Skip to comments.Any FR electricians? (12v DC Lead Acid Battery, Basic Q)
Posted on 02/22/2011 8:18:28 PM PST by Cringing Negativism Network
Hi a question for FR electricians please.
Probably a basic, dumb question, but hey - I don't know the answer and it might just be useful for other readers...
The concept will never go anywhere until batteries are a thousand times more efficient
There are a couple of possible ways to do that (carbon nano tubes for one), but the the danger of a cascade type of failure and catastrophic instant energy release would be very bad to say the least.
Short answer >> YES
There are some considerations. If one of the batteries goes bad like a shorted cell, It can drag the other one down,If batteries are left in a discharged state too long they will go bad.
You can isolate the batteries from each other using diodes.
Anodes of diodes go to + of each battery,tie cathodes together and connect to load. - of both batteries connect together.You will drop some voltage across the diodes (0.7 to 1 volt or so depending on diodes chosen and current going through them.Make sure your diodes can handle the load cuurent.
You could make one of these
I suspect you are starting to get an idea of how ludicrius the whole solar/wind power idea of the Libs to replace our whole electrical grid is considering how much power the modern world uses.
But it is fun experimenting with it for selected uses.
Nothing to do with your charging system, but if limited on battery size for emergency DC lightning go with LED stuff. At an automobile parts retailer the other day I saw some nice (low current) LED sets, for cheap. Strips, buttons and individual lamps.
Do it. There is a lot of good info on solar power systems and battery banks. Be sure to check out youtube videos. Around these parts, they are used at fishing and hunting camps in place of noisey generators.
You can make a DC dimmer that helps prolong battery life.
“The bigger concern is whether youre deep-cycling batteries that are not intended to be deep-cycled. If you are, youll get about 3 to 5 cycles out of them and then plates will start to disintegrate.”
Does immediate re-charge help mediate that?
Is there a percentage de-charged (for example on a 12-volt battery, down 25 percent percent to 9v remaining?) at which point the damage goes logarithmic?
"A DC Fester in an AC spaceship?"
The concept will never go anywhere until batteries are a thousand times more efficient and photovoltaics put out a thousand times more juice. And no, Im not exaggerating the numbers.
Yes, you are exaggerating the numbers. A flooded lead acid battery (one with "caps" that you can add water to) charge at about 90% efficiency, absorbed glass mat (AGM) charge at about 95% efficiency. I'd like to see you calculate how a ~90% efficient device can become 1000 times more efficient.
Consumer photovoltaic panels are in the neighborhood of 15% efficient in converting sunlight into electricity. The average solar insolation (total energy reaching the earth's surface) is about 1000w/m^2. My 10' x 10' array can produce ~1kw for ~5 hours per day. Not alot but it is something. If everyone had their roof covered in them, there might not be a reason to import oil from 6th century cavemen that would love nothing more than to slice your head from your neck or from turd world dictators that speak spanish.
Don't get me wrong, I'm not a proponent of "renewable" energy at all, I'm more of a slash-and-burn oil burner that enjoys going fast, cold air in the summer and hot air in the winter but spreading falsehoods about solar's capabilities is bull. Think about it this way, the more people that spend their money on those power sources, the more of the other there is for us.
How much money did you spend on these two batteries?
The best capacity for the $ is probably to go down to Wal-Mart and get a deep-discharge 12V battery. It can be an RV battery, a trolling motor battery, or any other deep discharge battery.
It will be about the size of a car battery and will be 80 to 100 Amp-hours for about $80.
For pete sake. According to the Battery FAQ posted just before your post, that 25% SWAG I used as an example was right.
I pretty much totally pulled that out of thin air, after watching the voltage on my first attempt to boil water - I could see the power delivery to the hotpot drop significantly about that point.
At 75% of capacity, sulfation begins. Lots of information here...
Good suggestion. Thanks.
If you want something that will provide emergency lighting, do what I do . . . . . use a generator!!
You typically do not want to do that with batteries of different sizes. Will it blow anything up? Probably not, and it’s probably *less* of a deal since batt types are lead acid. But it’s not what’s recommended. Usually you want to isolate each battery via the use of diodes.
Do some research on “dual-battery systems”...typically for boats.
I saw that discussed in a couple places, and another FReeper mentioned that upthread.
Gotta duck out now for some sleep, appreciate the feedback.
I personally would be far more careful. Two batteries aren't going to be exactly the same - not now and certainly not later, as they age. Two things result from this:
None of that is good. You can somewhat alleviate the problem #1 by using diodes. But you will be losing a lot of power on them, especially if the current is high (the forward voltage on a Shottky diode will be around 0.3V.) At 8A you will lose 2.4W per diode. This is unwelcome in itself.
The problem #2 may result in bad batteries, quickly. Batteries are generally delicate devices; more so as they get more and more sophisticated. A typical notebook battery has an integrated charging controller inside. It's because they will catch on fire if overcharged (and it happens now and then.)
To begin with, the whole idea of storing energy in a battery is not that great. Some people already commented on that. A battery that cycles so often won't last long. Note that car batteries and UPS batteries are used lightly, and kept charged all the time - that's how they get some reasonable lifetime out of them. Cell phones and notebooks have this problem - the number of full cycles of a LiIon cell is around 500, and then it's dead.
There are solutions that work. The most effective one is to use the electric grid as your battery. When you produce you send the energy into the grid, and the meter spins backward, giving you a credit. You can use that credit later on.
But, for purposes of the argument, if you want to use several batteries then the best way to connect them is in series. This is because batteries are charged by current, not by voltage. Voltage varies between cells, but it doesn't matter until the differences grow to be too large. Your 12V battery already contains several cells connected in series, and if you connect another box of them also in series then it won't change a thing, from the POV of one cell.
On top of that you need to build a small computer that manages the battery (regardless of how large it is.) This controller has to measure the charge (in coulombs.), this is usually done with an integrator. The controller then figures out how much energy can be transferred into or out of the battery, and allows that to happen. Since the voltage of the battery changes as it charges or discharges, you need a voltage inverter (DC-DC or DC-AC) to regulate the output. You will end up with a good part of Prius electronics.
If you want to install a solar (PV) system the best way to do it is by using panels and inverter(s) that are commercially produced. If you simply want to experiment with things, this particular setup is not the best. Talk to your local hams instead, they will throw a bunch of far better ideas at you, and on top of that they will advise you what to do (and what not to do :-)
You definitely need moe charging capacity, for AGM batteries like you have, figure on ~2% self discharge per day - you'll need to replace that even if you don't use that battery at all so the 18a/hr battery will need to be 'fed' about .36a/hr daily to maintain its charge. Also figure on only drawing down 50% of the battery capacity for decent battery life, the 18a/hr would be able to provide 9a/hr or 96w/hr before needing to be fully charged. Also, avoid "deficit" charging where you never fully charge the battery from the previous days' use. That will cause sulphation on the plates effectively ruining the battery, particularly AGM's since they can't be equalized like FLA.
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