How to set Gen. braker size with stacked XWs

wirenut · December 2011

I can't seem to find the answer to this question in the Xantrex XW manuals.
When you have 2 or 3 stacked XW inverters and they are all connected to a common generator, how do you determine what to set the AC2(gen) input amps at?
If the generator is a 12kw and therefore capable of 50 amps and it's connected to 2 stacked inverters do I set their AC2 amps to 50 and they will know to split it or do I have to tell each unit 25 amps so they don't both try to pull 50?

Thanks for any help you can give.

Cariboocoot · December 2011

Re: How to set Gen. braker size with stacked XWs

If the generator is capable of a maximum 50 Amps and both inverters try to pull 50 Amps at the same time the breaker will trip.

Divided the maximum current of the generator feed by the number of inverters its trying to supply. And yes if one draws only 10 Amps while the other draws 25 you will be "wasting" gen power.

BB. · December 2011

Re: How to set Gen. braker size with stacked XWs

Hmmm,

I was going to type up a complex method of looking at AC input current limits, and DC output current limits... But until you know if the generator load can be summed up across all 2-3 units, you do not know what to do.

You probably need to call Xantrex and ask them how to program the 2-3 XW's so they properly share one generator.

-Bill

Joe_B · December 2011

Re: How to set Gen. braker size with stacked XWs

In the install guide, there is a section (page 2-42) that describes a procedure for setting up a multi unit configuration. They also have a functional test for the charger.

For what its worth, I noticed that if I say set my max charge rate on my 4024 to 60%, it really does limit the charge current too 60% off AC1 however, AC2 draw seems only to depend on the AC2 breaker size. I dont run a multi inverter system though.

You dont say what version of firmware you are running but if current, then there may be issues with the gen support plus feature as well.

One other thought, If you have not changed the defaults on the inverter, I would think that your high battery voltage event would have caused a DC overvoltage fault.

RCinFLA · December 2011

Re: How to set Gen. braker size with stacked XWs

The AC breaker setting is ACin max + 20%, or 120% of the max limit you want. If you want to limit the inverter to sucking more then 20 amps off a generator then set AC2in breaker to 24 amps.

ACin limit is the definitive limit on its current. This current is split between ACout loads and charging. It overrides a max charger setting. If you limit AC2in to 20 amps and ACout load is 15 amps then charger will be automatically limited to 5 amps AC contribution. When ACout load drop to a low value, the full 20 amps will be available to charging.

There is some reaction time so surge ACout loads may momentarily exceed the ACin limit current setting. This may cause the inverter to disconnect from generator if generator voltage or frequency dips out of trackable spec for XW.

If you have load shaving on and AC2in limited to 20 amps and draw 30 amps of ACout loads, the inverter will pull from the batteries to make up the 10 amp shortfall.

wirenut · December 2011

Re: How to set Gen. braker size with stacked XWs

RC,
Thanks for that detailed response, it sounds like you've studied this quite a bit. My original question still remains unanswered. If I have 2 or 3 XW inverters stacked, are they smart enough to communicate and know how much the other(s) are drawing thru the AC2 gen input and limit the total draw of all of them to the setting? Or, do I need to divide my gen.'s max amp output by the number of stacked XWs and program that number as the generator breaker?
My generator is capable of 50A total. Do I tell a stacked set of 2 inverters that the AC breaker is a 50 or do I tell each unit that it is a 25?

Thanks,

Solar Guppy · December 2011

Re: How to set Gen. braker size with stacked XWs

wirenut wrote: »

If I have 2 or 3 XW inverters stacked, are they smart enough to communicate and know how much the other(s) are drawing thru the AC2 gen input and limit the total draw of all of them to the setting?
Thanks,

No, and its not a Xantrex issue but a UL concern, you can't have the inverters playing with setting on there own as the communications between the inverters isn't fault tolerant.

The 3 XW isn't a concern as two inverters can use everything your generator is capable of providing. For the 2 XW's split the value available in half for the maximum charge amps

RCinFLA · December 2011

Re: How to set Gen. braker size with stacked XWs

wirenut wrote: »

RC,
My generator is capable of 50A total. Do I tell a stacked set of 2 inverters that the AC breaker is a 50 or do I tell each unit that it is a 25?

Thanks,

AC2in breaker setting to 120% of 25 amps = 30 amps.

Then make sure your charging current setting is high enough to consume the 25 amps AC input. For XW6048, that would be input of 25 amps x 240 vac = 6000 watts. 6000 watts x 0.92 efficiency = 5520 watts to batteries. 5500 watts / 54 volts avg battery voltage = 101 amps DC into batteries. This is the maximum for an XW6048 anyway.

The second XW6048 will do the same so make sure your batteries can take 200 amps of charging current. That would be at least a 1000+ AH battery array.

If you want less charging current but max draw for AC loads, leave breaker setting to 30 amps and reduce charging current setting. If XW releases generator on ACout surge loads then reduce the 30 amp breaker setting a bit.

I would not run a 12kW generator with more then about 10kW continuous loads. Charging is pretty continuous load.

wirenut · December 2011

Re: How to set Gen. braker size with stacked XWs

Thanks for the help guys. I'll divide up the amperage and set accordingly. I'll probably base the calculation on a value of 45 instead of 50 so I don't load the generator to the max. The battery bank should handle the charge fine. It is 24 2v SunXtender PVX-915OTs in series.

How to set Gen. braker size with stacked XWs

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