Samlexpower SAM-250-12 - Cooling System and Operation; Modified Sine Waveform Characteristics

4 | SAMLEX AMERICA INC.
SECTION 2 | Introduction
Load Controlled Cooling Fan
Cooling is carried out by convection and by forced air circulation by load-controlled fan.
The fan will normally be OFF and will be switched ON automatically at the following
loads:
• SAM-250-12andSAM-450-12: Atloadof8Wto12W
• SAM-800-12:   Atloadof35Wto45W
Thiswillreduceenergyconsumptionbythefanandwillincreaseoverallefciency
Principle of Operation
Conversion of 12 VDC from the battery / other DC source to 115 VAC takes place in 2
stages.Intherststage,the12VDCisconvertedtohighvoltageDC(around160VDC)
using high frequency switching and Pulse Width Modulation (PWM) technique. In the
2ndstage,the160VhighvoltageDCisconvertedto115V,60HzModiedSineWaveAC.
(Note:115VistheRMSvalueoftheModiedSineWaveACvoltage.Thepeakvalueof
theModiedSineWaveACvoltagewillbeequaltothevalueoftheabovehighvoltage
of around 160V. See the Fig 2.1 below)
Modied Sine Waveform -
Characteristics & Comparison with Pure Sine Waveform
PleaserefertoFig2.1belowwhichshowsonecycleofModiedSineWaveand
Pure Sine Wave for comparison.
Fig 2.1 Modied Sine Wave and Pure Sine Wave - Comparison
TIME
180
160
140
120
100
80
60
40
20
0
20
40
60
80
100
120
140
160
180
Modified Sine
Wave sits at
0V for some
time and then
rises or falls
Sine Wave
Modified Sine Wave
Pure Sine Wave
crosses 0V
instantaneously
Legend
V +
V -
115 RMS