Date: Fri, 23 Feb 2001 08:35:07
From: "neil barnes" <[EMAIL PROTECTED]>
Subject: RE: Help this fuul out (Ha, beat you, Pres!)
>
>Date: Fri, 23 Feb 2001 08:08:29 -0000
>From: "Matthew Hanson" <[EMAIL PROTECTED]>
>Subject: RE: Help this fuul out
>
>John,
>
>I'm a bit behind on checking my list mail, so I don't know if someone
>addressed this yet or not, but I'm guessing that doing that monitor
>modification must shorten the life of the screen, doesn't it? My
>understanding of battery capacity vs load wasn't a very good one, and I'm
>not that sure about this one either.
>
>Matt
Matt,
Can't answer without guessing as I don't know how the screen mod works...I
recall though one mod which appeared to be a filter over the screen -
contrast enhancing? - which wouldn't affect screen life at all. Given that
the 'screen' bit of an LCD screen doesn't have any light generating
function, the only real way to make a screen brighter is to put a brighter
light behind it...have you seen how bright LCD projectors are?
Re the batteries: when a battery is charging and discharging, there is a
chemical change *somewhere* in there - e.g. lead to lead sulphate in a lead
acid battery. The speed at which that reaction can take place is
proportional mainly to the surface area exposed to the electrolyte, and the
conductivity thereof.
Cells are normally defined as having a given capacity in (milli)amp-hours -
when the current is taken at a specified rate. This rate is normally a long
way short of the maximum the battery can supply but is a rate at which the
chemical byproducts are easily absorbed. If the current pull is increased,
the byproducts get in the way of the reaction you need until they can be
removed (converted back) by recharging. This effectively stops the cell
working - so at a low rate, the capacity in Joules (=amps*volts*time) is
higher than at a high rate.
But if you have a bigger battery, the current from an individual cell is
reduced...so it can work more efficiently. So, it lasts longer.
An example - many years ago, I had a portable valve (tube) radio which
worked off two batteries - both carbon/zinc cells, one at 1.5v and one at
90v. The 1.5v cell was enormous as it had to drive all the heaters in the
valves and so had to provide a lot of current - but the 90v battery was tiny
- it only had to provide milliamps. It also lasted three times as long as
the 1.5v cell...
Cheers,
Neil
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