Learning and rethinking my cabin power system

16 Posts
Aug 6, 2008 11:45 am
Learning and rethinking my cabin power system

I’ve been learning a lot on the forums.  I’ve been asking questions regarding a cabin with a 2000W inverter system and the maximum current I can pull from a set of golf cart batteries. (See Lead Acid Max Discharge thread) I wanted to be able to run a couple of small kitchen appliances, along with CFL lighting.  At this point the appliances were a 1000W microwave and 800W toaster. 

I bought a remanufactured Xantrex Prosine 2000W Inverter/Charger.  I liked it because it has a built in charger, pure sine output, and a sophisticated remote display with a lot of monitoring functions and settings.  However, I underestimated the cost, wiring size and battery bank to provide this inverter with 200 to 400 AMPS of 12VDC.  1500+ Watt loads would be short term, but still the system needs to be sized to handle what the inverter can pull.

When looking at my other AC loads, they are 165W of CFL (Assuming all the lights are on) and maybe a small TV or a Fan.  I’m now rethinking my approach and considering a smaller inverter with the bigger loads run by the generator if needed.  The generator would also charge the batteries whenever it’s running.

With taking the big loads out of the equation, I now estimate 450 watt hours per day.  At 20% DOD, my battery capacity should be 222 A/H which can be met by a set of 6 Volt GC2(T-105) in series.

I’m looking for feedback on this new design and suggestions for the equipment. (My initial selections are in parens)

Inverter, pure sine.  (300W MorningStar SureSine)

Battery Monitor (MorningStar Remote Meter connected to Inverter)

Charger, Could I use a solar charge controller and feed it with a DC power supply or unregulated battery charger run by the generator?  When I add PV panels I could use a relay or diodes to allow either the generator DC power or PV panels to feed the controller? (Xantrex C35)

If I use a pair of T-105 225Ah Batteries in series, is 30A bulk charging current to much?

I know I need to fully charge the batteries on a regular basis, but do deep cycle batteries mind getting intermittent bulk charging as the generator is started and stopped for other uses? 

Thank you,

Jerry
 
351 Posts
Aug 6, 2008 04:30 pm
Re: Learning and rethinking my cabin power system

Jerry:
I am glad you took the warnings about battery sizing to heart. But I think you misunderstood the message.  There is nothing wrong with using the large inverter. You just have to be careful not to put too much load on it.

You can install the Prosine off of a breaker in your main electrical panel, using a 15-20 amp breaker. You tell the Prosine what size that breaker is.  You run the inverter output to another distribution panel, usually next to the existing main panel. You then transfer your lights and a couple of outlets to this panel.  This will involve some rewiring. How much, I can’t tell you.  In some cases it is easier to run a new system (wiring, lights, and outlets) off of the new panel, rather than to try to unscramble and reconnect “parts” of the old system.  It might look funny having 2 ceiling lights in the same room, but that would also give you generator driven lights, should the inverter/battery system fail for some reason.
I like to use different color outlets or label them, so that everyone has a visual reminder of which outlets are the inverter outlets.

By limiting the outlets (and lights) that are connected to this inverter distribution panel, you are limiting the load that you are placing on the inverter/batteries.  All other electric, remains in the main panel.  Your generator is connected to feed the main panel.

When you fire the generator to support the larger loads, the Prosine will limit the current that it draws for charging, so that it will not trip the breaker.  Because you tell it what size battery you have, it will limit the charging current to the battery to a safe level.

I would still give some thought to increasing the battery size. 4 T105’s would give you 2 days storage at 20% DOD.  Nice to have on that overcast weekend when the generator fails.  Also gives you better discharge/charge rates.  But whether the benefits of the larger battery, will offset the cost increase, is ultimately your decision to make.

Ken
 
16 Posts
Aug 6, 2008 05:50 pm
Re: Learning and rethinking my cabin power system

Ken,

Initially I wanted the convenience of the family being able to have lighting and use of small appliances "at their finger tips"  IE They need to conserve but power is there when they need it.  The 2 appliances I thought we would make intermittent use of were a microwave and toaster.  To run one of those at a time and have extra for lighting, I got the 2kw inverter.

After doing more homework, I began to realize the challenges and expenses of feeding a 2kw inverter with adequate DC power.

In looking at my loads, I had the 1000+ watts to run a appliance and 165 watts of lighting load.

It got me to thinking whether I could simplify and reduce costs on my system by giving up the ability to use 2 appliances or putting them on the generator.  I'm also thinking a 300W inverter is going to be more efficient at providing 100 watts of lighting load than a 2000W inverter.  I have questionable solar exposure and think I have a better chance of future PV panels keeping up with replacing lighting power than what the 2000W inverter will consume.  I also plan on eventually upgrading to a remote start genset so using kitchen appliances would be able to be used with the flick of a generator start switch.  A kitchen on a genset also allows the use of long running heating appliances like griddles, quesadilla makers, blow dryers etc.

I rushed into getting the 2000W inverter. But I have learned in the past weeks that off grid power systems require some thought to serve a family’s needs and still be cost effective. I want to step back and take a realistic look at what best fits my needs and budget.  The cabin is new, no wiring yet and the walls are wide open. 

My question at this point is do I spend the extra $500+ on upsized batteries & DC cabling/breakers or do I sell the Prosine and put in a system that can provide power for CFL lighting and other small loads.  I’m not in a rush to make that decision and I want to take the time to get the system right for our needs. 

This forum has been great for learning and I welcome more feedback.
« Last Edit: Aug 6, 2008 09:32 pm by Jerry Wenzel »
 
351 Posts
Aug 7, 2008 07:23 pm
Re: Learning and rethinking my cabin power system

Jerry:
What do you mean with “questionable solar exposure” ?? This is the first mention of that.
Also, what is the meaning of “future PV panels” ?  Is it just a general reference that the entire system is in the future, or are you thinking that the PV might be installed later than the batteries ??
Also, what size generator are you thinking about ?

Meanwhile, you can toss the idea of feeding a solar charger with a generator based dc source.

Ken
 
16 Posts
Aug 9, 2008 01:22 am
Re: Learning and rethinking my cabin power system

With my solar exposure, there are 2 trees south of the cabin that may block sun in the non-summer months.  I could cut them down if needed.

The reason I said future PV panels is because I was planning on not installing them until late fall or spring.  We are busy finishing the cabin and using a 3500W genset to run tools and it could charge the batteries at the same time.  However, if I want to leave the batteries at the cabin this winter, I think I should have the PVs up to keep a float charge on the batteries and prevent them from freezing.

I have a 3500 watt Kohler genset with manual start.  I also have access to a 1000 watt "cheapo" generator.  At this point I'm trying to decide if I should size my batteries and inverter to handle a 1000W kitchen appliance load and a 200W lighting/small TV/fan load or nix the ability to run kitchen appliances off the inverter and put in a 300W inverter.

If I do just the lights, I will likely put in a remote start genset for other high power, low use kitchen loads.  If I do that, I could possibly depend on the genset for most of my battery charging and use a PV to do the finish charging.

In regards to using a charge controller (cc) for charging from a genset powered DC supply.  It looks like some ccs can take DC from a variety of sources.  The Xantrex C series appeared to be able to do this.  I have a 24VDC 25A power supply I was thinking of putting between a genset and a cc. 

Could you let me know what problems you see with that approach?  I know its more pieces.

Also, do you know of AC multi-stage battery chargers that allow you to limit the max charge current so as to not exceed 10% of the ah rating of the batteries?

Thank you for you patience.
 
Aug 9, 2008 02:40 pm
Re: Learning and rethinking my cabin power system

If I may interject?
Did you know that the first electric lighting used in the White House was in 1891, during the Harrison administration? We all marvel at the Pyramids of ancient Egypt. More recently, at how this American nation gained its independence from Great Britain. All without utilizing the electricity we take for granted today.
Living "on grid," I think that we all would get accustom to using electricity how and when we feel like it, with no concerns as to, how much we use at one time. Living "off grid" can be like this, but at a great financial cost. In some ways I feel fortunate that I was able to live "off grid" with no electricity, what so ever, for a period of 20 years.
The very first item was electric lighting with 12 vdc 50 watt incandescent bulbs. Each evening when I got home, I would plug up the house to a cord hanging from the grill of my truck that was wired to its cranking battery. It took a while, about half year, but I eventually got a feel for how much and for how long I could "burn" lights and not have to push start my truck in the morning. This was in 1996 I think. Prior to that, I was reading the Mother Earth News by kerosene lamps, all the way back to 1975. I graduated high school in 1981. Prior to 1975, I was living the same "rubber stamp" life that millions of other kids my age where living. The change, for me, was like I had fallen off the edge of the Earth, and not just because of the lack of electricity.

Once again, fortune must have been smiling at me because the area I moved to, was then, a rural farming area and there was quite a few elderly people there that had spent their early childhood without electricity. I begged them to tell�  me stories of how they grew up with out (before) electricity. For them, it was simple. They didn't know any other way.
 There is an old house at the end of my path, its abandoned now, but it still has the remnants of the original 30 amp 120 vac electric utilities service clinging onto it. A peek inside revealed 1 receptacle, and 1 light in each room. A flue pipe in the kitchen and a pitcher pump at the back door. The oughthouse had long since fallen back into the Earth where now is a large growth of Honeysuckle vines. The man that built this house as a young adult was one of those "kids" that I begged a story of his childhood from. He passed away about 18 years ago, at the age of 98. May he rest in peace.
This all brings me to a fact that a lot of people are not aware of. Electricity, as we know it today, is only about 100 years old. For well over 7,000 years there was no electricity for mankind to utilize. We people today are a living testament, to the fact that, mankind does not need the electricity we take for granted today, in order live out our time on the planet Earth. We merely want it.
So, I guess the advice I am trying to convey is re-evaluate your wants and needs where electricity is concerned, and you might find out, you could live with a lot less electricity than you think. Best wishes to you.
http://www.kountrylife.com/content/mem18.htm
« Last Edit: Aug 9, 2008 02:48 pm by Thomas Allen Schmidt »
 
Aug 9, 2008 03:01 pm
Re: Learning and rethinking my cabin power system

If, by chance, you havent laughed yourself silly at my notions, and are considering them, do a search, type in < life before electricity > and you can find a lot of pros and cons and just plain old enertaining stories. Such as,
http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2005/06/19/RVG18D8F3E1.DTL&type=books
 
351 Posts
Aug 9, 2008 08:15 pm
Re: Learning and rethinking my cabin power system

Jerry:

A single Xantrex C series controller is designed to function as a charge controller with PV Panels.  When you connect it to a wind or hydro generator, you set it to function as a diversion controller.  Attempting to use it as a charge controller from some other power supply usually will result in damaging one or more of the power supply, charge controller, or batteries.

I think you should use the Prosine regardless of the battery size and loads. If there is a difference in efficiency, it is only 1-2 percent while running. Your load estimate will have a larger error than that. They are essentially identical in standby, which is where they will be 90 plus percent of the time. The added features of the Prosine make it worth the small difference, if it exists.

The battery charging efficiency of the Prosine also needs to be considered. It was designed to be as efficient as possible on 15 amps input.  Many of the larger battery chargers out there, are less efficient if limited to a 15 amp input.

My bet would be that your total system efficiency (generator run time, power into batteries, and power out) will be better with the Prosine. For a MorningStar based system to come close, you are probably looking at a $400-$500 battery charger. 

You are right about installing the PV system before fall, if you leave the batteries at the cabin.  As long as you are making regular trips in for construction and fully charging the batteries before you leave, not having the PV should not hurt the batteries.  But if you find your time interval between trips starts stretching out, or you find that time before you leave doesn’t allow the full charge, that would also be signal to start hauling them home, until the PV is installed.

But meanwhile, I think you need to backup and re-think what you are doing here.  You started with the idea of a solar system.  You have the inverter/charger and a generator. You need the charge controller, PV panels, and batteries.

The price of the batteries to support a large microwave/toaster scared you. You are downsizing the solar. Meanwhile, the costs of an ac system that you did not originally mention are growing.

Your 3500 watt generator is going to be good for about 30 amps. Normally, this is phase A and phase B, good for 15 amps each. If one phase goes to charge the batteries, you are still limited to 15 amps for the kitchen. That will not run the microwave and toaster at the same time.  If you take both phases for large load use, you have to perform some type of switching, to bring the battery charger into play.  This will happen whether you build in a cabin wiring system, or if you just use two extension cords.

To support the battery charging, microwave and toaster at the same time, you will be buying a 4500-5000 watt remote start generator (or larger).  What do you think that will cost? What about the duplicate wiring, switch panels, etc., that you will need ?
I don’t think you have been looking at the costs of that.

I would toss the toaster. Use a non-electric stove top toaster. They are still available.  I would really give some thought to the microwave.  Just how much is it worth to you ??  Whether you put it on the solar system or an ac system, it is still costing you money.  The only way you can run it inexpensively is with the generator you have.  If your family really “needs” the microwave, electric toaster, hairdryers, etc, make them run an extension cord in the window, and pull the cord on the generator. They won’t get used nearly as much that way.

The way to get out least expensively is size your battery system for the lights, fan, tv.  Use the inverter that you already have.   Save a lot of dollars by not having two ac systems. Put a few of the dollars that you are saving into your battery bank/PV panels. If you size it at 450AH, it will support additional small loads easily.  Conversely, if your lighting/tv/fan estimate turns out to be on the low side, you may already be in trouble.  You will find it far easier to live within the 450 AH rather than the 225AH.


Ken
 
16 Posts
Aug 10, 2008 10:23 pm
Re: Learning and rethinking my cabin power system

Ken,

Thank you for your on-going support.  The Prosine does have a good charger, it is a fairly efficient inverter and I already have it, so should probably use it. It also has a "shore power" current limiting feature.  It monitors generator power consumption and backs off charging current if other loads, connected through the inverters transfer relay, need the power.

I never planned on running 2 appliances at once.  I just didn't want anything to get damaged if it did happen.  The Prosine can provide 2kW continuous and 4.5kW surge.  Now that I'm planning on using it, I was thinking about putting either a 10 to 15A breaker on the AC output of the inverter to limit it to providing 1200 or 1800 Watts.

Leaving the technical aspects and looking some more at why I'm putting in a system that could handle an appliance.  Our new cabin is going up next to a multi-family cabin that has its only electric light in the outhouse and no running water. 

Its clean but primitive.  I don't much mind it and can identify with your and Thomas Allen Schmidt's comments on simplicity.  However, the rest of my family, particularly my wife and daughters, like being at camp, but don't like the outhouse, lack of running water, inflexible gas lights etc.  Along with building the new cabin for more room for our family, another reason was to give it some more conveniences without going overboard.  I enjoyed this area as a kid and I'm trying to strike a balance in creating something my kids and grand kids will enjoy.

In using the Prosine, I'll need the beefed up DC power system.  But once its in, with the exception of a bigger battery bank, I should be set for the future.  A friend has some 350 MCM cable for me.  I need to see if I can get lugs crimped on the 350 MCM or look at buying prelugged 4/0 cables.  I'd like to post my DC cabling and protection for review once I come up with a design.

My first question regards to the DC system.

If I'm committed to limiting the inverter output to 15A or 176A DC ((15A*120VAC)/12VDC/0.85 eff) should I use a 200A fuse even if the inverter and DC cabling can handle 300A?

If I use a fuse instead of a breaker, do I need a disconnect and if so are there any suggestions on disconnect types.
 
351 Posts
Aug 12, 2008 11:36 am
Re: Learning and rethinking my cabin power system

Jerry:

Unless you plan on down sizing the wiring, I do not see any advantage to downsizing the fuse.

You need to use some type of disconnect upstream of the DC fuse.  The disconnect is located as close as reasonable to the positive battery post.  What that disconnect looks like probably depends on who is inspecting your work.  In many cases I’ve used a marine type battery switch.
http://store.altenergystore.com/Enclosures-Electrical-and-Safety/Miscellaneous-Electrical-Parts/Switches/DC-Switches/Blue-Seas-OnOff-Battery-Switch-300-Amp/p250/

I’ve also had  “Nervous Nellie Inspectors” insist on Industrial grade DC load break disconnects.  That gets a bit more expensive.

Ken
 
16 Posts
Aug 12, 2008 03:27 pm
Re: Learning and rethinking my cabin power system

Ken,

Do you know if there are any known problems with a marine battery disconnect in off grid installations?  I was looking at using one and I thought I read where someone was not recommending them because they heated up.  The model you pointed out looks heavy duty, and the fact that its marine grade and designed for use in gasoline powered engine rooms leads me to believe it must be safe.  I don’t have inspectors to worry about, I just want something that’s long lasting and safe.

BTW, I decided to go with the 4 AWT cables so I don’t have to worry about upsizing later.  SAMs club has Energizer 220ah GC2 batteries for $65.  I’m thinking 4 of these would be a good set of “learning” batteries.  A local farm supply store has a small high strength plastic pickup truck tool box that will hold 4 L16s.  Any reason why I shouldn’t be looking at using that for a battery box as long as I vent it?

Thank you,

Jerry
 
578 Posts
Aug 12, 2008 06:58 pm
Re: Learning and rethinking my cabin power system

i tend to be a nervous nellie and prefer listed enclosures with listed circuit breakers acting as disconnects.

i think simple batteries are a good choice for a good starter set.  the toolbox would be okay, but another idea for battery boxes on the cheap are igloo coolers.  4 golf cart batteries fit great in one of the big ones.  one holesaw and 2 4" landscaping  drain hole covers later and we had a decent battery box on the cheap.  add a zephyr vent and you are really stylin.  wood is another good option if you are handy.

i would totally rather see you save dough on the batteries and box than the dc load center.  i like outback's flexware 500dc.  it is big, and probably bigger than your needs right now, but you would have to grow probably to 6kw or a ton of dc loads before you would outgrow it.  i think we may have done the dc disco sizing on another thread.

good luck,

james
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351 Posts
Aug 13, 2008 03:43 am
Re: Learning and rethinking my cabin power system

I am not aware of any problems with the marine disconnects, when they are from a good company and sized correctly.  I've used tons of them on DC installations, both in smaller Alt Energy applications and on boats.  Most of the heating of electrical equipment happens when you push it above 90% of its rating. You won't be getting close to that.  I am not pushing the switch over James recommendation, just replying to your question.

I like his recommendation of the igloo cooler. I don't remember where your cabin is, but have the impression that it gets cold there in the winter. I was going to ask where exactly you are going to put the batteries and how cold you would expect that area to get in the winter.

When you say 4 AWT I am assuming you mean 4/0, not 4 AWG.  I’ve seen that terminology from a couple of “inverter stores”. It’s a bit of a sore point with me. 4/0 is “four aught” or sometimes “ought”. It means four zeros.  Call me old fashioned if you wish, but I can’t help but wonder how much they know, if they don’t even get the name right.
« Last Edit: Aug 13, 2008 04:01 am by ken hall »
 
16 Posts
Aug 13, 2008 06:18 pm
Re: Learning and rethinking my cabin power system

Ken,

Yes, I'm using 4/0 cable.  And your right, I picked up the AWT term from someone selling battery & inverter cables.

In regards to the igloo cooler.  I don't expect to use my cabin much in the dead of winter in NE WI.  Gets below 0 sometimes, -10 below may on a couple days.

My batteries will be in the cabin.

I'm thinking the cooler is eventually going to get as cold as the outside.  If kept topped off by a PV panel, the batteries should be good for -40 deg F.  Here comes my next set of questions:

Does keeping batteries float charged with a PV panel warm them to any extent?

If I'm not using them and its not cold enough to freeze them, is there any advantage to having them in a cooler to trap that charge heat?

Thanx,

Jerry
 
351 Posts
Aug 15, 2008 02:25 am
Re: Learning and rethinking my cabin power system

Jerry:
I am not the best person to ask about real cold weather for long durations, and batteries (California). Perhaps someone with more cold weather experience will jump in here.

What I can tell you is that I do not like to see a working battery get below about 50 degrees internal temp. The batteries have a large thermal mass, so they do not change temps rapidly. Using an insulated battery box helps keep the ambient temp extremes (hot or cold) from affecting the internal temp too much.
The float charge and the insulated box will help, but I would still expect the battery temp to drop over time. If you do make a snow trip, you would need to treat the battery as cold, even though you may have heated the cabin to warm and toasty.

The other topic that I'll toss at you is the box venting. I would give some thought to venting the box outside the cabin. While that may raise some cold weather issues, I would not want a battery bank venting fumes and H2 into the living space of a small cabin. During warm weather, heavy battery use, equalizing charges, etc, you can get a fair amount. The smaller your cabin is, the larger this issue would become.

Ken
 
16 Posts
Aug 15, 2008 10:08 am
Re: Learning and rethinking my cabin power system

Ken,

I was planning on venting the top of my battery box to the outside of the cabin.  I have seen where some users have put in a small fan to assist venting during times of higher charge rates.  I'm not sure if the fan is overkill or not.

Your comments on the large thermal mass of the batteries is well taken.  My thought with the insulated battery box is that it would keep the batteries colder longer if we did do a winter trip.  Whenever we are at the cabin, we adjust the temp with windows or wood stove to be comfortable for us.  I also want the batteries to get to room temp ASAP, thus the uninsulated box.

Thank you,

Jerry
 

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