400 Hz

Charles charlesmorris800 at centurytel.net
Sat May 8 12:32:29 CDT 2021

On 5/8/21 12:00 PM, cctalk-request at classiccmp.org wrote:
> Message: 8 Date: Fri, 7 May 2021 21:59:08 +0000 From: W2HX 
> <w2hx at w2hx.com> To: Andrew Back <andrew at carrierdetect.com>, "General 
> Discussion: On-Topic and Off-Topic Posts" <cctalk at classiccmp.org> 
> Subject: RE: 400 Hz Message-ID: 
> <de37431b96cf4c82ba5ddb2b9daf1873 at EXBE015SV3.NA02.MSEXCHANGEOUTLOOK.COM> 
> Content-Type: text/plain; charset="utf-8" I will add that aircraft are 
> one of the main users of 400 Hz. This is because weight is always an 
> critical design consideration. So with smaller transformers, smaller 
> capacitors, etc, you can save a LOT of weight on electronic devices in 
> an aircraft. 73 Eugene W2HX -----Original Message----- From: cctalk 
> <cctalk-bounces at classiccmp.org> On Behalf Of Andrew Back via cctalk 
> Sent: Wednesday, May 5, 2021 11:26 AM To: cctalk at classiccmp.org 
> Subject: Re: 400 Hz On 05/05/2021 16:07, Grant Taylor via cctalk wrote:
>> Were the higher frequencies used because it directly effected the
>> amount of time / duration in (fractions of) seconds between peaks of
>> rectified (but not yet smoothed) power?
> Haven't read the rest of the thread and so at the risk of being profoundly wrong... Benefit of 400Hz mains is that transformers can be much smaller. Think of switching power supplies that rectify to DC and then switch up into kHz, which are then able to use far smaller transformer cores than an old linear PSU. At least this is a key motivation with 115V/400Hz 3-phase aviation power AFAIK.
> By coincidence we've just built a big 28VDC power supply, so that we can run a vintage 400Hz aircraft rotary inverter, which will then be used to power up old mil surplus kit that wants this. A classic adventure in yak shaving. Anyway, here's the 28VDC bit.
> https://www.rs-online.com/designspark/constructing-a-high-current-28v-dc-power-supply

That's a very neat repackaging of the Lambda power supplies! Do they 
have the surge capability to start that rotary inverter (which may 
require a LOT more than 44 amps until the armature gets moving)... I 
hope you tested them first ;)

I bought a 1 KVA 115V 400 Hz supply, a PP-7482/G from Fair Radio back 
when they still had them ("Reparable") a few years ago. The H-bridge 
TO-3 transistors were all blown, some with holes melted through their 
lids. I replaced them with BUX48A parts and it works again. It really 
sings that A-flat though ;)

But I don't have anything to run with it! When I was young, 400 Hz 
surplus gear was a dime a dozen because no one had 400 Hz power. Now I 
do and all that gear has disappeared...


WB3JOK/0 since '76 :)

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