Re: (ET) Batteries

["David Roden" <etpost drmm net>]

On 28 Apr 2014 at 15:04, Chad Bush wrote:

> I believe the correct parameter to measure a full charge would be the 
> current
> output of the charger, so that once it met a minimum amperage (floating
> current), the charger/controller would begin to maintain, restarting 
> ONLY IF
> the voltage dropped below a given level. Voltage can be misleading due 
> to weak
> or bad cells in the entire pack.

You're on the right track, except that the maintenance phase is 
unnecessary 
and even detrimental.

Here are good basic battery charging instructions:

http://www.evdl.org/pages/hartcharge.html

If you're holding voltage constant at the acceptance voltage (2.4-2.5vpc), 
when the current falls to < 0.02C (2% of the battery's rated amp-hour 
capacity expressed in amps), the charge is complete.  Then you STOP.  At 
this point, continuing to charge the battery will only degrade it by 
overcharging.  For a battery in cyclic use, as ours are, float or 
maintenance charging is nothing but slow battery murder - "battricide."

Mr Landis's device is an interesting design.  He is looking at battery 
charging from a different angle.  It's sort of a modified cycle-dropping 
charger.

A cycle-dropping charger has an output voltage high enough to charge the 
battery fairly rapidly.  During charge, it monitors the battery's 
on-charge 
voltage.  When the on-charge voltage reaches a threshold (typically around 
2.4 to 2.5 volts per cell), the charger shuts off its output and waits for 
the battery voltage to fall.  When it falls below some threshold voltage 
(there is some hysteresis in these voltages), the charger restarts.  

In theory, at some point as the charger off time approaches 100%, the 
battery is considered fully charged.  

Cycle dropping is about the cheapest and crudest form of charge control.  
It's better than none at all, though, and it's easy to implement.  I've 
used 
it for years in simple chargers with quite a bit of success.

Anyway, if I understand Mr Landis's algorithm aright, its approach is sort 
of similar.  He specifies a *minimum* voltage to turn *on* the charger, 
instead of a *maximum* voltage to turn it *off*.  Any time the battery 
falls 
below some voltage value, he starts the charger and runs it for a fixed 
time 
(5 minutes, IIRC).  

As a charge controller, I'm not sure what advantages, if any, this 
approach 
has over the more conventional design.  But then AFAIK it's not really 
meant 
to be a charge controller for daily use, though some folks use it that 
way.  
It's a battery maintainer.  

And I come back to what I said before.  In my experience, battery 
maintainers are just not necessary or even a good idea.

I think that folks who want better battery charging and longer battery 
life 
for their ETs would be better off with a  good smart charger.  A modern 3-
phase charger with temperature compensation would be a good choice.  
Delta-Q 
is one example, but there are many others.  

Another good choice (and one you can probably find used) would a golf car 
charger with a DV:DT algorithm such as a Lester Lestronic or Lestronic II. 
A 
DV:DT controller (Lester has a patent on it, I think) watches the slope of 
the battery's voltage on charge.  When the voltage is above a threshold 
and 
is no longer rising, it considers the battery fully charged and shuts off. 
 
The advantage is that the DV:DT algorithm naturally compensates for 
temperature, battery aging, and even a few questionable cells in the 
battery.  Maybe that's what Chad is looking for?


David Roden - Akron, Ohio, USA

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