![]() Reason being the wiring will have a fair amount of inductance which needs to be quenched along with the solenoid. ![]() Connect it across the solenoid terminals AT THE SWITCH. The fast diode is required as mentioned in the blurb. There is a good description on Core web site, read it. Also Amazon have nil stock of your original. This one has the distinct advantage of being locally available, has a good description on Core web site and has a schematic available. This is a high side switch as against the low side switches you have (which are US) but you need not concern yourself with the difference. The 32Ω measured across the solenoids is the coil DC resistance and indicates an operating current at 12V of 375mA. Forget about the MOV, you still need a diode. Indeed a lot of relays have this diode across the coil built in. With an inductive load (you can’t get much more inductive than a solenoid) you must use a fast diode to suppress the negative spike at switch off, Particularly when using electronic switching. Your drawings seem to indicate they could be reversed.ĭo you suggest the fast diodes be added as well? Please check and make sure you have got the “V IN” and V OUT connections correct. Core stock this SKU:CEO7844 or Jaycar ZR1039. In use it is common to connect the 2 outer legs together to obtain 20A capability and use as a single diode. The centre connection is cathode while the 2 outer legs are the 2 anodes. Actually 2 X 10A devices in the same package, common cathode. If you want the data sheet on your mosfet search D4184Ī suitable diode would be MBR20100CT which is 100V 20A schottky. The mosfet on your board is rated maximum 40V so you can see that unless you get rid of the generated voltage spike the applied voltage could be far in excess of what the mosfet is rated at and WILL be destroyed. In your case, I am only guessing here, it could be 100V or more (this can be measured with an oscilloscope) which is added to the original 12V. This can be many times the original voltage applied to the load and depends on many factors. When switching any inductive load a high voltage is generated at switch off by the rapidly collapsing magnetic field. Regardless what the supplier says, but I am sure they will agree. If the parallel connection is the case you WILL and I emphasise WILL need a fast schottky power diode across the solenoid. I will also check with the solenoid supplier re the fast diode. The Arduino is pretty limited in source and sink current capability and don’t forger the mosfet gate is s short to source at switch on because of this capacitor and pretty much a battery at switch off. If I am using an Arduino to operate a mosfet I try to use a device with a very small gate capacitor or use a NPN/PNP transistor driver circuit to supply or sink the required current alternatively there are mosfet driver chips available to do the job. You can check this by shorting the gate to source. I could not earlier locate a circuit for this board you are using to see exactly what it does so you will just have to have a look. There may be a bleeder resistor of about 10k between gate and source which should discharge the cap. You can even remove power and when you power up again THE MOSFET WILL LIKELY BE STILL ON. EVEN IF THE GATE (or trigger signal) HAS BEEN DISCONNECTED. Now if it hasn’t been discharged for some reason the mosfet will stay on. It has to be CHARGED to turn the Mosfet ON and DISCHARGED to turn it OFF. Refer earlier reply where I mentioned this capacitor. The second reason is if the gate capacitor has not been discharged by the Arduino properly. This is quite common snd this mosfet will probably have source and gate connected to keep the mosfet part off and just use the diode. I had assumed the second one has been connected across the solenoid and using the body diode for the flywheel suppression function. There seem to be 2 mosfets on that board. The one thing that will cause this is the non existence of a fast diode across the solenoid or the failure of this diode. The mosfets have failed as a short circuit. ![]() ![]() Yes there are a couple of things that will cause this.
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