> I've never cut into one of these "Tenders" but I'd bet a beer
> (and I'n not
> talking an Old Milwaukee or Coors light, but a good Old
> Speckled Hen ofr
> Belhaven Twisted Thistle)
Ok, Dave, you owe me a beer. (Good thing I don't care for it, I'll never
collect <G>)
> that it has an IC voltage regulator
> (LM317 or the
> like) with active current limit and will limit to 1/2 amp
> even if shorted.
They do current limit pretty effectively; but the limit is not in the
regulator. Instead the "wall wart" transformer has such a high winding
resistance that it just won't pass much current. If shorted for any
appreciable length of time (like connected to a deeply discharged battery),
the transformer burns out.
> You'd have to be pretty clever to make one of these start a
> fire.
Nope, all it took was replacing the transformer with a somewhat beefier one
(from an old Hayes modem), that would deliver maybe 4 or 5 amps into a
short. Didn't actually catch fire, but got hot enough to melt the plastic
case and char the label, before the pass transistor gave up the ghost.
> If you are using a larger unit (eg: 5 Amp) you would want to
> use larger
> speaker wire or 16 gauge zip cord from the hardware store.
Something to keep in mind; small wire also has a significant resistance,
which may affect your charger if you use a long enough length of it. For
example, 24 AWG has about .025 ohms per foot, so a 20' length (40' total)
would drop about 0.5 volts @ 500 ma. That doesn't sound like much, but it's
more than the difference between a fully charged battery and a 50% charged
battery (according to the table at
http://www.batteryuniversity.com/partone-13.htm
)
BTW, Jim, this is DC, so no RMS correction needed.
Randall
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