Directional actuator control circuit

[Rayhaan]

TL;DR 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

 

[Rayhaan]

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

 

[Baluncore]

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]

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.

 

[jrmichler]

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.

 

[Rayhaan]

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

 

[Rayhaan]

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.

 

[Rayhaan]

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

 

[jrmichler]

This datasheet shows how to connect two relays for a motor reversing application similar to yours (power window up/down): https://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=Automotive_Relay_Applications&DocType=CS&DocLang=EN

 

[Rayhaan]

ZAR 228.07 29%OFF | DC 10-55V 100A Motor Speed Controller Reversible PWM Control Forward Reverse Whosale&DropShip
https://a.aliexpress.com/_BSZHMf

 

[Rayhaan]

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

 

[Rayhaan]

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

 

[pbuk]

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]

Rayhaan, go with the circuit in figure 2 of the post by @jrmichler. That one is so simple, straight-forward, and common that ALL of us should have thought of it!

This datasheet shows how to connect two relays for a motor reversing application similar to yours (power window up/down): https://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=Automotive_Relay_Applications&DocType=CS&DocLang=EN

Cheers,
Tom

 

[Rayhaan]

Tom i looked at the H Bridge but I am having real trouble understanding what's going on there

 

[Rayhaan]

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

please continue

 

[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

 

[Rayhaan]

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

 

[Rayhaan]

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]

please continue

... 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]

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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View attachment 270077
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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
type of load current, voltage, and load.

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

 

[Rayhaan]

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 into this and post. You guys can tell me if I have the right idea or not

 

[Rayhaan]

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?

 

[pbuk]

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?

Usually, yes. But in an H bridge like the one pictured (which is sometimes called a half H bridge) the current is designed to flow in both directions so a flyback diode is no use. You could consider the solution someone else posted with two DPDT relays in a full H bridge configuration (which disconnects both motor terminals at once), however arcing may still be a problem and so this circuit should not be used in a critical application unless designed by someone qualified to do so.

I still don't see the point in illuminated switches in this application and latching switches are not appropriate.

 

[Averagesupernova]

I've never watched a thread about something that is so simple made unnecessaily difficult. I don't understand why a rocker switch is unacceptable. A 5 wire power windows switch will do the job without relays. Individual switches will too if momentary SPDT switched are used. I have refrained from posting because I find the schematics drawn are anything but standard and easy to follow.

 

[jrmichler]

Not knowing how much current a power window motor draws, a power window motor switch might be undersized for this 16 amp motor. Here is an example of a rocker switch rated for 21 amps DC. It's readily available - the catalog says over 1100 in stock at $6.47 for one switch. https://www.digikey.com/product-detail/en/cw-industries/GRB260K101BBNN/CW129-ND/2349709.

This is a DPDT MOM-OFF-MOM switch. That means that it is spring loaded to the center OFF position. You need to push one way or the other and hold it to run the motor. Let go of the switch and the motor stops.

Here is how to wire it:

The 12 volt positive supply is V+, the negative is shown as ground. The motor is M, and a transorb is wired in parallel with the motor. I'm not sure if a transorb is really needed, but it's good insurance. This discusses transorbs: https://www.mouser.com/pdfdocs/Semtech_Application_Note_TVS_Diode.pdf. Here is the first one that I found (one of the EE's here should be able to find a better one): https://www.mouser.com/ProductDetail/Vishay-Semiconductors/P6KE24CA-E3-54?qs=ACmI7jQvrjrsxOqaCdGyiw%3D%3D. They show over 10,000 in stock, and will sell you one for $0.46. Cheap insurance.

 

[Averagesupernova]

A quick Google for linear actuator switch turned up a 30 amp rocker from northern tool.
-
Again, such a simple thing and yet this thread is like a monster with five heads.

 

[Averagesupernova]

That last diagram is a bit sketchy. The way it's drawn implies that a few bad things could happen. First, upon hooking to power will cause the motor to run continuously. Second, to anyone who misinterprets the schematic as having two separate switches, a direct short across the power supply will occur when either switch is toggled. We need to remember that anyone can stumble across these posts long after we have forgotten them.

 

[Tom.G]

The recent posts by @Averagesupernova and @jrmichler are spot on.

I think one of the reasons this thread has gotten so tangled is we here at PF try to follow thru on the original intent of the OP. i.e. we avoid trying to re-engineer everything to our individual ways of thinking.

I contend that generally this is a good approach in that we can teach and lead the OP based on their current understanding.

For instance the particular pushbuttons that the OP specified have the advantage that they indicate the last known position of the load; UP Arrow or DOWN Arrow. Perhaps this is useful, or even vital, in the particular application, we don't know that yet.

Cheers,
Tom

 

[Averagesupernova]

I do have a question about the limit switches. If this is a two wire motor, how do the limit switches tie in? Usually limit switches in a linear actuator have to tie into the main switch because while one limit switch stops the motor in one direction, the motor has to be allowed to travel in the other direction while the first limit switch is open. Pretty sure linear actuators with built in limit switches require more than a pair of wires coming out unless they are using some pretty heavy duty internal diodes to accomplish the reversal. So, what gives?

 

[Rayhaan]

I do have a question about the limit switches. If this is a two wire motor, how do the limit switches tie in? Usually limit switches in a linear actuator have to tie into the main switch because while one limit switch stops the motor in one direction, the motor has to be allowed to travel in the other direction while the first limit switch is open. Pretty sure linear actuators with built in limit switches require more than a pair of wires coming out unless they are using some pretty heavy duty internal diodes to accomplish the reversal. So, what gives?

I really don't know.. I contacted the manufacturer whose told me the motor has 2 leads. The actuator specifies that it has limit switches built in. I agree on the potential simplicity of this entire thing. Thanks for pointing it out. Just want to understand how it could all tie in.. it's more for my own understanding then practical application. I didn't even know what relays were a week ago so this monster thread was great for me to learn. Thanks everyone

 

[Rayhaan]

So in my thread subject and initial post I did mention that I could change my component specs to suit myself. If I instead used a 24vdc actuator which can draw 8a (as opposed to 12vdc 16a max load) would this circuit be any safer? Would short circuit arcs still be a potential problem?

I have no intention of using latching buttons.. I see quite a few comments were made about that. Sorry if I mistakenly mentioned them?

 

[pbuk]

I do have a question about the limit switches. If this is a two wire motor, how do the limit switches tie in? Usually limit switches in a linear actuator have to tie into the main switch because while one limit switch stops the motor in one direction, the motor has to be allowed to travel in the other direction while the first limit switch is open. Pretty sure linear actuators with built in limit switches require more than a pair of wires coming out unless they are using some pretty heavy duty internal diodes to accomplish the reversal. So, what gives?

Linear actuators with built in limit switches have internal diodes; they only carry current for a short period until the switch closes. This is the default configuration provided by most suppliers.

Some applications require external limit switching which is often available as an option; the outputs from the limit switches are generally provided on 2 wires plus a common.

Schematics for linear actuators are available on the internet from many suppliers, it is easy to look these things up rather than guessing.