Xantrex SW4048 Grid tie help

fiddlehead · April 2011

Just connected a SW 4048 to the grid. Followed the manual and put settings where they were recommended. There is 1600 watts of solar and we have a 225AH battery bank.

I installed a separate solar meter (type 12S)to the system so we could track what the inverter is putting onto the grid. The system works very well when the sun is out. The problem (I think) is when you shut off the solar input, the Sw seems to charge a little, then sell a little. Sell volts and float volts are the same. I tried lowering both, same result. I tried "time of day charging", same result except instead of the float LED being on all the time, it was blinking. According to the manual, this means it is not charging?

The version is 4.2.

This seems odd to me because all the Outbacks I have set up, do not act like this. The meter just stays stationary. This one moves forward just a little and back just a little. I have seen this on one other SW 4048 set up, but I did not have anything to do with it, I was just an observer.

Anyone have any experience with this?

RCinFLA · April 2011

Re: Xantrex SW4048 Grid tie help

You did not mention what charge controller you have.

The charge controller float and absorb levels should be set higher then the SW4048 float level.

The SW4048 will regulate the battery voltage. Any attempt by the charge controller to push current into batteries resulting in a battery voltage rise above the SW setting will be sucked off and pushed as AC power to load. It will allow it to be pushed to grid if sell is enabled.

Key point is SW4048 is the battery voltage regulator for charging.

If you are off grid then charge controller float level should be dropped to about 0.2 to 0.4 vdc above SW4048's float setting.

SW inverter will shut down if it is not allowed to push excess battery charge current to grid and load is not consuming the amount generated. In this situation the charge controller's set point will determine battery float level.

fiddlehead · April 2011

Re: Xantrex SW4048 Grid tie help

The charge controller is a MX 60. Everything works fine when I let the MX charge the batteries. Yes, the charge settings on the MX are set above the sell setpoint of the SW.

I'm more curious about what it is doing when the solar goes away. (see my previous thread).

BB. · April 2011

Re: Xantrex SW4048 Grid tie help

XWguy went through a bit of the programming details for the XW hybrid inverter in this thread:

Two Xantrex MPPT60's don't auto-track.

-Bill

RCinFLA · April 2011

Re: Xantrex SW4048 Grid tie help

fiddlehead wrote: »

I'm more curious about what it is doing when the solar goes away. (see my previous thread).

When charge controller does not produce enough current to maintain battery float voltage set on SW4048 the SW4048 will supply the charge current necessary from grid to maintain battery float voltage. If batteries are fully charged it should not be very much power. For 225 AH battery should be about 50-200 mA @ 54 vdc on batteries.

fiddlehead · April 2011

Re: Xantrex SW4048 Grid tie help

Thanks RC,

So it sounds like this is normal? I take it you have seen this before? Still seems funny to me. I would have thought that it would be "smoother" than what it is. Do you think this "cycling" will increase as the batteries age? The batteries are 5 years old or so.

RCinFLA · April 2011

Re: Xantrex SW4048 Grid tie help

With the limitation of the three stacked transformers, the resolution to changes in AC grid and battery voltage is a bit coarse. (about 15 v increments on AC instanteous voltage). There is a maximum of 27 combinations from the series connected secondaries of the three transformers to cover from lowest/highest battery voltage along with lowest/highest ACin voltage. Typically the number of discrete steps used is about 22 to 24 for nominal battery voltage and ACin voltage. This stepped sinewave output give some noticable buzz in ceiling fans.

This causes a little 'breathing' of the charge rate current and voltage on the batteries. The processor within the SW4048 keeps track of the slight overages and underages and averages them out.

The variance is a bit dependent on the maximum ACin and ChgIn current setting. The 'breathing' current variations seems to be greater the higher the Max Chgr AC current setting.

As to battery longevity, I have not seen any effect on them. The 'breathing' may actually be good for the batteries.

fiddlehead · April 2011

Re: Xantrex SW4048 Grid tie help

Sounds like you have a lot of experience with how this unit operates. I may try changing the max charge current to see what it does, or I may just leave it alone.
Thanks!

System2 · January 2012

Re: Xantrex SW4048 Grid tie help

Sorry to hijack the thread but i have a revelant question concerning this controller with a battery backup system and tied to grid. About a year ago i noticed the power bill was going up so checked batteries over a period of a few weeks and realized that 6 of the 8 are kaput and wont hold a charge. I have since learned that I dont necessarily have to use the batteries to still sell back to the grid. I plan on getting a generac backup generator instead so i dont want or need the batteries. I was bending the ear of a solar contractor at a local home show and he thought it may be possible to either replace batteries with simple car batteries as long as the inverter still sees 48volts or get rid of them and use some kind of ac powered transformer to fool it into seeing the 48volts. I have no idea how to do this or what settings to put the inverter at, etc. etc.
this is my setup:
8 pvcs on roof i think they are 90watts each?
xantrex sw4048
xantrex power center pc250 with a tristar ts-60 solar controller
xantrex grid tie interface
8 deep cell batteries

I looked into replacing the batteries and thats going to cost upwards of 3k+ and if they only last about 8 years Id need a whole bunch more pvc's to make it cost effective. When we first bought the house I was getting $30 to $40 back from the power company. I really dont know much about solar power and even less after reading the xantrex manual lol. Any ideas would be great.

Thanks,
Nathan

BB. · January 2012

Re: Xantrex SW4048 Grid tie help

My two cents... You will not be able to "trick" the Xantrex hybrid system into GT mode without a battery bank. The batteries should be roughly 400 AH @ 48 volts minimum. You noticed that the Xantex output fell with a dieing battery bank.

You could use Forklift batteries and they can last 20 years or more--but are slightly less efficient and need lots more distilled water.

Otherwise, a generator for backup, and use pure grid tied setup (solar array + Grid Tied Inverter and no battery bank).

It is a choice. Me, I did the generator + pure Grid Tied solar and inverter (no batteries). For the little amount I have every lost power in 50 years, a battery backed whole home system just was not cost effective for me. Plus, our stuff hits the fan will probably be a huge earthquake. Old homes get knocked off foundations or burned down from neighbor homes. Power never went down for most of us in the last largish quake.

-Bill

System2 · January 2012

Re: Xantrex SW4048 Grid tie help

whats a decent grid tie inverter now? Ya when this system was installed by the guy who built it i think this was possibly the best setup available at the time. He could have bought a generator forless than the batteries. Low costs/keeping and modifying current system would be ideal.

BB. · January 2012

Re: Xantrex SW4048 Grid tie help

Realistically, 720 watts of solar panels for a GT system is probably not even worth the effort/costs to get the permits and inspections for Grid tied.

I would suggest a 3kW system is about minimum, but may people do 5-10kW systems today... Especially with full GT systems costing less than $5/watt installed for many region in the country ($50,000 for a 10 kW GT system).

And even much less if you do a lease/option to purchase (maybe $1 per watt or less--Installer keeps all of the tax credits/breaks/deductions and play funny math with the IRS).

Where do you plan to install the system (nearest large city) and how much power do you use per month (by season if A/C and/or heating is a major user).

And, lastly, does your utility support some sort of net metering plan (many smaller utilities do not have financially viable or even allow GT systems).

Moving around to first thing you should do--Review your power usage for conservation. Almost always (extreme) conservation is a better return on your money than installing a solar power system.

-Bill

mike95490 · January 2012

Re: Xantrex SW4048 Grid tie help

The XW6048 inverters have battery/ grid tie capability, with the ability to sell back to grid, and only leaving the batteries on float, I believe. I'm offgrid, so have never researched that configuration.

System2 · January 2012

Re: Xantrex SW4048 Grid tie help

Like i said I already have all this installed at my house with a second net metering can installed which stopped working because the batteries were dead dying so the inverter was spending power to keep them charge thus making my power bill go up. The batteries are dead and i dont want to spend 3k for new ones nor deal with the maintenance. Im not sure of the wattage but maybe its more if i was getting about $40 month back from power company when it was working? Maybe they are 110watt? Anyways, Mike, thats one option with the float that i think should have been done in the first place by previous owner to save the batteries as well as he should have put more pvc's on roof to make it more viable which i intend to do later. I think i may just get some deep cell marine gel batteries and install them, set the float high and see what happens. I probably dont need a high amphour since i dont intend to use them as a backup correct? I am just trying to find a less expensive way to get this to work without having batteries.

mikeo · January 2012

Re: Xantrex SW4048 Grid tie help

i dont want to spend 3k for new ones

You can get generic L-16 batteries for around 250 each, so that's around 2K and should last around 7 years. Or you can get T105 equivalent batteries at places like Sam's club for around 80 each, or $640 dollars and they will probably last around 5 years. Another option is a reconditioned fork lift battery which you can find for around 12 to 15 hundred dollars and will probably last 15 years or more.

BB. · January 2012

Re: Xantrex SW4048 Grid tie help

Also, when "electronics" get around 10 years old or older--They generally begin to fail and need to be replaced. Also, with 10+ year old hardware, it can be very difficult to find anyone to repair them and some parts are almost impossible to find.

I believe the SW line is no longer repaired by Xantrex, and few others out there repair them too.

So, in addition to the battery bank, you really need to think about the SW itself and what you would do if it failed in the near future too. Off grid power is expensive to install and maintain.

-Bill

Xantrex SW4048 Grid tie help

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