EMI emissions from power inverter messing with laptop's touchpad

[Gringo]

Hi guys!  Wondering if anyone could point me in the right direction.

I have a pure sine 1500 watt power inverter in my van.  It is properly grounded and using properly sized cables to connect it to my deep cycle battery (isolated from van's starting battery).

It works wonderfully, but when I connect my older Dell laptop to it (Precision M6300), the touchpad's behavior becomes erratic and after a while just stops working.  When I disconnect it from the inverter, it works perfectly again.  With household power, it works without an issue.

I have been reading in various corners of the internet to try an EMI filter, chokes, or toroids.  But without really knowing what frequencies are disrupting the laptop's touchpad, I don't want to blindly purchase different filters and then find out they are not enough.

Anyone in here know what frequencies I should be filtering out in order for my machine to work properly?  My case seems to be unique because not all laptops suffer the same faith, I guess because of different touchpad manufacturers.

Also, my inverter is made by Tigerclaw (or at least branded as). 
edit:  It is a 115 volt as well

Thanks a lot folks!

Jason

[nitro2k01]

Are you sure you have a ground connection all the way from the inverter to the ground pin in the outlet? Is the ground connected to the chassis of the car or it floating? Are you sure the Dell supply is genuine, or at least not the source of the problem? Try and see if you can reproduce the problem in the house by powering the PSU while somehow disconnecting the ground.

[Gringo]

The outlets are built-in to the inverter.  The inverter's chassis is grounded to the van's frame.  I'd imagine the ground pin of the power outlet is floating.  From all my reading, it appears the cheaper inverters are designed this way (not meant to be integrated to a home's grid for example)

It's definitely a genuine Dell power adapter (90 watts) with a three-prong plug. 

The funny thing is, if I keep my hand attached to the underside of the laptop, the problem is greatly reduced (but not entirely).  Once I remove my hand from the laptop's frame, the problem comes back in full.

[T3sl4co1l]

Easy solution: chuck it and buy a real inverter!

Frequencies to filter?  Anything in the 150kHz to 30MHz range, and probably worse.  You could run it through a few three phase line filters, working on the assumption that the ground isn't actually ground.

Capacitive touch is very susceptible, at basically any frequency, so it doesn't take much to screw with it.  It's a good "canary" to tell when equipment (chargers, inverters, etc.) sucks, really.

Tim

[Stonent]

Does the power supply on your laptop have a 2 or 3 pronged connection?

An alternative is Dell does make a cigarette charger for their D/E/M series laptops. Just DC completely through with no inverting.

[nitro2k01]

I'd imagine the ground pin of the power outlet is floating. 

Don't imagine. Pick up a multimeter and find out!

It's definitely a genuine Dell power adapter (90 watts) with a three-prong plug.

That's no guarantee. I once bought a "Dell" PSU which looked good on the outside but turned out to contain a smaller crap PSU, an ID chip from a genuine PSU and a bunch of scrap metal taped together to increase the weight. If you didn't buy the PSU yourself directly form Dell, you can't assume that it's genuine.

The funny thing is, if I keep my hand attached to the underside of the laptop, the problem is greatly reduced (but not entirely).  Once I remove my hand from the laptop's frame, the problem comes back in full.

Yes, you are capacitively (or possibly even resistively) coupling your body to the internal ground plane of the laptop. The inside of the plastic is likely covered with carbon to act as an EMI shield for the internal components. Now try plugging in a USB cable, and hold the shield (ie ground) of the receptacle end of the cable to the hand you use for the trackpad and see if the situation improves. You may want to couple the shield through another metal object to increase the metal to skin contact area and minimize resistance. This is not supposed to be your solution, but is part of diagnosing the problem.

[NiHaoMike]

Get a cheap little inverter and hack it to output DC. Optionally add some filtering (probably not needed) and it would be more or less the lowest noise inverter for electronics.

Pure sine inverters really are for niche applications. Most electronics work just fine off DC or filtered square wave. Motors without run caps work fine on square waves. About the only common loads that actually take advantage of sine wave are motors with run caps, analog audio stuff, and electronics with capacitive ballasted power supplies.

[Gringo]

I'm sure many of you know that the failed Tigerdirect stores are closing and are selling everything including the power strips they were using. 

I scored a UL listed power strip with built-in EMI filter.  I'm going to try it out and will report back.  Crossing fingers. 

[Gringo]

OK, nevermind.  The powerstrip with built-in EMI/RFI filter did not do the trick.  But it was cheap so I'm not complaining.

In a residential distribution system, you have ground connection, so floating voltage won't go into your trackpad.

Generated from an inverter, there is no real ground.

A simple solution is to connect the P/E pin directly to the chassis of your car (big negative conductor).

NEVER TRY TO GROUND ONE OF THE OUTPUT PIN FROM YOUR INVERTER. YOU WILL DESTROY IT AND POSSIBLY YOURSELF IMMEDIATELY.

I tried grounding the chassis of my laptop directly to the vehicle and that did the trick.  Problem completely went away.  Thanks!

It's definitely a genuine Dell power adapter (90 watts) with a three-prong plug.

That's no guarantee. I once bought a "Dell" PSU which looked good on the outside but turned out to contain a smaller crap PSU, an ID chip from a genuine PSU and a bunch of scrap metal taped together to increase the weight. If you didn't buy the PSU yourself directly form Dell, you can't assume that it's genuine.

The funny thing is, if I keep my hand attached to the underside of the laptop, the problem is greatly reduced (but not entirely).  Once I remove my hand from the laptop's frame, the problem comes back in full.

Yes, you are capacitively (or possibly even resistively) coupling your body to the internal ground plane of the laptop. The inside of the plastic is likely covered with carbon to act as an EMI shield for the internal components. Now try plugging in a USB cable, and hold the shield (ie ground) of the receptacle end of the cable to the hand you use for the trackpad and see if the situation improves. You may want to couple the shield through another metal object to increase the metal to skin contact area and minimize resistance. This is not supposed to be your solution, but is part of diagnosing the problem.

Well, I did ground the laptop's chassis directly to the van's chassis and whadayaknow, problem went away completely.  So a little befuddled, I checked all my connections to the inverter and everything looked correct.  Then checked the plug on the PSU itself and noticed the ground pin slightly loose.  Maybe this is the culprit since it is no longer making contact internally through that pin.  I may need to just cut off the plug and replace it with a new 3-pronged plug.

Get a cheap little inverter and hack it to output DC. Optionally add some filtering (probably not needed) and it would be more or less the lowest noise inverter for electronics.

Pure sine inverters really are for niche applications. Most electronics work just fine off DC or filtered square wave. Motors without run caps work fine on square waves. About the only common loads that actually take advantage of sine wave are motors with run caps, analog audio stuff, and electronics with capacitive ballasted power supplies.

from all my reading, modified sine wave inverters are awful for most electronics.  Since the main purpose of the inverter I bought is to power mostly electronic gadgetry and my 32" LCD TV during my trips, I decided to pay a little extra for cleaner power.  Also, I hooked up a small fan to an older mod. sine inverter in the past and it was VERY noisy.  Same fan on the new pure sine inverter, the motor is completely silent.  Definitely important when I sleep inside the van at an RV park.