[ale] Converting 600 old laptops into K12LTSP thin clients for 1:1 ratio at a middle school

James P. Kinney III jkinney at localnetsolutions.com
Sun May 21 17:12:39 EDT 2006


On Sun, 2006-05-21 at 14:20 -0400, Geoffrey wrote:
> James P. Kinney III wrote:
> > On Sun, 2006-05-21 at 10:07 -0400, Jeff Hubbs wrote:
> >> The only gotcha with old laptops is that many of their batteries will 
> >> likely have gone bad and are very expensive (think >$100) to replace.  
> >> So, having them run untethered may be a nonstarter. 
> > 
> > In fact, some laptop models won't run at all even tethered to power if
> > the battery is bad.
> 
> Why is that?  I've never encountered such.  Every laptop I've seen will 
> operate with AC power with the battery removed.  Would they operate in 
> this way?
Some Dell and some Sony laptops won't run at all without a battery. I
don't recall the models. A client had them and that was a real shocker.
As for running with dead batteries, it depends on the charger circuit.
Some thinkpads would eventually overheat and lockup because the charge
circuit detected the battery needed charging but it would charge. So it
kept dumping current into a heat sink. Some people found a way to extend
the battery life that involved running the Li-ion battery until the
system wouldn't boot, freeze the battery for 4-5 hours in a dessicated
ziplock bag (put a baked piece of chalk wrapped in paper towel for the
poor man's version in the bag during freezing), then plug it into the
laptop with the system off and parked in front of an air conditioner
blower or put the entire unit inside a large ziplock with more
dessicant. Once the charge light goes out, freeze the battery again for
4 hours and put back in the laptop for charging again. This second
charge cycle takes about half as long as the first and will fully charge
the battery. The freezing bypasses the current heating problems
associated with battery charging. Old batteries require more current to
charge and thus produce more heat which reduces available current, ad
nauseum.

> 
> By the way, the general rule is 3 years life on laptop batteries.
> 
Actually, the rule is charge/discharge cycles. NiCad was short
(100-200), NiMH is better at 300-600. Li-ion is much better at 500-1000
cycles. I haven't read the chemistry on the Li-polymer so I don't know
what they can do. But the power users that live on the laptop kill
batteries quickly. Hot charging can damage batteries as it can cause
off-gassing. Minor off-gassing creates pockets of non-conductive medium
that greatly alters the current flow. This leads to localized heating as
more current flows through a smaller cross-sectional area. More heat
means more gassing. Li-ion can explode due to this process. 

So a NiMH battery laptop can be used daily a bit over a year and a half
on the original battery. As they only power a laptop for at best 4 hours
per charge, each work day requires either 2 batteries or a full time
charger.

Battery lifetime with the charger always in use varies by model. It
depends on the charging circuit details (especially the temperature
probe hysteresis). Some are good and some a terrible. The newer ones are
MUCH better than the older ones. 

-- 
James P. Kinney III          \Changing the mobile computing world/
CEO & Director of Engineering \          one Linux user         /
Local Net Solutions,LLC        \           at a time.          /
770-493-8244                    \.___________________________./
http://www.localnetsolutions.com

GPG ID: 829C6CA7 James P. Kinney III (M.S. Physics)
<jkinney at localnetsolutions.com>
Fingerprint = 3C9E 6366 54FC A3FE BA4D 0659 6190 ADC3 829C 6CA7
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