[ARC5] Vibrator Power Supplies

[Michael Hanz]

If you look into the current and frequency limitations (and frequency 
stability) of vibrator contacts, you will discover your answer.  The 
need for AC distribution in aircraft skyrocketed in the last two years 
of the war with new loads like high power radars, servomechanisms for 
gun training, and the like.  The engineers quickly (and correctly) 
realized that aircraft primary AC power architecture needed to evolve to 
a common environment to be reliable and eliminate the dozens of small 
supplies (dynamotor and vibrator based) that had reliability and 
economic cost issues.  That meant going to a robust AC environment.  The 
Navy actually started this trend with engine mounted AC 
generators...they just chose the wrong frequency.

The stopgap solution for AC followed the old pattern of small(ish) 1kW 
inverters at first, like the 800-1 for 800~ and the MG-149(*) for 400~, 
but they were unsatisfactory for reasons which have been described 
here.  I have an NOS MG-149F that I tried to use for the surveillance 
suite in the "flight deck" for a while (AN/APR-4, AN/ARR-5 and AN/ARR-7 
receivers, along with their matching AN/APA-10 panadapter.)  Rather than 
the conventional carbon pile regulator, it uses a centrifugal switch to 
maintain voltage and frequency, and the constant switching required a 
hefty filter in the doghouse on the inverter.  But that wasn't the 
irritating part.  The constant switching causes the trace on the 
panadapter to frequently jump vertically up and down, making it hard to 
follow as you tune one of the receivers through a band of frequencies.  
It drive you nuts. Ever-larger inverters were designed and installed - 
the one for the APQ-13 radar in the Enola Gay is twice the size of the 
MG-149s used up front for the navigation equipment.  That trend 
continued for some time after the war, with rotary inverters requiring 
100-200 amperes of 28vdc to maintain three phase power needs to specific 
equipment.  But it wasn't to last, any more than we would want rotary 
inverters in our homes, all supplied from an Edison DC power supplier.

73,
  - Mike  KC4TOS

On 11/20/2017 8:32 PM, J Mcvey via ARC5 wrote:
> They did use vibrators in a lot of WWII equipment. BC659/620 series 
> and and BC1306 were just a few examples of that.
> Why they didn't use them in aviation may have something to with the 
> altitude and temperatures they may be exposed to?
>
>
> On Monday, November 20, 2017 8:12 PM, Robert Eleazer 
> <releazer at earthlink.net> wrote:
>
>
> The 800 HZ discussions have led me to once more wonder about 
> vibrator power supplies.  I have 1945 vintage Aviation magazines that 
> have full page ads for this wonderful new invention (the same mags 
> advertise something new called the Phillips Screw).  And I have an old 
> Heathkit VP-1 vibrator power supply that produces 60 ma at 250V with a 
> 12VDC input.  Let's see, now, do we know of any WWII aircraft 
> electronics that require that kind of power?
> As far as higher power outputs I have the transformers from an RCA UHF 
> Carfone I bought for $1.00 that are for a vibrator power supply.  I 
> don't know how much power that can handle but it is probably far more 
> than an SCR-522 or ARC-3 would require.  That set had 6146B's, I think
>
> So do we know why vibrator power supplies did not come out in the late 
> 1930's and get used in WWII?
> Thanks,
>
> Wayne
> WB5WSV
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