[ARC5] A pair of questions

[Scott Robinson]

Folks,

Once upon a time, in the mid-1960s, my college radio station needed to 
move to a different building, as its former home was being torn down. 
The chief engineer decided that the time had come to go solid state and 
stereo., and set about designing all  the bits and pieces.

He decided to run the whole station off one power supply, 20V at 10A. Of 
course, if it failed, the whole station would be of the air, so he, er, 
overbuilt it some: transformer about 6 inches on a side, big screw 
terminal filter caps and two diodes, the kind that attach to a heat sink 
with four screws each and have 1/4 inch braid leads coming out the other 
end.

If you shorted the output, it blew the 120V breaker in the panel over on 
the wall, leaving the power supply unharmed.

I like this design!

Regards,

Scott Robinson

On 11/14/17 6:36 AM, Bob Camp wrote:
> Hi
> 
> If they are designed like the rest of the high(er) power Mean Well’s 
> I’ve used, the over current
> drops the voltage to zero for about 10 seconds. It trips around 20% over 
> the nameplate number.
> 
> The main risk on the second design is the diode bridge. The same surge 
> stuff applies there as
> well. The gotcha is that with no protection, a “once and a while” event 
> takes out the bridge. Bumping
> it up to a 1,000A bridge might be a good idea if this is going to be 
> bulletproof.
> 
> If indeed you design for the 3X number, you really are after a 225A 
> supply. Carrying that requirement
> back to the power feed gets you well into 240V land. Do you design for a 
> <1 second surge or for a
>  >20 second slow start? For the surge, they make super capacitors (a few 
> hundred farads worth !!!)
> ….20 seconds at current will trip most breakers.
> 
> Bob
> 
>> On Nov 14, 2017, at 1:04 AM, WA5CAB--- via ARC5 <arc5 at mailman.qth.net 
>> <mailto:arc5 at mailman.qth.net>> wrote:
>>
>> The problem with switchers is that their regulator circuitry allows 
>> for little to no surge rating.  The standard rule-of-thumb with large 
>> dynamotors and inverters is that the starting surge current will be at 
>> least 3X the rated FLA on the nameplate.  Four of the 37A units will 
>> probably start a DY-17 or 17A reliably.  Whether three would work or 
>> just go into foldback every time is iffy.  What would happen if you 
>> tried with just one depends upon what the regulator current limiter is 
>> programmed to do.  If it just crowbars and shuts down, at least you 
>> wouldn't hurt the dynamotor or starter relay.  If it drops the voltage 
>> in order to maintain 37A output, you will probably damage the starter 
>> relay if you aren't quick enough on the OFF switch when it starts 
>> oscillating.
>>
>> Your second idea might work, though.
>>
>> Robert Downs - Houston
>> wa5cab dot com (Web Store)
>> MVPA 9480
>>
>> In a message dated 11/13/2017 17:03:44 PM Central Standard Time, 
>> kb8tq at n1k.org <mailto:kb8tq at n1k.org> writes:
>>> Hi
>>>
>>> A pair of Mean Well RSP-1000-27 supplies running in parallel would do 
>>> the trick if
>>> you are going the swisher route. You can go bigger if you need to. 
>>> They let you run
>>> as many as 4 in parallel at one time. Each one puts out 37A at 27V. 
>>> They will adjust
>>> up to 30V on the output.
>>>
>>> The switchers have the advantage of efficiency. At 100% efficiency 
>>> you will have
>>> 17.5A at 120V going into your setup.  That will squeeze into a 20A 
>>> circuit (sort of ….)
>>> A pure linear supply (as opposed to a pre-switcher / post linear) is 
>>> not going to be
>>> very efficient…..
>>>
>>> A 140A 20V transformer and a 200A diode bridge would be another 
>>> approach. Put
>>> a few big high current  caps on the output and you have a supply. 
>>> That sort of idea
>>> has been my approach over the years …. Not much regulation, but lots 
>>> of current.
>>>
>>> Bob
>>>
>>>
>>> >On Nov 13, 2017, at 5:05 PM, Scott Robinson <spr at earthlink.net 
>>> <mailto:spr at earthlink.net>> wrote:
>>> >
>>> >A switcher rated for 75A might be cheaper, but of course it can be a 
>>> source of RF noise.
>>> >/scott
>>> >
>>
>>
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