Refrigerators Without Compressors
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Transcript of Refrigerators Without Compressors
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Design of Apparatus:
The Parts:
First, let’s cover the basic parts and components that
make up a Peltier cooler device. Look at the pictures
below.
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The basic components of a thermoelectric device are;
two ceramic substrate faces, interconnect pads, the
semiconductor pellets (both P and N type), solder to
hold it all together, and lead wires. In addition theremay be moisture sealant applied to the edge of the
device. [Pellets are also commonly called elements,
junctions, or dice (dies)]
The ceramic substrates or faces are usually made of
Alumina ceramic Al2O3. Less frequently they are made
of more thermally conductive ceramics such as
Berrylium Oxide BeO or Aluminum Nitride AlN.
Attached to the ceramic substrates are interconnects
made of copper. These are either soldered to a
metalization on the ceramic or bonded on in a process
called Direct Bond Copper (DBC). DBC is the stronger
and more superior method of copper interconnect pad
attachment.
Soldered to the interconnect pads are the individual
semiconductor pellets. There are both N and P type
pellets. They are arranged in an alternating pattern,
much like a chess board, and form one long seriescircuit through the entire thermoelectric module.
Couples:
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If you look at the sides of a (unsealed) thermoelectric
device, you will see lots of “columns” of a dark silvery
grey material with space in between. Each individual
column is a pellet. These thermoelectric pellets do the
actual heat pumping work of a TE device. A
thermoelectric device contains both N and P doped
semiconductor pellets arranged in pairs called Couples,
so basically there are twice as many pellets as there are
couples. For example, a single 127 couple TEC will
actually contain 254 pellets (127 N and 127 P). Each of
these pellets will have two solder connections making
for a total of 508 solder joints!
Amperage (Imax):
This is the most difficult specification to determine
without specialized equipment. There are two methods.
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Pellet Dimension Method:
Using a dial caliper, carefully measure the width of 5 or
more pellets. Do this under a magnifier or low power
microscope if possible so that you can see that you are
not crushing the pellets. Find the average of your
measurements and make note of it as “W”.
Using the caliper, measure the length of several pellets.Measure only the pellet length and NOT the
interconnect pad. See the above image. Again, this is
method is more accurate if done under a microscope or
magnifier so you can see what you are doing more
clearly. Find the average of your measurements and
make note of it as “L”.
Now calculate the Length to Area ratio as follows;
= L / W2
Length to Area Ratio Table
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L/W2
(inches)L/W2 (mm)
Pellet
Amperage
(Imax)
55.2 2.17 2
36.8 1.45 3
27.6 1.09 4
22.1 0.87 5
18.4 0.72 6
13.8 0.54 8
12.3 0.48 9
11.0 0.43 10
9.2 0.36 12
7.9 0.31 14
6.1 0.24 18
Thermoelectric modules have a characteristic resistance
called ACR. ACR stands for AC Resistance. AC
resistance measurements should be made using a
specialized AC milliohmmeter, digital impedance
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meter, or LCR. All ACR readings should be done when
the thermoelectric device is at 23ºC. Even a few degrees
variation will cause significant changes in meter
readings since Peltier devices are so temperaturesensitive.
A typical DC input bench or handheld meter will give
an incorrect (and also constantly changing) value since
DC power applied to the TEC will produce a
temperature change (Peltier effect), and induced voltage
(Seebeck effect) and therefore a wildly changing
resistance value. Again, an ACR reading from a
damaged or heavily used TEC will be useless since the
resistance significantly increases with age and/or
damage. Rely on the Pellet Dimension Method (above)
for damaged or old TECs.
Module ACR to Amperage Table
CPLsAC Resistance
(ohms) @ 23ºC
# Couples &
Amperage
17 0.52 17 cpl, 3 Amp
17 0.39 17 cpl, 4 Amp
17 0.31 17 cpl, 5 Amp
17 0.26 17 cpl, 6 Amp
17 0.18 17 cpl, 9 Amp
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17 0.10 17 cpl, 14 Amp
31 1.0 31 cpl, 3 Amp
31 0.75 31 cpl, 4 Amp
31 0.57 31 cpl, 5 Amp
31 0.50 31 cpl, 6 Amp
31 0.34 31 cpl, 9 Amp
31 0.24 31 cpl, 12 Amp
49 1.21 49 cpl, 4 Amp
49 0.79 49 cpl, 6Amp
49 0.56 49 cpl, 9 Amp
49 0.39 49 cpl, 12 Amp
63 1.92 63 cpl, 3 Amp
63 1.44 63 cpl, 4 Amp
63 1.15 63 cpl, 5 Amp
71 2.17 71 cpl, 3 Amp
71 1.63 71 cpl, 4 Amp
71 1.30 71 cpl, 5 Amp
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71 1.08 71 cpl, 6 Amp
71 0.74 71 cpl, 9 Amp
71 0.65 71 cpl, 10 Amp
71 0.54 71 cpl, 12 Amp
71 0.36 71 cpl, 18 Amp
127 5.82 127 cpl, 2 Amp
127 3.88 127 cpl, 3 Amp
127 2.91 127 cpl, 4 Amp
127 2.33 127 cpl, 5 Amp
127 1.94 127 cpl, 6 Amp
127 1.33 127 cpl, 9 Amp
127 1.16127 cpl, 10
Amp
127 0.97127 cpl, 12
Amp
127 0.78127 cpl, 15
Amp
127 0.65 127 cpl, 18
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Amp
127 0.48
127 cpl, 24
Amp
127 0.40127 cpl, 30
Amp
Normal tolerance for an ACR reading is ± 10%, so
multiply each value times 0.9 and 1.1 to find the,
minimum and maximum values.
Can I use a thermoelectric cooler as a heater?
1. Thermoelectric coolers can indeed be used for very
effective and efficient heating. Since thermoelectric
coolers are solid-state heat pumps, they can
actively pump heat from the ambient in addition to
the heating effect that comes from the electricalresistance of the cooler itself. So, the
thermoelectric cooler can be more efficient than a
resistive heater (within limits). The heating can be
so effective that you could very easily cause the
module to reach the melting point of the solder!
Care must be taken to ensure that the module does
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not overheat.
Cooling Box
Thickness of thermocol -1.2cm
Thickness of ply -0.2cm
Outside
Length-27.5
Bredth-11cm
Depth-14cm
Inside
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Length- 24cm
Bredth8.5cm
Depth-13cm
2. Heat Sink
Length – 115mm
Bredth – 115mmHeight – 15mm
3. Fan
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Diameter of Fan – 100mm
4. Peltier Chip
Length – 45mm
Breadth – 45mm
Height – 3mm
Voltage Capacity – 12-15 volts
Current – 3.5 amperes
No. of Couples – 127 Couples
Semiconductor Material – Silicon, Germanium
Outer Coating – Ceramic
Wire Material – Lead
5. Battery
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Voltage Capacity – Up to 13.5 Volts
Current Capacity – Up to 7.5 amperes