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TC-3 Temperature Controller User’s Manual · Page 33
Compensating for Cable Resistance
Because the high currents the TC-3 can drive through the Peltier, the
voltage loss through the cable and connectors of the system can
significantly affect the TEC voltage measurement. In most cases,
accurate voltage measurements are not needed, and the default
compensation of the instrument is sufficient. To improve the
compensation, the
Cable R setting in the menu allows you to specify
the cable resistance, which is then used to dynamically subtract the
voltage drop by simply using the formula V = IR to calculate the
voltage loss, where I is the TEC ITE current, and R is the
Cable R
setting. This value is then removed from the voltage measurement to
display an accurate TEC voltage measurement.
The safest method of calculating cable resistance is to short the ITE+
and ITE– connections, making sure whatever you are using to short the
terminals is not itself adding resistance to the circuit. Use short, heavy
gauge wires, preferably soldered onto the terminals to minimize any
resistance the short might add. Place the short as close to the Peltier
as is reasonable. A simple approach is to unplug the cable from the
mount and place a shorting plug on the mount end of the cable, which
is easily made from a male DB15 connector and a soldering iron to
solder the ITE+ and ITE– pins together. Make sure the Peltier is
disconnected to protect it from current overloading during the test.
Change the instrument to ITE mode and set the current to 5A.
Depending on your setup, you may first need to change the Mount to
User Defined and adjust the limit to 5A. Turn on the output and after
the voltage has stabilize, make a note of it and turn the output off.
Enter the measured voltage into the following equation to calculate
Cable R :
Cable R = Voltage / 5
Enter the resulting values into the Cable R menu entry and return the
instrument to its original configuration. Typical values for Cable R are
0.008 to 0.040, but depend on your actual configuration.
Internal Power Management
The TC-3 is a powerful instrument, capable of delivering upwards of
180W in some custom configurations. When driving a low voltage load
at higher currents, a condition can arise where the voltage of the load
is too low, and unaddressed, would result in excessive heat inside the
instrument.