[ausev] Smart battery chargers worth the cost?????

[Gil Dawson]

I wouldn't discount computer-controlled-profile charging completely, 
certainly not for NiMH cells.  To tell when an NiMh cell is fully 
charged, for example, you're supposed to watch for a temperature 
spike after it's been on constant current for a while.

A simple charger will be either voltage-limited or current-limited 
throughout the charge cycle.  The optimum charging profile for any 
battery could conceivably be more complex than either of these, 
possibly involving cell history as well as temperature.  This would 
require a computer to interpret the specifications. 
Computer-profiled charging is what GM chose for the EV1 and S10E, 
both PbA and NiMH versions, and Toyota for the Rav4-EV.

Some chargers include software to detect a sudden spike in the 
internal resistance of one cell, suggesting a possible internal 
mechanical failure.  Continuing to charge in this situation could 
cause some types of battery to experience thermal runaway, with 
flames.

But how much is hitting the optimum profile worth, in terms of 
battery life and maximum range, or risk of fire, compared to either 
of the simpler profiles?  That's not an easy question. 
Computer-charged NiMh cells in Rav4-EVs have exceeded 100 miles range 
and 150,000 miles with no fires.  But how long might they have lasted 
with a simpler charger?

We've seen a lot of manufacturers' reccommendations about optimum 
charging profiles, but I've noticed very little quantitative 
information about what happens if we ignore them.  It might not be so 
bad.  Then again...

--Gil


At 11:25 A -0500 8/17/08, m. edmund howse wrote:
For the most part it is rubbish or as previously defined marketing 
propaganda.. There are advantages to switching supplies in that they 
don't get as hot, typically, as the old analog DC supplies and this 
may be one reason to claim they last longer than the analog design. 
However, the old analog designs are much simpler, usually less 
expensive and mine are thirty years old and still functioning. I 
wouldn't expect anything made today, especially if made in China, to 
last as long. As far as the battery sensitivity or extended life from 
the switching chargers, batteries don't care about the ripple in the 
output unless it is severe and extremely unusual. Most switching 
supplies have a lot of noise and spiking in the output including rf 
noise and the batteries ignore it for the most part. Like it's been 
pointed out the current smart chargers whether analog or switching 
will extend your battery life independent of their design as long as 
they are reliable and perform as expected. Overcharging typically is 
the most common enemy of battery life.

marv

Rob wrote:

Message
Joby,

Multi-mode chargers definitely extend the life of your cells compared 
to just dumping in electrons.  Some of the chargers are better than 
others based on their ability to sense and react to charging profile. 
I have only had 1 charger so I can't offer comparison, but I don't 
think it's snake oil.  However, it's still marketing speak.

Rob

-----Original Message-----
From: <mailto:ausev-bounces at austinev.org>ausev-bounces at austinev.org 
[<mailto:ausev-bounces at austinev.org>mailto:ausev-bounces at austinev.org] 
On Behalf Of Joby Wieser
Sent: Sunday, August 17, 2008 9:45 AM
To: <mailto:ausev at austinev.org>ausev at austinev.org
Subject: [ausev] Smart battery chargers worth the cost?????

I have an on topic question for those of you with experience.  In 
reading about various battery chargers, the switch mode power supply 
computer controlled types claim they charge faster, without risk of 
overcharge or damage in any way and they can actually dissolve life 
robbing sulfate crystals off the plates.  This is supposed to make 
your batteries last longer and even rejuvenate older ones.  Do they 
really work like this or is it snake oil hype?



Joby in Fredericksburg


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