Laptop power in the car

[S_Egbert]

I am trying to figure out the best route to go for powering my laptop on road trips.
One would be a DC to AC inverter which the laptop's AC power supply plugs in to.
The other is a DC to DC supply which replaces the laptop AC supply.
I can't find anything definitive as far as the pros and cons of each except that the AC inverter consumes a bit more vehicle battery power.
Google searches just want to sell me something without giving the info I want.
Any help is appreciated.

Thanks,
Steve

[brian.austin]

A DC to DC supply would probably still require a voltage change since most car battery systems kick out an unregulated 10-14VDC to the cigarette lighters/DC power points. It's been a while since I've worked on them, though, so it's possible newer autos have cleaner voltage regulation.

Personally, I'd just go for the inverter. You can use it for other things (like charging your camera batteries) and it's really only a "bit more" power consumption in the long run. Especially since the car system is recharging all the time anyway.

[JackAZ]

Be cautious of using an inverter to charge Li-ion batteries. An inverter doesn't generate a true sine wave like an AC power source. Because the inverter is taking a DC input and simply multiplying it several times to generate the specified AC voltage it clips both the high and low ends of the AC sine wave. Li-ion batteries are sensitive to this and charging them from an inverter can shorten their life.

Having said that, it's a decision you have to make about how expensive the battery is, what it's anticipated life expectancy is, and how long you will own/use the equipment in question. Even being aware of the above I have yet to replace my inverter with a quality DC to DC converter for using any of my Li-ion power devices on the road.

After about two years, probably just shy of that, my Li-ion laptop battery holds only about a 20 minute charge. Had I not been using/charging it from an inverter it would most likely still be running at full tilt as if it were new. For me this isn't a horrible consequence since actual use away from a power source is rare and usually for a brief amount of time. I haven't encountered a situation yet where I've felt it's time to replace the battery. I just know that I have to be plugged into something if I'm going to be using it for more than a few minutes.

[S_Egbert]

Originally Posted by brian.austin

A DC to DC supply would probably still require a voltage change....
Personally, I'd just go for the inverter.

Thanks Brian.
Yes, a DC to DC unit has to do a bump up in voltage as well as regulate it since laptops are in the 16 to 18 volt range.
I probably will go for the inverter. Most of the better ones have a self shutoff if the vehicle voltage drops below a certain point so even using it with the engine off won't leave you with a dead battery.

Originally Posted by JackAZ

Be cautious of using an inverter to charge Li-ion batteries. An inverter doesn't generate a true sine wave like an AC power source. Because the inverter is taking a DC input and simply multiplying it several times to generate the specified AC voltage it clips both the high and low ends of the AC sine wave. Li-ion batteries are sensitive to this and charging them from an inverter can shorten their life.

Thank you Jack,
I would think that once the square wave AC goes through the laptop's power brick and is converted back to DC that this would be a non issue.
No matter, since li-ion batteries have a finite lifespan not much longer than two years anyway I won't worry about that too much. Like you, my time spent on battery power is very small.

[JackAZ]

Originally Posted by S_Egbert

Thank you Jack,
I would think that once the square wave AC goes through the laptop's power brick and is converted back to DC that this would be a non issue.
No matter, since li-ion batteries have a finite lifespan not much longer than two years anyway I won't worry about that too much. Like you, my time spent on battery power is very small.

Because the sine wave is clipped it doesn't provide the full voltage swing the transformer is looking for so it, in turn, never functions completely properly. Not that big of a deal to me but to some it is.

[brian.austin]

Originally Posted by JackAZ

After about two years, probably just shy of that, my Li-ion laptop battery holds only about a 20 minute charge. Had I not been using/charging it from an inverter it would most likely still be running at full tilt as if it were new.

No, actually, that's not the cause for your poor battery performance now. It's because you're probably not "exercising" it.

Some history: I'm an IT manager who, during a previous job, managed about 25 laptops used for sales and tech deployments in a variety of conditions. I supplied each with APC inverters for their vehicles as part of their "mobile" package. I also taught and encouraged battery "exercise".

Here's what I found, from personal experience and from those following my recommendations:

1. Laptops that had no regular battery use that completely drained the battery every 30-45 days saw a significant decrease in battery performance after 1 year of daily operation.

2. Laptops that were intentionally run down on batteries once a month saw almost NO performance hits on their battery performance, even after 2 years of operation.

3. Inverters and alternate power supplies had no effect on 1 or 2.

4. Heat had a roughly 15-20% decrease in battery performance when running on batteries but almost no impact on battery life or performance during later cooler periods.

Here's what I did to get this performance:

1. Adjusted power management settings to warn me of battery failure at 3% rather than the default 10%.

2. Once a month (30-45 days or so), I'd take the laptop off the docking station or power supply and run it down to that warning.

3. At the next opportunity, I'd charge the battery back up. To get the greatest impact, this should be a FULL recharge cycle. Don't remove the power supply until the battery is completely charged. Yes, newer battery technologies have less "memory" but my personal experience has told me the greatest impact is a full cycle rather than partial.

I'd also do this within a few days of getting a new laptop. Let it charge up, run it to nothing, then recharge fully.

I have a laptop on my closet shelf that is 5 years old. When I bought it, I'd get roughly 2.5 hours off of it. Today, after a charge, I can still get 2+ hours from that same battery. I've never changed it. All I did was those steps above.

[S_Egbert]

Thanks for your insight Brian, very good to know.

[drkranger]

I have had no problems with an inverter and my laptop. There are some with higher power capabilities and multiple input plugs, but all in all, the 2 that I've used have worked well. I just turn on the car, plug in the box to the car power adapter, plug in the laptop, and turn it on. I just reverse all that when turning off the car...or at least unplug the laptop and then turn off the box before turning off the car.

Works fine. I got mine at the local electronics store for $30-$50 depending on power supply.

[Willymo]

Inverter also gives you a lot more flexibility. I've used mine for charging phones and running small TV monitors, battery operated tools, and probably a few other things.

[Songman45]

Great advice Brian. I also assert the same line of thinking works on cell phone batteries. Let them completely run down, then charge them completely. I agree that the "no memory" claim is inflated.

Also, when using an inverter be sure the output meets the requirment of the device you are powering. My folks got a compact inverter with the intention of powering a desktop replacement notebook computer in an RV only to find out the laptop was drawing more than the inverter could deliver.