Help ! Amps v Watts

[bennesspipers]

Which is the most powerfull, 500ma or 1.8 watts ?
I'm looking to buy a trickle charger, & trying to make my mind up whether a solar panel one will do the job, as a mains cable continuosly plugged in would be a nuisance.

 

[Stratman]

Power, measured in watts, is volts times current.

To know the power provided by the 500mA (half an amp) charger we need to know the voltage. Assuming it's 12V, 12 x 0.5 = 6watts.

 

[wemorgan]

I might be wrong, but is it possible to compare one to the other without knowing the voltage coming out of the transformer in each case?

 

[bennesspipers]

Thanks Stratman,thats me sorted.



Mods, please close this thread now, all finished, wonderfull forum.

 

[Stratman]

No. To use the usual water analogy, voltage is water pressure, current is rate of flow. You can have high pressure low flow (jet washers for example) or low pressure high flow (The Thames). Just knowing one of flow or pressure doesn't tell the full story. Consider two power supplies capable of providing 500mA, one of them at 500V and one at 6V. The first could deliver 250W, the second only 3W.

 

[Ted]

I might be wrong, but is it possible to compare one to the other without knowing the voltage coming out of the transformer in each case?

No. You cant tell watts without knowing both volts and amps.
On a resistive load, you can work out the watts without knowing the volts OR amps, but you must know the resistance (ohms).

 

[wemorgan]

No. You cant tell watts without knowing both volts and amps.
On a resistive load, you can work out the watts without knowing the volts OR amps, but you must know the resistance (ohms).

Sorry, my poor grammar. I meant to phrase that as a rhetorical question.

Thanks Stratman,thats me sorted.

Mods, please close this thread now, all finished, wonderfull forum.

If you had started this in the electrics sub-forum then you would have had the option to close the thread yourself

 

[bennesspipers]

What i was trying to compare was a mains powered 12v 500ma charger, against a solar panel 12v 1.8w charger.

Wemorgan, i thought if i did that i'd get wrong for posting in the wrong section, as usual !

 

[BTB 500]

As an aside, you need significantly more than 12V to charge a 12V battery.

The resting voltage when 75% charged is 12.4V (12.7V fully charged). You need to apply more than that to get any charge current to flow.

A 1.8W solar panel is almost pointless. That's the peak output in optimum conditions ... you will get less most of the time, and nothing at all for half the day (because it's dark).

 

[bennesspipers]

Thanks Bill

 

[verytalldave]

Post deleted

 

[Meldrew2]

What i was trying to compare was a mains powered 12v 500ma charger, against a solar panel 12v 1.8w charger.

Wemorgan, i thought if i did that i'd get wrong for posting in the wrong section, as usual !

The mains charger will be more powerful.

Especially at night

.

 

[bennesspipers]

Haha yes wise guy, going to buy one from Halfords,with my newly acquired Trade Card. Merry Christmas.