Suitable battery for offgrid?

[Jambonjoebob]

Thanks a lot!

[SunEagle]

Why do you multiply by 5 to calculate the capacity?
why do you multiply by 1.5 in wattage?

Sunking has not been around for a while so maybe I can answer your questions.

I believe he uses 5 to determine capacity because it allows you to use a 20% discharge amount on the battery.

The 1.5 value increases your watt hour usage based on efficiency of the system so you up-size the panel wattage to get what you need.

[Jambonjoebob]

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

Why do you multiply by 5 to calculate the capacity?
why do you multiply by 1.5 in wattage?

[John Galt 1]

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

Agreed, When my Crown 6CRP525 batteries were about 6 months old I had gotten tired of fighting with super long absorb times at the Crown recommended 58.1v and gave Crown a call. Their techs kicked things around for a while and told me to try 51.5v absorb which helped but after playing with things a bit and researching what other battery manufactures were using for absorb voltage I'm now using a higher absorb voltage. If I don't the battery SG slowly falls over a few weeks until it was sometimes as low at 1.248 at the end of a 5 hr absorb and I'd fight to get them back up.

I want to see at least a 1.265 SG after a good sunny absorb session.

A good hydrometer is your friend, use it regularly. I have 3 hydrometers and prefer the HydroVolt but you must really rinse it out after each use or it will not turn smoothly.

[John Galt 1]

Will Crown, or any manufacturer, ever tell us their exact Testing methodology to obtain 3,000 @ 20% DOD cycles?
1) C/4 or C/5 Discharge Amps ?
2) Using a Final Voltage or Amp-Hours to terminate the discharge test ?
3) Using a 3 Stage recharge?
4) Any periodic Equalizations?

To get 3,000 @ 20% DOD discharge - charge cycles, at a slow C/20 Rate, would take a like 4 years ???
I do not think that is happening.
So they must be discharging at a faster rate like C/4 or C/5 ?
Or are these "Cycles vs DOD" graphs just for Entertainment Purposes only?

Could they be using the BCI S-06 Cycle Test?

I spoke with Crown tech department. They discharge at a faster rate (I believe it was C/4) and keep the test batteries in a water bath to help keep them cool while charging. They do EQ some during testing but I don't know if they are using a 3 stage charge.

[PNjunction]

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?
Also, I guess the three phases are bulk, absorb, and float?
cheers,

Note that those instructions are for EV usage, where one typically very deeply discharges them, and has limited turn-around time (like maybe overnight at best) to put the vehicle back into service.

The 3 phases mentioned are the classic IUI protocol (current-voltage-current) for fast turnaround. Basically the first constant current stage is just the max current your charger can put out. In this case, they recommend anywhere from 40 to 100A. Once the battery reaches about 80% SOC, the "CV" constant-voltage stage is in effect, where the voltage is limited to 2.37v per cell. As the battery charges the terminal voltage rises to try and meet the charger voltage. The net result is that the *battery* is the one tapering the current, not the charger.

At this point, when current tapers off to about 15A, (or the time criteria where no further tapering occurs), ANOTHER constant current stage follows, not float.

This last stage of constant current is not voltage limited, and is an attempt to make up for the 12 hours of float one would need to TRULY charge the battery - but we don't have that kind of time in an EV (or solar!) situation.

The problem with solar controllers for daily cyclic users is that we don't have that much time available to us, as these instructions assume an ac charger. Also, no solar controller to my knowledge will do the fast-turnaround secondary constant-current finishing charge. Again, no time usually.

So this is just the very long way around to say that if you are doing cyclic duty, then the simplest answer is to just set your CV stage to 2.37v per cell, with no float (or set that to 2.37v as well). If you baby the battery in a cyclic duty situation, it will sulfate prematurely.

[NEOH]

Why do we allow the BCI, Battery Council International, to be so secretive about their BCI S-06 (Golf Cart Cycling and Repeat Reserve Capacity Cycling) Test, and their other battery test procedures? The "Cycles vs DOD" charts for many deep cycle batteries are "derived" from the BCI S-06 test. I think it would be highly informative to require the actual Amps and actual final discharge Voltage (definition of the Discharge Cycle) to be posted under the "Cycle vs DOD" graph. It is very inappropriate to disguise a "Marketing Hype" graph as a "Battery Specification'.
This issue reminds me of how the car manufacturers had previously manipulated their MPG ratings. We no longer tolerate false MPG ratings. VW has recently learned this lesson, the hard way. So, why do we continue to tolerate highly misleading "Cycles vs DOD" charts from the battery manufacturers? The BCI is the fox, guarding the hen house.
Maybe, this is a project for Consumer Reports ?

[SunEagle]

Will Crown, or any manufacturer, ever tell us their exact Testing methodology to obtain 3,000 @ 20% DOD cycles?
1) C/4 or C/5 Discharge Amps ?
2) Using a Final Voltage or Amp-Hours to terminate the discharge test ?
3) Using a 3 Stage recharge?
4) Any periodic Equalizations?

To get 3,000 @ 20% DOD discharge - charge cycles, at a slow C/20 Rate, would take a like 4 years ???
I do not think that is happening.
So they must be discharging at a faster rate like C/4 or C/5 ?
Or are these "Cycles vs DOD" graphs just for Entertainment Purposes only?

Could they be using the BCI S-06 Cycle Test?

I would imagine the testing procedure it probably something that is not available to the open public, but might be available to any Standardization authority.

IMO like most other industries there must be a way to use an accelerated testing procedure that simulates real time life cycles in some way to match their claim.

[NEOH]

Well the specs show the "typical" battery life at 20% DOD at 3000 cycles but I would think that is at lab conditions. But if you are only doing an 8% DOD with those 330Ah batteries you may get a long life out of the Crown. Although 10 years may be a stretch unless you follow all of the maintenance procedures perfectly as well as perform an Equalization charge per recommended time frames.

Will Crown, or any manufacturer, ever tell us their exact Testing methodology to obtain 3,000 @ 20% DOD cycles?
1) C/4 or C/5 Discharge Amps ?
2) Using a Final Voltage or Amp-Hours to terminate the discharge test ?
3) Using a 3 Stage recharge?
4) Any periodic Equalizations?

To get 3,000 @ 20% DOD discharge - charge cycles, at a slow C/20 Rate, would take a like 4 years ???
I do not think that is happening.
So they must be discharging at a faster rate like C/4 or C/5 ?
Or are these "Cycles vs DOD" graphs just for Entertainment Purposes only?

Could they be using the BCI S-06 Cycle Test?

[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,

[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.

[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.

[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?

[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]

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.