homemade auxiliary power system

[Manowar1985]

Hi everyone. I would like to ask for your help about my small elevator.I know this subject may seem irrelevant with this forum but I couldn't find any answers.Thank you for your time
So when the power is out I want the system to automatically switch to the power auxiliary system.So the only thing I came up with is the attached schematic but I fear the interference of the 220v of the ac outlet with the 220v of the inverter output.If you have any suggestions it would be appreciated. Thank you

[nosaj]

In the Us youd need a transfer switch. Code probably requires a professional installation and if you value your house you'd want one to as far as insurance.

nosaj

[Mick Bailey]

Connecting the mains across the output of the inverter could be hazardous for a number of reasons. The phasing of the inverter output and the incoming mains will not be synchronized and could cause overheating in the equipment you're supplying, or issues with the inverter overheating. Also, whilst the inverter is an AC source, there's no way of knowing how the incoming DC is isolated from the output and connecting it to the mains could lead to mains voltage appearing on the battery terminals with serious consequences. There's also the possibility of the input being 'floating' and not referenced to mains earth. There's no telling how the apparatus would behave under fault conditions.

This reminds me of the practice of using a petrol generator to feed into the ring main by attaching a mains plug to the output. When there's a power outage this works, but can be disastrous when the mains comes back on with the mains then appearing in parallel to the generator output.

The way commercial changeover units work is by switching isolating relay contacts so that you get either the mains or the backup supply, but not both at the same time. Sometimes there are multiple contact sets that are switched in sequence to ensure safety. There can also be a lock-out interval to prevent rapid switching between supplies in the event of a rapidly fluctuating mains supply. This can sometimes occur where there's a connection issue (such as intermittent overhead line contact). The changeover unit will ensure that there's a steady mains supply before switching back from DC standby power.

[nosaj]

This reminds me of the practice of using a petrol generator to feed into the ring main by attaching a mains plug to the output. When there's a power outage this works, but can be disastrous when the mains comes back on with the mains then appearing in parallel to the generator output.



In the US this is illegal.....in our area after hurricanes linemen were killed trying to repair power lines that had been fed by generators not isolated from the grid.
Please do NOT DO this.

nosaj

[Mick Bailey]

+1.

I wasn't recommending this and it's illegal in the UK as well.

[g1]

A proper legal type transfer switch may allow you to feed surplus energy (from wind turbine, solar, etc.) back into the grid as well. Some places will actually pay you for it, some give credit or 'net metering'.

[Jazz P Bass]

Good write up about 'Transfer Switches' here: https://www.homedepot.com/c/ab/best-...5fab902f44072d

[mikepukmel]

In the Us youd need a transfer switch. Code probably requires a professional installation and if you value your house you'd want one to as far as insurance.

nosaj

Good friend did it himself (he's a real wiz) said that it just has to pass inspection in NH, which are pretty strict. (In MA you can not even change a toilet legally <frown>. Unions)

[nosaj]

Good friend did it himself (he's a real wiz) said that it just has to pass inspection in NH, which are pretty strict. (In MA you can not even change a toilet legally <frown>. Unions)

I still think you'd want to pass whatever test the insurance company had. just as easily say you caused the house to burn down if something happened.

nosaj

[mikepukmel]

I still think you'd want to pass whatever test the insurance company had. just as easily say you caused the house to burn down if something happened.

nosaj

After watching videos of some house current electrical failures, I think this is one thing I would not do myself.

[Mick Bailey]

It's fairly common with UPS systems to run critical equipment directly off the battery/inverter for 100% of the time and not employ any transfer switching - referred to as an online UPS. This ensures clean power and full continuity. The same approach could be used in the case of the OPs requirement so long as the battery/inverter spec is up to the job. It all depends on balancing charge rate, battery capacity and inverter duty-cycle.