2004 dodge dakota ev conversion
Asked by:Jon Bottoms
Why use 6 or 8 volt lead acid in an electric vehicle instead of 12v or deep cycle 12v?
Electric Vehicles
Electric Vehicle Information Resource
Electric Vehicle Information Resource
2004 dodge dakota ev conversion
Asked by:Jon Bottoms
A 12V battery is six cells wired in series while a 6V battery is three cells wired in series. A battery is charged as soon as one cell is fully charged even if the other cells are not and a battery is fully discharged as soon as one cell is discharged even if the other cells are not. Also a battery is bad as soon as one cell goes bad. This is why the old batteries from before the no maintenance batteries had caps on each cell so you could monitor the condition of each cell individually by measuring the specific gravity and adjust it by adding distilled water or sulfuric acid. The no maintenance batteries with the window that shows if the battery is good or not is just a battery with a colored float in one cell under the window as a general indicator of charge levels but in truth only gives you an indication of the specific gravity of the electrolyte in that one cell. The only way to balance the cells that are wired in series is to overcharge it with what’s called a “balancing charge”, this boils away some of the water in the overcharged cells while the under charged cells catch up hence the need to add distilled water in the older batteries. With 6V batteries, you can wire and monitor in various configurations to better utilize and charge the batteries without resorting to overcharging. Of course, I doubt that EV builders are sophisticated enough to design in power rails and relays in order to reconfigure the battery packs while charging and discharging just to better utilize the batteries but even so, a lot of benefit could be had by strategically wiring a few 6V batteries in parallel before wiring them in series to get the voltage desired.
Packaging, Weight (per battery), Amp-hours
The runtime of Lead-Acid batteries is largely dependant on the actual physical amount of lead, lead oxide and sulfuric acid inside the casing. “Deep Cycle” 6V’s have larger, thicker plates, and more runtime then comparable sized 12V “Starter” batteries (the battery in a car, is a Starter Battery, made for short bursts of high amp draw not long duration power)
For example: a 225 Amp-Hour 6V battery (very common, golf cart type) is roughly the same size at a normal car 12V (which only have 100-110 Amp-hour capacity), and at 70lbs, quite a bit heavier than the car unit. I’ve also got some 390 Amp-Hour 6V’s…they weigh over 115lbs! A 12V of similar capacity would be…as logic would indicate, nearly double the weight.
So when swapping out batteries, which individual unit would you rather lift out?
You can get more energy per unit of volume with a 6V or 8V battery. Consider that a 12V battery needs 5 insulated separators while a 6V battery needs only 2. Since both have about the same thickness per spacer, more active cell area is available in a 6V battery.