Use external charge controller rather than internal inverter charge controller?

[dlenox]

All,

I have a Xantrex XW-6048 inverter that I recently purchased, it will be used in a 48v environment, grid-tied, along with a battery bank.  It will not be put into service until spring time.

The inverter user manual states that the battery bank should be connected for proper operation.  From what I understand, in a wind turbine environment that the battery bank caps the turbine output voltage to their float voltage.

I understand that the inverter contains a battery charge controller, but I am thinking of adding an external charge controller and a load controller.  

By using an external charge controller I can effectively disconnect the batteries from the turbine output when they are fully charged.  In addition by using a load controller the batteries can be connected to the inverter when they are required to be drawn from.

My question is - is this a good idea?

I have contacted Xantrex and asked their opinion as well as if I void any warranty by doing this.

thanks,

Dan Lenox

[wooferhound]

Do not use the charge controller for Wind power unless it has Dump Load capabilities. Do not disconnect the Turbine from the batteries ever. Your Turbine will Overspeed and self destruct. For a Wind Turbine you will need a Dump Load controller to dissipate the extra power.

For Solar power you will need a charge controller.

[crashk6]

Heed Woof's advice on the turbine.. you will have a problem if it has no electrical load to keep it's speed under control. It needs to be loaded under most any normal circumstance.

Secondly on the load control,

Do NOT use a load control between the batteries and inverter. The inverter will only draw from them when needed anyway. On Xantrex equipment in that power range every necessary function for the inverter battery interface is all done in software.

You stated you contacted Xantrex to ask this, but did not state what advice they gave. I imagine it was something along the lines of "That application is not covered under warranty" and there would be a reason for that!

Thirdly, the inverter does not contain a charge control for any charging source per se, what it does have is a battery charger to charge from ether the utility grid or a backup generator.

This seems to be an extension of one of your earlier posts http://www.fieldlines.com/story/2007/12/16/155529/12

Where people gave you some information on charge controllers already.. re-read it.

If you still can not get a picture in your mind look for drawings of these types of systems.

www.homepower.com

Would be a good place to start for very GOOD system schematics that would give you a feel for the equipment your working with. Mind the schematics may not be your exact situation however you will start to see the similarities.

Short of that you could have a Xantrex engineer fax or email you their recommended connection practices in schematic form for your application.

You have gotten lots of explanation from folks here but a visual aid may be in order so have a look at HomePower. The subscription is worth it, in fact get some back issues. They come in print and digital.

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crashK6

[dlenox]

woof,

I should have mentioned that I do have a dump load controller connected to the system as well.  I certainly understand the need for this with a wind turbine.

crashk6,

I have only sent the support request today, Xantrex typically takes a week or two to respond.

I stand corrected, the XW inverter does have battery charging capabilities, and it is not a charge controller.

Xantrex does have an MPPT Solar Charge Controller that they recommend for use with solar applications on the XW systems, it is not necessary with wind turbine.

I think that I have a pretty good understanding now about the circuits and connections that are required, and know about a lot of the implications that go along with them (one can not know all).

Perhaps my question was mis-understood and will try to rephrase it:

Here is a quick proposed system diagram.  Grounds and neutrals on the AC and DC distribution are not shown, as well as auxillary power panel:

I have a grid-tied system, which incorporates a Xantrex XW inverter as well as a dump controller in the system.

Since a battery bank tied to the turbine output caps the voltage at the battery banks float voltage, it would seem ideal if a fully charged battery bank can be disconnected from the turbine output so that the voltage is not capped, and more power/efficiency could be extracted from the turbine output.

One could use 2 devices: both a charge controller and a load controller to selectively switch the battery bank in and out.  The charge controller is used when the battery bank needs to be charged, and the load controller is used to sense when the inverter wants to draw from the battery bank.

There is Always a dump controller connected to the turbine output, which can keep the turbine loaded in case the grid utility was down.

Wouldn't this scenario provide the maximum extraction of power from the wind turbine?

Dan

[DamonHD]

I'm no expert at all, but my feeling from an engineering point of view is that having the voltage capped at the battery float voltage is very useful for protecting loads downstream, as it significantly narrows the range they have to operate efficiently and safely in.

So maybe you could extract more energy, but maybe only by frying whatever you are wanting to power in practice.

Rgds

Damon

[crashk6]

"Since a battery bank tied to the turbine output caps the voltage at the battery banks float voltage, it would seem ideal if a fully charged battery bank can be disconnected from the turbine output so that the voltage is not capped, and more power/efficiency could be extracted from the turbine output.

One could use 2 devices: both a charge controller and a load controller to selectively switch the battery bank in and out.  The charge controller is used when the battery bank needs to be charged, and the load controller is used to sense when the inverter wants to draw from the battery bank.

There is Always a dump controller connected to the turbine output, which can keep the turbine loaded in case the grid utility was down.

Wouldn't this scenario provide the maximum extraction of power from the wind turbine?"

You are onto the same line of thinking that lead to inverters such as the "WindyBoy" they take advantage of the peak power output of the wind turbine (or try to) and pump that power into the utility grid.

You can NOT do that with the equipment you show in your diagram, it simply will not work in the way you are expecting and may damage the inverter in that configuration; Plus smoke one or more of your proposed controllers.

I have modified the diagram you show for proper operation using equipment you have specified.

If you have DC loads where you have the desire for a low voltage disconnect or a PV array I can revise it further to reflect that schematically.

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crashK6

[TomW]

Dan;

I am not familiar with that particular gear but, couldn't the inverter itself be configured to not drain the batteries too far? This would eliminate the load controller. My Outback can be programmed to switch to using grid for AC loads and charge from the grid at a specific low battery voltage setting.

I don't know but it sure seems like any quality inverter will protect its battery bank from low voltage via either using grid or shutting down?

I am certainly no expert but it just seems like that load controller is redundant. It would be on my setup at least.

No sense in buying more "stuff" than you need.

Good luck with it.

Cheers.

TomW

[dlenox]

Unfortunately, I double checked my inverters specs and confirmed my inverter will only accept 44 to 64 volts, I had looked at so many inverters initially that I should have double checked this. So for my system this question ended up being a moot point.

But as a general statement, I think that using an MPPT charge controller 'could' be used if one existed were versatile enough for wind turbine (rather than solar). Assuming that enough of a load were put on the wind turbine to keep it in check.

Another assumption is that there is always a diversion load connected to the turbine output so that at 'some' point it kicks in...

Dan

[dlenox]

your diagram is currently how I have my system configured.

Dan

[dlenox]

Tom,

yes you are correct, I can program in the battery charge/float configuration information into it and the inverter will not allow discharge below a specified point of the battery bank.

my original thoughts were simply on how to extract more available power by not tying the turbine output to the battery float voltage.  but as it turns out the voltage range of my inverter will not let me play this game.

to bad there is not a versatile MPPT charge controller for turbines.

dan

[windstuffnow]

  I don't think it has a charge controller in the sense it controls outside inputs to the battery bank.  It has a battery charger to keep the batteries charged when it's on the grid and an auto switch to transfer to the DC power if the grid goes down.  Any external battery charging such as a wind system or solar would require their own controller.  In the case of wind a diversion load controller which would allow the turbine to be continuously loaded even when the batteries are charged.  Solar controllers simply shut off the input.

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