12V-240V inverters for a laptop

Have you considered a 12v - 19.5v inverter? Would save a box, a fair bit of cabling, and a bit of efficiency.

Jaycar also has these, I believe in a couple of different flavours. Might be cheaper than a 12/240 inverter if that's the only use you're going to get out of it.

Thanks John,

I actually HAVE one (19 or 20V, which I bought for the purpose - via an onlne HK source- and which referred to Dell in the advertising) , but the issue is the plug! The plug I need is not one of the 8 in the "kit" and these are not available from people like Prime OR Dell (of course!) I've also tried to find a blow power adapter for the machine as a source of the plug.

I could cut the present DC cable and put a 2 or 3 pin plug and socket on it and then make up the apprpriate c abvle to match the device I bought. I may have to go this way.

dave

I think you will find that most Dell laptops use three wires (inside and outside of the round connector, and the centre pin. The centre pin is used to communicate to an ID chip in the power adapter. If the correct power adapter ID chip is not found, then the laptop will not charge.

This means you need to get a proper Dell adapter, and a cheap generic one won't work.

David

vwq47 wrote:

I have a 150w model for a few years (not jaycar), it works fine with my Toshiba Laptop which has similar wattage rating to what you have quoted here.

Only thing i have noticed is that the laptop takes noticeably longer to charge compared to when powered off a domestic mains supply, but i havent studied this in great detail. Also, even though the laptop is only using about half of the wattage rating, I find that it wont effectively run some items like 20w plugpack etc at the same time. (IE plugpack powered mobile hard drive refused to work).

If you need to run other devices, it might be worth investing in a higher rated inverter, though if you were to go above about 150w, you would need a built-in unit with direct connection to the vehicle battery as 15 A is the maximum you can draw from a typical cigarette lighter socket,

Note that at the full 15A load, you are likely to have significant voltage drops by the time the 12v makes it to the inverter - that are going to reduce the available output even more.

Note that some devices (such as modern cordless drill battery chargers that have a series capacitor with the mains rather than a transformer) dont work properly unless you use a sinewave inverter to power them.

---------------------------

I don't like some of those aftermarket DC power supplies after I had a bad experience with one some years back that zapped a digital camera on me.

The other problem with them is that many laptops use a different DC connector, possibly different polarity and different DC voltage to boot. This is only going to be a pain in the arse as you will probably have to replace the adaptor every time you upgrade the laptop. Also, unlike an inverter, you cant use it to power other devices

Thanks David.

Yes, it looks as though there ARE 3 possible connections on the plug though in the socket it is pretty hard to see a third connection that would mate with the inner part of the outer cylinder of the plug . . BUT you have made me wary of going the DC route.

Dave

Thanks Ken,

I greatly appreciate the comments (and time you took to write them). Food for thought there.

I'm unlikely to want to run anything else from the Aux battery as it IS limited anyway as it has to run a fridge. (I have a USB hard drive that is powered by the USB port). The battery is OK if I am stopped for only a night and weould handle the laptop as well for much longer.

I think I am resigned to an inverter lik you have.

I actually have a thrown away UPS that runs on 12 V gel cells. The cells have had it and I wondered whether I could work out the circuit and convert the UPS to run as an inverter from the car. . but I can't do that by Friday when i need to have everything set up.

Thanks aga>> I'm looking at running/charging a Dell laptop within my vehicle from an

These sort of things, and other practices that I have seen in the past like having similar ID chips in battery packs, using different non- standard wiring pinouts on ATX supply plugs (forcing you to needlessly buy the much more expensive part from the maker) to me, is a very very good reason to avoid brands that do these things.

Arrg! What idiot designed this, and why is he still employed?!

I know WHY they do it, to force the hand of the purchaser to go with the same brand replacement device (and thus funnel profits to themselves).

The stupid thing is, this is one of the many purchase considerations we make when picking laptops. Which explains why there are no Dell laptops around here. And from the looks of things, never will be. So, in the end where ever they make their money, it's NOT with us.

(disclaimer: I was not around during the purchase of all the Dell desktops, it was done by some predecessor who didn't consider the little inconveniences and roadblocks involved with the bloody things)

Shoot me quickly, before I change my mind.

On Tue, 18 Sep 2007 10:46:46 GMT, "vwq47" wrote: (snip)

Be VERY wary doing that. On many of the cheaper ones, the AC neutral line is not at the same potential as the negative DC in, so there is a significant risk of an electric wakeup call. In normal UPS use of course the gel cells are nicely isolated inside the unit, and this isn't an issue.

That aside, no "conversion" is usually necessary to run a 12V DC-based UPS from the car battery. I do it myself but use either an isolation transformer or isolated loads (such as my modified Weller iron). Assuming your Dell PSU provides isolation (mine do) you should be jake - but CHECK PLEASE.

The UPS is a Data Guard 400VA UPSwith 3 x 240V outlets. It came out of a so,puter application where proper close down was necessary in case of a blackout.

Sorry, but I'm not sure how I tell whether the PSU provides isolation . . does one of the symbols on it tell me this?

I'm not familiar with the issue you raise.

that isnt easy to test, as often there are relays that cut the power coming in (so that the mains plug hasnt got live pins when its running in UPS supply mode) and also relays that isolate the mains socket when its turned off. When tested this will show isolation between the mains cord and battery terminals, fooling you into thinking its isolated.

About the only way I can think of, is to carefully study the circuitry of the unit (having a transformer in the unit does not necessarily mean the battery is isolated) or to measure for voltage between the battery (-) and the mains SOCKETS active or neutral. There should be

Nope, that only indicates "double insulated". See my other response.

Then - no offence intended - tread carefully or, more aptly, work with one hand always in your pocket when AC line voltage is present.

The UPS will take AC line input and (a) feed it to the output while also (b) rectifying it and charging the internal batteries. When the AC line input goes bye-bye, the battery drives an inverter which produces an AC output and feeds that to the outlets.

Manufacturing costs will always be shaved if they can. Thus the minimalist approach where - apart from sharing as many components as possible between the rectifier system and the inverter - they will avoid installing any measures to provide electrical isolation between the DC system and the AC system that aren't essential to function. This will meet safety requirements as long as the DC system cannot be accessed from the customer side.

In a normal electrical installation using the M.E.N. system, the neutral and earth are commoned so touching the neutral will provide at most a minimal potential above ground if there are no faults in the system. The earth will also be connected to the UPS case.

If the negative terminal of the battery is connected to the earth/neutral of the UPS AC output, Bob's yer uncle. If the positive of the battery ... then the scope for issues when run off an external battery system revolve around the fact that the battery neg is now at -12V w.r.t. the UPS case, and contact between the case and battery negative (which MIGHT include the bodywork of your car) will cause an issue.

The biggies though are the other cases:

A. Battery terminal commoned with output active/phase. This means the neutral/earth/case of the UPS are alive, which means you may not be for long.

B. Battery terminal commoned with centre tap of output transformer (I've seen this situation). OK, the voltage you are exposed to is half that of case 1, but still can be lethal.

C. Battery floating. If you can establish that it is indeed floating in all scenarios (mains present & no load, no main & load on battery/inverter etc - see krw post) then there is still the potential (no pun intended) for a zap but with less likelihood of serious outcomes if you contact the battery system (i.e.your car bodywork) while handling a non-double-insulated load. If truly floating, you would be able to solidly bond a battery terminal (the negative is the better bet) to the UPS case/earth/neutral_out to mitigate any risk. Bear in mind though that the AC input earth should be bonded to the case, but the incoming neutral will not be, and the neutral in-out may be a straight through connection.

Testing for isolation?

1. System off, no AC at input, healthy battery in circuit - first checking for DC volts between AC output line and neutral w.r.t. battey negative. No volts found, measure ohms between AC output line and neutral w.r.t. battey negative.
2. Set up your DMM to indicate AC volts between a battery terminal (- preferred) and the AC line output phase and then neutral. Provide AC input to the unit. Then turn unit on to power the outlets. Then turn off the input.

1. Get a test lamp and test it across the outlet to verify it works. Connect the test lamp between battery negative and outlet phase, and repeat the three configurations in 2 above. Ditto with test lamp between negative and outlet neutral. Ditto positive etc. If the lamp doesn't light in these latter tests, it's a reasonable assumption that the output is isolated from the battery. AT that point I'd stick the meter in series with the test lamp to check for low level currents which might indicate a high impedance path withing the unit. If zip, then it is isolated. These tests will aslo evidence whether the battery neg and the output neutral/earth can be bonded without issue. If they can, I would.

Caveat: If you don't feel comfortable doing this, then DON'T. The above describes the thorough way I'd approach the situation. The risk is yours.

FOFP

Dear Budgie,

Thanks SO much for taking the time. I greatly appreciate the tutorial, which is very useful. When the Internet started there were lots of people who gave of themselves to make the world a better place, but increasingly that spirit has been disappearing. I've had my nose really rubbed in it at times when I've been ignorant (or assumed something) on an issue and made a comment or question.

I greatly appreciate your help and attitude.

I am confident and comfortable to follow your process, but the risk IS all mine!

Look after yourself.

Dave

There are still a lot of "nice people" out there, it's just that the "bad people" are far more noticeable.

Dorfus