The technical aspects of Battery Charging

[The Wilsons]

Charles Shiplee wrote, "I have taken no offence and am safe in the knowledge that ... I am allowed at least one stupid question." Charles, what a magnanimous comment to try to end this thread and how pleasant it is in contrast to the inappropriate reply that started it all. Thank you! However, I think you have improperly characterized your original question. All the banter got me thinking about why, when charging a car battery, it doesn't make any difference how the battery is grounded. I realized that the issue is more subtle than it appeared and I think it is reasonable for a prudent person to wonder about it. It certainly COULD matter how the battery was grounded. The fundamental reason it doesn't matter is that the DC side of battery chargers always float relative to ground (i.e., are not electrically connected to ground). This is not true for all types of DC power supplies. Some supplies are even switchable so the output may either be floated or be tied to the power supply ground. If the power supply is properly grounded through the AC plug, grounding the output would tie the DC to earth ground. If such a power supply was used to charge a battery whose ground did not match the charger ground, an inadvertent connection between the car and earth ground (a jack would do fine) could cause trouble. Such earth-ground circuits typically are not very low resistance, so the low voltage from a charger would not be likely to produce a huge ground current. Still, the fix is trivial - float the output - and that is the way battery chargers are made. My point is that the original inquiry was not a stupid question. To the experienced gearhead, it may have had an obvious answer, but how many of us had thought about the underlying reason? Russ Wilson

[Austin R. Baer]

Right on, Russ, and I would simply add that another technical aspect of this "thread" includes the fact that over 75MB of disk space has been cumulatively utilized by our current roster of 349 members, not to mention the delete key wear on 349 keyboards. I point this out simply to remind the members (new ones in particular that we seldom hear from and who may be intimidated by the very quantity of exchanges we already deal with), that battery charging and screw head formations are just as important bits of information to those in need as the proper repair of a cracked transmission housing or stub axle. Perhaps it's time to start a parallel T-ABCs "chat room" for the (sometimes) worthwhile humorous banter, keeping the technical Q&A down to a manageable number of concise daily e-mails. The subject line could be kept the same as on the technical list Q&A's, but those of us who'd like to jab and parry could do so to our heart's content within the "subgroup". Any comments? Walter? Jim? Again, my interest is in widening our group without turning off people that just haven't the time to sort it all out, or keep their own batteries charged. Regards to [b]all[/b], Austin

[John Patterson]

GENTLEMEN- THE ONLY STUPID QUESTION, IS THE QUESTION THAT IS NOT ASKED! John Patterson TC 7025