pump circuit

medic29 · #1 07/08/2007, 11:57 AM

Okay....I know this has been discussed in the past and over the past couple of days I have read several posts from various threads, but being a visual learner at times, I'm still having difficulty wrapping my brain around the details of how to wire the circuit. The schematics didn't help much because of the symbols and it has been way too many years since my electronic classes. With that said, please bear with my simple drawings.

Now to the point, I'm basically trying to set up a circuit using float switches and a relay to power a pump. I would like the lower float switch to turn the pump on and pump water into the container, then the upper float switch will break the circuit and the pump will shut off. I've read that this involves a latch relay circuit and believe I understand the concept, but figuring out the wiring between the float switches and relay is what has me confused, so I made some simple diagrams which are shown below.

From looking at a diagram I found in one of the posts I believe Bean came up with, this is how I think the relay and switches should be wired.

The question I came up with in this situation is if for some reason float switch #2 failed to close and remained open, then as I see it the pump would never get power and if this was being used as a top off for a sump, the sump could essentially run out of water because it never got "topped" off - albeit rare.

Would wiring up the relay like this work. It seems it may do the same, but with one benefit...float switch #1 would always trigger the relay and thus power the pump. If float switch #2 failed and remained open, the relay would never latch and thus the "sump" or tank would never fill, but it would also not fall to a level below the level of float switch #1.

Is this correct? Am I understanding and seeing this the right way? And finally, do I have the wiring correct for a DPDT relay?

Any help and/or explanation would be greatly appreciated.

medic29 · #2 07/08/2007, 03:20 PM

.

medic29 · #3 07/09/2007, 07:57 AM

hmmph.....No one??

silverwolf72 · #4 07/09/2007, 11:57 AM

Yeah thats not right, I'd make up a drawing for ya but at work right now. The pump part is correct but the float switch side isn't. The Floats need to be in series with the top 2 posts and not connected to the vertical posts at all.

medic29 · #5 07/09/2007, 02:01 PM

Hopefully you understand the top 2 posts are the coil for the relay. The first diagram is very similar to what I've been using for my auto top off for a while now. Just trying to turn it into a latching relay circuit.

stugray · #6 07/09/2007, 05:29 PM

You need to show the relay coil and the contacts in the diagram or we cant tell how you are wiring it.

Stu

GuySmilie · #7 07/09/2007, 05:51 PM

Quote:

Originally posted by medic29

.....I'm basically trying to set up a circuit using float switches and a relay to power a pump. I would like the lower float switch to turn the pump on and pump water into the container, then the upper float switch will break the circuit and the pump will shut off. I've read that this involves a latch relay circuit and believe I understand the concept, but figuring out the wiring between the float switches and relay is what has me confused......

Like this, Rick?

medic29 · #8 07/10/2007, 12:19 PM

Okay, I put where the coil is. I hope that helps....maybe. I don't remember all the fancy symbols, thus the reason why I didn't use them

Guy....how about now??

GuySmilie · #9 07/10/2007, 01:49 PM

Can't tell by your drawing as the relay info is still too vague. Need more info besides the coil terminals. All relay terminal arrangements are not the same. Do you have a part number for the relay you are trying to use? Then we could look it up.

FuzzyLogic · #10 07/10/2007, 03:37 PM

medic29 · #11 07/10/2007, 04:03 PM

Guy

Okay, I'll work on that when I got home this evening.

BeanAnimal · #12 07/10/2007, 10:29 PM

With a quick glance... both of your drawings do the exact same thing. That is the switch logic is exactly the same in all cases.

One use the COMMON terminal to supply the 12V to the NO terminal, and the other uses the NO (normally open) terminal to supply 12V back through the common.

medic29 · #13 07/11/2007, 09:34 AM

Okay....I made another drawing this morning. I hope this is more clear. I'm trying to figure out if this will work as a latch relay?

Here is the drawing:

Let me know your thoughts.

Thanks Bean for your input. I'm checking to see if this will work as a latch relay.

Any input would be greatly appreciated.

Thanks,
Rick

BeanAnimal · #14 07/11/2007, 03:03 PM

Top switch closes and arms the circuit
Bottom switch closes and fires the coil
Coil latches through closed top switch
Bottom switch opens, circuit stays latched
Top switch opens, latch collapses

As mentioned the circuit operates the same. The only real difference is the logic at the output of the NC contact of the relay.

With my circuit the NC contact denotes the "armed" status of the circuit when the relay IS NOT actuated.

In your circuit the NC contact only denotes the position of the relay.

That may or may not help depending on what type of indication you are using (if any) and how the latch ties into any monitoring logic.

From a LOGIC standpoint with regard t the NO contact and switch operation, both circuits are exactly the same. In other words they output at the NO contact would have the same truth table for any combination of switch positions or failures in both circuits.