# Directional actuator control circuit

## Summary:

This thread is about connecting a DC motor driven linear actuator to a power supply and controlling the direction of it via push buttons. Safety measures will also be a topic
Hi there. I want to power and control a linear actuator that is considered heavy duty. I am contemplating either using an an existing control driver or building the circuitry with various components. i want to use these attractive control buttons which are led light up

https://www.aliexpress.com/item/4000027999336.html?spm=a2g0o.cart.0.0.784b3c00meRAaf&mp=1

This is the actual linear actuator

https://www.aliexpress.com/item/526760804.html?spm=a2g0o.cart.0.0.784b3c00meRAaf&mp=1

The actuator I am choosing is rated to push 2000N force at speed of 65mm/s. At a maximum load it can draw up to 16A current. the motor is 12V.

I can always change the components parameters and recreate the same work E.g i can pick a 24V actuator that draws 8 Amps at full load.
I am swaying to using 12V because power supplies are more easily available and allot cheaper. I don't have much experience with electrical applications so i want advice with this project

Related Electrical Engineering News on Phys.org
This is a circuit diagram for the controls. The high power source is connected to 2 double pole relays with different configurations. The relay coils are controlled by the led buttons to initiate either extension or retraction

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Baluncore
2019 Award
1. What do you want to happen if you press both buttons at the same time?
2. Does the linear actuator have limit switches?
3. How far from the buttons to the linear actuator?
4. Inside, outside, marine environment?

Tom.G
The links you posted for the parts are for your shopping cart at aliexpress. But those items are not in OUR shopping carts. Could you please post links to the pages on aliexpress that you found those parts and that show their specifications?

The LEDs are wired to be normally On, and go Off when the button is pushed. Is that what you intended?

As noted in your other thread, if both buttons are pushed then there is a short across the big power supply. I can think of four ways to solve this:
1. Use DPDT (Double Pole Double Throw) push buttons if available
2. Use two additional low power relays so the first button pushed disables the other pushbutton
3. Use 3PDT power relays (harder to find, may be expensive)
4. Add a diode in series with the coil of each power relay so they each operate with only one polarity of applied voltage
I've seen option 4 above used in some cars. Those relays have the diode already built in. I expect those relays would be very hard to find, and I don't know their current rating.

Option 1 would be the easiest if available.
Options 2 followed by 3 are the next easiest to understand.
Option 4 introduces some Electronic ideas that may be rather confusing if you are just starting your journey into electrical engineering; but would be lower cost than #2 or #3

Cheers,
Tom

pbuk
Gold Member
As noted in your other thread, if both buttons are pushed then there is a short across the big power supply. I can think of four ways to solve this:
There is a 5th option using 2 x DPDT relays as described here.

I'm not sure I see the point in illuminated push buttons though - you would normally use non-latching buttons in this application (i.e. you need to hold them down to keep the actuator moving) so you wouldn't be able to see the light.

Also note that the LEDs in those switches have built-in resistors: if you use one specified for 12V you don't need to use an external resistor.

hutchphd
jrmichler
Mentor
Automotive relays should meet your needs. Here is a link to the data sheet for one brand of automotive relays: https://b2b-api.panasonic.eu/file_stream/pids/fileversion/350. And the Panasonic Automotive Relay User's Guide has a lot of useful information: https://www.panasonic-electric-works.com/pew/nl/nl/downloads/ti_automotive_relay_userguide_en.pdf. Automotive relays are available at your local auto parts store.

For switching, consider a single rocker or toggle switch, with center off and momentary double throw contact. These switches are spring loaded to a center position. Push one way to go up, push the other way to go down, let go to stop. Digikey (and others) have 100's of these switches in stock for prices on the order $5.00 each. Here is the first data sheet that I found: https://www.nkkswitches.com/pdf/Btoggles.pdf. berkeman 1. What do you want to happen if you press both buttons at the same time? 2. Does the linear actuator have limit switches? 3. How far from the buttons to the linear actuator? 4. Inside, outside, marine environment? If I press both buttons at the same time this circuit would short circuit. I don't know how to solve this. Actuator has limit switches Controls are roughly 60 cm from the actuator Indoor environment inside lift chair Automotive relays should meet your needs. Here is a link to the data sheet for one brand of automotive relays: https://b2b-api.panasonic.eu/file_stream/pids/fileversion/350. And the Panasonic Automotive Relay User's Guide has a lot of useful information: https://www.panasonic-electric-works.com/pew/nl/nl/downloads/ti_automotive_relay_userguide_en.pdf. Automotive relays are available at your local auto parts store. For switching, consider a single rocker or toggle switch, with center off and momentary double throw contact. These switches are spring loaded to a center position. Push one way to go up, push the other way to go down, let go to stop. Digikey (and others) have 100's of these switches in stock for prices on the order$5.00 each. Here is the first data sheet that I found: https://www.nkkswitches.com/pdf/Btoggles.pdf.
Thanks so much these are great resources.

The links you posted for the parts are for your shopping cart at aliexpress. But those items are not in OUR shopping carts. Could you please post links to the pages on aliexpress that you found those parts and that show their specifications?

The LEDs are wired to be normally On, and go Off when the button is pushed. Is that what you intended?

As noted in your other thread, if both buttons are pushed then there is a short across the big power supply. I can think of four ways to solve this:
1. Use DPDT (Double Pole Double Throw) push buttons if available
2. Use two additional low power relays so the first button pushed disables the other pushbutton
3. Use 3PDT power relays (harder to find, may be expensive)
4. Add a diode in series with the coil of each power relay so they each operate with only one polarity of applied voltage
I've seen option 4 above used in some cars. Those relays have the diode already built in. I expect those relays would be very hard to find, and I don't know their current rating.

Option 1 would be the easiest if available.
Options 2 followed by 3 are the next easiest to understand.
Option 4 introduces some Electronic ideas that may be rather confusing if you are just starting your journey into electrical engineering; but would be lower cost than #2 or #3

Cheers,
Tom
Hey Tom. You've certainly given me allot to think about here. I'll look into all options please continue following the thread

I am fast coming to the conclusion that a premade forward reverse motor controller is much more economical then building the circuit myself. I also see heatsinks on allot of the products

pbuk and Tom.G
I made this circuit as a means to prevent shorting in the event that both buttons (up down) are pressed at the same time. Please take a look and comment. Not sure if it's right

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pbuk
Gold Member
You won't get a short because both relays connect the +ve supply to the same terminal of the motor, which means that...

Tom i looked at the H Bridge but im having real trouble understanding whats going on there

You won't get a short because both relays connect the +ve supply to the same terminal of the motor, which means that...

Tom.G
Referring to the diagram below, the Ubatt connection at the top is +12Volt. The bar at the bottom is -12Volt.

The relays are drawn a bit unusual
The relays show the coil at the top.
The NC (Normally Closed) contact is drawn as the lower contact, and the NO (Normally Open) contact is drawn as the upper one.

The motor in the middle, labelled "M", connects to the Common lead on each relay.

The relays are shown in the de-energized position, so the NC contacts are closed on both of them. This connects both motor leads to -12V.

When a relay is energized, the Common is connected the the NO. This applies +12V to that motor lead. Since the other relay is still de-energized, the other motor lead is still connected to -12V, and the motor runs.

To run the motor in the other direction, energize the other relay.

If both relays are energized, both motor leads are connected to +12V and the motor stays stopped with no voltage across it (both motor leads are at +12V).

By the way, you don't need two separate 12V supplies. Connect one end of each relay coil to -12V and the other end to a push button NO contact. Then connect the other, Common, pushbutton contacts to +12V.
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Cheers,
Tom

Hey Tom. Based on what you said I drew this up. I think I've got the right idea now. Thanks so much

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These spdt relays are quite cheap and readily available. It is more economical to build this circuit than to buy a motor controller. The H bridge system with 2 spdts seems very simple to build. Thank you so much. This was a huge help

pbuk
Gold Member
... the motor will not run in either direction. In order for the motor to run, one terminal needs to be connected to +ve and the other to -ve.

pbuk
Gold Member
Referring to the diagram below, the Ubatt connection at the top is +12Volt. The bar at the bottom is -12Volt.

The relays are drawn a bit unusual
The relays show the coil at the top.
The NC (Normally Closed) contact is drawn as the lower contact, and the NO (Normally Open) contact is drawn as the upper one.

The motor in the middle, labelled "M", connects to the Common lead on each relay.

The relays are shown in the de-energized position, so the NC contacts are closed on both of them. This connects both motor leads to -12V.

When a relay is energized, the Common is connected the the NO. This applies +12V to that motor lead. Since the other relay is still de-energized, the other motor lead is still connected to -12V, and the motor runs.

To run the motor in the other direction, energize the other relay.

If both relays are energized, both motor leads are connected to +12V and the motor stays stopped with no voltage across it (both motor leads are at +12V).

By the way, you don't need two separate 12V supplies. Connect one end of each relay coil to -12V and the other end to a push button NO contact. Then connect the other, Common, pushbutton contacts to +12V.
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Cheers,
Tom
Descriptions of this simple H-bridge have already been been linked to in this thread by @jrmichler, however they may or may not be suitable for this application.

The pdf linked to in @jrmichler's post #6 contains the following caution (on page 5):
Note that regarding the following circuit constructions with 2-coil relays (twin relays) or single-pole
relays, an arc between contacts may be generated when breaking of load current depending on the
The pdf linked to in @jrmichler's post #10 contains the following caution:
This means, H-bridge relays must be designed for high current-switching-capability, but not for high current-carrying-capability. Higher load voltages can be critical, due to possible short-circuit-arcs (see also short-circuit brake).
The problem we are dealing with here is contact arcing which will shorten the lifetime of the relays.

Note also that car electric windows (which is what these circuits are designed for) are always operated by a 3-way centre off switch which prevents both relays being 'on' at once and introduces a small time delay which avoids putting the back-emf caused by de-energising the motor windings back through the circuit. If you use separate switches you will lose this protection.

I come back to what I said right back at the beginning, if you want to switch high power relays then you should either use a controller designed for this purpose or contact the manufacturer to confirm what they recommended. However a lot depends on the application - if this is for a toy car then it doesn't really matter if the relays weld closed, but if it is a lift for someone with restricted mobility then that is a different matter.

Tom.G
That is why surge suppressors, of one sort or another, are often used with inductive loads. Someone mentioned them earlier in this (or maybe another) thread, but I can't find the reference now.

@Rayhaan, I don't have access at the moment, but I seem to recall that the pushbutton switches you chose were latching. That is not necessarily a problem, but be aware it means a relay remains energized until the pushbutton is un-latched. Since there are limit switches in the actuator, nothing bad should occur.

That also means that the other pushbutton will not move the motor until the first pushbutton is un-latched. Just thought I'd point it out in case you wanted the controls to act differently.

Cheers,
Tom

Tom and pbuk. In the other thread someone had mentioned transorbs and having in built transorbs to your relay as a means to handle the bank emf. I'll look in to this and post. You guys can tell me if I have the right idea or not

So I've read up on back emf a bit. It seems like you'd add diodes across your at risk components like the relays in this case. I feel like I could be missing something though.. is it that simple?