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I have set up a 400 watt (100 watt X 4 panels) that I have attached to a CC that can be switched from 12v up to 48v after rewiring the panels from parallel to series. I was given a 12v inverter that I want to put into service but my 12 volt x 2 "marine/RV deep cycle batteries" wired parallel seems to be not holding a charge well. I have purchased a Pulse Tech 12v On-Board Desulfator in hopes of restoring the batteries. Just want to start to look around for their replacements. What is your opinion of Energizer batteries? (available at Sam's Club in Phoenix) Also, Interstate is another brand available locally. What is the advantage of using 6 volt batteries wired in series to obtain 12 volts over a single 12 volt battery? 100 Ah my be a bit of over kill, but better over than under at time of need I feel. Besides keeping the battery lead plates covered with distilled water, battery posts clean and Pulse Desulfator, what other maintenance can be done to extend their life. Does the additive "battery equalizer" solution work? Any and all advice welcome. ThanksComment
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My golf cart batteries are 8 volt batteries X 6, so can't wire any comb to yield 12 volt and its a big hassle to rewire them. So for everyday (emergency back up) using 12 volt is my best answer. If everything goes deep south with the electric grid I'll hook up the golf cart to the 48 volt inverter and survive on it. (extremest thinking I know)Comment
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From battery C Hour Rates. Lead Acid batteries have fairly high internal resistances which limits the amount of current they can supply without significant voltage sag. The limit is C/8 on flooded and C/4 on AGM where C = the battery amp hour capacity. For example a battery you maybe familiar with a Trojan T-105 6-volt 225 AH golf cart battery has approx .008 Ohms. So a C/8 discharge current on a 225 AH battery is 225AH/8 Hours = 28 amps. OK if we connected two of the 6 volt golf cart battery in series to make 12 volts (.016 ohms) with 28 amp load current on a fully charged up battery open circuit voltage is 12.6 volts. That 12.6 volts will sag (28 amps x .016 Ohms = .448 volts) down to 12.1 volts or roughly 3.7% loss. Add in another 2% for wiring between battery and inverter and you are down to 11.8 volts at the inverter input . Well 28 amps x 12.6 volts would be roughly a 300 watt inverter.
Use the same pair of T-105's on a 12 volt 2500 watt inverter and max load current is 220 amps. So at 220 amps x .016 Ohms = 3.5 volts loss on the battery so the voltage drops from 12.6 down to 9.1 volts. Your inverter shuts off around 11 volts from under voltage. It will not work. So applying the C/8 rules to batteries using a 2500 watt inverter at 12 volts is going to require a minimum 220 Amps x 8 hours = 1760 AH battery. a 12 volt 1760 AH battery weighs in around 1300 pounds costing some $4000.
AGM on the other hand has lower internal resistance. About half of flooded, so you can run them as high as C/4. Oh that 2500 watt inverter will require about a 2/0 AWG cable between battery and inverter. Trust me you cannot terminate a 2/0 cable properly, you do not have the tooling or experience required. You would have to go to a cable shop who has the tooling and experience and have them fabricated.
With 12 volt systems, 1000 watts is the max you can safely handle. At 1000 watts still requires a 12 volt 650 AH FLA battery, or a 325 AH AGM battery.You are not even remotely close to that. The other thing you need to be aware of is Mr Peukert robbing you blind. . If you run a 225 AH battery drawing 30 amps changes that 225 AH battery into a 170 AH battery. Draw 200 amps like a golf cart and you are down to a 80 AH battery or about 30 minutes run time till dead.MSEE, PEComment
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So for practical purposes, a 12 AGM 100 Ah battery isn't really going to work very well for me. The 48 volt golf cart, that I already have, is a better idea for any long term power outage coverage and the 12 volt battery for small appliance used over a short term, i.e. open and close garage door, power drill, ect.. (items to use for short duration during power outage) Peukert's law is killing meComment
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That is what comes with lead acid batteries. Other battery types like lithium are not as significantly effected. It all has to do with internal resistance and chemistry efficiency conversions.
A goo example is the LiFeP04 aka LFP lithium battery. A 100 AH cell if discharged at C/100 (1 amp) has about 110 AH on average. Discharged at 4C or 400 amps average around 85 AH or 15% loss.
A 100 AH FLA rated battery at C/100 has about 170 AH capacity, so if loading lightly less than C/20 the FLA is a battery choice. That same 100 AH FLA at 1C or 100 amps is rated 45 AH and only 23 are usable. At 4C or 100 amps around 10 AH and only 5 usable.
So imagine a EV like a golf cart that can pull 2 to 4C load currents. A 48 volt 100 AH FLA battery will give you about 5 to 7 minutes run time at full speed. A like voltage 100 AH LFP will give you about 30 to 40 minutes, and only weigh 1/4 of that of a FLA. Question is are you willing to pay 200 to 400% more for LFP?MSEE, PEComment
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OK, for all those that have proven to be well past me, I'm still looking for advice on 12 volt AGM 100Ah, or less, brand of battery. Energizer, Interstate, MK, ect...? I do, from time to time, travel to the big city (Phoenix) where I can find just about all brands.Comment
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Whats your budget? Be prepared for sticker shock as AGM's are expensive. Odyssey, Concord, and Optima are some of the better brands. Store brands are all mostly made with Interstate and John Controls.
A good 12 volt 100 AH AGM is going to cost you around $300 to $400 like these.MSEE, PEComment
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I own 4 of the UB12500 50Ah 12v batteries wired to make a 12volt 200Ah system. I haven't put them into a lot of use but they do hold their voltage in between charging.
I thought that using this type of battery was the way to go but after spending $400 for the 4 and using a parallel wired system I realized I should have gone with 2 6v 232Ah Interstate batteries (~$115/ea) in series. First off less expensive and second I didn't have to wire them in parallel.
If you need a 12volt system the cost for AGMs goes through the roof above 55Ah and they are real heavy. You might want to consider going with FLA in the 6v size. They will be less expensive and you have the ability to check their SOC with a hydrometer where you don't really know what the true charge state is for the AGM.Comment
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FWIW you can get 2 golf cart batteries which are 6 volt 225 AH for $300. That is more than twice the capacity of 100 AHMSEE, PEComment
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