Team 3 Electrical and Electronics

Electrical Components

Lists of electrical components

• Motor
• Fan
• Heater
• Temperature/humidity sensor

Functions:

• Means to monitor and record the temperature and humidity
• Heater to heat the clothes in the dryer
• Means to rotate the drum constantly

Constraints:

• The maximum allowable electrical power consumption is 12 V AC, 12 VA.
• The voltage on the outside shell should be non-harmful to human body (Less than 36 V).

Objectives:

• High power efficiency
• Short drying time
• Little damage to clothes

Power source

The safety, cost and convenience can be modified when different power sources are used. Therefore, in order to optimize the electrical components of our dryer, we tested 3 different power sources, including 12 V AC, 12 V DC (converted by rectifier), and 5 V DC (powered by USB ports).

Table 5

	12V AC	12V DC	5V DC
Safety	S	1	1
Cost	S	-1	-1
Convenience	S	-1	-1
Sum	0	-1	-1

According to the table above, both the 12-power AC source is the best choice. The 12 V AC is not extremely safe and stable but enough for formal use. The 12 V AC power adapter of the power source is more affordable than its competitors’. Also, the 12 V AC power source is convenient since it does not need an external rectifier, which means that the dryer will be much easier to be transported and installed when the 12 V AC is applied. Therefore, we finally choose the 12 V AC power source as the one used in our circuit.

Direction of motor rotation

The direction of motor rotation of the dryer is also a factor that has influence on the cooling performance of the dryer. We decided to make a selection from 2 potential solutions, single direction and di-direction. The list of alternatives and corresponding descriptions are shown as the followings:

• Rotation in single direction:

1. Simple structure
2. Low cost
3. Possible entanglement of clothes

• Rotation in di-direction:

1. Relatively low likelihood for the clothes to get entangled
2. Relatively more area that the clothes get heated
3. Complex structure (Harder to repair)

The method of multi-voting is used to decide the direction of rotation. There were 5 members from our team participating in the voting. We got 4 votes for the single direction and 1 vote for the di-direction because most of us think that the low cost of the single-direction rotation can make our products more easily recognized by consumers. Finally, single direction is chosen and applied in our dryer. 

Relay for the heater

A MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is used for controlling and switching the loads of electrical circuits. It is a three terminal element which has source, gate, and drain. A Triac is a triode for alternating current. It is a three terminal component that is commonly used for controlling element such as power control in alternating current circuits.

As for the design of the relay for the heater, we come up with 3 different alternatives, including single Triac, single MOSFET, and the combination of both of them.

In order to make a selection among different design options, the Pugh method is used to compare several potential solutions based on a selected standard. If a potential solution makes the same performance with the standard, a “0” would be put in the cell. If it is better than the standard solution, a “1” would be put in the cell. Similarly, A “-1” would be put if the potential one is relatively worse than the standard. After summing up all the scores, the solution with the highest points would be selected as the final solution.

The triode for alternative current (Triac) is selected to be the standard solution since it is normally used for AC circuit, and the other three potential solutions are MOSFET, relay, and the combination of all.

Table 6

	Triac	MOSFET	Combination
Operation time	S	0	0
Cost	S	0	-1
Counter space	S	0	0
Versatility	S	-1	0
Sum	0	-1	-1

After comparing the total scores, the Triac is likely to be the final solution. It would be used for the power control in the alternating current circuit to control the heater. Also, the design of the use of Triac in the heater part is shown in the form of circuit schematics in Figure 1.

Figure 12. The circuit schematics for heater part.

Sensor position

The follow list includes all the potential positions to place the sensor.

1. At the bottom end of the filter
2. At the back of the dryer door
3. Attached with the drum

Figure 13. Sensor at the back of the dryer door

The sensor can directly detect the temperature and humidity within the drum. The sensor would not be hindered by clothes when the drum is rotating. However, some potential problems might occur due to the position of the sensor. For instance, when the dryer door is broken and needs to be replaced, the sensor must be replaced as well. It might cause the additional cost for maintenance of the dryer.

3. Attached with the drum

Figure 14. Sensor attached with the drum

The sensor can directly detect the temperature and humidity within the drum. However, the sensor might be hindered by the clothes when the drum is rotating. It is possible that the clothes might get stuck on the sensor, resulting in the inaccuracy of the temperature and humidity data detected by the sensor. Another advantage is that cotton or other dirt from the clothes might stick on the sensor bar since the sensor is planed on the side of the drum. This problem can be solving by cleaning the dryer after every use.

The Pugh method is used to make a selection among different design options by comparing the potential solutions based on a selected standard. In this case, the solution of placing the sensor at the bottom end of the filter is selected as the standard.

Table 7

	Alternative 1	Alternative 2	Alternative 3
Accuracy	S	1	0
Cost	S	0	0
Maintenance	S	-1	1
Sum	0	0	1

As can be seen in the above table, the alternative 3 is likely to be the selected design since it gets the highest total mark.