Powering my scope and devices

[profees]

OK i need some help. I have a convertor which i plan to run my laptop from can somebody help me calculate how long it will last.

2 setups

setup one.

Power (tank as it were)

max 200w @230v-240v output.

Storage is 5 amps/ph @12v.

Laptop (taking power from tank)

240v- 16.5 volts @ 3amps, 60 watts

SETUP 2

Power

max 200w @230v-240v output.

Storage is 36 amps/ph @12v.

Laptop (taking power from tank)

240v- 16.5 volts @ 3amps, 60 watts

Can somebody help me work out how long each setup would last.

Cheers

[Mikea]

Given that I am an optical fibre systems engineer, not a power supply designer....(that's just to cover me in case I make an error!)

Optoin 1 battery is theoretically capable of 60Watt.hours. So if your laptop supply truly takes 60 Watts, then it should run for an hour. The two flies in this particular ointment are the efficiency (power factor) of your laptop charger and the ability of the inverter to run with ever-decreasing battery voltage. I would say you would be lucky to get 30 minutes out of it.

Option 2 battery is roughly 7 times the capacity, so the supply should last 7 times longer, so I'll say 3 hours.

I have a feeling that these times are still optimistic, so the true engineering answer is: Try it!!

[profees]

Cheers i originally calculated it at around 3.5 hours (i have no idea what im doing) i wasn't that far off, for which im pleased, but i understand the only good way to test is to actually do it .

I have already brought the inverter and charging my battery now to do a test tommrrow.

Im using an apple mac white 2009 model it stats it runs at 55 watts on the mains charger.

DO YOU REAKON THIS IS ACCURATE ?????

GUess i will find out tomorrow.

Thanks again for your advice / info much appreciated

[brianb]

This obviously depends on the efficiency of the 12V - 16.5V converter you require but any laptop running off a 5AH battery will flatten it in no time. You will probably get ~10 hours off a 36AH battery at 3A current draw (plus whatever the laptop has in its own battery).

Personally I'm using an Asus eeepc 1000H at the scope which (a) has a much lower power draw than a normal laptop, ( takes 12V external power directly saving the complication & losses of a voltage converter. Runs a webcam for about 4 hours on its internal battery (7.4V 6600 mAh) takes 3A off 12V until the internal battery is fully charged then about 1.5A.

[profees]

my mac uses has a fairy good battery on a full charge about 5.5 hours or around 3.5 if im running Virtual machine e.g mac os and windows vista at the same time. cheers for the info. My 36amp battery should be ok for 2 nights viewing i hope.

[profees]

Incase anybody else has a simliar setup......

Conculsion - Mac had an empty battery running mac os + vmware vista (together) so it would be pulling the full load - running on this inverter "12v 5amp test" - charges the battery to around 30% and runs for 45 mins. Obvoiusly i hope this time will increase if i already had a charged mac battery.

So my 36 amp battery should in theory last for 5 hours 25 mins. (- 10%) 4hours 45 mins+/- a bit at full load. so in theory it should last for around 7 hours at normal operating load.

"Pleasently please" with that and all i spend was £30 for the whole lot..

[profees]

All i need now is the ability to charge it with moon light