Charging car battery from cigarette lighter

RoQuEr · 06-09-07, 09:55 PM

Does this product do anything special? http://www.improvementscatalog.com/h...y-charger.html

I was wondering if any 12v DC battery plugged into my cigarette lighter could charge a car battery. I know this is basic physics, but I'd rather not find out the hard way. Could I plug in my jump start battery to the cigaretter lighter overnight and expect the car battery to be charged, and the jump-start battery to be drained?

OldDude · 06-10-07, 07:14 AM

It obviously uses magic. Otherwise it is too small to hold enough charge to recharge a totally dead car battery.

If the batteries are the same technology, and number of cells, they will "share" their charge, and wind up with a partial charge on both. If the charging battery is a higher nominal voltage (different number of cells in series or a different technology), it will transfer "most" of its charge and be nearly discharged.

The question is how many amp-hours in the charging battery and how many amp-hours does the dead battery need. A typical car battery might be rated 50-100 Ah, and it needs about 20% more charge than it is missing to properly replace the charge. (Although you don't need a FULL charge to restart car)

Bottom line, if it is not as big as car battery (physical size), it is not as big as a car battery (electrical capacity). But maybe the charge fairy will step in and help.

Nick Danger · 06-10-07, 09:55 AM

Why is it hard to build small, powerful batteries? It's easy to set up a chemical reaction that produces a lot of heat energy in a short time, like nitroglycerin. Why can't we set up a chemical reaction that produces a lot of charge in a short time?

Or, what's so cool about lead-acid batteries?

OldDude · 06-10-07, 10:51 AM

Lead-acid batteries are not state-of-the-heart in charge per pound by any means. They are so-so, but dirt cheap and rugged.

Lithium and nickel metal hydride store more energy per unit weight, but are expensive and a bit fussy on charge/discharge cycles.

I don't know if nitroglycerin is a good or bad example. It actually has less energy per unit weight than gasoline, diesel, etc., but is capable of much faster reaction times (explosive). Gasoline has to be vaporized and mixed to correct air/fuel ratio to approach that reaction speed

Edit: Wikipedia has a pretty good summary on different chemistry. Also links with more detail for each kind. Some newer chemistries are 3-4X better than lead acid, nothing is 10X better. Generally lead-acid costs less, but is bigger, heavier.
http://en.wikipedia.org/wiki/Rechargeable_battery

krkuhl · 06-10-07, 10:58 AM

didnt work on my full size chevy truck in college but worked fine on my little saturn. no idea how/why. both had their lights left on overnight causing their battery to die. then again, my chevy was quite a bit older than my saturn at the time.

OldDude · 06-10-07, 11:56 AM

Quote:

Originally Posted by krkuhl

didnt work on my full size chevy truck in college but worked fine on my little saturn. no idea how/why. both had their lights left on overnight causing their battery to die. then again, my chevy was quite a bit older than my saturn at the time.

I'm guessing the truck had a much larger engine and therefore a larger battery, starter motor needed more current, etc. The little booster battery was less able to make a difference than on the scaled down system in the Saturn. But it's a YMMV situation, at best.

RoQuEr · 06-10-07, 02:16 PM

Interesting fact: A lithium ion battry, such as the one in your cell phone has half the potential energy as an equal amount of dynamite.

edit: Since the portable battery is 12v, and the car battery is really 14.8 or so, then I can expect it to only partially charge the car, if at all, correct?

06-09-07, 09:55 PM	#1
RoQuEr DVD Talk Limited Edition Join Date: Jan 2001 Location: Florida Posts: 5,456	Charging car battery from cigarette lighter Does this product do anything special? http://www.improvementscatalog.com/h...y-charger.html I was wondering if any 12v DC battery plugged into my cigarette lighter could charge a car battery. I know this is basic physics, but I'd rather not find out the hard way. Could I plug in my jump start battery to the cigaretter lighter overnight and expect the car battery to be charged, and the jump-start battery to be drained? __________________ Spoiler: "Our enemies are innovative and resourceful, and so are we," Bush said. "They never stop thinking about new ways to harm our country and our people, and neither do we.

06-10-07, 07:14 AM	#2
OldDude DVD Talk Legend Join Date: Jul 2001 Location: MI Posts: 24,497	It obviously uses magic. Otherwise it is too small to hold enough charge to recharge a totally dead car battery. If the batteries are the same technology, and number of cells, they will "share" their charge, and wind up with a partial charge on both. If the charging battery is a higher nominal voltage (different number of cells in series or a different technology), it will transfer "most" of its charge and be nearly discharged. The question is how many amp-hours in the charging battery and how many amp-hours does the dead battery need. A typical car battery might be rated 50-100 Ah, and it needs about 20% more charge than it is missing to properly replace the charge. (Although you don't need a FULL charge to restart car) Bottom line, if it is not as big as car battery (physical size), it is not as big as a car battery (electrical capacity). But maybe the charge fairy will step in and help. __________________ 9/11/2001 - You have awakened a sleeping giant, and filled him with a terrible resolve. - paraphrased from Yamamoto

06-10-07, 09:55 AM	#3
Nick Danger DVD Talk Legend Join Date: Mar 2001 Location: Albuquerque Posts: 14,520	Why is it hard to build small, powerful batteries? It's easy to set up a chemical reaction that produces a lot of heat energy in a short time, like nitroglycerin. Why can't we set up a chemical reaction that produces a lot of charge in a short time? Or, what's so cool about lead-acid batteries? __________________ Originally Posted by TallGuyMe: hoorah for Nick!

06-10-07, 10:51 AM	#4
OldDude DVD Talk Legend Join Date: Jul 2001 Location: MI Posts: 24,497	Lead-acid batteries are not state-of-the-heart in charge per pound by any means. They are so-so, but dirt cheap and rugged. Lithium and nickel metal hydride store more energy per unit weight, but are expensive and a bit fussy on charge/discharge cycles. I don't know if nitroglycerin is a good or bad example. It actually has less energy per unit weight than gasoline, diesel, etc., but is capable of much faster reaction times (explosive). Gasoline has to be vaporized and mixed to correct air/fuel ratio to approach that reaction speed Edit: Wikipedia has a pretty good summary on different chemistry. Also links with more detail for each kind. Some newer chemistries are 3-4X better than lead acid, nothing is 10X better. Generally lead-acid costs less, but is bigger, heavier. http://en.wikipedia.org/wiki/Rechargeable_battery __________________ 9/11/2001 - You have awakened a sleeping giant, and filled him with a terrible resolve. - paraphrased from Yamamoto Last edited by OldDude; 06-10-07 at 11:10 AM.

06-10-07, 10:58 AM	#5
krkuhl DVD Talk Ultimate Edition Join Date: Jul 2000 Location: houston, tx Posts: 4,826	didnt work on my full size chevy truck in college but worked fine on my little saturn. no idea how/why. both had their lights left on overnight causing their battery to die. then again, my chevy was quite a bit older than my saturn at the time. __________________ I got a sweater for Christmas. i really wanted a screamer or a moaner.

06-10-07, 02:16 PM	#7
RoQuEr DVD Talk Limited Edition Join Date: Jan 2001 Location: Florida Posts: 5,456	Interesting fact: A lithium ion battry, such as the one in your cell phone has half the potential energy as an equal amount of dynamite. edit: Since the portable battery is 12v, and the car battery is really 14.8 or so, then I can expect it to only partially charge the car, if at all, correct? __________________ Spoiler: "Our enemies are innovative and resourceful, and so are we," Bush said. "They never stop thinking about new ways to harm our country and our people, and neither do we.