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Re: (ET) charger voltage

(Nuts, sent this to Mike only originally.  Resend to list.  Darryl McMahon)

For sealed and gel cell lead-acid batteries, which are much more
sensitive to overcharge issues (venting), the manufacturers require a
charger that will put out 2.34 to 2.37 volts per cell.  That is intended
to produce a full charge over an extended period of time, without
overcharging.  It does not do equalization, which is unique to flooded,
unsealed batteries, in my experience.

I don't pretend to understand the electro-chemistry at the atomic level.

I do know that over 2.5 volts per cell (floodies) for more than a few
hours leads to gassing and water loss.  Charging at 2.4 volts per cell
leads to almost no water loss.  Charging at 2.36 volts per cell led to
no water requirement for over a year in my ET.  Charging at less than
2.3 volts per cell (end-of-charge, on-charge voltage) led to unbalanced
charge on the batteries and reduced capacity and performance in my
electric car in a matter of days.

My advice is, if you have time, charge at up to 2.37 volts per cell.
Safe for flooded, sealed and gel cells.  You can leave the batteries on
charge for days at this max voltage and see no perceptible water loss or
gassing, but equalization does appear to happen, but it takes days.  An
intelligent charger is better than a brute force charger.

If you only have hours, you have to play a compromise game.  You trade
gentle equalization and cell saturation charging and time for more
aggressive equalization via overcharging and speed of charge.  Livable
for flooded, recipe for disaster for sealed or gel cells.

Darryl McMahon

Michael S Briggs wrote:

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


--
Darryl McMahon                  http://www.econogics.com
It's your planet.  If you won't look after it, who will?