Erratic cursor when Inspiron power pack plugged into a dc-ac inverter

RE: erratic cursor when Inspiron power pack is plugged into a
DC-AC Invertor, e.g. for use in Recreation Vehicle

This message updates one I posted on July 21 concerning the
problem of my new Inspiron 1501 notebook when powered by
a (nominally 12 volt) DC to AC Inverter, causing the cursor to
become erratic when controlled by the touchpad. My previous
message was long and I will not repeat it here, but it can be
found by searching for the word 'cornwaab'.

There have been no Forum replies to my July 21st posting.
However, I have been in contact by phone with Dell technical
assistance who were very attentive to the problem and had me
refresh the touchpad, system, CPU, and BIOS drivers. This did
not resolve the problem, but eliminated corruption of these
drivers as a cause of the problem.

In my view at least, there was one test a Dell technician had me
perform that was particularly informative and demonstrated an
impressive built-in diagnostics capability of the Inspiron. A
detailed description of the test follows in case anyone wants to
duplicate it. To do this test I plugged the power pack into the
DC to AC inverter. Immediately upon turning on the Inspiron I
pressed the F12 key which allowed me to select 'Diagnostics'
from the Boot Menu. This runs an initial check of the computer,
including showing color bars on the screen, and operation of
memory , CPU, and other things (everything passed); and
eventually offers a prompt for the option of more memory tests
- which I declined by responding 'No'. (Note at this point the
cursor was active, but because it was erratic with the touch pad
I used an external mouse.) There was another prompt to 'Boot
Dell Diagnostic Utility Partition' to which I responded 'OK',
showing another screen and three more options; I selected 'Test
System' (note, cursor was not active for this menu, and cursor
up / down and enter keys were used). Another menu appeared
(now cursor was active again), and I selected 'Custom'. This
shows a device tree, and I clicked on 'Pointing Device', which
displayed a blue screen to test the touch pad mouse control.
Here the erratic nature of the cursor was very evident. As a
confirmation that power from the inverter was the culprit, I
turned off the inverter so the Inspiron would automatically run
on its internal battery. This time in the test the cursor worked
perfectly when controlled by the touchpad.

The importance of the above test procedure is that it bypasses
software and drivers except those in the BIOS and the Utility
partition. If a test fails using these diagnostics it is not due to
the operating system, device drivers, applications programs, and
viruses. To me this infers a hardware issue.

It seemed evident in my discussion with Dell technical support
that my difficulty is one not frequently encountered. Perhaps the
cause is a defect peculiar to my notebook (or power pack), or I
may be one of the first to power this model notebook with an
inverter.

I am pleased to report that Dell is still working on my problem
and seems committed to resolving it.

I look forward to any assistance Forum members can provide.
Thank you for you interest.

Andy

cornwaab@yahoo.com

RE: erratic cursor when Inspiron power pack is plugged into a
DC-AC Invertor, e.g. for use in Recreation Vehicle

Hello,

This message is a further update to my postings of July 21 and
24. The issue is erratic cursor movement by the touchpad when
my Inspiron 1501 notebook computer is plugged into a 12 volt DC to
115 volt AC power inverter. When AC power is provided by an
inverter, just laying a finger on the touchpad results in the
cursor moving erratically on the screen. An inverter might be used
to power a notebook computer while in a vehicle (the inverter
is usually plugged into a cigarette lighter) or in an RV or boat
that does not have an AC hookup. For further background please
read my earlier postings to the Dell Forum, by searching on the
keyword 'cornwaab'.

I have tried three inverters, of different brands and wattages
(140, 150, and 300 watts), with the same outcome. I also tried an
Uninterruptable Power Supply (UPS), which provides subsitute AC
power by means of a built-in battery and inverter when regular AC
fails. Significantly, there was not an erratic cursor with the UPS.
As I explain below, the difference in result between the inverters
and UPS may be due to the moderately different wave forms of the
inverters versus the UPS, although both types deliver modified sine
wave versions of AC.

I want to emphasize that this is NOT a problem that most
notebook users would encounter. Even if it occurs there are
easy 'work-arounds', such as to power the laptop from its
internal battery or use an external mouse. Indeed, the problem
may be unique to my equipment, although I have read of a few
similar cases on this Forum and the Internet generally.

There were not any responses to my earlier Forum postings.
But Dell technical and sales support have been very attentive in
trying to help me solve the problem. Dell sent me a replacement
notebook (and power pack) to try and supplied a Targus model
PA390C inverter, which Dell sells and supports. I am impressed
with and grateful for the efforts of Dell in this regard.
Unfortunately, the problem also occurred with the new
equipment. Nevertheless, my overall experience with my
Inspiron 1501 is positive. I like the notebook computer, it
seems well made, it is a great value, and I will continue to use
it. As already mentioned, there are work-arounds to the erratic
cursor / inverter problem.

I am still hoping that someone on this Forum or at Dell will find
a way to fix the erratic cursor issue with my Inspiron 1501. I
have ordered a variety of ferrite RF filters to try, in the event
the problem is caused by higher frequency leakage through the
power pack. My experiments with my two APC-500
Uninterruptible Power Supplies suggests, however,
that the problem may be due to the lower frequency component
of the inverter's modified sine wave AC.

I do not know how to easily describe a modified sine wave. It is
a variant of a square wave, having a positive voltage pulse
during one half cycle and a negative voltage pulse in the other
half cycle. If the 'duty cycle' of a true square wave can be
thought to be 100%, then the corresponding duty cycle of a
modified sine wave is substantially less. For example, looking at
the wave forms with an oscilloscope, I found the duty cycle of
the Targus inverter to be about 57%, but that of the UPS to be
about only 33%. To compensate for the shorter duty cycle the
voltage of the UPS' pulse is about 30% bigger. (When I have
the time I want to put pictures of the wave forms on my
website: www.geocities.com/cornwaab .) The wave forms of
both inverter and UPS are comprised of respective base
frequency and harmonics, but the longer duty cycle of the
inverter implies that its base frequency (and harmonic content)
would be lower. The longer duty cycle and lower frequency of
the inverter's power (associated with the erratic cursor) may
infer a way of analyzing the problem and finding a solution.

Anyway, this is the story for now. I welcome your advice.

Thank you for your interest.

--- Andy

cornwaab@yahoo.com

Hello Jimmy P.

In response to your suggestion that I plug a UPS
into an inverter, and plug my Inspiron 1501 power
pack into the UPS, I don't think this will work to fix
the erratic cursor / touchpad problem nor would it
be practical.

Most consumer grade UPS's (including my APC-
500's) are passthrough unless the AC voltage
feeding them has a problem. When the UPS senses that
the AC voltage is too low, too high, or has stopped,
it very quickly switches over to supply its
battery / internal inverter produced modified sine
wave AC. Unless the UPS senses a problem and switches
over, the AC electricity going into it is the same
that comes out. Thus feeding a UPS from a separate
inverter would not act to alter the waveform, and the
problem of the erratic cursor / touchpad would not
be fixed. (Indeed, if the inverter wavform is the cause
of the problem!) There is also the practical consideration
that a consumer grade UPS weighs about 15 lbs.
(maybe more) and can be bulky because there is a
hefty rechargeable battery inside. It would be
awkward to lug one around in a mobile situation.

A possible solution sometime in the future may be to
acquire an inverter that produces a 'pure' sine wave.
Until very recently pure sine wave inverters were
prohibitively expensive and not very electrically
efficient. Newer models still cost several
times that of modified sine wave inverters. If I
suspected that I would need to acquire a pure sine
wave inverter to operate my Inspiron 1501 the way I
want, I would have purchased a different notebook
computer. I am still hoping for a solution to the
erratic cursor / touchpad problem with the Inspiron
1501 and the modified sine wave inverters I own.

Thank you, Jimmy P., for your interest.

--- Andy

Hello Jimmy P.,

I have not tried an Auto/Air adapter, and did not think of it as a possible solution because I was focused on using an inverter, which I already owned. Since the Auto/Air adapter integrates the inverter and power pack functions they would presumably work perfectly together, and the adapter as a unit would be tested to operate with the recommended compatible notebooks.

Thank you for your suggestion.

--- Andy

Hello cornwaab,

Did your issue ever get resolved?

Stumbled across your post in Jan 2012 while investigating a similar issue with my 2007 era Latitude D830 using a 180W Wagan Pure Sine Wave inverter with a 90W AC adapter and the larger  battery pack.

Some history:

I used to use the D830 on a 2500W Heart Interface (now Xantrex) modified sine wave inverter built in to my 5th wheel with no problems.  The the physical location of the inverter was about 15 ft away in the forward cargo bay.  I sold the 5th wheel and tried to use it with a 400W Coleman MSW.  The D830 did not like that inverter and would not work at all.

Decided to try a pure sine wave inverter to see if anything improved.  The D830 mouse responded the exact same way you described. Shutting off the PSW inverter and running on battery restores the mouse to normal operation.  After a few more tries, clearly even a PSW inverter was apparently not going to solve the problem.  The PSW inverter was only ~1ft from the ac adapter and thought that might be the problem.  

So, I left this post for a few minutes to try a few tests to more clearly observe and document the issue and then move the AC adapter further from the PSW inverter to see if distance was the issue.

Am returning from testing and after trying several scenarios, even running the D830 in High Performance mode while updating programs with brightness all the way up and the battery charging still with only ~1 ft separating the inverter from the adapter, I COULD NOT DUPLICATE THE PROBLEM!!

So, am going to have to leave this comment as is for now and return to it with more information if anything changes.  For now, I have to report that the Latiude D830 is working just fine with the Wagan 180W Pure Sine Wave inverter.  That's not the way things started out!