New Xantrex SW4024 ordered, need advice-

rickeolis · February 2007

Hi everyone,
I've decided to go off-grid because my local power company nor state offer good enough incentives to do net-metering, so I've purchased about 27 Trojan T-105 batteries, and just ordered a new Xantrex SW4024 for my project.
I already have a small system running using a Morningstar 16 amp charge controller and about 250 watts of panels.
I plan on staying on the utility until further down the road when I have enough panels to meet my needs, so I want to set it up to where the SW4024 supplies as much as it can until the juice is gone, and then automatically switches back to grid power until the batteries are back up again. The idea is to have the built in charger pump power back into the batteries at night and be ready again to start off the morning in solar mode. As I add panels, I'm hoping the need for the grid supply will decrease over the years.
One question right off is whether to place a amp-meter inline with my panels before the SW4024 to monitor the watts being created at any given time, or will this cause any issues (ie. small amount of resistance, or the 30 amp meter will not handle larger loads down the road, etc.), is a shunt a better idea?
Also, because I want to house to run off of the SW4024, and just have the grid run the battery charger, is there suggestions that some of you have run into for such a project?
Thanks much!

-Rick Rutledge-

BB. · February 2007

Re: New Xantrex SW4024 ordered, need advise-

For measuring current a shunt (with fuses in the sense leads near the shunt) has the advantage that you can remote mount the meter almost anywhere without having to extend/route large cables. You can also look for a DC current probe--but those require a separate power source to power the electronics.

Also, for your next battery bank, you may want to look into AGM batteries as they are somewhat more efficient at storing power (roughly 90% efficient vs 80% for flooded cell).

You might also look into Time Of Use (TOU) metering with you power company and use your batteries to time-shift your loads. For my utility, there is almost a 3-1 difference between peak and off-peak pricing (at least if you stay in the base-line tiers). A few utilities also offer discounts if you can automatically shed loads (like an AC, electric hot water) during critical power periods. In the long term, it might make sense to keep the utility at $6 per month minimum charge as your standby generator (keep a small generator handy for emergencies).

-Bill

rickeolis · February 2007

Re: New Xantrex SW4024 ordered, need advise-

Thanks Bill,
I should have mentioned that I am on the 'Time of Use' option with my utility, it does help a lot. This will be another plus in charging the batteries at night.
I have not seen how a shunt is put into a system, I'll search Google.
My decision for the Trojans was based on several suggestions in this and a couple other web forums, but also that they have a longer expected life cycle that other styles. (Unless that's proved otherwise.) The battery bank and inverter will be setup in a small shop just near the house.
I appreciate the input!

-Rick-

crewzer · February 2007

Re: New Xantrex SW4024 ordered, need advise-

Rick,

Check this Home Power magazine file for how and where to connect the shunt:

http://www.homepower.com/files/houseskiz.pdf

"27" batteries doesn't make a lot of sense to me. When building a 24 V system from 6 V batteries, you need four batteries for each series string. So, 24 batteries (six parallel strings of four batteries in series per string) or 28 batteries would theoretically make sense.

T-105 batteries are good batteries. However, while building a battery bank from 24 each 6 V batteries may well work, it invites many opportunities for neglect and failure. For example, 24 each 6 V batteries means that there will be 72 cells that will require individual inspection and watering. That's a lot of work, and accidents involving battery acid are not fun. Also, there will be ~28 battery-to-battery interconnect cables that will require periodic inspection, torquing and test.

If you haven't already actually bought the batteries, I'd suggest you at least consider switching to L16's. At ~400 Ah each, you'll only need ~ 1/2 as many batteries, and, because their footprint is about the same as the T-105's, they take up much less floor space.

HTH,
Jim / crewzer

BB. · February 2007

Re: New Xantrex SW4024 ordered, need advise-

A shunt is nothing more than a large precision resistor placed in series with the "load"... Basically, just cut the wire and place one wire on each of the Shunt's main terminals (there are two main terminals).

Then, you attach your pair of sense leads from the two small terminals on the shunt to your "meter". the meter simple reads Vmeter=Ishunt*Rofshunt.

A couple of suggestions, at the sense terminal of the shunt place a small value fuse in each lead of the sense wire to prevent fires if the sense leads are shorted (remember you have 18-26 awg wire connected to your 4 'ought cables--lots of current available.

If you are using an electronic meter/A to D, and are sending the sense leads over a foot or two--twist the wires (2-6 times per foot). Or use shielded wire to prevent electrical interference with the very low voltage shunt leads.

Lastly, a good suggestion I read elsewhere here--place the shunt in the negative lead to ground (or ground bus)--if you are monitoring a battery bank... Typically, this is the easiest place to monitor all of the current into and out of your battery bank.

Here are some pictures of shunts and you can see the two main and two sense terminals.

http://store.solar-electric.com/metersmonitors.html

Since shunts only output a maximum of 0.050 volts or so at full current--make sure that all of your sense lead connections are clean and tight. Any poor connections or mixing of wire types (like copper and aluminum connections) will quickly lead to inaccuracies.

-Bill

PS, for others here, the details of TOU vary with utilities and rate planes. Also, time of year will affect your charges (warm 1/2 of the year, my rates are around $0.28 and $0.09 per kWhr--Cold months is around $0.12 and $0.09 per kWhr--base rate not TOU for my area is ~$0.115 per kWhr).

rickeolis · February 2007

Re: New Xantrex SW4024 ordered, need advice-

Thanks guys:
Crewser: That illustration is nearly perfect for my setup! Thanks. I see I need to purchase these lightning arrestors now. I have 27 Trojans now, and want to go to 32 all together based on a need calculator on Kyocera's website. The L-16 were well more than twice the price each than the T-105's, making them not very cost effective. I have plenty of room for them too. I know maintenance will be ongoing, but so will the entire project...
Bill: Thanks for the shunt explanation. How much wattage draw will the shunt be throughout the day? Any?

I have an Onan 6.5KW generator in my RV that will serve as a backup, but only manually started, which is fine. I'm also considering a wind generator to add to the project.
It seems that my three largest loads now are these: A 14.5 CF fridge\freezer that is about 7 years old; A new GE dishwasher; and a large Sony CRT style home theatre. I have yet to find out if this system will work them and the rest of the house too. I am replacing the electric water heater with a Bosch tank-less LP style, and the electric dryer to an LP model as well. I'm out in the country, so no natural gas.

-Rick-

rickeolis · February 2007

Re: New Xantrex SW4024 ordered, need advice-

Bill, based on the illustration Crewser showed me, I see that there is no load used by the shunt, thanks.

BB. · February 2007

Re: New Xantrex SW4024 ordered, need advice-

Rick,

Technically, there is a load from using a shunt... For example if you have a 50 mV shunt (maximum voltage) at 400 amps (maximum current)... Then

P= I*V = 20 watts...

For a 12 volt system, that would be:

efficiency = (12v * 400 amps - 20 watts) / (12v*400a) = 99.58% efficiency or 0.42% loss (at max current).

A smaller shunt (say 100 mV at 100 amps at 12 volts) would lose:

Loss = (0.1v*100a) / (12v*100amp) = 10watts/1,200watts = 0.83% loss

So, while a properly sized shunt does not consume much power relative to the system power levels--you must be able to (for a large shunt) be able to safely dissipate 20 watts...

However, there is no standby load from a shunt--which is a good thing with battery systems (there may be a significant standby load if you are using electronic meters/etc.--you need to watch that these phantom loads don't discharge your batteries--like during winter when the panels are covered with snow).

-Bill

crewzer · February 2007

Re: New Xantrex SW4024 ordered, need advice-

The L-16 were well more than twice the price each than the T-105's, making them not very cost effective.

Rick,

I respectfully disagree. Trojan’s new warranty for their L16 batteries used in solar applications is seven years. I believe the T-105’s warranty is for three years.

http://www.trojan-battery.com/

Assuming L16H batteries cost $3X each and last for seven years, you’ll need $48X just for the batteries to build a bank rated at 24 V x 420 Ah x 4 = 40 kWh, or $0.17 / kWh / yr for battery cost.

Assuming T-105 batteries cost $X each, you’ll need $28X just for the batteries to build a bank rated at 24 V x 225 Ah x 7 = 37.8 kWh. Assuming a three year life expectancy, you’ll spend $56X for batteries over six years, or $0.25X / kWh / yr for battery cost.

This is a simple model, but it indicates the T105’s will cost 47% more per year than the L-16’s. Accordingly, I’d suggest it’s the T-105’s that are not very cost effective.

Another problem is your plan to add more batteries (set #2) to your current crop (set #1), and then to add even more batteries (set #3) later. This is a bad idea, as the older/weaker batteries will essentially determine the battery bank’s overall performance.

Have you already bought the 4024? An alternative is the Outback VFX3524 at $1,695, although you’d need to buy / borrow a Mate in order to customize it’s programming / settings.

See: http://store.solar-electric.com/vfx3524.html

Best of luck,
Jim / crewzer

rickeolis · February 2007

Re: New Xantrex SW4024 ordered, need advice-

Hi again guys,
Jim, this is why I use these boards- you just pointed out something I didn't know: I've seen graphs from vendor websites showing the Rolls and Surrette batteries lasting 7-10 years, but they also claimed only 3-4 years on the Trojans of any type. I was unaware that the L-16's were supposed to last as long as 7 years. this would make them better for me, thanks. :roll: From this point on I will probably get those.
The SW4024 I have coming was found on E-Bay, and I got it for nearly half of the new price. It was used for show display purposes and only has a few days of actual use. It still has 80+% of the factory warranty on it. the Outback VFX3524 would have been the one to get from a local vendor at that price you quoted until I found this deal. 3000 watts for my home would not give me enough, but between 3500 and 5000 was what I was looking for. This SW model should do it well.
Bill, with your help and URL's sent, I now have a lot more knowledge of what meters and shunts can do for me, thanks.
I feel that right now the next purchase I make will be an outside mounted battery disconnect and breaker for the 24 volt side. Then, these lightning arresters. Then eventually a boatload more solar panels...

rickeolis · February 2007

Re: New Xantrex SW4024 ordered, need advice-

Jim
I'm seeing the Xantrex 250 amp breaker\disconnect box, and the the Outback too on the NAW&S website.
Don't I need about 500 amps with my SW4024 setup? (Max=8000 watts or 667 AMP)

-Rick-

crewzer · February 2007

Re: New Xantrex SW4024 ordered, need advice-

Rick,

I'm glad the information Bill and I provided earlier was useful to you.

The 4024 DC breaker's continuous current rating should be based on full AC output at low battery voltage plus the 125% NEC safety margin. Page 131 of the SW 4024 manual indicates the "NEC Amps" to be 267 A. I don't know what the next higher rated breaker value would be. I suspect that the 250 A DC breaker is the one typically used for the 4024. These big breakers don't trip the instant their rating is exceeded, so they can pass a short duration surge such as you've described.

Ref: http://www.xantrex.com/web/id/602/docserve.asp

HTH,
Jim / crewzer

crewzer · February 2007

Re: New Xantrex SW4024 ordered, need advice-

Update:

Carlingswitch makes a 300 ADC F-Series circuit breaker -- the next size up from 267 A -- but it appears to be two-pole minimum, which would make it pretty large, and I'd also expect it to also be expensive and hard to find.

See: http://www.carlingtech.com/pdf/f_series_circuit_breakers.pdf

Regards,
Jim / crewzer

rickeolis · February 2007

Re: New Xantrex SW4024 ordered, need advice-

Thanks for the info Jim-

James · February 2007

Re: New Xantrex SW4024 ordered, need advice-

ebay has several sellers listing 250 amp dc breakers right now. good prices, but you'll still need a cabinet. i believe outback has a nice little dc breaker discount cabinet that will accept them.

search DC breaker or dc circuit breaker...you willl find them.

crewzer · February 2007

Re: New Xantrex SW4024 ordered, need advice-

I urge caution in buying your breakers. First of all, ignore all AC specs and focus on DC specs alone. Second, there are at least three important DC specs for the battery-to-inverter breaker: Voltage, service Amps, and AIR, or Amps Interrupt Rating. The typical inverter breaker voltage is 125 VDC, the service Amps in your case should be at least 250 A, and the bigger the AIR, the better. For example, the single-pole Carlingswitch F-Series breakers used by Midnite Solar in their breaker boxes is rated at 50 kVA AIR -- yes, 50,000 Amps. This is probably enough to endure a battery terminal short through several feet of 4/0 cable and remain operable.

Midnite's list price for their 250 ADC breaker (MNEDC250) is $109. Under-spec'd cheap breakers will be false economy. Except for fairly small battery banks, I'd avoid a battery breaker with an AIR (or AIC) spec of just 10 kVA. 20 kVA-25 kVA should be the minimum, and 50 kVA is preferred.

Finally, note that some DC breakers are now polarized. This is purposely done to manage the arc flame in the event of a short. Although current can flow in either direction to/from a battery, the breaker's (+) terminal should be connected to the battery's (+) terminal.

HTH,
Jim / crewzer

James · February 2007

Re: New Xantrex SW4024 ordered, need advice-

crewser makes an excellent point....watch the ratings.

In some of the ebay listing no ratings other than amps is noted. I found looking closely at the photos, and in some listings, actually copying, pasting and enlarging the photos in order to read the case labels answers my questions better than an email to the seller.

There are several listings running right now for 250 amp breakers that do have the required AIR ratings. Also watch the terminals Some are lug type, some are bare wire set screw block type. Make sure you verify this with the seller as some use generic "file photos" which do not accurately depict the unit they are selling.

In addition, watch that the breakers you are considering are actually over-current breakers, not just a rated disconnect switch. I have found some listing out there that are just that,...a switch.
You can usually tell by thier part # and under the trip amps rating....It will show "SW"

A couple of current listing are actually surplus stock from Xantrex I believe.
I had grabbed some because of their excellent price and that they were new in box.

A watchfull eye may yield great savings

rickeolis · February 2007

Re: New Xantrex SW4024 ordered, need advice-

Hey, that sounds good. I normally check E-Bay for solar related deals daily...
Thanks-

rickeolis · February 2007

Re: New Xantrex SW4024 ordered, need advice-

http://store.solar-electric.com/dc250.html

Here is the Xantrex model at Northern Arizona Wind & Sun.
They don't state whether I'll need to install a breaker too, but probably so at the price.
I'm also wanting an outdoor style...
Thanks guys-

crewzer · February 2007

Re: New Xantrex SW4024 ordered, need advice-

The link says "Xantrex 250 Amp DC breaker w/enclosure", so it looks like you'll be getting both. The enclosure is rated for indoor use.

HTH,
Jim / crewzer

rickeolis · April 2007

Re: New Xantrex SW4024 ordered, need advice-

Hi again everyone,
Well, I've installed my new X-4024SW and I now have 12 T-105 batteries (again, I'll be buying L-16's from now on), and have one each lightning arrestor, one for the AC side and one for the DC panels side. I was shocked at the price of cables. I hadn't factored in that cost, but I have them now. Some time this year I will double the number of batteries for it too.
I took all of my roof mounted solar panels and rewired them to be in a series of pairs to make 24 volts per pair, then go to common positive and negative bus-bars. This then enters my garage and goes to the charge controller. From there the power splits between my battery bank and the inverter. I have one fancy solar energy based 24-volt gauge that I read daily, and the Xantrex shows me amperage use.
At this time, I'm only producing less than 200 watts from the few panels I have, but buffering that by feeding the Xantrex's battery charger from my grid power when it senses less than 24 volts from the batteries. This year's tax check went towards buying all of this hardware for the project.
Next year the idea is to buy as many more solar panels as possible and to continue to as long as I can afford them down the road.
Because of the low wattage collection I'm getting now, I only have the solar project running my home's lights at night and a computer too, via a dedicated circuit I have labeled just to provide the 'free' power. I'm trying not to invoke the grid power to charge the system, but just keep the needs down based on the power generated. The rest of the house is on the grid.
I like it so far, and I'm making sure not to tax the battery bank to keep them lasting longer, but I have tested the output of the system a couple of times by running high amperage things off of it to see how it holds up. I once ran a whole set of lights, a handheld hair dryer, and a power drill all at once for a few minutes, and it didn't skip a beat.
At this point, I'm really looking into an 800 watt wind generator for the system too. I like the idea af making up power regardless of the time of day. It turns out we get a good amount of wind, or at least have in the last few weeks since thinking about this!

-Rick-

crewzer · April 2007

Re: New Xantrex SW4024 ordered, need advice-

Rick,

I’m glad to learn that you’re up and running! I’m also corn-fuzed about your actual system configuration:

Current setup: 1500w modified sine inverter\7 panels for around 500watts\bank of T-105 batteries\ASC controller
More to come...

(Feb. 12) I've purchased about 27 Trojan T-105 batteries, and just ordered a new Xantrex SW4024 for my project….I already have a small system running using a Morningstar 16 amp charge controller and about 250 watts of panels.

(Apr. 4) Well, I've installed my new X-4024SW and I now have 12 T-105 batteries… At this time, I'm only producing less than 200 watts from the few panels I have...

Can you tell us a bit more about your system’s actual configuration (PV array size, controller, batteries, inverter); its location (i.e., city and state); the quantity, make(s) and model(s) of your PV modules; the physical installation (orientation, tilt angles); and any environmental considerations (i.e., shading from nearby buildings, trees, etc.).

We need to understand your system configuration and location so that we can help you with your planned upgrades:

(Apr. 4) … Some time this year I will double the number of batteries for it too. Next year the idea is to buy as many more solar panels as possible and to continue to as long as I can afford them down the road.

Regards,
Jim / crewzer

rickeolis · April 2007

Re: New Xantrex SW4024 ordered, need advice-

Thanks Jim, I see what you mean. I need to update my signature quote. That was the old system before I bought all this new stuff!

This is what I now have: One Xantrex 4024SW; fourteen brand new Trojan T-105 batteries; twelve 15 watt H.F. solar panels; lots of 2\0 cables between the batteries, and a set of voltage and amperage gauges; as well as the two lightning arrestors.
I live near Albuquerque, New Mexico, and the charts show I would optimally get about 5.5 hours of usable sun coverage, though most days we actually get more. The panels are mounted flat on my garage, and I have read them on a sunny day right at noon showing close to rated capacity (last September.) No shading issues, but it would be nice to have them mounted at 30 degrees towards the south upright.

The previously used Morningstar controller is only good for 12 volts, so I am currently not using a charge controller. I know this sounds bad on paper, but I monitor the voltage daily, and the panels I have are barely enough to recharge the amount I use from the lights on the previous nights. I'm nowhere close to exceeding even 26 volts at any time. I am looking at which controller to buy.
Also, the battery deal I had made a few months back went south, so I actually only have these 14 batteries, but they are new and wired correctly.

rplarry · April 2007

Re: New Xantrex SW4024 ordered, need advice-

Rick
You might want to consider hooking your x4024 to the grid and giving your batteries a good charge a couple times a week. If the batteries are undercharged for too long a time they will sulfate and go bad on prematurly. The last time I checked the price of the Trojan t-105 in San Diego it was $99 plus tax. I'd hate to see that large of an investment go to waste.
Just something for you to think about.
Larry
Check this website to see what Trojan recommends for chargeing their batteries: http://www.trojanbattery.com/Tech-Support/BatteryMaintenance.aspx

rickeolis · April 2007

Re: New Xantrex SW4024 ordered, need advice-

Hi Larry,
I appreciate that, but did mention this in my previous post: "At this time, I'm only producing less than 200 watts from the few panels I have, but buffering that by feeding the Xantrex's battery charger from my grid power when it senses less than 24 volts from the batteries."
I'm with you, I don't want to degrade these expensive batteries prematurely!
Until I get more solar panels, the system is a bit of overkill, but they will come in time... Also, I'll stop buying amorphous panels from now on too.

crewzer · April 2007

Re: New Xantrex SW4024 ordered, need advice-

Rick,

OK… The 4024 inverter established a key baseline for you system, and that’s the 24 V operating voltage. The ~200 W of HF (Homefare?) PV modules will deliver ~6 A to your 675 Ah battery bank (12 Trojan T-105’s wired for 24 V), or about 1% of the banks Ah capacity, so they’ll likely not cause any overcharge problems, especially if the inverter is always on…

In terms of growth, “big” 60 A controllers like the Morningstar Tristar 60 and the OutBack MX60 are rated to handle 60 A of output current. That corresponds to a PV array rated for ~1,600 W STC. And, a 1600 W array is a good match for a 24 V array rated at ~800 Ah.

So, if you’re planning on growing your system, one approach might be to:

1) Buy two more T-105’s, and, using the two “spares”, build a 24 V x 900 Ah battery bank from 16 batteries (4 x 4)
2) Buy a 60 AMP charge controller with a remote battery temperature sensor
3) Grow your PV array to ~1,600 W (STC)

The combination of the 4024 and the items listed above would integrate into a nicely balanced system. Considering your location, such an objective system should be able to run an Energy Star fridge (i.e., ~450 kWh/year), a home A/V system, and a few other loads year ’round.

Insolation data for ALB: http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/sum2/23050.txt
Real time insolation info for ALB: http://www.sandia.gov/pv/weather/Weather.htm

HTH,
Jim / crewzer

rickeolis · April 2007

Re: New Xantrex SW4024 ordered, need advice-

Thanks again Jim, that is about what I had in mind. I'm looking at a Xantrex 60 amp controller and two more batteries, then next year to buy solar panels like a crazy man!
I'm doing other things to help myself become more independent here too: As we speak, I'm talking with a plumber to install the Bosch Aquastar Tankless gas water heater that I just bought. This replaces my current 40-gallon electric model ($$$$$$\month); and I'm also changing out my electric dryer to a gas model too.
I have nothing but CF lights in the house now and have added more insulation to it recently as well.
I'm checking out those insolation charts you sent me, a guy can learn a lot from them, thanks.

-Rick-

crewzer · April 2007

Re: New Xantrex SW4024 ordered, need advice-

Rick,

The Xantrex C60 is a good controller as far as PWM controllers go. So is the Morningstar TriStar 60, but I'd recommend that you consider the OutBack MX60 instead. The MX60's MPPT feature will increase your array's energy production in the winter by converting "excess" PV voltage into additional charge current. Additionally, the MX60's DC-DC down conversion feature allows to use a high voltage array to charge a low voltage battery.

Combining both features, you could wire your array for 36 V to charge your 24 V battery bank. There would be sufficient voltage in the summer (when the array is hot and the output voltage suffers) to correctly charge and equalize your battery bank, and "extra" voltage in the winter would be converted to additional charge current.

8-)

HTH,
Jim / crewzer

rickeolis · June 2007

Re: New Xantrex SW4024 ordered, need advice-

New things added to my project!
I bought a new 800watt 24volt wind generator and added it to my solar project.
It took me about a week to buy up all the related parts I needed for it and to put it up and get it tied into the project, but it's all running and charging now!
I purchased about 25 feet of 2" galvanized steel pipe, 50 feet of stranded stainless tie down wire, several clamps, and straps to hold things in place, then began to put it altogether over two days.
Once I had it running, I put a 30 amp ammeter inline with it to see how much it was putting out. Of course there was plenty of wind in the last few weeks, but now barely enough to make it run once in a while, but I have seen it push nearly 5 amps through under a minor gust for a couple of minutes.
The windmill I bought has 6 carbon fiber blades, and the thing runs smooth when turning. Each blade is about 2 1\2 feet in length, so it's about 5 feet in diameter or so.
I keep waiting for some good winds so I can see what it can really do.

rickeolis · June 2007

Re: New Xantrex SW4024 ordered, need advice-

Oh, and additionally, I did find a Xantrex 250 amp breaker box finally.
It came with two breakers, but I'm only using one right now on the positve leg of the battery bank.

-Rick-

niel · June 2007

Re: New Xantrex SW4024 ordered, need advice-

so tell us what wind generator you bought and keep us posted as to its performance.

New Xantrex SW4024 ordered, need advice-

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