Power question on B737 and others
 

Greetings all...

Right behind my head on the 737NG is a pair of electrical outlets. One is 115VAC at 400Hz. There is also one in the galley that our FAs use to charge the credit card processing machine they keep on the cart.

Does anyone know the specs and/or where to get something that will "step down" the 400Hz to 50/60Hz?

I checked at my local radio shack and found no help there.

Thanks!

Frequency vs. Voltage
 

Matt:

You can't "step down" frequency--only voltage.

If you want to run a device from this socket, most items would probably be ok.

For example, if you want to plug in your cell-phone charger: the charger does step-down the voltage to something between 3 and 12 volts, depending on model. There will be diodes in the charger to change the AC to DC, and a filter--composed of capacitors, resistors, and sometimes coils, to smooth-out the peaks and valleys of the former AC current.

This capacitor-resistor-coil circuit is optimized for 60 HZ. However, the slightly "wavey" DC that would result from such a power supply with 400HZ should be OK for most phones and/or laptops, as the phone or laptop has additional Cap-res-coil circuits, and the charging of batteries doesn't really depend upon a stable frequency.

Of note: AC motors don't work with incorrect frequencies. Electric razors, and vacuum cleaners, margarita blenders (probably aren't taking these on your trips) should NOT be used with 400 HZ current!

Bottom line for common electronics: plug it in. If it works fine, use it. If it acts strange, then don't--but it shouldn't damage it.

T38 is correct. I have never had a problem with non-motorized devices such as cell phone and laptop power supplies, but the potential exists. I have heard anecdotes of FAs burning out their chargers, but they use the outlet far more often then pilots on the CRJ because it's in the galley, not the cockpit.

Those vacuum cleaners that the cleaning people use do have 400hz motors. A 60hz motor would probably work...seven times too fast, for a brief period of time :rolleyes:

You could step the frequency down using motor-generator arrangement, but that would be ridiculously complicated for the application.

Thanks for the replies, guys. I'll try a test the next time I am out.

It would seem like an easy way to convert any form of AC power to any other form of AC power would be to put it through a transformer rectifier to convert AC to DC, and then a static inverter to convert the DC to AC.

Joe

Relative Complexity
 

Joe:

Transformer-Rectifiers can be relatively small, especially if the power (Watts) is small.

Static inverters used to be electro-mechanical. Cumbersome, and prone to failure. New solid-state types are more reliable, but require very heavy-duty components to handle the amperage. That makes them expensive.

Just a quick thought...

Have you ever wondered WHY the power used aboard Boeing airplanes IS at 400hz?

'leave you with it!

Cheers...E...;)

Industry Standard
 

EWSP:

Well, its not just Boeing...it is aircraft industry standard.

Why 400Hz? That, I am not sure of.

EWSP,

Not too sure if the reason still holds today, but one of the reasons for 400 hz systems being used originally was for weight. 400 hz generators weigh less (& are smaller) than 60 hz generators. Unfortunately the 400 hz generators suffer from voltage drops more than the 60 hz brothers (lower frequency reduces loss over long distances).

& now back to other useless trivia!