Control terminals, with programmable functions, are provided for input commands such as run,
stop, forward, reverse and speed reference. Additional output terminals are provided to supply
signals to run peripheral devices or for monitoring and reporting status.
The control card logic is capable of communicating via serial link with outside devices such as
personal computers or programmable logic controllers (PLC).
The control card also provides two voltage supplies for use from the control terminals. The 24
VDC is used for switching functions such as start, stop and forward/reverse. The 24 VDC supply
is also capable of supplying 200 mA of power, part of which may be used to power external
encoders or other devices. A 10 VDC supply on terminal 50 is rated at 17 mA is also available for
use with speed reference circuitry.
The analog and digital output signals are powered through an internal adjustable frequency drive
supply.
Two relays for monitoring the status of the adjustable frequency drive are located on the power
card. These are programmable through parameter group 5-4*. The relays are Form C, meaning
it has one normally open contact and one normally closed contact on a single throw. The contacts
of the relay are rated for a maximum load of 240 VAC at 2 Amps resistance.
The logic circuitry on the control card allow for the addition of option modules for synchronizing
control, serial communications, additional relays, the cascade pump controller, or custom oper-
ating software.
3.2.2 Logic to Power Interface
The logic to power interface isolates the high voltage components of the power section from the
low voltage signals of the logic section. The interface section consists of the power card and gate
drive card.
Much of the fault processing for output short circuit and ground fault conditions is handled by the
control card. The power card provides conditioning of these signals. Scaling of current feedback
and voltage feedback is accomplished by the control card.
The power card contains a switch mode power supply (SMPS) which provides the unit with 24
VDC, +18 VDC, -18 VDC and 5 VDC operating voltage. The logic and interface circuitry is powered
by the SMPS. The SMPS is supplied by the DC bus voltage. The adjustable frequency drives can
be purchased with an optional secondary SMPS which is powered from a customer supplied 24
VDC source. This secondary SMPS provides power to the logic circuitry with main input discon-
nected. It can keep units with communication options live on a network when the adjustable
frequency drive is not powered from line power.
Circuitry for controlling the speed of the cooling fans is also provided on the power card.
The gate adjustable frequency drive signals from the control card to the output transistors (IGBTs)
are isolated and buffered on the gate drive card. In units that have the dynamic brake option, the
driver circuits for the brake transistors are also located on this card.
High Power Service Manual for VLT
®
FC Series
Adjustable Frequency Drives
3 Internal Adjustable Frequency Drive Opera-
tion
MG.90.L1.22 - VLT
®
is a registered Danfoss trademark
3-3
3
Summary of Contents for VLT HVAC FC 100
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