ammeter wiring - SailNet Community

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Old 11-20-2010
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ammeter wiring

Hi
I have a 20amp analogue ammeter that I want to install into my switch board to monitor amps being used from the house batteries.I have a negative feed wire running from the house batteries,to a negative bus board behind the switch board.Do I wire the ammeter into this negative feed?
Any help would be appreciated.
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Old 11-21-2010
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Is it + or - ground?

If it's - (neg) ground then the ammeter should be wired onto the + side that feeds the panel to get total amps feeding the panel load.

The ammeter should be rated for total amps of the board or at least 75-80% of total draw (add up the of total fuses/breakers), not a 20 amp unit like you have, that would only work on 1 circuit.

ground - |battery| + > -ammeter + > panel + feed wire connection should be what you want IF it's - (neg) ground.
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Old 11-21-2010
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re ammeter wiring

It is a negative ground.I already have a volt meter that monitors house & start batteries.So only needing the ammeter wired to tell me the draw off from the house batteries,not amps going in.Is this possible?
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Old 11-21-2010
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It is possible if the total amps drawn at any one time is under 20A. If it is more you will damage the ammeter.
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Last edited by nickmerc; 08-18-2011 at 07:04 AM.
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Old 11-21-2010
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volt meters measure volts only, ammeters measure "running" Amps. and have to be rated at the total Amp draw (or if between engine and batteries, charging Amps) of the panel for what you want to do. If you put a 20Amp meter, it will burn out at 30 or so continuous use when multi things are using current.

The way I said to do it will show the total Amps (up to the max of the panel) that are being used like you asked.
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Old 11-21-2010
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If you really want to measure amps both in and out and want to know exactly where your batteries stand get a real monitor. Comes complete with shunt.
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Old 11-21-2010
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I run an ammeter to do just as you are wanting to do, panel consumption only, but 20 amps is awfully low for measuring panel loads. If you are sure you won't ever go over 20 amps then it can be done. Does this ammeter have its own shunt?

As Brian said above a much more useful tool is a true battery monitor. Volts really tell you little about state of charge while actually using the boat. I use my panel ammeter to determine consumption isolated from my solar or engine charge systems when compared against the whole system battery monitor. By having both it allows me to see both what is going out and what is going in...

In this photo I can see that my water pump is drawing an actual -4.6 amps but my batteries are only seeing a -3.7 amp load, thus my solar panel is providing roughly +1 amp of charge current.
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Last edited by Maine Sail; 11-21-2010 at 04:35 PM.
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Old 11-21-2010
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Thanks everybody for your info.I realise that a true battery monitor is the ultimate,but I can buy a 25 ammeter with internal shunt for $80.My house panel,only has a fridge.sailing instruments,nav lights,chart plotter & led interior lights.It would not exceed 20 amps.How do I wire this into the panel to give me the amps being used?
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Old 11-21-2010
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1. It *does not* matter whether you wire your ammeter into the positive or negative portion of wiring, so long as all the current (all circuits) are going through it. It's basic physics - current is the same in a circuit, from beginning to the end (voltage drops differ though).

2. So, where you wire your ammeter depends mostly on what's more convenient - i.e. where you can find a wire that carries all circuits. On my boats I find these wires more often on negative side, because I run common (negative) ground and pretty much everything has to go through it.

3. Ammeters with internal shunt are a bit difficult to use because you have to run a potentially thick main cable to and from the device, using under-sized contacts on ammeter itself. I would select ammeter with a shunt instead - that way a shunt (with properly sized bolt connectors) can be installed in a location convenient to main wiring, and appropriately sized (quite small) wires from there to the actual ammeter. External shunts also tend to be quite a bit more sturdy and less liable to be damaged.

In fact, on my current boat with very modest draw I ended up making my own shunted ammeter for 20 amps. You can buy shunts rated 10 amp and 20 amp online, and use a body of a higher-rated ammeter, as they are mostly 50mv voltmeters actually, including those from Blue Sea. I did have to re-label it.

So, assuming you do have a single negative wire going from the panel back to the batteries, and no loads connected elsewhere, I would wire a shunt into the negative cable from the panel - right next to the panel, and connect ammeter to the shunt.
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Old 11-21-2010
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Hi Brak
Thanks for the help.I have calculated my total current draw.If everything was on at once.I could have up to 40 amps,so will buy a 50amp with external shunt & wire it into the negative feed behind the panel
Cheers
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