Been busy updating and repairing the coach electrical system. Replaced the old converter/charger with a new 35 Amp converter/ 4 stage battery charger. Installed a 12 Volt outlet for a new Magestic 12 volt color TV and power booster antenna. Did a complete rework of a very scary 12 volt outlet that could have burned the entire thing down. I am not an electrical engineer but I have done my fair share of adding circuit branches and electronic widgetry over the years. I am in the process of installing a 6-18 Volt Meter and a 30-0-30 Amp Meter with an INTERNAL SHUNT. Both meters are an analog made by VDO @ a medium price range that typically are used on the front driving dash. I thought I could use them in the coach. I want to monitor the battery voltage as it discharges/charges and measure the current going in and out as we use the appliances. We have one 12 volt 100 ohM battery. Maybe in the future we'll add another. Plain Jane - nothing fancy! Both meters are set up on a temporary test board. The Volt Meter and the lights to the meters are wire with a fused 10 AWG wire to the distribution board. They work beautifully. Here's my dilemma - no matter how I wire the Amp Meter in line to the positive or negative side of the battery it still reads zero when there is load put on it. I have tested all the wires in the circuit with my multimeter = good. What the devil! It's driving me crazy. My question is did I GOOF UP trying to install an internal shunt Amp Meter. Are the built in shunts not rated @ small/ fine enough increments to read the current resistance in the application I am trying to use it in. Should I have purchased a Blue Sea analog meter 50-0-50 external shunt rated @ 1 Milliamperes @ full scale or can I add a 30 Amp, 60 mV external shunt to the amp meter I am trying use? VDO makes a really nice 30-0-30 external shunt gauge approx $200. Yikes it is a little bit more than what I want to spend to have a matching gauge. Am I on the right track or do I have to rethink this monitoring circuit? I am going to take an aspirin - now I really have a headach. Pamela
Dave- thanks for feedback. I hope to clear up some confusion. All of our gauges in the cab dashboard work just awesome; as old as they are. The gauges we are adding in the coach will go on the wall over the thermostat by the refrigerator. These will monitor the state of the HOUSE battery not the starter battery. I included the schematic below. Option 1 or 2 will work just fine for our application.
Pretty cool! I placed an order for the amp meter with the external shunt from Blue Sea. It should be here by next weekend. I will post on the final results. Pamela
Sorry, I just don't know the problem that ammeter/shunt has... The only thing I can think of is if there are different size (ohms) shunts that correspond with different range values of the ammeter. The analog ammeter I installed was a straight in/out 30 amp with no external shunt so I have no idea about your problem other then the needle should surely deflect. An "ideal" ammeter would have ZERO resistance and an external shunt resistor in parallel serves as a current divider so x% flows in the shunt while the other flows in the meter itself so it doesn't have to pass high current like a full 30 amps. I would be interested in the ohms value of the shunt itself and then the meter itself if its possible to disconnect/isolate the two. The fact remains however that the ammeter and/or ammeter plus parallel shunt should be of extreme LOW resistance. Conversely, an "ideal" voltmeter would have INFINITE resistance.
I placed my analog in/out 30 amp direct ammeter in series between the solar charge controller and house battery bank so I can directly observe the solar charging. If I had another one and didn't have solar, then it would wire in series between the Converter/Charger output and battery bank to monitor what amp charge the batteries were receiving via the Converter/Charger. I also have a digital voltmeter on the house battery bank as their voltage provides information of their state of charge. Another ammeter could wire between the house battery bank and the loads, but that's not as important to me since my input charging ammeter along with the voltmeter tells me all I need to know.
If you talk to the Vendor ask about shunt sizes and proper matching them with a particular ammeter movement??? Again, there's a current divider between the shunt and meter itself.
I just cant say what your meter problem is....
John T Leaving for Florida TODAY
I thought I would chime in on this for what it's worth. from looking at the wiring diagram and please I'm old school but I can't see a reason the amp meter would work at all because there is no potential difference for current to flow.