Suitable battery for offgrid?

[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]

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

[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]

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]

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]

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?

[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,

[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]

Well that sounds about right.
Cheers,

[jflorey2]

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.

Well, batteries are almost never treated perfectly - which is why the manufacturer's life specs are rarely seen in real life. And it is important to periodically get the battery to close to 100% charge through a long float. But if that only happens every few days (due to clouds or whatever) it's not the end of the world. And that's why many people use generators, for a periodic 100% charge no matter what the insolation.

[asdex]

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.

[jflorey2]

Rereading the specs on this battery, the minimum 40A is for constant current charging.

In this case, "constant current" refers to the phase of charging (i.e. the time when current is maxed out and the voltage is below the absorb voltage.) It does not mean it has to be constant.

[asdex]

Rereading the specs on this battery, the minimum 40A is for constant current charging.
No way you can achieve this with a solar panel system unless a generator is cutting in and out every time a cloud comes over.
I suspect this is optimal charging for all deep cycle batteries if your on the grid.

[Mike90250]

The charging instructions attached must be similar for other batteries people use in solar power system. How do you get on if there are days the array can't produce 40 amps? Say a week of rain when the batteries only charge up on say 10 amps?..........

That's when I fire up one of the 2 generators I have. Most of the time, both are working. It's important to at least charge above 85% daily, and get to 100% once or twice a week to keep hardened sulfate crystal buildup at a minimum, Once formed and hardened, each crystal (looks like rock candy) reduces the strength of the electrolyte, till you have water left.

[solar pete]

Howdy, the week of rainy weather is why you need a genny cheers.