what amp/hour deep charge battery

[Arthur Alchin (Arthur Alchin)]

I have a Sony Vaio laptop that i use out on dark nights with no mains power around. It is used with the Meade DSI

I have a small ( but sufficient) 12v to 240v inverter that has modified sine wave (150w) but i need to find out the minimum size battery (?deep cycle) that i would need for up to 15 hours of computer use: this also includes starting off with a totally charged laptop in the first place.

The power supply for the laptop states Output 19.5v and 4.7 amps, Input is 100-240v and 1.3 amps

all comments welcome

[Calibos (Keith)]

Someone else correct me if I am wrong but isn't the rule of thumb to multiply the amps by the hours you need. I think the 100-240v 1.3amp can be ruled out as thats on the mains side of the powerbrick. Its the output of 4.7 amps thats the figure we need....I think.

BTW you would be best getting one of those Airtravel laptop 19v power bricks to suit your laptop which connects to 12v power sources with a cigaretted type plug, saves the conversion losses using an invertor converting from 12v to mains voltage for your current powerbrick that is converting it back to 12/19v again for the laptop anyway. Invertors waste a huge amount of battery energy.

Anyway 4.7 amps x 15 hours = 70ah

I don't know whether that formula takes into account the need not to drain a battery completely though I do understand that Deep cycle batteries are much better at handling significant drainage.

Probably best to be safe with a 100ah Deep Cycle.
Oh and get one with a built in extendable handlebar and wheels. Your back will thank you!

NB* Wait for more replies, I am no expert!! Just going on what I have read, or think I remember reading

[sheeny (Al)]

G'Day Arthur,

Calibos beat me to it.

I was going to suggest a 12V air/travel plug pack to go direct from the 12V battery to the lappy and skip the inverter and normal plug pack.

19.5V x 4.7A / 12V = 7.6A ... say 8 or 9 A with losses.

9A x 15h = 135 Ah, but that draining the battery to 100%.

You probably want to drain the battery no more than 50% to give it reasonable life, so that means about a 270 Ah battery!

What sort of battery life are you getting out of your laptop battery? 2-3 hours?

Let's say 3 hours on the lappy battery and assume 8A @12V (might be a bit light on) then 8A x 12h / 50% = 192 Ah... say a 200 Ah battery.

I have just killed my 37Ah battery for the lappy after about 2 years. I probably only got about 40 or 60 recharge cycles out of it because I obviously used it well below 50%... ... so I have been doing some homework on making the observatory solar powered, but in the end I have decided that because of the lappy power drain, I'll just put the power on...

Al.

[koputai (Jason)]

The laptop won't be using the full 4.7A all the time, that's the max output when the computer is running hard, and the internal battery is being charged at the same time. You should find that the lappy only needs between 1.5 - 2.5 amps when it's running.
I bought a deep cycle 200Ah 12v AGM battery a few weeks ago and that sort of thing is definitely NOT portable, it weighs 62kg and is BIG.
Definitely get a deep cycle sealed (either gel or AGM) rather than a regular car battery or float type gel, and you really don't want to discharge to less than 30% capacity. A 100Ah should do the job fine, as long as you charge it properly. (Correct charging is a whole other world of complication!)

Cheers,
Jason.

[erick (Eric)]

A tangential thought? What about leaving the battery out of the laptop so the charging of that isn't a drain on the external supply? Is that possible? Would it lower consumption from the external battery?

[Arthur Alchin (Arthur Alchin)]

I bought this particular laptop because it had "advertised" great battery time: about 2.5 hours but i suspect that that is not entirely true unless you run in a miniature size display which is not appropriate for astrophotography.

maybe i should just bite the bullet and but a petrol inverter, eg a 1kW honda or something, i am scared that i will kill the battery by discharging and recharging incorrectly.

Are they quiet enough??

[koputai (Jason)]

Crank one of those up at an observing night and I think you'd be killed!

Cheers,
Jason.

[Merlin66 (Ken)]

Go for a series of 20Ah gel cell batteries; you also need an electronic type charger. I also use the Jaycar 12V to 18V car -computer transformer.
I have four of these batteries so there's always at least a couple charged ready to go. These drive the LX200 and the HEQPro5 as well as cameras and laptop.

[erick (Eric)]

Originally Posted by Arthur Alchin

and buy a petrol inverter, eg a 1kW honda or something....

Are they quiet enough??

I recently trialled a 600W chinese clone - 2 stroke. At the end of a 25m extension cable we knew it was there but it was not obtrusive at all.

[Arthur Alchin (Arthur Alchin)]

i actually have 2 of those 600 amp jump starters (with cigarette lighter socket) from S/Cheap auto that i use for the LXD75 SN 8", the inverter is being currently (no pun intended) used to power a powered USB hub that the DSI is run through: trying to conserve as much laptop power as i can

[Arthur Alchin (Arthur Alchin)]

Before i forget, thankyou everybody for your ideas i am taking them all in

[Merlin66 (Ken)]

Those "600Amp" boxes don't last long! and when you open them ( don't we all??) all they contain is a 20Ah battery anyway!