Rechargeable Lead Acid and NiCd Batteries in Vehicles

Finished the Schallenberg book today, a bit anti-climactic in the sense the battery designers never come close to solving all of the problems that make battery use in electric vehicles problematical. In the best tradition of a technology in search of an application, electric batteries were tried in just about every application where electricity was used, showed great promise on paper, and failed to deliver in the field. Obviously, lead-acid batteries did find a place in everything from car starters to powering submarines, and of course providing back-up to critical systems, but on the whole, storage batteries had enough going against them that they never took the world by storm.

It’s interesting to look at all of today’s battery powered technology and realize that it’s been made possible not by vast improvements in battery design but by vast improvements in solid-state electronics. It’s the low power demand of the devices that make them practical, not the high capacity of the batteries, though rechargeables really have made a difference in markets like power tools, cameras and cell phones.

Oddly enough, one of the first jobs I had as a co-op student in electrical engineering was helping a consulting firm determine why the NiCd battery packs of a major manufacturer were failing to perform well with their medical tools. Unlike many non-critical applications, it’s a bit inconvenient to have your drill run out of juice when you’re making holes in somebody’s skull or sawing through a tibia. The power packs were very similar to today’s power tool batteries, containing a large number of low voltage cells in series to make up the proper voltage and capacity, but the application called for fast recharging. A little processor controlled charger would track the charging current and look at the first derivative to see when the curve bellied over, but it didn’t work for beans. The problem turned out to be that individual NiCd cells charged at different rates, in part according to their individual state of discharge, introducing all sorts of sub-inflexions on the curve, and in the worst cases, reverse polarizing the cells. The only solution offered was to make sure battery packs were fully discharged before attempting to recharge, and then doing that on a timed basis.

It was interesting to read that some Edison utilities, in the in the second decade of the 20th century, actually constructed recharging garages where they would recharge electric vehicles during off-peak (night) hours for the sake of load leveling. They did so at a reasonable monthly fee that would be cheaper than the customer buying electricity directly from the utility. Such solutions would actually work well today in areas with a high percentage of nuclear power, like New England, since it’s highly advantageous to run those plants near their peak output. But, I suppose the grid is such that New England nukes probably provide power up and down the East coast at night while fossil fuel generating stations are taken off line.