[Swansea Hackspace] New Project - Powerpack for a laptop

Fri Sep 12 09:53:45 BST 2014

Long post warning - Batteries are a  bit of a passion of mine...

these little battery packs you linked to are wonderful - I have a
'waterproof' one from Maplin for my iPhone etc - I used parenthesis because
it isn't waterproof by any stretch of the imagination!

http://www.maplin.co.uk/p/maplin-waterproof-power-bank-7800mah-n03qn

I bought mine when it was on offer - I paid 19 quid for it - well worth
keeping an eye on their special offers - a couple times a year they have
something really good in their 'powerbank' section.

Apple iPhone/iPad chargers deliver 2.1A for a fast charge - the good car
chargers from the likes of Belkin will also offer 2.1A

The 'easiest' way to charge a laptop is from 240VAC using the supplied
mains charger - and the safest batteries to use in a 'project' are SLA
(Sealed Lead Acid) - Lithium battery packs used incorrectly _can_ explode.

This is a dire warning - misuse of LiIon or LiPo can and will result in
fire and possibly an explosion!

In my line of work we tend to put SLA batteries into small Peli Cases - we
often build the charging circuitry into the same Peli

Mike Harries (top bloke) has this page of examples -
http://www.mikesfilmsound.com/new_batterys%20&%20ChargersQ.htm

We use 4pin XLRs for 12V in Film & TV - Pin 1 (negative) and can you guess
yet? Yes, pin 4 for positive (because they look like a '-' and '+') source
always on Female connectors - and equipment always on Male.

A tidy sized SLA could power a 200W - 300W inverter for a while, enough to
power your laptop.

These are also very handy (search for LM2596 on eBay or Ali Express), they
take any DC volts from 4V to 40V and you can set it to output any DC
voltage from 1.25V to 37V.
They are a bit noisy as DC-DC regulators are prone to be, but you could
filter that if it became a problem (if you were to use one to power a small
audio amp for example or a ham radio TX)

http://www.ebay.co.uk/itm/LM2596-LED-Voltage-Regulator-DC-DC-Buck-Adjustable-Step-Down-Converter-Module-/161206839226

This one is interesting, it has a current limiting option on it, useful for
charging a small battery

http://www.ebay.co.uk/itm/Power-LM2577S-LM2596S-DC-DC-Step-Up-Down-Boost-Buck-Voltage-Converter-Module-/371050459165

Their perfect use is for making 5V to provide volts for USB sockets!

Talking about USB sockets, I like these... ready built... and cheep and a
total of 3A for both sockets

http://www.ebay.co.uk/itm/DC-DC-Converter-Module-12V-To-5V-3A-15W-Dual-USB-Output-Power-Adapter-OZ-/321460838700

A Peli case with a nice big battery inside peppered with these would
provide an excellent power source for a long camping weekend for the whole
family... you could even fill the lid of the Peli with some strips of LEDs
to provide in-tent lighting!

This should be chunky enough to power a laptop

http://www.ebay.co.uk/itm/300W-Watt-Car-Battery-Power-Inverter-Auto-DC-12V-To-AC-230V-USB-Adapter-Voltage-/151262613703

Remember that at 300W - with a 12V source, you will draw 25A from your
batter!!!! (can you see why LiPo is now a very bad idea?) So for two hours
use you will need at least a 50Ah battery that is capable of delivering 25A
constantly... (a tall ask)

We are almost in the realm of a caravan Leisure Battery already - 100Ah and
deep cycle - and certainly not something that you will want in your
rucksack for your train commute to London

If you power your laptop while it is fully charged then the inverter
wouldn't have to work so hard... simply powering your laptop. On the other
hand if you run your laptop until it is flat, then plug in to your inverter
- your inverter would have to power the laptop AND charge it at the same
time... At 240V, each amp drawn is 240W - starting to get critical here...

Some laptops manage this better - my old dell would draw 3.5A (Almost a
kilowatt) from mains regardless if the battery was full or not - but if I
took the battery out and just powered it from the mains, the current draw
would be down to as little as 0.5A (120W) from the mains... My Apple
Macbook Pro seems to be very power efficient, only drawing what is
absolutely necessary - I will plug it into an ammeter one day and do some
better checks.

Going back to the SLA batteries - most of these are designed to stay at
full charge - for example in your home burglar alarm where they are trickle
charged all the time - these can not withstand being discharged until flat
and recharged to full time after time... for this application you would
need a deep cycle battery (leisure battery) - these are more expensive!

It is worth watching out for the chaps who come to service the UPS power
supplied in your office - they should change the batteries in UPS at least
every two years - as long there hasn't been a prolonged power outage in
that time those batteries should have some life in them.

They can be 12V 30Ah or 12V 100Ah batteries... and they will be glad to
give them to you FOC as they are a pain to get rid of in big quantities.
Nine times out of ten they are worth having, but don't expect them to last
years... 12 months will be good. And you will be able to dispose of a
couple at a time at your local dump

I did warn you it would be a long one! LOL

see you later

Emyr

On 12 September 2014 09:12, Justin Mitchell <justin at discordia.org.uk> wrote:

> On Fri, 2014-09-12 at 07:50 +0100, Richard Morgan wrote:
> > Hi All,
> > I'm looking to 'make' a battery pack that I can use for travelling and
> > charging up my kit (iPhone, iPad, Mi-Fi and laptop) - laptop is a
> > priority.
>
> Laptops have some pretty crazy and varied voltage inputs, so purely off
> the shelf parts is unlikely.
>
> You'd need a fairly large LiPo battery, but these are cheap and easy to
> get from the likes of HobbyKing
>
> Charging, your going to need a fairly sophisticated multi-cell lithium
> charging circuit, preferably one with a thermistor and auto-shutoff if
> it starts to over-heat.  as charging is the most dangerous point.
>
> for discharge, either you have enough cells to get close to the right
> voltage, or you use a custom switch mode psu circuit, or a buck
> convertor, linear regulators suck for efficiency.
>
> but i'm no expert, and this is a project i would be wary of working on.
>
> if you were to bodge something simple, use a stand alone dedicated
> charger for the battery, and then just build, possibly from off the
> shelf parts, the dc output stage, it would be a lot simpler.
>
>
>
>
>
>
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> Hackspace at swansea.hackspace.org.uk
> http://swansea.hackspace.org.uk/mailman/listinfo/hackspace
>

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