From: muratlanne@gmail.com   
      
   "ads" wrote in message news:p0vlqglr23e76f65688m0dh3hn39sa1g92@4ax.com...   
   .........   
      
   Some of my AGMs had charging parameters written on the side. I found I   
   didn't have to monitor them if I stayed within those parameters, which   
   requires only a voltage adjustable and current limited power supply. The   
   home made one that works best for me is based on an LM350 regulator. I added   
   a digital voltage+current meter from Amazon and a Schottky diode in the   
   output to protect the regulator and its power source from reverse feed from   
   the battery. A large discharged cap in the supply could cause a heavy surge   
   current from the battery through the regulator's intrinsic reverse diode.   
   The caps in my homebrew supplies are 78000uF, bigger than beer cans.   
      
   Available meter brands and models change so I didn't reference mine. The 3A   
   flavor resolves down to 0.1mA which is nice for other testing, the 10A is   
   good enough for charging larger batteries.   
      
   The input supply can be a solar panel or an old 19V laptop supply, etc. For   
   Dells power is the inner and outer shell rings, the center pin is data that   
   indicates the brick's wattage. I made a mating connector from hobby store   
   brass tubing to test them non-destructively.   
      
   The LM350 self-limits at around 4A which the 3A version of the digital meter   
   has survived. I haven't needed adjustable current limiting for this use.   
   When the AGM reaches full charge at ~14.7V the current drops below 1% of the   
   A-H rating, for instance 180mA for a 12V 18Ah battery. That's from the spec   
   sheet, not my experiments. If it doesn't the battery may have a weak cell,   
   which will soon show up as <12V if you load it though it might not from   
   charging voltage alone.   
      
   A sulfated (high impedance) wet battery may respond to charging at 16-17V.   
   If so the charging current will slowly rise so a current limit or series   
   resistance (brake light bulb) is needed. I've read and seen experimentally   
   that this doesn't work on AGMs, but it's greatly extended the life of U1   
   tractor batteries. AFAICT the only advantage of pulse desulfating is that   
   it's inherently (and cheaply) current limited, whereas DC desulfating   
   requires more care from the user. OTOH the pulse voltage can damage   
   connected equipment.   
      
   An extreme case of this is when a car battery connection vibrates loose   
   while the alternator is producing full power. The magnetic field in the   
   rotor winding turns into a high voltage pulse of considerable energy.   
   https://en.wikipedia.org/wiki/Load_dump   
   I built a machine to simulate this for GM and watched it quickly destroy a   
   prototype fuel injection computer they hadn't hardened well enough to absorb   
   the rapidly repeated pulses they had requested from my machine because they   
   couldn't generate them with normal lab equipment. That may have been why   
   they changed to side terminal batteries. I've built some pretty odd stuff on   
   special order, projects the degreed engineers wouldn't risk their   
   reputations on.   
      
   With practice you can quickly determine the SOC and condition of a battery   
   by the charging current it draws as you vary the voltage. I haven't seen   
   this in print and am not ready yet to write it up, since I don't neglect my   
   batteries enough to encounter all conditions. My neighbors do so I have a   
   few data points. I don't think they understand why I'm so happy to mess with   
   their dead batteries.   
      
   The LM350 charger may revive a discharged NiCd or NiMH power tool battery   
   that an automatic charger rejects. I bought a batch of Lithium cell phone   
   chargers whose voltage had fallen below the BMS cutoff and used it to   
   restore most of them.   
      
   An LM317 works pretty well too. They self-limit at around half the current.   
   I was once the tech for the test stations Analog Devices used to confirm   
   their product met data sheet specs so I know better than to give close   
   values, some devices were a little better than spec and others were way over   
   it, depending where they were on the wafer.   
      
   At Unitrode rejected IC wafers went into a box that was set out like a   
   cookie bowl, take what you want. The ink-dotted bad devices formed blotchy   
   patterns that hopefully revealed correctable nonuniformity in the   
   fabrication processes. I used rejects to practice the delicate skill of   
   probing to test them.   
   jsw   
      
   --- SoupGate-Win32 v1.05   
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