ECN Forum Forums Technical Discussion Electrical Theory and Applications diode on relay

ECN 7 Topic: Topic: diode on relay {CRW} ../Forum7/HTML/000402.html

A bit of O.B. yappin’ here.. {not under the immediate influence of headache pills}

This may be sortta’ gameshow-wrappup or color-commentary, but never any crested-suit with gold buttons, or even denm oxferd opncoller buttondwn with clipon mic or fake·pred’stressd a&f/o·n/gupy·jeenz. More jerrygarcia@1130am·wid·abowluhcornflayks·wardrowb..

• 1N400x-type {simple silicon—PN-junction, epoxy-potted <offshore>97¢-a-pegboard-bag} diodes are DC-mode, id est; polarity-sensitive devices that make extry-fast “fuses” if reverse connected.
  
  Else, lower-microfarad {±±±~~±~±±1 &#956;fd nonpolarized electrolytic <or> nonpolarized tantalum) or series resistor-capacitor networks are genrally considered oprating in the (DC or) AC mode, which means they will snub or ‘absorb/transcend’ a few low-nrgy, fast transients of both polritys.
  
  As mentioned by all in this thread it is not a trivial matter. and should not be passed up, for you or some of your peers will be faced with self snot-nosed self-important production MBA-wannabe puissants fretted with personally justified [surely sloppy·lortis-v2.11-extrapolated-over-stale-twwinkies] sophomoric-debated J·i·T and ever-looming carrot / mangeral ‘threats’ 2 theiyr precius vision o’ th’ anuual bonus pot.]
  
  Eboneezr Scroooge and his integagaltic corporate metacila Hävðrrd Bizînsss Shcool would kave newer beean so Platinum–Berkelium-Iridium GPS-sans–SA Magna—Cüum-Ladæ doern Successful.. [/i]

***BUMP***

Bumping the thread to life again!

Scott35

Scott35 brings up an interesting concept in his last "full" posting.
Having a capacitor as part of the load and drawing vis Current makes it hard on a set of contacts.
Considering that a relay coil could be fed via the Collector of a Power Transistor, makes the transistor vulnerable to over-currents from the coil.
Cascading relays/contactors,for more or heavier contacts makes this situation worse.

Hi, does anyone knows what is the consequence of accidently reversing the polarity of the diode (i.e. the cathode connecting to the negative side of the relay)?

Hello "Greenr" - welcome to the Forum!


This will result in the Diode being connected in the "Normal" Forward-Biased direction.
Unless there is a Resistor, or some other means of limiting the Current (AKA: "Ballasting"), the Diode will draw high Current - acting as a Short Circuit.

Results will be:
<OL TYPE=A>

[*] Relay's Coil unlikely to latch closed - due to the extreme voltage drop,


[*] Diode will lose smoke, and after all smoke is lossed, it will become an Open Circuit - or,


[*] High Current level will either/or:
- melt fuse / open thermal cutout,
- damage DC power supply.


[*] Or all of the above - depends on how sturdy the Diode is.
</OL>

The reason to Reverse-Bias the Diode, is so clamping may be achieved during the time when the "Saturated" Coil reacts inductively to the rapid change in current flow.
The "Inductive Kick" flows in the opposite direction - and such, a Reverse-Biased Diode may work effectively in an active circuit, as a clamp during the inductive kick, and still block current while the Coil is in normal "On" operation.

Make any sense?

Let me know if Yes / No

Scott35