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Battery disconnect.........

 
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Fergus Kyle



Joined: 03 Jun 2007
Posts: 291
Location: Burlington ON Canada

PostPosted: Wed Apr 08, 2009 1:21 pm    Post subject: Battery disconnect......... Reply with quote

Cheers,
I for one am indebted to OCBaker and RNuckolls for the exchange of
views recently - prompted by a question of battery disconnect under load.
This is must-read material for all us newbies in the build status.
My question is prompted by the above. I have built a coming monster
due to wanting to populate it with amateur radio "electro-whizzies" (as Bob
says). This brought me to wondering how I can reduce longterm demands on
current supply. I have a 914 which requires constant electrons for
electrical fuel pumps. I added an SD20S but a 100watt HF transceiver can eat
20amps easily, I know (car history).
This led to the idea that the master contactor wants an amp or so all its
life - that is a lot of juice - a thousand amp-hours if I don't prang. SO I
installed a racing car cutoff switch instead on the firewall with an
eleven-inch wooden key through a hole on the instru panel. If you can
recognize the hole for what it is, you might steal the machine by
fabricating my key.
My question is:
Have I done a useful thing? What is the expected useful life of a fairly
simple (and supposedly rugged) device compared to these usual contactors?
[Price was also a pleasantry].
Expectently, Ferg


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christoph.both(at)acadiau
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PostPosted: Wed Apr 08, 2009 6:50 pm    Post subject: Battery disconnect......... Reply with quote

Hi Ferg,
I thought about this a lot while designing my panel. In the end I
decided to go with a 150 amp continuous, 500 amp peak switch from a
marine supplier. Same idea as you: have it mounted on the firewall side
and drilled a hole through the instrument panel where I can insert a RED
key. Panel comes off in under 1 minute.

ON-OFF markings for everyone to notice when leaving the aircraft or
during emergency landings. However, I have it mounted on the co-pilot
side, within view of the pilot. Saves me the special long key through
the instrument panel to reach the firewall in case things get heated up
in the cockpit. If I manage to get the battery mounted starboard forward
engine compartment the lead between battery and starter will be
extremely short (under 1 foot), saving weight and giving full voltage on
starting my 912S. I have a classic engine mount and installed the
standard engine starter.

Without the battery solenoid (more prone to failure than a big size
marine switch believe me!) it saves me at least 1 ampere of load on the
electrical system which I designed to draw no more than 2.5 without
strobes then (5 amp with single strobe). I have Microair transceiver and
Transponder pair).

Furthermore, I have glider wings in the waiting and need to keep the
current down while gliding. So I have a 3 way panel master avionics
switch planned which has 3 modes: OFF - ON - GLIDER. The glider
essential bus services only essential electronics and will draw less
than 1.5 amps/hr. That gives me 3 hrs glider flying without draining the
16 AH main battery too much for a secure start. It would be easy to
power the glider essential bus with a small NIMH battery (RC Car 10
cell) I take home after flying. Cost me maybe $40 at the most. Marine
switch was $30. You can start a truck with this. RNuckols is, I agree,
an absolute must read.

Christoph
(at)223 Wolfville, Nova Scotia

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frans(at)paardnatuurlijk.
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PostPosted: Thu Apr 09, 2009 1:42 am    Post subject: Battery disconnect......... Reply with quote

Fergus Kyle wrote:
Quote:
My question is prompted by the above. I have built a coming monster
due to wanting to populate it with amateur radio "electro-whizzies" (as Bob
says). This brought me to wondering how I can reduce longterm demands on
current supply.

Here are some ideas:
1) Spend more time listening than transmitting. With a duty cycle of
25%, you need only one quarter of the alternator supply. During
listening it can charge the battery, and during transmissions the
battery can supply part of the power.
2) Go QRP. Or at least, use only half te power. 3dB less signal is
barely noticable on the other end, but cuts the power demands in half.
It has the advantages of causing less RF-related troubles in the ship as
well.
3) Use SSB with not too much compression.

Quote:
I added an SD20S but a 100watt HF transceiver can eat
20amps easily, I know (car history).

Yes, on constant carrier. But why would you want to do that?
With SSB with a reasonable compression power demand would go down to 5
amps average, with 3db reduction it is already down to 2.5 amps, and
with a duty cycle of 25%, your average power demand would actually be
less than 1 amp.
So what is your problem?

Quote:
This led to the idea that the master contactor wants an amp or so all its

Well, electronic shops sell relais (mainly targeted to the car industry)
capable of handling 40 amps, and using less than 200mA or so for the coil.

Quote:
My question is:
Have I done a useful thing? What is the expected useful life of a fairly
simple (and supposedly rugged) device compared to these usual contactors?

Well, to be honest, I don't find it useful (otherwise I would have done
something similar Wink ). I too have a SD20S, but a split main battery so
I have fully separate electrical systems, and switch them with high
quality "car-type" relais (with good paperwork) to keep the unswitched
leads as short as possible for highest safety and have the power
switches at a logical and convenient location at the same time. And in
the very unlikely case that a relais would fail, I would always have
another independent bus going. I would without hesistation connect my
Icom-706 to this electrical system, without any other changes than
bonding all electrical parts of the airplane together and installing
bridges over all hinges and bearings to minimise receiver noise (which
is most likely going to be your biggest challenge). I also suspect that
you are going to need to do "something" to the ignition system of the
Rotax which is probably designed for max performance and reliability,
and not for best RFI-suppression on the HF-bands.

Frans


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