XPost: sci.electronics.basics, sci.electronics.components, sci.e   
   ectronics.design   
   XPost: sci.electronics.repair   
   From: ham789@netzero.net   
      
   On 2/28/2013 9:23 AM, Ian Field wrote:   
   >   
   >   
   > "mike"  wrote in message   
   > news:kgm2o9$pn9$1@dont-email.me...   
   >> On 2/27/2013 12:09 PM, John Fields wrote:   
   >>> On Wed, 27 Feb 2013 16:17:04 -0000, "Ian Field"   
   >>>  wrote:   
   >>>   
   >>>>   
   >>>>   
   >>>> "John Fields" wrote in message   
   >>>> news:mcbqi8t00ur6s6sk6kmuskjtkpg28fegtm@4ax.com...   
   >>>   
   >>>>> My request was about having you describe the dynamics of a   
   >>>>> light-bulb-in-series-with-a-battery current limiter which, no matter   
   >>>>> how loudly or how long you squeal excuses about why you can't, you   
   >>>>> can't, of course.   
   >>>>   
   >>>> The bulb trick isn't that great because of its pronounced PTC   
   >>>> characteristic - as the filament voltage decreases the current doesn't   
   >>>> decrease in due proportion.   
   >>>   
   >>> ---   
   >>> ???   
   >>>   
   >>> If a you want the current to change linearly with voltage, then a   
   >>> simple resistor will do the trick so, obviously, you don't understand   
   >>> how the bulb trick works.   
   >>> ---   
   >>>   
   >>>> I did try to dumb it down for you - I do hope I didn't use too many big   
   >>>> words for you!   
   >>>   
   >>> ---   
   >>> The words are no problem but it seems, for you, the theory _is_.   
   >>>   
   >>> Would you like me to explain how the bulb trick works in terms even   
   >>> you could understand?   
   >>   
   >> I understand how the light bulb works, but I'm very interested in   
   >> hearing YOUR explanation.   
   >>   
   >   
   > When the battery terminal voltage is low and the drop across the   
   > filament is high; the bulb does its best job of current limiting - just   
   > when high charging current would be no bad thing. As the battery   
   > terminal voltage approaches or exceeds the required voltage, the   
   > inherent PTC characteristic of the filament means as it cools its   
   > resistance falls, its much less effective as a current limiter - just   
   > when the (possibly overcharging) battery needs it most.   
   >   
   > The bulb as a current limiter is less than ideal for battery charging -   
   > but better than nothing if you don't have a float capable charger to hand.   
   >   
   > I didn't bother to dumb it down for JF - you can draw pictures for him   
   > as a homework excercise.   
      
   So, you're saying that a light bulb can work very well for current charging   
   as long as you pick the voltage and the bulb correctly.   
      
   Also, a light bulb can work well to limit the maximum charge current   
   to stay within the limits of the battery and charger, even in the event   
   of shorted cells or other faults...as long as you pick the voltage   
   and bulb correctly.   
      
   You can do better.  You can abuse any charge method.   
   IMHO, the bang for the buck of a light bulb current limiter is   
   second to none when properly applied.   
      
   --- SoupGate-Win32 v1.05   
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