Date:         Sat, 3 Aug 2013 18:11:49 -0700
Reply-To:     Don Hanson <dhanson928@GMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Don Hanson <dhanson928@GMAIL.COM>
Subject:      Re: Battery Charger Sizing (Amperage) Woe and Warning (?)
In-Reply-To:  <201308031939.r73JdGo44776@sbw.org>
Content-Type: text/plain; charset=ISO-8859-1

  Ok semi-thread-jack....my experience with Smart Chargers...Unsatisfactory
in almost all  cases for me.  The Suckers just never work for me when I
have a dead battery...What good is a battery charger that won't charge a
dead battery?  The basic 'dumb' chargers or 'manual chargers'....those WILL
charge a dead battery most of the time, again, in my own experience.
  Now maybe I have just coincidentally got 3 or 4 faulty Smart
Charges...but when they don't work on dead batteries they almost always
will work on a charged battery that is just low..
.I tend to want the charger only to charge a battery when it won't get me
going, or when it dies....not a charger to keep a good battery charged
up...I have a battery tender for that....
Lately I have taken to using my solar panel to charge up dead batteries
because I can't seem to find simple basic charger being sold anywhere any
more and mine like that is so old it works only intermittently now....
  So are Smart Chargers only  good to top up a low battery?   Seems like
when I put one on a dead battery, it tells me "Dead Battery"  or 'faulty
battery' or some other indication that the battery is dead (no s**t, Smart
Charger, thanks a lot) and won't attempt to charge them for reasons I don't
care about... Where can one get a low-priced simple standard manual
old-style charger that just puts out the juice without having to get any
'feedback' or read from the battery first? Or do they still sell these at
all?
  Don Hanson


On Sat, Aug 3, 2013 at 12:39 PM, Steve Williams <sbw@sbw.org> wrote:

> neil n wrote:
>
>> ... I had to review Ohms Law again.  If I look at voltage as the
>> "push" ... a charger capable of a higher voltage output to push Amps
>> into the battery, would be more beneficial?
>>
>
> OK, well, not exactly a higher voltage rating, but rather a higher
> current rating (amps).  But, yes, there is an optimal voltage for
> each charging mode, so we'd like the charger to maintain that
> voltage, if possible.
>
> However, a given charger can provide only so much current.  A small
> charger may not be able to provide enough current to bring a
> deeply-discharged battery up to the optimum voltage.
>
> A discharged battery is a resistive load.  The more discharged it is,
> the lower its resistance.  As it is charged, its resistance gradually goes
> up.
>
> From ohms law, you know lower resistance means higher current.  So a
> deeply discharged battery requires more amps to reach the optimum voltage.
>
> Maybe more amps than the charger can provide.  That was Karl's point, I
> think.
>
> My little 8-amp ProSport charger will try to bring the voltage up to,
> say, 14.6 volts for its lead/acid bulk-charging mode.  But my
> 100-amp-hour battery, if deeply discharged, may present such low
> resistance that the ProSport reaches its 8-amp limit at a voltage
> lower than 14.6 volts.
>
> When that happens, the ProSport keeps the current at 8 amps, charging
> the battery more slowly than if it could provide enough current to
> get up to 14.6 volts.
>
> As the battery (slowly) charges, its resistance increases, so the
> ProSport, sticking to its 8 amp limit, can gradually increase the
> voltage until it reaches 14.6 volts.  After that, the ProSport will
> reduce the current to maintain 14.6 volts.
>
> There's a chart in this ProMariner PDF: http://urlzr.mp/hcb
>
>  "an appliance cycling on/off (like a fridge) may confuse or mess up
>> the automatic or intelligent aspect of an intelligent charger"
>>
>
> Sure.  Even a continuous load must confuse the algorithm.
>
> Some charger brands talk about a "dockside" or "power supply"
> mode.  I'd be curious to learn more about that.  Do any chargers
> isolate and power the loads while charging that battery?  That'd be
> the only way to completely eliminate this effect, and I have to
> believe it'd increase the complexity of the charger a
> lot.  (Increased complexity implies higher cost and/or lower
> reliability.  Hard to imagine it's worth it.)
>
> =====
> A note on charger ratings:
>
> Strictly speaking, it might make more sense to rate a charger by its
> POWER limit, rather than its current limit.  Power is measured in
> watts, that is, amps times volts.  We probably rate chargers by
> current rather than power because the voltage output is variable by
> design, so it would be more confusing to talk about power limits.
>
> Also, wire size is determined by current, not power, so knowing the
> maximum current is more useful in choosing the right wire and fuses
> for the charging circuit.
>