Inverter problem

I have an HP laptop that I am trying to use via an Inverter power
supply. I bought a 400W inverter, and the laptop DC transformer says
90W. I plug the inverter into my vehicle cig lighter, from the
inverter is the DC transformer to the laptop. As soon as the inverter
see's the laptop load, it starts squeeling like a pig. The inverter
cig plug almost blistered my hand when I dosconnected. This happened
with a 200W inverter that I originally bought. Figured it wasn't quite
big enough, so went with 400W and getting the exact same result.

Since this is a different inverter, I am ruling this out as the
problem. Is there something going on with rectifying the inverter
output using the laptop DC converter? This came with the laptop by the
way. Any feedback welcome. Thanks as always.

 

Most inverters don't produce a true sine wave. While this doesn't matter
much for most mains loads it may well for a switch mode power supply.

 

What happens if you connect other loads like lightbulbs? When 100W or even
200W bulbs give no problem it's unlikely the seize of the load that causes
the problem.

Unless you have a high quality (and expensive) inverter, it will not produce
sinewaves but so called modified sinewaves. The shape of the load performed
by the laptops powersupply may cause the problem in this case. Try a choke
between the inverter and the power supply to smooth that modified sinewaves.
I suppose a 1H/1A/60Hz type will do. The choke should not go into saturation
as it may make things worse.

petrus bitbyter

 

I have a 400 watt inverter (peak 800). I have an old PII laptop with no
battery. In the interest of science, I hooked them up. No problems.
The laptop power supply says DC Output 19V 2.6A.

 

Forgot to add that I am in the US. That I don't use the cigarette
lighter, just a direct to the battery connection using cables. If
overloaded, my inverter doesn't say much. It just shuts down, but if the
connection is hot, that indicates something is overloaded.

 

What kind of power does the hole in the back of the laptop want? I'll bet
good money it's a DC voltage with relatively low current. What I'm getting
at is that rather than convering DC to AC and back to DC to use your
existing AC adaptor, you'd be better off using a true DC-DC converter... I
think my Toshiba runs at about 15VDC, so you'd need to actually increase the
voltage which rules out most Radio Shack cig lighter power adaptors.

You could build something cheap using a 12V regulator and a couple of diodes
to bring up the voltage, or buy one of the many commercially available dc-dc
converters. I've seen them as cheap as about $10 as surplus, you'll have to
poke around a bit to find one with the right specs.

Or, as another poster has suggested, try placing a 1H choke on the output of
the inverter to smooth out the power a bit. If the inverter is squealing,
it's working very hard and soon the magic smoke will escape.

Dave

 

If the cigarette lighter plug is becoming too hot to handle it sounds like
the socket could be dodgy and therefore may be incapable of supplying
sufficient current to the inverter, is there any way you can try connecting
the inverter with a pair of croc clips directly to the battery?

Also although the output from the inverter may not be a true sine wave it
will usually be fed straight into a bridge rectifier and reservoir capacitor
arrangement and then as circa 320V DC onto the switch mode power supply
circuit, so will probably not be that critical anyway.

 

A better solution for powering a laptop is a mobile DC power supply,
which is a DC-DC converter with 12 volts in and your choise of volts
out (typically 15-19).

It's more efficient than the DC-AC inverter > AC-DC power supply
combination and draws less current than the DC-AC inverter does.

It's also a lot cheaper, starting under $20US:
http://www.geeks.com/details.asp?invtid=MWS2466W-1&cat=NBB

John

 

How heavy are the wires? The wattage on the input will be a bit more than
the wattage drawn from the output, but given the voltage is lower by a
factor of 10, the current draw will be 10X what it would be at 120V so you
need some pretty heavy wiring for anything over a few tens of watts.

 

Most inverters come with a fitted lead and plug to fit the cigar lighter -
and one for clipping direct to the battery if they can exceed the 10 amps
or so allowed by most cigar lighter sockets. So saying not all cigar
lighter sockets are identical and mate well with these plugs at higher
current.

I'm actually surprised a new standard for a car power take off hasn't
evolved given just how unsuitable the cigar lighter idea is since it uses
steel contacts.

 

The leads are about 2 feet long and are made from 12 gauge wire. They
came with the unit. I didn't think the cigarette lighter business was a
very good idea, so I've never used it.

 

Golf you have a real curiousity there. I have been doing this for years.

Just some questions\\

Does your HP work fine when it is plugged into a normal socket?
Can your inverter power a 100 watt light bulb?
Is your PS cable unmodified and in good shape

If all above is OK then your problem must be "fm.".

yours jim

 

The answer is yes, yes, and yes. I have since found a DC/DC converter
made for auto cig lighter plug made by HP. It is about $75.00. Had
found another brand that had higher power limits for about $100.00,
but figured the HP would be fine. I should state that I listed all
this info on behalf of a friend. I probably would have looked for a DC/
DC converter before I bought an inverter soley to run my laptop in my
auto. Kinda strange going DC/AC/DC. Thanks for the reply.