Alternator Affect on the Battery

[Frank Howard]

I've always used a group 51 Sears Die-hard battery in my Elan because it barely fits, it's reasonably priced, carries a good warranty, and replacements are readily available all over the States. I use the term "barely" because my car has the federally mandated side marker lights and the battery tends to push against the back of the rear left one causing the fiberglass to crack around it.

Four and a half years ago, I upgraded to a Mitsubishi alternator that I yanked out of a 1988 Mazda 323. I fabricated a new bracket and reused the same two bolts that had held the generator bracket on. One of the best upgrades I ever made. I installed a matching Lucas ammeter at the same time. Last week, while traveling at night, I noticed that the instruments appeared to be difficult to read, then the CD player began to have trouble staying on track to the point that it began flashing on and off and then finally shutting down. I tried the windows and found them to be unusually slow. It was then that I decided to check the ammeter (duh) that I had gone to considerable trouble to install years earlier. Sure enough, it showed that the charging circuit was discharging.

I got home and took the alternator in for testing. As it is Japanese, naturally it checked out fine. Upon re-installing it, I noticed that the bracket was loose. Upon further investigation, I discovered that the front bolt had snapped in two. The resulting stress on the bracket caused it to snap in two as well. After welding the bracket back together and installing a new bolt, I re-installed the alternator and after charging up the battery, everything was back to normal.

A couple of days later, I noticed that my Super starter wasn't turning over as fast as it usually did. The next morning, it wouldn't turn over the engine at all. At this point in time, the Sears battery was 70 months old and it carried a 72 month warranty so I had it tested. Sure enough, the battery was done.

I considered purchasing another group 51 Sears battery and relocating it to the front of the boot so as not to interfere with the side light, but Sears had raised the price of their $60 battery to $90. I read through the archives and I decided to upgrade to an Oddesy PC 680. As it is 3" deep vs. 5" for the Sears battary, it allowed me to install it in the original location with no chance of touching the side marker light.

It seems to me that it is one heck of a coincidence that the battery died just a few days after the alternator bracket broke and one of the bolts attaching it to the block snapped. My question to the group is this: Did the Sears battery go bad because it was 70 months old and Sears engineers their batteries to die just prior to the end of the pro-rated warranty which in most cases encourages the consumer to take the pro-rated credit and apply it against a new one rather than switching brands, or did the badly grounded alternator somehow damage the battery?

[paddy]

Have you measured the charging voltage you're getting from the alternator? I had one once with a voltage regulator failure which caused the charging voltage to be much too high and this destroyed the battery. I don't see why this would happen as a result of a snapped mounting, however.

Also, you should check because the Osyssey batteries seem to be more sensitive to the correct charging voltage than a conventional battery - I think I remember reading in the Odyssey leaflet about this in connection with conditioners.

Paddy

[Frank Howard]

Paddy,

Thanks for your response. You asked if I measured the charging voltage. Actually, I said,

"I got home and took the alternator in for testing. As it is Japanese, naturally it checked out fine."

If the charging voltage was too high, the guy who tested it would have pointed that out to me as he was motivated to sell me a new alternator. He suggested that I check for a bad ground. That turned out to be the case as the alternator is grounded through the alternator bracket.

[bob_rich]

Hi Frank

Not familiar with the alternator or battery type but assuming it is a lead acid battery and I assuming the the broken bracket meant the alternator was not charging because of no earth return so that while driving you would have run the battery down quite low. U stated low lights, slow windows etc. Lead Acid batteries do not like to go much below 1.7 to 1.8V per cell so if the battery was marginal and U ran it down quite low I wonder if that might be the last straw so to speak. Not all cells would have to go duff perhaps just one has let U down? It is a long shot because while not good for the battery over discharging to <1.7V in a reasonably good battery it should not finish it off. just a thought though. A check with a DVM in your car while running to see what the off load (~12.4V) and charging voltages (~14.3V) are might give a clue.

best of luck

Bob