Laptop PSU questions

[David M]

On a boating forum where I am a moderator, we are having a debate on whether or not a laptop can be plugged directly in to a boats 12VDC system. Some people say you can and others say you cannot. Some people have actually done it. We know about external voltage regulators but that's not the debate. We just want to know if hard wiring the boats DC system directly in to a laptop can be done. On sailboats this matters because they run on batteries most of the time which means they must be efficient with the loads on the DC system. Every time power is converted, a percentage of it is lost as waste heat. BTW, a sailboats DC voltage might varie from between 10 volts up to 14.5 volts. Many Sailors frequently use laptops connected to a GPS to run chart software which shows the boats location on the water.

My thoughts are that whether or not you can is determined by the laptops internal PSU. Basically, the range of voltages that the PSU can accept must be greater than and lower than the range of voltages that the boats 12VDC system goes through. If this is true then you will be okay. Is this pretty much true?

So given that, how do you determine which range of voltages that the internal PSU for a laptop can accept? I went in to the Dell website to their specifications pages for their laptops and Dell does not list the acceptable range of voltages for their laptop PSU's. Where might a laptop owner find this information? I realize that desktop PSU's list the acceptable AC voltage ranges and was hoping that the same can be obtained about the input DC voltages of laptops.

[tmathews]

I expect you _can_ power it directly, but whether you _should_ is another matter.

In the absence of specs, I'd assume computer stuff would be designed for a tolerance of +/-5% and that most units would work on +/-10%. A range of 10 to 14.5V already exceeds 10%, plus there may be spikes and sags beyond that (e.g. a bilge pump motor switching on and off). You could probably fix most of the noise with a big inductor on the PC's supply line but that won't fix the DC range.

If you've got room you might consider a separate battery (or two, if you need really long run times) and an inverter so you don't have to worry about draining the boat's battery or converter efficiency.

[Panama Red]

I'd rather think an adapter like used in a car would be a better choice. Seems like supplying 12-14 volts to a laptop requiring 17-20 volts dc would either result in an overheated power system due to lower voltage/higher current or the laptop wouldn't even run because the voltage would be out of operating range.

[glc]

Use a car adapter. You saw mine in my truck, didn't you?