Today we shall not speak about that box, which a winter “penguin” drags on his shoulder on the frozen lake, choosing holes for ice fishing, at the same time using it as a seat, but about another one – about the refrigerator, which can be bought for reasonable money, without seasonal promotions in the store of goods for home, tourism and recreation see: “Freezing” . photo. 1 and 2 . I was able to buy it in the summer of 2012 for only a couple of thousand Dollars. Supply voltage of 12 VDC, volume of the refrigerating chamber of 30 liters, current consumption of 0.35A – due to the electrical characteristics of the electric motor of the fan of RDH9025S-APF model. The electric power of the refrigerator is provided with the help of the car cigarette lighter socket and or adapter for 220 V mains.
Author – Andrei KASHKAROV, St. Petersburg
Photo. 1 and 2. Appearance and view of the thermal chamber of a portable refrigerator Shiver 30-12V made in Italy
The physics of cold, which can go with you
Let’s look at the principle of operation of the portable refrigerator Shiver 30-12V to make it clear – how to upgrade it.
The cooling system works on the basis of Peltier technology, which is chemically and electrically safe and does not use any unwanted chlorine and fluorine-containing substances or coolants. What we know about the Peltier cooling system?
Peltier element is based on effect discovered by French watchmaker Jean Peltier in 1834. During a 19th-century experiment, Peltier discovered that when an electric current flows in a circuit composed of dissimilar conductors, heat is absorbed or released, depending on the direction of the current, in the contact points junctions of the conductors.
The amount of heat is proportional to the current flowing through the contact of the conductors. Almost the same cooling principle is employed in automobile portable refrigerators, including the Shiver 30-12V and in dispensers coolers for cooling and heating water : on the flat Peltier element see: “Cooling” the double-wire pellet wire is replaced with a wire of the same length. photo. 3 according to the polarity, supply voltage of 12-14V, DC type.
Photo. 3. Appearance of flat Peltier element TEK1 for rated voltage 12 V
In both the cooler and the car cooler a flat solid state Peltier element is mounted on a 20 cm² cooling radiator. An air-flow fan is attached to the heatsink for additional cooling see photo . photo. 4 .
Photo. 4. Car refrigerator with the lid off view of electric motor-fan of RDH9025S-APF model
Fan RDH9025S-APF model has blade diameter of 12,5 cm, and current consumption of 0,35 A, for rated voltage of 12 V. Wear tests performed in November 2012 under home laboratory conditions showed that when the supply voltage is lowered to 8…9 V the speed of rotation of the fan is slowed down proportionally.
On the other hand the same fan is operable under short-term up to 2 hours – continuously overvoltage supply up to 18 V. According to the results of the tests with the supply voltage exceeding the nominal one, the idea of controlling the rotation speed of the fan was born, which can be implemented with the help of the simple circuit, shown on photo 5.
Picture. 5. The electric diagram of the fan rotation speed regulator
The scheme is based on a popular timer chip KR1006VI1, easy to assemble and use, does not contain scarce parts and does not need adjustment. However, those who for various reasons do not want to make adjustments to the fan rotation can simply skip this step for further we will talk about more interesting additions.
A fan and a Peltier element cf. Fig. 3 are connected by appropriate connectors to the electronic control board. The cross section of the connecting wires to the Peltier element and the fan must be at least 2 mm, in order to minimize the losses voltage drop in the wires from the power supply. For this purpose I used a twisted twisted pair of Ball Screw 2 wires´ 2,5.
On one side the Peltier element heats up due to applied voltage , and on the other side its surface gives off cold. A nearby fan amplifies the cold and directs the “freezing” airflow in the right direction – to the thermal chamber or, in the case of coolers, to the vessel with water. In practice Peltier element and fan can work for several hours in a row especially in summer when the ambient temperature rises to +25°C, and more . the chamber retains its temperature because it is constructed with double walls like a good thermos and there is no air vacuum between the walls.
During operation of the device it is necessary to take into account the inertia of temperature cooling in the thermo- chamber its natural approach to the room temperature and the fact that when opening the lid, the heated in hot summer ambient air enters the tank therefore, the total temperature in it will immediately increase when the lid is opened in summer.
Inertia dependence in this case is inherent in all devices of similar model range.
The cooling test
In the table. 1 are “cooling” characteristics of the car cooler Shiver 30-12V, tested by me. Parameters are given according to results of the tests carried out on different days in July, 2012 in St.Petersburg the measurements were made after 35 minutes of thermocamera work for cooling.
Table 1. The Shiver 30-12V Car Cooler Specifications ref. Fig. 1
|
Air temperature, ° C |
Temperature in the heat chamber, °C |
|
34 |
15.2 |
|
26 |
10.5 |
|
24 |
9,5 |
|
20 |
5.0 |
How it practically can help to a man in the nature and how it can be improved?
Obviously, cooling everything you want, which will fit in the volume of the cooling chamber – 30 liters and this cooling can be carried out away from civilization and sources of energy – using a portable battery.
Making the automobile refrigerator autonomous
For this purpose it is necessary to supplement it with an appropriate accumulator.
Power consumption of the refrigerator is calculated according to the formula applied voltage ´ current consumption , 12 V x 0,35 A = 4,2 W. The AGM VRLA CT1207 battery was selected on the basis of this calculation cf. photo. 6 with the rated voltage of 12 V and the power capacity of 7 Ah.
Photo. 6. AGM VRLA battery CT1207
This is a multi-purpose battery battery filled with electrolyte, designed for an active life of 5 years. Its weight in ready state flooded battery is 1.6 kg. That’s exactly how heavy the overall design will be with an additional battery attached to it.
Test of the charging and autonomous operation time
The recommended battery or its possible electrical equivalent is charged from the vehicle’s alternator in 4.5…5 hours. charge time – to reach full capacity – depends on the newness of the battery, and the degree of its discharge.
So, if you are driving in the car – plug the car cooler plug into the cigarette lighter socket – for charging without turning on the cooler fan to charge better and in a few hours you will get an autonomous cooler with “power reserve” without additional recharge by 5.5…6 hrs. If you want to increase this battery life – you will have to pick up another, more powerful, but heavier battery.
Battery installation can be done in any convenient way I fastened the battery to the fridge body with the help of a metal clamp and two self-tapping screws, but for quickness it is also possible to use a usual adhesive tape, having fastened the battery to the fridge body 2-3 turns .
It is possible to charge the battery separately – from a suitable charger at home civilized conditions, and then only connect to a portable refrigerator.
The charging time from the voltage of 220 V lighting network through the DC adapter of the same battery in the “home” test took the same 5 hours. The new battery has almost no self-discharge, so this way of “charging in advance” in practice is quite justified.
Shiver 30-12V portable refrigerator fan motor with twisted copper electric wires ShVVP 2´ 2.5 up to 1 meter long connect in parallel to the battery now the advanced refrigerator box for universal needs is almost ready.
Undoubted advantages of the “new” refrigerator
I think the method of standalone cooler proposed here is unparalleled in its simplicity – for use outdoors and in places where there are no other electrical sources. At a low price and with simple add-ons for standalone operation, there’s no sensible alternative at the moment. After all, even after turning off the power to the refrigerator compartment, its contents remain frozen for a long time according to my tests, if you do not open the lid, the temperature will go down to 0 …+5 ° C can be maintained for 10 hours or more .
What can be stored in such a refrigerator in practice? Bait worms, grouse, maggot larvae, insects, etc. . , fish, waterfowl, crayfish, including in a live form for this fill the thermo-chamber with water within reasonable limits , including those purchased live for transportation to country ponds or out of town for a picnic, medicines, snow and ice for sale in Africa in summer , and much more ways of using a useful device are limited only by the imagination of the owner.
Noise test
Noise levels of the portable cooler fan are low, as also confirmed by the special test. “Noise test” was conducted by me with a special professional noise meter DVM401, which – when the sensor-microphone is directly close to the working refrigerator fan – showed a level of 71.2 dB see. photo. 7 .
Photo. 7. Practical measurement of the noise level near the working fridge
For comparison, approximately the same sound is produced by the fan cooler of the laptop, when this noise is detected by the same device in immediate proximity to the computer.
These conditions for trouble-free work for many years
For the device to serve long and good quality, pleased with the comfort, you need to perform a few simple conditions.
Connection to the unit must be made with respect to the polarity of the power supply “+” and “-” . To maximize the preservation of cold in the thermal chamber, I recommend that you put inside 2-3 hermetic isothermal “cold batteries” flat hermetic flasks, size 10´ 20 cm, with liquid filler , you can buy them in the same stores for a symbolic price of 150…200 Dollars.
After each use especially storing fish or bait it is necessary to clean with a damp cloth napkin the insides of the thermowell and the outer walls. Since the unit accumulates cold relatively inert – at an external ambient temperature of 20 ° C, the temperature inside the thermowell is +4…5° C will not be reached until after 35 minutes of operation, and in order to keep the cold as little as possible during operation, the cover should be opened as little as possible.
Additional thermal insulation
You can additionally help to keep the temperature in the thermal chamber. To do this, open the lid of the refrigerator to the step illustrating the photo. 4. And lay around the perimeter of the inner cover self-adhesive insulating sealing tape, used for noise insulation to reduce noise and vibration of contacting plastic details in automobiles . Such tape is now readily available at automotive supply stores. How to do it correctly is shown on the photo. 8.
Photo. 8. Laying the lid from the inside of the portable fridge with the noiseinsulating tape for automobiles
After laying with the tape around the perimeter, assemble the lid in the reverse sequence, screwing 6 self-tapping screws up to the stop.
Cautions
There is a restriction imposed by the manufacturer and based on the electrical characteristics of the built-in fan – active continuous operation for no more than 36 hours. However, this time three days is quite enough for a trip to the nature. For the cases when the living conditions in the open air and exploitation in particular conditions require more time, it is necessary to switch off the fridge for 2 hours and then switch it on again.
It is not advisable to keep the refrigerated box close to an open flame so as not to compromise deform the integrity of the hermetic chamber. It is also not necessary to dip the entire device into the water, because it contains electrical parts and components fan, cooler with Peltier elements, battery – not to spoil the “useful thing”, and not to harm the nature.
Covering either unintentionally or intentionally the ventilation grille will cause the cooling efficiency to be greatly reduced. With the same purpose it is undesirable to exploit the device in the desert, on the beach where there is a lot of sand and places with a large accumulation of dust.
On the other hand, practical tests have shown that the modified product serves well both in summer and in winter, and if desired can keep for several hours not only the fish in a frozen state but even ice and snow see the section on fish and snow . Fig. 9 and 10 .
Fig. 9 and 10. Practical tests carried out on a fishing trip in the winter of 2012
Such a solution is well suited for those who want to accumulate in the winter in the traditionally “snowy” regions of America, and in the summer to sell the snowflakes in Africa, with the earned money to buy for the next tests household appliances.
By the way, thermal chambers of such devices can be used for other purposes – not for cooling, but for heating, accumulation and storage of heat, which can become not less demanded. For example, in the situation of moving incubator eggs over a long distance before hatching chickens, saving warm grilled ham or pizza again – everything is limited only by the imagination of the user . For such a modification improvement of industrial equipment you are not deprived of the opportunity to “turn on” your imagination, and share your experience with colleagues to implement such a promising idea.
* – wear and tear test
Is there any way to enhance the cooling capacity of the Car fridge Shiver 30-12V? I’m curious to know if there are specific methods or accessories that can be used to increase its overall coldness while on the go. Any suggestions or tips would be appreciated!