[ALUG] lappy aboard

Noel Galer noel at abasys.co.uk
Mon May 8 20:27:01 BST 2017

>-----Original Message-----
>From: main [mailto:main-bounces at lists.alug.org.uk] On Behalf Of Phil
>Sent: Monday, May 08, 2017 7:41 PM
>To: main at lists.alug.org.uk
>Cc: relay at wrexham-lug.org
>Subject: [ALUG] lappy aboard
>This is Linux related, sort of, so I hope ALUG don't mind the
>random question. (cc'd to my old LUG in Wrexham, they're used to mad
>from me).
>I have just bought a canal/river boat and want to use my Linux laptop
on >it. 
>The PSU for it is labelled 19v, 4.7 amps. The boat runs on 12v. The
>but quite pricy option is to get an inverter to create 220v AC then use
>standard PSU but apart from cost it lacks elegance.
>The boat has 2 completely separate circuits (at present, I'll probably
>it next winter). There is a 12v battery charged by the engine that is
used >for 
>the engine starter and a few ancillaries such as the horn and nav
lights. >The 
>there is another 12v battery charged by a solar panel on the roof used
>cabin lights.
>If I connect the two in series I should get 24v then I should be able
>acquire (or even assemble) a DC-DC voltage regulator to bring it down
to >19v.
>Anyone see any problems with that?
>Phil Thane
>phil at pthane.co.uk
>01767 449759
>07582 750607
>Twitter @pthane

May I make an alternative suggestion ?

There are lots of really inexpensive 'Boost' or 'Step-Up' regulators now
available on eBay.  These are switch mode and therefore very efficient

It is a common application to use one of these to provide 24V from a 12V
system and 19V would not be a problem as they are mostly adjustable.

Here is a link to such an item that might be suitable ( I have no
financial or other interest in this item or supplier, it was picked at
random ):-


This is just an example, there are plenty more, larger and smaller, but
this might do the job with a bit more heat sinking as is recommended.

There are a few caveats too.  Some laptop power supplies, Dell being an
example, use an extra wire ( with Dell it's a small signal only pin in
the centre ) to provide a power pack identification.  If not present,
things don't work too well despite supplying the correct voltage and
sufficient current.  This is supposedly to ensure the correct power
rated pack is used, but you and I might just think it is to prevent
after market PSUs from being used.

If your source battery goes flat ( under 10.5V = zero charge ) a boost
regulator will just keep sucking charge out of a lead acid battery and
damage it, but then so might any other drain on that battery, e.g.

If you connect the two 12V systems in series as you suggest, you will be
ok as long as both do not share a common ground line.  I have no idea if
this might be the case.  Also, when one system is depleted, lets face it
they are unlikely to have the same capacity, i.e. one goes flat as above
( < 10.5V ) damage could still occur to one system.  But if you do, a
quick look on eBay for a 'Buck' regulator similar to the link I gave,
would do that job.

If you decide to use a boost regulator and end up with one that has a
Constant Current control, don't be tempted to set this to the current on
the laptop power supply.  I would set it somewhat higher, in your case
6A or more, or to maximum to handle transients when switching on etc.
The laptop will only pull the current it needs.

I use these things all over the place including my 'Demonic' WolfLite
handlamp that instead of a 3W bulb, now has a 40V 1A LED unit running
from 18V of LiPo batteries.

Best regards,

( Xorsyst )

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