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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
Posted to sci.electronics.repair,sci.electronics.misc,sci.electronics.basics
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Automotive relay question
I have a 12V SPST cube relay in my junque box. The diagram molded into the
relayıs housing includes a component connected in parallel with the coil which looks suspiciously like a resistor. Itıs not a back-emf diode: I connected the relay coil using both polarities (using a current-limited power supply) and the same current draw is measured. What is the purpose of this resistor? Thanks, Dave |
#2
Posted to sci.electronics.repair,sci.electronics.misc,sci.electronics.basics
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Automotive relay question
On Fri, 17 Oct 2014 06:38:27 -0700, DaveC wrote:
I have a 12V SPST cube relay in my junque box. The diagram molded into the relayıs housing includes a component connected in parallel with the coil which looks suspiciously like a resistor. Itıs not a back-emf diode: I connected the relay coil using both polarities (using a current-limited power supply) and the same current draw is measured. What is the purpose of this resistor? Thanks, Dave And what voltage is across your coil as you measured this 'same' current? |
#3
Posted to sci.electronics.repair,sci.electronics.misc,sci.electronics.basics
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Automotive relay question
On Fri, 17 Oct 2014 06:38:27 -0700, DaveC wrote:
I have a 12V SPST cube relay in my junque box. The diagram molded into the relayıs housing includes a component connected in parallel with the coil which looks suspiciously like a resistor. Itıs not a back-emf diode: I connected the relay coil using both polarities (using a current-limited power supply) and the same current draw is measured. What is the purpose of this resistor? Thanks, Dave Don't know about that specific case, BUT envision current flowing through the inductor, then you turn it off and the current has to go somewhere, it goes through a resistor. Since you knew the current through the coil, you know the voltage that can 'pop' across the resistor [equal to the drive current times the resistance, but reverse polarity] This technique is sometimes used to 'dump' the current out of an inductor faster. A small catch diode can take a LONG time, but the higher voltage of the current going through the resistor dumps the energy pretty fast. The area under the curves is pretty constant. High voltage is fast, low voltage takes a long time. |
#4
Posted to sci.electronics.repair,sci.electronics.misc
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Automotive relay question
On 17.10.14 15:38, DaveC wrote:
I have a 12V SPST cube relay in my junque box. The diagram molded into the relayıs housing includes a component connected in parallel with the coil which looks suspiciously like a resistor. Itıs not a back-emf diode: I connected the relay coil using both polarities (using a current-limited power supply) and the same current draw is measured. What is the purpose of this resistor? Thanks, Dave Congratulations. You found the perfect way of killing a protection diode. After this the diode will bother you no more. Dont touch my car please. |
#5
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Automotive relay question
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