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Q & A: battery options

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Most recent answer: 10/22/2007
Q:
I was up late one night and I was wondering if you could use citric acid in a realistic application. I understand 2 lemons only produce 1.5 volts and no real AMPS.... but could the amps be stepped up, by say, capacitors and or maybe a power supply from radio shack? How long would you say maybe a mason jar of acid would work...? Or is there a magic there in the lemons make up balancing the water and acid perfectly in its makeup? (I understand a car battery for example uses distilled water (because it carries no current) I guess I mean, even to a survivalist point could a realistic battery be made using lemon juice? I need to look up the exact role the water plays and how its implemented.... [Mad scientists laugh]
- Chris (age 29)
Las Vegas NV
A:
For a particular battery type, the maximum voltage is fixed by the chemical reaction. The maximum current (amps) before the voltage starts to drop depends on how big a surface the electrodes have, how well mixed the liquid stays, etc. The power is the product of the current and the voltage. Capacitors don't supply and power and don't help increase the power you can get from a battery. A store-bought power supply works nicely if you plug it into the wall and pay your electric bill. Then you can skip the lemons altogether.

How long would you say maybe a mason jar of acid would work...? Or is there a magic there in the lemons make up balancing the water and acid perfectly in its makeup?

A good-sized mason jar would work a lot longer than a lemon, if you have a nice way of holding the zinc and copper electrodes in place. The electrodes might get used up before the zinc concentration in the solution got high enough to require replacing the acid.

There's no special magic in the lemons, although I think acid solutions should work better than alkaline ones for getting the zinc electrode to dissolve.

The fluid in a car battery DOES carry current, and is not anything like distilled water. I think it's largely sulfuric acid. (and it has a lot of lead in it- nasty stuff) When it starts to dry out, you add distilled water because it's the water that's evaporated, more than the other components. Various crud in tap water (calcium salts) would just make trouble.


In my experience you couldn't power anything like a useful light with a lemon battery. Hooking lots of lemon batteries up in parallel will help get you more current at the same voltage. Maybe you could get some very low-power electronic device to work for a while. Under the right circumstances, a GPS device could be important for survival.

Mike W.

(published on 10/22/2007)

Follow-Up #1: Battery charging

Q:
I want to "graft" a deep cycle battery power supply onto my regular use of my 92 Chev. Van (G-20). The aim is to
be able securely at night to carry into my ( off-grid )
camper a deep cycle that I can use for 12v lighting and
maybe to run a portable TV for DVD viewing ( I donít plug
into the "media" tee vee ). If I had a regulator involved
along a set of jump cables, why couldnít I just bore a couple holes into my passenger side floorboard and charge
the deep cycle, sitting on the passenger side floor, by
hookingthe cables to my Die Hard under the hood.
- Andy Summers
Harrison, AR
A:
Hi Andy,
In principle you can do this.  However, I don't think you should make a direct connection to your Die Hard  because it would probably cause too much wear and tear on it with all that discharging and recharging due to imbalance in the loads.  The issue is whether or not you can find a clever regulator that will take care of this problem.  Check around in the RV mags.

LeeH

(published on 10/22/2007)

Follow-up on this answer.