DC Ammeter wiring

[thaeni]

I bought an ammeter to monitor ampere usage on my boat. My boat
has a master DC panel with a switch at the top that turns on all equipment
that is supplied by 12volts. Can I just wire the ammeter to the master switch
that enables all the other devices.
Thanks

[hellosailor]

You CAN install the shunt anyplace you please, but it will just measure the amperage at that point, through that circuit. The normal place to install it is in the battery common negative/ground cable, so it measures all current being drawn through the battery bank.

[thaeni]

thanks for advice, but where do I connect the positive too.

[hellosailor]

A typical digital ammeter will have four leads. Plus and minus, tht go to a 12V power connection like any other electronic device. And two lead for the shunt. One goes to either side of the shunt, plus and minus being only relative for those two. If your display shows minus when it should show plus, reverse those two.

[erps]

Hello,

Doesn't the old style analog amp meter go in series on the positive side though?

[Omatako]

My understanding of the connection is that the shunt has four connectors, two large and two small. The large connectors go in line (series) with the +v line from the battery bank to the load side (distribution panel in this case). The small connections go to the back of the ammeter.

In the image below the large holes in the ends take the battery feed to the load. That is those marked as "Diameter 8.5", the small ones marked "M5" go to the ammeter.

The negative connections in the system have nothing to do with the shunt or ammeter.

[HDChopper]

Correct Omatako.
Yes erps , what HelloSailor mentions would ive you te other use of an Ammeter which would be current draw lso hooked up his way would let one see if thay have a negitive draw while everything should be off...or known as exessive draw which is a good thing to know if it's hapening to your system.

[LakeSuperiorGeezer]

Normally you want to measure the current going into the battery banks because when the amps taper off, you know the battery banks are charged up. The alternator will be supplying current for both charging the batteries and for electronics, lighting, pumps, whatever and this includes charging the engine battery bank and any engine electronics. There are usually two battery banks, one for the engine and the other for everything else. With the engine running, usually a relay connects everything together so all banks get charged. So, the problem is finding a place where all the current flows together into one cable. If all the negative cables are brought together at one point and the shunt is connected to that point with the other side of the shunt goes to a common ground, usually on the engine since the starter on a diesel uses many hundreds of amps, then all the current is measured for both banks. Otherwise, if you want to have a shunt on the positive side, you have to choose one bank or the other. However, maybe you want to know how many amps are being pulled from the bank that supplies everything but the engine. When the engine is shut down, knowing the amperage draw will tell you how long you can go without recharging if you calculate amp-hours that are being discharged and know how many amp-hours the batteries can supply. In this case you would put the shunt on the positive cable going to that bank of batteries that supplies the buss and alternator relay connection. You could also tell when that bank is nearing full charge because the amps on the charging side of the meter would taper off. A voltmeter could be used for monitoring both banks, maybe with a switch between banks to you can measure resting voltage (no charging or current draw for at least six hours) to determine how charged up each of the battery banks are. However, be aware that a relay that connects all banks together while the engine is running to charge both banks will show the same voltage on both banks. The relay ties both banks together. The resting voltage varies depending how the state of charge for the battery banks. Trying to describe all this is difficult. A picture would be better. Check out of the library, Boatowner's Mechanical and Electrical Manual: How to Maintain, Repair, and Improve Your Boat's Essential Systems by Nigel Calder

[Padeen2]

I have a clamp-on dc ammeter. Isn't there a similar style permanently installed ammeter that would be much easier to install, as well as move about to give you different readings for different applications?

[LakeSuperiorGeezer]

Originally Posted by Padeen2

I have a clamp-on dc ammeter. Isn't there a similar style permanently installed ammeter that would be much easier to install, as well as move about to give you different readings for different applications?

It depends on what you want the instrumentation to do. The above shunt type amp meters also integrate the amount of current with respect to time so you get a good idea of how much amp-hours you have used and how much is left, how close the battery bank is to being dead. The amp guages in cars sixty years ago showed the amps flowing to and from the battery. These guages were placed on the hot side of the battery and the rest of the car, but did not include cranking amperage. If the generator were not putting out enough amps to charge the battery, the needle would be to the left of zero on the minus side. If to the right, then the generator was staying ahead of demand, and if the needle gradually came down a little above the plus side of zero amps into the battery, then it was assumed the battery was becoming charged and the voltage regulator was cutting back the generator to not overcharge the battery with too high a voltage. Now days if you want this kind of information, you use a voltmeter to directly measure the charging voltage. You can even buy little LED indicators now that plug into the cigarette lighter that show green yellow red lights for different voltages and tell you a little about what is happening, but not sure how well these would work in salt spray.