Inverter Will Not Work If Not Plugged Into Mains

Thank you for your response. However, the inverter works perfectly fine for hours when there is a power cut. But if I take out the input plug connected to the mains socket (which is anyway not supplying power during a power-cut), all appliances connected on the inverter line will immediately switch off. Why is this happening? Thanks.

What did the inverter manufacturer say during the last telephone call on this topic?

I agree with SE. I've had to replace several sealed Lead Acid (SLA) batteries in Uninterruptable Power Supplies (UPSs). The battery is the most likely point of failure, SLA batteries have a limited lifetime.

Thanks Rixter. As I was pointing out to SE, the batteries works decently and can power the the connected appliances for 4-5 hours. But during this time, if I decide to disconnect (pull out the plug literally and not just switch off) the input from the mains (which is not supplying power during a power outage), the inverter stops powering the connected appliances immediately. It is still drawing from the battery as evident from the hum that the inverter is making.

That's very strange. Does your inverter have a make and model number?

It's a Luminous Sine wave inverter. I will look up the model number tomorrow.

The manufacturer's contact details are here. Include in the next post details of the telephone calls that have taken place for the benefit of forum subscribers, please.

Have you checked your inverter owners manual to see if it has a low voltage safety ? Some units shut off the power in order to protect downstream devices and to prevent repeated low battery voltage levels. These are also known as a battery protection circuit.

Back when I was a trucker, my Volvo truck had a built in 1000 watt inverter, if I used the battery to power the inverter, like when I was watching TV or using the microwave and the battery charge got low, the circuit would cut off the inverter and my tv or microwave oven would shut off, ( although there would be sufficient charge to start the engine ) then I would start up the engine and let it run for about an hour and have another 4 hour charge with the engine off to operate the inverter.

Leave your inverter plugged in at all times and find something else to puzzle over.

Maybe there's a relay inside your inverter that needs to sense the main line's presence to switch on and off.

Thanks Lyn. You are probably right. Of course, this is not a desperate situation. It's just something I discovered while trying to carry out some maintenance. But my worry was whether the battery power was just leaking back into the mains and degrading the performance while there is a power outage. Being a bit handicapped in electrical circuits also does not help either :)

<...whether the battery power was just leaking back into the mains...> That's nonsense.

some people use to worry about electricity leaking out of those unused lighting sockets around the house. Really....Of course, they also believe in aliens from outer space.

...and the jolly green giant.

My grandmother was one of those. It didn't matter what I told her, she was convinced that she needed to plug all the holes (her outlets) to avoid having huge power bills from all of the electricity leaking out.

One day when she was in her 90s, one of her outlets in an exterior wall of her mobile home actually caught fire and spewed sparks out of it (a phenomenon known to happen on mobile homes because the exterior walls leak). No serious damage, but that served to absolutely convince her that I was wrong and she was right all along...

...but did it let the smoke out? We all know that electricity is smoke and distribution has to do with mirrors.

....pass me my foil helmet please?

OK, I think what's happening is this. You have a high resistance leakage path between the inverter output and the input. That is why you read voltage there.

When it is plugged in, there is low impedance through the line transformer feeding your mains, so this leakage voltage drops to zero. The UPS has a sensor that detects when power has failed. When you unplug it, it senses this voltage and connects the output to the input, as if the mains voltage had been restored.

Thanks Rixter. This seems to be a plausible explanation. There is however one thing which is still unclear. 1) During a power outage, if the switch to which the inverter outlet is connected is turned off (which will disconnect the live), the appliances are still running fine on the battery. It's only when I pull the input plug out, the inverter shuts of the output (or as you said connects the output to the input sensing line voltage). However, shouldn't both the cases result i similar behavior? 2) When i check the input plug of the inverter there is a voltage even on the neutral pin. So, we can assume that leakage voltage drops to zero when plugged in. But then why sense neutral voltage to sense if power has failed (it will always be zero)?Again, my apologies, I may be missing out on something very basic.

Maybe the power switch is on the neutral side instead of the hot side, or the hot and neutral are reversed somewhere.

This means that NEUTRAL and GROUND are wired together for SAFETY and LEGAL reasons.

Can you test if that is the reason your inverter does not work?

Try it by unplugging and wiring the metallic parts of the plug together. (if that is too much work, place it in salty water)

Anyway, when you turn on the inverter, make sure to be away. I would be surprises if something bad happened, but you never know how it was designed!

So, why does an inverter that is not connected to the incoming mains need an electrical earth/ground connection referenced to the incoming mains?

I am not an expert on electrical systems, but would suggest that maybe the following is happening:

The inverter provides backup power when there is no incoming electricity. If you unplug the system, it cannot sense when the main supply returns to normal operations, creating a potentially dangerous situation where the mains are supplying and the backup is supplying.

To me this would be a basic safety feature of the invertor to protect the system.

Skpal

Recently read about inverters for solar panels which as a safety measure will not pass current from the panels when inverter disconnected from the mains. I think this was for micro inverters that sit behind each panel feeding the central control unit that needs to be connected to the mains, whether there is power in the mains or not

Can't find the article or site Solar Edge ? not Solar Century.?

Check the docs. on yours, it may have a similar condition in which case I would suggest it may not be the ideal for your application should you want to go off grid.

Correction to self. It is the power optimisers that sit near the panels and their output is fed to an inverter. These inverters detect whether or not they are connected to the mains (even if mains down) and will close the output from panels if the inverter is unplugged. If skpal's inverter is this type even used for batteries then it looks like consistent operation.

Possibly your inverter uses the neutral return in the power cord for it's output and when you unplug it then it is outputting 120 volts between it's output and neutral but unplugged the neutral is not connected to the loads. Try connecting a jumper from neutral of power cord (wider blade*) to house neutral. Be careful not to get SHOCKED. Safest way is to plug into an outlet that is dead (breaker tripped) but still has intact neutral.

* I assume you have normal (for United States) wiring as I am Familiar with.

Inverter should always be connected to main via 3- pin plug and socket ( phase, neutral and ground ) and inverter switch should always be kept in ON position. Reason for this is:

During normal power condition the charger circuit of the inverter is in charging posion and entire load is passing through the phase via inverter. Also neutral is continued through the inverter. When there is power cut immediately power is available through change over relay or electronic circuit of the inverter.