Off-Grid Power and Water Supply Proposal...

[jaransont3]

Here is my proposed plan for our small (420 sq ft) cabin in Northern MN.



We don't mind running off the generator while we are awake and at the cabin. It is a Honda inverter generator and is very quiet. Plus it will be remote from the cabin in a separate shed. We only spend 2-4 weeks per year, a week at a time, at the cabin right now and the fuel costs are reasonable enough.

However , I can not see running it through the night when the only thing that might need it is the occasional cycling of the frig, the 2W of idle power needed for the water heater, and a night time trip to the bathroom. Same goes if we are out and about for several hours...trip to town, canoeing, hunting, etc.

Thus the batteries and inverter/charger for some of those items. I figure the batteries would be topped off any time the generator is running and given those load requirements, easily give me 1/2 a day of autonomy, especially if the only thing on is the frig and the water heater.

The shallow well pump and cistern lift pump are powered by the generator and would be used as needed to fill the cistern and holding tank respectively.  We would rely on the 12V demand pump and the holding tank for daily water use and overnight use.  Would probably try to make sure the holding tank is full each night.

As for the well AND cistern system, this is driven by the desire to have water available when we come in the middle of the winter when it is well below freezing. (no pun intended) The shallow well pump would only be run as needed to fill the cistern. Then daily needs would be met with the smaller cistern submersible pump. The cistern would be buried and insulated to prevent it from freezing. This way we can fill the cistern at the end of our last visit in the summer or fall and winterize the shallow well pump and well to prevent it from freezing. Then use the cistern during our winter visit and fill it again when we arrive in the spring or summer.

What do you think of the plan? Recommendations and comments welcome...especially with regards to type and brand of inverter.

[Squirl]

Safety first. Disconnects.

One of the most over looked aspects of offgrid systems and are required by the NEC.
They can be in the form of breakers.
You seem to have a fairly low wattage setup and the breakers should be less expensive.
By my read even if you shut off the main panel you still have a DC system going, their needs to be a way to shut off those batteries.  They have enough juice to kill.  If you touched a piece of metal between the leads, you would find that out quickly. 

I agree with you wanting to add batteries.  Running a generator (specifically the Honda, one of the most expensive on the market) for low wattage uses is a waste of the life of the generator.

[jaransont3]

Disconnects, yup.  I guess I need to update the schematic again.  I do plan to split the main panel, with one side fed by the generator and the other fed by the inverter.  The only 12V "appliance" planned right now is the demand pressure pump.  I will be sure and fuse that connection.  I also plan to install a fuse between the batteries and the inverter as recommended by Tripp-Lite.

I have no plans for 220V so spitting the main panel shouldn't be a problem.  I am just jumpering the two sides now since the Honda only supplies 110V anyway.

Thanks for the input.  Keep it coming.

[rick91351]

You might keep an eye out for a travel trailer / fifthwheel  newer style that has been in a wreck and an insurance total.  Sell the frame and axles,  take the duel fuel frig, the water tank, the electrical, and plumbing.  Send the balance to the landfill.  What you salvage is pretty close to what you need.  A new RV frig is like $1200 on up.  If you don't want it sell it.  Just a thought       

[Dave Sparks]

Adding on to the disconnect, it needs overcurrent protection. Either in the form of a circuit breaker rated for DC or a class T fuse for a battery system. The goal is a way to shut down the system by hand or autmatically if unattended.

[MountainDon]

class T fuse for a battery system.

I just wanted to emphasize the fuse should be a class T. Even if there is also a breaker in the line as an easy to manually trip method of circuit isolation, I believe a class T is also a good idea. The class T is a fast blow type. Other class fuses can have a slow blow delay to allow for some surge. If there is a dead short the delay/slow blows can take too long and damage can occur. A class T blows "right now" if a dead short occurs. Dave will correct me if I have something wrong about that.

[Dave Sparks]

Hey Don,

We were within minutes of eachother on the last post The other reason that a class T is desired close to the battery is it's very high rating for interupting and staying interrupted during an internal fault in the inverters output circuitry. Other types of fuses may actually arc over and not break the current path. The time that it takes to blow is secondary to it staying open at high current to avoid a battery fire/explosion/other really bad thing. This spec is AIR amphere interupt ration and good DC breakers have a high AIR but not as good as a Class T. So your advise is perfect! Use both a breaker or switch and a class T.

I have a client sort of near you guy's and I am hoping to get down your was this summer. Maybe another eyeball is in order?

[MountainDon]

Give us a holler, Dave, whenever you know any dates. I'll send a PM along to you with numbers

[jaransont3]

Time for an update on the power plan.  Jill and I spent last week up at the cabin.  My brother came out one day and rewired everything in the main panel and the inverter/batteries.   



Some if it is still temporary. 



Next trip up we will hook the generator to the triplex and the triplex (at least one branch of it) to the panel.  Right now we are just connected with a heavy duty extension cord.  The inverter connection to the panel is also only temporary.

Obviously some of this is also temporary.


I brought the batteries and inverter back with me.  I plan to build a box for them with carrying handles, battery hold-downs, a mounted fuse block and inverter.  It will slide into a cabinet built into the kitchen with a simple plug-in connection to the panel.

The inverter powers one side of the panel and the generator the other.  Only a few lights and outlights and the frig and water heater will be run off the inverter.

The inverter works great. It is completely silent when passing generator power through it.  The transfer switch works flawlessly when you kill the generator.  When it is in inverter mode there is a slight buzz.  The fan does NOT run continuous.  It all works great.......however.....

I do have to upgrade one component.  I undersized the Class T fuse.  It is only 30 amps.  I read the rating for the AC side instead of the DC side.  Duh-Oh!  The 30 amp fused worked fine for the lights, but blew as soon as the frig tried to cycle on.  We just put the frig on the generator side of the box for the time being.

I need to update to a 70 or 80 amp fuse, I think.  The DC rating for the inverter is 72 amps.  From my research, I think the 80 amp fuse would be a good choice.  I am open to being better educated on this aspect of the system.  Thoughts/suggestions?

Also, I see a bunch of folks using ANL fuses in this type of application.  With my two battery/750W inverter, is this a good option?  They are much cheaper than the Class T fuses.

Overall, I recommend the Tripp-lite!

[MountainDon]

Also, I see a bunch of folks using ANL fuses in this type of application.  With my two battery/750W inverter, is this a good option?  They are much cheaper than the Class T fuses.

1. see my signature line. It is very applicable to this situation.

2. one of the important things about fuses and breakers is their AIR number. AIR = Arc Interrupt Rating, or something like that. This is measured in amperes.  Lead-acid batteries under dead short circuit conditions, have the ability to deliver huge amounts of current in an extremely short period. Melting insulation and wires, fire and exploding battery cases, that sort of thing.  Class T fuses like the JLLN have an AIR of 20,000 amps.  Class ANL have an AIR of 2700 amps.  Class T are required to meet NEC in code compliance situations as far as I know. ANL, ANN and CNL are often used in non-code setups. They probably work. I have seen websites recommend them for "small" battery systems. No definition of what small is though.     I have seen, from a distance, what can happen when a dead short happens on a small 24 volt (2 x 12 volt) battery system. Fortunately the greatest injury to the person was in the form of embarrassment, plus a lot of under the hood rewiring and clean up.  I do not consider my own system top be small, so I elected Class T. Everyone can decide on that for themselves.

One major difference Dave Sparks reminded us of recently, is that the Class T fuse is also designed to smother a direct current arc when the fuse blows. Other fuses may not smother the arc and can even flow melted material across the gap to permit the current flow to continue. Cheaper doesn't count for much if that happens.

I don't know where you got your Class T fuses, but I have found the best prices every time I have checked to be at solarseller.com. Class T link here

As for the fuse size, what could that inverter draw in a surge? I don't think there would be any harm in using a 110 amp Class T to cover any surge amount. Maybe bigger if the inverter allowable surge might need it.   That is supposition on my part, but seems reasonable. A dead short will still blow the 110 or a 200.   I have seen vehicle winches pop a 400 amp fuse (ANL) under heavy load. I've also seen a vehicle winch melt the internal side terminal connections on an Optima battery. 

I want to inject a little thread drift on this subject for a moment. Many folks know that SquareD brand, QO model circuit breakers are rated for DC use with a maximum of 48 VDC. What is not often mentioned is that the QO has an AIR of 5000 amps and could under some circumstances suffer from the arc over when used on DC. So the couple of QO breakers I have are preceded by a Class T fuse to properly cover the eventuality of a dead short arc over.

[MountainDon]

The Class T fuse that is wired to our inverter feed has a higher amp rating than my DC breaker that is after the fuse and before the inverter input.  My thinking there is that under a catastrophic dead short the fuse will no doubt blow. There are a lot of potential amps available from our 12 golf cart batteries (24 vdc, three series strings in parallel)   But under a more "normal" overcurrent situation the breaker will release before the more expensive, one time use, Class T fuse would need to blow.

we have;   batteries  --  class T  --  DC breaker  --  inverter  --  AC to service panel

and:  batteries  -- class T (a different one)  --  SquareD QO panel for DC loads with QO breakers  --  DC loads (ceiling fan, shurflo water pump, cistern submersible pump, three thinlite FL lights.

EDIT:  A few years back I spoke with an engineer at Outback and he strongly recommended using a Class T fuse ahead of the QO breakers. It was his opoinion that a catastrphic short could easily overwhelm the QO breakers at 24 vdc with the ampacity of the batteries that I have.

Read, think and decide what is best for your situation. You do have fewer batteries for what that is worth.

[jaransont3]

Thanks for the replies and the link to the Class T fuses.  Certainly better prices than McMaster-Carr.

The Tripp-lite APS750 is rated at 72A for the 12VDC input for the continuous output rating of 750W.  I am using very short (less than 2 feet) 4GA 80 degree C cables to hook the batteries to the inverter.

I think I will go with the 110A fuse and holder they sell on the link provided by Don.  Will handle the continuous load and provide some surge capacity.  I would ideally get a 140A fuse to handle the whole 1500W peak load...assuming of course it scales linearly.  But I haven't found that online anywhere. McMaster has 125A and 200A, but nothing in between.

Other comments/suggestions/experiences are always welcome.

[jaransont3]

Just order a Class T holder and a couple of 110A fuses from solarseller.  I also order a 200A fuse just in case.  Once they show up, I will build my battery box and make all the connections.  Then I will be ready for the next trip up to the cabin.

Thanks for the input.

[MountainDon]

I may be too late.... there are 2 different lengths of holders they carry and I don't recall the amperage cutoff point. I do know the 100 are shorter than the 250.   the shorter case could be cut and the longer fuse then used. 

[jaransont3]

No worries. The small holder is good upto the 200A fuse. The bigger one starts at 225A and goes up.

[jaransont3]

Got my battery box just about fully fabricated.  Started by drawing it up in Adobe Illustrator...



Going to make it all out of 1/2" plywood.  Then I went over to TechShop Detroit and used the large ShopBot CNC router to cut out all the pieces...









After some sanding the pieces are ready for assembly...



Managed to get it all dry assembled to check fits...



The top lid will be hinged to allow access to the batteries...



Batteries drop right in and fit good...

[img=http://www.carartbyjohn.com/2013Misc/BatteryBox_09.jpg]http://[/img]

Still have access to the electrical connections and the fill ports.



Inverter and fuse block will be mounted to the top hinged lid...



Nice compact unit, but very heavy.  Probably around 150 lbs...



Still need to glue/screw the box together, get a couple of coats of polyurethane on it and get all the hardware mounted and wired.  Might add some wheels to make it a little easier to move around, but it is already better than lugging the individual pieces around.

[jaransont3]

Finally finished up the battery box/inverter for the cabin tonight.  Several weeks ago I put a few coats of polyurethane on the box.  Tonight I hinged the lid mounted the inverter and the fuse block to the lid and hooked up all the cables.  Got it plugged into the house right now and the batteries are getting topped off.  Will actually be sort of nice having it here at the house too for power outages.

Here are some pictures....


Top view with everything hooked up.  Nice short cable runs.  110A fuse.


Front View.  Easy access to the fuse and the plugs and switch on the inverter.


View showing the hinges.  Cables have enough length to easily open the lid up and not stress the cables or the connections.


With the lid up, I have easy access to the battery connections and the fill caps to keep them maintained.


Slightly different shot of the lid with the inverter and fuse block mounted to it.


Overall shot.

I think I am still going to add at least some wheels on one end.  It is really heavy.....

Can't wait to get it back to the cabin and put it to use.

[firefox]

Very nicely done!

[jaransont3]

Added a couple of wheels to the battery box tonight.  Also added a couple of short feet to the front to get it all back to level.  Will make it much easier to move around considering the whole deal weighs over 150 lbs.

Need to get a couple more washers for the one side, but it is otherwise good to go...

[jaransont3]

Happy to report that the battery box and inverter are working great. We got up to the cabin yesterday and got it all plugged in. The inverter runs the compact frig just fine. We shut the generator down at 10:30 or so last night and it still indicted a full charge this morning after keeping the frig cold all night and running a few lights.

Only negative to the whole set-up is that when the frig starts, the surge from the start-up causes the cooling fan to run on the inverter and it is a little loud when everything else is absolutely quiet. All and all a pretty decent compromise.

[jaransont3]

Little more update on the battery/inverter set-up we use at the cabin.  We used it the entire time we were at the cabin for the week of the 4th of July.  During this time we had the compact frig hooked to it and few CFL lights, and occasionally a cellphone charger .  Really nothing more at this time.  We typically ran our Honda i3000 generator for a few hours each day while using the power tools and such.  This is sufficient to charge the two batteries from about half charge (based on the 3 LED lights on the inverter).

With the batteries fully charged, we could turn the generator off over night and use a few lights and keep the frig cold without coming off the full charge light on the inverter.  At one point during the trip we went for a day and a half on just the battery/inverter combo since we weren't using any of the high amp power tools.  The battery charger indictor got to the point that the mid-charge and low-charge lights were light, but no lower than that.

We were blessed with really nice weather (upper 70s to low 80s with low humidity and cool nights) while we were there so the frig wasn't working real hard.

We used about 5-6 gallons of gas in the generator for the entire trip at about $3.50/gal.  Total cost for power this trip was under $25.  Over course this doesn't include any amortized cost of the generator, inverter, or batteries.

We are pleased with the system we have and it looks like it will easy handle the requirement we had to not run the generator over night or when we leave the cabin for the lake or town or whatever.

BTW, I took the wheels that I added off when we got there.  The extra width of the wheels made it difficult to get in and out of the space behind the driver's seat in our Ford Flex that we carry it in.  I am going to re-think the wheels (it really is too heavy to carry easily) and make a separate wheel dolly that fits underneath the battery box and has 4 wheels so that you can roll it around without having to lift any of the weight.

[jaransont3]

If you have followed along in our project thread, you know that we are planning to collect rain water instead of put in a well at our cabin.  We got our 300 gallon cistern buried last week and some of the plumbing done. 

The plan is to get the gutters and plumbing to the cistern done the next trip back.  One of the things we will need is a couple of first flow diverters, one for each downspout on the cabin. I decided to try make one myself from some PVC fittings and a 5 gallon bucket.  This is what I came up with...















It works great with the garden house here at home.  The tennis ball makes a very effective cut-off ball float valve.  I still need to figure out a weep hole drain system for the bucket since we won't be there to empty after each rain.

I also plan to build a wooden (cedar) barrel to go over it and hide all the green and white plastic.

Less than $30 in PVC fitting and such including the bucket.

[OlJarhead]

Not sure I understand the ball?  If it sits inside the tube it will shut off all outward flow from the bucket so is this just to get water into the bucket?  How do you draw it out?

[UK4X4]

I think the idea is -

Dirty water runs off first- into the bucket- when the ball comes to the top the water gets diverted to the tank "clean"

[OlJarhead]

I think the idea is -

Dirty water runs off first- into the bucket- when the ball comes to the top the water gets diverted to the tank "clean"

Oh!  That's makes sense