How can I charge a 12V Car Battery?

This may sound a bit of a silly question, but currently I use one of the small 12V 7Ah sealed lead acid batteries to charge my lipos with
(via a lipo charger) - but I only get about 3 charges before the 12V has dropped too far.
...so the obvious solution is to buy a 12v car battery (about 70Ah).
The question is; will I be able to charge the 12V car battery with the same charger that I use to charge the 12V sealed lead acid?
As I understand it a car battery is just a lead acid battery? So same technology and same voltage just higher Ah. Will I blow myself up if I use the small 12v lead acid charger on the big 12v car batt?
Thanks
David Bevan http://www.davidbevan.co.uk
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Hi David, The charger you have will charge the larger battery but will take longer. Car batteries are pretty heavy to be lugging around. Regards, Tom
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snipped-for-privacy@davidbevan.co.uk wrote:

The voltage should be OK if it is the same kind of battery. There are Gel-cells around, that require less voltage. So make sure the charger is for liquid acid lead batteries. It might get more hot when charging and it will take forever with that car battery, but it should be suitable.
--
ciao Ban
Bordighera, Italy
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I think its one of these...
http://www.jperkinsdistribution.co.uk/detail.php?JPNOU10050&activepage=1&Navmain Ίtteries/Chargers&subcatname=Lead%20acid%20-%20gel%20cells
...the output from my charger is 12V/450mA so I guess it would take

Is it safe to charge a car battery unattended? I usually just leave my current 12V on charge permenantly in the garage and just take it off charge to go flying. I always supervise LiPos when I charge them, but they only take 1h, I dont really fancy baby sitting a 12V car battery for 100h!
Thanks
David Bevan http://www.davidbevan.co.uk
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You'll quickly ruin the car battery if you charge it constantly. You need to charge it and then put it on a trickle charger if that's what you want to do.

http://www.jperkinsdistribution.co.uk/detail.php?JPNOU10050&activepage=1&Navmain Ίtteries/Chargers&subcatname=Lead%20acid%20-%20gel%20cells
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Or buy a deep cycle RV or marine battery.
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Alternative sugestions:
1. Walk back to your car to charge the lipos (or the lead battery) 2. Since car batteries are huge, maybe another 7ah battery will give you enough charges. 3. How about some sort of foot pump like generator that you can pump the small lead battery back up, or possibly a lipo directly to save a few strokes, perhaps even while you are flying. 4. Buy more lipos and pre-charge them?
If you can shlep a battery to the pit area, then your car probably isn't that far away and is an excellent source for 12 volts (at least here in the states).

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buy a cheap car charger from a car shop and buy a car battery from Macro for £17/£19 and its got 3 a year guarantee that's what I use
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Funfly3 wrote:

Beware of cheap (unregulated) chargers used routinely. They will boil your electrolyte, and generate excess hydrogen while they're at it.
--
John Miller
email domain: n4vu.com; username: jsm(@)
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What's the price of a regulated charger that will charge a car battery routinely??? a 10AH charger is around £45 so a 50AH is going to be a lot more and the battery has a 3 year warranty all for £17 cook it then take it back
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You're getting Amps and Amp-hours confused. A 10A charger can charge a 100Ah battery.
Tim
--
Don't tell me I'm still on that feckin' island!

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I bought a charger for 69 dollars from Sears. It charges anything that is 12V lead acid under 200 AH, including small gel cells. You can connect the battery up backwards with no harm to charger or battery. It can also provide a 100A burst to help start an engine (car engine, that is).
I have been charging 7AH gel cells with no problem after every use. It normally takes less than a minute. I suspect most of them die from overcharge or being left in a discharged state. I have also been charging 30 AH deep-cycle batteries for field use.
I know that it is a lot of bucks for a charger, but I wanted an automotive charger that worked better than the one I had. It is quite an amazing gadget.
-- Mike Norton

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Mike Norton wrote:

Something is very wrong. A battery that charges in less than a minute either did not need to be charged, was charged *WAY* too fast, or wasn't really charged, due to the charger shutting off when it shouldn't.
Check the instructions for your charger - is there something different you need to do when charging gel cells vs car batteries?
Ed
<snip>

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I got a 50A regulated charger that automatically goes to trickle. I think it cost about $25 at Checker Auto.

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Charging from my car is an option I had thought about since it has got a 12V output in the back. The thing that put me off was that the LiPos are best charged outside of the car (since in certain circumstances they can catch fire) and I didnt really want to leave 2 or three LiPos (at £50 each) laying around on the floor where someone might walk off with them.

Not too sure if thats a serious suggestion? :-)

At £50 each I have bought 3 batts and 2 chargers as this allows for almost continuous flying.
Thanks
David Bevan http://www.davidbevan.co.uk
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Just tryin to think outside the box. I didn't know if the car was anywhere nearby or if you were hiking somewhere remote and wanted a more self sufficient solution. It might not take that many pumps to charge a battery, lessee if I can take a quick guess:
Lets say your setup can make two pounds of thrust for 600 seconds (10 minutes), or 1200 lb. seconds.
Lets also say you weigh 200lbs.
that means for you to make the same output, you would have to put all your weight on the pedal for 1200/200 seconds or 6 SECONDS!
Of course there are losses all over the place in this analogy, and the lipo battery will complain if you charge it in 6 seconds, but it is just a quick starting point for a guess.
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| >>3. How about some sort of foot pump like generator that you can pump the | >>small lead battery back up, or possibly a lipo directly to save a few | >>strokes, perhaps even while you are flying. | | >Not too sure if thats a serious suggestion? :-) | | Just tryin to think outside the box. I didn't know if the car was anywhere | nearby or if you were hiking somewhere remote and wanted a more self | sufficient solution. It might not take that many pumps to charge a battery, | lessee if I can take a quick guess: | | Lets say your setup can make two pounds of thrust for 600 seconds (10 | minutes), or 1200 lb. seconds. | | Lets also say you weigh 200lbs. | | that means for you to make the same output, you would have to put all your | weight on the pedal for 1200/200 seconds or 6 SECONDS!
Your understanding of the idea of work (in the physics sense) is very flawed.
Mere thrust (force) does not do work. Force * distance is what gives you work (energy) -- you'd need to not only push on that pedal, but actually move it. A long distance.
Assuming that you could push down on the pedal with 200 lbs of force, if you moved it one foot that would produce 271 joules -- which would give you one watt for 271 seconds or some combination thereof.
Assuming you had a 7Ah 12 volt battery (a popular size for field boxes) and it was completely discharged, and you wanted to completely charge it by pushing on your pedal with 200 lbs of force, you'd have to push it 1116 feet. (This is assuming that everything is 100% efficient, and that the voltage is exactly 12 volts and stays there, of course -- assumptions that are not accurate. In the real world, you'd have to push the pedal more to compensate for the losses and the increase in voltage.)
That also means that this battery has enough power, fully charged, to raise your body (if it weighs 200 lbs) 1116 feet in the air, assuming all is 100% efficient.
It certainly is possible to charge batteries via muscle power, but a lot more muscle is required than one might think.
I believe that a top athlete can produce about 1/2 horsepower (380 watts) for several minutes. Making the same (incorrect) assumptions as before, this would mean that the athlete could charge that battery in about 13 minutes, if the athlete could keep up that rate of work.
And this is just for a pretty small battery ...
To make this R/C related, your LiPo battery in your plane is probably smaller than this field box battery. Perhaps 1/4th the size, So your athlete could charge it in about three minutes, which is more realistic, except that the battery couldn't tolerate that :)
--
Doug McLaren, snipped-for-privacy@frenzy.com
When I die, I want to donate my body to science fiction.
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[...]
Yup. In the real world, you probably can't get much more than 50% efficiency in the generator, and the voltage is closer to 14V.
That translates into pushing with 200lb of force through a distance of about 2600 feet (let's just say a half a mile).

If I remember correctly from articles on human powered flight, 1/2HP (373W) was about the best you can get from a trained cyclist for any decent period of time. IIRC, an average joe probably can't produce more than 50-100W for more than a few minutes.
7AH @ 14V == 352,800 Joules.
Assuming a generator efficiency of about 50% and somebody pedalling at 100W, it would take about 7000 seconds (352800/(100*0.5)). Roughly two hours.
--
Grant Edwards grante Yow! Yow! Maybe I should
at have asked for my Neutron
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wrote:

the
anywhere
battery,
your
I guess you missed the relationship between thrust and time. Hint: pretend the airplane is just a fancy rocket. In this example it is putting out 2 lbs. of thrust, for 600 seconds, we are disregarding the weight of the rocket.
Yes, you actually have to be moving the pedal with your entire weight for those 6 seconds, but with a spring and proper gearing or leverage, you can reproduce the same two pound push for 600 seconds.
Reaching for the work formula will not help you see this relationship without a bit of algebra, and that woud be contrary to my stated goal of a quick guess ;).
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Wrong.
Gears and levers do not provide a ratio between thrust/time and thrust/time. The ratio provided by gearing/leverage provides ratios of thrust/distance -- which is what was explained to you using the formula for work.

Because there is no such relationship.

Quick, but not founded in real physics.
--
Grant Edwards grante Yow! Boys, you have ALL
at been selected to LEAVE th'
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