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Sequence for bringing alternators on line.

 
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PostPosted: Tue Jun 12, 2018 2:46 pm    Post subject: Sequence for bringing alternators on line. Reply with quote

I am writing checklists for a new homebuilt I will be doing the flight testing on. Aircraft has a 40A main alternator and an SD-8 backup alternator. The alternator switch allows either the main or backup alternator to be on and also has an off position. I'm thinking of leaving the switch on the main alternator all the time, except for a test of the SD-8 during the runup. Does anyone see a problem with this plan or should I wait until the load on the electrical system has come down to a certain point before switching to the SD-8? As far as I know the SD-8 will put out whatever it can and any load in excess will simply come from the battery. 

Is it reasonable to test the SD-8 every flight or is this something that can be done on a monthly or quarterly basis? Also I have run into a couple pilots recently who start their engines with the alternator off in order to "prevent damage to the alternator during start". I can't remember any mention of this in the AEC. Is there any basis for this? Should I turn the alternator off before shutdown and then on after startup?

I have attached the main electrical system diagram for the aircraft in question.
Thank you,
Sebastien


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PostPosted: Tue Jun 12, 2018 6:07 pm    Post subject: Re: Sequence for bringing alternators on line. Reply with quote

The two relays and starter contactor should all have diodes just like the battery contactor does. Connect banded end of diodes to positive.
Can the start switch handle the start contactor coil current? Or is the E-123 Relay necessary?


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PostPosted: Wed Jun 13, 2018 7:30 am    Post subject: Sequence for bringing alternators on line. Reply with quote

Regarding the SD 20, does anybody know what its output should at 1,000 RPM (engine idle) and also at 2400 RPM Cruise?

Thanks,

Bill Hunter
On Wed, Jun 13, 2018, 11:23 Carlos Trigo <trigo(at)mail.telepac.pt (trigo(at)mail.telepac.pt)> wrote:

Quote:
Bob

Are your assertions below, about the SD-8, also valid for the SD-20 (now BC-410H)?
Thanks
Carlos

Enviado do meu iPhone

No dia 13/06/2018, às 14:19, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> 
Quote:
  The SD8 is very reliable . . . especially
  when held in reserve, It's output at
  run-up rpm will be rather limited. If you
  run up at 1800 rpm, the SD8 will be turning
  ~2340 and produce about 4A of output.

  Depending on the type and condition of
  battery . . . and system loads . . .
  you'll need to look closely at
  bus voltage to make sure it changes
  upward by any observable amount
  when turned ON.

  Testing ever so often while in-flight
  would be easier to do . . . you can also
  use the flight test to verify your plan-b
  loads such that the battery is not discharged
  during the en route phase of flight and
  held in reserve for descent, approach
  and landing.

  The risk of damaging an alternator
  or other electrowhizzies by the mismanagemet
  of alternator switches during normal operations
  is a myth. You may sequence their switching
  in any manner that makes sense to you.



  Bob . . .




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PostPosted: Wed Jun 13, 2018 12:16 pm    Post subject: Sequence for bringing alternators on line. Reply with quote

The starter contactor is a B&C S702 and SD-8 relay is included in the PMOV kit so I think the diode is built in as well.

The E-123 relay is not necessary in the current setup but this system was originally designed for P-Mags and the start switch was going to be an S2000 button. I'm guessing that the S2000 needed the relay and when it was replaced with an ACS switch the relay was left in for later conversion.
Thank you all for the replies, I'll just leave the alternator switch on Main all the time since there's no advantage to turning it off for engine start. Once the aircraft is through its test phase we plan on testing the SD-8 on an every 4 months schedule.
On Wed, Jun 13, 2018 at 6:22 AM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
Quote:
At 09:07 PM 6/12/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>

The two relays and starter contactor should all have diodes just like the battery contactor does.  Connect banded end of diodes to positive.
  Can the start switch handle the start contactor coil current?  Or is the E-123 Relay necessary?

  The ACS/Bendix/Gerdes key switch will handle
  the automotive starter contacter that's fitted
  with a supression diode. Many (like the B&C
  S702) have the diode built in. If in doubt,
  install a second one . . . two are better
  than none. The buffer relay is not necessary
  but doesn't hurt anything . . . if left in
  add the diode to it too as Joe suggests.



  Bob . . .


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