Digital meters and common ground effect

Do you have a name or part # or link to the power modules?

Here is the link And a photo.  Hopefully I got the link pasted in properly.

thanks,

Ed 

http://www.banggood.com/Isolat...-12V-1W-p-85294.html

The specs say 10 to 16 vdc in, so try 12 (which is the design input) and see. Also if you still get nothing, connect a small load to the output for testing.

Chuck,

I tried sending it 12vdc but I still can't get any output and the meter is dark.  I am wondering now if because of the isolation modules I need to have at least 2 of them connected at once.  I was wiring them one by one and since I couldn't get the first to work I stopped.  

I am am leaving for a Dr. Appt. so I can't get to trying to connect 2 Of them to see if it makes a difference.  

Thanks,

Ed

Perhaps a diagram of how you're wiring it would be useful.  Also, I'd test the isolation modules with 12 VDC in and make sure you're getting around 12VDC out.

I don't want to hijack the thread but- what is 'common ground effect'?

Does it only affect digital meters, or are analogue meters also affected?

I believe in this case he's talking about the digital meters that REQUIRE a totally isolated power supply from the load voltage being measured.  Many of the cheap eBay Chinese models have that requirement.

Some meters require meter power that is isolated from the voltage or current that they are wired to measure. One way to do this is to power the meter with a floating 9Vdc battery. Or, you could buy these dc to dc isolator modules, and power the meter that way.

"Common ground effect" is probably not the best way to describe this situation. Maybe just say that you cannot have the same ground connection for the meter power as the measuring circuit.

If you look hard enough, you can find meters without this restriction.

Thanks for clarifying this.

I'll post a wiring diagram tomorrow showing how I have it wired.  

Gunnerjohn - When I give the module 12vdc in I get 0 measurement on the out side.  I don't know what is going on inside the module so I am not sure what I should see on the meter.  As I mentioned, when I first tried to re-connect this back up I gave it 12vac by mistake instead of DC.  That is why I am wondering if the modules all friced from the AC.

Thanks,

Ed 

Hi Ed

I am building a Volt meter and Amp meter system. Here is my thread on this system, I hope it helps. https://ogrforum.com/t...03#43806663836401503

Here is also a diagram on how the Amp meter and Volt meter should be hooked up.

Kris,

Thanks for for all the info.  

I have mine mine wired exactly like stan2004's design With the exception that I have 4 volt meters installed as well.  Like Stan I am also using a walwart.  Although I am not sure if mine is regulated.  I will have to check that.

i am convinced now that I must have blown the isolation modules when I applied 12 AC by mistake.  I reconnected them to 12dc and now  I read 12dc going into the module and 0 coming out.  

Thanks,

Ed

AC likely didn't do the modules any good, you may well have cooked them.  They should produce voltage stand-alone with just a 12VDC input.

edit: fixed typo!

I think GRJ meant AC.  In any case like he says if you put 12V DC in, you should get something out even with nothing hooked up as a load. 

No, I really meant DC!  The DC-DC isolation modules require DC voltage.

The part that Paul is using...

Isolated Power Module 4 Pins DC-DC Converter In 10-16V Out 12V 1W

Putting AC on that will probably cook it.

Exactly.  That's why I think you meant to say,

AC likely didn't do the modules any good, you may well have cooked them.

Oh Stan, I didn't notice that typo, let me go fix that!

And, thusly, order has been restored to the universe.

Well... sort of...

Thank you guys for correcting that info.  My eyes immediately glazed over when I read GRJ's statement about the DC cooking the modules. 

Thanks for all the help from everyone. I really appreciate it.

Ed

That was just to see if you were paying attention!

GRJ, I'm not sure of what you mean when you say that some meters require a totally isolated power supply.  Are you saying that the internal battery doesn't power the meter---only supplies power for ohm testing?

Internal battery?  We're talking about a panel meter from eBay, it's a simple electronic module and needs an isolated supply.  Since it's going to be a permanent installation, a battery would be a large PITA.

Panel Meter Link

I originally thought analog meters would be a lot less trouble.  However I could not find any  that had large print scales, like Reader's Digest has the large print editions. ��

GRJ, you're right.  I was thinking about portable meters. I have never used digital panel meters; always analog & it's been years.  I assume from reading this thread that they have terminals for a separate external power supply?????

FWIW, I got some analog meters from ebay a couple years ago. They were about $5 or so each and required no external power. They were 0-15 amp and 0-30 vac and about 2-1/2" wide by about 2-1/4" high. Probably not quite Readers Digest sized print, but I had my eyes fixed this summer and I can see them now.

I have been thinking about switching to the digital ones, but haven't yet made the switch. GRJ already helped me with the isolation converter on the voltage box car of his I was trying to copy a while back. Good thing these things are cheap on ebay as I am on the 2nd set of meters in the voltage car, the first two didn't last very long...  

When I connect them up correctly the digital meters work fine.  I've had no failures.  i knew nothing about isolation when I first installed the meters a couple of years ago.  If memory serves it was GRJ who helped me then with info about the  isolation modules.   

I find it interesting to see the differences in amp draw between the various engines and rolling stock.  The meters also give me a reminder when the track starts getting dirty.

Ed

I haven't had a digital meter failure since I added the isolation converters that GRJ pointed out.

I also like watching the amp draw, but mine don't change much. Smoke unit increases amps a bit as does adding another engine, but I usually don't get much over one amp or so, and maybe around two or so with two engines and smoke on.

You need a VL-BB, turn on all the smoke units and it can suck up about 4 amps without even adding the load of any cars!