I have built a cargo lift to carry materials up two story's, I have the existing controls and have put nc limit switches on the upper floor and bottom, having difficulty putting one on the middle floor and going up or down from there, want to eventually use a hand held remote, does anyone have an electrical circuit or experience in this? I have been reading this form and it looks to be a great place for educating oneself. Thank you in advance for your help!

 

More info, I used a 1 hp 220 v single phase motor, it's off of a boat lift, so it is reversible by using two 24 volt three pole contactors, one for up and one for down.

 

could you post up a quick drawing/schematic of what you've got wired up currently? Do I understand correctly that:
when the bottom switch is tripped, it will not go down anymore,
when the top switch is tripped it will not go up anymore,
and when the middle switch is tripped it will just stop, but you can continue up or down by pressing the button again?

 

I don't have a drawing, basically the control circuit is 24 volts, worked by a three position switch. Up off down. This completes the 24 v circuit to the chosen contactor. The upper and lower limits do not allow for further travel as you mentioned. The middle floor, I tried to put a limit on, but the limit I have won't work, if I go up to the second floor trip the limit, I can only go down, not up from there. The limit is a rotating cam that open the contacts. I think I need a limit that is like a momentary open, then back to close for further travel? ....is there such a thing? Thank you for your imput!

 

I haven't seen a limit switch like you describe, but that doesn't mean it doesn't exist.

You could, instead of running your signal through the center limit switch, run it through a time delay relay. Run power to the relay through the limit switch.

 

Look here for a few that may work. Roller arms with a proper trip device will work. We used one of these with a triangular pivot on the switch and a triangular tab on the moving part so the actual tripped range was less than 0.2"

 

is there supposed to be a link bill?

 

OOOOPS!!!!!! Here it is:

http://ab.rockwellautomation.com/Sensors-Switches/Limit-Switches

These switches are very flexible as to actuation method. A wide variety of heads are available with either plunger or rotary mechanical input.

 

Legacyone

There are just too many unknowns to give any kind of accurate help. Not knowing whether or not the switch is maintained or momentary is quite a hinderance. However, if you switch is momentary, making both sides of the second level limit common (see attached) "MAY" provide enough time for the contactor (up or down) to drop out thus stopping the lift. If it's your desire to continue up (or down) to the third (or first) level simply press the up (or down) control once more.

If anyone thinks this not a good idea please speak up.

williamj

 

Williamj That's an out of the box idea. It might work as long as the LS is break before make. Never tried it, but I find now that I want to.

 

Forgot to mention that the L.S. for level two must be either a DPDT L.S. (one for both directions) or two SPDT L.S. ( one for each direction). See attached.

williamj

 

Oooops...

strantor, Forgot to say that you are of course correct. The limit must be break before make. Now, if I could just remember where I put my memory... :/

williamj

 

Legacyone,

Been thinking about your project overall and I heartily suggest you replace the two 3 pole relays with a single 3 pole motor reverser. The reverser comes with a mechanical interlock which prevents both up and down contacts from trying to energize at the same time, where as with the two 3 pole relays that is a very real possibility. Also with the 3 pole reverser you can set up an electrical interlock which does the very same thing. This way almost all possiblity of direct shorting of contacts is eliminated. (There's always the unexpected and the unlown.)

Remember... safety, safety, safety.

williamj