Suitable battery for offgrid?

[asdex]

Well that sounds about right.
Cheers,

[Sunking]

Thanks, and I have just received info from Crown with the voltage settings to use.
I see a slight problem with the info where the person mentions "It is important to allow the battery bank to float (rest) before the next discharge cycle begins. It is ideal to have the battery bank fully charged by late morning or early afternoon to give the battery bank rest time throughout the balance of the afternoon before the next discharge cycle."
Once my bank is charged usally late morning it is still in use running the fridge and freezer and water heating. Most of the time the panels are putting out the needed amps but I wouldn't actually call the batteries floating for the rest of the day as clouds come and go and although most of the current comes fro the panels, the batteries will be filling in the low spots.

I have been over this many times. Use your hydrometer to set the voltage. Solar is a piss poor source of power to charge batteries with. There are simply not enough hours in a day to go through any 3-Stage algorithm You want simple CC/CV charge. To make you Classic a CC/CV charger set Bulk = Absorb = Float. Use the hydrometer to find the right voltage. It is going to be from as low as 27 up to to 32 volts. Start at 30 volts

[asdex]

That's an interesting approach. Once I get rid of my AGM's and gain the use of a hydrometer I'll have a much better idea of values I can use and how the batteries perform.
Thanks,

[asdex]

I have been over this many times. Use your hydrometer to set the voltage. Solar is a piss poor source of power to charge batteries with. There are simply not enough hours in a day to go through any 3-Stage algorithm You want simple CC/CV charge. To make you Classic a CC/CV charger set Bulk = Absorb = Float. Use the hydrometer to find the right voltage. It is going to be from as low as 27 up to to 32 volts. Start at 30 volts

If the bank gets to float voltage each day and the charge controller sits on float for a while, is this an indication they the system is charging the batteries successfully and the Bulk=Absorb=Float wouldn't be needed in this case?

[Sunking]

Not necessarily. You need to understand there is no difference between Bulk/Absorb/Float/Equalize. All are CC/CV algorithm. The only thing different between the modes is the VOLTAGE SET POINT.

A Solar Charge Controller is really piss poor for a charger. To perform an adequate Absorb cycle is to hold the voltage to say 30 volts on a 24 volt battery and hold that 30 volts until Current tapers off to 3% of C. So 3 amps on a 100 AH battery. That takes 6 to 12 hours depending on how fast you charge. No solar controller does that. Absorb is just a fixed default time of 4 to 6 hours, then lowers the Voltage to Float or 27 volts. The battery may or not be fully charged.

So what can you do?

Simple use your hydrometer and use only 1 Voltage Set Point. At the end of the day when the sun is no longer producing power measure the Specific Gravity. If it is low, raise the voltage. If it is too high lower the voltage. You want the Specific Gravity to be a little high side aka slightly over charged. If you are like 95% of most people, there is no voltage high enough and your batteries are chronically undercharged. Why? Because most do not have enough panel wattage to get the job done.

[asdex]

What happens though if you batteries are 95% state of charge and it’s very sunny and you have set your single voltage figure at 30 volts when the recommended float is 27 volts? I expect you would boil away your water while shopping in town.

That's the problem with solar If you use your hydrometer in a week of less sun to gain a suitable charging voltage then you get more sun and or have less battery usage.

[Sunking]

What happens though if you batteries are 95% state of charge and it’s very sunny and you have set your single voltage figure at 30 volts when the recommended float is 27 volts? I expect you would boil away your water while shopping in town

Quit making things up. It means you charger timed out to soon before the battery was charged up. Assuming you have the voltage set to Absorb, you do not terminate Absorb before the current tapers down to 3% when the battery is 100%.

Your argument does not hold water or make since. If you went to Float before you reached 100%, you are undercharged and never made it to 100% because you terminated Absorb to soon. As I said the Solar Charge Controllers do not have the smarts or enough sun hours to complete a proper Absorb phase. Instead they use a timer, vs current. A good Smart Charger will terminate when the current tapers off to the right value or .03C regardless of how long it takes. Then and only then lower the voltage to FLOAT.

So now think of this. You turn up Bulk, Absorb, Float to say 32 volts a voltage your battery will never reach in a day of normal use. This forces the Controller to stay in Constant Current from sunrise to sunset. For Solar that is really Constant Power meaning the controller delivers every bit of power the panels can produce in a day. Hopefully you never get to that point because it would mean you simply do not have enough Panel Wattage to recharge in a day. You are in Deficit Charging.

Ideally you would like to to see your batteries voltage top out at 28.8 volts at around noon, and current taper to 3% and see the Specific Gravity at 100%, then use Float and lower the voltage to 27.2 volts, and let th epanels supply power until sunset. Then go on 100% batteries.

[asdex]

I'm not ignoring you, I'll just have to think on this for a day or so.

[Sunking]

I'm not ignoring you,.

Never said nor never meant to imply you were. Look there is more than one-way to charge a battery, and no one method is perfect or suitable for all applications.

If you had to pick the kindest gentlest method known to make batteries last 10 or more years is what the industry called Float Service. The word Float has a few different meanings depending on how the term is used. Like Aloha, depends on how it is used. Float Service is what utilities uses on their Stationary Batteries. A utility uses the batteries as Emergency Stand By power for when commercial power fails. All the equipment runs directly off the batteries. Example -48 Volts is default standard in Telecom, 24 for Transport and Radio. Electric utilities use 140 volts in Sub Station on the switching equipment and SCADA.

So what is Float Service. Real dang simple A set of Rectifiers supplying the batteries and equipment. The rectifiers are Chargers, just simple high quality CC/CV charger that you can set the voltage to whatever you want. The rectifiers or Charger is sized to power all the load equipment and recharge the batteries in as little as 2 hours. The Voltage never changes. You set it to the Batteries specific Float Voltage that holds the battery at 100% SOC round the clock 365 days a year. On a 24 volt plant is around 27.00 to 27.40 volts depending on battery type and temps.

Float Chargers are great for batteries used in Standby Service, but really SUK big time for daily cycle applications. Even though you can size a Float Charger to fully recharge in 2 hours say 50 amps on a 100 AH battery, it takes up to 24 hours for the battery to Saturate or Adsorb to 100% at the lower voltages. You do not have that luxury of time on a daily cycle application. Means you gotta do something else.

So now we take that same Rectifier and replace the Potentiometer used to set the voltage and replace it with a micro-controller. We now program the controller to apply a higher voltage say 30 volts. So now we pump in 50 amps until the voltage reaches 30 volts, and wait until current tapers to 3 amps on a 100 AH battery. Once that happens we can do 1 or two things.

1. Terminate the charge, the EV is ready to go.

2. Reduce voltage to 27.2 volts and Float the batteries allowing the panels to supply the loads with power while there is still daylight conserving your batteries until night.

Now which method do you think works best for Solar? You have 3 choices. One method is unacceptable, two are doable but one of the two is a better fit.

Bottom line is you cannot switch to Float before the battery is fully charged. To get there means you need enough horse power to get there before the day is over. Otherwise you are undercharged.

Slightly over charged batteries last longer than undercharged batteries. There is no Equilibrium in a Daily Cycle application like there is with Float Service application. You are either over charging or under charging. If you have enough panel wattage you want to live on the over charge side of the knife edge. Unfortunately most do not have a choice as they lack enough panel wattage and there is no voltage high enough. The sun will have long before you get fully recharged. Those that do, do not know how to set it up.

[asdex]

Sorry, I meant I would think about what you have written for a day or so so I can get back with some sensible understanding of it.
Looking at the options I would think option 2 is best.
Set the absorb voltage to quite high so you get maximum amps into the battery in shortest time sounds good to me as my batteries sit in absorb at 3 or 4 amps for a long time (hours) even in good sun.
Then once absorb time is up, my CC switches on an SSR for water heating and the currents goes to 26 amps often more from the panels. So the energy potential is there but not being utilized.
The batteries I am just buying are 430AH and my panels are 1920w. so I'll need to work that out in regard to capacity.
Equalizing voltage is 31 volts while absorb is 29 volts so I could start at 30 volts and set absorb ending amps at whatever the current is when the batteries are 100% charged (hydrometer)
Found this in another thread: "The general rule of thumb with flooded lead acid batteries is 1 watt per amp hour of battery. " So I'm probably good for capacity.

[jflorey2]

Found this in another thread: "The general rule of thumb with flooded lead acid batteries is 1 watt per amp hour of battery. " So I'm probably good for capacity.

That makes no sense without knowing battery voltage. You can compare watts to watt-hours (for ensuring sufficient charging capacity available) or amps to amp-hours - not watts to amp hours. The above might work OK for a 12V battery although it would be on the low side (would end up being about C/15 or so which is pretty low.) It also assumes a solar watt (i.e. the STC watts printed on the panels) are real watts, which is almost never true. Temperature, dirt and non-ideal exposures conspire to significantly reduce your solar output most of the time.

In general you want to charge at between about C/5 and C/10. You can get better numbers from your battery spec sheets, although sometimes you have to dig to find it. (Trojan, for example, recommends between C/8 and C/10 based on the 20 hour capacity, but that's from a separate document and isn't on their spec sheets.) So if you have 400 amp-hours of Trojan batteries you want between 50 and 80 amps of charge current coming out of your charge controller.

[asdex]

Oh well, it sounded like a nice easy rule to follow and was said by someone with more knowledge than me.
I haven't read about the C ratings and is CC amps calculated or what you see occasionally?
What say I have 400AH of Crown batteries?

[Sunking]

That makes no sense without knowing battery voltage. You can compare watts to watt-hours (for ensuring sufficient charging capacity available) or amps to amp-hours - not watts to amp hours. The above might work OK for a 12V battery

It was pretext to 12 volts and just a quick gut check to see if you are in the Ball Park. Quote was taken out of context.

[Sunking]

Oh well, it sounded like a nice easy rule to follow and was said by someone with more knowledge than me.
I haven't read about the C ratings and is CC amps calculated or what you see occasionally?
What say I have 400AH of Crown batteries?

More General Rules, for FLA you want no less than C/12, and no greater than than C/8 charge and discharge rate.. That is a safe rule that applies to any Pb battery. However Rolls, Crown, and a few Trojans can go as high C/5 charge rate, that does not mean you should. Some AGM's you can charge at 1C, but again does not mean you should.

Don't get to wrapped up in charge rate and make yourself paralyzed. Following proper design guidelines takes care of most of that. Let me give you an example. lets say we want 2 Kwh per day, 24 volt battery, and shortest Winter Sun Hour day is 3 Hours.

Immediately we can find the right battery capacity without much thought AH = [Daily WH x 5] / Battery Voltage. So [2000 WH x 5] / 24 volts = 417 AH. So you go shopping for a 24 volt 400 AH battery. Sound familar? Don't even concern yourself with charge rates at this point.

Next is to find Panel Wattage. Super Easy to do. Using a MPPT Controller Panel Watts = [Daily Watt Hours x 1.5] / Sun Hours. So [2000 wh x 1.5/ / 3 h = 1000 watts. So go shopping for 1000 watts of panels.

Last we need a MPPT Charge Controller. To find the minimum size controller we need to know how much current are panels will produce at full power. Super Easy Amps = Panel Wattage / Battery Voltage. So 1000 watts / 24 volts = 40 amps

Charge Rate took care of itself, and Charge Rate is determined by Sun Hours and Reserve Capacity. As a sanity check we want to know if the Charge Rate falls within the Charge Window of C/12 to C/8. Using our example 40 amps on a 400 AH battery is C/10, perfect right dead in the center of the window.

So when do you have to worry about charge rates. When you fall outside of the C/12 to C/8 window. Let's say you move to Hell, some place you know Seattle WA or Portland OR or other like city where in winter Sun Hours fall to 1.6 Sun Hours. Panel Wattage = [2000 wh x 1.5] / 1.6 h = 1875 watts. What size Controller? 1875 watts / 24 volts = 78 amps, lets just call it 80 amps charge current. Battery size remains at 24 volts @ 400 AH, but 80 amps on a 400 AH battery is C/5. That falls outside the generic safe window of C/12 to C/8 charge rate. That forces you to be very selective on batteries that can handle a C/5 charge current.

What can you conclude from the above information. For me it is never ever move to Seattle or Portland and become one of the suicide statistics. Portland and Seattle have the nations highest suicide rates and no wonder why. As for the rest of us it tells you when your Sun Hours drop below 2.5 Sun Hours is going to require a battery that can handle high charge rates.

It also tells you immediately what panel wattage is required for a given size battery. You can do it in your head without any thought. Example a 24 volt 400 AH battery requires a minimum panel wattage of 24 volts x 33.3 amps = 800 watts, and no greater than 24 volts x 50 amps = 1200 watts.

Like i said super easy 5th grade math.No calculator needed, it can all be done in your head or on fingers and toes if you are a Hillbilly, Redneck, or voted for Obama.

[asdex]

Thanks, thats really useful and explained in good logical steps. It was hard for me originally to decide where to start when designing my system. Battery size or panel size. I pretty much took some guesses. I got usage and battery size ok but have 2kWs of panels instead of the calculated 1kw as in the above example. Its fine for when the water heating is on but if the water is hot the CC will need to limit the current.
Cheers,