Im using this radioshack relay:
http://www.radioshack.com/product/index.jsp?parentPage=search&summary=summary&cp=&accessories=accessories&productId=2062482&kw=relay&techSpecs=techSpecs¤tTab=features&custRatings=custRatings&features=features&origkw=relay&support=support&tab=summary
there is no mention that there is a diode protecting it, so is there a risk that it will damage my computer's PSU and compontents in the circuit? How can I prevent this, which diode and how to install it?
2007-01-02 06:12:44 · 3 answers · asked by amir_elmaani 1 in Science & Mathematics ➔ Engineering
The coil in a relay can cause a voltage spike which can cause damage to electronic components. The spike is caused when the current through the relay coil is stopped. The spike is most noticeable with DC powered coils.
Current flowing through the coil creates a magnetic field, so if the current changes so does the magnetic field.Electricity is created when ever a conductor is moved across a magnetic field. Electricity is also created when a magnetic field is moved across a conductor.
When the current in a relay is stopped the magnetic field will collapse. The collapsing magnetic filed cuts across the windings of the coil and generates a current.
The polarity of this spike is in the opposite direction of the current that created the magnetic field.
To control the spike a diode is placed in parallel with the coil. A diode only conducts in one direction. So when the coil is energized to activate the relay the diode is not conducting, but when power is removed from the coil and the reverse polarity spike is generated the diode will conduct. The conducting diode provides a low resistance path which connecting the lead of the coil together. This allows the spike coil potential to equalize through the diode and not the rest of the circuit.
2007-01-02 07:42:44 · answer #1 · answered by MarkG 7 · 0⤊ 0⤋
It should not hurt your power supply as long as the power to the relay is fused to prevent overcurrent from your supply.
The problem usually comes with the switch that turns the relay on/off. The short burst of current can sometimes fry out the switch.
A diode will help. Mark G is correct: install it across the coil from COM to +12VDC. Get a diode with the correct voltage rating (>12VDC) and current rating. 1N4001 (catalog number 276-1101 from Rad-Shack) should do. Put the side with the line on the hot 12VDC side.
2007-01-02 11:47:54 · answer #2 · answered by PAUL K 3 · 0⤊ 0⤋
u always have something in series with the relay coil even if it is only the power supply---usually you are switching the coil with something also 'protect' the ic with a resistor (value depends upon application) in the supply line (close) with a 'small' cap (value de......) across the supply lines as close as possible to the ic (across the top is as close as u can get it) strangely enough if you want the relay to de-energize (open) quickly leave out the diode
2016-05-23 06:49:16 · answer #3 · answered by Anonymous · 0⤊ 0⤋