Michael Ross wrote: > When you say lead is the fuel - how does that work? I wouldn't have > expected it unless it means the grids (my word for whatever they are > called. plates?) are bigger... > > I guess you could make the grids heavier better life in severe conditions. > How do you know the extra weight is in grid area and not structure? > > Or do I have the wrong idea altogether?
You have the right idea. Lead is the main active ingredient in the battery, and it is quite dense, so it is a reasonable approximation to state that the heavier a lead-acid battery, the greater its actual capacity is likely to be. But, as you say, even if the battery is heavier, you don't know if the extra weight means more active material (e.g. paste) or beefier grids (the lead structure of the plates that supports the paste) or beefier internal interconnections. Beefier grids or internal connections can both contribute to a more robust or longer-lived battery, so this doesn't contradict the "heavier is better" philosophy. I think David makes a good suggestion, which is to dig up specs on the particular batteries you are considering and compare their capacities at the discharge rate that you will operate them at. The 20hr rate is meaningless for a mower that will likely deplete the batteries in about 1hr, and different makes handle high rate discharge quite differently. Also, as David notes, different manufacturers may state their battery's rated capacity at different discharge rates; e.g. Hawker/Enersys often states the rated capacity at the 10h rate while others may use the 20h rate. Note also that the weight metric really does not mean to shop by the best $/lb value, but rather that for two batteries of the same physical size or same rated capacity, the heavier of the two is likely to deliver greater actual capacity and/or provide greater service life. One caveat I would offer is that I think especially for AGMs there is more to the story than simply weight. With sealed batteries (AGM/gel), one of the keys to long service life is avoiding venting since this corresponds to (generally) irreversible loss of electrolyte. This is where a quality brand can impact the outcome of your buying decision. The manufacturing quality can affect the performance of the pressure relief valves that allow the cells to vent in a controlled manner. It is not unusual for Chinese AGMs with lower quality control to have vents that open at lower than desirable pressures and/or open at pressures that vary from cell to cell. Good luck! ;^> Roger. _______________________________________________ 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)
