DC power supplies from various manufacturers are available in many different sizes and total power (watts) from the single 15 Volt @ 3 Amps maximum to the dual 50 Volt @ 20 Amps maximum unit.

The method of calculation the maximum watts that a power supply can provide is to multiply the maximum volts by the maximum amps that are available. For example the Mastech HY3020D has a rating of 30 volts and 20 amps maximum so 30 times 20 equal 600 watts potential.

It is not recommended to exceed 80% of the maximum rated watts usage.

Always purchase a more powerful supply than your minimum requirements to allow for future growth and for out of spec devices.

All of the dc power supplies that are being discussed are variable both for volts and for watts but there is a difference in the absolute voltage control and the maximum amps control. When a given voltage is dialed in on the display (say 24 volts) the power supply will give exactly (+/- 2% accuracy on most units) that much voltage to the unit that will be powered.

On the other hand the amps control works differently because the power supply cannot be forced to provide more amps than the hooked up device requires. If a particular device needs 7 amps the power supply will not give it more even if the amp control is set at maximum (10 amps for the Mastech HY3010E). Once the hooked up and the equipment is running the exact amp level that is being used will be displayed on the meter (+/- 2% accuracy on most units). You can lower the amps that are provided and the corresponding new level will be displayed but you can't increase the level that it will draw.

There are two primary design types available. One is the traditional LINEAR design and the other is a newer SWITCHING design.

The LINEAR models will work for any application as long as the maximum power is not used on a continuous basis. The SWITCHING  models are best for radios, RC cars and trains and other non sensitive electronic equipment. They are not recommended for plating or ionizing.

The benefits of the LINEAR power supply is that they are heavy duty units that can handle continuous use and produce very low line noise that can effect sensitive equipment. There design of using large DC transformers, heat sinks and fans causes them to be heavier and more costly than their switching power supplies. Be careful when reading the details in an ad as some can be misleading regarding if they are linear or not. A 0-30 volt @ 0-5 amp dual linear power supply typically weighs between 30 and 35 pounds so a 15 pound unit will be a switching type even if the ad's description states linear.

The main benefits of a SWITCHING power supply are that they are much lighter and less costly over their switching counterparts. For example the Mastech HY3020D linear power supply weighs 41 pounds while the Mastech HY3020E switching power supply weighs less than 17 pounds.

Their display screens can come in many varieties: backlit LCD meters, red LED meters, green LED meters and the newest dual color LED meters such as the Mastech HY3005F-3 which has red and green LED meters.

 Many of these power supplies come in DUAL VARIABLE configurations which mean the supply has two independent supplies within the cabinet and they can be used in INDEPENDENT, SERIES or PARALLEL operation which can provide either dual 0-30V @ 0-5A or one 0-60V @ 0-5A or one 0-30V @ 0-10A connection for the Mastech HY3005D-3 for example. Dual supplies have -2 after their model numbers.

Triple power supplies provide dual variable and a third FIXED output which is usually 5 volts at 3 amps.

One important deciding factor that you should use after selecting a Mastech power supply for purchase on the Internet is to find out if the seller has a technician available. Most sellers do not and if something goes wrong with your supply during the warranty period there could be a delay in replacing it if the seller is out of stock.

Stock levels fluctuate and some times out of stock conditions can occur and the next replacement container ship could be months away. We have a full time technician available for Mastech and spare parts for them at the warranty center.

How to use a Multimeter

The basics or instructions of how to use a multimeter, including how to use an analog or analogue multimeter, or a digital multimeter, DMM, and using multimeter their best advantage.

Multimeters are one of the most commonly used pieces of electronics test equipment. Although basic operational multimeter instruction may be given when the test meter is bought, details of how to use the multimeter to test circuits and gain the maximum use from them are not always available.

Although there are major differences between the internal circuits within analogue and digital multimeter, the way in which they are used is comparatively similar. However separate sections are given below with instructions on how to use a digital multimeter and how to use an analogue multimeter.

How to use a digital multimeter

The operation of a DMM, digital multimeter, itself is normally very straightforward. With a knowledge of how to make voltage, current and resistance measurements (see the "Related Articles" on the left hand side of this page for further details) it is then a matter of putting the multimeter to use. If the meter is new then it will obviously be necessary to install a battery to power it. This is normally simple and straightforward and details can be found in the operating instructions for the DMM.

How to use an analogue multimeter

The operation of an analogue multimeter is quite easy. With a knowledge of how to make voltage, current and resistance measurements (see the "Related Articles" on the left hand side of this page for further details) it is only necessary to know how to use the multimeter itself. If the meter is new then it will obviously be necessary to install any battery or batteries needed for the resistance measurements.

Follow a number of simple steps:

1. Insert the probes into the correct connections - this is required because there may be a number of different connections that can be used. Be sure to get the right connections, and not put them into the ones for a low current measurement if a high voltage measurement is to be made - this could damage the multimeter.

2. Set switch to the correct measurement type and range for the measurement to be made. When selecting the range, ensure that the maximum for the particular range chosen is above that anticipated. The range on the multimeter can be reduced later if necessary. However by selecting a range that is too high, it prevents the meter being overloaded and any possible damage to the movement of the meter itself.

3. Optimize the range for the best reading. If possible adjust it so that the maximum deflection of the meter can be gained. In this way the most accurate reading will be gained.

4. Once the reading is complete, it is a wise precaution to place the probes into the voltage measurement sockets and turn the range to maximum voltage position. In this way if the meter is accidentally connected without thought for the range to be used, there is little chance of damage to the meter. This may not be true if it left set for a current reading, and the meter is accidentally connected across a high voltage point!


Multimeters are very easy to use, and they are the most essential piece of test equipment that is needed if any electronics construction work is to be undertaken. Fortunately the multimeter instructions of how to use them are straightforward, and they should give many years of good service is treated well. Additionally it is possible to use a multimeter to perform many types of test. Even the older analogue meters can be used in a variety of ways, and digital multimeter often have many measurement capabilities beyond the basic amps volts and ohms measurements.

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