
PROBLEM : The output voltage is 0 V or very low
PROBABLE CAUSE SUGGESTED REMEDY
Input voltage is very low Check that the input voltage is 120VAC
The unit is in current limit condition Check the output terminals are not
due to overload caused by large reactive shorted. Remove the load. If the output
loading or by the output being voltage gets restored, the load is shorted
short circuited or is offering large reactive impedance.
Unit is shut down due to over Check that the fan has not failed or
temp. (SEC-1223) the vent openings are not blocked
PROBLEM : Output voltage drops as soon as the load is switched on
PROBABLE CAUSE SUGGESTED REMEDY
The unit is going into current
limit protection mode Reduce the load current to less than the
current limit value. Motors, pumps,
compressors, relays, incandescent and
halogen lamps and large capacitors in
the input section of the DC devices draw
very high inrush or starting currents of
up to 10 times their normal operating
currents. Ensure that these inrush/
starting currents are below the current
limit value of the power supply.
6.
4. Thereceivermay“hear” the power supply.Aslowlymoving, slightly
buzzingcarrierheardinthereceiver may be caused by the antenna being
too close.As with the transmitter related noise pick up, a loose coaxial
connectororabrokenoramissinggroundmay aggravate this problem.
Normallythesenoiseswillbebelowthe background or “band” noise.
Increasethe separation between the powersupplyandthe receiving
antenna.Useanoutdoorantenna.Thiswillreducetheamountofsignal
picked up from the power supply and also increase the amount of the
desiredsignal.
5. Theconducted and radiatednoises are limited as per theappli-
cablenational/internationalstandards.In NorthAmerica,the applicable
standard is as per FCC Part 15(B) for Class “B” digital devices. The
EuropeanstandardisasperEN55022,Class“B”&EN610000-3-2,3.
Thus, the RF interference is limited but not entirely eliminated.
6. The conducted RF noise from these power supplies is limited to
themaximumallowablelevels by internal filtration. The filtered RF noise
currents ( normally < 5mA ) are bypassed to the chassis of the power
supply.The chassis is, in turn, connected to the earth ground pin of theAC
inputpowercord (for Class 1 units). Thus, the filterednoise currents are
intentionally leaked to the earth ground. This is termed as the “Earth
Leakage Current”. For safety against electric shock, this earth leakage
current is also required to be limited. It will be seen that these two require-
mentsareconflicting.
NOTE: In some cases, to prevent electric shock hazard due to
abnormal leakage current (like in marinas, spas, hot
tubs, wet spaces etc.), the AC outlet circuits / receptacles
in these areas are served through a GFCI ( Ground Fault
Circuit Interrupter ). This GFCI is normally set to trip when it
senses an earth leakage current > 5 mA.Asingle GFCI may
be serving multipleAC outlet circuits / receptacles and
therefore, will be sensing the sum of all the leakage currents
of the devices connected to these.As the switching power
supplieshave intentional leakage currentasexplained above,
it may trip a GFCI feeding multipleAC outlet circuits / recep-
tacles. In such cases, disconnect devices connected to the
otherAC outlet circuits / receptacles served by this GFCI.
9.
Downloaded by
RadioAmateur.EU