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

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

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

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

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

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
AltE staff

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

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