Is there a device that can sense load on a circuit even if the circut isnt powered up

Thread Starter

JcR

Joined Aug 15, 2017
10
I need somthing that can sense load on a circut even if it isnt powered up and give me a hard trigger to switch said circut power sorce on
 

Thread Starter

JcR

Joined Aug 15, 2017
10
If there is no power then all you can sense is that there is no power.
What are you actually trying to achieve?
I have a inverter system in my home but dont want it to switch on if there isnt any load for example a light or tv excetra

What kind of load is it that you are trying to sense the presence of?
I have a inverter system in my home but dont want it to switch on unless ther a load for example a light a tv or any such appliance
 

recklessrog

Joined May 23, 2013
985
Well you could monitor the resistance on the load side and when a predefined level is reached, use this to operate a a simple turn on circuit to actuate relays (solid state maybe) etc.
 

Thread Starter

JcR

Joined Aug 15, 2017
10
Well you could monitor the resistance on the load side and when a predefined level is reached, use this to operate a a simple turn on circuit to actuate relays (solid state maybe) etc.
Do you maybe mean i can use a transiter or something like that
 

AlbertHall

Joined Jun 4, 2014
10,390
Well you could monitor the resistance on the load side and when a predefined level is reached, use this to operate a a simple turn on circuit to actuate relays (solid state maybe) etc.
The problem with that will be if the item which is switched on has a switch mode power supply. At low voltages (DC or AC), such a supply will draw no current except the leakage of the storage capacitor(s).
 

Thread Starter

JcR

Joined Aug 15, 2017
10
The problem with that will be if the item which is switched on has a switch mode power supply. At low voltages (DC or AC), such a supply will draw no current except the leakage of the storage capacitor(s).
So if the light is switched off the resistance is zero and when its on lets say for example 15 ohm could this actually work ?
 

AlbertHall

Joined Jun 4, 2014
10,390
So if the light is switched off the resistance is zero and when its on lets say for example 15 ohm could this actually work ?
When the light is switched off its resistance should be infinite, not zero.
You could detect a filament lamp this way but if it was a CFL or LED light it wouldn't work as these generally have some form of switched mode supply.
 

Thread Starter

JcR

Joined Aug 15, 2017
10
T
When the light is switched off its resistance should be infinite, not zero.
You could detect a filament lamp this way but if it was a CFL or LED light it wouldn't work as these generally have some form of switched mode supply.
and my home has led bulbs no incandescent as led is more energy efficient
 

WBahn

Joined Mar 31, 2012
26,143
I have a inverter system in my home but dont want it to switch on if there isnt any load for example a light or tv excetra


I have a inverter system in my home but dont want it to switch on unless ther a load for example a light a tv or any such appliance
That's going to be virtually impossible. You are basically talking about random loads whose behavior at low voltage is going to be all over the map. Plus, some of those appliances, such as many televisions, have phantom loads so that you can turn it on with your remote. Other appliances have microcontroller circuits in them that need to be powered continuously for the device to operate normally and will draw a small amount of power any time they are plugged in. So are you planning to have physical switches on everything in your house (or to unplug all of your appliances and only plug them in when you want to use them). What about your clocks? What about your refrigerator and/or freezer? What about your furnace?

Since it appears that you already have things set up to run off the inverter, you are in a position to take some basic measurements to see how reasonable your idea might be.

Configure everything they way you would have it when you don't want the inverter to run. Disconnect the inverter and measure the resistance of everything. Now turn on the lowest power thing that you want to be able to detect and repeat the measurement. Do that for several different items. Is there enough of a difference to be noticeable?

Even if there is, you will need to implement a means of making the measurements that will not interfere (or be interfered with) the inverter when it is in use. But you can kick that can down the road since it's a moot point until you figure out some detectable difference between load and no load conditions.
 

Thread Starter

JcR

Joined Aug 15, 2017
10
That's going to be virtually impossible. You are basically talking about random loads whose behavior at low voltage is going to be all over the map. Plus, some of those appliances, such as many televisions, have phantom loads so that you can turn it on with your remote. Other appliances have microcontroller circuits in them that need to be powered continuously for the device to operate normally and will draw a small amount of power any time they are plugged in. So are you planning to have physical switches on everything in your house (or to unplug all of your appliances and only plug them in when you want to use them). What about your clocks? What about your refrigerator and/or freezer? What about your furnace?

Since it appears that you already have things set up to run off the inverter, you are in a position to take some basic measurements to see how reasonable your idea might be.

Configure everything they way you would have it when you don't want the inverter to run. Disconnect the inverter and measure the resistance of everything. Now turn on the lowest power thing that you want to be able to detect and repeat the measurement. Do that for several different items. Is there enough of a difference to be noticeable?

Even if there is, you will need to implement a means of making the measurements that will not interfere (or be interfered with) the inverter when it is in use. But you can kick that can down the road since it's a moot point until you figure out some detectable difference between load and no load conditions.
The whole reason i have this question is i fear the inverter system kicking in while im not home and the inverter burning its transformer due to no load . Also i would like to say thanks to all you guys taking the time to advise me on this matter it really appreciated
 

WBahn

Joined Mar 31, 2012
26,143
The whole reason i have this question is i fear the inverter system kicking in while im not home and the inverter burning its transformer due to no load . Also i would like to say thanks to all you guys taking the time to advise me on this matter it really appreciated
That part might be more tractable. You could build a sensing circuit that monitors the current output of the inverter and if it falls below some threshold for a certain amount of time shuts the system down. It might do so permanently (meaning that it won't come back on until you manually reset something) or perhaps gives it a time out period before it is allowed to come on again. Which approach is better depends on the kind of loads that might be connected.

Another option is to monitor the critical variable (the temperature of the transformer, perhaps?) and shut the system down if it goes out of the allowed operating range.
 
The whole reason i have this question is i fear the inverter system kicking in while im not home and the inverter burning its transformer due to no load . Also i would like to say thanks to all you guys taking the time to advise me on this matter it really appreciated
This might be similar to a real power company problem because the inverters they used were not equipped to produce all reactive power, just real power.
 

tcmtech

Joined Nov 4, 2013
2,867
The whole reason i have this question is i fear the inverter system kicking in while im not home and the inverter burning its transformer due to no load
How is the transformer going to burn out with no load? :confused:

Overloading is where things get burned out. not underloading.
 

Thread Starter

JcR

Joined Aug 15, 2017
10
That part might be more tractable. You could build a sensing circuit that monitors the current output of the inverter and if it falls below some threshold for a certain amount of time shuts the system down. It might do so permanently (meaning that it won't come back on until you manually reset something) or perhaps gives it a time out period before it is allowed to come on again. Which approach is better depends on the kind of loads that might be connected.

Another option is to monitor the critical variable (the temperature of the transformer, perhaps?) and shut the system down if it goes out of the allowed operating range.
Hi WBahn i like your advice but as im a novice could you maybe post a diagram for me how to build such a circut
 

WBahn

Joined Mar 31, 2012
26,143
Hi WBahn i like your advice but as im a novice could you maybe post a diagram for me how to build such a circut
Are you offering to hire my services at my normal charge-out rate?

Didn't think so.

I'm willing to discuss things and give suggestions for you to explore, but I'm not in a position to design something for you for free -- I just don't have THAT kind of spare time.

But tcmtech's question is very valid. I know very little about whole-house inverters and such, so I just took your concern at face value. But it sounds like you don't really have the knowledge or experience to be making the claim that your inverter is going to burn up some transformer if there's no load. While I can't rule out the possibility, it seems very strange that anyone would design a system that behaved that way. So why do you believe that this will happen?

And if you think that letting it come on when there's a load such as a light and that that is sufficient, then you can just put something like a 40 W lightbulb permanently across its terminals. The four or five dollars a month it would cost you can chalk up as an insurance policy for your inverter.

But I think you probably need to look into why operating the inverter with no load is supposed to be so bad -- if it really is, you might want to get a different system.
 

Thread Starter

JcR

Joined Aug 15, 2017
10
Are you offering to hire my services at my normal charge-out rate?

Didn't think so.

I'm willing to discuss things and give suggestions for you to explore, but I'm not in a position to design something for you for free -- I just don't have THAT kind of spare time.

But tcmtech's question is very valid. I know very little about whole-house inverters and such, so I just took your concern at face value. But it sounds like you don't really have the knowledge or experience to be making the claim that your inverter is going to burn up some transformer if there's no load. While I can't rule out the possibility, it seems very strange that anyone would design a system that behaved that way. So why do you believe that this will happen?

And if you think that letting it come on when there's a load such as a light and that that is sufficient, then you can just put something like a 40 W lightbulb permanently across its terminals. The four or five dollars a month it would cost you can chalk up as an insurance policy for your inverter.

But I think you probably need to look into why operating the inverter with no load is supposed to be so bad -- if it really is, you might want to get a different system.
Where im staying in South Africa we can go for prolonged periods of time without supply from the grid so i would also like to save my batteries and the equipment available to us is very expensive and the cheeper options isnt always very safe therefor i would not want it to be on unattended
 
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