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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.basics,sci.electronics.components,sci.electronics.misc,sci.electronics.repair
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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
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Automotive relay question
In article ,
says... 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 more than likely a snubber network, they normally have a resistor and cap in a single component.. Many times, they simply show it as a R across the coil because it's in series with a cap. http://en.wikipedia.org/wiki/Snubber |
#3
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Automotive relay question
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#5
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Automotive relay question
Followups set to sci.electronics.components .
In sci.electronics.components DaveC wrote: I have a 12V SPST cube relay in my junque box. The diagram molded into the relay's housing includes a component connected in parallel with the coil which looks suspiciously like a resistor. [...] What is the purpose of this resistor? It suppresses the inductive spike when the relay turns off. See page 3 of the Tyco application note http://www.te.com/commerce/DocumentD...=CS&DocLang=EN or http://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=Automotive_Rel ay_Applications&DocType=CS&DocLang=EN or even http://is.gd/uGsYcA I knew you could get automotive relays with nothing, a diode, or a resistor across the coil, but I'd never heard before that any of these shorten the life of the relay. I wonder what the mechanism is... does it damage the coil winding insulation, or does it try to move the armature a little, or what? Matt Roberds |
#6
Posted to sci.electronics.basics,sci.electronics.components,sci.electronics.misc,sci.electronics.repair
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Automotive relay question
In article ,
says... more than likely a snubber network, they normally have a resistor and cap in a single component.. Many times, they simply show it as a R across the coil because it's in series with a cap. http://en.wikipedia.org/wiki/Snubber I haven't ever seen a snubber in a relay. It usually has the iron designed to short-circuit fast field changes. -- We buy 24VDC relays with snubber networks in side on the coil, it removes the need to put one on the terminals. It comes in handy when you're doing a few rows of relays with PLCs and micro controllers involved. They don't like the little pulse noise in the lines. Those with diodes in them are ok for driver component protection but they still can generate a noise pulse, just not a damaging one. When you have bundles of wires tightly packed together, in race ways and wire harnesses, like in cars, it can cross talk very well. Jamie |
#7
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Automotive relay question
"Maynard A. Philbrook Jr." wrote in message ... In article , says... 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 more than likely a snubber network, they normally have a resistor and cap in a single component.. Many times, they simply show it as a R across the coil because it's in series with a cap. Looking at a data sheet for an Omron automotive relay that shows this 'unknown device' across the coil, it appears to detail it in the specs as "1.1k suppression". It gives the coil resistance with and without this included. If there was any series C involved, then the coil resistance would not change with or without the device. This leads me to believe that it is nothing more or less than a simple current dumping resistor with a value of 1.1k Arfa http://en.wikipedia.org/wiki/Snubber |
#8
Posted to sci.electronics.basics,sci.electronics.components,sci.electronics.misc,sci.electronics.repair
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Automotive relay question
On 10/17/2014 8:57 AM, 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 It's usually a suppression resistor. Bosch used them a lot. |
#9
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Automotive relay question
It's usually a suppression resistor. Bosch used them a lot.
So the resistor dissipates the coil energy as the magnetic field collapses? You still get back-emf; more than with a diode but less than without anything? This one is a Bosch. Thanks. |
#10
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Automotive relay question
On 10/19/2014 3:30 AM, DaveC wrote:
It's usually a suppression resistor. Bosch used them a lot. So the resistor dissipates the coil energy as the magnetic field collapses? You still get back-emf; more than with a diode but less than without anything? This one is a Bosch. Thanks. Pretty much. |
#11
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Automotive relay question
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#12
Posted to sci.electronics.basics,sci.electronics.components,sci.electronics.misc,sci.electronics.repair
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Automotive relay question
"DaveC" wrote in message ... 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? There are such things as bidirectional transient suppressor diodes. Although I've never seen it on a car relay - a resistor isn't impossible, it could act as a "Q-spoiler" to damp inductive ringing. Or a bit more likely - a VDR. |
#13
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Automotive relay question
On 10/24/2014 2:02 PM, Ian Field wrote:
"DaveC" wrote in message ... 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? There are such things as bidirectional transient suppressor diodes. Although I've never seen it on a car relay - a resistor isn't impossible, it could act as a "Q-spoiler" to damp inductive ringing. Or a bit more likely - a VDR. Think of it as an RC snubber without the C. The capacitance will be whatever the coil and wiring supply. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net |
#14
Posted to sci.electronics.basics,sci.electronics.components,sci.electronics.misc,sci.electronics.repair
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Automotive relay question
Think of it as an RC snubber without the C. The capacitance will be whatever the coil and wiring supply. Cheers Phil Hobbs Don't you think that's starting to get a bit complicated Phil ? I would have thought that the amount of C in the coil and associated wiring was comparatively small - even given a car wiring loom. I reckon that its just a simple damping load across the L to encourage it not to 'ring' so fiercely as the field collapses ?? Arfa |
#15
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Automotive relay question
On 10/25/2014 08:54 AM, Arfa Daily wrote:
Think of it as an RC snubber without the C. The capacitance will be whatever the coil and wiring supply. Cheers Phil Hobbs Don't you think that's starting to get a bit complicated Phil ? I would have thought that the amount of C in the coil and associated wiring was comparatively small - even given a car wiring loom. I reckon that its just a simple damping load across the L to encourage it not to 'ring' so fiercely as the field collapses ?? Arfa The reason you care about the ringing is primarily insulation degradation due to the peak voltage. If the parallel resistor is six times the coil resistance, the peak voltage kick will be close to six times the drive voltage of the relay (because the coil current wants to be constant). That's how RC snubbers work, except that since they don't represent a DC load, you can use lower value resistors (with a tradeoff in switching speed, of course). The speed of the ringing is set mostly by the capacitance of the winding, unless the snubber resistor is very small. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net |
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