Low battery-how to recharge

I have 4-100 watt solar panels and two 12 volt marine batteries. We have had one solid week of rain and no son. Last night I turned on my lights (9 watts total) and they flickered and were dim. I figured the batteries must be getting low so I'll deal with the problem tomorrow and went to bed at 8:00 p.m. At 11:45 p.m. my inverter started beeping. The only thing I had on was a cell phone charger. I turned off my inverter and went back to bed. So my problem is now how do I charge my low batteries without blowing everything up and having no sun until next week (so the weather people say). Are there any resources on how to recharge low batteries -videos, articles-I want to do it right.

And

To prevent this from happening or lower risk of running out of energy is to add more batteries. What is the limit on batteries I can hook up?

I dont use a lot of things but realized the laptop charger and cell phone booster are energy suckers-Lights -only 9-15 watts on at a time for 8 hours a day=72-120 watts, Cell phone charger about 6 watts for four hours=24 watts, laptop charger 57 watts X 8 hours=456 watts, cell phone booster 24 wattsx24 hours=576 watts, and a tankless water heater-2wattsx24=48 watts idle but while in operation-117x1 hr=117=about 1,341 a day. I guess I know what are the energy suckers

So my panels can get 1,200 watts a day if I go by 3 solar hours a day (our shortest day of the year).

I have a generator that I can for back up but I need my laptop and cell phone charger and cell phone booster for work as I work from home due to COVID.

Any helpful feedback would be greatly appreciated. Thanks in advance!!

I see no harm is adding a battery.

Hi Diane;
Yes adding another battery will help.
But when the sun doesn't shine you will need your generator to run several hrs a day .
Its just how it is with solar power. At least until your system is larger than your needs.

Buy a good modern battery maintainer.   Any time your genny is running it should be plugged in.
Be sure to unplug it when not using the genny.

thomas rubino wrote:Hi Diane;
Yes adding another battery will help.
But when the sun doesn't shine you will need your generator to run several hrs a day .
Its just how it is with solar power. At least until your system is larger than your needs.

Buy a good modern battery maintainer.   Any time your genny is running it should be plugged in.
Be sure to unplug it when not using the genny.

Do you know of any good videos or articles on how to hook up the generator to the system? Where do I even plug the generator in at? I have a breaker box that is connected to the inverter and the inverter is connected to the batteries.

Hi Diane;
It depends on your inverter. Larger more expensive ones usually have an input spot for generator power.
Smaller ones do not.
I suspect you have a smaller one with no spot to hook in a generator.
If that is the case then just use a good extension cord.

thomas rubino wrote:Hi Diane;
It depends on your inverter. Larger more expensive ones usually have an input spot for generator power.
Smaller ones do not.
I suspect you have a smaller one with no spot to hook in a generator.
If that is the case then just use a good extension cord.

Um.

If you have an inverter-charger, it will have a way to hook up AC power to do the charging part. See the manual. Be careful.

If your inverter doesnt do charging, you need a battery charger. An extension cord is... not going to do anything desirable without an appropriate charger being involved!

I have been unimpressed with the only lead-acid chargers I have used, so cannot suggest one.. you will want to size it for the maximum charge rate that your batteries can handle, as long as that is within what your generator can handle, to minimize generator run-time...

ive read that golf cart batteries last longer and hold charge real well when compared to car or marine batteries, but I'm no expert. when the sun comes back out won't the batteries you have just start charging again?

I was recently talking to an old friend who knows a little bit about batteries and he was saying that surplus submarine batteries may just be the best solution to off grid solar but fork lift batteries are also a great solution for lots of storage capacity.

Thanks D. Nikolls;
My original response talked about battery chargers to plug into that extension cord.
That response got partially deleted into the one I posted... Don't ask me how...
So yes Diane, use a battery charger with your generator.

If you are uncertain about charging batteries vs damage to your system. It sounds as if your system is relatively simple. You could disconnect the system from your batteries and then charge them.

That's a worrisome situation. Lots of good advice above. Hope it doesn't sound man-splainy, because it's really not -- it's just difficult to try to help long-distance.  

Your panels are still sending a small trickle of charge to the batteries, even in overcast conditions. It sounds like your inverter cut out at a low voltage to protect the batteries from discharging dangerously low; that's good.

If you disconnect from the inverter and attach a battery charger powered by the generator, please make sure you charge both batteries equally. This is important from a safety persective. It would be enormously helpful to see a picture of the connections in your battery bank and your breaker system.

In the bigger picture, I get the impression that you have a lot of loads for 400 watts of generation and 2x12VDC batteries. From my experiments, I find that I always need at least 50% more generation and 50% more battery storage than I expected. Some would argue that it's always 100% more, and I think they are more-or-less right. Something to consider.

Luck!

Now that I have an actual keyboard, a couple more thoughts.



1) Adding more batteries:

You can keep adding batteries until you're happy, if you are running a parallel setup.

In series, mixing is a bad idea. See here https://rvnerds.com/2017/08/07/electrical-myths-part-3-mixing-batteries-different-agescapacities/


There is increased risk as you add batteries that a damaged or failing battery will end up damaging other batteries..



2) Looking at your loads... keep in mind that the inverter itself may be drawing a bit, even without other loads. If no important loads present at night, no need for it to be on..




3) What sort of charge controller do you have? An MPPT controller may help with cloudy day performance if you are using a PWM unit currently.



4) I strongly agree with Douglas, that's a lot of load for the system.

I started with 2x 300W panels and a pair of 100AH 12V batteries in series. It was NOWHERE near adequate in a pacific northwest winter, even for very minimal loads. Adding 2 more panels for 1200W total was minimal help. I didn't add batteries because I had a 400AH LiFePO4 bank on order, but the wait was many months longer than I expected...




5) Generator use; several hours a day is hopefully pessimistic..

A typical charge rate for lead acid is 0.25 x rated capacity. So, if your batteries are 100AH, and in parallel, you could charge at 50A. Since you should NEVER discharge below 50%, you would have 100AH total usable capacity.

It would take you about 2 hours to charge from 'empty' to max, IF you have a charger that can sustain this rate, and a generator that can power it.. but that is only about 600W, so even allowing for conversion losses it would hardly be a massive generator.

If you are upgrading to a bank of 4x 100AH batteries in parallel, you would instead want a 100A charger in order to keep the generator runtime from doubling...




6) Solar input: your panels can get 1200W a day... if they have 3 hours of noon-time sun, and are mounted at the right angle for max efficiency at this particular time of year! In fact if it is very cold you might exceed 400W for a little while at noon.. but the point is even 1200Wh is a lot to expect in the real world on that rare sunny day.


Hope something in there is of use...


(Thomas, I've done the exact same thing!)

i think you would like to add something like this --->
sealed battery

--> a solar generator/ different type of sealed battery

--->charger

or this-->
external charger

adding another battery to your battery bank will also help, add 2 or more if you can.

those above...the sealed batteries, usually have inverters in there. you can plug things right into them, and either use solar power or regular power to recharge them.
alternatively if you travel alot, you can recharge them through a car lighter port, the DC plug in a car or off your car battery.

if you have somewhere with access to the grid, you can plug in and leave it overnight to recharge that every few weeks to 100%
then when you bring it back to your system it will boost everything.

you can either use the jumper cables to attach to your last battery in your battery bank, or usually they have input plug ins for solar or DC input....to connect it into your system. but you can also remove it, have it be a standalone and mobile unit, recharge on regular outlet at someone's house.
anywho i dont know what your budget is like, but some thoughts. the ones made as jump starters are less expensive than the ones as "solar generators" and they are basically the same thing, a sealed battery...usually with a 400-1000W inverter...these are some of the bigger ones, they make them cheaper, but you want as much watts as possible, or get a smaller cheaper one with only DC output...then plug your inverter into that.

Diane Maldonado wrote:

Do you know of any good videos or articles on how to hook up the generator to the system? Where do I even plug the generator in at? I have a breaker box that is connected to the inverter and the inverter is connected to the batteries.

it's hard to answer without all the specifics because theres a lot of different options and set ups. most of the different components are sometimes combined, and some have multiple inputs and outputs.

as above i think your best bet is to get one of those mobile power units/sealed batteries, and also have the option of using grid power at someone's house or elsewhere to charge that to full, that will give you power for your laptop and cellphone charger.
or a smaller mobile unit/ power pack / external batteries, they are called different things but are similar. charging that to full at someone's house, you could get a few days of charging your phone.....and any other USB powered things.

i used to have a very simple one that would work off of batteries, almost curious to look it up, although they make better ones these days. but this one could run on regular or rechargable batteries, and was like days of usb powered speakers and cell phone and anything else USB powered. that was nice cause i could recharge the batteries once a week or so, and in a pinch have a stash of regular batteries too.

but anywho if you want specific help, we need more details.
adding a battery in is not that hard. you need the connector, you can buy them at an auto parts store, you can even buy a bunch of wire and buy just the connector part that goes on the battery and wire them up. you can just take the connectors off of one, put those on your new battery (observe + or - obviously), use the new connector to connect to the first one.
if you put in a freshy full charged battery your whole system will get boosted.

alternatively you can take off one of the batteries, and go charge it elsewhere, as likely all your neighbors and every backyard mechanic has a trickle charger to let you leave it over night. this option kinda sucks, but it is free =)

I like the idea of a separate backup unit for critical stuff (cell phone, emergency lighting).

Consider also the value of direct to DC options, bypassing the inverter. The main batteries are not fully discharged, and can still power some minor, critical loads through a direct connection.

I would be pretty careful about connecting a fully charged new battery to a discharged battery system, though. The super-intense charging of the existing batteries, possibly boiling the electrolyte, could generate a lot of corrosive and explosive hydrogen. Slow and steady is always best.

As mentioned above change the charge controller to an mppt model preferably a name brand unit. Even on cloudy days you will generate a good portion of your array wattage per hour. A pwm you get nothing without good sun. Looking at the loads I would turn off the cell booster at night for the best bang for my buck. If you do not want to buy a generator I have had good success running a battery charger off of a cheap inverter hooked into a running car's battery. Not the most fuel efficient solution if you have a truck but it's quiet, has a starter and will get you out of a low battery situation, so for occasional charge ups it is fine. I like the iota 12 volt chargers myself.
Top of my head...
Cheers... David

I'm going to diverge from the group here and say the adding parallel strings of batteries is not a great idea.  For a lead acid battery to live a long healthy life, you should try to not pull it down below 80% capacity and then charge it back as fast as you can when you can. So basically you only get to use 20 percent of your battery. Now most of us probably run down to 70 percent and 60 percent on bad days just because the convenience of electricity outweighs the harm we know we are doing to the battery bank.

If you add parallel strings of batteries in order to obtain higher capacity, you run the risk of of not being able to charge the bank back up at all. Without a larger solar array, you could get into a pickle one day of needing to pull out 50 percent of your battery bank and a month of good sun cannot get your bank back above 70 with charging your batteries plus your daily load.  A perpetual state of under charged batteries is really hard on their life.

To correct this you need more panels. Then you end up with so many panels that on good days, your batteries are charged by 11am and your making so much power that you cant use it.

There are really only two solutions to this. If you want to be off grid, you must have a generator. This has maintenance costs and is expensive to run, and I'm going to say it, they will put out far more pollution then burning coal at a power plant to produce the same amount of power.

The other better option is grid tie.  I've been off grid for 8 years and have sworn that the electric company is evil etc etc.  I have changed my opinion on this 180 degrees and now I believe that the ONLY option to have the most efficient solar system is to be grid tied with battery backup.  For a small monthly fee/ service charge. Mine is 27.50 usd and is pretty high around here, you are basically renting a battery of INFINITE capacity, NEVER goes bad and has ZERO maintenance issues, and very minimal losses.  When you batteries are charged at 11am, instead of you panels putting out zero electricity, you get to charge the grid at full capacity.

There is a point where batteries simply cannot accept any more electricity as they get up to 80 and 90 percent charged. You may have an 80 amp solar charger and 2000 watts worth of panels, but when your batteries can't physically take more the 15 amps in full sun it's almost sickening and extremely wasteful.  Grid tie fixes this and increases the efficiency of the system 10 fold. WITH GRID TIE YOU CAN ALWAYS CHARGE 100 PERCENT OF THE SOLAR PANELS CAPACITY!   That's a huge statement that should be yelled from roof tops!

Do not hesitate to get grid power !  

This less then ideal charge profile of batteries where they wont accept much as they become fully charged is really bad for generator run time as well. It's a horrible feeling to have your batteries refuse to take anymore amps as they approach fully charged. You can watch the battery gauge accept 400 watts for 2 hours while your 3000 watt generator is wasting fuel.

If your hooked to the grid and you need your battery bank charged, something that may cost you 2 dollars of fuel in a generator will cost you cents in grid power. For example, I ran a bank of 4 batteries of 1200 watts each for a long time.  If you pull them down 1200 watts, your at 75 percent to charge this up with a generator is about a half a gallon of gasoline for me. Right now that's about 1 dollar. But there are hidden costs with the generator, oil changes, spark plugs, fuel and air filters, the time servicing etc.

To purchase the 1200 watts I need to go from 75 to 100 percent from the grid costs me  about 12 cents, with no maintenance costs and if I stored that power in the infinite battery that is the grid, it could potentially be free!

There are really only two solutions to this. If you want to be off grid, you must have a generator. This has maintenance costs and is expensive to run, and I'm going to say it, they will put out far more pollution then burning coal at a power plant to produce the same amount of power.

respectfully disagree, you do not NEED a generator, though it may be convenient.

the OP may agree, because she is trying to maintain a job and needs the laptop and equipment, but i think it is in error to say you need a generator. it would be true to say you must have a generator if you want to maintain a certain lifestyle that you want, but not the same as need.

you can just do without. shut off everything and learn to enjoy the dark, get lanterns that run on batteries, light candles, enjoy the rest when its too dark to work, wake with the sun earlier.
play music instead of listen to it, meditate, and just let your solar system recharge itself. i am saying this as someone who has experienced it, with less solar power than the OP, i lived with a very small system for many many years contentedly, although i know i am a strange one. i've also lived off grid with no electricity, no solar- no anything modern. it changes your perspective on what you really NEED.

also eventually i got a nice sealed battery to get some extra juice, as above, and that helped with having more time on the computer, more entertainment and more staying up later than i should. another nice feature of those sealed batteries is they have a gauge to be able to tell what percent full everything is. by supplementing my very small system by being able to charge that to full once a week or so, it would boost my system to 100%.

The need for a generator is for the batteries not the humans. They cannot stay in a state of discharge and live a happy life. It is a need.

It's like running your car 3 quarts low on oil all the time.  Your ruining your investment of money in the batteries.

anyway thats the obvious solution for the OP, but i knew, she would not want that!

just shut off everything and don't use the system for a day or so and it will help. or just shut it off at night, and use it most when its over full...the middle of the day is the time to do any high power things....

although it sounds like the whole system needs some upgrading too. more batteries, at least 2, means they get less taken out of them as a whole...it stabilizes the system because its more spread out, better for night when its all draw and no recharge.

as far as a generator or grid tie, well i would never want to use a gas generator, nor could i afford to even buy one- so thats out for me.
most of the places i have been off grid it wasnt even an option to tie into the grid, being way too far remote.

i definitely done the whole...turn on my car and let it idle just to get the alternator and car battery to charge me up routine.
the first community i lived at we did use a car, but it just sort of accidentally happened. my friend's volkswagon rabbit (diesel) had the transmission fail, so that it would start and run good but couldnt get into gear or go anywhere, and she had no money to fix it. we emptied out the inside and filled it with batteries, had our own simple bio diesel making deal =) and starting using it as power generator...the rabbit that ran but never got anywhere was our small electric plant =) we would shift out the batteries to take one to our tiny houses...run off of direct current...and run the rabbit every other day or so for a couple hours.

not sure any of that is relevant...but yeah ...i know i am coming from a different place than most...

I have added a small 400w windmill to help out with the dark season.  This time of year always sneaks up on me.  We have had 20-30 mph winds for days and no sun.  With the daylight savings time change we use more lighting, because of the long evenings.  The corn sheller and grinder tend to be used at night now.  I put together a small biodiesel generater with a 10si gm alternator and a 3.7hp hatz. I also put together a junk pressure washer with a 10si on it so it is portable.  I probably am overkilling with my backups, but I built the one for around 50 bucks.  I posted a picture of it a couple years ago here somewhere.

Eric Hammond wrote:The need for a generator is for the batteries not the humans. They cannot stay in a state of discharge and live a happy life. It is a need.

It's like running your car 3 quarts low on oil all the time.  Your ruining your investment of money in the batteries.

well i am getting at, dont get to that point by not running it at night, or very little, get alternative sources like battery powered lanterns (on rechargables) and adjust your lifestyle to extreme minimalist.
turn the whole system off once it's dark and just rest, drink tea and think too much. !
it will slowly get back up to near full by shutting off the consumption while still slowly charging, even in winter. or by very minimal use when you know its getting lower.

for me this is less relevant anyway, i generally get free ish/cheap batteries, salvage, or junk yard batteries. i know that sounds not great, hey maybe it isnt, but i say you would be surprised how many pefectly good batteries are in a salvage stash. there were a few places i could go to get a battery for $5-10$ bring my volt meter, test them and pick out the best ones from trade ins at the store, or from junk yards by pulling them out of trashed cras....

I haven't used a generator to charge my LiFePO4 battery bank in the 20 months since I got it.. and that is with PWM charge controller in the pacific northwest...

The total system ran me about 20% of the cost of putting in a grid connection..

D Nikolls wrote:I haven't used a generator to charge my LiFePO4 battery bank in the 20 months since I got it.. and that is with PWM charge controller in the pacific northwest...

The total system ran me about 20% of the cost of putting in a grid connection..

Those are the batteries to have.  LIFePO4.  Basically it's taking the Edison battery and merging it with Lithium technology.  

Solar and wind together will keep the power flowing.

I'm running 280W in a 12VDC system.  No inverter for the lighting.  Keeping most things at 12VDC directly with fuses like automotive makes the system easy.  Although the well pump does take the inverter to power.  I'm in zone-4, and gray skies are plenty now till mid April.  And I still get charging in cloud skies with my PWM controller too; Renogy Adventurer 30A 12V/24V Negative Ground PWM Flush Mount Charge Controller.  https://www.amazon.com/Renogy-Adventurer-Charge-Controller-Compatible/dp/B07BBKFTNV/ref=sr_1_4?crid=2YWLV6XJQZU6V&dchild=1&keywords=pwm+charge+controller+solar&qid=1604363323&refinements=p_89%3ARenogy&rnid=2528832011&s=lawn-garden&sprefix=pwm+charge+controler%2Caps%2C378&sr=1-4

Love your non-grid connection.

The grid tie solar options I've seen are basically direct feed with no local storage. You are not even legally allowed to use your panels when the grid is down, lest you fry some poor linesman. I mean, you certainly could if you had the technical chops; but you would have to be on your game. This makes me think the rules vary per jurisdiction.

Know what? All this "grid tie solar -- yay or nay?" would be a valuable thread on its own. Easier to search. Pretty hard to parse this thread without shorting out the conversation though.

If you still need help .. I would, in your place, disconnect all the loads and stay without electricity until you get an ok charge on your batteries.
To know that you don't kill your batteries .. search for "battery protect" from Victron. It is pretty easy to setup and it will kill your loads if the voltage drops so it hurts your batteries.
Also .. with so little power .. don't waste it on an inverter if you really don't need it. I mean .. probably yours is 80% efficient so a lot of power wasted. You wrote about bulbs and a phone charger .. they can run directly on 12/24v, there are a tone of cheap chargers with USB outputs (for the phone charger).

HTH

The trick to avoiding this dilemma is to look for a 100-watt panel with bypass diodes or other technologies that allow it to minimize a drop in your solar energy’s power even in low-light areas. Or you can consider low-light solar panels, they can work well in low-light weather.