Low-end generators & inverters and compatibility/safety:
I guess we need to talk about this. Sadly, even electrical contractors and solar salespeople don't know about this one. In all my research I h... View MoreLow-end generators & inverters and compatibility/safety:
I guess we need to talk about this. Sadly, even electrical contractors and solar salespeople don't know about this one. In all my research I have NEVER seen anything about this online.
* The standard for alternating current (AC) power is to have 120 volts presented on the smaller of the two tabs in your power outlet, zero volts presented on the larger of the two tabs and the round receptacle is the electrical ground.
https://images.wisegeek.com/standard-us-power-outlet.jpg
* Sadly, low-end inverters and generators cheat at this. When you test their output they present 60 volts on the shorter of the two tabs and—unexpectedly—60 volts again on the longer tab.
If you test across both tabs on the cheap inverter/generator then you see the expected 120 volts. This seems to work fine with power tools that you might plug into them, for example.
Now imagine that you connected that output from the cheap inverter/generator to the power panel of your off-grid house. Normally all of the power is presented on that short tab (the black or "hot" wire). This black wire in a power panel in your house would represent the back plane of the panel, it's what the circuit breakers attach to. Normally the white wire is the return and represents that longer tab in the outlet. There is supposed to be zero volts on this.
So now what happens in this scenario? You wire things up inside the house and it seems to work. But if you turn off a circuit breaker it only interrupts power for the black wire; it does nothing for the white wire. The power outlet goes from 120 volts to 60. It doesn't actually turn off!
There's an advanced part of that power panel. It's called the "binding screw" which is located somewhere inside the panel at the white electrical bus. You're expected to screw this in all the way for the first panel in your installation. What's supposed to happen then is that the green electrical ground (the metal of the panel itself) is shorted to the white return wire.
Assuming that your panel has the binding screw in place, what does it mean then to have 60 volts on the white wire (which is now the same as green)? It means that your cheap inverter/generator is pumping 60 volts into the Earth. You're wasting half the power by energizing the Earth ground.
As if this wasn't already bad enough, imagine that you've used 14AWG wire for a circuit in your house and you've protected this with a standard 15A circuit breaker. Normally since the black wire is expected to carry all this current attempting to plug in and run a 20A appliance should trip that circuit breaker. But if your cheap inverter/generator is providing 60V + 60V then the black wire only sees half of this current. The circuit breaker won't trip off if you are trying to run a 20A appliance since it's seeing ten of those amps. So next the wires start heating up because they're trying to carry too much power through them. There's a possibility of starting a fire like this.
Next, your electrician wants to do some work for you. He turns off the circuit breaker, removes the plate for the outlet and promptly gets shocked by the 60 volts on the white wire.
What if you have GCFI outlets in your house? It is unlikely that they'll behave at all since they have something inside that's supposed to detect anomalies.
So what do you do?
* If your setup produces 60V + 60V from your cheap inverter/generator then I'd strongly suggest not marrying it to your home's power panel for the reasons I've suggested.
* Buy a more expensive generator like the Predator 9000W that's sold at Harbor Freight, for example.
* There is no easy way to answer this question about "what does it produce?" since there are no working models in stores. This information is not available in any manual for the product nor on any website which sells it.
* Most inverters sold for vehicles and semi trucks usually have the 60V + 60V cheap technology. In many cases this also includes those sold for RVs and campers.
* The low-end Victron Phoenix Inverter falls into this 60V + 60V category. Most portable generators below the $600 price are the same. The higher-end Victron Multiplus inverters provide the expected 120V output.
In summary, many providers of inverter technology have taken a shortcut to minimize cost. This shortcut often can lead to poor performance, an unsafe working environment and possibly equipment damager for electronics.
