Amp Meter Troubles

[csdurand]

After purchasing two Amp Meters, building a nice custom mount and hooking it all up they don't seem to be working... The readings seem to jump around not even close to what they should be. Without sharing wiring diagrams is there something simple I am missing or does anyone have any experience with digital Amp/volt meters. The shunts are matched to meters and the volts are reading correctly but I just can't get the Amps to read right. Thanks in advance!

Here is a link to one if I am able to post it:

AMP METER

-Chuck

 

[Rich Stidger]

Chuck,

We really need a bit more info in order to attempt help. Can you describe exactly how the meter displays are behaving? Can you tell us what readings are displayed and why you think they are wrong?

 

[Ivan]

Shunts?

Chuck:

While Rick is right, and we need much more information, here are some general thoughts.

Since the voltmeter appears to read well and the amp meter does not, the problem is probably the wiring of the shunts. This is because the voltage will appear without any current flowing, but as soon as the current starts there is a voltage drop somewhere in the circuit, and the fact that the meter reading fluctuates says that the current fluctuates (I am assuming the meters are OK because they are new and therefore reading correctly the fluctuating current). So what you need to do is to find out why the current is fluctuating.

The connections at both ends of the shunts must be very clean and must have contact with the full cross section of the wires they connect to. Since your meters are designed for 500 amps, which is a huge amount of current, I suspect the shunts are inserted into the battery cables. The shunts should be as close to the batteries as possible--the length of the wiring from the shunts to the meters is not important, as those wires carry very little current. The usual arrangement calls for lug connectors to be attached to the battery cables, which are then fastened by tightening a nut or a bolt, squeezing the lug between two washers. The lugs should be crimped or soldered to the cables, but it's best to buy new cables of the right lengths.

There is also the possibility that the battery cables have poor connections to the batteries, or to wherever they connect to--master switch, engine ground, etc. You have to look at the entire circuit.

So unless the meters are defective, you just have to proceed methodically, sleuthing out bad connections.

 

[Bill Roosa]

Or you could have the wires to the new meters loose. The meter is just measuring the voltage drop across a portion of the shunt. This voltage is directly related to the amps going through the shunt. so if you have loose meter wires at the shunt or at the meter, or a kink in the meter wires you can get "jumpy" readings. you are reading milivolt level stuff so clean tight meter wires are a must.

 

[sail_4_me]

I installed a Blue Seas electrical panel with AC and DC digital meters. The attached picture is from the DC multimeter installation guide located on the Blue Seas website:

http://bluesea.com/files/resources/instructions/8732.pdf

Are you sure your shunt connections are not reversed? Voltage is not read at the shunt. For the Blue Seas meter you have 1 or 2 connections with fuses that power the meter and also monitor voltage. The shunt connections only measure amperage. I installed a single shunt closest to the only negative connection on the battery bank, to ensure it would pickup all changes.

If you have other negative connections going directly to the battery, and not through the shunt, that would also throw off the meter.

-Colin-

 

[Bill Roosa]

How shunts work

a shunt is just an engineered cable that has a very well known resistance. By placing two wires along its length (the meter wires) and noting the differance in voltage across them (the voltage drop) you can calculate the amps flowing through the shunt.
So while the volt meter is connected across the battery + and - terminals the ammeter (voltage not amp sensing) wires are connected (in the proper polarity else they read backward) to the shunt.
Both meter heads are volt meters, the voltage head is measuring real live volts and dispalying the same, the amp head is also measuring volts (milivolts to be precise) and converting that into a value of amps then dispalying that.
Technicaly there is no such thing as an amp meter that actually measures amps. You could build one but it is more practical to build a volt drop meter and make the dial face read in amps. Many similar exampls in measuring temp and pressure also exist.

 

[Bill Roosa]

Try using a twisted pair of wires. As shown on sail-4-me's diagram the wires between the shunt and the meter head are twisted. this is to limit/reduce the "stray induced voltages" from nearby current carrying wires. This is a milivolt meter. pass a 5 amp current carrying wire near it and it is going to creat a voltage change which will be interperated as a change in the voltage drop across the shunt.
This is VERY important to keep the meter from jumping all over the place.

 

[csdurand]

Thanks Everyone for the help & suggestions!

I am headed to the boat this weekend and will give this another try. I will post additional pictures and provide more detail early next week.

Thanks again!

- Chuck

 

[csdurand]

OK - after a weekend on the boat and finding the time for a nice sail the meters are still not working... The readings jump a couple times each second for example - it will read 84 then 134 then 212 then 43 then 172 and on and on... I even brought it home and wired it up trying to track down the issue and still had the same results. Here are a few pictures including on of the shunt on the boat. I am starting to think the Meters are bad. Thanks again!

 

[Don12364]

This may be a red herring but, on reading your original posting, I studied the range of ammeters listed by your e-bayer. I noted there are two types of meter. One requires a separate power source isolated from the current being measured and a second, a more expensive version, which will operate from the same source which is as you are doing.

Again the numbers shown in your photos would appear to be of the second (correct) type but I am just wondering if there has been a mistake in the supplier's product.
You might try asking him.

We presume from the black wires that the shunt is in the negative battery connection.