How can I power both sides of breaker box with two 120 volt battery backups?

Question

I have two vtoman 1800 battery generators. Is there any problem powering my breaker box (main breaker off to street power) by using a dual pole 15 amp breaker and hooking up one hot from each generator to one of the dual poles then hooking up neutral and groung from both generators to the ground bar in the breaker box? Seems ok because each of the two bus bars has one hot input from a separate generator but what about the fact that neutral and ground from both generators will be hooked to the same ground bar in the breaker box that every neutral and ground wire in the house is hooked up to?

Answer 1

Assuming that the two battery backups are not designed to be synchronized, the problem is that the two together will not produce true 240 volts: this requires that the two generators run at exactly the same frequency and are 180 degrees out of phase. Most likely, the generators will be a fraction of a hertz off and will drift in and out of phase.

The result is that any 240 volt load will not work properly. More significantly, if you have any multi-wire branch circuits (two 120 volt loads from a 240 volt breaker using two hots and a neutral), you run the risk of overloading the neutral wire if the generators actually run in-phase instead of 180 degrees out of phase.

In addition, as @nobody pointed out, trying to get 240 volts out of two unsynchronized 120 volt generators is likely to damage them.

Unless you know exactly what you’re doing, this is a really bad idea.

Answer 2

Don't - but alternatives

The "generators" you list are very small. 1.5kWh. It does not make a lot of sense to run those through your panel.

• Any non-trivial load will run them down quickly. What's the BARE MINIMUM? A gas boiler, a few light bulbs, your modem and router, the fridge, a couple of phone chargers? You'll be lucky to run that for 90 minutes with one of those batteries.
• If you run them into your panel you need an inlet and an interlock. There is enough written on this site about that so I won't get into details, just don't even think about doing this without an inlet and interlock.

Best alternative

Here's the nice thing about battery "generators". They can be indoors, they can be anywhere because they aren't burning gas. With such a small one you should just carry it into the kitchen, plug a power bar into it, plug in your fridge, a couple of phone chargers that you leave on the kitchen table, and that's about it. If you want to run a gas boiler to heat your house, install a dedicated one-circuit transfer switch at the boiler. Run the boiler for an hour and the fridge for an hour by carrying the generator back and forth. It won't last long enough to do this twice. Then repeat with the other one.

For lighting esp in the bathrooms, get Lithium lanterns that you leave in the rooms that need them. They will last far longer on their own batteries than this generator. Same with your phones actually, just buy a lot of power bricks for them.

Bad alternative

If for some reason you want more flexibility to power lots of low-power things all over your house so you really want it in the panel. 1) Install an interlock and an inlet, 2) Move all the breakers that you want backed up onto the same phase. There can't be THAT MANY. There just can't. 3) Run one generator til it dies, then the other. If you can buy a piggyback battery for the first generator instead of a whole second one, that would be better. Forget about powering both sides of your panel with these. Not practical.

Gratuitous advice

That's a lot of effing money for 1.5kWh. YOu need to think about what you'll achieve at a higher level. You won't make your house habitable through a multi-day outage or even through a single cold night. You won't really extend your fridge life much. They're good for 24 to 36 hours with no power if you leave the door closed. This will add another day. Your phones can run off their own batteries and use cellular instead of WiFi. You're not Working From Home with one of these, not even for one day.

I understand why these are called "generators" ... compared to what came before them, they are enormous. They are not portable and they are capable of powering high voltage equipment so it's not totally wrong to label them that way. But your particular ones are on the tiny side of the battery generator world and they are expensive .... I don't see the point.

EITHER use them for single appliances or buy a gas generator that can run ALL essentials in your house for days. You don't need a huge gas generator for that. If you don't have sump pumps and multiple fridges a 5kW one will be PLENTY, will cost FAR less than your TWO battery ones, and with a supply of fuel will run for days or weeks.

Answer 3

1. You can only do this for your 120V loads. All 240V loads must be off or let's just say bad things will happen. Note that this means you have to go through a set of steps prior to switching this on that you may or may not perform correctly during a time of no power, which is to say a high-stress time. You really just shouldn't.

2. I have never seen an interlock kit that supports 2 120V supplies. Anything you rig up is likely out of code and potentially very dangerous.

3. A battery "generator" like this just isn't made to power your house. It isn't a generator, it's a battery. A 1548Wh capacity is the equivalent of running a 2 kW small Honda generator for an hour. A window air conditioner might run 2 hours on this. So unless your design condition is to prevent relatively short power interruptions, I doubt you will be happy with this. I suggest using the battery as a stand-alone unit and just plugging things into it that you want to keep running.