Posted by Timberwoof on April 19, 2008, 7:07 pm
> >> > I'd be utterly amazed if any charger said to have a maximum output of
> >> > 1.5 amps managed 4-6. The reverse I would believe...
> >> >
> >
> >> That IS somewhat of a stretch but not totally impossible. The max.
> >> current output shown is at the rated voltage. So, for instance, a
> >> device rated at 1.5A, 12V should supply 12V up to the rated current load
> >> of 1.5A (or somewhere close). If you continue to increase the load,
> >> the amperage may increase beyond 1.5A......as the supplied voltage
> >> drops below 12V.
> >
> > It would be a strange power supply that allowed that. Although it might be
> > possible with different tappings on a transformer.
> >
>
>
> If you put the ammeter straight across it, shorting the output of the
> charger, it would not surprise me at all if it managed 4-6A, obviously this
> is not a useful measurement and it wouldn't take long for it to overheat
> though.
Or blow a fuse or the shunt in your ammeter. An ideal ammeter has zero
ohms across its test leads.
--
Timberwoof <me at timberwoof dot com>
faq: http://www.timberwoof.com/motorcycle/faq.shtml
Ten Steps to Fascism: http://www.guardian.co.uk/usa/story/0,,2064157,00.html
Posted by James Sweet on April 19, 2008, 7:17 pm
>> >> > I'd be utterly amazed if any charger said to have a maximum output
>> >> > of
>> >> > 1.5 amps managed 4-6. The reverse I would believe...
>> >> >
>> >
>> >> That IS somewhat of a stretch but not totally impossible. The max.
>> >> current output shown is at the rated voltage. So, for instance, a
>> >> device rated at 1.5A, 12V should supply 12V up to the rated current
>> >> load
>> >> of 1.5A (or somewhere close). If you continue to increase the load,
>> >> the amperage may increase beyond 1.5A......as the supplied voltage
>> >> drops below 12V.
>> >
>> > It would be a strange power supply that allowed that. Although it might
>> > be
>> > possible with different tappings on a transformer.
>> >
>>
>>
>> If you put the ammeter straight across it, shorting the output of the
>> charger, it would not surprise me at all if it managed 4-6A, obviously
>> this
>> is not a useful measurement and it wouldn't take long for it to overheat
>> though.
> Or blow a fuse or the shunt in your ammeter. An ideal ammeter has zero
> ohms across its test leads.
But only if the meter is not capable of measuring the absolute max current
that a transformer can produce into a short circuit. If a 1A transformer
manages 6A for a few moments into a short, and the ammeter is good for 10A,
it won't blow a fuse or shunt in the meter.
Posted by Rick Cortese on April 19, 2008, 3:35 pm
Dave Plowman (News) wrote:
>
>>>I'd be utterly amazed if any charger said to have a maximum output of
>>>1.5 amps managed 4-6. The reverse I would believe...
>>>
>
>
>>That IS somewhat of a stretch but not totally impossible. The max.
>>current output shown is at the rated voltage. So, for instance, a
>>device rated at 1.5A, 12V should supply 12V up to the rated current load
>>of 1.5A (or somewhere close). If you continue to increase the load,
>>the amperage may increase beyond 1.5A......as the supplied voltage
>>drops below 12V.
>
>
> It would be a strange power supply that allowed that. Although it might be
> possible with different tappings on a transformer.
>
Thinking about it, it could also happen with a battery that had some or
all cells shorted.
Easy<and potientially dangerous> test to see the quality of your charger
would be to just short the leads together at a low amp setting. i.e. set
it for two amp charge and watch what happens when you short the leads
together. If the amp gauge goes full excursion or greater then 2 amps
anyway, you don't have real current regulation on your charger.
I don't know that I have ever seen a battery charger that has real
current regulation although there may be some. Typically you have to pay
through the nose for a lab bench type of supply or build one yourself. I
can't remember who made the kit, IIRC you used to be able to buy a dual
output power supply with variable voltage and current for about $20.
That is, you could set it for voltage 0-30 and current 0-1 amp, and if
the drain was greater then the current set point it would limit the
current. A setting of .8 amps in a dead short would produce .8 amps on
the amp meter and no more. Thanks for the trip down memory lane, I think
I have to find one of these or maybe hit up a surplus house to find
something similar.
Rick
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> >> > 1.5 amps managed 4-6. The reverse I would believe...
> >> >
> >
> >> That IS somewhat of a stretch but not totally impossible. The max.
> >> current output shown is at the rated voltage. So, for instance, a
> >> device rated at 1.5A, 12V should supply 12V up to the rated current load
> >> of 1.5A (or somewhere close). If you continue to increase the load,
> >> the amperage may increase beyond 1.5A......as the supplied voltage
> >> drops below 12V.
> >
> > It would be a strange power supply that allowed that. Although it might be
> > possible with different tappings on a transformer.
> >
>
>
> If you put the ammeter straight across it, shorting the output of the
> charger, it would not surprise me at all if it managed 4-6A, obviously this
> is not a useful measurement and it wouldn't take long for it to overheat
> though.