Newbie tyring to understand battery types for emerg solar setup

[mattro]

I am new to solar (sighs from crowd). I am wanting to build a small system on a VERY tight budget, trying to buy decent stuff that will have many years good use and a system I can grow. Intended use is to charge AA batteries, charge handheld electronics (phones and such); run future small HAM radio, and run a string of LED lights; all in the unlikely event of "lights out" SHTF. I understand the basics of calculating demand and recharge. I am planning on a Renogy 100w panel and hopefully an entry level MPPT controller.

My big question is the batteries. I would like to keep the initial battery cost at $100 but dont want to throw money away. I am not understanding the difference in usability and life span between Walmart 29DC and a true deep cycle. The usable AH is almost impossible to compare and I think the hybrid Walmart battery's tolerable discharge level is no where as deep as a true deep cycle. I cant really afford two Sams Club GC2 batteries at $85 bucks (to get to 12v) each but will if it makes a world of difference, but it appears (without better knowledge) that the Sams 29DC has a similar capacity to two GC2 batteries??? Quality 20AH 12volt deep cycle batteries run about $45 each, but how would two of those compare to the Sams 29DC? If the 29DC serves its purpose for 3-4 years then junks out with light usage, that is not completely unacceptable.

Harbor freight has 12 Volt, 35 Amp Hour AGM for $73. That would give me true deep cycle without having to buy two right away to get to 12v.

Finding 12v appliances for a prolonged lights out would be nice but I understand I would quickly outgrow this small setup. Being able to smartly add panels and increase the capacity of battery bank would be nice without throwing the initial batteries away.

Any help understanding the differences in the 29DC, 12v 20AH, and the Sams golf cart GC2 (or maybe I am missing a better option) would be greatly appreciated. Trying to go cheap but not stupid.

[Naptown]

With that size panel you are actually looking at around an 80 AH battery
For starters I would start with a dual purpose group 31 marine type battery. They are reasonably inexpensive and since most people trash their first set it is not a big money loser. Consider it a learning battery.

[mattro]

With that size panel you are actually looking at around an 80 AH battery
For starters I would start with a dual purpose group 31 marine type battery. They are reasonably inexpensive and since most people trash their first set it is not a big money loser. Consider it a learning battery.

Why do you say to look at 80ah battery with a 100w panel? Is that due to reasonable recharge time from that panel?

What about the following reply by 'billvon' to a newbie that used 29DC walmart battery with his first install?
"Are you really using a starter battery? If that's the case, then the first time you use it it will give you about 50ah to 50%. The second time it will give you 49a, the third time 48ah etc. Expect about 50-100 cycles out of it before it's dead."

I am seeing 12 volt: 35ah SLA for around $65 and 55ha SLA for around $120.
So, comparing the 35ah SLA and the 29DC (since they are similar cost) which will I get better capacity out of? Will the 35ah discharge lower to a lower level then the 29dc without problems? Which would you go with and why?

[lkruper]

Why do you say to look at 80ah battery with a 100w panel? Is that due to reasonable recharge time from that panel?

What about the following reply by 'billvon' to a newbie that used 29DC walmart battery with his first install?
"Are you really using a starter battery? If that's the case, then the first time you use it it will give you about 50ah to 50%. The second time it will give you 49a, the third time 48ah etc. Expect about 50-100 cycles out of it before it's dead."

I am seeing 12 volt: 35ah SLA for around $65 and 55ha SLA for around $120.
So, comparing the 35ah SLA and the 29DC (since they are similar cost) which will I get better capacity out of? Will the 35ah discharge lower to a lower level then the 29dc without problems? Which would you go with and why?

There are two kinds of capacity. There is the size of the battery in ah and then there is the number of times (cycles) you can access the energy before the battery is spent. You reference both in your comments above. When you say that the two 6v batteries give the same capacity as the Marine battery, you are wrong on both counts.

Two 6v batteries from Sams club or Costco are about 207 ah each and make a 207 ah battery bank at 12v.
One Marine battery at Costco (and probably Sams too) is about 70 ah. So right off the bat, the battery capacity is 1/3 of the two 6v batteries. But I agree with Naptown that it might be your best low cost entry point for a learner battery.

But you should also compare the second critera of capacity, cycles. The Costco/Sams 6v batteries will arguably get 1220 cycles at 50% DOD. The Marine battery will get 150-200 cycles.

Don't buy anything yet. You should first calculate your loads with realistic measured watts and hours per day you want to run from the battery. There is a link in Naptowns signature that leads you to a spreadsheet where you can estimate the size of battery and size of panel you need for those loads.

It is well worth your time to do this first.

[mattro]

lkruper, thanks for reply.
I really want to avoid the Walmart hybrid battery if possible.
It appears a quality deep cycle is about twice the cost of a dual purpose battery (with cranking amps). Where the Walmart 29DC is around $86 and a deep cycle agm 35ah is $75 and 55ah is around $110.

I will take your advice and try and analyze demand, thought it will not be easy. Charging a usb battery backup, then some ni-mh aa batteries, and a manually wired string of led bulbs, the infrequent usage will be hard to judge.

Seems a waste to spend the same money on half the capacity (deep cycle). Are the discharge levels similar, meaning can the deep cycle be discharged to a lower percent without hurting the battery comparatively?

Is a MPPT charger a waste of money with this small and simple of a system?

Would a 50w mono panel and 35ah battery be a balance, or is the 100w panel better balance?

Sorry I know these are naive questions. I just want to get started and not waste too much money on mistakes...

[lkruper]

lkruper, thanks for reply.
I really want to avoid the Walmart hybrid battery if possible.
It appears a quality deep cycle is about twice the cost of a dual purpose battery (with cranking amps). Where the Walmart 29DC is around $86 and a deep cycle agm 35ah is $75 and 55ah is around $110.

I will take your advice and try and analyze demand, thought it will not be easy. Charging a usb battery backup, then some ni-mh aa batteries, and a manually wired string of led bulbs, the infrequent usage will be hard to judge.

Seems a waste to spend the same money on half the capacity (deep cycle). Are the discharge levels similar, meaning can the deep cycle be discharged to a lower percent without hurting the battery comparatively?

Is a MPPT charger a waste of money with this small and simple of a system?

Would a 50w mono panel and 35ah battery be a balance, or is the 100w panel better balance?

Sorry I know these are naive questions. I just want to get started and not waste too much money on mistakes...

Both batteries are flooded lead acid batteries. For longevity a good percentage for discharge to shoot for is 50%. Going to 80% won't hurt them, but you get less cycles. The Costco golf cart batteries which are Interstate batteries give 650 cycles at 80% and 1220 cycles at 50%. Some people think that the 1220 is a bit overstated. You cannot always trust sales and marketing people.

Its all about what you need. If your batteries will be sitting charged and waiting for a power outage before being cycled, the 200 cycles might be sufficient. Batteries also have a chronological age. They will last only so long even if they are not being used.

To size a panel and battery without your loads is risky. But a rule of thumb is that the battery should be charged at about 10% of its 20 hr AH capacity. The Costco battery bank of 2 6v batteries would need about 20 amps at 12v, because those two batteries make a 12v 207 AH bank.

Also, in order to size panels you need to know your solar insolation values. Naptown's .sig has that information. You will also need to learn how to read the specs on the panels. They put out a certain voltage and also an amperage in full sunlight. As an example, lets assume a 100w panel that is a 12v panel that puts out 18v. This example is an oversimplification and an inaccurate estimate, but take 100w / 18v = 5.5 amps. If you discharge your 35 ah battery to 50% that means you need to replace 18 ah. 18 / 5.5 = 3.2 hours. But that is only one stage of charging, you will need a few more hours on top of that. You might not have 5 hours of full sun in the wintertime. Also, the panels won't put out 100% and the charge controller won't put out 100%, so you need to fine tune those numbers. The spreadsheet in Naptowns .sig has formulas for that.

It probably won't be cost effective to buy a MPPT controller for a tiny system, but it might be more efficient.

One more thing. You cannot use nameplate wattage to estimate your loads. They are not accurate and may be on the high side. There is an inexpensive meter called kill-o-watt that does a good job of this. I have one and it works great.

[mattro]

lkruper, thanks for taking alot of time to share great and usable information. Your specifics and inserting real (estimated) numbers is the exact info people like me need to make an informed decision! Thanks!

[Mike90250]

So, my suggestion is for the big box store, marine deep cycle battery, size Group24 or Group27, whatever you can find and is cheap. It's going to most likely die of old age, not cycles, if you are only using on weekends or SHTF usage.

A 100w panel will service it, but not if you run a lot of daytime battery charging or Ham radio usage, that will subtract from the recharge amps, and you may end up in the hole after a couple days of heavy usage. Having a 2nd panel you can bring into service would be handy, or use your car alternator to boost up the battery for 20 minutes.

[PNjunction]

I'm with Mike on this one - a so-called "dual purpose / hybrid marine" learner battery is your best bet until you get all your power needs calculated and a bit of experience under your belt. Waste one of these accidentally and you won't have blown your budget too badly.

One interesting one that I am playing with for non-critical purposes is an Exide Edge dual-purpose 75ah agm - and this has graphite to help withstand psoc (partial state of charge) better - which is VERY likely when doing solar among other things.

An interesting rebadge of this very same battery can also be found as a Rural King Marine/RV Dual Purpose AGM Group 24DP Battery RK-AGM24DP. Seems to be a bit cheaper than the Exide sticker-ed version. Note that the Exide / Rural King is only charged to 14.4v, and not 14.7v like some other agm's.

When starting out, it is important to have manufacturer charging data and Exide has a nifty chart for this depending on your model:

http://www.exide.com/Media/files/Downloads/TransAmer/Battery%20Care%20and%20Maintenance/Battery%20Charging%20&%20Storage%20Guidelines%20%205_9_13.pdf

Yes, you could start out with a TRUE deep cycle, but this is inexpensive enough to get your feet wet with a bit of capacity for your intended needs.

[mattro]

PNjunction, curious, why do a dual purpose (so many solar gurus say if it has cca then its crap for solar) when you can gt this for $10 more? Trying to learn.

http://www.ebay.com/itm/New-UB12750-45821-12V-75AH-Grp-24-Battery-Scooter-Wheelchair-Mobility-Deep-Cycle-/191091465824?hash=item2c7df05e60:g:E~wAAOSwT6pVgcW1

[lkruper]

PNjunction, curious, why do a dual purpose (so many solar gurus say if it has cca then its crap for solar) when you can gt this for $10 more? Trying to learn.

http://www.ebay.com/itm/New-UB12750-...wAAOSwT6pVgcW1

$10 more than what? $140 is expensive for 75AH. Also, this is an AGM which has a life 1/2 that of Flooded. You can get a 70AH Marine battery from Costco for $79.

[mattro]

Rural Kings website shows the AGMdual purpose you referenced was $130. I was showing a true deep cycle of the same capacity was $140 and was wondering if it was better since it was a true deep cycle...

[lkruper]

Rural Kings website shows the AGMdual purpose you referenced was $130. I was showing a true deep cycle of the same capacity was $140 and was wondering if it was better since it was a true deep cycle...

I don't believe that anyone here was recommending an AGM battery for the first starter battery for the OP. I didn't and my reasons would be twofold. First, the reason for recommending the Marine battery for the first starter battery is the low price. As I posted, you can get a 70ah Marine battery at Costco, and at any big box store for half of that price.

Second, one cannot learn by measuring the specific gravity of an AGM battery, and fix mishaps with the battery by adding water.

Yes, Marine batteries are hybrid and dual purpose, but the dual purpose aspect is not what recommends the battery for the starter battery, it is the lower cost. AGMs are not lower cost.

[PNjunction]

PNjunction, curious, why do a dual purpose (so many solar gurus say if it has cca then its crap for solar) when you can gt this for $10 more? Trying to learn.

Anything with a CCA is really an SLI or starter battery, not designed for major cycling. However, you can put it to use, as long as you understand that the battery is not really designed to be deep discharge nor last long in that scenario. If one sees an "RC" rating instead of they usual 20ah rating, then you can multiply the RC * 0.6 for an approximation of ah capacity.

In regards to the UB battery - that is a bog standard lead-calcium agm, and general purpose to boot. Really designed for emergency hallway lighting, UPS duty and the like. Vendors like to portray them as being ideal for powering everything, including solar, which is not really the case. Wheelchair use is a total joke upon the unknowing due to the high internal resistance.

Internal resistance is pretty high for GP types. That means that part of your charge current goes into heating the battery instead of charging, whether you feel it or not. Lower internal resistance of higher quality batteries means a faster charge for the same amount of current, higher voltage under load etc, but the GP's are not intended for that use.

Note that UB, PowerSonic, CSB, Yuasa and the like actually do have deeper-discharge models available, but they are not usually found as easily as commodity GP types.

Still, they belong to the UPS type of application family.

When playing around with these commodity GP type batteries, you need a trustworthy source to get you a fresh battery, and not new-old-stock that has been sitting around in the retail chain sulfating.

Upon receipt, measure your open circuit voltage. If it is less than 12.5v at the terminals, then there is a high likelyhood that they have been in the retail chain for 6 months to a year or longer - and/or stored under high-heat conditions.

The likelyhood of getting a dual-purpose marine/hybrid a bit fresher than that is better at the larger stores. Ask your online vendor if they will accept returns if you find the voltage below 12.5v. Online resellers might just ignore you and tell you to pound sand.

[PNjunction]

I don't believe that anyone here was recommending an AGM battery for the first starter battery for the OP.

I do since he's just starting out for an emergency amateur radio setup.

Agm's have lower internal resistance than flooded, and that means higher voltage under load. Some amateur gear goes flaky under 12v, puts out poor signal quality etc. Thus, there may be true deep cycle capacity that won't be available to him anyway.

For an emergency setup, it is not always stationary. If the desire is to be portable / luggable, then lugging an agm up and down the mountain may be more convenient / safe than doing so with flooded.

Still, it can be done with flooded as long as the op does his homework and knows his own abilities go as far as maintenance.

Like lifepo4, despite the higher initial cost, other factors may weigh more in the decision, so even here, one has to make sure the battery fits the application and environment.