erspert@athena.mit.edu (Ellen R. Spertus) (10/05/90)
I saw a car battery recharger for $60 in the Rand McNally map catalog. If your battery is dead, you plug this into your cigarette lighter, and it recharges the battery (enough to start) from a D battery. It seems like a neat idea. I have a few questions: 1. Has anyone used one of these? Any comments? 2. Can I build one of these myself? I've built computers, etc., before, and I have access to lab equipment. Anyone know where I could get plans? Thanks. Please direct follow-ups to the appropriate group or email me. Ellen
jgd@rsiatl.UUCP (John G. DeArmond) (10/06/90)
erspert@athena.mit.edu (Ellen R. Spertus) writes: >I saw a car battery recharger for $60 in the Rand McNally map catalog. >If your battery is dead, you plug this into your cigarette lighter, and >it recharges the battery (enough to start) from a D battery. It seems >like a neat idea. I have a few questions: >1. Has anyone used one of these? Any comments? No, but I do have some comments :-) >2. Can I build one of these myself? I've built computers, etc., >before, and I have access to lab equipment. Anyone know where I could >get plans? The math does not add up. A typical D cell battery has between 4 and 6 amp-hours capacity if discharged to total exhaustion which you could not do easily in this application. Be generous and give the charging process 60% efficiency. Now ask the question, "would 2 to 4 amphours of charge in a 60 to 100 amp-hour battery make much difference?" Probably not except under ideal circumstances, which is how the product is tested. Plus you've got to assure that the dry cells are in good shape. If you've got enough presence of mind to do this over the long term, you could probably put that effort in to keeping the battery in good shape to begin with and remember to turn the lights off. A much better solution to this problem is to get one of these new batteries that are actually 2 batteries on one with a switch on top. run one down and flip the switch for the other. Or you could just install 2 batteries. That is my solution. Get a charging bridge from any RV shop and install a battery transfer switch to select which one is connected to the starter. Easy, straightforward and stone cold reliable. BTW, several racing component companies are now selling compact, dry batteries that consist of the GATES starved acid cells of the X capacity strapped together in a nice package. High surge capability, low weight and no acid to deal with. And it will relieve you of about $200 or so. John Pl -- John De Armond, WD4OQC | We can no more blame our loss of freedom on congress Radiation Systems, Inc. | than we can prostitution on pimps. Both simply Atlanta, Ga | provide broker services for their customers. {emory,uunet}!rsiatl!jgd| - Dr. W Williams | **I am the NRA**