View Single Post
Old 12-02-2002, 01:29 AM
Medical Dave
Posts: n/a
Auto Electrics


You're absolutely right; H2SO4 (aka Sulfuric Acid) is wicked stuff. Don't get it anywhere near your clothes or you might soon be running around in your birthday suit!

For charging purposes cable removal is ok, but certainly not necessary. The way to avoid sudden battery expansion (as in 'explosion') is to allow the gas generated as the battery charges to vent freely and gradually, as opposed to building up and then releasing suddenly. The best way to do that is to remove the battery caps and then set them down lightly on the cell holes for the duration of the charging process. This will allow the gas generated to vent away as soon as it is produced. The only caveat here is to totally prevent sparks from occuring in this area on top of the battery while it's charging/venting. If you leave the caps on tight while charging you're in for a nasty surprise, as you may have acid in your eyes the next time you remove them, or they may self-remove, spraying that nasty H2SO4 all over everything.

I agree w/ Richard Wooldridge concerning your charging glitch. You more than likely have a loose and/or defective belt. What you're observing as the cut-in point of your alternator is actually the RPM point at which it actually starts turning at the correct speed for that engine RPM. In other words it's slipping up to that point, and then it finally catches up to where it should be speed-wise.

Many years ago I was a Professional Wrench at Sears Roebuck in Ann Arbor MI where I ran the Battery and Electrical Department. One day a guy came in who was about ready to pull his hair out. He had the same symptoms you have. I put his car on the VAT 28 (state-of-the-art equipment at the time) and observed something I had never seen before: when we revved his engine to a steady 2,000 RPM his alternator output started out way low but then gradually came up to the specified value. I told him I had never seen this before but that I thought what was happening was that the belt was slipping, not enough to squeal (which it wasn't) but just enough to behave in this erratic manner. We tightened his belt just a tad (too tight will fry your alternator bearings) and retested it on the spot. It was perfect! We had located his problem and I was a little smarter than when I went to work that morning.

Richard Wooldridge,

Thanks for your post. I'm glad you caught my mistake. I went back and read my post and realized I hadn't said what I intended to say. It is true that "alternators have no residual magnetism". I should have ended the sentence right there. "It is possible to reverse your battery polarity if you let it go dead". This is also a true statement, but it's not related to alternators, but it is to generators. You're absolutely right; an alternator is not going to charge your battery backwards, as a generator can.

Whenever you install a generator (obviously this is going to be on an older vehicle) you must momentarily touch the Battery and Armature terminals on the voltage regulator with both ends of a wire so as to properly set the system polarity.

I agree wholeheartedly with you on your call re: JR's charging problem (see first part of this post).

Two good calls, Richard. Sorry for the confusion. I'm kinda new at this forum stuff. Please be patient w/ me.
Reply With Quote