Cor van de Water via EV wrote:
My pack of 20 Golfcart batteries is now almost 4 years old and it has brought my truck over 14k miles so far, but tonight when I inspected a couple of the batteries I noticed something strange - while some cells had minimal water loss (level about 1/2" under the top of the cell) there were several other cells that barely had their plates covered, the level had gone down more than a full inch in those! How can this difference be explained?
4-5 years is about right for Sam's Club (Eveready a.k.a. Interstate) golf cart batteries. That's what I've been getting, too. Trojans and US Battery brands are a little better.
As others have noted, water usage increases as a flooded lead-acid battery ages. This happens for several reasons; some due to the battery, and some due to the charger.
Flooded batteries use a lead-antimony alloy for the plates. The antimony hardens the plates (makes them stronger), which extends life. But it also increases water usage, the self-discharge rate, and lowers the fully-charged voltage.
As the battery ages, the antimony migrates to the surface of the plates. This worsens all these effects. The battery gasses more, uses more water, and its fully charged voltage will be less. (It doesn't otherwise affect the amphour capacity, though. Loss of capacity comes from other effects.)
Most chargers do not compensate for new/old batteries. They blindly charge all batteries as if they are new. This means that old batteries get charged to too high a voltage. That significantly worsens gassing and water usage. The resulting chronic overcharging also shortens life. (This is why the batteries in an old batteries tend to "suddenly" all die together).
Big industrial EV chargers use the dv/dt or di/dt algorithms to compensate for battery age, and thus extend their life. Rather than charge to a specific ending voltage (or current), they charge until the *rate of change* in voltage or current goes below some limit. If your charger has this option, use it.
If not, your best bet is to reduce your charger's end-of-charge voltage (for example, from 2.5v/cell to 2.45v/cell). Also increase your final charging current (from 4 amps to 8 amps). In other words, rather than shutting off at 7.5v at 4 amps, change it to shut off at 7.35v at 8 amps.
Old batteries also need more frequent equalization. While you might only need to do this every 2 months when new, it could need to be done ever 2 weeks when old. "Equalization" is a long slow low-current charge to an "unlimited" voltage. Basically, you charge at something like 2-4 amps until the voltage stops rising.
If you take care of them in their "declining years", the batteries can easily provide double the life and number of miles before the pack needs to be replaced. :-)
-- Do the thing that needs to be done, even if no one else yet notices that it needs doing. -- anonymous -- Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
