Interstate GC2, keep or replace?

[garyb1st]

Our house GC2 batteries are almost 4 years old.  Last week while boon docking our Victron battery monitor indicated less than 12v first thing in the morning.  It also indicated about 7 - 8 Amps being pulled by our fridge.  So the actual voltage when not under load is maybe 12.1 - 12.2.  Still very low after one night.  Since our 12V fridge only draws 50 to 60 Amps a day, I was thinking the batteries must be almost dead.  A few days latter when hooked up to 50 amp shore power, the Victron was showing about 14.4V. I don't recall a reading that high anytime while boon docking. 

This morning, after about 10 hours with nothing running but the fridge, the Victron monitor showed that the batteries were just under 12.5V with no or minimal amp draw.  So that makes me think there is still some life left in the batteries.  So my questions.

Will our Honda eu2000i generator and a 100watt solar suitcase keep our batteries topped off?  That's while running a Mac computer that probably uses about 5 - 6's an hour while computing and the fridge that probably cycles on more during the day with frequent door openings.  The Honda runs maybe 3 or 4 hours and the solar generates about 6.5 amps an hour for maybe 4 or 5 hours.  Probably on the computer for 4 or 5 hours. 

Will the Onan 5500 top off the batteries?  If so, how long does it need to run?
 

 

[Mark_K5LXP]

the actual voltage when not under load is maybe 12.1 - 12.2.  Still very low after one night.

How long since "under load"?  A battery needs to rest for several hours before a static terminal voltage can give you a close SOC.

I was thinking the batteries must be almost dead.

12.2V under load is only around 25% DOD and resting is about 50% DOD.  Far from dead in either case.

  A few days latter when hooked up to 50 amp shore power, the Victron was showing about 14.4V.

That's absorption voltage, perfectly normal and expected.  It needs to be held at this voltage several hours to complete a charge.

Will our Honda eu2000i generator and a 100watt solar suitcase keep our batteries topped off?

Absolutely.  The question becomes, how quickly.  A 100W panel is not enough to keep up with a residential fridge but after a few days with everything turned off it could charge the bank and maintain the charge.  The genset easily can keep up with your loads, and charge your batteries at the same time.

The Honda runs maybe 3 or 4 hours [and the solar generates about 6.5 amps an hour for maybe 4 or 5 hours

So you're in deficit mode pretty much any time the generator isn't running, just a little bit less so with the solar input.  Which is what you'd expect for what you have.

Will the Onan 5500 top off the batteries?

It will do that, run all your stuff, and an air conditioner all at once.

If so, how long does it need to run?

Your converter should have the proper charge profile, which you can separately verify if you're not sure.  Your solar controller probably has a charge profile too but you don't have enough solar input to ever get out of bulk mode long enough for that to kick in.  Your Victron will tell you how many Ah's in and out, which is a pretty good indicator of what SOC you're at.  Generally it can take a good 2-3 hours to finish the absorption phase after all the  bulk amps have been restored, as indicated by a multistage converter switching from absorption to float mode.  Total run time will be determined by how many Ah you need to restore, what rate your converter is supplying them, plus absorption time.  Since it's usually not realistic to run your genset for that long every day to restore 100% of the charge, the usual protocol is to use the genset to restore the bulk amps and let the solar do the absorption phase during the solar day.  Since you have a fridge and other stuff running all the time you may never really get to 100% and if you did, stay there for long.  So you're always somewhere between empty and not quite full.  This is known as "PSOC" in the solar world, Partial State of Charge.  More detrimental to some battery types than others but it is what it is.  If your pack has sufficient margin you run what you run and recharge when you can.  To me it sounds like your batteries are doing just fine, you just need to know what the terminal voltage means under load and during charging, and learn what features and indications the Victron potentially and actually can tell you.  If you want to know battery merit you can do a measured capacity test and know exactly how many Ah your batteries are capable of as they sit today.  That might be a useful number to plug into the Victron to more accurately gauge remaining Ah/run time.  The residential fridge load means you need to run your genset longer/more often to keep up with it if you're concerned about maintaining a certain number of reserve Ah every day.  Or beef up the solar input so that at least during the day you're not in deficit mode as much.

I'm running a propane fridge so I've never tried it, but I've wondered with residential fridges how long you can go with the thing unplugged overnight.  I guess I could experiment with the one at home but it would seem that if it's not being opened it'd be good for several hours, if not all night before the temperature inside gets "too warm".  Guess it depends on how much thermal mass is inside of it plus whatever ambient temps are and the running duty cycle but that'd be something I'd look at.  If you can go even a few hours without the thing running that'd make your energy budget that much easier to manage.

Mark B.
Albuquerque, NM

 

[garyb1st]

Mark, a few things that make a difference.  Our refrigerator is an off-grid 12V compressor type.  On average, it's rated power consumption is about 50 amp hours a day.  Our computer is a 27" Imac desktop and probably uses far more energy than I estimated. 

We got home yesterday and left the refrigerator on to see how much power it consumed over the night.  So it was on for almost a full day before turning it off.  The voltage when I turned if off was 12.2.  After a few minutes the voltage increased to 12.37.  It could go up a bit more as it rests, but I'm satisfied that our batteries are probably OK.  In the future, I'll use the Onan to keep it fully charged. 

 

[Mark_K5LXP]

Our refrigerator is an off-grid 12V compressor type.  On average, it's rated power consumption is about 50 amp hours a day.

So based on your reported current draw it's running about 15 minutes every hour, or about 2.1 Ah per hour.  So if you were to shut it off for 8 hours you'd save about 17Ah but when you turned it on it would run 100% for a while to recover.  But if that's when the generator is running too, you're "banking" thermal storage.  Maybe worth it, maybe not depending on what other loads you have going on (like a furnace).

Our computer is a 27" Imac desktop and probably uses far more energy than I estimated. 

Your Victron can tell you precisely what it draws.

left the refrigerator on to see how much power it consumed over the night.
The voltage when I turned if off was 12.2.  After a few minutes the voltage increased to 12.37.

That really doesn't tell you a lot.  Using your Victron to count Ah will tell you exactly. 

I agree the batteries are probably OK but a capacity test will give you a hard number and you won't have to wonder or guess.  Or most importantly in my opinion, alter your lifestyle by self limiting the use of equipment based on a perception of how things are working.  If the batteries are on their way out I would want to know that.  If they're fine but I'm hitting their limit I want to know that too.

This topic came up in another thread about running the furnace all night and there were all sorts of responses about how to just put put more blankets on the bed or suck it up and tough it out with the heat off.  If I want to go somewhere and freeze at night I don't need a $100K 10 ton motorhome, I can do that in a tent.  I'm running that furnace all night, along with a TV, lights and whatever else because that's what motorhomes do.  If it doesn't or can't, fix it so it does.  That's what it's for.  There are those that put kilowatts of solar on the roof and bunches of expensive batteries in the basement to run their stuff.  Not my cup o tea but they decided they're going to run their stuff and made it happen.

Mark B.
Albuquerque, NM

 

[John From Detroit]

 

Will the Onan 5500 top off the batteries?  If so, how long does it need to run?

Depends on the converter but 6 hours minimum for a full charge from 50%..

Suggest the batteries be tested.. I use a load tester from harbor freight. this one has two meters (Amps and volts) and claims to be able to pull 500 amps. the proper pull for testing on those batteries is around 650 so the test is not 100% with my tester but it's close.

A battery store can do a much more elaborate test.

Mine lasted 9 years (interstate U-2200s) but likely should have been replaced at 8

 

[Kevin Means]

Gary, at night, if you reverse the polarity of the wires coming out of your solar panel, you'll have a lunar panel, and it will charge at night. It charges best when there's no moon and with a heavy cloud cover. I can't believe no one has thought of this before.

Kev

 

[garyb1st]

I've actually thought about this Kev but I'm not sure I'll be able to convince Maria to get up every 45 minutes throughout the night to reposition the panel.  It is however a great idea and if you're able to develop a reverse polarity switch you should consider selling it as the Day-Night Upgrade to your Solar Vector System.  Once I resolve the rather high kindling point of my fire starter muffins I plan on devoting considerable time to maximizing the effectiveness of my solar suitcase. 

 

[Heli_av8tor]

Once I resolve the rather high kindling point of my fire starter muffins...

I?m afraid this may be a lengthy process 

 

[Frank B]

There are those that put kilowatts of solar on the roof and bunches of expensive batteries in the basement to run their stuff.  Not my cup o tea but they decided they're going to run their stuff and made it happen.




Solar is quiet, both for the user, and those around the user.

 

[John From Detroit]

There are so many places where a solar farm could be installed and not loose so much as one square inch of tillable land.... I keep wondering why they don't do it..

Example.. Roof over parking lots/structures.

 

[SargeW]

Lots of good info already on supply and demand.  I don't boondock for long periods, so I haven't pulled the trigger on solar on the roof.  With our style of camping, we just run the gen for a few hours in the morning while making coffee and breakfast, then shut down and run again during making dinner.  If I can get to a 70-80% SOC and call it good. But I am running six 6 volt batteries and a 3000 watt Inverter with a residential refer. 

That gives me enough power to run everything I need to (within reason) and still be at 40-50% SOC in the morning. That 10,000 watt Onan is fairly quiet, and I try to stay away from others while  dry camping.

Now I know Kev loves to boondock, and his set up is perfect for him. He can go days without ever turning  on a gen unless he wants to microwave something.  It's just different strokes for different folks. 

All of your usage numbers sound perfectly normal and adequate Gary. With everything turned off if you were at mid 11 volt range, then it may be time for a battery swap, but I don't think you are there yet.

 

[Frank B]

Our house GC2 batteries are almost 4 years old.  Last week while boon docking our Victron battery monitor indicated less than 12v first thing in the morning.  It also indicated about 7 - 8 Amps being pulled by our fridge.  So the actual voltage when not under load is maybe 12.1 - 12.2.  Still very low after one night.

FWIW, I just ran into a low voltage problem on our unit as well. As it was rather sudden, and our batteries are only three years old, I decided to check the wiring. I found a loose terminal on one of the batteries, and it had been hot. After I cleaned up the terminal and the wire connections, and then tightened all of the terminals, voltage is back up to normal.

 

[Old_Crow]

There are so many places where a solar farm could be installed and not loose so much as one square inch of tillable land.... I keep wondering why they don't do it..

Example.. Roof over parking lots/structures.

The VA hospital in Little Rock, Arkansas has about 1/2 of it's parking under solar panels.  The Pima Air and Space Museum in Tucson is about the same.

 

[John From Detroit]

Since I have already sent this idea to folks who can act on it .....

You know about Covered bridges (No they were not covered to protect the bridge from weather. but for a different reason.. but I'll let you have the fun of finding out what it was)

How about we cover the  roads with Solar panels.... Might even cut down on crashes as we could also provide a nice even LED light under the panels at night and help shed rain and snow.

 

[Mark_K5LXP]

How about we cover the  roads with Solar panels....

http://theconversation.com/solar-panels-replaced-tarmac-on-a-road-here-are-the-results-103568

 

[keymastr]

I carry a small 1000 watt inverter generator that is about the size and weight of a bowling ball in it's bag for $200 on Amazon for those times when I need a charge. Quiet, small, light, cheap and runs for 5 hours on a pint of gas. Won't run my AC or microwave but plug it in to my shore power cable and it runs the on board charger just fine.

 

[Frank B]

How about we cover the  roads with Solar panels....

http://theconversation.com/solar-panels-replaced-tarmac-on-a-road-here-are-the-results-103568

There is also the issue of trenching the road every few feet a week after installation to fix or install a pipe. 

 

[Domo]

The first question is whether the batteries are any good.

RV batteries last about 5 years with normal usage. My 12 year old MH is on it's third set of coach batteries. 5.5 years out of the first two sets.

The first thing I'd do is go to a battery shop and have yours load tested. They'll tell your if they are failing or not. Anything else is playing with number and conjecture.

The second question that seemed to appear is what current draw you should have from the fridge - I'd say to get the battery/power problem figured out, then tackle the fridge/draw.

I didn't read much past the confusion being sewn about fridge draw...

 

[garyb1st]

The fridge is a Unique Brand, 12V off-grid refrigerator that uses at most 1/2 the energy of a residential.  Compared to a simiilar sized 13 cu ft residential refrigerator is uses maybe 1/3 the energy.  So the fridge draw is not the issue.

FWIW, after a week sitting unplugged, the voltage shown on the Victron is about 12.4.  That was after the fridge was left on for one full day before we removed all the food.  So I'm pretty sure the batteries are OK.