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About the device
4. General
4.1
Prologue / Warning
This user instruction manual and the device are intended
to be used by users who know about the principle of an
electronic load. The handling of the device should not
be left to persons who are unaware of the basic terms of
electrotechnology, because these are not described in this
manual. Inappropriate handling and non-observance of the
safety instructions may lead to a damage of the device or
loss of warranty!
4.2
Mains connection / Grounding
The unit is grounded with the mains cord. Thus the unit may
only be operated at a mains socket with grounding contact.
This must not be interrupted with an extension cable without
grounding wire!
4.3
Cooling
The air inlets on the front and the air outlets at the rear have
to be kept clean to ensure proper cooling. Take care of at
least 20cm distance (at the rear) to any surrounding objects
in order to guarantee unimpeded air flow.
Caution! Hot air can emerge from the air outlets!
4.4
Disassembly
Warning! The unit must not be opened and repaired by the
user.
When opening the unit or removing parts from the inside with
tools there is risk of electric shock by dangerous voltages.
Open the unit only at your own risk and disconnect it from
the mains before.
Any servicing or repair may only be carried out by trained
personnel, which is instructed about the hazards of electrical
current.
4.5
Temperature shutdown / Ventilation
The device is equipped with temperature controlled fans
which are permanently running. At higher temperatures,
the RPM will increase and result in a certain noise deve-
lopment.
In case of overheating the device is automatically switched
offline (standby). After cooling down to the allowed tempe-
rature range it is automatically switching online again.
New since firmware 3.01: the error remains indicated in the
display until it is acknowledged by using the „Input on/off"
button or read out by a remote command. An internal error
buffer stores up to three different alarms and is purged when
read.
4.6
Dynamic characterics and stability criteria
The electronic load is characterised by short rise and fall
times of the current, which are achieved by a high bandwidth
of the internal regulation circuit.
In case of testing sources with own regulation circuits at the
© 2008, Elektro-Automatik GmbH & Co. KG
load, like for example power supplies, a regulation instability
may occur. This instability is caused if the complete system
(feeding source and electronic load) has too little phase and
gain margin at certain frequencies. 180° phase shift at > 0dB
amplification fulfills the condition for an oscillation and results
in instability. The same can occur when using sources without
own regulation circuit (eg. batteries), if the connection cables
are highly inductive or inductive-capacitive.
The instability is not caused by a malfunction of the load, but
by the behaviour of the complete system. An improvement
of the phase and gain margin can solve this. In practice, a
capacity is directly connected to the DC input of the load.
Recommended is 1µF, for slower systems some 100µF can
be necessary.
4.7
Temperature characteristics
Addtionally to the technical maximum power of 7200W, to
which the device is limited to, it features a temperature-de-
pending power derating. This is in effect if the device gets
heated up by high power input. The figure below shows the
progression of the power in relation to the time. For example,
three different start, respectively ambient conditions and their
effect to the power derating. This is only a guide to how the
power derating works. Depending on many factors, the actual
behaviour of the device and its derating will differ more or
less. Explanation:
Cold start 20°C = cold unit at 20°C ambient temperature.
Warm start 25°C = warm, running unit at 25°C ambient temp.
Cold start 20°C
8000 W
7000 W
6000 W
5000 W
4000 W
000 W
2000 W
1000 W
0 W
0s
100s
200s
4.8
Relation between input voltage and input current
When working with applications that input only low voltages to
the load, it becomes necessary to know the minimum input vol-
tage that is required for the load to draw the full input current.
That minimum voltage is not zero and, depending on the num-
ber of transistors inside, it varies from model to model.
On the next page three diagrams depict the relation of input
voltage and input current.
Cold start 0°C
Warm start 25°C
00s
400s
500s
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