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View Full Version : OT laptop in the car - help with inverters



Mcgyver
04-30-2007, 09:44 AM
I've been doing some work recently where i need to have the laptop on the car, obviously not while driving, but it's on all the time and used either as a map and/or place to take notes.

I purchase one of the Jensen cheapo (square wave) 12vdc to 120 AC inverters, after reading most devices including laptops are fine with a sq wave output. its 160 watts, computer AC power supply is iirc 80 so that should be ok.

What happens is the computer will just completely turn off, at random times but usually within 10 minutes of booting. its like an instant off, no power down. The battery checks out, the fan is working and the bottom doesn't feel hot. at home, it is stable. tried messing with various power options, didn't do anything.

any idea what is happening or how to fix it?

thanks

Evan
04-30-2007, 11:12 AM
It obviously doesn't like the square wave power. Are you certain it's square wave and not modified square wave? If it is square wave try a modified square wave inverter.

Swarf&Sparks
04-30-2007, 11:39 AM
LC filter will knock some of the harmonic corners off the square wave.

Weston Bye
04-30-2007, 12:14 PM
A while back I needed to do some surveillance in a parking lot. A deep cycle battery, an el-cheapo 140W inverter driving a VCR and monitor, 12V direct from the battery to the camera. Everything worked great, hours on end.

I suspect, as others have said, the laptop supply doesn't like square wave. Try a simple experiment by plugging in a small AC induction motor (small fan?) along with the computer. The inductive reactance of the motor might knock the corners off the square wave. A capacitive load would be better, but there are few plug-in products/appliances that present a capacitive load.

J Tiers
04-30-2007, 01:09 PM
A laptop almost certainly already has a switchmode power supply that charges its battery. That will be "between" your inverter and the computer, and should isolate the computer from the inverter.

However, that also introduces another variable.......

The inverter has an RMS voltage that is correct. HOWEVER, for the "modified square wave" inverters, which are the normal type, the PEAK voltage is significantly LESS than with a sine wave such as is normally supplied by the AC mains.

For 120VAC , the PEAK is normally 170V, the RMS is 120V. For a "modified square wave" inverter, the PEAK may be quite a bit less, possibly as low as 130V or 140V.

First,
The SMPS may be responsive to the peak voltage, since they usually charge a capacitor right off the rectified line, and then use the DC as input. With 130V peak, the equivalent rms is about 90V, and may trigger a shutdown of the SMPS.

Second
The SMPS may falsely detect an overcurrent condition due to either input noise from the inverter, OR due to the fast rising charge current supplied by the inverter square wave.

Third,
the inverter may be "unhappy" with the capacitive load, and IT may current limit, which might reduce the effective output voltage without shutting it off. In the car you will typically not hear the characteristic "squeal" or "sizzle" of the inverter when in a state of current limiting.

In any case, the result can be the SMPS shutting down. The overall result depends on whether your laptop runs on battery if power fails, or if it detects the charger plugged in, and runs on the charger only, possibly also charging the battery (or not).

It sounds a bit like the laptop quits when the SMPS charger shuts down.

If the charger is internal, then it might indeed be coupling noise in and getting a false "shutdown" signal. Most of the laptops have an electronic switch, and the circuit may get confused and shut down.

IOWOLF
04-30-2007, 01:10 PM
Try just charging the L/T battery in the car ,and run the L/T on its own battery till it runs down.
This may get you by.

BadDog
04-30-2007, 01:30 PM
J said what I would have said, and a whole lot more I wouldn't know to say. :D

CCWKen
04-30-2007, 01:57 PM
You can get a full sine wave inverter. HF had them for $169? a while back. IIRC, they were 300/600 Watt peak. Another option is to run off a battery backup (UPS) box. A 420-650W box will last a long time on a charge. The only problem is silencing the alarm. The older APC brand allowed you to turn the alarm off but the newer ones don't. At least I haven't figured it out yet. It's not bad though. It beeps about once per minute. I run my PC and TV through 420w APC-UPS boxes. I've also got an old 650w I keep for emergency use around the house.

Forgot to mention: You can get used ones cheap. I got the two 420's for $10 each. All I had to do was buy new batteries. The batteries are about $20-$25.

Mcgyver
04-30-2007, 02:40 PM
yes it is a modified sq wave, ended up phoning Audiovox who owns Jensen, despite claims that laptops work with these inverters i guess mine won't :( I'll try the induction motor idea, I'll also hook it up and put a meter on it (I know, should have done that in the first place, the brain is exhausted from the barrage of crappy products sent to try me)

Thanks very much for the ideas and info. may have to get a full sine wave inverter, darn it, didn't want to spend more money.

Doc Nickel
04-30-2007, 04:32 PM
I continue to wonder why people always add that extra step of bumping the voltage up to 120V AC, before dropping it back down to 16V or so for the laptop. That's expensive and inefficient and unnecessary.

I needed to run a laptop in my truck for a while, and the original '96-era battery is long since used up to the point it doesn't even supply the power necessary to even boot the thing.

Anyway, I went to Radio Shack and bought a $35 "universal power adapter". It gives me anything from 9V up to 24V, and has interchangeable tips so that I was able to plug it directly into my laptop.

I used a meter to set the voltage (dial on the converter box is a bit off) and the polarity, taped the adapter to the end of the wire, and it worked great. Ran the laptop for full days, never affcted starting the car at the end of the day, and was a fraction the cost of either a new battery, or an inverter.

Doc.

aboard_epsilon
04-30-2007, 04:37 PM
You have over-heating cheapo inverter problems ...
They have a heat sensor that turns them off ..

better models have a built in fan ..
that will solve your problems.

when they say they are 160 watts.... this is not continuous ...
and you have found out not even 80 watt is continuous ..

so buy one with a built in fan.

mines a 150 watt and it cuts out after 15 Min's in the winter ...so god knows how long it will stay on now its the summer ..


btw.... it will be trying to charge your laptop battery as well ...if its flat ......this will make it want to supply more than 80 watts your laptop requires

all the best..mark

BadDog
04-30-2007, 04:59 PM
The thing that gets me is that it turns the laptop off instantly. It should go into battery mode unless they are removed or completely dead. At least all of mine respond that way to loss of line power, though it's been said that some do not auto switch?

Anyway, assuming 160W peak and 80W steady. That's ~13A/6A at 12V, and assuming (incorrectly) that there is no loss in conversion, that's only ~1.4/.72A at 110V. Quite a bit of that goes up in heat, so maybe 0.5A at best? I'll bet that power supply needs more than .72A continuous to run the computer... But again, why does it shut off instantly?

BadDog
04-30-2007, 05:03 PM
Oh, and Doc, those universal adapters aren't really so universal. For instance, they don't fit my current Dell Inspiron... So the only true "universal power" is in the form of a 110 inverter that lest you use the line charger that you undoubtedly have for your laptop. :(

aboard_epsilon
04-30-2007, 05:25 PM
The thing that gets me is that it turns the laptop off instantly. It should go into battery mode unless they are removed or completely dead. At least all of mine respond that way to loss of line power, though it's been said that some do not auto switch?

Anyway, assuming 160W peak and 80W steady. That's ~13A/6A at 12V, and assuming (incorrectly) that there is no loss in conversion, that's only ~1.4/.72A at 110V. Quite a bit of that goes up in heat, so maybe 0.5A at best? I'll bet that power supply needs more than .72A continuous to run the computer... But again, why does it shut off instantly?

Right ......think it shuts off instantly because its still plugged into the inverter ...
think.... if you have it on charge from the mains and then you pull the jack out ...it disconnects internally at a spring loaded doofer switch on the jack input ...that switches mode to charging mode in normal operation.

if you were to turn the charger off at the wall it would act like the inverter.


when the inverter cuts out ....and spring loaded doofer is still in the mode...so cuts the comp out

all the best...mark

BadDog
04-30-2007, 06:08 PM
Not on mine. I can leave the charger plugged in to the computer and unplug at the wall, keeps right on running with batteries. As far as I know, all these laptops are always running through the internal PS with batteries in-line at all times. If it were a mechanical switch, there would be dip/spike problems, and computers don't do well with those.

Lew Hartswick
04-30-2007, 06:17 PM
I continue to wonder why people always add that extra step of bumping the voltage up to 120V AC, before dropping it back down to 16V or so for the laptop. That's expensive and inefficient and unnecessary.

Doc.
Yea. I wonder about that also. Why go to all that hashed up AC and
back to low voltage DC when it can be often just regulated from the
car battery. if it need more than 12 volts a very simple boost ckt.
can take care of that with a lot more eficiency.
...lew...

Rich Carlstedt
04-30-2007, 08:21 PM
You are making this way too complicated guys.
I have a Dell Inspiron laptop.
I have a Dell "Auto-Air" Adapter
pn DE2035A-259.
It has a 12 volt Auto power point plug on one end, and a Laptop
connector on the other. Plugged in, it charges the Laptop batties and will run the whole day in my truck.

rich

Try Lind Electronics in Minneapolis.
I understand they make them.

Bruce Griffing
04-30-2007, 09:29 PM
I bought one of these:

http://www.cputopia.com/car-universal-notebook-power-adapter-kit.html

It works fine on my IBM, despite the fact that the label suggests that it is slightly underpowered for the job. No affiliation, etc.

Weston Bye
04-30-2007, 10:04 PM
You are making this way too complicated guys. I have...

Not to be argumentative, but McGyver has what he has, and he's trying to make what he has work - in the noble tradition of, uh, McGyver. (the resourceful but ficticious TV character)
If he can get past the glitch with minimum outlay, he's money ahead. Otherwise, he'll have to get what you got.

Mcgyver
04-30-2007, 10:14 PM
hehe yeah i'll just whip one up with some bubble gum and a twist tie. for $15 that would be that way to go, didn't know there was such a thing. I'll see if i can find it locally.

i don't understand the instant off either, other than some protection circuit in the computer because its not see what it wants to see from the power supply. it keeps going on batteries when i unplug from the wall.