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If the current through a coil is interrupted, the coil generates a high voltage (such as in the old car ignition coils). The diode provides a path for the current to decay naturally, thus avoiding the high voltage.
Wiki User
∙ 13y ago
Wiki User
∙ 8y agoIt's called flywheel diode and the purpose is for the diode to pass the current when the relay coil is switched off. Without a flywheel diode the inductance of the coil would produce sparking in the switch, but the diode allows the current to decay slowly with so sparks.
Wiki User
∙ 10y agoA diode is used across the relay coil to absorb the back emf pulse that occurs when the power to the coil is interrupted.
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How can you reduce back current while using relay?
You put a diode in parallel with the coil. The cathode end of the diode connects to the plus side of the coil and the anode connects to the negative side. The cathode is usually marked with a line at one end of the component.
How do you check a relay coil?
Put an ohm meter across the coil and read the resistance. Usually they are quite high depending on the voltage and the size. If you can compare with an known good one then you can know what to expect give or take say 15%. If there is no reading it is open circuited and if it is very low then it has a short within it. Some times the smell will show a short.
How do you test diode using multimeter?
A Diode will pass the electrical current into one direction, and will produce high resistance in the opposite direction. To check a diode, use an Ohm-Meter or a "multi meter", and set to measure resistance "Ohm", in the 1k Scale. You will have two leads in the ohm meter + and - (Red and Black) If you measure the resistance in one direction ( red lead touching one of the diode leads , and the black is touching the other lead ) , and you found a low resistance in one direction, and a very high resistance in the other direction ( by reversing the red/black leads) , this diode should be ok. If you find low resistance in both directions, this diode is shorted, and is damaged If you find high resistance in both directions, this diode is open circuit, and is damaged
What the Generator lockout relay?
generator lockout relay is a relay that the output of other relays energize this relay and its out put use for tripping of generator. this relay must be reset manually
What happens to the load if reverse the polarity of diode?
if you reverse the diode in a half wave rectifier, you would expect the A- Ripple to increase B- output to be less filtered C- out put polarity to be reversed D- output voltage to decrease
How can you reduce back current while using relay?
You put a diode in parallel with the coil. The cathode end of the diode connects to the plus side of the coil and the anode connects to the negative side. The cathode is usually marked with a line at one end of the component.
How do you test a relay if it is faulty or not?
Put a voltage(12V dc) across the coil terminals and see if it clicks. At the same time put a test light (battery operated) across the switched terminals and see if the light lights up. If if does, the relay is good. If it clicks and the light doesn't light up, the contacts are band. If it doesn't click, the coil is bad. OR GO to any auto parts store, buy a new relay( about $2.00) and plug it in.
If you put a new coil on an 88 Ranger and there is still no fire or spark on coil what should you do?
Try The Relay On the Pass side under the hood.. it fixed mine
How do check a for a bad fuel relay on a Volvo 740?
I don't have the pinout, however you can put your fingers on the relay, put the ignition on you must feel a click at the fuel relay coil. However, the contacts relay are maybe defects, if you have a doubt change it. It's maybe 20$. Be sure about fuses.
How do you check a relay coil?
Put an ohm meter across the coil and read the resistance. Usually they are quite high depending on the voltage and the size. If you can compare with an known good one then you can know what to expect give or take say 15%. If there is no reading it is open circuited and if it is very low then it has a short within it. Some times the smell will show a short.
How do you test diode using multimeter?
A Diode will pass the electrical current into one direction, and will produce high resistance in the opposite direction. To check a diode, use an Ohm-Meter or a "multi meter", and set to measure resistance "Ohm", in the 1k Scale. You will have two leads in the ohm meter + and - (Red and Black) If you measure the resistance in one direction ( red lead touching one of the diode leads , and the black is touching the other lead ) , and you found a low resistance in one direction, and a very high resistance in the other direction ( by reversing the red/black leads) , this diode should be ok. If you find low resistance in both directions, this diode is shorted, and is damaged If you find high resistance in both directions, this diode is open circuit, and is damaged
What way does a diode conduct?
A typical diode has a band on one end of the diode. That is considered the positive end. Current is considered to flow from the negative end to the positive end. In power diodes, they can be of two types-- positive polarity and negative polarity. Power diodes are usually designed with one end of the diode to be mounted in a heat sink. Since the desire is to allow current to flow in only one direction, the engineering of the circuit determines which way the current is designed to flow, hence the designation of positive or negative diodes especially for power diodes. A typical car alternator has 3 positive diodes and 3 negative diodes for a total of six.
How can you replace a diode with a relay in a circuit?
In certain cases, yes. A diode is a valve for current. A relay is a switch that is actuated by current. If you have a flow of current going from A to B and you only want it to go from A to B you can use a diode in series between A and B. You can also use a switch in series between A and B that is controlled by a relay that is in parallel with the switch. Add a large resistor in series with the relay so that it does not permit too much current to back flow through it. Configure the relay to open the switch when the current is trying to go from B to A and to close when the current is trying to go from A to B. This is not a leak free valve. Current will be going back through the relay while it is holding the switch open. As mentioned put a large resistor in series with it to reduce this. You cannot have this resistance too large though or the relay will not have enough current to maintain the switch. Another caveate is that this will not be a fast acting valve. There will be some time during current direction changes when the switch will be spending time openning and closing. It is a mechanical switch after all.
What value resistor and diode would you need to drop voltage from 12 volts ac to 1.2 volts dc?
I'm not sure you understand what you're asking. A diode will have a voltage drop of ~.5-.7 volts. If you put a diode and resistor in series, the voltage across the diode will be .5 - .7 volts, and the voltage drop across the resistor will be (supply voltage - diode voltage drop). If you are trying to rectify to DC, you need at the least a half wave rectifier (two diodes), and some system to remove the ripple. The rectifier simply chops the AC waveform, so for the part of the supply sine wave that is ~.5 or less, the output of the rectifier will be zero. The top part of the sign wave will show up on the output of the rectifier, but will be slightly smaller (due to the voltage drop across the diode). You'll need to get ride of this rippling for true DC. One fairly easy way to do this is to use a zener diode. It will attempt to keep the voltage drop across it the same, so purchase a 1.2 volt zener diode. The problem with this is the zener diode will saturate if you have too heavy a load. What I've done on simple projects is to use a zener diode to bias the base to collector voltage of a transistor, with the emitter acting as the output (an NPN BJT usually). I also used a fairly large capacitor to help minimize the ripple as well, although this may not be necessary for you.
Where is the ac heater fan relay located?
The AC/heater fan relay on most vehicles is located next to the blower motor on the firewall. It is inside the engine compartment. Some vehicles also put this part in front of the heater coil which is usually under the dash on the passenger side of the vehicle. To access the relay here, the glove compartment might have to be removed.
What does it mean to say a diode has a forward bias?
Diodes allow current to flow in only one direction, and if the diode is put a certain way around in the circuit such that it DOES allow current to flow, then it is forward biassed. If the diode is put in the circuit so that it doesn't allow the current to flow, then it is reverse biassed.It is just a term used to describe the orientation of the diode relative to the (conventional) flow of current through the circuit.
How can you say diode is gone in generator bridge rectifier?
The most straightforward and unbiased way is to remove the diode from the circuit and check it with a diode tester. Alternatively, if the diode is shorted, the bridged will measure shorted. If it is open, running the generator and monitoring the output with an oscilloscope will reveal a missing phase. One example of an open diode problem in an automobile alternator application is that the alternator will put out enough current to keep the system fail light off, but not put out enough current to meet rated output load.
