refrigerators without compressors

7/31/2019 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.



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:



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.



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



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



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



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



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



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



not overheat.

Cooling Box

Thickness of thermocol -1.2cm

Thickness of ply -0.2cm

Outside

Length-27.5

Bredth-11cm

Depth-14cm

Inside



Length- 24cm

Bredth8.5cm

Depth-13cm

2. Heat Sink

Length – 115mm

Bredth – 115mmHeight – 15mm

3. Fan



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



Voltage Capacity – Up to 13.5 Volts

Current Capacity – Up to 7.5 amperes

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