Re: Battery Contactor Diode?


"Morgans" <jsmorgan@xxxxxxxxxxx> wrote in message
news:o7nLg.817$2J4.186@xxxxxxxxxxxxxxx

"Scott" <acepilot@xxxxxxxxxxx> wrote in message
news:4qSdnV92labCZmDZnZ2dnUVZ_s6dnZ2d@xxxxxxxxxxxxx

Nope, not really a concerning factor. Any of the "garden variety"
diodes in the 1N400X series should be fine. Just be sure to put the
cathode to the +12 or +24 volt side of the contactor coil and the anode
to the ground side (assuming a negative ground system).

Scott, at and above the 1N4004, the chip inside the case is physically more
robust and will take a spike of current a little better than, say, a 1N4001.





I am not very good with the electron understanding, but I would be
grateful
to understand this whole discussion.

Is the cathode normally the downstream side of the diode? What does the
installation like this, do, to help with the current spike?


Jim, as you know, a diode conducts current in one direction and blocks it
from conducting in the other direction. A positive voltage on the anode
forward biases the diode and the voltage will appear as a positive voltage
(less some small conduction drop of a volt or so) at the cathode. A
negative voltage on the anode will reverse bias the diode and it will not
appear as a negative voltage at the cathode.

Likewise, a negative voltage at the cathode will appear as a negative
voltage at the anode.

When a coil has a collapsing field, it produces a spike of energy as the
field attempts to keep the current through the coil constant. THis large
negative spike can and will cause some of the aircraft electronics to fail
catastrophically. One way of making sure that negative spike doesn't kill
the avionics is to shunt it to ground through a forward biased diode. That
way the most that can sneak through is a volt or so as opposed to several
hundred volt spikes without the diode. How do you forward bias a diode with
a negative voltage? You connect the CATHODE to the "hot" +12 volt terminal
of the coil and the ANODE to ground. THe negative spike is effectively
clipped at a volt or thereabouts.

Jim


.

Relevant Pages

  • Re: Sony STR-DB940 help..
    ... finding a short in the 15 volt line is tough. ... work on pinball machines .4 - .6 is ok diode but could possiable ... The shorted or leaky part is probably on the DSP board or an input switching ... If it's really a dead, dead short, i.e. zero point zero ohms, ...
    (sci.electronics.repair)
  • Re: does this circuit use conventional current?
    ... And current flows from anode to cathode. ... LED is just a diode. ... Looking at the simple circuit diagram, there's a 3V battery and two ... forward-biased diode permits current to flow, ...
    (sci.electronics.basics)
  • Re: does this circuit use conventional current?
    ... And current flows from anode to cathode. ... LED is just a diode. ... Thanks for the explanation of hole/electron flow. ...
    (sci.electronics.basics)
  • Re: Battery Contactor Diode?
    ... With the diode connected with its cathode to the positive voltage and its anode connected to ground, it is reverse biased and looks like an open circuit during normal operation. ...
    (rec.aviation.homebuilt)
  • Re: difference between anode and cathode?
    ... With a diode bridge, the positive ... > output comes from the cathode end of the diodes. ... making that the positive output of the bridge. ... That's not confusing. ...
    (sci.electronics.basics)