-----Original Message----- From: main [mailto:main-bounces@lists.alug.org.uk] On Behalf Of Phil

Thane

Sent: Monday, May 08, 2017 7:41 PM To: main@lists.alug.org.uk Cc: relay@wrexham-lug.org Subject: [ALUG] lappy aboard

This is Linux related, sort of, so I hope ALUG don't mind the

apparently

random question. (cc'd to my old LUG in Wrexham, they're used to mad questions 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 simplest but quite pricy option is to get an inverter to create 220v AC then use

the

standard PSU but apart from cost it lacks elegance.

The boat has 2 completely separate circuits (at present, I'll probably

re->wire

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

for

cabin lights.

If I connect the two in series I should get 24v then I should be able

to

acquire (or even assemble) a DC-DC voltage regulator to bring it down

to >19v.

Anyone see any problems with that?

-- Phil Thane

www.pthane.co.uk phil@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 too.

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 ):-

http://www.ebay.co.uk/itm/New-DC-Converter-150W-10-32V-to-12-35V-Boost-S tep-up-Power-Supply-Module-/252691490519?hash=item3ad59626d7:g:LxQAAOSw2 41YWsVX

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. lights.

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,

Noel ( Xorsyst )

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