Need help with time delay relay powered by 120 volts switching a 12 volt DC pump

[Strouty]

I have the basic idea of things figured out, but I am having trouble actually finding a timer delay normally closed relay that can handle what I am doing. I'm running a 12 volt powered sump pump as a backup in my basement and I need it to only run when we have a power outage. I would like the delay so that a standard power glitch won't automatically kick it on. The pump is about 10 amps, so I was trying to have the relay capable of handling 20 amps, so I don't have any issues with the pump. At this point I am thinking that I could do a smaller relay that would run a larger relay, just figured I would get some opinions before I get too deep into the rabbit hole.

 

[mike93lx]

Maybe a simpler option could be to locate it a little higher than the other pump(s) so it only activates when it's needed?

 

[Strouty]

That is my problem, the sump has developed a leak that basically bypasses the higher level we had the 12 volt pump set at. I just want them both at the same level, then I do not have to worry as much about flooding, been through it twice this year.

 

[Innovate1]

As it sounds like you have discovered, it's easier to find higher current relays in NO than NC although both are available. Smaller delay relay running a larger standard NC one seems like a simple way to do it.

 

[LXCam]

You won’t find what you want strouty without an alternate means of a power source to keep it closed for X amount of time. You could use a line voltage relay that is energized the entire time that when it loses power triggers a 12v dc time delay relay to actuate the pump.

 

[joe_padavano]

Am I missing something here? I seen a number of SPDT and DPDT time delay relays for 120V.

 

[jlv03]

What’s the harm if there is no delay? Is the 12VDC pump also on a float switch?

 

[LXCam]

Am I missing something here? I seen a number of SPDT and DPDT time delay relays for 120V.

A time delay relay needs power to maintain state. He wants something that will maintain state without power applied to it. They don’t make anything like that.

 

[fitter30]

Motor amps for 12vdc including lock rotor and run amps. Contact the pump manufacturer for run and lock rotor amps.

• 0.1 HP = 8 amperes
• 0.2 HP = 17 amperes
• 0.5 HP = 42 amperes
• 1.0 HP = 85 amperes

 

[inphx]

Well.. being an EE i thought about a simple resistor/capacitor delay to energize the 12v circuit... but then i asked AI to sort it out.


Creating a circuit with two relays where one is activated by the loss of 100VAC to subsequently control a second 12V relay with a delay is a task that involves both relay logic and a time delay mechanism.
Here's a basic outline of how you could design such a circuit:

1. First Relay (100VAC Sensing Relay): This relay would be normally energized when 100VAC is present. It should be a type that de-energizes (i.e., its contacts switch from their normal position) when the 100VAC supply is lost.
2. Time Delay Mechanism: To introduce a delay before activating the second relay, you could use a time-delay relay or create a simple RC (Resistor-Capacitor) delay circuit. The time delay is typically achieved by charging a capacitor through a resistor. The values of the resistor and capacitor determine the time delay. For a 10-minute delay, you would need to calculate the right values of R and C.
3. Second Relay (12V Relay): This relay would be connected in such a way that it is activated only after the time delay has elapsed following the deactivation of the first relay.

To calculate the values for the resistor and capacitor in the RC delay circuit, you would use the formula for the RC time constant: τ=R×C. The time constant τ is the time it takes for the voltage across the capacitor to reach about 63% of its final value. For multiple time constants (e.g., 5τ for over 99% charging), you can calculate the total delay.
Let's calculate appropriate values for R and C to achieve a 10-minute delay. We'll assume you want the capacitor to be fully charged (or very close to it) in 10 minutes.

For a 10-minute delay, you would need an RC time constant (R×C) of 120 seconds. To achieve this, you have multiple combinations of resistor and capacitor values that you can choose. For instance, a combination of a 120-second time constant could be a 1 megaohm resistor with a 120 microfarad capacitor, or a 2 megaohm resistor with a 60 microfarad capacitor, and so on.
Keep in mind the following:

1. The actual delay can slightly vary due to the tolerances of the resistor and capacitor.
2. Ensure that the capacitor's voltage rating is suitable for the circuit.
3. This RC circuit would be connected to control the coil of the 12V relay, but make sure it's configured so that the relay is activated only after the capacitor charges to the required level.

 

[jlv03]

Here is a SPDT relay I have used in the past for 120VAC circuits: https://www.amazon.com/American-Zet...80-1C-120A/dp/B07587NZTC?tag=atomicindus08-20

 

[CoogarXR]

If you are electronically inclined, you could make a circuit using a 555 timer chip.

If not, google "12v timer module", and see the dozens of options. I would use a 120v NO relay that would close when it loses power, that would start the 12v timer, and the timer would close a 12v relay to start your pump. Then, I would probably use another set of contacts on the 120V relay to reset the timer when power is restored.

 

[alfredeneuman]

That is my problem, the sump has developed a leak that basically bypasses the higher level we had the 12 volt pump set at.

Why don't you patch the leak in the sump before trying to figure out a work around?

 

[Strouty]

Why don't you patch the leak in the sump before trying to figure out a work around?

The way it is currently setup, the sump was raised above the floor, it is currently leaking at the seam, I do not see an easy way to patch things, I just want the float to be below the floor so there isn't even a possibility of a leak. If it does leak, it floods, I don't want that as a future possibility. I plan on installing a better sump, this one is old, the house was built in 1905 and I am guessing it has always had water issues.

LX, thanks for pointing out the time delay issue, I didn't realize they would need power to function. I guess I could go really goofy and use NC relay to sense the 120 volts, then when it engages, it runs a NO time delay relay from the 12 volt source, that would run its course to finally activate a NC 12 volt relay???

So 120 volts goes out, NC relay engages the 12 volt delay relay, this temporarily kicks 12 volt power away from third and final relay, then once the timer is done 12 volts flows to the relay???

No, that won't work either, or will it? I have to play around with things a bit more.

To answer some other questions, the backup pump does have a float, but it will need to be at the same level as the primary one, my sump is too small to make them at different elevations.

 

[Strouty]

I see they do make a relay that might work, just need to find one.

"Normally-closed, timed-closed. Abbreviated “NCTC”, these relays open immediately upon coil energization and close after the coil has been de-energized for the time duration period. Also called normally-closed, off delay relays."

 

[LXCam]

Last idea won’t work. But this one will.

120v relay. Wire NC set of contact to energize the 12vdc time delay (on) relay. Depending on if the contacts can handle the pump load you can switch it there or get a higher amperage rated unit and have the TD relay actuate it.

I know you get it, hell ya wrote it

The way it is currently setup, the sump was raised above the floor, it is currently leaking at the seam, I do not see an easy way to patch things, I just want the float to be below the floor so there isn't even a possibility of a leak. If it does leak, it floods, I don't want that as a future possibility. I plan on installing a better sump, this one is old, the house was built in 1905 and I am guessing it has always had water issues.

LX, thanks for pointing out the time delay issue, I didn't realize they would need power to function. I guess I could go really goofy and use NC relay to sense the 120 volts, then when it engages, it runs a NO time delay relay from the 12 volt source, that would run its course to finally activate a NC 12 volt relay???

So 120 volts goes out, NC relay engages the 12 volt delay relay, this temporarily kicks 12 volt power away from third and final relay, then once the timer is done 12 volts flows to the relay???

No, that won't work either, or will it? I have to play around with things a bit more.

To answer some other questions, the backup pump does have a float, but it will need to be at the same level as the primary one, my sump is too small to make them at different elevations.