I have a 12V SPST cube relay in my junque box. The diagram molded into the
which looks suspiciously like a resistor.
(using a current-limited power supply) and the same current draw is measured.
What is the purpose of this resistor?
Thanks, Dave
I have a 12V SPST cube relay in my junque box. The diagram molded into the
which looks suspiciously like a resistor.
(using a current-limited power supply) and the same current draw is measured.
What is the purpose of this resistor?
Thanks, Dave
I have a 12V SPST cube relay in my junque box. The diagram molded into the
which looks suspiciously like a resistor.
(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?
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.
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.
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.
Also, it could be a bidirectional TVS diode, those will clamp either polarity when ever the voltage exceeds the coil rating.
Jamie
Not really, could be a bidirectional TVS of sorts.
Jamie
I haven't ever seen a snubber in a relay. It usually has the iron designed to short-circuit fast field changes.
-- I will not see posts from astraweb, theremailer, dizum, or google because they host Usenet flooders.
It suppresses the inductive spike when the relay turns off. See page
3 of the Tyco application noteI 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
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
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.
:) Jamie
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
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