netbook pwr supply

[salty]

Sorry if this is off topic for this forum but the computer guys don't seem to have anything to say on the subject .I have an Asus netbook I use for navigation on my boat. I dropped the original pwr supply in the bilge so bought an after market replacement unit which caused noticeable radio interference with my VHF radio. Anyway it recently quit working.
My question is since the output of this pwr supply is 12V and my boat has nominal 12V power do I even need the power inverter. My concern is that when the engine is running and the alternator charging the voltage is up to 14V.
Connecting it up would be dead simple using the existing jack and matching the polarities and there would be no requirement for an inverter.

[dnix71]

For $6 shipped from China on eBay there are dc-dc converter boards originally made to go in laptop power supplies. Feed them 10v up and set the output voltage to whatever you want. I bought 2 recently to boost my 12v bank voltage to about 18 so I can run a battery powered weed whacker on an extension cord connected to the 12v bank.

This is the eBay item number: 281041084321 He has sold hundreds.

The minimum output cannot be lower than the input, though. So you would be overcharging if you ran the engine at the same time.

[vtpeaknik]

Yeah for this application the inability to REDUCE the voltage makes those boards not quite the thing to use.  If the netbook really wants 12V (not even 12.5!) then a simple reducing-only regulating circuit (as simple as one power transistor plus zener diode and resistor) could convert an input of 12.5-14V to a steady 12V output.  Not sure whether such a circuit would work well down to only 0.5V difference between the input and output?  A Rube Goldberg way around that is to use the circuit that increases to voltage to create a steady output of, say, 16V, and then reduce that to 12V using a simple regulator circuit.

It would be nice to know what is the real range of voltages the netbook would safely accept.

[joestue]

Generally the way laptops work is they buck the voltage down to an intermediate voltage with fets rated for 30 volts, which blow up at 31-33volts. they run other dc-dc converters off that intermediate voltage to charge/discharge the battery, supply 5, 3.3, 2.5, 1.8, .8-1.4, etc.

The biggest constraint on your netbook is likely 16 volt tantalum capacitors on that 12v input rail, so if you exceed that they will explode.
but other than that it might work safely all the way through 24 volts.

[salty]

Thanks for your replies.
The pwr supply I think is meant to charge the battery that runs the lap top. Will one of  those lithium batteries take the extra voltage or just catch fire.

It has to work when the motor is running because I am using it with navigation software.

[dnix71]

Your netbook's internal charge circuit should prevent over charging, but if you over do it you still risk setting fire to it. That's a bad idea at sea, esp. if it's your navigation guide.

[margusten]

Hi,

I have this netbook for 4 years now. ASUS Eee PC 900
It has 12V power supply.
Also I have home made wind generator and batteries 12V.
Using this netbook directly connected to 12V battery bank.
Only problem is too long (40 meters) cables to battery bank.
When netbook battery is fully charged, all working well.
But when netbook internal battery needs charging, I can't switch on netbook. 3A max current.
I have to wait when battery charging red light goes off.
Then current is about 1,5A. Charging voltage must be over 10V or netbook not accepts this.
14V voltage didn't made any damage.

[Simen]

Margusten;
It is probably the loss in your long cable that saves your netbook. Most computer equipment that specifies 12V, have a +/- 5% margin; that means 11.4V to 12.6V.

[margusten]

Instead of long cable, You can use power resistor, 1ohm or less.
I think this netbook survives 10V to 14V instead 12V.

[OperaHouse]

I think I would put two diodes in series to drop the voltage about 1 1/2 volt to be on the safe side.  Also I would place an inductor in series to filter out any spikes with 1,000uF electrolytic to common.

[equiluxe]

What you need to look for is is a buck boost converter they work both ways, something like this one, it keeps the output steady whether the input is above or below in voltage.

http://www.ebay.co.uk/itm/DC-to-DC-converter-Automatic-Boost-and-buck-power-supply-car-Voltage-Regulator-/131035575818?pt=LH_DefaultDomain_0&hash=item1e8254360a