wiring up an amp meter

I'm not sure if this belongs here, so I apologize if it's in the wrong place, I couldn't find a place for general wiring stuff.Anyway I picked up an amp meter from an ebay seller "Asia Engineer" and it comes with a shunt and some instructions. The instructions are pretty clear, but it says that you cannot measure both voltage and amperage from the same source using these meters. You also cannot power them from the same power source, and you especially cannot measure amperage and current from the power source running the meters.I've also purchased a couple of DC-DC isolators so that these meters can be powered in my car(a car is only a single power source afterall)I've talked to the seller, and using the isolators the meters can be put in my car, but I'm now left wondering about the measurement aspect of it. The sellers english isn't great and he seems to have trouble understanding me at times.I'm going to measure current from the alternator, the amp shunt will be bolted directly onto my alternator post, and I was going to measure voltage from the battery.Would this be considered measuring voltage and amperage from the same source? THESE are the isolators I bought to power the meters(VB1212S-1W - YUAN), and here are the instructions

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Having a degee in electronics and just running into Asia Engineer, I do understand what you are saying and understand what the english speaking person from the company is trying to say. Here is some insight that I hope is helpful and if not just e-mail me and I will try to help in more detail. The volt meter and amp meter are not to be hooked up to the same working voltage. The voltage meter reads your car voltage and uses your car battery for a little eneregy to run volt meter display on. The amp meter will read your car battery amps plus uses energy too. They both can not use the same energy source. Thus to run (amp meter) the input (working power or energy to work from) needs to be different that what the voltage meter is using. Purchase form Asia Engineer a < color=#ff9933 >DC-DC Converter Isolated Power Supply In10V-16V Out 12V. I think the part number is 1212s-1w or purchase the item on e-bay. Buy from seller named giorgio11185 he has been a great help for me on this subject. Hook it up to your car and then you will have a different energy source to give to your amp meter. The part is like ten dollars, cheep to fix your problem and for you one less head ach.If it don't bight then your still alive

If you have not ordered those parts yet, look into Murata Power Solutions. They bought Datel, which is the meter I have in my car. Reasonable prices, and fast shipping, as well. They have both volt- and am- meters, in blue, red, and green LEDs, and they offer all of their models with non-isolated power supplies. So much easier to install! The actual page you need to make your decision is this one...It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

ya ive been dealing with Asia Engineer/Giorgio, he's a good guy. I did get this all sorted out for the most part. I got a couple of the isolators, but they are 12v, so I had to make a circuit with 2 7805's so it is isolated 5v. it works well. basically the converter/isolator powers the 7805, and the 7805 grounds through the isolator. I'm currently working on another circuit to read the probe voltage from some of the temp displays he has, and it will allow me to activate a relay when the temp display hits a certain temp. HOWEVER, adding an additional wire to the probe for measurement/comparison has changed the actual display by about 1*C less, than without the extra wire. I need to figure out how to compensate for that.

ya ive been dealing with Asia Engineer/Giorgio, he's a good guy. I did get this all sorted out for the most part. I got a couple of the isolators, but they are 12v, so I had to make a circuit with 2 7805's so it is isolated 5v. it works well. basically the converter/isolator powers the 7805, and the 7805 grounds through the isolator. I'm currently working on another circuit to read the probe voltage from some of the temp displays he has, and it will allow me to activate a relay when the temp display hits a certain temp. HOWEVER, adding an additional wire to the probe for measurement/comparison has changed the actual display by about 1*C less, than without the extra wire. I need to figure out how to compensate for that.