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5
Dependencies of system parameters
Contactless power transmission is a system which depends on many variables. These are primarily the size of the air
gap, eccentricity, ambient temperature, cooling, input voltage and secondary current rating. If one variable changes, the
transmission behaviour changes too. For example, efciency usually improves as the load current increases and falls when
the air gap or eccentricity increases.
These dependencies are of course not linear. Diagrams are the best way of explaining this. In the scenarios outlined below,
all variables are kept constant and only the dependency between efciency and load current / air gap is shown.
Typical diagram for contactless transmission
Benets of contactless transmission
The main reason for using contactless power transmission is that the conventional form of connection using plug-in
connectors may cause problems in some applications. These include, for example, contact erosion with increased contact
resistance and the resultant high level of warming, no transmission due to a missing contact resulting from a high level of
wear to the contact surface or failure caused by mechanical problems such as bent contacts.
Contactless transmission technology not only eliminates such problems, but also offers more mechanical freedom and a
range of applications that is not possible with a conventional plug connection.
In contrast to the conventional plug-in connectors, FreeCon Contactless from Weidmüller allows the connection to be
controlled by a PLC. The system is activated by a PLC output for this purpose. An additional contactor for switching the load
is superuous.
Of course, the main benet is due to the fact that the transmission is contactless so there are no mechanical problems
and there is no wear. The connection components, i.e. the primary and secondary sides, also always have IP protection (in
accordance with IP 65 for example) – regardless of whether the connection is closed or not. A plug connection on the other
hand is not protected when unplugged and therefore becomes contaminated.
The benets of contactless power transmission do come at the cost of a considerably higher purchase price than the plug-in
connector. However, in the applications stated below the additional costs very quickly pay for themselves because the costs
for maintenance and replacements during operation are much lower. Especially in the case of interruptions to production
due to a defective plug-in connector, the contactless system pays for itself immediately.
50
55
60
65
70
75
80
85
90
95
20%
40%
60%
80%
100%
%
Laststrom (% von Nennstrom)
Wirkungsgrad / Laststrom
50
55
60
65
70
75
80
85
90
95
0,5
2
3,5
5
Wirkungsgrad / Luftspalt
Luftspalt (mm)
%
Load current (% of rated current)
Efciency / load current
%
Efciency / air gap
Air gap (mm)
%