Manual Push Button Starters vs Automatic Starters

 Manual Push Button Starters vs Automatic Starters

Manual push-button starters are used for fewer numbers of motors or temporary motor running operations. These starters are made with two or three load contacts. Two load contact starters are used for single phase motor starting or DC motor. Whereas the three load contact starters are used for three-phase motors operation. Manual Push-button type starters are made integral and not fractional power size or horsepower size. The two load contact type starters are generally used to control 5 horsepower single-phase motor or 2 horse-power DC or direct current motor. The three-load contacts starter is capable of controlling three-phase motors powered up to 10 horsepower or 7.5KW.

A manual three contacts push-button starter is shown here below.

Manual Push button starter

Also, you can see the circuit schematic for such a start below as in industry you will deal with the circuit schematic and not the actual starter drawing.

Manual Push Button Starter Schematic

In a manual push-button type starter, there are two pushbuttons for a basic type starter. Whereas there are three push buttons for forward reverse starter. One button is for Start other button is for Stop and the third button is for Reverse in case of forward reverse starter.

In this type of starter, the overload is thermal type. Nowadays electronic overload Relays are also common. In case of thermal overload, if any of the phases to the motor draws more current, the bimetal strip attached to it will tilt and will break the current path to the contactor coil which will trip the motor by switching the contactor off. Later the thermal overload or electronic overload can be reset by pressing a reset button on the overload relay. Pressing the reset button resets the mechanism attached to the tripping system of the overload. The function of the buttons is to Start or Stop the motor. There is a seal-type contact on the contactor which is used to hold the motor in the Start condition.

Motor circuit Troubleshooting. Reasons for Motor overloading

Motor circuit Troubleshooting. Reasons for Motor overloading

In the process industry motors are used all over. Thousands of motors in the single process industry are not a big number. Such electric motors are used to drive different types of mechanical loads like pumps, fans, belt conveyors, mixers, grinders, or cutters. Mostly Induction motors are used in industry. They can be single-phase or three-phase. Three-phase motors are very common in the industry due to their efficient operation and robust design. In normal conditions motors are running smoothly without giving any trouble. But sometimes when load running conditions are not even, the motors trip on overload. This motor tripping on overload is necessary to prevent the motor from blowing and burning. If the motor is not tripped in case of an overload, the motor takes more current which heats up the motor, and eventually motor burns due to much current consumption. To prevent the motor from such catastrophic burning an overload protection relay is used in the motor circuit. The function of the motor overload relay is to monitor the motor current all the time and trip the motor in case of any overload detected.

Three-phase motor starter circuit diagram

Now in the case of an overloaded motor, the service technician or engineer must check the motor as well as the motor circuit. There should be no obvious damage to the motor or its circuit. All three phases should available in the case of a three-phase system. In the case of a single-phase motor, it should be confirmed that the phase and neutral both are present. Also, the motor should be checked that there should no restriction to motor rotation. In the case of a small motor, the motor shaft could be rotated with hand along with load connected. But in the case of a very big motor, the motor shaft can't be rotated with a hand. It's a must to confirm motor and load bearings. Sometimes the motor or load bearings are damages due to which the motor is overloaded. Also, the mechanical process load must be evaluated so that there should be no excessive load on the motor. If the load is too much, it is recommended to decrease the load before giving a start to the motor after resetting. At the restart, the motor load current must be checked and measured with the help of a clamp meter. In the case of a single-phase motor only one phase current would be measured. Whereas in the case of a three-phase motor all three-phased would be measured. The motor-rated current could be obtained from the motor nameplate.

motor current measurement

All three phases current in the case of a three-phase motor should be closely the same. The large difference is the current shows motor internal winding short circuit which could be phase to phase winding short circuit or phase to ground short circuit. In case of any abnormality in the current reading, the service technician must evaluate the case of the problem and must solve the problem before putting back the motor into service. Motor overload settings are made on 100% to 125% of the motor rated current depends upon the motor and the process conditions.

Motor overload tripping reason is not only the motor's high current consumption. Thermal overload responds to heat. The tripping principle of the thermal overload is based on heating. So any heat source can activate the thermal overload and can cause a false motor overload trip. In such a case the service technician should evaluate the reason for the heat source and should solve the overheating reason of the overload protection relay. The main cause of the heating is the surrounding of the motor or ambient. The main reason for overheating can be a loose connection. Any loose terminals on the motor starter cause overload terminal overheating which further trips the overload relay. Tightening the motor terminals and starter terminals would solve the issue. Also if the starter is located in the location where excessive heat is acting on the thermal overload relay, the heat caused by the motor current and the external heating would be enough to trip the overload. In such a situation an exhaust fan blowing air around the starter would help to reduce the ambient heating on the thermal overload. Mostly manual starters which are installed in a closed box affect more due to heating problems. In such a case special ventilation arrangement is a must to keep things cool.

Supersonic anti-ship missiles – not very stealthy!

 Supersonic anti-ship missiles – not very stealthy!

The advantage of a ship with a low radar signature is that it is less visible to anti-ship missiles that typically have active radar homing during the terminal phase. There are other missiles that use infrared homing, so a low infrared signature is important as well.

A more advanced missile also can cheat the ship’s electronic signature, for example, the JSM mentioned above which has an RF sensor under development in Australia.

As mentioned earlier, ships rely on a close-in weapons system (CIWS) to destroy incoming missiles. The supersonic missiles give the CIWS very little time to react before it hits the ship. There is cur-rent controversy since Russia and China have supersonic anti-ship cruise missiles and the United States and allies only have relatively few in service.

There are several reasons for this. Faster missiles tend to fly at higher altitudes where the air is thinner, making them visible from a greater distance as compared to a sea-skimming sub-sonic missile.

A missile flying at 10m above the surface can be detected at 31km with a radar 20m above the surface, but a Russian Kh-32 missile with a speed of approximately Mach 4.1 flies at 40,500m altitude and could theoretically be detected at a range of 845km away. This means longer-range anti-missile missiles could en-gage it before coming into range of the CIWS.

So a less speed, lower flying missiles are only detectable much later than a faster, higher-flying ones. Therefore, faster missiles are not necessarily better.

Car immobilizer defect and problem needed to be solved

Car immobilizer defect and problem needed to be solved

A high-quality cassette deck has been given which is by Grundig which I would like to use, but it needs a set of drive belts. I have not had good luck obtaining suitable belts here or overseas and wondered if any readers could suggest a source.

Also, we recently purchased a 1994 car which had an engine immobilizer fitted from new. The documentation for the car means the service manual indicates it was installed by Fortronic Forcefield Car Security Systems. All of their communication contact listings in the paperwork for them are no longer valid.

I am sure some readers here know anything about these systems and particularly, how to bypass or disable such immobilizers. 

It is operated in the way that a 6.35mm phono plug is inserted into a stereo headphone-type socket on the dashboard and then removed. We would have 60 seconds time or one minute time to insert the ignition key and start the car.

I see no brand on the immobilizer module. The phono plug measures 9kW tip to sleeve, 13kW ring to sleeve, and 22k W tip to ring. We have three plugs that all measure the same, but one does not work; that’s a separate puzzle. It would be very appreciative and be grateful if anybody had any information.

Finally, after 50 years or so of being an electronics hobbyist and building many loudspeakers, amplifiers, etc from different manufacturers, I am reaching a point where I cannot continue this at the same pace. 

I have the inevitable collection of bits and pieces leftover from projects that will not proceed as things are changing so rapidly in our modern world.

Rather than just dump all this stuff into the trash bin, I would like to see if any enthusiasts want all/ any of it at very reasonable prices. If anyone is interested, please feel free to e-mail me as I can send a full list back as an e-mail attachment for perusal. It is a mix of mostly new parts and a small number of slightly used parts.

I’m selling the items on an as-is “lucky dip” basis, and I am not offering returns/ refunds. I would prefer to strike an overall price or a price for groups of items, but do not want to sell them individually.

The list includes 8W l-pads, pan -el meters, 25 & 50W resistors, fuses, crossover PCBs, diodes, regulators, transistor mounting hardware, poly -switches, speaker connector strips, headphone sockets and plugs, RCA socket plates, plastic and aluminium knobs, Jiffy boxes, 100V line trans -formers, CB microphones (still in bub -ble wrap), heatsinks, RCA leads etc.

Medical thermometer accuracy

 Medical thermometer accuracy 

In this current blog post, I am discussing a chronic shortage of thermometers, and many of them may be inaccurate, as I pointed out in my article on thermometer calibration.

Many cheap digital thermometers are only accurate to ±2°C, and in some cases can be worse than that. Even high-quality branded thermometers which are from pharmacies and hospitals can be inaccurate. If you get a high temperature reading and worry that you may be sick, only to find out that the thermometer was reading high!

We have an infrared thermometer. This cost me $15 some years ago (currently they cost a minimum of $80) and I checked it on the calibrator as being accurate to within ±0.5°C. We had pointed a medical thermometer at our foreheads, and we have been checking ourselves every day, even though we know we are well. My body temperatures readings vary quite a bit, depending on the time of day and whether we have recently eaten.

Now I have a baseline for my own healthy temperature, so if we do contract the dreaded virus and our temperature increases, we will know instantly that we are in trouble.

There are many people in this world who worry a lot about their health (especially in the current environment) so I can only stress that you need to set your baseline when you are healthy. There is no problem if you are using the same thermometer at all times when you are checking your body temperature as this way you will be comfortable with one thermometer and its readings.