[ARC5] A pair of questions

[Bob Camp]

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> 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 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> 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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