alt switc
Thanks for your wisdom Bud
(Hope youre well)
I was under the impression that you weren't supposed to run the alt without
batt although it is ok to run the bat without the alt. Is this incorrect?
Will
William Daniell
+1 786 878 0246
On Tue, May 12, 2020, 19:55 budyerly@msn.com <budyerly@msn.com> wrote:
>
> Will and other builders,
> It seems like the department of redundant redundancy to have a separate
> alternator and master switch. For many it is a matter of "That's the way
> we've always done it!" .
>
> The Rotax manual actually implies a switch breaker not just a fuse/circuit
> breaker (aka Off Load Fuse Switch). The Europa manual shows a switch or
> solenoid of course as does Bob Knuckles in Aeroelectric Connections
> (aircraft electrical bible).
>
> Rational for a Rotax: In the event of a battery problem, the battery has
> a switch we use to control power to and from the alternator and bus via a
> master contactor "kerchunk" solenoid or relay. Others have used a manual
> marine battery switch or as I call them "Igor Switches" which can be very
> heavy. Batteries normally do not give problems today, but if overcharged,
> they can. If a cell shorts, one may detect nasty odors, high amps, and
> isolating the battery helps shorten the problem by isolating the battery
> from the charging and aircraft bus system. In the event of a imminent
> crash landing, one should consider isolating the battery from the
> electrical system and cockpit as a spark prevention measure since we occupy
> the same space as the fuel tank.
>
> The Alternator system has had a switch for three reasons in my opinion.
> To eliminate the chance of an overcharging alternator which can damage
> avionics and over-charge a battery. Or in the event of a battery problem
> or master solenoid failure the alternator will still allow electrical power
> without the battery. Or the need to disconnect the alternator due to
> electrical fires/forced landing situation as above to kill all power.
> Hence, there is a separate alternator switch to kill any spark in our fuel
> filled cockpit from that electrical source even forward of the firewall.
> Normally we separate the alternator from the bus via the C or control
> voltage bus feed switch or a 30 amp solenoid/relay controlled by a DC
> switch.
>
> Why control the C or control voltage from the bus through a switch is, if
> the C wire is open, the regulator is shut down. Typically most in the US
> wired the alternator in this way. I have a 914 so my R,Band C wires go to
> a relay, on the firewall controlled by the cockpit alternator switch to
> simply remove the alternator power from the charge circuit on the firewall.
> (The alternator output goes through the firewall plug to the 914 Aux Boost
> Pump in the panel still, so I can't really kill all power in the panel.
> UGH!) In the event of a runaway Ducati regulator, a C wire of higher
> voltage from the bus, signals the regulator to decrease the voltage
> normally. Although highly unlikely in a B&C type alternator this can
> happen (but I haven't seen it ever). Kill the C voltage and you kill the
> faulty regulator output if the regulator is working. That said, Duati
> regulators don't tend to over volt and a crowbar or any type of over volt
> protection is not necessary either. However!
> , if using a power management system for your bus, the bus will never run
> at full alternator output voltage going to the bus, therefore, a C wire off
> one of these PTC controlled bus outputs will input a C voltage that is
> lower (nominally a half a volt) than the actual output from the regulator
> and the regulator will be forced to charge at a higher rate. Not bad for a
> LiFe type battery or even some AGM types, but could be harder on the poor
> Ducati in my opinion. In a low amp draw aircraft a little overcharge (14.5
> volts) helps some of the AGM and LiFe batteries charge better. (Note,
> supposedly there are two instances of the Schicke GR6 with LiFe has had a
> steady "voltage creep" issue in the Remos and Pipistrel climbing to 15
> volts, but not the Ducati). Today's avionics can take up to 30 volts
> without worry, it's the battery that normally can't. So I'm not a fan of
> crowbars or experimenting with alternators without switch protection and
> extensive testing. Another topic o!
> f contention we won't go to.
>
> With a 914, wired via the Rotax manual, one can isolate the battery in the
> event of a short or smoking panel and with the battery off, the alternator
> will supply power through the aux boost pump switch preventing a flame
> out. For those with the 912 series, this is not a problem.
>
> The Ducati type voltage regulator normally fails in a safe mode (dead)
> preventing a potential sparking mess on your firewall from the AC current
> being supplied by the engine stator. So very safe from runaway problems.
>
> For a simple 912 with the battery located forward of the firewall, in a
> protective battery box, AND the regulator is wired to the same contactor as
> the alternator output (R,B and C connected together) the system would be
> safe for most automotive thinking types. One switch, ON or OFF forward of
> the firewall like a auto. This system is car like as you in the cockpit
> have no control over the electrical system. It is either ON or OFF.
> Backup batteries in avionics keep power alive so one must plan how to shut
> that off quickly in an emergency also. Another topic we won't go in to.
>
> Normally a split master switch from suppliers has tabs to make the two
> switches work in unison. Those of us who are control freaks, cut these
> tabs and create a true split master/alternator.
>
> My vote is do a split master in any aircraft so one has modest control
> over the electrical system. Especially if the battery is in the baggage
> bay or essential power is necessary in the event of a master contactor
> failure or battery issue. I can run both battery and alternator or one or
> the other to isolate a problem in foreseeable emergencies.
>
> Best Regards,
> Bud Yerly
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=496297#496297
>
>
|