Category Archives: Electrical Electronic Design

Hot Air Sterilizer Oven Principles

Hot air sterilizer Hot air or oven is a device in use to sterilizing items that moist should not penetrate. That is items that will damage by exposure to moist heat. Such items include powders, sharp instruments and petroleum products etc. In other words, we use dry heat sterilization for articles for which other methods such as using autoclave are not good. At the same time, hot air ovens are in use for articles that can withstand high temperature.

Hot Air Sterilizer Description
There are two types of hot air oven. One type is electrical home appliance for baking and the other is used in sterilization. In this text, we have more in hot air oven sterilizer. It finds uses in laboratory, pharmacy and in surgery. The oven uses dry heat to sterilize articles. Temperature range for this device is from 50 to 300 °C (122 to 572 °F). It has double wall insulation which keeps the heat in and conserves energy. However, the inner layer is a poor conductor and outer layer is metallic.
However, the internal wall is isolated from the external wall by insulating material which keeps internal high temperature conditions and delays the transfer of heat to the outside.
There is also an air filled space in between to aid insulation. An air circulating fan helps in uniform circulation of the heat. The inner space contains adjustable wire mesh plated trays or aluminium trays and may have an on/off rocker switch. The capacities of these ovens vary. Most hot air sterilizers receives power from electricity. This is either 220 v, 50 Hertz or 110 v, 50 Hertz  depending on the country
Hot Air Sterilizer Principles

The oven produces heat through sets of resistance heating elements, The heat  energy is being transferred to the chamber by natural means as well as by forced convection if there is a fan. The heating elements are located in the at the bottom of the oven

In order to use the sterilizer/oven, first activate the main switch, press the button or dial the knob to set the oven temperature and set the sterilizing timer. The inner chamber of the sterilizer will heat up till the oven reach the set temperature. When the sterilizer reached the set temperature, a thermostat activates the timer and the timer begins to countdown until it reach the set time. At this time, it switch off power to the heating elements. However, the elements continues to work via the thermostat control until the set time.

Hot Air Sterilizer Parts and Functions
Hot air oven controls make use of the following components

There is a thermostat controlling the temperature. The thermostat automatically regulates  and maintains already set temperature. It on or off a device such as an heating element when the temperature reaches a certain set point. Some types are of simple rod thermostat while some are electronic or digital. 

Glass thermometer is an instrument for measuring and indicating temperature. Typical one consist of a narrow, hermetically sealed glass tube marked with graduations and having at one end a bulb containing mercury or alcohol. The mercury or alcohol expands and contracts in the tube with heating and cooling. In our context, the thermometer visually indicate the working temperature of the sterilizer.

Basic Hot Air Sterilizer Circuits Diagram

Hot air sterilizer oven circuit diagram

Use of Hot Air Sterilizer

A complete cycle involves heating the oven to the required temperature.  Likewise, it maintains that temperature for the proper time interval for ‘that temperature’. Then turning the machine off and cooling the articles in the closed oven till they reach room temperature.

The standard settings for a hot air oven are:

  • 1.5 to 2 hours at 160 °C (320 °F)
  • 6 to 12 minutes at 190 °C (374 °F)
We use temperature sensitive tapes or other devices like those using bacterial spores to work as controls, to test for the efficiency of the device in every cycle.

Dimmer Switch Replace How to Install

Dimmer switch replace for small appliances like laboratory microscopes, slit lamps, and others as you may think of, Sometimes, the circuit is bad and its taking too much time to find out the problems in the course of diagnose. Find below the schematics diagram for a dimmer switch replace suitable for a low voltage appliances. It is a  Pulse Width Modulation based module suitable for light source of Microscope, Slit Lamps and portable light source. Meanwhile, for small DC electric motor and lots more.

You could actually ask for a replacement dimmer switch from the manufacturer of your product, But if you still have warranty on the appliance, the manufacturers or suppliers would be in a position to help in the repair or replacement.

dimmer switch replace
About the Schematic

The circuit module above consists of three circuits put together. The circuits are 12 volt positive regulator, an oscillator, and a voltage comparator. Other are an integrator, and a driver. The oscillator and the integrator employs an LM324. The comparator is also one of the LM324 package with supporting components.

For this circuit to work, you need a source of unregulated dc power supplies or a battery. Besides, the PSU should be more than voltage of the ic regulator. For example, if the Ic voltage regulator is 12V as shown in the schematic, then, the PSU voltage should be at lear 2.5 volt more than 12 volt. That is, 14.5 volts. Learn more about unregulated power supply unit.

Meanwhile, for more information regarding for specifications; theory; construction; alignment/calibration/configuration; how to use and Bills of Quantity, check here Motor Speed Controller and or DC Light Dimmer (2016_06_01 10_11_06 UTC). 

We can adapt the simple dimmer schematic to control high power load by simply change few components. The main component to change is the Field Effect Regulator (FETs) and the fuse.

Add IC Voltage Regulator to Wall Adapter

How to Add IC Voltage Regulator to Wall Adapter/Battery

Often what you required to run an equipment or device is a well-regulated source of DC power.  To do this, you need to add ic voltage regulator Regulated power supplies gives out stable desired voltage output. You will even need one for your projects. In its simplest form they call it a battery eliminator. For some application the simple battery eliminator is less desirable. Therefore, you need a well-regulated for equipment from batteries and from a wall adapter that outputs a DC voltage

add IC voltage regulator

You can construct a well-regulated power supply. To do this, you add a voltage regulator IC to ordinary DC output from wall adapter or a battery. The voltage regulator is either a fixed type positive (+ve) or negative (-ve). Available also are adjustable voltage regulator. The regulated power supply unit finds application where you require stable power output. They are to power device such as indirect ophthalmoscope, portable light source and host of others. It also functions as a small power supply unit for electronics experiments.

Example for add IC Voltage Regulator:
  • 78xx typical example: 7812 is a positive 12v fixed voltage regulator IC. For example 7805 voltage regulator IC
  • 79xx typical example: 7912 is a negative 12v fixed voltage regulator IC
  • LM317 Adjustable positive
  • LM337 Adjustable negative

The ic voltage regulator for example LM317 looks like power transistor but is a complete regulator on a chip.

Here is a typical circuit:    It is important to identify the pinouts to add IC voltage regulator and to use it appropriately. Here are pinouts for the most common types:

Note: Various manufacturers may label the pins differently than shown. Best approach is to check the datasheet if you are in doubt.

Design Information to add Variable IC Voltage Regulator

For the LM317 circuit above,

  1. R2 = (192 x Vout) – 240, where R2 in ohms, Vout is in volts and from design it’s between 1.2 V and 35 V.
  2. Vin is at least 2.5 V greater than Vout. Select a wall adapter with a voltage at least 2.5 V greater than your regulated output at full load. However, note that a typical adapter voltage may vary quite a bit depending on manufacturer and load. You will have to select one that isn’t too much greater than what you really want since this will add unnecessary wasted power in the device and additional heat dissipation. For example: if expected maximum Vout is 15v. Then R2 = (192 x 17) – 240 = 2,784Ω or 2K8. Vin, then is at least Vout + 2.5v = 17 + 2.5 = 19.5v
  3. As indicated in its data sheet, maximum output current for LM317 is 1 A. Your adapter or battery must be capable of supplying the maximum current safely and without its voltage drop below Vin + 2.5v minimum as declared in 2 above.
Choice of Capacitor
  1. You may add extra filter capacitance (across C1) on the adapter’s output to reduce its ripple and thus the swing of its input. This may allow you to use an adapter with a lower output voltage. This also reduce the power dissipation in the regulator as well. Using 10,000 uF per “amp” of output current will result in less than 1 V p-p ripple on the input to the regulator. As long as the input is always greater than your desired output voltage plus 2.5 V, the regulator will totally remove this ripple resulting in a constant DC output independent of line voltage and load current fluctuations.
  2. Select a capacitor with a voltage rating at least 25% greater than the adapter’s “unloaded” peak output voltage and observe the polarity! For example, if the “unloaded” peak output voltage is 19.5v as calculated for the Vin in 2 above, then voltage of the filter capacitor would be 19.5v + 25% which is approximately 45v.
  1. Wall adapters as battery eliminator may not have any filter capacitors so we will need IC regulator with this type. Quick check: If the voltage on the adapter’s output drops to zero as soon as it is pulled from the wall – even with no load – it does not have a filter capacitor.
  2. The tab of the LM317 ic voltage regulator is connected to the center pin – keep this in mind because the chip will have to be on a heat sink if it will be dissipating more than a watt or so. P = (Vout – Vin) * Iout.
  3. There are other considerations – check the datasheet for the LM317 particularly if you are running near the limits of 35 V and/or 1 A.
  4. For a negative output power supply, use the corresponding negative voltage regulator and note that their pin-out is NOT the same as for the positive variety. See above!

For any support in your design and construction or you get stuck somewhere to add ic voltage regulator, simply Contact Us describe in details how we may help.


Various Schematics and Diagrams

Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied: This notice is included in its entirety at the beginning. There is no charge except to cover the costs of copying. Introduction High Voltage Power Supplies – Home-built and commercial units.