Transfer Switch

Re: Transfer Switch

czars wrote: »

Thanks for the reply. I'm an Electrical Contractor and my client is buying a Xantrex XW4548 and has fed me little info to date.

First, there is a very small price differential between the XW4548 and the XW6048, and I think the benefits of the larger XW6048 can far outweigh the added price. I think the XW6048 is also slightly more efficient than the XW4548, although you'll have to check at the specific output levels expected with the PV array.

As far as battery bank size, a suggested minimum would be 100 ah (48 volts) x array size (kw). So a 3kw system would need a minimum of a 300 ah, 48 volt battery bank. The manual says a 100 ah minimum battery bank, but that is not the real world situation. If you get too small a battery bank there will be major problems with the operation of the inverter, both selling and charging.

And finally, there is an easy way to figure out everything you need to know about the XW series inverters. Just search the forum for posts by Solar Guppy. He is the expert here.

Re: Transfer Switch

The transfer switch is just a closure contact relay between either the AC1in (typically grid connection) or AC2in (typically gen connection) to ACout which is hardwired to inverter. Only one ACin is selected, and which one takes priority if both are present is user settable.

When the ACin is qualified, meaning it is within freq and voltage specs and the inverter controller establish syncronization, the relay closes putting the inverter in parallel with the grid.

The inverter can be deactive or active. The inverter is bi-directional. It can take power from the ACin/ACout node to charge the batteries, or push power to the ACin/ACout node. It makes measurement of current flow in and out of ACin, ACout, and inverter so the controller knows which way power is flowing and makes adjustments to the PWM control on inverter to either push or pull power from the battery node.

When selling to grid is enabled, any attempt to raise the battery voltage (by a PV controller or any other charging source) will cause the inverter to pull current from the battery line to maintain the inverter's charge float voltage and push the excess power to the ACin/ACout node. It will be used by ACout loads or if pushed power is greater then ACout consumes then is will be push excess to grid.

If selling is not enabled, but grid support is enabled, it will do the same as described above except it will not allow any excess power to be pushed to grid. The battery voltage will be allowed to rise where, presumably, the PV controller takes over battery charge voltage limit control to avoid overvoltaging battery.

Load shaving is putting a criteria on maximum allowed current draw from ACin (very useful for smaller generators), where if ACout load demand is greater then this set limit, the extra needed ACout load power is supply by inverter, taking power from batteries. This caps the maximum current draw from the ACin.

Setting of all these functions is sometimes challenging because of the the user interface control naming conventions and how the software manages these functions.