[ARC5] High current 28VDC power supply?

[JAMES FALLS]

I lucked out and a car lkeague have me a couple hefty 28 V transformers so I built one to feed my PE-73 and BC-375. I used NTC thermistors to help the parallel bridge rectifiers live longer. The design was basic, but worked well. 

Jim Falls K6FWT 

> On Dec 28, 2022, at 10:05, Charles via ARC5 <arc5 at mailman.qth.net> wrote:
> 
> The problem is the startup current. Dynamotors typically need a starting surge of (IIRC) about six times the nameplate rating. Switchers cannot put out more than their rated current for even a brief surge without shutting down. There are various crutches such as large capacitors (and relays to avoid shutdown when they're discharged initially), or float batteries, but there's no substitute for a brute-force linear (transformer/rectifier/capacitor) power supply.
> 
> I have a 2 KVA 400 Hz aircraft rotary converter that is rated at 27.5 VDC, 115 amps. It takes a peak of over 700 amps for the first tenth of a second! So I built a power supply capable of doing that :) Transformer weighs 41 lbs and it runs on 240 VAC input.
> 
> -Charles
> 
>> On 12/28/22 11:32, arc5-request at mailman.qth.net wrote:
>> Date: Wed, 28 Dec 2022 17:31:53 +0000
>> From: Adam Castellani <adamcastellani at yahoo.com>
>> To: arc5 at mailman.qth.net
>> Subject: [ARC5] High current 28VDC power supply?
>> Message-ID: <085EF965-E98C-476C-8013-9246CD7305DF at yahoo.com>
>> Content-Type: text/plain; charset="us-ascii"
>> 
>> Hope the experienced and bright minds here might add their views on the suitability of this unit <https://uk.farnell.com/tdk-lambda/rws-600b-24/ac-dc-conv-1-o-p-24v-25a-600w/dp/2444011?st=600%20watt>, a 600 watt, 25 amp switcher adjustable from 21.6 to 27.6 volts for command and liaison set use.
>> 
>> 1) Do you think 25 amps will be enough to power both a DM-33 and single DM-32 simultaneously as part of a complete SCR-274-N? (actually the transmitter portion is SCR and the receiver portion and modulator are ARA ATA)
>> 
>> 2) How about starting a PE-73 dynamotor to power a BC-375?
>> 
>> 3) Could the 25 amp unit simultaneously power a BC-375 and BC-348 as part of a complete SCR-287?
>> 
>> 4) Would it have a hope of powering both an SCR-287 and an SCR-274-N at the same time?
>> 
>> In addition to the PP-1104-C units, which I wish were available in the UK, are there other ready built PSUs worth considering?
>> 
>> The 25 amp models are available. Unfortunately, the next size up <https://www.farnell.com/datasheets/3651152.pdf> which is 1000 watts, 42 amps adjustable from 20.4 to 28.8 volts is on back order for a year.
>> 
>> Thank you for your views and help. Photographs of these two projects are here <https://i.imgur.com/Tfeb5vg.jpg>, here <https://i.imgur.com/Bo124sl.jpg>, here <https://i.imgur.com/rLCeL3M.jpg> and here <https://i.imgur.com/95VhA7U.jpg>.
>> 
>> Merry Christmas and Happy New Year,
>> Adam
> <IMG_20220324_171445.jpg>
> <IMG_20220324_171525.jpg>
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