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Model Forum / Radio Controlled / Air Models / June 2005How 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 > 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 [quoted text clipped - 14 lines] > David Bevan > http://www.davidbevan.co.uk 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 > 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 [quoted text clipped - 14 lines] > David Bevan > http://www.davidbevan.co.uk 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.  Signatureciao Ban Bordighera, Italy I think its one of these... http://www.jperkinsdistribution.co.uk/detail.php?JPNO=5510050&activepage=1&Navma in=Batteries/Chargers&subcatname=Lead%20acid%20-%20gel%20cells ...the output from my charger is 12V/450mA so I guess it would take >100h to fully charge a flat /70Ah car battery? 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 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. >I think its one of these... > [quoted text clipped - 13 lines] > David Bevan > http://www.davidbevan.co.uk > 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 [quoted text clipped - 17 lines] >> David Bevan >> http://www.davidbevan.co.uk Or buy a deep cycle RV or marine battery. > ...so the obvious solution is to buy a 12v car battery (about 70Ah). > [quoted text clipped - 4 lines] > 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? Not quite the same I'm afraid. A car battery will not withstand deep cycling, go and buy either a 'Leisure' battery or a larger, sealed 'traction' one. Either way, use the right charger, or you'll write it off in no time !! - Steve 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). > 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 [quoted text clipped - 14 lines] > David Bevan > http://www.davidbevan.co.uk 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 > 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 Beware of cheap (unregulated) chargers used routinely. They will boil your electrolyte, and generate excess hydrogen while they're at it. SignatureJohn Miller email domain: n4vu.com; username: jsm(@) >> 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 > > Beware of cheap (unregulated) chargers used routinely. They will boil > your electrolyte, and generate excess hydrogen while they're at it. 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 >>> buy a cheap car charger from a car shop and buy a car battery from Macro >>> for [quoted text clipped - 7 lines] >more and the battery has a 3 year warranty all for £17 cook it then take it >back You're getting Amps and Amp-hours confused. A 10A charger can charge a 100Ah battery. Tim SignatureDon't tell me I'm still on that feckin' island! >>>> buy a cheap car charger from a car shop and buy a car battery from >>>> Macro [quoted text clipped - 14 lines] > > Tim No I am not, a decent charger that bulk charges then float charges has a maximum capacity battery size it can cope with a charger that's designed for a small battery will not bulk charge a car battery but your right a normal 10 amp charger will charge any battery but it will cook it if left on two long 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 >>> buy a cheap car charger from a car shop and buy a car battery from Macro >>> for [quoted text clipped - 7 lines] > more and the battery has a 3 year warranty all for £17 cook it then take > it back > 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 [quoted text clipped - 3 lines] > I have been charging 7AH gel cells with no problem after every use. It > normally takes less than a minute. 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> > -- Mike Norton I set it at two amperes charge rate, low-maintenance (gel cell or AGM). These are separate settings. In many cases, I suspect you are correct about not needing to be charged; at least, it does not overcharge it like the WallWart charger does. One time, after using the starter on a recalcitrant .91 for what seemed like an hour, it took 2 hours to charge it. >> 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 [quoted text clipped - 20 lines] > >> -- Mike Norton I got a 50A regulated charger that automatically goes to trickle. I think it cost about $25 at Checker Auto. >> 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 > > Beware of cheap (unregulated) chargers used routinely. They will boil > your electrolyte, and generate excess hydrogen while they're at it. > 1. Walk back to your car to charge the lipos (or the lead battery) 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. >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? :-) >4. Buy more lipos and pre-charge them? 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 >>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! 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. | >>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 [quoted text clipped - 14 lines] | 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 :) SignatureDoug McLaren, dougmc@frenzy.com When I die, I want to donate my body to science fiction. >> 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. [...] > Assuming you had a 7Ah 12 volt battery (a popular size for > field boxes) and it was completely discharged, and you wanted [quoted text clipped - 5 lines] > the pedal more to compensate for the losses and the increase > in voltage.) 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). > 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. 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. SignatureGrant Edwards grante Yow! Yow! Maybe I should at have asked for my Neutron visi.com Bomb in PAISLEY-- > | >>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 [quoted text clipped - 17 lines] > Your understanding of the idea of work (in the physics sense) is very > flawed bla bla bla. 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 ;). >> | weight on the pedal for 1200/200 seconds or 6 SECONDS! >> [quoted text clipped - 10 lines] > gearing or leverage, you can reproduce the same two pound push > for 600 seconds. 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. > Reaching for the work formula will not help you see this relationship Because there is no such relationship. > without a bit of algebra, and that woud be contrary to my > stated goal of a quick guess ;). Quick, but not founded in real physics. SignatureGrant Edwards grante Yow! Boys, you have ALL at been selected to LEAVE th' visi.com PLANET in 15 minutes!! > >> | weight on the pedal for 1200/200 seconds or 6 SECONDS! > >> [quoted text clipped - 12 lines] > > 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. Thanks, I am quite familiar with the formula. The point of the SPRING was to store the energy that it could be dissapated as a two pound push for a longer period. > > Reaching for the work formula will not help you see this relationship > > Because there is no such relationship. What are you afraid of?!? > > without a bit of algebra, and that woud be contrary to my > > stated goal of a quick guess ;). > > Quick, but not founded in real physics. Ok, if you don't trust my instincts then look at Newtons second law and pretend we are pushing on a large rock in space with our pedal. We have known forces( 2 and 200lbs.) , assume a large mass, the times are known(600 and 6 seconds), the terminal velocities can be computed and will be the SAME if we push for 600 seconds with 2 lbs or 6 seconds with 200 lbs. The only trick here is in finding the right sized rock to limit how far you have to move the pedal in those 6 seconds. >>>> | weight on the pedal for 1200/200 seconds or 6 SECONDS! >>>> [quoted text clipped - 21 lines] > to store the energy that it could be dissapated as a two pound push for a > longer period. I realize that. However, you seem to think that force integrated over time is energy. It isn't force integrated over _distance_ is energy. Energy is conserved. Thrust-time is not. >>> Reaching for the work formula will not help you see this >>> relationship >> >> Because there is no such relationship. > > What are you afraid of?!? Well, there's a pretty long list, but I don't think it has anythign to do with this discussion. >> > without a bit of algebra, and that woud be contrary to my >> > stated goal of a quick guess ;). [quoted text clipped - 4 lines] > second law and pretend we are pushing on a large rock in space > with our pedal. > We have known forces( 2 and 200lbs.) , assume a large mass, > the times are known(600 and 6 seconds), the terminal > velocities can be computed and will be the SAME if we push for > 600 seconds with 2 lbs or 6 seconds with 200 lbs. Only because the mass you're accellerating is the same in both cases. This results in the distance moved by the smaller force being much larger. > The only trick here is in finding the right sized rock to > limit how far you have to move the pedal in those 6 seconds. I give up. SignatureGrant Edwards grante Yow! I just forgot my at whole philosophy of life!!! visi.com ... > > We have known forces( 2 and 200lbs.) , assume a large mass, > > the times are known(600 and 6 seconds), the terminal [quoted text clipped - 4 lines] > cases. This results in the distance moved by the smaller force > being much larger. True, but the resulting energy that you can extract from the same sized rock moving at the same velocity is the same. > > The only trick here is in finding the right sized rock to > > limit how far you have to move the pedal in those 6 seconds. > > I give up. That is an acceptable answer, I would have also accepted "you idiot!!!" or "remind me to slap your mama!!!" Really, it doesn't work, I'm quite aware of that. (hint: momentum != energy), I really just like messing with fizzycists like Doug "Watch out for that slow moving meteor!!" Mclaren 8^o ... | > | 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 [quoted text clipped - 4 lines] | | I guess you missed the relationship between thrust and time. No, I understand the relationship. It's just not relevant to figuring out how hard and long a person would have to work to recharge a battery. | 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. You are grossly mangling the physics involved and using that to come up with absurd answers. This is not rocket science, an airplane is not a fancy rocket, and when we're talking about charging a battery with human power, there's no need to involve an airplane. Hint: I have a degree in physics. I spent several years in school studying this stuff, though this is _the_ basics, Physics 101. They go over this stuff in the very first physics class in college, and probably in high school too (I don't really remember what we covered there.) | 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. So, what I really need to do is put this magic pedal under one of the corners of my bed (so it's supporting much of my weight), and then take a nap on it. Unlimited free energy! I could put one of these pedals into an electric R/C plane, wrap it in rubber bands (so there's a constant force on it) and use that to fly my electric plane across the Atlantic. Look out Maynard! Look out laws of thermodynamics -- I've got a perpetual motion machine, in R/C form! | 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 ;). I didn't make a quick guess. I did all the math and algebra involved (it's not very much, actually -- took a few minutes) and gave you exact figures (and explicitly stated all the assumptions/simplifcations I made.) Actually, I used the `units' program to do most of the heavy lifting for me -- % units 2084 units, 71 prefixes, 32 nonlinear units You have: 200 pounds-force * feet You want: joules * 271.16359 once I had that figure -- 200 pounds * 1 foot = 271 joules, the rest was just simple algebra and arithmetic. Oh, you'll also need to know that power = voltage * current (watts = volts * amps), one watt = one joule/second, that there's 3600 seconds in an hour (to convert volts and amp-hours to joules) and 746 watts in a horsepower (though somehow I originally had it in my head that it was 760 watts. Not sure where that mistake came from ....) http://en.wikipedia.org/wiki/Mechanical_work may be of some assistance if you still don't understand the physics involved. Go down to the `Simpler formulae' part -- there's no need to use integrals to get a good approximation of the human work needed. SignatureDoug McLaren, dougmc@frenzy.com Computers make it easy to do alot of things, but most of the things that make it easier to do don't need to be done. -- Andy Rooney > | I guess you missed the relationship between thrust and time. > > No, I understand the relationship. It's just not relevant to figuring > out how hard and long a person would have to work to recharge a > battery. There are tons of losses to consider, nevertheless there is a direct relationship between an airplanes battery capacity, and how hard and for how long it can push against the air. If my guess was within an order of magnitude then I'd call it a good guess. > | 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 [quoted text clipped - 4 lines] > not a fancy rocket, and when we're talking about charging a battery > with human power, there's no need to involve an airplane. I am not attempting to mangle physics, and I did mention that "there are losses all over the place in this analogy" and I am well aware of what they are though I choose not to ramble on and on about them. > Hint: I have a degree in physics. I spent several years in school > studying this stuff, though this is _the_ basics, Physics 101. They > go over this stuff in the very first physics class in college, and > probably in high school too (I don't really remember what we covered > there.) Intelligence is no defense against stupidity ;) > | 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 [quoted text clipped - 3 lines] > corners of my bed (so it's supporting much of my weight), and then > take a nap on it. Unlimited free energy! ... Thats cute, I can imagine you doing a little dance showing off an imaginary magic pedal to the room while you typed that. > | 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 ;). > > I didn't make a quick guess. That wasn't the point, and you grossly deviated when you made the comparison of a ~1500mah 9.6 power pack to a 12V 7000ah battery. With a more correct battery pack for the thrust and duration given it comes out to just under 120 strokes, or about a minute on the treadmill, which happens to be within an order of magnitude of my 6 second guess. So thanks for lending validity to my theory, which BTW didn't take me years of specialized college coursework to realize. [snip] >That wasn't the point, and you grossly deviated when you made the comparison >of a ~1500mah 9.6 power pack to a 12V 7000ah battery. With a more correct [quoted text clipped - 3 lines] >to my theory, which BTW didn't take me years of specialized college >coursework to realize. Dude, you're funny. Tim SignatureToday's message was brought to you by Mary, Jane and a big number two. In sci.chem.electrochem.battery Steve Banks <none@here.isfine> wrote: <snip> > That wasn't the point, and you grossly deviated when you made the comparison > of a ~1500mah 9.6 power pack to a 12V 7000ah battery. With a more correct [quoted text clipped - 3 lines] > to my theory, which BTW didn't take me years of specialized college > coursework to realize. 1.5Ah * 9.6V = ~15Wh. To recharge in a minute (which will kill the cells) you'd need a power of 15W*60 = 900W. Say a efficiency of 80%, and you'r up to 1100W. Trained athletes can't provide that much power, unless ground up and mixed with oxidiser. >So thanks for lending validity >to my theory, which BTW didn't take me years of >specialized college >coursework to realize. You need years of specialized college coursework, or actual experimentation with human-powered generators, to realize just how far off you are. Any kid who has visited a science center and pedaled one of those little generators to power a small television (maybe 75 or 100 watts) quickly understands that it takes a LOT of work to generate any significant amount of juice. Makes one appreciate cheap electricity... Dan > That wasn't the point, and you grossly deviated when you made the comparison > of a ~1500mah 9.6 power pack to a 12V 7000ah battery. With a more correct [quoted text clipped - 3 lines] > to my theory, which BTW didn't take me years of specialized college > coursework to realize. OK, we'll try this again. 1.5A * 9.6V * 3600s = 51840 joules. Somebody in decent shape on a bicylce (far more efficient than a treadmill) can put out 50-100 joules/second for an extended period of time. On the conservative side, we'll say 50W. Assuming 50% efficiency for the combination generator and whatnot: 1.5 * 9.6 * 3600 ------------------ = 2074 seconds = 35 minutes. 50 * 0.5 Assuming 100W (you'd better be in pretty good shape), and a 100% efficient generator and battery (let me know where you plan on buyign those) it's a fourth of that -- about 9 minutes. Still not within an order of magnitude of 6 seconds. SignatureGrant Edwards grante Yow! My polyvinyl cowboy at wallet was made in Hong visi.com Kong by Montgomery Clift! what a silly thread. GO FLY!! >> That wasn't the point, and you grossly deviated when you made the >> comparison [quoted text clipped - 25 lines] > > Still not within an order of magnitude of 6 seconds. >> Yes, you actually have to be moving the pedal with your entire >> weight for those 6 seconds, but with a spring and proper [quoted text clipped - 4 lines] > of the corners of my bed (so it's supporting much of my > weight), and then take a nap on it. You think too small. Park your car on it overnight! After eight hours, you could store up enough thrust-hours to accellerate your car at 1G for eight hours! That should be more than enough thrust to get it into orbit. Remember to take some O2. Oh, you might want to save up some thrust-hours to make a controlled re-entry. > Unlimited free energy! I could put one of these pedals into > an electric R/C plane, wrap it in rubber bands (so there's a > constant force on it) and use that to fly my electric plane > across the Atlantic. Look out Maynard! Look out laws of > thermodynamics -- I've got a perpetual motion machine, in R/C > form! On my way to the patent office, looking over my shoulder for snipers working for the oil companies.... SignatureGrant Edwards grante Yow! Pardon me, but do you at know what it means to be visi.com TRULY ONE with your BOOTH! > 1. Walk back to your car to charge the lipos (or the lead battery) 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. >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? :-) >4. Buy more lipos and pre-charge them? 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 If you're worried about a LiPo burning up your vehicle, make yourself an extension cord so your charger and LiPo are away from it. If you're flying from a grassy area, it would be a good idea to bring something like a bucket of sand or some other nonflammable substance to put your pack on or in while it's charging. You could also fix up a lockable top on the bucket and chain it to your vehicle's frame if you're worried about theft! (just kidding) Morris > 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 [quoted text clipped - 14 lines] > David Bevan > http://www.davidbevan.co.uk I OK I'll 'fess up - I don't know - WHAT'S a LIPOS ?????? AWEM >> 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 [quoted text clipped - 21 lines] > > AWEM Lithium Polymer or LiPo for short at the moment these are the way forward for a lot of electric flying my 11.1v 2600mah LiPo weighs 140 grams, my 9.6v 2400mah NiCd pack weighs 500 grams, LiPo have a much greater charge density than normal packs or in other words are lighter and smaller for the same capacity >>> 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 [quoted text clipped - 27 lines] > greater charge density than normal packs or in other words are > lighter and smaller for the same capacity And they have an unfortunate propensity to spontaneously burn up SUVs. Exhibit A: http://www.rcgroups.com/forums/showthread.php?t=140641 ... | > Lithium Polymer or LiPo for short at the moment these are the way | > forward for a lot of electric flying my 11.1v 2600mah LiPo weighs 140 [quoted text clipped - 3 lines] | | And they have an unfortunate propensity to spontaneously burn up SUVs. And if you'll read the description of the story you linked to, they didn't `spontaneously' burn up that SUV. The pack was damaged -- that's hardly spontaneous, even if it was slightly delayed. And to be fair, NiCd batteries can cause fires too when damaged. Yes, LiPos do require that some care be taken with them, and if you fail to take proper care of them they can catch fire. But 1) under the right (wrong) conditions, other batteries can cause fires/catch fire too, and 2) they're not the sticks of unstable dynamite that people seem to make them out to be. | Exhibit A: | http://www.rcgroups.com/forums/showthread.php?t=140641 SignatureDoug McLaren, dougmc@frenzy.com She gave me a look you could have poured on pancakes. > ... > | > Lithium Polymer or LiPo for short at the moment these are the way [quoted text clipped - 19 lines] > | Exhibit A: > | http://www.rcgroups.com/forums/showthread.php?t=140641 lead acid batteries can go with a hell of a bang too if they generate enough hydrogen gas wich then gets ignited. (like if u acidently short one out after over charging it !) Colin =^.^= Andrew I have been away from this discussion group for a long. Now I am on a roll. Good to be back. I thought everyone knows what a Lipo (Lithium Polymer) is by now. This is the type of battery that is all the rage now. Beats NiMh, Nicad. Lipos are lighter, smaller, longer flight times. I am by far not an expert, been using them for about 3 years. Loved them. Wan Andrew I have been away from this discussion group for a long. Now I am on a roll. Good to be back. I thought everyone knows what a Lipo (Lithium Polymer) is by now. This is the type of battery that is all the rage now. Beats NiMh, Nicad. Lipos are lighter, smaller, longer flight times. I am by far from being an expert, been using them for about 3 years. Loved them. Wan >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). Is this for charging in the field or at home? If it's for use at home, get a 13.8V (or 12V) power supply. I've got the Pro Peak 20A one. £35 and it's got more than enough oomph for everything I need. I've not seen another PSU with similar capacity anywhere near the price, except in a PC of course :) http://www.sussex-model-centre.co.uk/Pro+Peak+Power+supply-5167.htm If it's for the field I wouldn't get a car battery. Decide how many charges you want, then buy cyclic or deep-discharge rated SLA of appropriate capacity. Do you really need 30 charges out of a field battery? Lugging a car battery around is no fun, if you drop it acid pours out and they aren't rated for deep-discharge cyclic use so you'd be lucky if it lasts a year. A cyclic-rated SLA will give you over 500 genuine cycles, which is several years of flying for most of us. Tim SignatureDon't tell me I'm still on that feckin' island! > Decide how many charges you want, then buy cyclic or deep-discharge rated SLA of appropriate capacity. Is SLA short for sealed lead acid? As thats what I have got now and I cant seem to find them over 7Ah? I am charging 1600mAh LiPo packs, and get 2 or 3 charges before the charger refuses to charge (as input voltage has dropped) I guess if im realistic then I will go to the patch with 3 charged LiPos and probably wont want more than 10 flights which will mean 7x1600mA = 11Ah - so I guess I would need a minimum of 15Ah in the 12V. Please let me know if you can find such a battery. Thanks David Bevan http://www.davidbevan.co.uk >> Decide how many charges you want, then buy cyclic or deep-discharge rated SLA of appropriate capacity. > [quoted text clipped - 7 lines] >7x1600mA = 11Ah - so I guess I would need a minimum of 15Ah in the 12V. >Please let me know if you can find such a battery. Search for "sealed lead acid" on your favourite search engine and you'll find loads of suppliers. One at random: http://eurobatteries.com/sitepages/sla.asp Tim SignatureDon't tell me I'm still on that feckin' island! >Is SLA short for sealed lead acid? As thats what I have got now and I >cant seem to find them over 7Ah? You haven't discovered the 'Cyclon' range then. I've been using a pair of small 2.5AH Cyclons in a flashlight since about 1982 with no problems until just last week when one of them developed an internal short. That's longevity for you! You can get 2v cells in 25AH, so you'd need 6 of them. An advantage of building using single cells is that if one goes bad you don't have to replace the whole lot--just the one cell. Search: hawker cyclon lead SignatureJohn Savage (my news address is not valid for email) Buy a small tractor battery. They're about $18 at your local auto parts store. Buy a cheap auto battery charger for it. You should be able to get one in the $20-30 range. I have two tractor batteries. (They're not very heavy) I keep 'em both charged. Of course the simplest solution is to use your CAR BATTERY to charge your lipos! That's what I do when I'm at the field. A final solution is to buy a 12V power source to use your li-po charger in the house! The little gel cells just don't have enough amp hours to last long. > 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 [quoted text clipped - 14 lines] > David Bevan > http://www.davidbevan.co.uk It'll work just fine, only very slow. Go to Walmart and get a cheap auto charger. Prolly not more than $20.00. > 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 [quoted text clipped - 14 lines] > David Bevan > http://www.davidbevan.co.uk I use a Die Hard lawn tractor battery for my electric flying. I charge it using one of those Battery Tender charger/minders. Much smaller than a standard car batt with a high capacity. Cool thing with the tender is you can leave it hooked up all week and it keeps the battery up without overcharging. The lawn tractor battery also fits in the bottom of a rolling plastic tool box I have keeping me self sufficient at the field. SignatureDan AMA605992 KE6ERB http://www.fubar1.net "I've heard the screams of the vegetables..." Take out the "trash" to reply > 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 [quoted text clipped - 14 lines] > David Bevan > http://www.davidbevan.co.uk but I only get about 3 charges before the 12V has dropped too far. You need to use a power supply. Using a battery to supply voltage to a battery charger is a no win situation. It works with field chargers only because the supply battery is MUCH larger than the battery being charged, and can be kept peaked by the car's engine. (about 70Ah). Good luck finding a car battery that small. They usually come in ratings of 600Ah or more. 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? Yup <giggle> but you may be there for days. Dr.1 > but I only get about 3 charges before the 12V has dropped too far. > You need to use a power supply. Using a battery to supply voltage to a [quoted text clipped - 5 lines] > Good luck finding a car battery that small. They usually come in > ratings of 600Ah or more. I think on this point your are way of the mark a 600Ah battery is massive fork lift truck sized, the maximun sized battery fitted to my Vauxhall Astra is 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? > Yup <giggle> but you may be there for days. > > Dr.1 >> (about 70Ah). >> Good luck finding a car battery that small. They usually come in >> ratings of 600Ah or more. > I think on this point your are way of the mark a 600Ah battery is massive > fork lift truck sized, the maximun sized battery fitted to my Vauxhall > Astra is 70Ah FWIW - car batteries are supposed to be used to start engines and nothing else. The most important number therefore is the maximum current that can be drawn.. Logically - thats the number placed in the big letters on the side of batts:) Biggest 'car' batts I have personally seen are 100AH capacity - these delivered 700A - at least thats what it said on the side;) Methinks if you were to drain it in 8 mins it would be a bit warm! SC > 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 [quoted text clipped - 14 lines] > David Bevan > http://www.davidbevan.co.uk I hope you can forgive me. This way off topic. I don't know what happened, but I have been unable to log onto this usenet for the longest time and am just trying to see if I could do it. Strangely, now I can whereas I could not for almost a year. However I do know people have been using car batteries for charging Li Polies sucessfully. They just use a 12 volt charger to recharge the batery. No problems. Wan Er, i think the best way to charge a car battery, is to leave it in the car. >> 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 [quoted text clipped - 25 lines] > > Wan >Er, i think the best way to charge a car battery, is to leave it in the car. --- And drive around for a while. SignatureJohn Fields Professional Circuit Designer >>Er, i think the best way to charge a car battery, is to leave it in the car. > >--- >And drive around for a while. That might not be safe! greg |
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