Moving an Actuator from a 3v output

[travis_floyd]

First post here, however ive been browing here for some time now getting lots of ideas.

My current project is trying to control a 12v Linear actuator from a 3v output.
i have converted the 3v to 12v with a relay now i am having some trouble getting the actuator to reverse its polarity so it always stays closed. And when given the 12v signal it switches open until the signal is gone, then back to close.
I believe it can be done with a couple relays but ive been messing around with them for quite some time and no luck.
Please, any input would be helpful. Thanks.

Travis.

 

[Reloadron]

Hi Travis and welcome to the forums.

If you have a link to the data sheet for the actuator that would help considerably. Polarity is generally reversed in a case like this using what is called an "H Bridge" circuit. If you better explain for example where the 3 volts is coming from that would help and exactly what you are trying to do?

Ron

 

[travis_floyd]

This was the diagram i was provided by the manufacturer.
https://static.speedwaymotors.com/images/charts/wiring_diagram.gif
The 3v is being provided by an output from a GPS unit. I have stepped the voltage to 12v for the actuator. I am now trying do have it so the actuator is always closed and when the 12v signal is sent it will open and remain open until the signal is stopped. thus closing the actuator again.
Thanks for your assistance.

Travis.

 

[alec_t]

Actuators often require considerable current. Is all the current supplied from the GPS unit (presumably via a 3V-to-12V DC-DC converter), or do you have some additional power source?

 

[Reloadron]

I agree with Alec. Looking at the images I would guess this to be an actuator used maybe in automotive applications. Even though they are geared they require considerable current at 12 volts. If you look at the upper image they show a simple DPDT (Double Pole Double Throw) momentary (center off) switch used to extend and retract the actuator. Note how the switch simply reverses polarity for extend and retract. You need enough current to drive the actuator as well as a means of reversing polarity to extend and retract it.

Ron

 

[colin55]

Just put a double-pole double-throw relay on the actuator. let the limit switches in the actuator stop the movement at the end of travel.

 

[travis_floyd]

Thanks for your posts, they helped me alot today on finishing up this project.
I have the actuator doing what i would like now. Staying closed when there is no power for input and opening when the input is on.
However it will only work from 12v input and the one from the GPS unit is 3v.
Can anyone recommend me a circuit that will allow the 3v to work with the 12v relay for the input?
Thanks again.

Travis.

 

[colin55]

Use a 3v relay or add a transistor

 

[KeepItSimpleStupid]

Can you give us an idea of the current the actuator needs at 12V?
Can we assume that the actuator has limit switches?

If you had a DPDT switch and crossed the wires at ends of the switch and then connected 2 wires to the center terminal and 2 to one of the ends you would have a polarity reversing switch. Attach power to the center terminals and the actuator to the end terminals and the switch would change the polarity of the 12 V going to the actuator.

a) A DPDT relay could do this
b) An "H-bridge could do this". H-bridges can use direction and not enable or be able to perform fwd, rev, brake, coast functions.

 

[alec_t]

Can anyone recommend me a circuit that will allow the 3v to work with the 12v relay for the input?

You can use the 3V GPS output as a control signal, and we can probably come up with a suitable control circuit including the relay; but the actuator will need an additional 12V power supply. You still haven't told us how much current the actuator needs and if it has built-in limit switches.

 

[travis_floyd]

I have an additional 12v power source on board that is powering the gps unit that I can tap into. The actuator itself draws 4.5 Amps and it does have built in limit switches.
A diagram or control circuit explaining how it can be moved with the 3v would be much appreciated.
Thanks.

Travis.

 

[colin55]

Operate the relay with a transistor. Put a 2k2 on the base and connect the 3v output to the resistor.

 

[travis_floyd]

Thanks for the quick reply but unfortunately everything you said went right over my head.

 

[alec_t]

Is the 3V output from the GPS a continuous DC signal, or a brief pulse, or a coded pulse sequence?

Edit: How often is the actuator expected to operate? Every few seconds? 10 min intervals? Once a day?

 

[travis_floyd]

The 3v signal is constant. And the actuator will be used once or twice a day. Sometimes once a week.

 

[travis_floyd]

How can this be done with a transistor? And what kind would I need. I've never used one before.

 

[travis_floyd]

I did some more searching on this site and found someone with a similar problem.
this was their solution.

The relays are just 12v SPDT and are configured as follow:
pin 30 is +12v from the car
pin 86 is ground
pin 87 is my output which will go to the valve (12v)
pin 85 is my input from my board.

would this work?

 

[alec_t]

Here's a design which should do what you need. A relay powered for the lengthy times you envisage would be a considerable current drain, so has been replaced by a MOSFET H-bridge. Standby current (i.e. actuator stationary) for the circuit is ~1mA. The GPS signal controls Q1. When GPS = 3V Q1 turns on, which turns off Q2. When GPS = 0V Q1 turns off, which turns on Q2. The voltages at Q1 and Q2 collectors control the H-bridge MOSFETs, rather like a see-saw, to reverse the current flow through the actuator motor. It is assumed that the limit switches 1 and 2 are normally closed. C1, C2 and C3 provide supply decoupling to damp spurious signals. The transistor types are suggestions only: many possible alternatives exist.

 

[Reloadron]

Nice circuit Alec. However, looking at the original link to this type actuator the actuator motor does not appear to have limit switches so those would need to be added. This looks to be the type actuator used in automotive applications to for example raise and lower a plow blade on a truck. The operator is watching as he/she raises or lowers the plow blade. The switch in the illustration is a DPDT momentary switch with a return to off center. While this may not be of any importance it may aso need considered.

Ron

 

[alec_t]

the actuator motor does not appear to have limit switches so those would need to be added.

Interesting. The OP says the actuator has limit switches ;-). The OP hasn't specified any manual over-ride of the GPS control signal, so not sure if we need a centre-off switch.