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CHARACTERISTICS OF SINUSOIDAL AC POWER

Voltage, current, power factor, types of loads

The voltage waveform of 120 VAC, 60 Hz mains / utility power is like a sine wave. In 
a voltage with a sine wave-form, the instantaneous value and polarity of the voltage 
varies with respect to time and the wave-form is like a sine wave. In one cycle, it 
slowly rises in the positive direction from 0 V to a peak positive value 

+ Vpeak

 = 170 

V, slowly drops to 0 V, changes the polarity to negative direction and slowly increases 
in the negative direction to a peak negative value 

- Vpeak

 =170 V and then slowly 

drops back to 0 V.  There are 60 such cycles in 1 sec. Cycles per second is called the 

frequency

” and is also termed “

Hertz (Hz.)

. If a linear load is connected to this type 

of voltage, the load will draw current which will also have the same sine wave-form. 
However, the peak value of the current will depend upon the impedance of the load. 
Also, the phase of the sine wave-form of the current drawn by the linear load may 
be the same or lead / lag the phase of sine wave-form of the voltage. This phase 
difference determines the “

Power Factor 

(mathematically = the cosine of the phase 

difference)” of the load. In a 

resistive type of load

 (like incandescent lamps, heaters 

etc) the sine wave-form of the current drawn by the load has 0 phase difference 
with the sine wave-form of the voltage of the AC power source. The Power Factor 
of a resistive load is unity (1). 

The rated output power (in Watts) of the inverters is 

normally specified for resistive type of loads that have unity (1) Power Factor. 

In a 

reactive type of load 

(like electric motor driven loads, fluorescent lights, computers, 

audio / video equipment etc), the phase of the sine wave-form of the current drawn 
by the load may lead or lag the sine wave-form of the AC voltage source. In this case, 
the power factor of reactive loads is lower than unity (1) – generally between 0.8 and 
0.6. 

A reactive load reduces the effective wattage that can be delivered by an AC 

power source.  

RMS and peak values

As explained above, in a sine wave, the instantaneous values of AC voltage 

(Volt, V)

 

and current 

(Ampere, A)

 vary with time. Two values are commonly used – Root Mean 

Square 

(RMS)

 value and peak value. For simplicity, RMS value can be considered as an 

average value. 

Mathematically, Peak Value = 1.414 x RMS value. 

For example, the 120 

VAC, 60 Hz. mains / utility power is the RMS value. The peak value corresponding to 
this is = 1.414 x 120 = 170V.

The values of the rated output voltage and current of an AC power source are their 
RMS values 

AC power – Watts / VA

The power rating of an AC power source is designated in Volt Amperes (VA) or in 
Watts (W)
Power in Volt Amperes (VA) = RMS Volts (V) x RMS Amps (A)
Power in Watts = RMS Volts (V) x RMS Amps (A) x Power Factor

NOTE :   The rated power of the inverter in Watts (W) is normally designated for a 

linear, resistive type of load that draws linear current at unity (1) power 
factor. If the load is linear and reactive type, the rated power of the inverter 
in watts will be limited to its normal rated power in watts (W) x Power 
Factor. For example, an inverter rated for 1000 W ( at unity power factor) 
will be able to deliver only 600 watts to a reactive type of load with a 
power factor of 0.6. 

Summary of Contents for PST-30S-12A

Page 1: ...300 Watt Pure Sine Wave DC AC Inverter PST 30S 12A PST 30S 24A Owner s Manual Please read this manual before operating your DC AC inverter...

Page 2: ...and Grounding 9 10 11 Limiting Electromagnetic Interference EMI 11 Powering direct embedded SMPS 12 Principle of Operation 13 Layout 13 Specifying Batteries Chargers and Alternators 14 15 16 17 18 In...

Page 3: ...s To ensure proper ventilation do not install in a low clearance compartment Preventing fire and explosion hazards Working with the inverter may produce arcs or sparks Thus the inverter should not be...

Page 4: ...it phase transformer isolated or auto transformer of suitable wattage rating 25 more than the wattage rating of the inverter with primary of 120 VAC and secondary of 120 240 VAC Two 120 VAC split phas...

Page 5: ...ble for use in buildings including homes for recreational vehicles boats and portable applications Will it be connected to the utility grid in some way Electrical conventions and safety standards diff...

Page 6: ...er will further limit its ability to start a motor A battery bank that is undersized in poor condition or has corroded connections can be a weak link in the power chain The inverter cables and the bat...

Page 7: ...0 VAC To obtain 240 VAC from a 120 VAC inverter use a 120 VAC to 240 VAC transformer If you do not already have a pump installed you can get a 120 volt pump if you don t need more than 1 2 HP Idle pow...

Page 8: ...for resistive type of loads that have unity 1 Power Factor In a reactive type of load like electric motor driven loads fluorescent lights computers audio video equipment etc the phase of the sine wav...

Page 9: ...wave form is a sine wave with very low harmonic distortion and clean power like utility supplied electricity Inductive loads like microwaves and motors run faster quieter and cooler Reduces audible an...

Page 10: ...ected to earth Examples are the neutral conductor in AC wiring and the negative conductor in many DC systems A grounded system is a system in which one of the current carrying conductors is grounded A...

Page 11: ...to the AC power source The plug of the power cord has three pins two flat pins also called poles that are connected to the two current carrying conductors and a round pin which is connected to a non...

Page 12: ...bare metal Use star washers to penetrate paint and corrosion The inverter contains internal switching devices which generate conducted and radiated electromagnetic interference EMI The magnitude of EM...

Page 13: ...f up to 4 This will mean that for a particular rated RMS current applicable for a linear load the general purpose SMPS will draw much larger peak currents approx up to 4 times more than its rated RMS...

Page 14: ...o a reference sine wave 1 2 3 1 120V AC output receptacle 2 L E D indicator 3 On Off Switch 4 Input terminals back of unit not shown RED Positive BLACK Negative 5 Cooling fan back of the unit not show...

Page 15: ...of deep cycle lead acid batteries wet and sealed A wet cell battery has a high tolerance to overcharging However it will release hydrogen gas when charging that must be properly vented and the water...

Page 16: ...is not linear but is more or less according to the table below Table 1 Battery Capacity versus Rate of Discharge Hours of Discharge Usable Capacity 20 100 10 87 8 83 6 75 5 70 3 60 2 50 1 40 Using th...

Page 17: ...connection of batteries When two or more batteries are connected in series their voltages add up but their AH capacity remains the same For example when two 12 V 105 AH batteries are connected in ser...

Page 18: ...bove may be used to calculate the AC watts by multiplying 120 VAC by the AC current in Amperes The next step is to derive the DC current in Amperes A from the AC watts as per formulae 2 above An examp...

Page 19: ...should be powered from the deep cycle batteries For charging the SLI and the auxiliary deep cycle batteries the output from the alternator should be fed to these two sets of batteries through a batter...

Page 20: ...ol dry environment Do not expose to moisture rain snow or liquids of any type To reduce the risk of overheating and fire do not obstruct the suction and discharge openings of the cooling fan To ensure...

Page 21: ...the solar wind hydro charging source directly to the battery through the series connected switching MOSFET s The battery is a capacitive type of load and will thus dampen the input voltages of the cha...

Page 22: ...e inverter and the battery assuming that two one positive and one negative cables are used for the connection Distance up to 3 Distance up to 6 Ampere rating of fuse PST 30S 12A 12 AWG 8 AWG 40 A PST...

Page 23: ...may also pose a fire and safety hazard If an electrical breaker panel load center is fed from an inverter and this panel is also required to be powered from additional alternate AC sources the AC pow...

Page 24: ...ck by detecting leakage and cutting off the AC source Installation in recreation vehicles RV may require GFCI protection on the AC output In addition electrical codes may require GFCI protection for c...

Page 25: ...the DC side circuit will still be alive even when the switch is in the off position Hence disconnect the DC and AC sides before working on any circuits connected to the inverter When the inverter is s...

Page 26: ...the inverter cable and fuse sizes on page 20 If the voltage at the DC input terminals falls below 10 5 V for PST 30S 12A or 21 V for PST 30S 24A a buzzer alarm will be sounded The LED 2 will continue...

Page 27: ...ssistance Shut down due to over temperature In case of failure of the cooling fan or in the case of inadequate heat removal due to higher ambient temperatures insufficient air exchange the temperature...

Page 28: ...y input circuit are tight Correct the polarity of the input connections and replace the internal fuse Note Reverse polarity may cause permanent damage If the unit does not work after replacing the fus...

Page 29: ...s working check that the ventilation slots on the suction side and the openings on the discharge side of the fan are not obstructed 3 If the fan is working and the openings are not obstructed check th...

Page 30: ...actor of 0 8 to 0 6 The power that can be delivered to such type of loads will reduce by this factor See page 7 for details Low Input Voltage Warning Alarm 10 5 V 21 V Low Input Voltage Shut down 10 V...

Page 31: ...attempt to remedy the defect by anyone other than the Warrantor shall render this warranty void There shall be no warranty for defects or damages caused by faulty installation or hook up abuse or misu...

Page 32: ...34 2009 017_PST 30 12A_PST 30 24A_Jan2010 e mail samlex samlexpower com website www samlexpower com 110 17 Fawcett Rd Coquitlam B C Canada V3K 6V2 T 604 525 3836 F 604 525 5221 Toll Free 1 800 561 588...

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