Power inverter help please

i want to put a "spycam" in the car
it's a computer which draws 60w at 240v

i have a power inverter rated 150w continuous 300w peak
but when i switch the computer on the inverter whistles and switches off :-(

now i know that w=va
so 150w=240v*a
a=0.6
or
150w=12v*a
a=12.5

the inverter has a fuse labeled "20" (presumably 20 amps)

so why won't it power my computer ?

dB

 

Is it a sine wave inverter that gives a proper sine wave output? Some
don't and that can really mess up a switched mode power supply in a
computer. Switch on surges can also be much higher than the rated power
required.

You may be better off getting rid of the inverter and the mains psu in
the computer and fitting a DC converter instead. Also the computer
takes a lot of power for a vehicle one and is likely to flatten the
battery overnight if you use it without the engine running.

See http://www.mini-itx.com/store/?c=10#dcdc for DC converters. They
also have a range of lower powered computers that may be more suitable
and housings for them.

 

the computer is powered by an external power supply (like a laptop)
unfortunately i need to power 3 devices: computer, monitor, camera(s)
the computer+camera works but it won't handle the monitor as well
the monitor is a small lcd(?) screen

dB

 

What does the external power supply for the computer output? If it's
12v you may be able to power the computer directly from the car supply
but you need to find out if the computer has 12v regulators built in
since the car will be supplying 14v or more.

How much power does the monitor use and was the 60W just the computer
or the monitor as well?

You could try turning the brightness right down on the monitor and see
if that helps. Are you switching them all on at once? If so try
switching the computer or/and the monitor on one at a time in case it's
just the switch on surge causing the problem.

 

the psu supplies 12v but the connector to the pc is a 4 pin din thing
the whole lot uses 60w including the monitor
i thought about the surge and switched them on seperately without effect

i'm actually using one of those powerpack things like a portable battery
that you use to quick start a car ?

dB

 

Does it have a voltage meter? I know nothing about them but wonder if
it can't supply the continuous current at the voltage required. Last
suggestion has to be try it in the car with the engine running.

 

Sorted
i got a "heavy duty" Quick start powerpack and that did the trick !
now all i need to do is see how long it lasts with the engine turned off

dB

 

Congratulations.

Well 60watts of 12v is 5 amps and a 70ah battery can thus power it for
14 hours but car batteries are not efficient for that sort of use so
you won't get anything like 14 hours. Once the battery is flattened
it's damaged and won't last for many cycles.

You can get deepcycle leisure batteries that you can charge from the
car but even they won't last long being completely flattened.

Best of luck but be prepared to buy a new battery before long although
presumably you can switch the monitor off when you are not looking at
it so that will save some energy.

 

Six hours or less, if you want more than a single cycle out of the rig.

Brian W

 

got 3 hours on the quickstart using a mains "charger" and the monitor
mostly on standby
i'll wait for the next long car trip before trying that.

and i'll take a spare quickstar just in case

dB

 

Computer may be "60w" but it may not be at power factor of 1 (ie peak
volts and peak amps not in sync) The inverter may not like this. In
similar applications I have fixed this sort of problem by adding a
resistive load to the system. Something like a 15w lamp might be enough
to stabilise things

 

thanks for the info
i "cured" the problem by running everything from a heavy duty "jump
start" box

dB