115 V car outlets

On Sun, 24 May 2015 13:28:15 -0500, Jon Elson Gave us:

Just BUY a REAL "inverter" and plug it into the cigarette lighter receptacle. Try to find one that puts out 120V, and something other than square wave. 300 to 500 watts should be out there.

On Sun, 24 May 2015 17:43:01 -0500, Jon Elson Gave us:

Most laptops run on 19V (that I have familiarity with). You should make sure. Then, you have to match up the jack, and also worry about overcurrent modes.. You should limit the available current.

On Sun, 24 May 2015 16:43:30 -0700, Jim Thompson Gave us:

There are plenty of under-the-hood AC alternator (generator) sets out there. Most are engine (belt) driven, not DC motor driven.

On 25 May 2015 05:36:50 -0700, Winfield Hill Gave us:

One must remember that these are the idiots (chrysler) that used a resistor-on-the-firewall "ignition resistor" that was so damned problematic, literally for decades, because it brought dopes who did not know any better into the service shop.

Another f***ed in the head way to generate revenue.

On Mon, 25 May 2015 10:15:23 -0400, Phil Hobbs Gave us:

Any AC inverter which cannot handle the inrush of a simple 95 watt DC power supply should not be allowed to be sold, much less placed into a motor vehicle as an "alternate power source feature".

On Mon, 25 May 2015 08:16:53 -0700, sms Gave us:

We made 220 volt inverters that got used in the earliest "steady cams", which had military gyros in them, back before the cantilever days. 400Hz though, IIRC. Still got the schematic 'round here somewhere.

On Mon, 25 May 2015 11:14:28 -0700 (PDT), Lasse Langwadt Christensen Gave us:

That is what that big thing along the keel is for. ;-)

Except if a fault ever occurs for which the fuse was intended as the mechanism of stopping the fault from causing a fire. Probably changing the fuse to a DC rated one would be a good idea, or adding an external protection circuit that replaces the function of the fuse.

On Mon, 25 May 2015 14:17:12 -0400, rickman Gave us:

Typically, they rate what the produce, not what they use.

So a typical "95W" DC dongle supply needs 125W or so to make it. Some are even worse.

"Gold Rated" PC supplies are the only things that even come close to proper LV DC supply design these days. (besides commercial stuff)

On Mon, 25 May 2015 11:55:23 -0700 (PDT), Lasse Langwadt Christensen Gave us:

Try it for a few hours and get back to us.

Oh well, 500 watts at 12 volts is more than 41 amps.

You will never get that current from a cigar lighter socket.

I got a 400W one from Newegg for $18.99 US. It came with cig lighter plug and battery clips for higher power. You might be able to get 200W out of a cig lighter socket, especially with the engine running.

Well, it sounds like a crappy inverter, for sure. I have an old one that I bought from Radio Shack when my previous model emitted magic smoke during a road trip. This one has been working fine for a decade or so.

I imagine that different laptop bricks have different inrush behaviour, due to PFC and inrush limiting circuitry, but I haven't measured it, and as I say, I'm not a big SMPS guy. I have noticed that when first plugged in, some tend to produce bigger snapping sounds than others.

Cheers

Phil Hobbs

The outlet is going to be square or the three step "modified sine" wave output so the PF doesn't come into play. There's a pulse of high power loss on each cycle but it's short enough that it doesn't add up to much.

The mostly likely cause is that the inverter has a cheap PTC fuse giving it a rating of 120W momentary and 75W continuous (on a cool day). That's not enough for a laptop.

This is also in the realm of automotive electronics where extreme bullshit ratings are the norm. Just look at all the "300 Watt" audio amps using using obsolete TDAxxxx chips at 14V.

Yes, i have a 100W inverter with a 5A fuse. Had the fuse replaced couple of time. Wonder how they drive 100W with 12V 5A. On the other hand, i have another smaller plug that can run a desktop and LCD monitor without problem, at least for a while.

my laptop (with 90W power brick) runs ok from a 150W inverter. I've not noticed any problems.

Yes, that is my point. If it had been a 150 Watt inverter it would have worked ok. Instead it was very marginal and when the battery needed charging in addition to running the laptop, I would see the cycling that the OP described.

But you do understand that a 95 watt laptop will draw a lot more than 95 watts from the inverter, right?

The standard 'modified sine wave' inverter designs electronically shut down and restart on overload- makes them pretty much bulletproof - something like a motor load won't work unless the inverter is rated way above the running VA. It's likely the capacitive load is being detected as an overcurrent. A PTC would probably give it enough time to start up properly. I had some time to contemplate this when I couldn't get a 1/3 HP pump running on a 400W inverter..

Just sounds to me like they grossly underestimated people's expectations for such an outlet. Adequate perhaps for charging a cell phone or tablet, but not a notebook. A USB socket would make more sense for small loads. I guess it would be handy to run a soldering iron- I have actually used that in a car to do an hour's work or so (modifying items received in the courier parking lot before shipping them out again) but that's not what most people will do with it.

I'll bet there's a story behind that!