12V Linear Actuator for snow plow-needs up/down limit switches and relays

[EzRidr62]

Greetings All;

Let me preface this by saying I have searched for answers on the threads previously posted before giving you a ? that may have already been answered or posted elsewhere, so I appologize in advance if this question is redundant.

I have a small homeowner-sized plow that uses a 12v linear actuator to raise/lower. The actuator has to be replaced, (i found out that these actuators are not meant to use their on-board slip clutches as a means to stop full extend/retract cycles- they are meant to be wired with limit switches to accomplish this...mine no longer stays up with a load,but lowers by itself after pwr. is cut)
I need to build a limit switch box for the plow frame, and wire it to my DPDT switch in the cab. The actuator draws too much current to use snap-action micro switches wired directly to motor voltage. I need a schematic (in laymen's terms) that uses 2 micro switches with 2 diodes to allow current reversal after one switch is tripped, which in turn runs through 2 30 amp 12v relays to run the actuator motor. I have come close to the answers, but not found exactly what I need.

Thanks in advance for any help you might be able to provide.

 

[Grossel]

Well - such a schematic isn't very hard to to.

But it will be wasted big time if you thinking again and suddenly found a actuator with feedback. Having feedback means that you can adjust the upper and lower limits, and probably is more reliable (snow + ice + water + switch = likely to fail).

And of course - if switch fail, the actuator might get broken because you'll not react fast enough to stop it before it bottles.

 

[EzRidr62]

Well - such a schematic isn't very hard to to.

But it will be wasted big time if you thinking again and suddenly found a actuator with feedback. Having feedback means that you can adjust the upper and lower limits, and probably is more reliable (snow + ice + water + switch = likely to fail).

And of course - if switch fail, the actuator might get broken because you'll not react fast enough to stop it before it bottles.

Thanks for that.... I guess I should have stated that I already have the new actuator rather than stating that it needed replacement- I would have to have spent much more $ for the model that included built-in limit switches, and also waited more time for a special ordered unit, which I am running out of. Snow can start here as early as the end of november, and we already had a freak storm that dumped 21 inches on us 2 weeks ago. If the limit switch box failed, the worst case scenario is twofold- 1.-the limit switches wired as normally closed would not complete the circuit, 2.- the switch shorts, allowing the actuator to ride to it's fully closed or open length, causing the slip clutch to angage, which I will hear, and release the momentary DPDT switch that controls it.

 

[tcmtech]

Personally I would try designing the limit switch system around two simple two reed switch's or proximity sensors that get triggered by the positions of a magnet or two.

Your up and down function is most likely controlled by simply reversing the polarity of the motor so by using two SPDT relays its possible to make a simple but effective limit control system that works with a simple SPDT switch the two sensors and the two relays.

Each SPDT relay gets wired with its NC contact wired to ground and the NO contact wired to power. The common connections from each relay goes to the each lead of the motor. Which ever relay is activated feeds power to that motor lead to make it go that way and should both relays get activated some how both leads of the motor get power and the motor does nothing.

The two reed switch's or proximity sensors get wired in series with the power to the coils of each relay. When the limit is reached they open the related coil circuit thus automatically stopping the motor in that direction only.

 

[EzRidr62]

I didn't think it would work until I drew it out....but it's so simple it's genius...eliminating all the water-resistant box and linkage designs I was dreaming up.
So, if I understand correctly, depending which side of the switch I throw to, I am really only sending out a (+) voltage from the switch through the respective reed switch (NC I assume) which effectively reverses the voltage to the motor, by energizing the coil of the relay that provides (+), the opposite relay already providing the ground path in it's non-energized state. This sure beats all the hijinx I was going through to build a mechanical rod and linkage system that tripped 2 roller-tipped snap action switches. The reed switches can be mounted to a bracket and the magnet can be practically anywhere in the pivot system... Thank You SO MUCH!

 

[tcmtech]

I didn't think it would work until I drew it out....but it's so simple it's genius...

Well it is part my current signature of course.

"Sometimes genius is simply having the ability to see and understand the obvious. " -- tcmtech

( I am not typing small on purpose. The dam reply editor decided it likes this size and will not let me change it.)