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...
Figured a couple basic lessons already:
Lesson one: You need a bigger solar cell, than you think you do.
Lesson two: Your bigger solar cell than you think you need, will cost you an astonishing amount of money more than you originally even considered likely.
But the real clear lesson I'm learning is - battery capacity is actually rule number one.
I started out with a simple 8 amp-hour 12v battery. It charges slowly, but it charges, from a basic solar battery tender. So far so good.
However 8 amp-hours it turns out, really is only large enough to run some 12v lights full time with in a backup situation, or maybe an hour of browsing FR. Solar charged or any other way. After which, you're stranded in the dark, without any FR (which is the worst part!) until well into the following morning earliest.
Granted if the power's out, that's useful. Though, only just.
Lesson learned. So I got a larger capacity battery. Same manufacturer. Same voltage. 18 amp-hours.
The larger battery is actually useful. But I've also now got that perfectly good, yet smaller, too limited to do anything with, except run emergency lighting with, battery as well.
Rather than set up two backup systems as I go, one for lights (off the smaller battery) and a larger one for some more useful amount of power - I am wondering whether the two equivalent though different-capacity 12v batteries can be combined, for one additional step forward?
So: my greenhorn electrician question is: Can a 12v 8 amp-hour lead acid battery, be connected parallel to a 12v 18 amp-hour lead acid battery (safely) to in effect create one virtual single, larger 12v battery?
(both batteries, sealed lead acid)
Or am I likely to blow up both batteries, perhaps even blinding myself with battery acid in the process? Which would be inconvenient.
Thanks for any feedback! Cautionary posts will be given proportionally more weight when considering possible options. :)
Yes
Check out homepower.org
I’m not an electrician. Yes you can connect batteries in parallel or in series and it doesn’t cause explosions.
You won’t hurt a thing.
Join these 2 groups. The first is extremely friendly. The second not as much but you learn a lot. You will really enjoy the camaraderie of the first group.
simplysolar@yahoogroups.com
12VDC_Power@yahoogroups.com
As long as the two batteries are the same type and voltage, no problem, just parallel ‘em. Lots of alternatives to consider such as having separate charge controllers to provide redundancy, keeping one battery in reserve, etc. Sounds like you’re on the right track - good luck.
You can run them in parallel. And that setup will approach the sum of the amp hour ratings of the two individual batteries (18+8=26 amp hours total).
You will need to make sure that both batteries are in a similar state of charge before connecting them in parallel. Use a digital volt meter and get them as close to the same voltage as possible.
If you have one fully charged and the other fully drained, you’ll have a huge current spike as the drained battery takes massive current from the charged battery to reach equillibrium. This will cause a lot of heat, and the battery that is charging could be damaged badly (a shorted cell is very likely to develop).
Absolutely
Before you parallel the batteries, fully charge each one separately.
You’ll be fine with them in parallel.
Battery banks consist of many batteries connected in series to provide the correct voltage for a system. Typical system voltages are 12, 24, 48, & 120 Volts DC. These can consist of many individual batteries, either 12, 6 or 2 volts connected in series. Occasionally batteries will be connected with 2 (or 3) parallel strings to increase the overall capacity of a battery bank.
Yea, you’re ok. The bigger concern is whether you’re deep-cycling batteries that are not intended to be deep-cycled. If you are, you’ll get about 3 to 5 cycles out of them and then plates will start to disintegrate. That’s why you get about 2 chances to leave your car lights on before the third time kills the battery for good.
Yes, you can connect it - in parallel that is + to + and - to -. You will still have the same voltage but the combined amperage of the two batteries.
Will just take your solar panel longer to charge it though.
You are going to find out the same thing I found out in college. Using wind and/or solar to charge batteries(especially lead acid batteries) is an utter waste of time. there is too much loss (ie efficiency is poor) in the charging and draining process in lead acid batteries. In short, they suck. They suck real bad. They also don’t last very long when you discharge them very deeply very frequently. They are designed to be used only a little bit and not very often.
lead acid is too inefficent and photovoltaics make too little electricity.
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, I’m not exaggerating the numbers.
Wow.
Who knew? What a lot of great advice, thanks!! FR rocks.
E x I/R
Ohm’s Law
E is Voltage. That’s like pressure in a water hose, especially when talking about DC. Amperage is the AMOUNT of water that comes out the hose. You can hook them up in parallel, just make sure you use big enough wire. The thicker the better. The electrons won’t care.
I can’t imagine what you could do with a tiny battery like that. The basic minimum would be a group 24 deep cycle battery which is 96 amp hours (x 0.40 = 38 useable amp hours)
That might run a radio or a laptop computer during the summer, but to do it in the winter you need three times as much generating power, which means at least 360 watts of solar panels, which will cost about $750 - $850 on todays market.
Yes. The larger battery will drain faster as per it capacity but in the end they will reach their minimum at about the same time.
It is the total capacity that is your concern, not how much each individual contributes.
Right. That’s one lesson I’m learning already. Scaling up (big) is necessary to actually have a useful source of electricity.
Though it’s probably better for me (total novice) to start small, so when I epic fail numerous times, it’s at least cheaper.
Attempting this in SoCal, so low temps aren’t a factor much. Not trying to run a house with it, just learning how in a pinch - maybe a large quake perhaps - how to get by for a few days maybe a week or two worst case. I’ll perhaps scale it up later, right now just trying to build a subsistence sort of basic backup test system...
It’s fun anyway! Agreeing so far with all the advice (and reality checks) It’s ironic that conservatives are, I would say, more capable of the very sorts of energy advancements, that bubble-heads on the left dream about.
Thanks again all, for the great feedback.
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