power inverters and laptops question

Submitted: Sunday, Apr 06, 2008 at 12:56
ThreadID: 56359 Views:4389 Replies:11 FollowUps:2
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G'day all. I'm planning to run Oziexplorer on my laptop with a GPS mouse for my next trip. But I've struck trouble with the power inverter and the laptop. Would appreciate some advice from anyone with experience of the following:

I've purchased an IFONX 150 watt inverter. The back of the package, and everything I've read elsewhere, suggests that a laptop draws about 80 watts. So that should be plenty of room. So long as the laptop is not turned on, I have a green light on the inverter that says 'everything's cool'. However, if I turn on the laptop, then I get the red overload switch. This seems odd, since the DC output from the inverter on the laptop is 16V x 3.75 amps. So given Ohm's law, should draw 60 watts.

The other thing that crossed my mind is that the laptop may want a pure sine wave, but the output of the inverter is a modified one. But this contradicts the advice I was given by the bloke at TJM. Since the power supply charges the laptop's battery and the battery supplies power to the laptop when it is running, this shouldn't matter. It would matter if you were running a desktop PC in your truck, but not a laptop.

Or is it possible that different laptops do it differently? For the record, the laptop is an old Fujitsu Lifebook S6120. Not particularly flash, but compact, rugged and lightweight.

Would love to hear from anyone who's got any insight into this problem.
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Reply By: obee - Sunday, Apr 06, 2008 at 13:16

Sunday, Apr 06, 2008 at 13:16
I used to run and old 150 watt inverter but it used to get hot. Maybe the computer power supply was complaining because it wanted pure sine. Dunno. Anyway the inverter cooked the trannies which were obselete (mosfets) so now I have a pure sine wave 150w from jayco. All is cool.

If tjm said it would do the job then take it back and see if another one will not overload. Take the laptop with you so the man can see.


AnswerID: 296967

Reply By: DIO - Sunday, Apr 06, 2008 at 13:19

Sunday, Apr 06, 2008 at 13:19
My preference is to run a laptop power supply to keep the battery charged if/whilst mobile. These are readily available from places like Jaycar, Dick Smith/Tandy etc. I am opposed to having 240 volt power within my vehicle whilst mobile. In the event of an accident, rescue workers may be subjected to fatal shock. I consider that imposing such risks on these people as totally unacceptable. My choice.
AnswerID: 296969

Reply By: Beetle1 - Sunday, Apr 06, 2008 at 14:02

Sunday, Apr 06, 2008 at 14:02

I had a similar problem but it turned out to be the inverter. What I did to check its capacity was to plug in various wattage light bulbs to make sure it wasn't something to do with my PC supply. Incandescant Light bulbs are nearly a purely resistive load so ohms law works well.

I have always used a pure sine wave inverter as the cheap modified square wave types can cause interference etc.


AnswerID: 296976

Reply By: Member - Kiwi Kia - Sunday, Apr 06, 2008 at 14:16

Sunday, Apr 06, 2008 at 14:16
I have had this problem in the past. One brand laptop workd ok and another did not. As soon as the hard drive was being accessed the small inverter did not want to know and shut down. You may have to get a minimum of 300 watt before things work ok.
AnswerID: 296979

Reply By: Member - Davoe (Yalgoo) - Sunday, Apr 06, 2008 at 14:32

Sunday, Apr 06, 2008 at 14:32
Is the engine running? the cig plug wiring is too thin and will cause overload shutdown without it running or low power whatever. The inverter alarm gos of when i pull up and the inverter shuts down. When I use the allogator clips direct to the battery it is fine
AnswerID: 296984

Reply By: Member - joc45 (WA) - Sunday, Apr 06, 2008 at 15:12

Sunday, Apr 06, 2008 at 15:12
Hi Dirk,
Some laptop power supplies require quite high transient input current pulses. Some smaller inverters cannot deliver these high current pulses, and a higher wattage inverter is required. This does not mean that the laptop will consume more than the 60 watts specified.
But really, I suggest you look at a DC-DC converter. Places like Dick Smiths and Jaycar flog a range of them, especially made for laptops, with selectable output voltages and a range of dc adaptor plugs for the laptop. eg, Jaycar CAT. NO. MP3463 for about $35.

AnswerID: 296987

Reply By: Mikee5 (Logan QLD) - Sunday, Apr 06, 2008 at 17:40

Sunday, Apr 06, 2008 at 17:40
I use a Kerio laptop power supply from Dick Smith. It converts 12 volts to a voltage selected by you. From memory they come in 75 and 90 watt models. They also come with a variety of output plugs. Just make sure that one fits your laptop.
AnswerID: 297006

Reply By: Member - Jim S (NSW) - Sunday, Apr 06, 2008 at 19:01

Sunday, Apr 06, 2008 at 19:01
I have no trouble running my laptop from a 150W modified sine wave inverter .... (It's a Toshiba 100 with 14" screen purposely bought for low power consumption) A friend had heaps of trouble (tripping out) but it turned out to be the aux battery was buggered and voltage was low ... Installed new aux battery .... BINGO works fine..... (he had a 17" screen Toshiba, too big for the bush)

If you measure the current on the DC side of the inverter for your laptop it's would be about 6 amps (may be higher) allowing for the efficiency of the inverter,etc .... You could try connecting your inverter directly to the battery and run a 240V lead to the PC, can help sometimes as voltage drop on the 12V side can have quite a large effect on the inverter ... Plugging inverters into cigarette lighter sockets can cause problems with voltage drop also ....

The best solution is to get a 12V power supply to suit your laptop but ensure that it has enough power to run the laptop as they are not always available or able to run large laptops ....

NOTE: Some large Laptops, eg. those with 17" screens, powerful processors and DVD players need a 300w inverter .... (If the battery is low, the inverter will trip out when the laptop is connected) Also note that running a DVD movie uses quite a bit of power and the laptop needs to be connected to the inverter while running the movie .... The internal battery will only last about 15 minutes .....

With regard to getting an electric shock from a 240V inverter .. You would need to be connected between the active and neutral as inverters are usually isolated from earth so VERY unlikely ...

J Sutton

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AnswerID: 297014

Follow Up By: Member - Graham H (QLD) - Sunday, Apr 06, 2008 at 20:27

Sunday, Apr 06, 2008 at 20:27
Projecta make several models of laptop 12volt converters.
I see they are up over 90 watts now so you should be able to get one to suit. If you are worried about the battery take it out.

Most will run on exterior power Ok.

I also have a WAECO 100watt can type inverter which runs my 14 in Compaq ok but prefer the low voltage way.
The 65 watt Projecta runs it fine with all the bells and whistles like Bluetooth, 4 way USB hub, cordless mouse USB wireless internet etc
FollowupID: 563083

Reply By: Dunaruna - Sunday, Apr 06, 2008 at 20:19

Sunday, Apr 06, 2008 at 20:19
I cannot get my dell to play nice with anything other than a pure.
AnswerID: 297038

Reply By: GerryP - Sunday, Apr 06, 2008 at 21:08

Sunday, Apr 06, 2008 at 21:08
Sounds very much like the 12 volt wiring to the inverter is undersized causing too much voltage drop. Had similar prob's once, upgraded the wiring and no issues since. As stated in an earlier reply, ciggy lighters are general not adequate - wire in your own socket direct from the battery (with suitable fuse), both active and earth and I reckon you'll have fixed your problem.
Cheers and good luck
AnswerID: 297051

Reply By: Member - Dirk B (VIC) - Monday, Apr 07, 2008 at 06:01

Monday, Apr 07, 2008 at 06:01
Thanks to everyone for all the splendid advice. Hadn't thought enough about DIO's point and it's a good one. I think I may try the DC to DC inverter just so there's not 240v running through the truck all the time.

I'll hang on to the 240 inverter just for the odd camera battery, mobile phone, etc. 150 watts is probably a bit over the top for that, so perhaps I'll see if TJM will swap it for something lower (and cheaper). Hardly their fault that the advice didn't work out. It seems that laptops in trucks with 240 inverters is an area where there are lots and lots of variables.

AnswerID: 297101

Follow Up By: KSV. - Monday, Apr 07, 2008 at 09:05

Monday, Apr 07, 2008 at 09:05
DC-DC will work for laptop, but inverter is far better and more universal solution because you can charge camera, camcoder, phone, CB – name it. Plus you can plug printer if you wish. However IMHO buying cheap MSW inverter is false economy (I did it and now it staying in garage and doing nothing), so get PSW and get as big as you comfortable can afford – they not that expensive these days. DIO point is somewhat moot IMHO – installed permanently and properly it is not more hazard in accident that say LPG gas bottle or LiIon batteries found in all modern laptops. Everyone entitled on his/her opinion and this is mine.

FollowupID: 563139

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