OFF GRID POWER; various thoughts on...

Started by MountainDon, January 13, 2009, 02:18:39 AM

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Is the generator used as a portable device? No permanent connection between it and the battery charger?
Is the generator output also connected to any cabin wiring, service panel, etc?

Is the power output from the inverter used directly via plugging into the inverter AC outputs?  Or does it feed into a service panel of any sort?

Looks like maybe a 12 volt battery system?  The distance between batteries and charger and batteries to inverter would be less than 10 feet? #4 AWG wire would be more than adequate.

No PV panels?  No charge controller?

The fuses should not be in the same enclosure as the batteries just in case one blows when hydrogen is present in a combustible mix, unless the fuses are fully encased to keep the arcing within a shell. A fast-acting class T fuse is best for use in a DC line connected to a battery bank. They can be mounted directly to a battery or in a case. Others may have to be mounted in a case to contain arcing. Fuses / breakers must be rated for DC use when used in DC circuit.
Just because something has been done and has not failed, doesn't mean it is good design.


The generator will pretty much permanent in an enclosure. Battery charger is an Iota plugged into the generator.  No hard wiring of the generator to the cabin.

For now I will be plugging into the inverter to run a fan and charage phones.  When I get a bigger inverter it will be connected to a service panel.

Yes 12 volt system...battery bank is four 6v golf cart batteries. Will be 5 foot from batteries to inverter.

No pv panels or charge controller yet.

I got class RK5 time delay dual element (FLNR 50) 125V DC fuses.  Will those work?

Thanks for the help!


Generator.  Used as described it more or less is much like using a portable generator on a job site to power tools. According to OHSA regs that does not need a ground to earth.

Inverter. Used as described it would be as intended, more or less a portable device. No need to have an earth ground. Things change when a service panel is introduced though.

House wiring, done according to code, has a bond of the neutral and ground at one place in the system. That is usually a green screw that bonds, or connects, the ground and neutral within the service panel. If you connect a MSW inverter to such a system, the MSW inverter will be toasted, the magic smoke is released and the MSW inverter is no good anymore. It seems odd to me but any MSW inverter I have checked out has 60 volts between ground wire and neutral and 60 volts between hot and ground. Add those up and you have 120 VAC. But introduce a N-G bond and you produce smoke.  PSW, pure sine wave, inverters designed for hard wiring should not have an internal bond and should be okay wired to the typical bonded service panel. I don't know about PSW inverters with built-in outlets. ???

Small portable generators with built-in outlets,  often have the neutral conductor bonded to the generator frame, which equates to a neutral-ground bond. In that case, when the generator is connected to a service panel there should NOT be a bond in the panel.  My Honda EU2000i is one w/o the internal bond. But the Honda EB200 does have a N-G bond. It can get confusing.

Fuses. I'm not familiar with the ones you mentioned. The idea of the fuse is to protect the wiring, not the charger or inverter. A lead acid battery can supply thousands of amps with a short circuit. If the time delay is too long the wiring could be damaged.  Time delays are most often designed for use with circuits that power motors that may have a large startup surge, then fall to normal ranges. So I can't say those are good or not.

The NEC used to exempt 12 volt systems from needing a ground to earth; higher voltages required an earth ground of the battery / DC negative. 

Once PV panels are installed that has some rules too. PV systems are now supposed to have a GFP (ground fault protector).  And with panels the lightning issue can become a serious concern and will need protective devices and good grounding.

I am not an electrician so take what I stated above as a place to start your own research from.
Just because something has been done and has not failed, doesn't mean it is good design.


Thanks Don.
My Ryobi generator has a "neutral floating" ground lug on the front. I should probably start with reading the manual to see what it says.  d*

I double checked the specs on my fuses. I got them from AltE it says they are good for inverters up to 700 watts so I think I'm good there.

My electrical knowledge is very little.  One of the big reasons I'm starting with such a small system. I'll definitely continue reading up and learning more.

Dave Sparks

Is there a solar charge controller? I probably missed this as it is changing before my eyes d*
"we go where the power lines don't"


Nope. No solar yet. I'm a total electrical I'm starting very basic and slowly working my way into things.


In July of 2009 we installed golf cart batteries (12 - 6 volt in a series/parallel 24-volt arrangement) for the then new solar electric system. Today I replaced them. Not bad; 9 years service.

Last year I had noticed some of the cells were not coming up to the full charge specific gravity reading (1.265)as quickly as the others, no matter what I did. In fact, some cells would never make it past 1.225. This spring water use went way up on about 10-12 cells. Yesterday it was obvious most of the batteries had reached the end of their useful life. Several cells had very low sp. gr. and no volts. That resulted in cooking away the water in one series string during our three week absence to Canada.

Over the years we have actually reduced the amount of energy we use at the cabin. No more TV; we use a laptop with a TV tuner whenever we want to watch something. LED lights have supplanted the CFL lights. I think 8 batteries will be more than ample for our needs.

I wanted lithium-ion, but stayed with the tried and true, familiar flooded lead-acid. Considerably less out of pocket, even with the liklihood of longer service life and much reduced maintenance.
Just because something has been done and has not failed, doesn't mean it is good design.


Good to hear MD! :)

Only 8?  For the cost (to me anyway) I'd keep the 12 because it gives you longer discharge time to 20% DoD without sunlight which means more days in the winter to not worry :) but you know what you are doing, it was just something I've pondered since I use more power than you.  Just posted some on my setup in my thread, but in short I use about 50AH to even 55AH overnight so without sun I can use more than 20% of my 660AH bank in one full day (or darn close to it but I can conserve more if need be and get by for about 36hrs  on 20%) so my bank is a tad small but I'm upping to charging power by several factors which I think will reduce gen use.

Dave Sparks

Hey Don, Did you use the costco golf batts? I recently did for a friend as they are easy to get and pretty cheap. We had to go to 2 different costcos to get the same date code.


We have 4 people staying here who were evacuated/lost power and they go home today :) The town has placed dumpsters everywhere as all of the food is spoiled. Yuk in 100F heat.. Not good times :'(

This has been going on for 15 days/50K acres but we had little wind. The Carr fire in Redding has done 80K acres in 3 days because of the 70 mph winds.  7 people dead and 35K evacuated. Quite few homes burnt.

We never planned for any help in a fire and designed for it.  We use to load the truck in case we decided to leave but have stopped doing that as it is more dangerous on the roads with all of the dead bark beetle ponderosa.  Nasty business. Still Love it here but some big changes are coming or the whole west is in trouble.
"we go where the power lines don't"


Hi Dave, glad to hear you are still safe.

Batteries:  I used Sam's Club as the clubs near me carry GC-2 batteries and the Costco's do not. Go figure? I got lucky and found a shelf full of same batch batteries.

Fires: We are very happy that the FS began some very serious thinning around us a few years ago. Google Earth/Maps now has recent images that clearly show the vastly reduced tree density. That should help a lot if, or should that be "when" another fire comes too close.  Between the FS contractor thinning and the wildfires (3) that have been close in the past few years I am hopeful.  A nephew used to live in Redding. Real bad there.

We have had maybe an inch and a half of rain quite recently   :)

Just because something has been done and has not failed, doesn't mean it is good design.

Dave Sparks

Rain ! Maybe in October... Day 22 tomorrow of being indoors much more than I like. Smoke on the Water :P 
"we go where the power lines don't"


The new rainfall amount for the Jemez is now 4.21" of rain since July 17    ;D   

However, most of northern NM is still in what is called an "exceptional drought"    :(
Just because something has been done and has not failed, doesn't mean it is good design.


OK, I have been pondering something of late:  When you are at your cabin using power in an off-grid scenario as I am it seems to make sense to have the charge controller (s) go into absorb long enough to push the total Amp Hours used since fully charged back into the bank before going into float.  If in my case you tend to use between 45 and 65AH overnight it stands to reason that Absorb, if pushing 40amps into the bank, should run for about 1 1/2 hours (maybe more?).  Once Absorb has run long enough to put the bank back to 100% (by the meter not SG) then it makes sense to have it float as long as possible as this will provide power during the day to run various items (fridge, fans, radios etc) while maintaining the bank until the sun goes down so you have full capacity before the night starts -- right?

OK so now here is the real question (though the above poses some too):  What about when you leave the cabin and the system will be sitting dormant for some time?  For example, my system only really uses about 1 or 2 amp hours overnight when I am not there and the inverter is off.  I run two computer fans in the back composter / water entrance room and a bilge fan/blower for the solar heater.  Even if I used a total of 6AH overnight (close to 1% DoD) the system doesn't really need to Absorb for so long -- at least to my thinking.  Wouldn't it be better to drop Absorb to a shorter period and extend float?

The Morning Star controller can provide 16amps at full sun on the old panels and allows me to set float as well as aborb extension times but the Outback does not (I am actually disappointment in the Outback a little because of this),  So, would it make sense to only use the smaller bank when I am not at the cabin?  To run a diversion load with the Outback which has 6 305w 8amp panels running to it that really aren't needed when I am not there?

Or, would it make more sense to leave the inverter on to maintain the generator battery and draw a small load overnight (I'd have to do the math but I'm guessing 25AH or less) just so the bank is being used?  The problem, of course, with this is when the clouds and snow come and there is no solar charging for days and days.  In that case the generator will run often or I'll have to disconnect the system when the time comes (which could be any week now).

Just looking for some ideas and thoughts on this. 

Oh and here is what I am running now:

Array one:  3 205w 12v panels in series feeding a Morningstar MPPT charge controller.  Max battery charging about 16.5amps @ 29.6vdc -- pretty much infinity adjustable for Absorb and Float times.
Array two:  6 305w 24v panels in series parallel (two panels in series, 3 sets in parallel) feeding an Outback Flexmax 80 charge controller.  Max charging should be over 40amps but I've not seen it do that yet and need to calc (which I've done but not sure where it's hidden).

Battery bank is 12 GCB's from Costco providing 660AH @24vdc
Inverter is Aims 4000w pure with 55amp charger
Magnum Research Autogen switch (max volt start point is 24v and max run time is 5 hrs)
Generac EcoGen 6kw

Nate R

I've had similar thoughts recently.
I've also read that absorb should be longer than you'd think, but would be limited in solar applications by day length.

Some CCs adjust Absorb time based on how much the battery was discharged. The Morningstar will allow an absorb extend based on the low voltage the night before, right? There might be an option in there....Do a short absorb unless the battery was discharged below X, and then add 2 hours then?

Other CCs have the ability to adjust absorb based on the ending amps.....Morningstar doesn't do this IIRC, but I think Midnite has the option on some controllers. Not sure about Outback. But that might be another solution, absorb being based on end amps (Because the amps taper at absorb voltage as the battery gets closer to 100%). This would accommodate for use or lack thereof overnight, having a short absorb time when you're not there.

Not sure which Outback you have, but it looks like some of them DO have the end amp option:

Nate R

Hmm, good discussion on this very issue here:

Also, I can't think of any reason you'd NOT want the batteries to float until sundown once absorb is completed.....


Thanks or the replies.

The MS does allow absorb extension based on voltage settings so I could set absorb to go to any additional length of time based on voltage.  This is 'ok' since voltage on the string doesn't really represent SOC since under a load the voltage drops and then rebounds after the load is off.  This is why the battery folks say not to bother using SG readings unless you've allowed the batteries to rest at least 12hrs but 24 preferred.

I could set the MS to run a short absorb and extend at say some voltage that represents 80% SOC perhaps.  But I can float the MS all day too so really, leaving it at 1.5hrs Absorb and float for 3+ should use all sun.

The problem I see is that the Out back only allows an adjustment to absorb time.  So I can set that to absorb for 1.5 hrs (which is about right under use) and shut off at 0amps (batteries are charged) but with the MS sending amps also this might confuse the OB and I can't set it to float longer than 1 hr


Quote from: MountainDon on August 03, 2018, 03:58:06 PM
The new rainfall amount for the Jemez is now 4.21" of rain since July 17    ;D   

However, most of northern NM is still in what is called an "exceptional drought"    :(

If I had a way to send you some rain I would.  We are getting close to 50" this year. Glad it wasn't snow .  That would be close to 50 feet. :(


We are having some rain now and on-off over the past couple of weeks. Could still use some more.
Just because something has been done and has not failed, doesn't mean it is good design.


So Outback responded with "there is no way to change the float time on our controller".

??? ???  Not sure why you would do this and must admit, I'm regretting my decision to move to Outback at this point.  My Morningstar is far more flexible.

Dave Sparks

Who is telling you that you can't use a hydrometer?
I think you are mixing up resting voltage? SG can be measured anytime!

SG is the one strength of this slowly fading technology with quite a few weaknesses these days.
"we go where the power lines don't"


Not that I can't, that it doesn't mean much unless the batteries are at rest long enough.  Other than making sure they are all about the same SG reading.


For sp gr they don't need to be rested. Perhaps the sp gr readings should not be taken when being rapidly charged or discharged so to minimize gassing and the possibility of bubbles adhering to the float.
Just because something has been done and has not failed, doesn't mean it is good design.


Perhaps the confusion on my part is that Trojan told me to not take the SG readings unless the batteries had been at rest for at least 12hrs because they would not represent a true reading.  Meaning that under a charge or load the SG reading isn't the same as under rest.

Same with looking at voltages to decide a SOC.  The voltage under load does not represent the SOG vs the voltage at rest does

Dave Sparks

Just because someone tells you something???

Due diligence is required.

Sorry, but SG can accurately measure state of charge, anytime! Even with bubbles there are ways to get a good reading. Been doing this a few weeks ;)

I run into this sometimes with Outback, Schneider, Midnite etc. There are new people who really are not up to speed (especially in Support) and you can get information that is "not quite right".  You can digest it faster if it is from Engineering, most of the time....
"we go where the power lines don't"


New system build

I am new here and am working on setting up a small solar system to run my deep water well off of in the event of power outage on my small homestead which my area is known to have from time to time. A few years ago we had a pretty heavy ice storm and power was out for about 2 weeks. The people who lived in this home built house said they melted ice sickles for drinking water. My wife said she did not want to go through that so we installed a 22KW generac so we would have power.

I have been sitting on four brand new Renogy 300 watt solar panels for about 5 years (still in the box) and we have decided after watching our electric bill continue to rise month after month to set them up. I bought these panels to use on an off-grid cabin that I own in the mountains but never installed them because there is a theft problem there and I'm afraid they will be stolen. I have been using a EU2000 generator to recharge a 12 volt battery bank there for the last 3 or 4 years and it has worked great considering I'm not up there very often.

I was helped by @MtnDon (Thank you again @MtnDon!) on another site 4 years ago to design the solar plan for that location so I now am pulling out the plan and readjusting it to set up a small non- grid tied system here on our small homestead to run the well if need be but also maybe when not using it for the well to run a fridge or some outbuilding lights etc. and cut back on our grid use.

Here is what I own so far: Four 300 watt Renogy solar panels, one Midnite Kidd charge controller and I also have about 100 feet of copper 2AWG wire I bought from a contractor who had left overs from a job.

I have found a dealer who is offering me a great price on eight Trojan T105 batteries for $116 a piece ( which I think is a great price) and I'm looking at a AIMS 6000 watt pure sine wave inverter. 110/220 output ( this is changeable for sure) What I'm trying to figure out is do I run this in 24 volt or 48 volt?  My distance from panels to Kidd will be about 20 to 30 feet. The distance from my controller and panels to well is about 50 feet. 

My well pump is 230 volt and I can not find any info on what the startup draw is or the running draw. I guess after searching around for info that a 4000 watt or 6000 watt Inverter/charger should handle the pump.

Any ideas from you who are experienced would be greatly appreciated. Other places I have mentioned this system at have really pushed the Lithium Ion batteries at me and I know that I can not afford to go there even though I would love some so maybe we can avoid that discussion if possible.

We hope to be able to double the panels and the batteries after this system is up and running so information on how to keep this system under it's limits so we can would also be great!

Here are the specs for my panels:

Maximum Power a t S T C ( P m a x ) 300W
Optimum Operating Voltage (Vmp)   37.46 V
Optimum Operating Current (Imp)   8.01 A
Open-Circuit Voltage (Voc)              46.12 V
Short-Circuit Current (Isc)              8.56 A