OFF GRID POWER; various thoughts on...

[glenn kangiser]

Note that the cables coming off of the new batteries are  something like 000 aluminum service entrance cable with the ends protected with the special dissimilar metal grease and then a copper pipe sleeve smashed flat over them and drilled.  No corrosion of any kind on them noted in a couple years.

[MountainDon]

The batteries with the straps invite maintenance   , whereas with the rat's nest it's difficult to see the cell caps let alone get at them at times.      I use cables in the 4 GC2's in the RV and I'm afraid it looks a little scary too. I was going to do cables (home made) but I believe the straps are now a no brainer.

[glenn kangiser]

I use a gallon water jug with a hose in the cap to get through the mess but it's still not fun.  I like the straps.

[Pritch]

Hey Glenn, I'm not sure if it is appropriate for this application, but you could mask off the ends of your straps and dip them in that plastic dip coating they make for tool handles. 

-- Pritch

[glenn kangiser]

That is a good idea, Pritch.  Plastic is plastic I think. Good idea.

As an alternative rather than that I could likely also get away with the 2" wide 10 or 20 mill tape they make I think - that would be easy.  Not as heavy but likely sufficient.

[MountainDon]

To DC or to AC the small off grid cabin?

With apologies to William Shakespeare.

When I began to design my cabin I knew it would be off the electrical grid; the connection would cost more than the land and the cabin. Way more. I first thought I would build a power system that used a lot of the DC power directly to power DC lighting. The first advantage to going in the direction of a DC power based cabin that I thought of was the apparent simplicity. No inverter losses involved to run simple things like lights, I thought. I was willing to include a medium size inverter of 1100 to 1500 watts to enable the use of a microwave, perhaps a vacuum cleaner or the occasional use of a toaster.

I discovered the availability of DC voltage CFL lighting;12, 24 or 48 VDC. Good I thought. Yes they cost more than the 120 VAC CFL I could buy in bulk at Costco, Sam's or even Lowe's. Yeah, and I'd have to order them and pay for shipping. Fair enough.

So I drew plans. I had a DC panel. I had an AC panel. Even though I was building off the beaten track, under the radar I wanted to keep the building and it's components within the scope of the building codes and the NEC. Pretty much. Therefore I would need to keep the DC separate from the AC. I soon discovered that automotive type fuses and switches would be problematic. But then I got lucky and discovered that the Square D line of circuit breakers were UL approved for up to 48 VDC! On-off switches remained a problem. Let it be noted that virtually all on-off household switches are not DC rated. They will burn out quickly when used on DC circuits. Automobile switches are not UL listed. I did find some DC rated switches, UL listed for about $12 apiece.

My wife wanted to use some table lamps in the cabin. Alright no problem, I can use some of those DC CFL's in them. Ooops, the socket switches would not survive the DC experience for long. Well, OK, I'd figure something out on that.

The next thought was how to ensure keeping the DC separate from the AC, for it was a 'given' that there must be outlets for the microwave, toaster, possibly a vacuum cleaner, and now outlets for the DC lamps. Not a big deal I said.  I knew that the NEC allowed the use of 240 VAC receptacles and plugs for DC use as long as there was no 240 VAC power systems in the cabin. Home free, I thought.

For the AC power I figured I'd use either a modified square wave inverter or possibly a pure sine wave inverter such as the Exeltech 1100 watt unit in the RV. (Note: I refer to a modified square wave inverter. I refuse to call them a modified sine wave inverter as that is a marketing lie. Square wave is square wave, modified or not. Some devices work fine on square wave; incandescent lamps for example. Some devices work, but under duress; like motors. Motors run slower and hotter. They waste power. In some cases they burn out prematurely. Some devices simply won't work at all. The microwave in our RV is an example. It makes all the proper noises, the turntable turns, and after nuking a cup of water for 2 minutes it emerges as cold as it was when it was placed in the microwave. Some devices like a small battery charger for NiCad cells destroy themselves when powered by square wave power. I had a very odoriferous event on a camping trip in UT when I attempted to recharge some flashlight batteries. I was very leery of allowing my wife to use her computerized sewing machine off a square wave inverter.

Ok, I said. I'll move the Exeltech pure sine wave 1100 watt inverter from the RV to the cabin. Perfect! NO, wait a sec. Not so perfect.  How many times has my dear wonderful, beautiful, warm, loving, adorable, accepting of all my foibles and idiosyncrasies, wife started the microwave (it needs 1000 watts to run) and then simultaneously attempted to use some other AC operated appliance. This won't fly, I realized. Add to that the different outlets, some for DC, some for AC; this was becoming complicated. Momentarily I considered no electricity at all; Aladdin oil lamps for lights and the rest be dammed.    No. 

FYI, Exeltech makes some very fine pure sine wave inverters that are stand alone, no battery charger included and priced fairly. They also have a stackable series.

OK. I know there are many folks out there who have a DC based power system; some are members of this forum. What they have set up works for them according to what I see. That's great! More power to them!  My point in this is that you should take the time to run through your expectations of your off grid power system before deciding on the final plan.

My hybrid AC/DC system had me using more wire. DC systems usually require larger gauge wires because of the higher amperage the wires are asked to carry. There is the problem of DC listed switches. Then there's the fact that DC powered CFL's cost more than the commonly available SC versions. FYI, the only difference between an AC fluorescent lamp and a DC powered one is the ballast. The tubes are the same. It had two service panels instead of one, and more wire of a heavier gauge.

After the considerable amount of time devoted to considering all the above I decided that for this particular cabin of ours it did not make sense to do a DC based system. The PV panels have remained more or less constant. Ditto the charge controller and batteries.

However the big change comes with the wiring. Our cabin is basically wired like the typical home. AC circuits for virtually everything; 14-2 wire; the AC power coming from a pure sine wave inverter capable of supplying 3500 watts continuously (30 amps). I have fudged a little; I have three 12 VDC lights that will operate directly off DC , just in case the inverter craps out at some point. I also have a 24 VDC ceiling fan because it's efficiency is so vastly superior to the best of the 120 VAC units. Everything else is just like at home on the grid. No strange light bulbs, no strange receptacles, no wondering if I can use the microwave and the toaster at the same time.

Anyhow, my purpose here was to incite thought. I'm sure there are folks who will have no issues with a DC based system To them, I say, good show! You have simplified beyondd where I draw the line. I'm just not quite ready to venture there. Think it through before you finalize your off grid plans.

I hope all that makes some sense. Any comments will be appreciated.

[glenn kangiser]

I agree with you, Don. 

With the efficiencies of modern Sine Wave inverters, and the lower cost of standard A/C equipment plus the availability of the normal A/C items, it only makes sense to me to run standard A/C for anything other than a small system.  Even the small system is likely easier to do with A/C in my opinion.

[MountainDon]

My brain cells got prompted to recall this by a comment in another topic.

In our cabin wiring I have wired several outlet halves to be switched (on-off) by a wall switch. Some of these are designated for items like the microwave, the TV and the stereo. All these have phantom loads; the clock in the microwave and the remote control circuitry in the TV and stereo. For those who are not aware, anything that has a cordless remote control is using a small amount of power even when turned off. While it sits there waiting for the wake up signal it uses a timy bit of power.

Same thing applies to the cordless phone base station, and many other items in any home. Around home I don't worry about it. Right now I know there are a couple battery chargers in the garage that are sitting there wasting a little power. Plus there's the garage door opener waiting for the signal to open the door. And the sensor activated lighting around the building exterior. And the sensor activated light that turns the front entry light on when one comes through the front door; handy when carrying stuff. Also guaranteed to surprise anyone breaking through the door.

Back to the topic of switched outlets for off grid power. I also used a switch with a pilot light. The light is low power neon and only comes on when the switch is in the ON position, no light when turned off. I've also used those for the exterior lights. A glance at the switches by the door will let you know you forgot to turn off the lights outside.

Similar to this one (mine are the standard toggle type)...



Also available in a three way type.  If you go for these beware that some pilot eqipped switches have the pilot illuminated when the switch is off; handy for finding in the dark, but not what we want for this purpose.

[MountainDon]

topic on battery cable connections

[MountainDon]

Off Grid Power System Calculators.

Here are several sites I've had bookmarked for some time. I like some more than others. Some have online forms that can be filled in. You click a button and it does the math. Others have print out forms and you do the math yourself. They may not be perfect in that the resulting recommended configuration is not necessarily the only way or the best way. However, they are a reasonable place to start. Remember, as always, garbage in = garbage out. You must enter realistic power usage, not want to wish for, but what you will use. Then add a little extra as insurance.

I think this one is my favorite
http://www.wagonmaker.com/script_calculator.html

Not bad either
http://store.altenergystore.com/calculators/off_grid_calculator/#load-calc

http://www.me.utexas.edu/~me374s/javatop.html

http://www.evsolar.com/worksheet.html

And a few more...
http://www.bigfrogmountain.com/calculators.cfm

http://www.solar4power.com/solar-power-sizing.html#battery

http://www.green-trust.org/2003/pvsizing/default.htm

http://www.solar-power-answers.co.uk/design.php

PLUS, the following is a good one that is meant for determining how many panels of your choosing can be safely used with your Outback Charge Controller. It was mentioned previously.
http://outbackpower.com/resources/string_sizing_tool/

[MountainDon]

Batteries, Series VS Parallel

Most of us will likely end up with batteries in some sort of a series - parallel system, partly because golf cart and L16 style batteries are reasonably priced and because our system may need to be enlarged at some point. I figure that eight 6 volt golf cart batteries will fill our needs; two strings of four in series connected in parallel. If I need to increase capacity I'll add another string of four in series to be paralleled with the others. I'll know about that soon after getting it going. My battery box is going to be sized to accept up to twelve batteries of the L16 size just in case.

There are advantages and disadvantages to this. On the advantage side we just added batteries, didn't have to ditch the ones we had and buy larger ones. We can add four of the same capacity and increase our reserve power. One disadvantage to this series / parallel system is the large number of cells to maintain. Another is the increased number of cable or buss connections.

Another disadvantage to paralleling may be viewed as a positive to some. That is that a failed cell will not drop the design voltage as there are the parallel ones to make up the difference. It may not be obvious that there is a problem, until you notice that cell requiring more watering. So while the battery bank will maintain design voltage and still have pretty good capacity it will self discharge at a higher rate. A parallel bank with a bad cell will sap energy as the other cells try to charge it (this occurs continuously, even with no system load, which adds up in sapping energy).

This does not occur in a series only string. A bad cell in series will drag the voltage of the system down, but it will not absorb power from the other cells. The power passes through the bad cell. The failed cell may add some resistance (which does sap energy, but only when a load is applied) and, since it does not contribute any voltage, it will show as a reduced battery bank voltage. The lowered voltage makes it easier to spot a bad cell.

Bigger cells in series also mean fewer cells to maintain. Of course bigger cells also mean heavier more bulky cells, a downside in many remote locations.

My dream battery bank for our cabin would be:
- Twelve 2 volt 845 amp/hr HUP-One cells in series for a 24 VDC system; approx $7000+. There are some others by Rolls or Surette, but they are in the same price range. These are expected to last 15 - 20 years. Many have been in service longer.

So while the ideal may be a series only string, you need deep pockets to start with that.

[MountainDon]

Further to the above. A series /parallel also have the advantage of redundancy. A bad cell or battery in one series string could be temporarily dealt with by removing that string from the parallel array, until the cell/battery is replaced.

However to counter that a properly maintained battery bank consisting of HUP's or Rolls/Surettes is not very likely to give problems for many many years.

[glenn kangiser]

I knew you'd have some good points on this.

Now how to handle this problem of a cell dropping in a series of a parallel set.  I found that equalizing as you and a dealer mentioned to me seems to help greatly -- head for 32 volts for a few hours.  This is a hard one.  Many chargers or inverter chargers don't want to go there. 

I find that a charger working on just 2 of the 6 volt batteries - since I have a 12 volt charger can remove power from the group and charge certain parts of the series group without pulling the group down much -- recycling - pull it out of all and put it into 2 of them only, bringing them back up to meet the rest.  The most effective is using the welder to get the equalization charge for me.

Soon I hope to be able to report on a new charger - MikeyB is checking on it tomorrow.

Locating the bad cells is easy - I pull all of the caps off of one series group and check every cell with the Hydrometer. 
when done with that group I do the next one.  Record the readings or mark the low cells for future monitoring after charging or equalizing.  Specific Gravity of all should be in the good range.  If one cell is significantly lower than the rest, then it needs attention or the whole pack will suffer.  Distilled water only as necessary then equalize them.

[MountainDon]

-- head for 32 volts for a few hours.  This is a hard one.  Many chargers or inverter chargers don't want to go there. 

That is yet another wonderful thing about the Outback equipment.    The charge rates are all user programmable. On a 24 VDC system the EQ charge can be set all the way up to 34 volts.   

[glenn kangiser]

The Trace 4024 kicks out at 30.4 or maybe .2 I think as far as when inverting and equalizing with an outside source.   Once it hits that voltage the system shuts down untill the voltage drops back to within he normal range.  I have not checked for programmable settings as I don't use it for equalization.  I should check it to see -- it is not fun to get lost in the programming menus on the Trace.  Lots of owner manual study might help.

I did not notice sulfation releasing and battery improvement until equalization voltage got to 31.2 then the voltage would drop back to 30.8 as internal resistance dropped and additional charge was allowed in by the battery.  SG (specific Gravity) improved in my worst cells also.  I had at least 3 that were below to well below normal.  All it takes is 1 below the rest in the string to kill a string of batteries.

[glenn kangiser]

Here are the Trojans that were given to me - they were a bit over 3 years old.



An inadequately sized system and overuse along with insufficient equalization and lack of sufficient maintenance has caused sulfation to the point that the owners couldn't get them to keep enough charge to keep their house running.

Somehow they had changed them out and just wanted them removed from their crawlspace.  I thought this would be a great opportunity for me to play with desulfation.  Here is one of the cells that is in worse shape.  I marked it and took a pix so I could keep track of progress.  I filled adjacent cells with rain water as one was dry on top and put the small desulfator on the two worst batteries until I get a bigger desulfator through Mike.

As you can see, the plates are nearly not visible through the sulfate crystallization in the above pix.  I was able to get the 2 volt and 4 volt batter to take a charge with my 10 amp NAPA PWM charger.  Some of the new NAPA chargers use pulse technology and are superior to the old chargers using much less power to make a better charge.  I heard about it but they don't give any info in their catalog.  I went to the Shumaker website to verify what the charger did.  They manufacture it.

I have found this battery listed from $389 to $559 each  on the net depending on the quality of dealer - some seem a bit unscrupulous.

I can still buy them in other brands for around $250 or maybe a bit less wholesale - just a guide price so you don't get taken advantage of.

The moral to all of this.  I guess it would be, take good care of your Trojans and they will take care of you.

[glenn kangiser]

Here is a link to another picture of the Two batteries I currently have the desulfator on showing what you should be able to see if the batteries were not sulfated as well as some more commentary on my tracker.

Trojans being repaired at the Underground Cabin!

[MountainDon]

Tesa, I split your questions off to  "tesa's Off Grid System"

http://countryplans.com/smf/index.php?topic=6230.msg81195#msg81195

[Blake]

Don,
I may have missed it, but if you don't mind, have you had a hard time keeping your system charged from the panels alone down there?  I helped a friend install his genset on his system in Fort Davis a month ago,  and he is having a problem getting  a good charge during the day.  We sized the system properly,  but he bought the pv panels on his own.  Another outfit installed his controller, batteries and inverter.  He's been telling me even during the sunny days,  at night the genset kicks on twice for about a half hour.  His genset is used soley for charging the batteries right now.  Panels are in an open area at the highest point on his property.  I am going off by assumption and the last time I was over your way,  but I remember Jemez mountains being simiar to the fort davis area.  Any pointers are greatly appreciated,  as I am lost on the solar side of things.

[glenn kangiser]

If he has clear skies and no shadows over his panels then there is something wrong - maybe not enough panels or wired wrong.

Cold does not matter.  Cloudy skies will drop panel output to maybe 1%to 5% in my experience.

Too much voltage loss on the wire - Long wire run?  Small wire?

My panels put out great when the sun is out in the winter.

[MountainDon]

Lots of possible reasons this is happening...

The first thing I would do is to check the specific gravity of the battery electrolyte in each cell. Does the hydrometer reading indicate full charge after the charge controller indicates it's full? Is there one or more low cells? Some charge controllers are programmable; perhaps it is not allowing the batteries to actually reach full charge.

Check all the DC connections for corrosion and tightness. Using a non contact infrared thermometer on all connections with a good load applied can help find a connection with high resistance.

If the batteries check out fully charged on all cells after solar charging, then it would seem he's using, or losing, more power than anticipated. Or the battery bank is simply too small for what it's being asked to do.

The set points for the auto start generator may be set incorrectly. It seems to me if the generator is coming on for only a half hour something is wrong there.    I'd tell him to go and take a reading on the cells with the hydrometer when the generator kicks in. See what the state of charge really is; if charging is really needed at that point.

Does the generator only kick in during or immediately after a heavy load like running a big microwave for a while? That could be indicating battery capacity is insufficient to prevent rapid draw down of the battery voltage, which would cause the generator to kick in.

Anyhow that's where I would start.

[MountainDon]

How cold do the batteries get? Capacity of the batteries fall with cold. 32 degrees F = approx 20% less

Correct the sp gr for temp.

If the batteries are AGM's forget all the above about checking sp gr. That's the only thing I don't like about AGM's.

[glenn kangiser]

Update on the tracker and how to tell the level of propane in the pressure tubes. 

http://countryplans.com/smf/index.php?topic=151.msg81271#msg81271

[Blake]

His panels are in the sun almost all day. 

Don, 
I appreciate your help.  I have forwarded your response to him and am going to let him look at it and confront the people who installed/programmed his inverter.  I just dropped it off of the back of the truck,  hooked up the two wire-start,  hooked up the l.p..  and test ran it.  The brief tour I took of the setup looked professionally done.  Thanks for the help and maybe I can help him out.

[Windpower]

This a great topic
I plan to be off grid later this year (I hope)

I am trying to decide what batteries  to buy

Someone here mentioned "HUP" -- not sure what these are

I have some experience with Trojan 'cart batteries' and they seem ok but for a serious system I think I need a serious battery bank

I have 6 AirX 48 volt wind generators (from Ebay at a very good price)

the plans call for 1500 watts of PV planels too

I am having difficulty calculating the size of the battery bank

On another note ...

I just bought a 8000 watt inverter from ebay -- made in Taiwan

I looked great and was priced right at $2700 --free shipping

now for the rest of the story

Yesterday I hooked it up to some four 12volt batts   in series


the output is 218 VAC across the 'N" and "L" lines but

ground an "L" reads 125 VAC

and ground and "N" reads only 85 VAC 


email to KIPOINT in TAiwan says they will get back to me after "new moon holiday"  Feb 2

anyway back to the batteries

I am almost decided to go with the 12V L-16 Trojans

but maybe Concord or Surrette would be worth the money