Relay to control dc current

Other Hardware General Electronics
1

HI guys,

I am a noob to real life electronics and Arduino (though i have watched hours of videos, and i have a mechanical engineering degree)

I am currently trying to turn a DC device off (quietly), when a PIR senses movement, and after a 1 minute delay I want the device to start working again.

I have already built the circuit using Arduino uno and a solid state relay, and after all the process, I have realized that the ssr doesn't turn off and on my dc device.

Reading some more on the web, and I have understood that these ssr's are made for DC or AC only, and I assume that mine is an AC one.
(5V 1/2/4/8 Channel SSR G3MB-202P Solid State Relay Module For Arduino | eBay)

is there a quiet relay to control dc current (12v, 1A) instead of ssr ?
or is there an ssr for dc that can be used along with the arduino ?

I have been searching for a while until I decided to ask you guys.

please supply a link for these creatures, if they exist at all.

many thanks

doron

2

There are DC SSRs, I have used them. Do a parametric search at Digikey, Mouser or your favorite vendor.

What is the load (volts , amps, Inductive?)?

You may be able to use just a MOSFET. Way cheaper than a DC SSR.

3

Thanks for your answer,
I will be searching for these dc ssr's,
and also, dedicate the next hours to learn how to incorporate a mosfet in my circuit,
using a mosfet (if i have one in my electronics beginner sets) will probably be faster than waiting to get an ssr from some vendor.
BTW it's 12V, 2Amps.
doron

4

Is the load a motor, solenoid or other inductive load? What, exactly, is the load?

Can you post the part number of your MOSFET?

5

  1. I still don't have MOSFET, I am currently checking for the right one for my project.

  2. The load are some computer fans in parallel, each is 12Vdc, 0.2A.

  3. I want the fans to work, and when the PIR senses movement, to stop the fans from working for 5 minutes and then turn turn on.

  4. I think that I need p-channel mosfet, so when the load is on (normally) I am not wasting the Arduíno battery, and when the PIR sends HIGH, it will send HIGH to the p-channel MOSFET and the fans will turn off. offcourse, I will add a desired delay in the code.

but now i have 2 questions :

  1. Am i right about p-channel MOSFETs ?
  2. If the MOSFET is indicated 100V, 30A, will it work with my load ?

Thanks

6
  1. Am i right about p-channel MOSFETs ?

Not really. Unlike a bipolar transistor it takes virtually no current to keep a MOSFET turned on. Some current will flow into the gate when the voltage is first applied to the gate to charge the gate capacitance. Once the gate cap is charged the gate becomes a very high resistance (no current can flow). So switching the low side (ground) of the fans with a N channel MOSFET would work. Switching a P channel on the high side is more complicated, usually requiring another transistor to drive the gate.

If the MOSFET is indicated 100V, 30A, will it work with my load ?

To work with an Arduino, the MOSFET must be a logic level device. That means that the MOSFET is fully turned on by a 5V (Uno) output. Look at the Rds(on) spec of the device. Is the Rds(on) specified at 5V or lower? Also the drain-source resistance needs to be as low as possible.

I repeat, post the MOSFET part number.

7

Here are 2 types of MOSFETS, both are logic level, in the end of the post I have 2 questions about them.

N-chanel MOSFET :

P-chanel MOSFET :
https://www.ebay.com/itm/10-x-RFP10P03L-Logic-Level-P-Channel-Power-MOSFET-TO-220-30V-10A/184022255709?hash=item2ad894c85d:g:IxsAAOSwaTtdwBKc

I will probably play with both MOSFETS, in order to learn by action what is the difference in their configuration in a circuit.

  1. both are rated 100v, is this the maximum voltage that it accepts ? so 12V is no problem ? or it needs a high voltage to function, and 12v might not be enough ?
  2. the threshold is min 1v, max 2v, what does it mean ? the arduino sends 5v in HIGH, will it be ok ?

Thanks.

8

For the arduino start with and become familiar with N-Channel MOSFETs, they are much easier to interface to Start with a Logic Level Avalanche Rated FET. Package etc depends on your preferences. For only a few use the high amp devices they will run cool and save you a heat sink. For LEDs 2N7002 work nicely. Connect the source to ground, the gate to the arduino pin (you can use 50 Ohm or less if you like in series) with a 10K pull down resistor at the gate. The 10K keeps the MOSFET off when the arduino is in reset The drain goes to your load which has its other end connected to the + voltage, can be 3V 5V 12V etc depending on the FET. In all the examples you see MOSFETs connected to motors, with a diode across the motor, this diode is not needed with the avalanche rated MOSFETs. Look at this link for some ideas. http://www.irf.com/product-info/datasheets/data/irlz44n.pdf Here is another link that well help: https://www.quora.com/What-amount-of-voltage-is-required-to-switch-MOSFET
This response is to help you get started in solving your problem, not solve it for you.
Good Luck & Have Fun!
Gil

9

Thanks

10

The "standard" circuit:

For a two-terminal device, you use a logic-level N-channel MOSFET - far easier to come by and much more practical than the additional complexity (and cost) of a high-side driver. :grinning:

11

Thanks

12

Just a note on grounding. The Arduino, Mosfet and 12V supply have to have the same ground connection.

13

Thanks