# Energy Monitor with Timer & Alarm

#### gturnbull

Joined Jun 19, 2008
100
Afternoon,

I'm looking for some help or pointers where I could source (Or Build) an energy monitor that will sound an alarm when the power drops below a set level, this would also need a timer function.

Is this relatively easy to build?

Any help would be much appreciated.

#### AlbertHall

Joined Jun 4, 2014
11,102
AC or DC?
What voltage and current would it be monitoring?

#### gturnbull

Joined Jun 19, 2008
100
AC or DC?
What voltage and current would it be monitoring?

240v AC and the current would be 1.5a

It would be monitoring a 90w power supply unit with an output of 24v DC

I want to plug the power supply in and monitor the wattage, the wattage on standby will be minimal and a peak output will be 90w, the alarm will sound if the wattage drops below a preset number during the hours set by the timer.

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#### andrewmm

Joined Feb 25, 2011
1,131
Do you mean power ?
as in measuring amps and volts ?

also having confusion, you say 240 V at 1.5A, thats 300 Watts, yet you say to measure 90 watts .

Any chance of a diagram and some more details as to what you have / want

#### gturnbull

Joined Jun 19, 2008
100
Do you mean power ?
as in measuring amps and volts ?

also having confusion, you say 240 V at 1.5A, thats 300 Watts, yet you say to measure 90 watts .

Any chance of a diagram and some more details as to what you have / want

I want to plug something in and monitor the wattage of that appliance, if the appliance falls below a pre-set wattage after 10 minutes during the Active time set, an alarm will sound, if the wattage goes back up during those 10 minutes it wont sound, during the inactive time the unit wont do anything but allow the appliance to be active.

It will be running on 240v AC and power unit plugged into it will be rated as below,

Input AC 100-240v 1.0 -1.5a
Output DC 240v -3.75A

I will need the unit (Monitor) to be rated at 240v as it will be plugged into a socket and the appliance (Power Supply) will be plugged/wired into that.

#### andrewmm

Joined Feb 25, 2011
1,131
Ok, thanks,

Im wondering do we have to look for a big difference between the unit being on and off, or a variable amount of power that might dip below a set level ?

#### gturnbull

Joined Jun 19, 2008
100
Ok, thanks,

Im wondering do we have to look for a big difference between the unit being on and off, or a variable amount of power that might dip below a set level ?
Thanks for your help on this Andrew.

The load can vary In use but the power when in alarm state would be the same, i‘d need to confirm exactly what that is but I’m assuming it will be minimal but when in use it could be be about 100w

For example, in use anything above 5 watts, alarm state would be below the 5 watts for 10 minutes.

#### MisterBill2

Joined Jan 23, 2018
8,214
The requirement is rather confusing to me. Is the issue that your supply voltage varies and thus the appliance power changes, or is it that the mains voltage is stable but the appliance varies?
Measuring power or energy is a bit more complex than measuring voltage or current. For a power supply claimed to be a 90 watt output device the power in will be a bit more. It would be fairly simple to monitor the supply current draw and send an alarm if it changed beyond some limit value. And the same can be done with the supplied voltage.
Of course if the power supply is a switch-mode regulator there will be changes in the current if the mains voltage changes.
What is the ultimate goal of the project? There may be a simpler approach.
My guess is that it is monitoring a computer system during startup, or the running of some program.

#### slackguy

Joined Feb 11, 2016
67
LED are current sensitive. mA meters are not too expensive. You may only need to attach a resistor with an appropriate resistor, rather than a whole power circuit detector. You'd only want "power components" if you were attempting to control all that power. Oh! if your 240AC you'll need a diode to protect reverse current on that led. Just look at the LED you would see power by continued brightness.

That all "omitted a timer". But you never said what the timer would do / trigger. Discussing that is useless if we don't know what kind of alarm and why. You also didn't say WHAT is being timed. A microsecond of power lost or an hour or time expired since loss or?

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#### andrewmm

Joined Feb 25, 2011
1,131
You have a few things here.
measuring time , and doing some thing upon an action, probably a bit of filtering, reporting , control
sounds like a processor type project , Arduino comes to mind.

measuring power. Power is volts * amps . Its "easy" to measure volts, but the mains voltage is wobbling around a lot, the mains frequency itself, and lots of "noise" on it form all the switch mode power supplies etc on the lines.

measuring AC current is easy if you don't want "very accurate" , you use a clamp on current transformer, that clamps around the line.

https://www.electronicshub.org/current-transformer/

this one of many ,

https://uk.rs-online.com/web/p/curr...Slj_pAsCTeNlvWaGU_caApIEEALw_wcB&gclsrc=aw.ds

In principle, if you assume mains voltage is constant, which it basically is ! then just reassuring current is all you need.

like this

https://learn.openenergymonitor.org...to-build-an-arduino-energy-monitor-measuring-
current-only

As you only want a go / no go signal, with quite a big window, I'd suggest this is the starting place.

#### MisterBill2

Joined Jan 23, 2018
8,214
So far all that we have is that the TS wants to measure the "power" into a 90 watt power supply and send an alarm if there is a deviation. What is not mentioned is if the cause would be a change in the mains supply, a variation in the load on the power supply, or a partial failure in the power supply. We see no response to questions in posts 8 and 9. There are power monitoring devices made by several companies, with products available world-wide. FLUKE has an excellent line and at least one of the models could deliver every bit of the data requested and also a detailed record for the entire time.

#### gturnbull

Joined Jun 19, 2008
100
The requirement is rather confusing to me. Is the issue that your supply voltage varies and thus the appliance power changes, or is it that the mains voltage is stable but the appliance varies?
Measuring power or energy is a bit more complex than measuring voltage or current. For a power supply claimed to be a 90 watt output device the power in will be a bit more. It would be fairly simple to monitor the supply current draw and send an alarm if it changed beyond some limit value. And the same can be done with the supplied voltage.
Of course if the power supply is a switch-mode regulator there will be changes in the current if the mains voltage changes.
What is the ultimate goal of the project? There may be a simpler approach.
My guess is that it is monitoring a computer system during startup, or the running of some program.

I will be monitoring an pump essentially.

This pump has an auto start stop facility but should not be off for longer than 10 minutes at a time, if it does go off for longer than 10 minutes I want it to sound an alarm until it's restarted.

LED are current sensitive. mA meters are not too expensive. You may only need to attach a resistor with an appropriate resistor, rather than a whole power circuit detector. You'd only want "power components" if you were attempting to control all that power. Oh! if your 240AC you'll need a diode to protect reverse current on that led. Just look at the LED you would see power by continued brightness.

That all "omitted a timer". But you never said what the timer would do / trigger. Discussing that is useless if we don't know what kind of alarm and why. You also didn't say WHAT is being timed. A microsecond of power lost or an hour or time expired since loss or?
You have a few things here.
measuring time , and doing some thing upon an action, probably a bit of filtering, reporting , control
sounds like a processor type project , Arduino comes to mind.

measuring power. Power is volts * amps . Its "easy" to measure volts, but the mains voltage is wobbling around a lot, the mains frequency itself, and lots of "noise" on it form all the switch mode power supplies etc on the lines.

measuring AC current is easy if you don't want "very accurate" , you use a clamp on current transformer, that clamps around the line.

https://www.electronicshub.org/current-transformer/

this one of many ,

In principle, if you assume mains voltage is constant, which it basically is ! then just reassuring current is all you need.

like this

https://learn.openenergymonitor.org...to-build-an-arduino-energy-monitor-measuring-
current-only

As you only want a go / no go signal, with quite a big window, I'd suggest this is the starting place.
Thank you I will look into the above.

So far all that we have is that the TS wants to measure the "power" into a 90 watt power supply and send an alarm if there is a deviation. What is not mentioned is if the cause would be a change in the mains supply, a variation in the load on the power supply, or a partial failure in the power supply. We see no response to questions in posts 8 and 9. There are power monitoring devices made by several companies, with products available world-wide. FLUKE has an excellent line and at least one of the models could deliver every bit of the data requested and also a detailed record for the entire time.
I want to monitor a pump, during use the pump draws 100w, when in standby it will draw 5w, if it is in standby mode for more than 10 minutes it will trigger an audible alarm, this will only be active for a pre-set period by means of a timer, when not in the 'active period' the unit will do nothing but still allow the pump to be in standby mode, the wattages mentioned are approximates and would be confirmed.

Joined Jan 15, 2015
5,876
It will be running on 240v AC and power unit plugged into it will be rated as below,

Input AC 100-240v 1.0 -1.5a
Output DC 240v -3.75A
I want to monitor a pump, during use the pump draws 100w, when in standby it will draw 5w, if it is in standby mode for more than 10 minutes it will trigger an audible alarm, this will only be active for a pre-set period by means of a timer, when not in the 'active period' the unit will do nothing but still allow the pump to be in standby mode, the wattages mentioned are approximates and would be confirmed.
One post you have a power supply with 240 VAC in @ 1.0 to about 1.5 amps. Then you reflect a DC out of 240 VDC @ 3.75 amps. You can't get more out than you put in.

Moving along since the pump apparently runs on 240 VDC or any fixed voltage all you should care about is the current I would think. 100 Watts @ 240 VDC = 0.416 amp and 5 Watts @ 240 VDC = 0.021 amp. In order to get good answers you need to provide good numbers? Again if the pump is merely a DC motor pump running at a fixed voltage forget about power expressed in watts, all you care about is current. The only issue is knowing how much current?

A common trick is just wrap several turns of your pump (+) lead wire around a simple reed switch so when enough current is drawn by the pump the reed switch closes. Create a signal using the magnetic reed switch for a watchdog timer where unless it is retriggered inside ten minuets you get a latching alarm needing a manual reset. You also mentioned, at the beginning:

240v AC and the current would be 1.5a

It would be monitoring a 90w power supply unit with an output of 24v DC
What's that all about with the 24 VDC?

Ron

#### MisterBill2

Joined Jan 23, 2018
8,214
One post you have a power supply with 240 VAC in @ 1.0 to about 1.5 amps. Then you reflect a DC out of 240 VDC @ 3.75 amps. You can't get more out than you put in.

Moving along since the pump apparently runs on 240 VDC or any fixed voltage all you should care about is the current I would think. 100 Watts @ 240 VDC = 0.416 amp and 5 Watts @ 240 VDC = 0.021 amp. In order to get good answers you need to provide good numbers? Again if the pump is merely a DC motor pump running at a fixed voltage forget about power expressed in watts, all you care about is current. The only issue is knowing how much current?

A common trick is just wrap several turns of your pump (+) lead wire around a simple reed switch so when enough current is drawn by the pump the reed switch closes. Create a signal using the magnetic reed switch for a watchdog timer where unless it is retriggered inside ten minuets you get a latching alarm needing a manual reset. You also mentioned, at the beginning:

What's that all about with the 24 VDC?

Ron
WRONGO!!! The TS said 24 volts out, not 240. Big difference there.
Now I am thinking that if the pump operation is so important then it would make more sense to monitor the flow or possibly thr discharge pressure, since a pump can be in a failure mode and still draw close to the same power.
Whenever performance must be monitored it is ususlly better to monitor downstream from all of the possible failure points. Pump discharge would be the logical place for that. One little pressure transducer could verify that the flow is the proper value. And it would be totally isolated from all other electrical stuff.

Joined Jan 15, 2015
5,876
WRONGO!!! The TS said 24 volts out, not 240. Big difference there.
Now I am thinking that if the pump operation is so important then it would make more sense to monitor the flow or possibly thr discharge pressure, since a pump can be in a failure mode and still draw close to the same power.
Whenever performance must be monitored it is ususlly better to monitor downstream from all of the possible failure points. Pump discharge would be the logical place for that. One little pressure transducer could verify that the flow is the proper value. And it would be totally isolated from all other electrical stuff.
I quoted the original poster.

Anyway while I agree flow would likely do fine since then you know it's there the thread starter never mentioned a budget? I used and like GEM Flow Switches but again, no mention of flow rate, pipe diameter or much of anything else. Why look at power when there is a fixed voltage? So use a flow switch which does guarantee there is actually flow when the pump runs. The rest I would do as I mentioned, setup a watchdog timer with an audible and light alarm.

Ron

#### MisterBill2

Joined Jan 23, 2018
8,214
Use a pressure sensor at the discharge end of the line. Flow switches can have quite a few problems, depending on what they are flowing. End of line pressure does work.

Joined Jan 15, 2015
5,876
Use a pressure sensor at the discharge end of the line. Flow switches can have quite a few problems, depending on what they are flowing. End of line pressure does work.
Well just maybe if the thread starter was a little more descriptive we would know a little more and be able to make well informed suggestions rather than just toss things out? Wouldn't that be novel?

Ron

#### MisterBill2

Joined Jan 23, 2018
8,214
I have requested additional information a few times and we did get the information that the device being powered is a 24 volts DC motorized pump that has specific running current and standby currents. Evidently the power needed, and hence the current, varies depending on just what the pump is doing. And evidently that variation is important to the TS. And from my industrial equipment experience, monitoring the end of line pressure is a fair way to verify delivery of whatever.

#### djsfantasi

Joined Apr 11, 2010
7,551
WRONGO!!! The TS said 24 volts out, not 240. Big difference there.
Now I am thinking that if the pump operation is so important then it would make more sense to monitor the flow or possibly thr discharge pressure, since a pump can be in a failure mode and still draw close to the same power.
Whenever performance must be monitored it is ususlly better to monitor downstream from all of the possible failure points. Pump discharge would be the logical place for that. One little pressure transducer could verify that the flow is the proper value. And it would be totally isolated from all other electrical stuff.
WRONGO!!! Take a look at post #5. it may have been a typo, but he clearly stated 240V out. This post was more recent than the 24V in post #3. People have been responding to the most recent post.

#### gturnbull

Joined Jun 19, 2008
100
Evening,

Thank you for the replies.

My fault it should be 24v DC output, sorry about the confusion.

Thank you for all the suggestions, but end of line monitoring isn’t an option, they way I would like to set this up is as described previously.

Monitoring the Power consumption, be that wattage or whatever, during a set time, if it falls below x value for a set time, it triggers an alarm, alarm resets when it rises above x figure.