Diodes for 12v
Diodes for 12v
(OP)
I'm not an electrician so bare with me.
I'm designing a simple circuit to operate warning lights and hydraulic valve solenoids and the circuit will only operate together if there is some sort of non return "valve" (diode?) in the line.
Question - will a diode work for a 12v circuit, ie allow current to run one way then if another part of the circuit is energised, will stop that current bypassing the diode?
I'm designing a simple circuit to operate warning lights and hydraulic valve solenoids and the circuit will only operate together if there is some sort of non return "valve" (diode?) in the line.
Question - will a diode work for a 12v circuit, ie allow current to run one way then if another part of the circuit is energised, will stop that current bypassing the diode?





RE: Diodes for 12v
Barry1961
RE: Diodes for 12v
RE: Diodes for 12v
In our systems each sensor activates a relay (as Barry said), the normally open contacts of which are all series-wired together. In this fashion the "good" light is on only when all sensors report everything is fine. From the normally closed pole of the relay we activate the "bad" light for each sensor to help operator find problem area.
RE: Diodes for 12v
RE: Diodes for 12v
Putting diodes across solenoids also affects the release time of the solenoid but is generally a necessary evil. Other schemes can be used to reduce the release time of the valve vs. just a diode. The affect is relatively small, usually around 20-100ms.
Don't spec something elaborate like a 12V diode because it is to small. The inductive kick will produce a large voltage at the time of de-energizing. This can be up to 20 times the voltage of the coil as a worst case. I would use the common 1N4004 which has a rating of 400V and they are cheap. A faster acting diode could be used as well but probably unnecessary.
Don't forget about the voltage drop across the diode in your application. The diode across the coil of the solenoid is not a concern here but diode used to block flow in one direction will be. It will be around 0.6-1V drop depending on the current going through it. If this is a concern, you can use diodes with a little less drop. Here is a data sheet link:
http://www.fairchildsemi.com/ds/1N/1N4004.pdf
RE: Diodes for 12v
I used some from International Rectifier that were rated for 70A as battery isolation for multiple generator batteries. The diodes supplied the "best battery" to the gear and kept from backfeeding the other systems. Slick.
Remember reverse voltage rating (higher the better), amp rating, and voltage drop across the diode.
JTK
RE: Diodes for 12v
RE: Diodes for 12v
Take two identical diodes. Connect the anodes together.
Connect this common point to one coil terminal. Connect the cathode of the first diode to the other coil terminal. This is the surge prevention diode. Apply the operating voltage to the cathode of the second diode. The current caused by the inductive discharges through this diode and the energy is disipated in the coil winding resistance. The current at the moment of de-energisation will be the current that was flowing in the coil. The voltage will be the voltage that was present at the time of de-energisation. The diodes do not have to be physically mounted on the coil, or even both in the same place, but I find this a good way to describe the proper polarity of the connections.
Both current and voltage will decay to zero, but the decay will not be instantaneous, and this is what causes the slow release of the solenoid.
The surge prevention diode may be rated the same as the operating diode. This is a conservative rating.
Other protection schemes allow a higher surge voltage which decays faster, giving a faster release time for the solenoid.
good luck.