3 Phase System, How to Charge with a Single Grid Phase

[greeksolar]

Hello, I'm trying to put together a new hybrid PV system with batteries.

We have 3 phase grid service here, but its extremely unreliable, usually at least 1 phase is down, sometimes 2. The PPC probably won't ever fix it, so don't offer that as a solution please

Most of our loads are single phase, except the large heatpump, swimming pool heater, and the EV charging station. These are all 3 phase.


My question is. can a system be designed, so that the batteries can be charged with only 1 or 2 phases from the grid? We can't go totally off grid, as we would need 150 -200 kwh in battery capacity, which is too expensive, needs too much space, etc.

Is there a way for us to "trickle charge" (probably a bad analogy) the batteries from a single phase? What kind of inverter, charge controllers, battery setup would be required?

Also we are not net metering, since for various reasons the PPC isn't allowing it yet.


thank you

 

[timselectric]

My question is. can a system be designed, so that the batteries can be charged with only 1 or 2 phases from the grid?

Yes
Use single phase chargers.

Also we are not net metering, since for various reasons the PPC isn't allowing it yet.

Then you don't need a hybrid system.
Just an off-grid system with grid backup.

 

[saen]

Then you don't need a hybrid system.
Just an off-grid system with grid backup.

If Phase is down then will not work
No Grid No Power.

 

[timselectric]

If Phase is down then will not work
No Grid No Power.

If only one phase is down. You can still charge from the other two phases.

 

[timselectric]

A common way to deal with unstable grid is charging batteries from grid and powering loads from batteries through inverters.

 

[wheisenburg]

Just how often are you working on only one of two phases and what is your typical current draw? If you are running a pool heater that could draw many thousands of watts. If you are looking to build what is essentially a high current single phase to three phase converter there are devices specifically for that. See "rotary phase converter".

If you want battery backup as part of this, it will be far more expensive. A 3 phase inverter will still draw power from a single 48V battery bank. So it appears that what you need is a three phase inverter hooked to your battery bank. There maybe some 3 phase specific inverters or you may need to use three single phase inverters working together. It should also be possible to hook your existing three phase power to the inverter(s). If all three phases are fine, the inverter should go into pass through mode. It will just pass your power through to your loads. If one or more phases are down then the inverter will automatically switch over to Invert mode. The issue is that if this is an Inverter/Charger, it will not charge from the grid unless all three phases are good.

So all you really need then is single phase charger. With three phase you should have two voltages available Line-to-line or line-to-neutral . The charger does not care that you have a three phase inverter connected to your battery. All you have to do is match the charger AC input voltage and DC output voltage with what you need. It might be 208 -> 48 or 120 -> 48. If it is the same phase that is always dropping out, just use the most reliable phase for the charger. If it varies you might need to use some kind of rotary selector switch to choose the phase.

So as a hypothetical you could use 3 Schneider XW pros working together as your 3 phase inverters and 2 Schneider XW pros each working independently as your chargers. This would allow you to convert 13,600 watts continuous from 2 phases into 3 phase. You would probably want to add some large capacitors to the DC bus to avoid hitting the battery with lots of ripple current.