Re: DC Voltages

From: (Terra Corp.)
Organization: Rt66.COM, Public Internet Access in New Mexico
Date:         10 Jun 96 12:22:24 
References:   1 2 3 4
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David T. Medin ( wrote:

: In article <airliners.1996.788@ohare.Chicago.COM>, Steve Lacker <> writes:
: |> > wrote:
: |> >>
: |> >> I have a question about the 28VDC used on commercial aircraft.  Are
: |> >> there any special or unusual characteristics about this current?  I
: |> >> have a need to take the 28VDC and convert it to 12VDC in an aircraft,
: |> >> any ideas?
: The original poster didn't mention what aircraft was the target for
: the project. Make sure you check out the applicable FAA regs for
: onboard appliances. In the case of air transport category aircraft
: (most of which use 28 VDC for the battery bus), DO-160B is the most
: common standard. This is apart from the STC you might need for
: installation.

Two comments and one plug.

1)  For a 12V airplane, you want to provide *14 volts* not 12V. Twelve
volts is the battery voltage, the "system" operates on 14V, and many
avionics will start to act strange if they get less than the desired
voltage.  Our avionics want at least 11 volts and are much happier if
they get *over* 12V. The wiring between your power source and the box
being supplied can easily result in a 1 or more volt drop. Get a voltage
converter that can provide 14V out with 22-30 volts in.

2) Dave is right about verifying the FAA's requirements, but the spec he
quotes (RTCA/DO-160C) is an environmental spec only. The airworthiness
requirements are under FAR Part 21 for Air Transport A/C, and Part 23 for
general aviation.

The plug:  We, along with several avionics manufacturers, make just such
converters. Ours converts 28V to 14V and is rated at 5 amps continuous.
Contact your local avionics dealer.


  Gerry Caron               "Opinions are mine, not my employer's."            PH: 800-328-1995 or 505-884-2321
  Terra Corp.  ABQ           FAX: 505-884-2384