Battery Charging

[desinor@sympatico.ca (Désinor Jean-Claude)]

  I have been exploring battry chargers since we had the famous ice
storm here in 1998 :-)

  My interest in this was to have an emergency battery backup in case of
power failure. It had to be as maintenance free as possible, able to
take over whenever utility power failed.

  That means keeping a battery in float charge for long periods of time.
There is more to it than that, but in general terms once an automotive
type charger says the battery is charged, it is safer to disconnect the
battery.

  A cell voltage is nominally 2.2 volts, this is when you have "100%"
charge.There are six cells in a "12 volts@ battery, in effect yielding
13.2 volts.

  Now, a typical charger will monitor current flow. When both battery
and charger are at 13.2 volts, there is no current flow, for all
practical purposes, and the battery is considered "charged".

  However, in real life, things are not that simple. Stop charging and
the battery immediately starts discharging.

  Also, if you just maintain 13.2 volts, the battery will take forever
to trickle charge.

  A cheap charger will start at maybe 15, 16 volts. Current will flow at
maybe 10 amps then. Eventually, as the battery charges, current flows at
a lower rate, maybe 1 or two amps, maybe lower. Voltage is still at
around 14 volts. Then the cheap charger STOPS.

  Somewhere around 13.5 volts, the cheap charger starts again, at a high
voltage, and eventually stops again. The charger is not sophisticated
enough to maintain a safe level, and at that point you better disconnect
the battery.

  I use a fairly expensive charger. It fluctuates between 13.1 and 15
volts, and current is between a few milliamps and 20 amps. It charges
constantly, and the battery can be left connected for months at a time,
years if you have a "maintenance free" battery.

  Our automobile batteries are wonders of engineering, and given the
conditions under which they operate, we are lucky that they last over
three years at all.

  I made a search on google for "battery charger maintenance care
feeding", came up with quite a few pages, but this one is not too bad:

	http://www.ingenuityinc.com/ttssla.htm

  Of course, if you really want to get down to the nitty gritty, just
refine the search to add "schematic" or "deep discharge".

  Thry this one also:

	http://www.repairfaq.org/ELE/F_Battery_info.html

  My charger is a Statpower Truecharge 20, the battery is a Thermoil
deep discharge lead acid battery with a special oil in teh electrolyte.
I use that particular one because I can add water when needed, and the
oil reduces the release of hydrogen gases, thus reducing chances of
explosion - the battery is inside the house after all. This is the same
type used in wheelchairs, which also sit inside the house with
potentially smoking users, so I figured I'd better use that.

  That drives a Stabylex 1012 Inverter, generating enough power to drive
the gas furnace for a couple of weeks, thus keeping the house warm.
Maybe also drive a few fluorescent lamps. The rest of the time, teh
system is eeesntially maintenance free.

  Now that was only a start. Get out there on Google and have fun :-)

	Jean-Claude
	84 8v (no, automative battery only here!)
	Stabylex 1000 watt inverter (emergency power)

Larry a écrit :
> 
> Brian-
>   Here's my non-EE's view:
>  Overcharging: a charger is made to put out a maximum voltage (mine says
> 12.6VDC), since voltage is electrical "pressure", the charger will pump
> current into the battery until the battery reaches that 12.6 volts
> potential.  At this point, the "pressure" (voltage) is balanced, i.e. just
> as much voltage trying to come OUT of the battery as is trying to go IN. The
> charger cannot force any more current(amps) into the battery and charging
> stops.
> Which begs the question: don't they ALL have "overcharge protection"?
> 
>  I'd go with a charger that has an output of at least 13VDC, since a healthy
> battery can operate at 13 to 13.5 volts. I'd also look for one that has a
> "trickle" feature (2A or so) along with something around 15-20A for those
> occaisions when you don't have the time to wait.
> I know that sounds pretty simplistic, and I may be wrong....what do the
> elect/techs out there say?  Allyn, this is right up your alley....
> 
> Larry   sandiego16V
> 
> > Specifically, I'm wondering about trickle chargers.  How do they prevent
> > overcharging?  I assume that once the battery reaches some level of
> > proficiency, then the charging circuit is interrupted, but how is the
> charge
> > level determined
> > BH