On Fri, 28 Jul 2006, Elie, Larry (L.D.) wrote:
"Car" batteries have 6 cells. The ET has 18 cells. The more cells, the more potential for not getting the cells fully charged. If I need an extra 2.9% on 6 cells, I'll need several times that for 18 cells. Cheap fix; add voltage.
As a percent, you shouldn't need more voltage for a larger pack. The amount of extra voltage will be more, but I wouldn't think the percentage needs to be greater.
The issue I'm still trying to get answered is what exactly is the voltage of a fully charged pack. The reason I initially asked this is because of the discrepancy between the recommendations that a charger should put out around 45V, compared to the Landis controller which has a default set point of 38V for ending charging (so what I'm trying to figure out is if I should raise that set point, and if my charger needs to put out more than 39.5V). What I'm thinking is - if the pack NEEDS to be charged to something like 42-45V, then presumably the set point on the Landis charger needs to be higher. It seems to work by shutting of the charger every few minutes, measuring the voltage of the pack, and only turning the charger back on if the pack voltage is below 38V. So, if the pack can be charged up to something lik 42V, then if you don't raise that set voltage of 38V on the Landis controller, I'd think it wouldn't be possible to fully charge the pack, since it won't turn the charger back on once the pack is up to 38V. If, on the other hand, a fully charged pack has a voltage of 38V, then I would think that a charger voltage of 39.5-40V would be perfectly fine, since you would be able to charge it up to its full voltage, and would have some additional potential there to account for weak cells. So, what I'm still not clear on is what the voltage of a fully charged pack is. If it's something like 42V, then I would think I'd need to adjust that cutoff point on the Landis controller, as well as replacing the cap on my charger to see if that gets its output up higher. If a fully charged pack only has a voltage of 38V though, then I'd think that a charger voltage of 39.5V would be fine. No?
Mike