XPost: sci.electronics.basics, sci.electronics.components, sci.e   
   ectronics.design   
   XPost: sci.electronics.repair   
      
   Followups set to sci.electronics.repair .   
      
   In sci.electronics.components Mike Cook  wrote:   
   > Can the car charger be used to charge this battery?   
      
   Probably.  Do you know what the amp-hour capacity is of the battery that   
   is in there now?  A little Googling *1 suggests that the original 12 V   
   battery might have been six Gates/Hawker/Enersys "Cyclon" 2 V cells in   
   series; the replacement that one site sells looks suspiciously like the   
   common or garden 12 V 7 amp-hour "gel cell", plus a couple of brackets   
   to make it fit.  If the battery capacity is around 6 or 7 amp-hours,   
   then the 0.5 A charger will work OK, as long as you don't mind it taking   
   12 or more hours for a full charge.   
      
   One manufacturer of these batteries *2 says this is how you charge the   
   12 V, 7 Ah size:   
      
   "Limit initial current to 2.1A. Charge until battery voltage (under   
    charge) reaches 14.4 to 14.7 volts at 68°F (20°C). Hold at 14.4 to 14.7   
    volts until current drops to under 70mA. Battery is fully charged under   
    these conditions, and charger should be disconnected or switched to   
    "float" voltage."   
      
   So... the 0.5 A car battery charger should be OK.  The charger you have   
   may not do the automatic float and shutoff - more below.   
      
   The voltage output by the car charger will be slightly different than   
   what a sealed battery needs; this is probably not too important in this   
   application, but may reduce battery life a little.  If you want, you can   
   get an "official" charger for sealed batteries for $35 or so; *3 has   
   0.8 A output and will work a little faster.  Or, get one of the   
   automatic car battery maintainers like a Deltran Battery Tender or   
   Schumacher Battery Companion; these usually have 1.0 to 1.5 A outputs   
   and will automagically switch to a low-current charge once the battery   
   is full.  These are easy to find at local stores.   
      
   > He can install a timer to limit charge time if that's something   
   > required.   
      
   If the charger doesn't have any kind of automatic shutoff, then this   
   might not be a bad idea.  The million dollar question is "how long is   
   enough".  The answer depends on how discharged the battery is.  The   
   simple answer (for a 7 amp-hour battery) is 7 amp-hours / 0.5 amps =   
   14 hours.  But: the charge won't be 0.5 A for the whole time.  It may   
   start off that way but it will go down as the battery charges up, so   
   a full charge will take longer.   
      
   At a guess, I would get one of those 12 hour spring wound timer switches   
   (often used with attic fans) from the hardware store, and put it in an   
   outlet box along with an outlet and a cord.  Maybe set it for 2 or 3   
   hours the first time, then when it shuts off, measure the battery   
   voltage to find out how full it is.  If not full enough, repeat.  After   
   a few runs you will know what to set the timer to initially.   
      
   *1 http://www.ereplacementparts.com/ryobi-150r-41ae150f034-volt-   
   attery-trimmer-parts-c-7931_15633_18531.html   
      
   *2 http://www.power-sonic.com/images/powersonic/sla_batteries/ps   
   psg_series/12volt/PS-1270_11_Feb_21.pdf   
      
   *3 http://www.mouser.com/ProductDetail/Power-Sonic/PSC-12800A-C/   
   qs=XATL/JQ9g1zerdAMdrMzKQ==   
      
   Standard disclaimers apply; I don't get money or other consideration   
   from any companies mentioned.   
      
   Matt Roberds   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)