Any Electrics Geniuses About

[deuc02]

About to install a mac mini on the boat and wondered if anyone knows how I go about getting the right DC supply (18.5v) to it from the house batteries (24v). Been googling away and not being too bright in the electrical department have ended up getting myself more confused. From what I've gathered there are a couple of ways to step the voltage down but essentially I'm after a magic box I can buy to do this efficiently. Tried various suppliers sites but not knowing exactly what I'm looking for is just making it all more confusing. Any advise?

 

[lw395]

There are plenty of '12 to variable' boxes on ebay. Check the current rating.
24 to variable is less common.
This sort of thing might do it.
You may need to keep it cool!
http://www.ebay.co.uk/itm/15A-DC-DC..._Measurement_Equipment_ET&hash=item27d032420f

 

[nimbusgb]

Dc to dc converter.

Search rs components or farnell for a dc/dc converter with say 32v input and 18.5 v output, you may have to find an ajustable unit to get 18.5. Btw you will need 4.6 amps at 18.5 v - pretty hefty.

 

[nigelmercier]

There may be more to this than just getting the correct voltage, there may be an intelligent part that tells the Mac Mini what type of supply it is.

@nimbusgb, isn't that an AC power unit?

 

[sarabande]

why not go for a 24v (truck) charger

e.g.

http://www.ebay.co.uk/itm/NEW-IN-CAR-CHARGER-FOR-APPLE-IPAD-IPAD2-2-12V-24V-/200617094930

 

[nigelmercier]

why not go for a 24v (truck) charger

Because that is for an iPad.

 

[jamie N]

I believe that there are many options for this from a 12VDC supply. Does the OP have (at least) 2 separate 12VDC batteries so that he could take a supply from 1 of these; his 24VDC is probably a series of 2 X 12, so as to take the power from the front of the series perhaps?

 

[No Regrets]

240V Inverter and just plug it in with the standard mains supply lead!?

 

[nigelmercier]

I believe that there are many options for this from a 12VDC supply. Does the OP have (at least) 2 separate 12VDC batteries so that he could take a supply from 1 of these; his 24VDC is probably a series of 2 X 12, so as to take the power from the front of the series perhaps?

There seems to be a lack of DC power units for a Mac Mini, but perhaps something like the item below could be fitted with the right plug: http://www.amazon.co.uk/exec/obidos/ASIN/B00517GKVK/dolcetto-21

Might be worth asking in an Apple forum.

 

[deuc02]

Thanks for the ebay link - looks like the sort of thing I'm after. The mains adapter that comes with the mac shows output at 18.5v 6 amps so I'm assuming that if the converter is rated up to 15amps I shouldnt have any problems. One quick question though - why should it get so hot. Will the heatsinks on the unit suffice or will it need some fan assistance. Thanks

 

[deuc02]

There may be more to this than just getting the correct voltage, there may be an intelligent part that tells the Mac Mini what type of supply it is.

@nimbusgb, isn't that an AC power unit?

you've got me worried know - the connector that runs out of the macs mains power supply has 5 pins in it.
Also someone has suggested an inverter and use the supplied adapter. Have one on the boat but I though this would be more inefficient than using a dc/dc converter. Am I wrong?

 

[nigelmercier]

[inverter] would be more inefficient than using a dc/dc converter. Am I wrong?

You are not wrong. But it would be worth asking on an Apple forum if anyone has run one from a car, then start looking at a 24V option.

 

[prv]

Worth noting that the last several models of Mac Mini (I have one) have the power conversion built in, with just a standard figure-8 240v connector on the back. So if you want a ready-made converter you're looking for an old one that may not still be made.

Pete

 

[deuc02]

Just got hold of one of the pre 2009's with external power supply to get round that little problem. Nigel you were right about it wanting to use its own power supply. Seems one of the pins is something called iSense which will stop it booting up if not connected. Seems there is a work round though http://www.blisstonia.com/eolson/notes/kensingtonmacmini.php

 

[Blueboatman]

Don't know if this helps much but I run a iMac/large screen from an inexpensive Sterling inverter ( not pure sign wave) and two 110a batteries...
Ok there is solar and wind generator but the drain is never silly stupid..
Btw worth driling a hole thru the screens baseplate for a bolt and wingnut if your screen stands the slightest chance of tipping over?

 

[prv]

Btw worth driling a hole thru the screens baseplate for a bolt and wingnut if your screen stands the slightest chance of tipping over?

Far better idea to get a proper VESA mount which will bolt onto the back with holes put there for the purpose. For Apple kit you need an adaptor which replaces the big metal "foot".

Pete

 

[nigelmercier]

Nigel you were right ... Seems there is a work round though ...

Good find.

 

[deuc02]

Don't know if this helps much but I run a iMac/large screen from an inexpensive Sterling inverter ( not pure sign wave) and two 110a batteries...
Ok there is solar and wind generator but the drain is never silly stupid..
Btw worth driling a hole thru the screens baseplate for a bolt and wingnut if your screen stands the slightest chance of tipping over?

Screen's already well and truely fixed into the instrument panel. Unfortunately it's attached to a windows pc - but not for much longer. Inverter will be the second choice supply but reckon I've got enough info from the above answers to go direct to dc - or blow it up

 

[lw395]

Thanks for the ebay link - looks like the sort of thing I'm after. The mains adapter that comes with the mac shows output at 18.5v 6 amps so I'm assuming that if the converter is rated up to 15amps I shouldnt have any problems. One quick question though - why should it get so hot. Will the heatsinks on the unit suffice or will it need some fan assistance. Thanks

Possibly you will want a fan if iti's enclosed, or not in free air.
The average current is often much less than the peak, so it may be OK.
You could try it and see, but back up your data first in case the PSU shuts down.
If it's too hot to touch, that's probably not right for something that's on for long periods.