# 300w power inverter, laptop problem.



## mrblitz (Nov 21, 2009)

I have a problem with my 300w inverter. 

It is solely used to charge (and hopefully power) my laptop.

The facts first. The inverter is a 600w peak/300w cont. It is connected to the power centre of my van. I have run 30mm cable to the 12v dist board from my bank of leisure batteries...390ah of 'em. There is no voltage drop. I just tested 12.99v at the leisure batteries and 12.99v at the 12v dist board.

The laptop power supply is 72w (IBM T42). The other laptop power supply is similar (an apple ibook). Both are fine just for charging, but the inverter fails when the laptops are switched on....after about 1 hour first time, then it resets, ok for 30 mins, then resets, ok for 10 mins, resets, then fails and stays failed until i switch off for 30 mins or so.

It's ok...its usable...but its annoying. Especially when its late at night or early in the morning as the fail warning makes a loud beep. Rubbish.

The only time that it has been ok is when we completely discharged out leisure batteries (stayed static with no hook-up for 8 days) and when we started rolling and our sterling alt2batt charger kicked in it was fine for hours.

I thought that os the sterling was giving a boost to the charging voltage this stopped the voltage sensor from faulting. But after checking the vltage drop situation i am not so sure any more.

The wires i have used throughout the van are as follows.

eng batt to sterling = 3m at 30mm
leisure batt to sterling = 3m at 30mm
leisure batt to 12v dist = 3m at 30mm
12v dist to inverter = 6inches at 4mm
inverter supply cable 12awg soldered = 6inches at 3.3mm

It has always been like this in every car or van i have used it in. Fine for charging phones, nds, camera, laptop...but when just one laptop is on and running the problem starts again.

ANY help would be very gratefully received.

I will try a friends 750w inverter at the weekend to see if it works for me.


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## teifiprt (Oct 2, 2007)

Hi,
Try removing the battery from the suspect laptop and then use on the inverter. Batteries that are at the end of their life have given me trouble with power supplies in the past.

HTH,
Peter.


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## mrblitz (Nov 21, 2009)

tried that...

the battery is fine lasts for 2+hrs normal power....4+hrs reduced cpu speed etc

the laptops (individually) stayed on for longer without batteries installed, but still eventually ended up tripping the inverter, and when they did, they obviously went off too!!!!


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## sallytrafic (Jan 17, 2006)

I doubt that its the power available that is the problem nor in your case the voltage drop (do you really have 30mm² cable - if so great) its much more likely to be the wave shape/power factor.

What you have is a square wave output that approximates to a sine wave (and mathematically is made up of a lot of different sinewaves at multiples of the fundamental frequency - 50Hz) now if this feeds into a purely resistive load ( say a lightbulb) then it is always ok but fed into an inductive load (most fans) or to SOME switched mode power supplies then all is not well. The device you are powering may overheat and certainly your inverter may shut down 

My own experience is that the apple power supply and a 300W inverter is OK with low power ie just charging but it cannot support the computer when on.


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## cater_racer (May 1, 2005)

The power supply for the laptop has a high frequency switch mode regulator in it, it pulls from the main supply in sharp peaks, that are proabably giving your inverter grief.

I'd not remove the battery from the laptop it providing smoothing capacity.

I'd go for surge suppression type mains adaptor:

http://www.maplin.co.uk/module.aspx?TabID=1&criteria=usb&ModuleNo=27247&C=SO&U=Strat15

HTH


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## mrblitz (Nov 21, 2009)

you really reckon a surge protector could help?

i am in france for the foreseeable future and an new inverter costs twice what it does in the uk.

i can get a surge protector easily...if it is really gonna do the trick?

and yeh...i went berserk for big cables in the van to try and avoid any problems. especially as the sterling is throwing large voltages around on a daily basis.


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## Fatalhud (Mar 3, 2006)

Why not just use one of these

http://www.maplin.co.uk/Module.aspx?ModuleNo=44736

Alan H


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## wilse (Aug 10, 2007)

I had this problem on my last van with a 600w inverter, and was too lazy to find out why.

Cheers for this...

PS if you don't want to buy a surge plug, why not just charge the laptops when they are not being used?
My macbook pro charges from a 150w inverter when not operating connected to the cigarette lead 8O .


w


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## inkey-2008 (May 24, 2008)

I think you are overloading the inverter my compaq used to make my 300w bleep all the time.

I found if you plug it in when you use the laptop and the bettery is full it draws less and behaved it self.

Is the 75w the out put or the input to the transformer.

Andy


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## mrblitz (Nov 21, 2009)

laptop psu draw from power source 72w max (16v at 4.5amp standard) the psu is slightly variable...max power output is 16.5v...min is under that just for battery charging.

when not plugged into the laptop, the psu tests at 16.6v at the tip of the psu plug, i assume ths is to make up for smaller cables inside the laptop and the relative voltage drop.

Any ideas where i can get one of those maplin universal car power supplies in france?


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## pippin (Nov 15, 2007)

Alans suggestion is the better one.

By using an inverter you are involving two sets of voltage converters.

The 12V DC to mains 50Hz one and then the lap-top (or whatever) one that converts the mains 50Hz down to (say) 17V DC.

Both involve complex electronic switchery which can fight against each other. 

Use of a dedicated 12V DC to (say) 17V DC converter simplifies the situation and is also vastly more efficient.

I have never quite understood why people use 12V DC to mains inverters and then tag on another piece of kit that drops it down to low voltage DC again.

You will almost certainly find that Trust universal 12V PSU on the shelves of the Hypermarché.

PS - doubt that the filtered multiblock will make a ha'porth of difference.


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## ianandsue (Jul 11, 2009)

*apple laptop chargers*

Take care with your apple charger!

I have a 500W (continuous) modified sine wave inverter which we have used for charging the laptops, camera batteries, etc. for several years with no problems.

One day whilst using and charging the new Macbook Pro at the same time, the inverter tripped out. I reset it and a few minutes later it tripped again, this time the apple charger died as well!
When I took it to an apple shop in Lorient the guy wouldn't take my word that it was knackered, plugged it in and tripped his main breaker! Took him half an hour to get his lights and computer u.p.s back on!

We've since had another small charger die as well, so I'm now looking at a full sine wave inverter - expensive and more bulky, but I don't think apple units like modified sine wave. If I blow up another one it will cost £80 to replace, never mind the inconvenience of finding an apple shop abroad.


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## pippin (Nov 15, 2007)

That reinforces my suggestion in my previous post.

These 12V Trust power supplies cost less than twenty quid!

And you can use them in aircraft!!


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## ianandsue (Jul 11, 2009)

Only one snag - I don't think they come with apple magsafe adaptors!

One of the joys of owning a mac!!


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## Ericbunny (May 1, 2005)

Best advice is to simple use a pure sine wave inverter at all times.It stops the buzzing in the tv,the laptops not charging or working properly.Pure sine wave is very close to electricity at home,so any device will work properly, and it will not damage your electrical items,unlike a normal wave inverter.


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