Using cig. lighter - is 5A enough power?

shizzle · 03-21-2005, 05:16 AM

I bought a 300W inverter for my carputer (mac mini) because I will be taking the MM inside with me when I go certain places (work etc), and also would like to use it for various purposes (any device i'd like) . I also was GOING to use a splitter for the lighter plug, so that I could also use that for various purposes (phone charger, etc) WHILE I used the carputer.

My question is one of basic elem. electricity.
If the splitter has a 5A fuse on it, will that really limit me?
I am a n00b, but I was thinking 5A x 12V = 60W ???? Do I need a splitter that handles 8A or more? Is that right? Should I forget the splitter?

Any ideas (even alternative suggestions) are very appreciated. I'm trying to make this setup simple.

I love this forum!!!

Details: Mac Mini
8" lilliput touchscreen
7port USB hub (w/ power supply)
700W (max) inverter

Scouse Monkey · 03-21-2005, 05:24 AM

Oh dear! oh dear oh dear!

300W at 12V = 25A.

Your mac mini system will not use all that but after taking into considerationt he efficiency of the PSU and the inverter you need more than 60W.

Go

for a thread on wiring an inveter up to the battery directly. There is lots and lots of em. I answered onw the other day with a nice big 'spoon feed'.

Cris · 03-21-2005, 05:31 AM

All the cig can do without a problem is recharge your phone...any thing else just wasn't meant to.

Scouse Monkey · 03-21-2005, 05:33 AM

Quote: Originally Posted by Cris

All the cig can do without a problem is recharge your phone...any thing else just wasn't meant to.

it's good at lighting fags too! And if you run an intverter off it for a long time it will light a lot more than your fags!

Cris · 03-21-2005, 05:39 AM

You can even celebrate the 4th of July of it...

shizzle · 03-21-2005, 07:01 AM

ok ok ok
i am a little confused
the plug is 12v 11A (14.4v when car is running) The power inverter offers 120V ac 400-700W max. I was under the impression this would work just fine for a mac mini, and a usb hub powered from the second ac receptacle. They are well within its wattage capacity. I have done much

ing and concurred with many that this was suitable. ASSuming so...

Am I right that you kind lads were telling me that the splitter with the 5A fuse is where the fireworks will be lit?
Because I can just ditch it, plug the lcd into the second ac receptacle
(it would have gone into one of the split lighter plugs)
and forget the powered usb hub. But I really think that if I just split the lighter with an 8A fuse it would be plenty of power. I even tried the wattage calculator. HELP!!!!! Please keep in mind that I am a n00b in your details... I learn well but I havent learned this quite yet.

shizzle · 03-21-2005, 07:09 AM

Quote: Originally Posted by Scouse Monkey

Oh dear! oh dear oh dear!

300W at 12V = 25A.

Your mac mini system will not use all that but after taking into considerationt he efficiency of the PSU and the inverter you need more than 60W.

I definitely wont need 300W. heres the link to the inverter on ebay ... check it out its nice... even has a display!

Quote: Originally Posted by Cris

All the cig can do without a problem is recharge your phone...any thing else just wasn't meant to.

Do you mean just with the splitter? is it fine without it?

My power needs are quite low for a carputer, no? mac mini is rated around 80W ! thanks for your help... I would be willing to connect to the battery direct... I just dont see the advantage.

Scouse Monkey · 03-21-2005, 07:17 AM

Quote: Originally Posted by shizzle

I definitely wont need 300W. heres link to the inverter on ebay... check it out its nice... even has a display!

My power needs are quite low for a carputer, no? mac mini is rated around 80W ! thanks for your help... I would be willing to connect to the battery direct... I just dont see the advantage.

I know you won't need 300W - that is why i said you won't - read my answer again.

YOu have answered you own question - 12V at 5A is 60W, your macmini needs 80W. Evena t 14V you are running close to the limits and htis in never good thing.

but...

Your inverter is say 70% efficent, your mac minis (i am gonna rename them mini-macs) is say 90% efficent (these are guestimates to rpove a point). Then to get 80W for the macmini....PSU out = 80W, (/0.9) PSU in = 89W. inverter out = 89W, (/0.7) inverter in = 126W. That is 10.5A at 12V (less at 14V).

save yourself a lot of worry and trouble and run your inverter off a dedicated power line from the battery with a fuse and a relay to turn it on - go find my and other people previous answers to wiring inverters.

Don't forget you will also want to tun things like your screen and external devices off the inverter - before you ask - do not run the screen off unregulated car DC - the spikes will kill it.

Scouse Monkey · 03-21-2005, 07:20 AM

Quote: Originally Posted by shizzle

I would be willing to connect to the battery direct... I just dont see the advantage.

The advantage is not frying your cars electrics and risking a fire!

You wouldn't run 20 sockets off one wall socket in your house so don't risk overloading the ciggy lighter socket in your car.

You have no idea how thin the cables to your lighter are or what connections are made along the route behind your dash. All it takes is a for a thin wire or bad connection to heat up and you are in trouble. Spend an extra $10-15 on some wire, a fuse and a relay and do it properly.

Matthew230 · 03-21-2005, 07:35 AM

I run a 150w Opus attached to an matx and p4 2.4 ghz celeron processor from the 12 volt cig socket in the boot.

Will it not work ?

Scouse Monkey · 03-21-2005, 07:59 AM

The boot 12V socket is likely to be designed to run things like portable TVs, mini-fridges etc (but uses a ciggy lighter socket for compatibility).

Personally i would run my own line as for a start i don't trust those crappy ciggy lighter sockets - when i used to race Rc cars we ran the charger through the ciggy lighter - the conenction was always a little dodgy and got warm and the batteries recieved a much better charge when we wired the charger direct to the car battery.

Check your car handbook to find the current rating of the socket/wiring. It should state it. but you need to have about 15A minimum rating to be safe - that is what size fuse i would fit to an Opus 150 supply run (or possibly 20A for a bit of margin to stop fuses blowing with spikes on PC/Opus startup etc)

shizzle · 03-21-2005, 08:09 AM

Thanks very much! I see your point. I failed to mention though that my lighter plug is just for power, its the smoke free edition accord. Not even an ashtray. Which is part of the reason I may end up doing like you suggest and wiring to the battery... I need a usb hub just for this and maybe gps reciever soon....

Again, thanks.

shizzle · 03-21-2005, 08:10 AM

then again that ashtray can be battery powered

Scouse Monkey · 03-21-2005, 08:17 AM

No probs, if you are running a USB hub you can power it using the wall adapter into the the inverter so you odn't overload the MACs USB port.

Have you looked at using a DC-DC solution for the MiniMac? i'm pretty sure there is one and it would be more efficent.