Close-up side view of a thermoelectric cooling module.
obvious when the motor was spinning. My mug, with five
converters on it, ran this motor for about 24 minutes
before the voltage dropped too low.
Some Closing Thoughts
Be careful! Hot liquids can cause nasty burns.
Remember also that the cooling fins may be hot, so don’t
jab them into your face if you drink from the mug. Also, if
you hammer an enameled steel mug to make flat surfaces
for attaching the converters, beware of the enamel spalling
Of course, if you want to explore or demonstrate the
performance of thermoelectric converters, you needn’t
use an actual mug. You could attach the converter to a die-cast aluminum box and use that as a receptacle for hot
water. A limiting performance factor in the mug is the
“cold end” temperature afforded by the heatsink. You can
get much higher performance from the converter if you
sandwich it between two boxes: one with hot water and the
other with cold water — or better yet, ice.
Don’t be tempted to go too far with pushing power out
of your converters. If temperatures exceed 100° C signifi-
I-V characteristic of cell. The datapoints are the voltage and current I
measured with various temperature differences ( 9, 18, 26, and 35° C)
across the converter (∆Tconverter). The higher the current drawn,
the lower the voltage, although it is a very nonlinear function.
Arrows show schematically how the curves must turn over to reach
a “short circuit” current, though I didn’t measure that. The dotted
lines show schematically how different load impedances will draw
power. To be efficient, a load impedance of 1 W or less is ideal.
cantly, the semiconductors can degrade and the solder
that bonds the junctions can melt — a eutectic bismuth/tin
solder that melts at only 138° C is widely used to make
This is a somewhat expensive project, given its rather
frivolous nature. New thermoelectric modules sell for
about $20.00 apiece, so there is about $100.00 of
converters in the five-converter mug. You might want to
experiment first with a single converter. However, as these
devices become ubiquitous in CPUs, they may start
appearing in surplus outlets and become available
at lower prices. You might be able to salvage some from
old PCs. NV
Circle #140 on the Reader Service Card.