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VARIABLE FREQUENCY DRIVE – BTH 400 and 500
The Cyclone Xi BTH 400 and 500 models have a variable frequency drive (VFD) that
controls the rpm of the blower motor. The VFD receives a signal from the central control
board that instructs the VFD to transmit the proper frequency to the blower to produce the
proper blower speed and proper input.
Three conditions must be met for the frequency drive to start the blower:
1. 120VAC must be supplied to the VFD 120VAC input.
2. The ignition control board closes an enable circuit – terminals LI1 and +15V
3. The ignition control board sends a 1-10VDC instruction – terminals 0V and AI1.
on the next page for voltage and frequency information.
GROUND
HOT
R/L1
G
BLOWER MOTOR WIRES
BLACK
WHITE
U/T1
V/T2
NOTE: BE SURE TO MATCH WIRE
COLORS WHEN CONNECTING BLOWER
WIRES OR BLOWER MAY RUN
BACKWARD AND CAUSE A FAULT.
RC
RA
1-10 VDC Speed Instruction
A.O. Smith – Technical Training Department
CYCLONE Xi COMMERCIAL GAS WATER HEATER
BTH 120 thru 500 SERVICE HANDBOOK
NEUTRAL
N
RED
W/T3
0V
AI1
Servicing should only be performed by a Qualified Service Agent
VARIABLE FREQUENCY DRIVE
+5V
DO
LI1
Enable Disable Circuit
38
See table
155
LI2
LI3
LI4
Ashland City, Tennessee © 2009
+15V
316586-000
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