Hi,
I want to use a 5vdc electromagnetic lock such as this one:
It says that about 0.8A are being drawn when power is on(and unlock).
Is the current being drawn all the time the lock is unlocked or is it momentarily?
Thanks,
Omri.
It is a solenoid! In order for the pin to be pulled, it needs power. If you design your project so the door or whatever is being unlocked, is able to be moved so the latch is open, then there is no need for continuous power.
In short, yes, continuous to pull the pin.
Paul
Most solenoids like that are not rated for continuous duty (they overheat if left on continuously), note...
Do not drive the solenoid with the Arduino, you will only wind up replacing it. You can use a simple Avalanche Rated logic level MOSFET to do the job. No fly back diode is needed the MOSFET will do it for you. It is in the UIS rating on the data sheet. As far as the lock apparently you are designing it so how it works is up to you. From the data sheet "Note: When using an electric lock, the unlocking time should be controlled within 0-5 seconds, avoiding the excessive unlocking time and causing the electric lock temperature to rise, resulting in electric lock damage" That time is a design parameter you need to consider.
gilshultz:
Do not drive the solenoid with the Arduino, you will only wind up replacing it. You can use a simple Avalanche Rated logic level MOSFET to do the job. No fly back diode is needed the MOSFET will do it for you. It is in the UIS rating on the data sheet. As far as the lock apparently you are designing it so how it works is up to you. From the data sheet "Note: When using an electric lock, the unlocking time should be controlled within 0-5 seconds, avoiding the excessive unlocking time and causing the electric lock temperature to rise, resulting in electric lock damage" That time is a design parameter you need to consider.
I was not intending unlocking it with the arduino power(only the open signal itself)
What diode are you talking about?
Are the 0-5 seconds that cause the temperature to rise refer to the operating sognal(which should very short using microcontroller) or the time the lock is open?
Thanks,
Omri.
gilshultz:
Do not drive the solenoid with the Arduino, you will only wind up replacing it. You can use a simple Avalanche Rated logic level MOSFET to do the job. No fly back diode is needed the MOSFET will do it for you. It is in the UIS rating on the data sheet. As far as the lock apparently you are designing it so how it works is up to you. From the data sheet "Note: When using an electric lock, the unlocking time should be controlled within 0-5 seconds, avoiding the excessive unlocking time and causing the electric lock temperature to rise, resulting in electric lock damage" That time is a design parameter you need to consider.
You are still obsessed with avalanche rating and thus getting this wrong.
All inductive loads should be switched with a free-wheel diode to prevent huge voltage spikes that cause
interference to other parts of the circuit and may destroy the switching device.
For instance:
The free wheel diode should be rated for the current taken by the solenoid. The MOSFET on-resistance should
be appropriate to the load current (it will dissipate I-squared-R when on), and the MOSFET needs to be
a logic-level n-channel device.
Mark, maybe you should take a course or two on MOSFETs. If you understood the data sheet and what it is telling you you would maybe understand what I am saying. The article you quote is several years old and does not consider UIS (avalanche rated) MOSFETs. As Defined a TTL Signal is a kind of hardware interface standard based on the electrical properties of TTL (Transistor-Transistor Logic). For a TTL input this means that anything below 0.8 volts is a “zero” and anything above 2.4 volts is a “one,” and that it presents a load of less than 1.6ma to the driving circuit. Other then that is is reasonably close. Consider Many also show a repetitive UIS rating. Contact your local FAE from one of the MOSFET suppliers, they may explain it to you. If you look at the UIS test shown on many of the data sheets you will understand how this is tested. Look at the size of the inductor used to perform the test. Many manafacturers do this as a 100% test. It has a lot more inductance then the solenoids and motors typically used here. I have set up the tests, wrote the specifications and validated it. When doing it with the MOSFET or diode there is no spike generated, it is a small negative transient. When an inductor is charged it takes some time, it does not draw the current instantly. However when it is disconnected the load the polarity REVERSES and the voltage rises until something limits it and its energy is dissipated. When you connect your diode look at how you connect it, it is set up to conduct in the opposite direction of the voltage used to drive the load. That is the same direction as the substrate diode. I tend to use a lower RDSon device because in many applications it eliminates the need for a heat sink. Many times it is more cost effective to put the money in the MOSFET instead of the heat sink and more reliable. This is important when making lots of units. It makes it easier for people to use the MOSFETs if they do not have to go through the heat sink calculations etc. There are many applications notes available for MOSFETs, read some of them, you might even find my name on some. As for background I worked for the MOSFET manufacturers since they first came out many years ago and taught a lot of people how to use them, both in the US and Europe.
MarkT:
You are still obsessed with avalanche rating and thus getting this wrong.All inductive loads should be switched with a free-wheel diode to prevent huge voltage spikes that cause
interference to other parts of the circuit and may destroy the switching device.For instance:
Using FET’s to Switch a load – Arduino, ESP8266, ESP32 & Raspberry Pi stuffThe free wheel diode should be rated for the current taken by the solenoid. The MOSFET on-resistance should
be appropriate to the load current (it will dissipate I-squared-R when on), and the MOSFET needs to be
a logic-level n-channel device.