On Nov 4, 6:23 am, "Dave" wrote:
what does the voltage read when it is turned on? an rs-20a is probably not
so old that caps would go bad, and the low voltage left over when you turn
it off probably means the caps are holding a charge.

"Steve" wrote in message

ups.com...



I pulled an old Astron power supply out of mothballs today. It's a
13.8 volt / 20 amp supply (the RS-20A). I find that there's a
noticeable hum when I plug it in, and I also notice that a small
output voltage of one volt or so is measureable on it even when it's
turned off and unplugged.

What should this tell me about the condition of this supply? As it is
I'm nervous about using it.

Thanks,

Steve- Hide quoted text -

- Show quoted text -

When it's turned on the voltage reads 13.92.

Steve

Steve wrote:
When it's turned on the voltage reads 13.92.
============================
If you subsequently switch-off the unit does the output voltage rapidly
decline or is the change very slow (assuming you do not have any
external load)


Frank GM0CSZ / KN6WH

On Nov 4, 7:28 am, Highland Ham
wrote:
Steve wrote:

When it's turned on the voltage reads 13.92.
============================
If you subsequently switch-off the unit does the output voltage rapidly
decline or is the change very slow (assuming you do not have any
external load)

Frank GM0CSZ / KN6WH

The output voltage drops slowly when the unit is switched off. In
fact, I compared the voltage drop on the RS-20A to the voltage drop on
an RS-12A that I currently have in use. The voltage drop on the RS-20A
is much slower than on the RS-12A, and when the voltage has dropped
down to around 4 or 5 volts then it really slows to a snail's pace.

Steve

The output voltage drops slowly when the unit is switched off. In
fact, I compared the voltage drop on the RS-20A to the voltage drop on
an RS-12A that I currently have in use. The voltage drop on the RS-20A
is much slower than on the RS-12A, and when the voltage has dropped
down to around 4 or 5 volts then it really slows to a snail's pace.
==========
Steve , The above indicates that the electrolytic cap or caps seem to be
OK. That the output voltage on the RS-12A declines faster is that its
electrolytic cap(s) highly likely have a lower capacity value and hence
store less charge.

I do have a RS-50A (not in use) capable of delivering 13.8 V-50 Amperes
, although the terminal connectors look like only good to pass up to 20
Amperes.
There was a sticker showing input voltage 220 V but when removing it,it
shows 115 V The primary winding of the transformer must be
two times 115V. The unit works but hums heavily (the transformer sits
close to the metal enclosure).
I fear that the USA made unit is actually designed for the US power
frequency being 60 Hz ,whereas here in Europe we have 50 Hz.
For large transformers it can be unacceptable to run a unit designed for
60 Hz ,on 50Hz.
When time permits I'll have a closer look.
I would like to sell it in the USA where I shall be shortly for 2 months
,but the unit's weight is prohibitive, (19 kg or 42 lbs) to bring it as
air luggage .


Frank GM0CSZ / KN6WH