Arduino to control 24 motor

Hi -

I am currently trying to create a project to basically turn on and off a 24v motor. Now this may sound simple, however - I need for the arduino nano to be able to do this for as long as possible on a 9v battery! Bare in mind that I need to keep the relay / motor on for 20 second burst.

So in summary :

Use arduino nano powered by a 9v battery to turn on a 24v DC motor for 20 sec bursts. This may need to happen for up to 20 times a day.

So whatever solution I adopt must be as lean as possible when it comes to choice of switching device. Here is what I have tried so far and a summary of the result :

  1. Use mechanical relay. This works fine - but draws too much power when activated (about 9 mA)
  2. Use SSR. This seemed like a greate solution as the relay only drew 3 mA when active. However, I cant seem to find one that switches DC. I made the mistake of buying this unit SSR

But I realised too late that it is only meant to switch AC not DC! Doh!

  1. I tried to use an N-Chanel mosfet. This seemed ok but it seemed to generate a lot of heat! So either I was not doing it correctly or its just not efficient.

Any help would be much appreciated. Please keep in mind that I am a relative novice with regards electronics :slight_smile:

Cheers..

What about using a bistable relay like the RT424F05. Pulses on and pulses off so no hold current required. Amazon sells this board. goo.gl/21Sw2X

Any SSR can switch DC just as well. It's a relay after all. They' mostly used for AC but should do DC just fine.

Then the MOSFET: you probably have the wrong type (not logic level so not opening completely, or underspecced for your motor current) or wired it wrong.

Power supply: why not use the 24V to power your Arduino as well? Just add a step-down converter and you can do away with the 9V battery and all it's related issues (it may not be powerful enough to activate a relay coil). Arduinos as such are not that great for battery powered operations, way too many components that can not be switched off. For true low power you'd have to do away with the Arduino overhead and just get an ATtiny or so (more than enough for this application).

Hi,
Welcome to the forum.

Please read the first post in any forum entitled how to use this forum.
http://forum.arduino.cc/index.php/topic,148850.0.html

Can you please post a copy of your MOSFET circuit, in CAD or a picture of a hand drawn circuit in jpg, png?
Also what was the part number of the MOSFET?
What are the specs of the 24Vdc motor?

Thanks… Tom… :slight_smile:

Thanks for the reponses guys and apologies for some of the vague aspects of my post. Honestly, I dis-assembled the MOSFET circuit so cannot remember how I wired it. I did use a "LM7805CV L7805CV 5V 1A Voltage Regulator from ST Microelectronics " . In hindsight, I now realise that I the MOSFET was only rated for 1A output - and the motor was drawing at least 2A, so maybe that was the problem ?

With regards the SSR, I did think it SHOULD switch DC as well as AC but I cant get it to work. I am sure I connected it correctly but it just wont work for some reason.

This is the SSR I am using https://www.ebay.co.uk/itm/2-Channel-5V-Dual-OMRON-SSR-G3MB-202P-Solid-State-Relay-Module-Resistive-Fuse/132227809093?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

The reason I thought I the relay could not be used to switch DC is from this post..

I using the same connections as the original author. So that DC + goes to VCC DC- goes to GND and the 2 inputs go to digital pins on the arduino which I then send HIGH and LOW in code to control the relay.

At first I thought it was working ok - I could see the LED's on the relay turning on when I activated the input. It was when I tested it with a load that I realised it did not do anything.

Can these relays be used to switch DC ?

Here is a link so a simple outline of the circuit I was trying to use..

I cant really get the specs for the motor I will be using as I dont have these. I am actually trying to control an existing stairlift and all I know about it is that the switch controlling the motor is supplying 24v DC.

I do like the idea of maybe replacing the arduino with ATTiny45 but will try get this approach working fist. So again, any help would be great :slight_smile:

Cheers.

Hi,
Where I have circled tells you AC load, so it will not work for DC loads.
1_1_45.jpg

Tom… :slight_smile:

Hi Tom -

OK so thats confirmed then :(. Anyone know of a digital relay that will work with a DC load ?

Thanks,

DaveLister:
Thanks for the reponses guys and apologies for some of the vague aspects of my post. Honestly, I dis-assembled the MOSFET circuit so cannot remember how I wired it. I did use a "LM7805CV L7805CV 5V 1A Voltage Regulator from ST Microelectronics " . In hindsight, I now realise that I the MOSFET was only rated for 1A output - and the motor was drawing at least 2A, so maybe that was the problem ?

A 7805 is a 5V linear voltage regulator, nothing to do with switching power at 24V.

You need an n-channel logic-level MOSFET configured as a low-side switch. The load is inductive so
must have a free-wheel diode across it.

To select a MOSFET ignore the current rating - ensure the voltage rating is plenty (40V or more),
choose one whose on-resistance is low enough that the heat dissipation is managably (depends
on whether use a heatsink and how big a heatsink).

You need to measure the current of your motor (under load) so you know what kind of current
rating is required of the switching device. The motor stall current should also be determined, but
thats just the motor voltage divided by the motor winding resistance.

If you still want a relay solution, Seeed sells a latching relay with the transistor drivers built-in and with contacts rated for 3A 35V

http://wiki.seeed.cc/Grove-2-Coil_Latching_Relay/

Adafruit sells a smaller one called the FeatherWing but it is only rated to 2A

Ok thanks for that, must admit the latching option does appeal given power restrictions. In the meantime I am going to give the MOSFET one more go. I think based on the reponses I have received, I was using the incorrect component before (a BUZ11A.)

I have ordered a IRL540N which seems like it may do the trick ?

Thanks.

Those work great for me with 5V to the gate.
Don't forget the pull-down resistor to prevent the gate from floating upon startup.