Basics of Off the Grid Help

[nycabin]

I'm in need of a starting place. I have a cabin in upstate NY and every year my farther-in-law lugs two marine batteries back and fourth from Florida to NY. He would like to keep the batteries there so I need suggestions to keep them in good condition throughout the winter. I'm thinking of a solar system, batteries and all the necessary items to put a system in place. Can someone point in the right direction.

One battery is used to start a generator and the second to run a few DC lights and a 12 volt pump. Both are charged when the generator runs. Overall the impact on the batteries is very minimal and all I need is a system to keep them throughout the winter with temp ranges down to -20F.

Your help is appreciated.

[Cariboocoot]

Welcome to the forum.

What you've got there is a couple of RV/Marine batteries probably no more than 100 Amp hours. This would be normal.
To keep them from losing power while sitting (the dreaded self-discharge) does not take much: less than 3 Amps each. To get that kind of power (and it does not need to be constant; on those rare occasions when the sun shines will do) requires about 40 Watts of panel and a small charge controller. Probably the best bargain would be connect the two in parallel when they're being stored and use a Kyocera 135 Watt panel (you really only need 80 Watts but the smaller panels can sometimes cost more - look for bargains) and a small PWM type charge controller.

Small panels: http://www.solar-electric.com/1to39wasopa.html (The 135 Watt is about $300, just so you know.)
Small charge controllers: http://www.solar-electric.com/stpwmchco.html

If there were grid power available a small charger on a timer that comes on about once a month would do.

[Photowhit]

What Coot said, plus if you have a basement, likely it won't reach much below freezing. Also it's not uncommon for this type of use to mount the panel vertically facing south for winter time exposure and least likely to accumilate snow or debris.

[SolaRevolution]

nycabin,

Even a few Watts of PV can help keep your batteries from dying from self discharge. As long as they don't freeze, the cold storage temps will help too. I don't know what your entire situation is, but it could be ideal to have enough PV for the battery "finish amps".

(Some of this was part of another discussion. The system was fairly large and had an Auto Start for the generator but the idea is the same)

Think of how the battery will be charged and discharged. (assuming your system components are properly proportionally sized)
It is likely that you will run the generator sometimes manually, and sometimes automatically.

When you first arrive at the cabin, the system will have been slowly discharging since the last time someone ran the generator. If the system is to be unattended for several months it should be completely turned off. Any device which is attached without a hard disconnect will be drawing some level of current. When you arrive at the cabin and make yourself at home you will draw energy which can only be replaced by generator run time. You could stay for several days or you could leave later the same afternoon, but in the end, if you do not want to leave your batteries at some degree of discharge, you will need to run the generator as the last thing you do before you turn off all of the breakers and leave. You will have to plan what time you start the generator in order to leave on time if you are on a schedule.

Keep in mind that finish charging is the slowest part of the charging process. It also is the least efficient use of generator fuel.

If you stay for weeks or longer you can cycle your battery SOC (state of charge) between 60% and 90% for several days and do a finish charge once a week or so. If you start your generator at 60% SOC your batteries should be able to take in your charger's full capacity. If your charger is sized for 15% of your battery's C20 rated Ah capacity, you would run your generator for two hours and be close to 90% SOC. As charging voltage reaches the bulk voltage setting, the charging current begins to decrease (otherwise voltage would continue to rise). It will take longer to charge above 90% because the batteries can no longer absorb as much current.


Alex Aragon

[icarus]

A fully charged FLA battery won't freeze till below -40. Even partially charged, it won't freeze until it is quite cold. A small charge regimen will keep batteries topped up enough not to freeze.

Tony

[waynefromnscanada]

A fully charged FLA battery won't freeze till below -40. Even partially charged, it won't freeze until it is quite cold. A small charge regimen will keep batteries topped up enough not to freeze.

Tony

Exactly! You just need something to counteract the normal self discharge, so they stay topped up. A small solar panel that won't be buried under snow. I mount mine vertical in winter, on a south facing wall. The snow won't collect on them and the sun is low in the southern sky, so all is good.

[nycabin]

Thanks for the help as you are heading me down a path that will make life much easier.

Two questions:

Would golf cart batteries hooked in series be better than the marine batteres and should a I use a mppt or pwm. I think these are similar units with the mppt being more sophisticated (corrent me if I'm wromg).

[BB.]

Yes, golf cart deep cycle batteries will probably last longer than marine batteries (which are sort of 1/2 way between car and deep cycle).

I prefer to get larger (Amp*Hour) batteries and put them in series vs a whole bunch of 12 volt batteries in parallel (best is usually one string in series. And I would try to avoid more than 2-3 strings in parallel).

Some battery information (post from Working FAQ thread):

... Victron has authored a great paper that covers some interesting material on charging forklift batts: http://www.victronenergy.com/upload/...yUnlimited.pdf

From Mike90045,

A nice 54 page book on batteries--even includes a Battery 101 primer (series/parallel connections, etc.) (see original post for attachment):

Only if your battery stays below 70% charged for more than 24 hours. The lead sulphate crystals will harden, and not dissolve during discharge. This is called sulphation.

Say you loose 1% capacity each episode, and one episode a week. In a year, you have 50% degradation of your battery. That's what insufficient charging gets you.

See attached battery file for in depth explanation.

Sulfation - Formation of lead sulfate crystals on the plates of a lead-acid
battery.

Here is a nice thread on why I/we suggest not paralleling batteries if it can be avoided:

Series rule of thumb

-Bill

[Cariboocoot]

Thanks for the help as you are heading me down a path that will make life much easier.

Two questions:

Would golf cart batteries hooked in series be better than the marine batteres and should a I use a mppt or pwm. I think these are similar units with the mppt being more sophisticated (corrent me if I'm wromg).

The type of battery used depends on what you do with it. For starting the generator the RV/Marine is fine (and auto type might be even better, but not significantly). For the lights and pump, so long as the battery gets recharged promptly that won't matter either. The need to switch to deep cycle is dependent on how much the battery will be drawn down and for how long between charges. Factor in the cost and availability and you're probably better off without the golf cart units in this case.

For the amount of charging you're looking at here there is no need for the extra expense of MPPT. The PWM controller will work fine, and be hundreds of dollars less.