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--></style><title>Re: [ausev] Smart battery chargers worth the
cost?????</title></head><body>
<div>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.</div>
<div><br></div>
<div>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.</div>
<div><br></div>
<div>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.</div>
<div><br></div>
<div>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?</div>
<div><br></div>
<div>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...</div>
<div><br></div>
<div>--Gil</div>
<div><br></div>
<div><br></div>
<div>At 11:25 A -0500 8/17/08, m. edmund howse wrote:</div>
<div>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.<br>
<br>
marv<br>
<br>
Rob wrote:<br>
</div>
<div>Message</div>
<div><font color="#0000FF">Joby,</font></div>
<div> </div>
<div><font color="#0000FF">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.</font></div>
<div> </div>
<div><font color="#0000FF">Rob</font><br>
</div>
<div>-----Original Message-----<br>
<b>From:</b> <a
href="mailto:ausev-bounces@austinev.org">ausev-bounces@austinev.org</a
> [<a
href="mailto:ausev-bounces@austinev.org"
>mailto:ausev-bounces@austinev.org</a>]<b> On Behalf Of</b> Joby
Wieser<br>
<b>Sent:</b> Sunday, August 17, 2008 9:45 AM<br>
<b>To:</b> <a
href="mailto:ausev@austinev.org">ausev@austinev.org</a><br>
<b>Subject:</b> [ausev] Smart battery chargers worth the cost?????<br>
</div>
<div><tt>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?</tt><br>
</div>
<div><tt> </tt><br>
</div>
<div><tt>Joby in Fredericksburg</tt><br>
</div>
<div><br></div>
<div><tt>No virus found in this incoming message.<br>
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<div><tt>Version: 8.0.138 / Virus Database: 270.6.4/1617 - Release
Date: 8/17/2008 12:58 PM<br>
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