First I wat to go all the way up and down. There is no reason to stop short in either direction. I figured momentary switches woul add a level of safety in the event the limit switch failed. As for the motor it is 12 Vdc. Max draw at lockup is 900 watt. The power supply is rated for 85 amps

I am sorry, but, for me at least, that does not answer the questtion.

The question is whether a press and release of the pushbutton causes it to go all the way up or down, or whether you must hold the pushbutton down until it is all the way up or down.

The second part of your answer,

" I figured momentary switches woul add a level of safety in the event the limit switch failed. ",

makes me think you want to hold the button until the movement is finished. Otherwise, the buttons would not provide the added level of safely you mention, since it would continue going whether the button is pressed or not.

Bob

 

Also, an afterthought; since the relays are going to be high current devices, their control coils will likely be heavier current draw as well. You need to be sure your switches can handle that current. If not - you need heavier PB's.

 

It appears to me that in this case the TS is more cincerned about safety than convenience, and so holding the button fro the duration of the move is the desired mode. I have observed over the years that occasionally things do not go exactly as intended, And leting go of a button is much simpler than trying to stop a hoist by finding the off switch. Since there was no E-Stop included in the latching relay circuit.

 

The question is whether a press and release of the pushbutton causes it to go all the way up or down, or whether you must hold the pushbutton down until it is all the way up or down.

Makes me think you want to hold the button until the movement is finished.

Yes, his intent is to hold the button while the trolly is in transit. When the trolly reaches its limit the limit switch disables the relay coil and thus stops the motor where it is. An added benefit is that of dynamic braking IF the motor is a PM (Permanent Magnet) motor.

 

Yeah! That's great! Actually, you don't need the steering diodes in that configuration.

You changed the ground symbols from common ground to earth ground. Not that it's important, but at 12 volts, you really don't need to earth ground anything except the 100 - 220VAC input. But I suppose it's OK to earth ground the system. The 12V negative line from the PS probably is already grounded inside the PS. The downward pointed triangle is a common ground, not necessarily tied to earth ground. But it looks good. As long as your relays are rated for the high current the motor will demand.

Didn't know the difference in ground symbols. Mechanical engineer by trade. You sparkys blow my mind it's another world. Never the less THANK YOU SO MUCH!

 

Chassis Ground

Common point (or ground)

Earth Ground
These are the most common ground symbols.

The chassis ground is typically the metal casing or frame that some electronics are mounted on. With points that are all tied to ground, the chassis ground reduces the amount of wiring needed. The chassis ground is sometimes ALSO grounded to Earth ground. The Common Point is just a reference point. It can be a chassis ground with points on the electronics above and below the middle voltage where that middle is typically considered to be zero volts. You can always have points (volts) above or below ground. Ground is most commonly considered the zero volt point.

 

Here's another approach.
I think its self explainatory...

 

Didn't know the difference in ground symbols. Mechanical engineer by trade. You sparkys blow my mind it's another world. Never the less THANK YOU SO MUCH!

Many previous ones here on the subject.
See this one, particularly #8 !
https://forum.allaboutcircuits.com/threads/grounding-in-electronics-question.114100/#post-888131
Don't feel bad, many make the same mistake that should know better!
Max.

 

Here's another approach.
I think its self explainatory...

View attachment 226653

Interesting arrangement for self latching relays that break only when the limit switch opens. Good design. However, the TS wants to be able to stop the trolly should a limit switch fail. TS feels safer that way. This way - your way - once the trolly is moving it will continue till it reaches the end with no way to stop it should a problem arise.

 

That's OK if you are the only one using it, but if it had to pass NFPA79/OSHA it would require an emergency stop method.
Max.

 

My question now is where will you find the limit switches good for 65 amps running current? They might exist but they will not be cheap..

Interesting arrangement for self latching relays that break only when the limit switch opens. Good design. However, the TS wants to be able to stop the trolly should a limit switch fail. TS feels safer that way. This way - your way - once the trolly is moving it will continue till it reaches the end with no way to stop it should a problem arise.

NO, it is not a good design. A hoist circuit with no shutoff available is not a good design, AND, when the limit switch opens the EMF generated by the motor will tend to keep the relay energized . In addition, It is a poor choice to run both drive current and control current through the same contacts.

 

Interesting arrangement for self latching relays that break only when the limit switch opens. Good design. However, the TS wants to be able to stop the trolly should a limit switch fail. TS feels safer that way. This way - your way - once the trolly is moving it will continue till it reaches the end with no way to stop it should a problem arise.

if the limit switch fails, the circuit will break and the motor will stop automatically.

 

My question now is where will you find the limit switches good for 65 amps running current? They might exist but they will not be cheap..

NO, it is not a good design. A hoist circuit with no shutoff available is not a good design, AND, when the limit switch opens the EMF generated by the motor will tend to keep the relay energized . In addition, It is a poor choice to run both drive current and control current through the same contacts.

the limit contacts could be replaced with relay contacts from relays energized thru normally closed limit contacts.

 

That's OK if you are the only one using it, but if it had to pass NFPA79/OSHA it would require an emergency stop method.
Max.

That is easy to implement.

 

NO, it is not a good design. A hoist circuit with no shutoff available is not a good design, AND, when the limit switch opens the EMF generated by the motor will tend to keep the relay energized . In addition, It is a poor choice to run both drive current and control current through the same contacts.

Diode transient surpressors (or other) could be used across the motor to supress the EMF.

 

Here's a version with additional modifications to make it an even better design....

 

Interesting arrangement for self latching relays that break only when the limit switch opens. Good design. However, the TS wants to be able to stop the trolly should a limit switch fail. TS feels safer that way. This way - your way - once the trolly is moving it will continue till it reaches the end with no way to stop it should a problem arise.

If failure of the limit switch is a concern, then there should be at least two limit switches at each end to reduce the chance of an unsafe failure.

 

Here's a version with additional modifications to make it an even better design....

I'm sorry but Good Lord, seriously?
The failure of the limit switch issue was based on your design to run the high motor current through them, that's all.

 

if the limit switch fails, the circuit will break and the motor will stop automatically.

The last two limit switch failures that I saw were the switch coming loose from it's bracket because of a loose screw.

 

I'm sorry but Good Lord, seriously?
The failure of the limit switch issue was based on your design to run the high motor current through them, that's all.

didn’t mean to cause you a religious experience..
But is the limit switch still a problem?