[sdiy] Power-One HAA15-0.8-A Power Supply Questions

[J. Larry Hendry]

> ----- Original Message -----
> From: Scott Stites <scottnoanh at peoplepc.com>
> What is common wisdom for selecting a fuse value - does one select a fuse
as close as possible to the rated maximum current of the power supply, or
would a 1 Amp fuse for a 0.8 amp power supply be reasonable?

That's a good question that I guess depends on the power supply efficiency.
I wonder what the AC current is on a supply that has 0.8 amps of +15
and -15.  I guess the easiest would be to put load on it and tong the AC
side it at a known load and multiply up.  I have a couple of AC tongs I use
with my digital fluke. One is about the size of a clothes pin.  But, I admit
to fusing mine at about 1 amp of AC per 1 amp of +/- 15 and not thinking
more about it.

Warning OT:

Since we are on the subject of being conservative, switch failures, and tong
meters, I'll share something interesting that happen to me last Friday.  I
was directing a job to remove a 138/12KV, 44,000KVA transformer from service
at a Chrysler plant for maintenance.  With all the customer's load removed
from the transformer, the ammeter still indicated 125 amps on 1 phase at
12.5KV.  Oddly enough, that is the normal load of one of 4 capacitors on
that 12.5 KV bus.  So, I checked all the capacitor switches as "open" by
their mechanical indicators. Still puzzled, we pulled out a tong meter good
for up to 69 KV (not in everyones tool box I know) and put it over the lead
into the "open" vacuum switch.
See:  http://www.wiseguysynth.com/larry/misc/open_vac.jpg

Now, can you imagine the result of opening the disconnect associated with
this capacitor thinking the vacuum breaker was open. Since this is seriously
OT, you can e-mail me privately if you want a description.  So, I do lean
toward conservative after 2 years of messin' with this stuff.

Larry