Pure sine wave inverters. 12v /230v

Scots John · Oct 20, 2020

I routinely upgrade Motorhome systems. I do use Chinese made pure sine wave inverters from evilbay, usually 2500w/5000w (peak). I always sum the maximum off grid Continuous draw and double it or more. No problems so far, BUT I have heard of others Having problems.

i have pushed consumption higher than continuous max to check the thermal overload kicks in, and it does.

last point is when the Motorhome is hooked up to external mains, do you isolate your inverters from the circuit or leave them connected but not on? I have done this accidentally once and no I’ll effects, I just have limits how far I trust them.

James · Oct 21, 2020

You need to recall all the units you have sold.
Instructions supplied or not, what you are selling is a device with a potentially fatal design flaw.

A judge is likely to give a custodial sentence to you when someone is killed by one.

pc1966 · Oct 21, 2020

The answer is, and always should have been, a change-over switch so you have a male socket for feeding power in (i.e. safe to touch female plug on the inverter output) that can never be live as is is only connected when the mains supply is disconnected. Or have the inverter hard-wired to the change-over switch if the inverter is not frequently removed.

If you only need 16A or less you can use the IEC style C19/C20 that you see on the likes of 3kVA UPS, they are muhc smaller than commando style connectors (but not as strong, watrerproof, reliable, etc, so pay your money and take your choice).

It is absolutely insane to have a live plug, further to have the potential to be in parallel with the AC supply without means of isolating/shutting down on supply failure to protect utility workers from back-feed!

Lucien Nunes · Oct 21, 2020

What needs to be said has been said but I would just like to add my voice. Configuring the plns of a plug to be live from the inverter is a serious violation of all normal safety standards, non-compliant, probably uninsurable and frankly irresponsible. The same is true of connecting an inverter output to a circuit that can be simultaneously energised from the mains. Units so equipped need to be recalled and rectified.

On a purely electrical note, the outputs of normal (non grid-tied) inverters are not capable of withstanding the kind of transients that can occur on the mains. One spike and the transistors in the output H-bridge will shoot through and be blown to smithereens. If the transformer insulation or RF bypass capacitors fail, the mains will be connected to the 12V circuit.

davesparks · Mar 15, 2023

Scots John said:
The plug cannot be live unless the inverter is connected and switched on!

In other words the plug will be live if the inverter is connected and switched on.

This arrangement is commonly known as a widow-maker.

Lucien Nunes · Mar 15, 2023

It's the most ludicrous proposal I had seen in a long time which I suspected to be trolling and not a real thing. After a while it started to nag me that he might actually be doing this for real, so I replied. I wonder how many people have had shocks since the thread was current 2 years ago.

Hi @HowelGrace, welcome to the forum. I get that your post is ironic, but I'm not sure what the OP would make of it? I worry that it might be taken as a compliment! Being over here in the UK I'm a bit rusty on the NEC, can you remind me which code chapters deal with back-feeding of panels and interlocks?

plugsandsparks · Mar 15, 2023

Quite frankly its a bizarre solution for a problem that i solved over 30 years ago. I had Motorhome, needed 240V for phone chargers, nice TV, sat receiver and playstation, so wired an inverter, as you do, BUT it was terminated to a dedicated double socket where all the above were located and next to a double socket which would be powered under hook up conditions. All i needed to do was unplug the stuff from inverter socket to hook up socket. Terminating on a plug and then backfeeding the whole electrical installation was simply not necessary so i do not understand what problem is trying to be solved here.

Lucien Nunes · Mar 15, 2023

If the OP was serious, neither do I. Or rather, it's a common problem with a very simple solution - a 3-position DP transfer switch. The OP claimed there was no room for the switch and I appreciate that not every motorhome has a conveniently located engine room like my boat (where my ATS is). OTOH I presume there was still some space at the morgue.