12V-240V inverters for a laptop

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I'm looking at running/charging a Dell laptop within my vehicle from an
auxilliary battery.  The ouput of the existing mains charger is 19.5V at
3.34A, so say 70W.
Does anyone have experience with the 150 watt (round, $50) Jaycar devices or
with the larger rectangular 150watt models?  Is the modified sine wave
output likely to be an issue for the Dell Charger?
dave




Re: 12V-240V inverters for a laptop



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  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.

--
Linux Registered User # 302622
<http://counter.li.org

Re: 12V-240V inverters for a laptop


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

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Re: 12V-240V inverters for a laptop


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:
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Re: 12V-240V inverters for a laptop


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

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Re: 12V-240V inverters for a laptop


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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.



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<Rant>

  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)

</Rant>

  Shoot me quickly, before I change my mind.
--
Linux Registered User # 302622
<http://counter.li.org

Re: 12V-240V inverters for a laptop


I was talking to a second hand compuer guy today whilst looking for a blown
power pack for the Dell.  It was pretty obvious the way he was talking that
most Dell machines go to Governement Departments where the sorts of issues
arising here are of little consequenmce - though they would have been for me
in the past running laptops from 12 V batteries in the bush (for months at a
time) .  Acers and Toshibas didn't have any of this fancy "force the
customer to buy lunches from us too" issue
dave
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Re: 12V-240V inverters for a laptop


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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


Re: 12V-240V inverters for a laptop


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 again Ken.
dave

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Re: 12V-240V inverters for a laptop


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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.

Re: 12V-240V inverters for a laptop


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.

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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
0v if its isolated. Be really careful as we are talking 240v here !



Re: 12V-240V inverters for a laptop



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

<tutorial>  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. </tutorial>

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.

3.  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

Re: 12V-240V inverters for a laptop


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

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


Dorfus

Re: 12V-240V inverters for a laptop


Sorry . . but is this the two concentric squares?
The Dell PSU HAS this amongsth a dozen or so symbols.

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

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