Re: Need a lead to attach inverter to 12v socket

On Sat, 21 Apr 2007 22:47:27 +0100, Alasdair <mail@xxxxxxxxxxxxxxx>
wrote:

Although the inverter is rated at 600 watts, with 85% efficiency
making a draw of approx 59 amps at 12 volts, this implies maximum
power draw. If the inverter is only going to be used to, say, drive a
laptop or a TV, there will only be a draw of 150 watts meaning a draw
at 12 volts of around 15 amps.

I am no mathematician but I worked it out thus: 150/12 = 12.5 amp.
Because it is only 85% efficient the formula is (12.5 x 100)/85 = 14.7
amps.

The formula for working out the current (amps) is the power (watts)
divided by the volts.

A very good rule of thumb given me by a company that builds small 12v
inverters, is to assume a current of 1 Amp drawn for every 10 Watts of
the equipment's power demand(note *). It's always been a good
approximation in my experience.

Note * - Actual power demand in use, rather than the rated maximum
power printed in/on the equipment's spec.

Measurements I made some years ago using an ammeter in the feed to a
250W inverter, showed that a small colour TV rated at 40W in the spec,
only drew 3 amps from the 12v battery, unless the brightness was
turned right up and the volume turned up loud, which increased the
current draw to 4 amps. Conversely, with the sound muted and the TV
displaying teletext only, the current draw was below 2 amps.

HTH

Neil

(Reply via NG please)
.

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