[Milsurplus] power supply question

[Jim Whartenby]

OK, take two,If the line rectifiers have a relatively long reverse recovery time then they may not be able to turn off fast enough at the higher line frequency.  If so, they may get quite hot.  Faster switching power diodes will then be needed to replace the original rectifiers. AFAIK, when you calculate the filter inductance and capacitance values needed, you are looking for minimum values.  Larger values of inductance and capacitance do not help all that much in the filtering process but they do provide a safety margin for parts on the low side of their tolerance.  
Larger caps will increase the charging current so IR losses will increase.  At higher AC line frequencies, larger inductors may counter the current demand of the larger capacitors.  Don't know if it is a wash or if there are parasitic elements in the 60 or 120 cycle inductors and capacitors that will become dominate at a higher line frequency?
AC power is considered a pure sinewave but there seems to be a lot of trash along for the ride.  We don't know if the designer had taken this into account or not.  Sounds like a test is needed with the power supply lightly loaded to see if any components get hot.  If it passes this test, then see if the power supply can supply rated voltage and current at the higher line frequency.YMMV,Jim

Logic: Method used to arrive at the wrong conclusion, with confidence.  Murphy

-----Original Message-----
From: Jack Antonio <scr287 at att.net>
To: milsurplus at mailman.qth.net
Sent: Sat, Jul 23, 2022 8:45 am
Subject: Re: [Milsurplus] power supply question

I'm not trying to make 400 or 800 cycle, I'm wondering if there is any 
problem in running
one of these switching type supplies *from*  a 400 or 800  cycle 
source.  Is there some
limiting factor that restricts it to a 50 or 60 cycle input?

Jack Antonio
WA7DIA


On 7/23/2022 9:33 AM, Jim Whartenby via Milsurplus wrote:
> Jack
> I successfully converted an older APC computer UPS to 400 cycles, see 
> ER 282, November 2012.
>
> I would think that any power supply that directly rectifies the AC 
> line or charges a battery like the above APC power supply is a 
> candidate.  There are several articles on the web that show various 
> solutions.
>
> eBay item # 223984571313, SG3525 LM358 Inverter Driver Board Preamp 
> Drive Board 12-24V, has all of the electronics, excluding the power 
> transformer, rectifier and filter.  The schematic for this module is 
> available on the web, just takes a little searching.  Since it uses 
> the SG3525, a resistor or capacitor or both will change the switching 
> frequency to any frequency desired.  You can use either a center 
> tapped power transformer or one without a center tap.  Did I mention 
> that this module goes for $3.02?
> Jim
>
> Logic: Method used to arrive at the wrong conclusion, with 
> confidence.  Murphy
>
>
> -----Original Message-----
> From: Jack Antonio <scr287 at att.net>
> To: milsurplus at mailman.qth.net <milsurplus at mailman.qth.net>
> Sent: Fri, Jul 22, 2022 3:42 pm
> Subject: [Milsurplus] power supply question
>
> Regarding switching type computer and modular power supplies.
>
> Will they work on 400 Hz , or even possibly 800 Hz power?
>
> Off hand, you'd think so. as generally they rectify the AC line to make
> DC, but is there something that ties them to strictly 60 Hz?
>
> Thought I'd ask before I blow something up.
>
> Thanks
>
> Jack Antonio
> WA7DIA
>
>
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