will not show up if your voltmeter and low voltage
warning LED happens to be on the alternator circuit and the battery is
disconnected from the alternator - which is one of the reasons I had problem
convincing myself it was anything other than a fuel problem - but, it was
solely electrical, inadvertently (you don't think I did it on purpose do
you?) induced by the pilot and supported by a design deficiency - no
isolation diode between battery and alternator only a switch(which ended up
in the wrong position).
Next morning, once switch was placed in the proper position (connecting
battery to alternator) a test flight was made and all checked out and I
continued on to Texas. Flew back with no incident. However, I doubt the
battery would do as well a second time as the voltage had dropped to 6 volts
by the time I checked on the ground. From what I understand is that once a
battery undergoes that degree of discharge, its capacity is less than it
was.
The battery is rated at 17 AH, don't know how much the engine start drained
but at 400 amp for say 5 second for engine start = 0.55 amp-hour leaving
theoretically 16.45 amp hour in the battery. Flew for 45 minutes before the
dropping voltage started undesirable things happening so 45/60 = .75 hour of
battery powered flight. That theoretically would indicate a 16.45/.75 = 21
amp/hour load. Clearly lots of estimation here but that load (with two 50
watt landing lights on) does not seem unreasonable to me. YMMV
But all things considered - the battery did a credible job of lasting as
long as it did. Just wanted to post a real world example of battery power
duration.
Lessons learned - stick in the isolation diode so battery will get
alternator juice regardless of essential bus switch
position
- Put check of Essential bus switch on emergency as well
as regular check list
- Don't fixate on what you "THINK" the problem is, check
both fuel and electrical
Ed Anderson
Rv-6A N494BW Rotary Powered
Matthews, NC
eanderson(at)carolina.rr.com
http://www.andersonee.com
http://www.dmack.net/mazda/index.html
http://www.flyrotary.com/
http://members.cox.net/rogersda/rotary/configs.htm#N494BW
http://www.rotaryaviation.com/Rotorhead%20Truth.htm
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_________________
Ed Anderson
Rv-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com |
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