Trying to Figure out Z's Watt Needs for Car Power Inverter

Hey all, I need to purchase a new power inverter for my car and am trying to figure out how many watts my Vaio Z11 requires. I'm by far no expert with electricity, but looking at the AC adapter, it looks like the input it needs is between 0.5 and 1.1 amps (does that mean when the laptop is, say, outputting a video, it will need a maximum of 1.1 incoming amps?). So according to the interwebs, you multiply amps by voltage to get the watts. Power inverters supply 110 volts, so that would be 110x1.1=121 watts. So does my Vaio Z need a maximum of 121 watts, or am I doing all of these calculations wrong? Thank you in advance!

 

I would agree with that. My AC adapter says 100-220V and 1.1 - 0.5A, so it requires 1.1A at 100V or 0.5A at 220V. 1.1*100 = 110W and 220*0.5=110W. That doesn't mean it always needs 110W, but that's the max it will require from your inverter, probably when it's charging the battery.

On the output, it's 19.5V * 4.7A = 91.65W and that's the max power the Z will get.

The difference, 110 - ~92 = 18W is what's heating the adapter.

 

^ Correct. But why buy an inverter? You actually convert your 12V car DC to 110V AC and back to 19.5V DC. There are a lot of losses involved. You can buy DC-DC converters that plug into your lighter jack and output the voltage you need (you can set various voltages to fit your notebook). They often come with interchangeable DC tips so you can run different notebooks with one converter. In addition to that they are much more power efficient and smaller than AC inverters.

Unless you do not plan to use other AC devices than your notebook PSU in your car, I'd def recommend to go for a DC-DC laptop power converter.

 

^ I actually use a lot of devices in my car. I was more asking this to figure out what size inverter I should get.

 

~90W should more than suffice.

 

120W or 150W inverter is good enough for you.

 

Actually know what? I'm planning to hard wire the inverter to my car battery, which means I won't be able to take it with me when I'm in my parents' cars, friends' cars, etc. So I guess I will actually buy a DC adapter too just for convenience.

I always thought DC laptop adapters were like $150 for some reason, but they seem to be around $10-40. What do you guys think of this one:

90W Universal Power Supply for Car DC Adapter Sony Vaio Toshiba Battery Charger | eBay

Only $12! Might be too cheap to be true... what do you guys think? Also, the specs say this:

Output: DC 15V/16V/18V/19V/20V 4.5A max/ DC 22V/24V 3.75A 90W max

It says 19V/20V @ 4.5A max. But the Vaio Z AC adapter says it outputs 19.5V and 4.7A (meaning with this adapter, it's either 0.5 volts too low or high and 0.2 amps too low). Is this going to be a problem?

EDIT: Also, it only provides 90W? That's not enough, right?

EDIT 2: Or wait, since it's DC we're dealing with, the laptop only needs 19.5Vx4.7A = That's 91.65W. So cutting it a little short...

 

your calculation about the laptop's required DC power is correct. and the current is not very important unless you're doing some very compute-heavy task with your laptop; however, i'm not sure if 19V is going to cut it given that the laptop's power circuitry needs a constant 19.5V to operate properly.

 

If it's 20V will it blow it out or something?

 

Too high voltage will damage the computer (/charging circuitry), but how much above 19.5V it can tolerate is hard to know. In my opinion it will probably handle 20V fine, but there is no point risking it.

For extended power when traveling I have one of these:
Tekkeon - myPower ALL, MP3300/MP3400/MP3450
It has a selectable voltage, and my Z (both VGN-Z and new Z2) charge just fine with lower voltages than 19.5V as well. 19V volts will work fine.

Regarding inverter, if you have the Z2 with PMD its able to supply 120W with the PMD power supply. Taking efficiency/heat generation into consideration I would buy a 150W inverter just to have a bit capacity overhead.

 

can you explain why want use inverter?

12V to 110V (220V) and back to 19.5V - non effective!!!!

use changer voltage

laptop car adapter | eBay

not will not 20V is when no loaded if conect and start laptop Voltage goes to 19.6V

Iam using approx 5 years and in car for fews laptops and fine

 

20V what? You are using an inverter that outputs 110-120V and then your stock, 19.5V sony adapter, right?

 

Use DC to DC converter at 20V. Even if the output is 20V the laptop will only draw the voltage and current that is needs.

 

I want to get a DC power cord too, so since the one I was asking about only supplies either 19 volts or 20 volts and the Z1 needs 19.5 volts, I was asking if 20 volts would blow it out or something.

Really? The laptop knows how much to suck in? If I plugged in 50 volts it would still only take what it needs out of that? I always thought if you plugged a Christmas light bulb into a 120 volt outlet, you'd blow it up.

EDIT: Hey this one seems cool too. It's got a USB:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=320845788875

 

Careful. The laptop will draw as much current as it need, but the voltage must be the specified by the manufacturer or it could blow something

 

^this. 20V "should" be close enough to the 19.5 your laptop is looking for.

 

Nope, if you put 50V across it, then it will fry, if you put 20 volts across it, then thats fine.

 

The statement that the laptop will "only draw the voltage it needs" is incorrect. Current is drawn by the laptop, but voltage is set by the adapter. 20V "should" be close enough, but the laptop will be receiving 20V, not only taking the 19.5V it "needs".

 

I should have been clearer. With a 20V DC / DC converter, the laptop will draw the Power (Current and Voltage) that is required.

My bad

 

^Still incorrect. I'm not trying to flame you, but the laptop will draw the current (amps) it needs, but it will receive (and draw) 20V, when the design calls for 19.5. That said, 2% over volt probably isn't enough to cause any damage here.

 

Isn't it better to underpower it (19V) than overpower it (20V)?

 

^No.

Undervolting can be more dangerous in some instances as it can cause a higher current draw to produce the needed energy (remember V*A=W), and that higher current draw can cause component failure. Regardless, I think you're likely safe here.

 

Beaups no offence taken, and I don't think you'll ever flame anyone.

I used to design switch mode and capacitive droper PSU's (back in the day). Also worked with DC /DC inverters. I prefer the cap dropper as you can use a cheap zener to regulate the voltage, so typically even though it says 20V unless you're using high cost accurate zeners, (0.05% tolerance) they are usually 5% to 10% out.

From my experience they under-perform, but in my defense (and from your statement), I admit its been several years since I designed a PSU / DC/DC converter.

I'm now going to dig out my old engineering log books to go over this. Thanks.. More work lol!

 

Now I'm tempted to dig out an old copy of Vutrax. PCB design software and design / simulate a DC/Dc inverter at 19.5V and 20V, just for comparison.

I'd use EED3, but cant find that anywhere anymore. Plus the libarys were always expensive to buy. Vutrax allowed you to create custom components and set the tolerance manually.

 

^You are likely more knowledgeable about much of this than I am. I was a VERY early EE dropout. All I'm stating are two things:

1.) The power board on the Vaio (or any device) receives the full voltage you send it. Now, there are obviously tolerances as to what voltage the device would like to "see", and ~2% seems quite reasonable. Likely a VRM on the board can tolerate a much greater range here.

2.) If you are going to over vs. undervolt, to my knowledge a slight undervolt is safer, as the device won't need to draw additional current to get the job done. And additional current is what requires larger components, leads, etc. Again, within reason and it probably doesn't matter much in this situation.

I do think you'll have a hard time simulating a DC to DC inverter as to my knowledge inverters specifically convert DC into AC But again, I'm no expert on the matter.

 

So the Z needs 19.5 volts and 4.7 amps, which is 91.65 watts (let's just say 90 watts). What if you got something that outputs 10 volts and 9 amps, which equals 90 watts? Or is that not how it works?

BTW I need your guys' opinion! I'm interested in getting this adapter, which apparently detects the voltage based on the tip used. There's one tip which has 19.5 volts and it says 90 watts, which comes out to 4.6 amps. Should I try to get a 100 watt adapter just in case, or would that be overdoing it?

I'm just being anal because I don't want to damage my Z.

 

Yes V*A=W. If you got something that outputs 10V @ 9A that would be 90W. But 9A is a lot of current which means thicker gauge wire is needed, larger components, etc. That's why devices use higher voltage to get to the same amount of energy (e.g. 19.5v)

90W or 100W adapter will be fine for your Z.

 

Apologies all

After looking at some after market products, and creating a simulation of a DC to DC converter (not inverter... my bad) A 20V 90amp will do the job.. However, I would not recommend it unless I knew the exact tollerances of the device. Will it hold 19.4 V at 4.7 Amps?