[ARC5] A pair of questions

[Michael Hanz]

On 11/14/2017 10:44 AM, Craig wrote:

> Hey guys, I'm basing my load information off what I can find in the 
> various manuals that I have, and giving myself some padding. The 
> SCR-274 book shows something around 15 amps for the configuration my 
> airplane had. When you delve into the SCR-269 books, the info get 
> really screwy. One book lists the input power as only .5 amps @ 24VDC, 
> but when you look at the schematics, it has internal fuses of 20 or 35 
> amps for the inverters, depending on which one gets installed, if I'm 
> understanding the drawings correctly. It also has another call out for 
> either a 2 amp or 5 amp fuse for power in the same section of the 
> book. What else is weird, is that the marker beacon receiver gets it's 
> power from the -269 and it draws about .5 amps itself.

It might be useful to get back to basics for a moment.  With the lineup 
below, I am assuming you are sticking with a 28v DC supply for all of 
those components.  That rules out the PE-109, which is 14v input.  The 
SCR-269 manual states that the 28vdc load is a maximum of 1.95 amps 
(when the bandswitch is operating) and the corresponding AC power 
consumption is .85 amp at 115vac.  That's 98 volt-amperes of 400Hz 
power.  Further on, in paragraph 9.c.(13)(c) */Separate Inverter Power 
Supply/*, it says to use a 250va inverter. A 250va inverter should have 
a 20 amp fuse in the 28vdc line because of starting current.  Its actual 
_running_ current will be somewhere in the 5-7 amp region with the 
SCR-269 load even with the beacon receiver being supplied.  The RC-36 
interphone dynamotor is a PE-86, which is basically just another command 
receiver dynamotor. So your largest starting current in that lineup will 
be the DM-33, and the timing of that one will depend on if you are going 
to use voice or CW.  As I think someone else mentioned, starting them up 
sequentially should lessen your 28v power supply requirements by quite a 
bit.  That's the way they did it back in the day, IIRC.

I'm a little confused about your operational concept, though.  You 
started out talking about a test bench supply, and then shifted to 
actual aircraft wiring diagrams, so does your 28vdc power supply need to 
eventually handle both for test purposes?

           73,
  - Mike  KC4TOS

> Here is a quick run down on what has to be powered:
> BC-696 Transmitter
> BC-458 Transmitter
> BC-453 Receiver
> BC-454 Receiver
> BC-455 Receiver
> BC-456 Modulator
> RC-43 Marker Beacon
> RC-36 Interphone
> SCR-269 Compass system
>
> There are a total of 5 dynamotors and 1 inverter that power all this 
> equipment. There are  (3) DM-32's, (1) DM-33, (1) PE-86 and (1) PE-89 
> or PE-109. There is one more big inverter that provides more 115/400cy 
> and some 26/400cy power for other things onboard, but that isn't 
> included, as it's a huge power hog (250 watts per phase). It's 
> probably why each engine run a 100 amp generator.
>
> I probably need to dig out the microfilm and chase down the wiring 
> diagrams for the power panels, as they have breakers and fuses that 
> range from 1 amp to 100 amps, all accessible from the cockpit, and I 
> can't tell from what I have on the desk here, what goes with what 
> circuit.
>
> Craig
> ______________________________________________________________ 

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