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Aerospace power supply on aeroplane?

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Flyback

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We are working with a 28vdc Aerospace input which is tested to DO-160. So it is 28VDC... Does this mean that it is derived from a 3 phase distribution bus where each phase is 230VAC at 400Hz…then a three phase transformer knocks it down, then a three phase 6 pulse rectifier gives us the 28VDC?

I noted that the actual frequency range is 360Hz to 800 Hz…is this right?
We have been told the voltage ripple is 4V pkpk…so therefore I take it that this ripple will be up to 6*800Hz = 4800Hz?
 

MikeMl

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Lots of smaller modern aircraft use 28Vdc for their main power distribution. They use a 28Vdc battery system and a 28V engine-driven alternator (puts out six-phase rectified DC, battery acts as a filter, so the bus ripple is only a few mV). This is just like an automotive 14Vdc charging system, except it uses a 12cell battery instead of a 6cell battery. Both my Piper and Cessna are older models which use 14Vdc alternator systems (actually derived from automotive systems).

The alternator ripple varies with engine speed, but is typically between a few kHz up to about 10kHz. If you create ground-loops in the audio/avionics suite, you hear the alternator whine, and it is very annoying. Most factory aircraft have alternator whine in headphone audio; they don't seem to understand "single point grounding".

Only large turbine-powered Biz Jets (Falcon) and Commercial Airliners use 400Hz three-phase AC primary power.
 

Flyback

Well-Known Member
Thanks, this is for a customer who wants to install a phased array antenna on their aircraft, so i dont think it can be a small aircraft, but i could be wrong.
 

Misterbenn

Active Member
For the AC distribution there are two types, 400Hz +/-10% fixed frequency or variable frequency which is 400-800Hz +/-10%

Mike is correct regarding the 28Vdc using a battery and alternator system. buss ripple should be low however DO-160 also gives you supply under-voltage and over-voltage and transient conditions which are very important. Hold-up time and inrush current limit need to also be considered.
 
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