help understanding IG on 12V inverter

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monkey

Senior Member
Location
Arizona
I recently purchased AutoEnginuity for my laptop. It comes with a USB cable that plugs diectly into the OBDII port of the car for code scanning and live system monitoring. There is a warning on the OBDII end of the cable that says to only use a power inverter with an isolated ground to prevent a ground loop.

I know on an AC system, an isolated ground is connected to the grounding pin only, and runs straight to the panel. I am confused how a 12 volt inverter can have an IG. Do they mean the grounding pin on the 120 side should not be connected to the car's chassis ground? Would it require the inverter to be connected directly to the battery as opposed to the cigar lighter, or power point?

Would it be better just to use a cheater to lift the ground on the 120 side? The PC charger does have a 3 prong cap, but the case is entirely molded plastic.

Sure would appreciate some help understanding this.
 

hurk27

Senior Member
most of the small inverters also connect the grounding prong to the neg side of the lighter cord, this is so a hot to car chassie will provide a fault path and shut down the inverter, but almost all laptops only use a two wire cord, so there is no problem, and the power supply of a laptop is isolating at the same time so I don't see a problem.

I didnt see the part that your laptop charger has 3 prongs? I havent seen this before:-?
 
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hurk27

Senior Member
I know on an AC system, an isolated ground is connected to the grounding pin only, and runs straight to the panel. I am confused how a 12 volt inverter can have an IG. Do they mean the grounding pin on the 120 side should not be connected to the car's chassis ground? Would it require the inverter to be connected directly to the battery as opposed to the cigar lighter, or power point?Would it be better just to use a cheater to lift the ground on the 120 side? The PC charger does have a 3 prong cap, but the case is entirely molded plastic.

Sure would appreciate some help understanding this.

even then if there is a ground to the negative terminal bond it would still have a parallel path with the USB to OBD2, if a isolated inverter cant be found then maybe one wired to a battery in the back floor board will work, that is kept isolated?
 

hurk27

Senior Member
Would it require the inverter to be connected directly to the battery as opposed to the cigar lighter, or power point?

even then if there is a ground to the negative terminal bond it would still have a parallel path with the USB to OBD2, if a isolated inverter cant be found then maybe one wired to a battery in the back floor board will work, that is kept isolated?
 

monkey

Senior Member
Location
Arizona
I didnt see the part that your laptop charger has 3 prongs? I havent seen this before:-?

Yes the PC has a 3 prong, also my Mac has a power supply with two prongs directly on the case, with a 3 prong cord extension that slides onto a metal retainer. The 3 prong must be just to ground the little metal retainer, which is completely covered when in use! I would use the Mac without the 3 prong extension but Auto E will only work on a PC.
 

monkey

Senior Member
Location
Arizona
even then if there is a ground to the negative terminal bond it would still have a parallel path with the USB to OBD2, if a isolated inverter cant be found then maybe one wired to a battery in the back floor board will work, that is kept isolated?


That's what confuses me. In a building, you could say the same thing, everything is connected at the main panel.

I think I will just use a cheater to eliminate contact of the grounding pin, which makes no sense to me why it is even there.
 

monkey

Senior Member
Location
Arizona
On second thought I think the best thing to do would be to just run the laptop off battery. That will work for diagnostics, and I can't really see the need for live monitoring for hours on end, although it would be cool to be able to keep tabs on everything on long trips. I have it set up on my Ford Powerstroke.
 

Besoeker

Senior Member
Location
UK
I recently purchased AutoEnginuity for my laptop. It comes with a USB cable that plugs diectly into the OBDII port of the car for code scanning and live system monitoring. There is a warning on the OBDII end of the cable that says to only use a power inverter with an isolated ground to prevent a ground loop.
The AutoEnginuity software runs on your laptop. That plugs into the OBD2 vehicle port via a USB cable.
So what's the inverter for?
 

hurk27

Senior Member
The AutoEnginuity software runs on your laptop. That plugs into the OBD2 vehicle port via a USB cable.
So what's the inverter for?

To power the laptop off the vehicle, laptop batteries only last so long.:grin:

I did this when I was taking trips to my IAEI meetings, across the country, I also ran GPS and weather radar through my ATT/Cingular internet connection while on trips.
 
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gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
090809-1021 EST

There need to be clear definitions of terms.

What does PC mean? Personal computer. This does not define the operating system even though Microsoft seems to be pushing this definition. A PC could be running Windows, DOS, Linux, none, Mac software, and so on. In the early days of PLCs they were called programmable controllers and therefore PCs.

What ever your computer is, the critical concern is having only one ground path connection. Thus, the reason for isolation on the power supply connection to the computer. In fact the only place that a ground (common) connection to the computer should be is thru the one USB cable to the OBDII connector.

Any laptop computer that I have owned only used 2 pin AC cords. This includes my IBM ThinkPad. However, I realize that some laptops have 3 prong connections. If you have a 3 prong AC cord, then check for continuity from the power cord ground pin to the chassis of the laptop. Probably any metal shells around any connectors are useful for this test, especially D connectors. If this continuity exists, then you must have isolation somehow in this ground path.

.
 
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