Ammeter question

jaschrumpf · #1 (**permalink**) 07-31-2007

I've got the instructions for my particular ammeter, and I've read elsewhere that it's recommended that the DC distribution panel should be powered either from the common terminal on the battery switch or where the battery lead connects to the starter solenoid (either end of the same battery cable).

My problem is I don't see how this circuit allows the load going to the DC panel to be measured by the ammeter. If the meter has to be in series with the load, wouldn't the run for the DC panel have to go through it as well?

If so, where should the run for the DC panel come from on the ammeter: the I terminal or the S terminal?

Thanks!

stevemac00 · #2 (**permalink**) 07-31-2007

I've read your question a few times and you seem to be asking different questions. Put the ammeter on (hall effect) the wire or in series (shunt) with the wire you want to measure.

If you have two banks you're probably only interested in measuring the load on the house bank so put it on that wire.

jaschrumpf · #3 (**permalink**) 07-31-2007

I should have been clearer. The ammeter instructions say a run should go from one terminal of the ammeter to where the battery cable attaches to the starter solenoid, and from the other ammeter terminal to the BATT connector on the key and to the OUTPUT of the alternator, i.e., that terminal has two wires running from it, one to the BATT on the key and one to the alternator OUTPUT. That way all the current in the igniton system passes through the ammeter, and the drain or charge on the battery system can be monitored.

My question is, how can this be done and also monitor the drain to the DC panel if that connection does not also go through the ammeter? There must be a way to view the total system current, right? Wouldn't running a lead off the BATT post on the key to the DC panel ensure that that current (whether it comes from the battery bank alone or from the alternator output) passes through the ammeter and is measured?

Thanks again!

Faster · #4 (**permalink**) 07-31-2007

Typically you would install a low resistance shunt in the line from your DC panel to your ground - and the "ammeter" senses the voltage drop across the shunt to infer the cct amperage. Since it's on the final return path it will sense any and all loads on the system.

It would not be usual to have ALL your current actually pass through the ammeter - the meter would have to be quite robust, whereas a shunt only puts millivolts across the meter for its indication.

Lancer28 · #5 (**permalink**) 07-31-2007

If you have a meter like my greenlee hand-held (I think it is a DMM210-C or something, about $180.00 IIRC), for a single circuit or item test place the meter in series with the load, allowing the electricity to pass through the meter itself. I use the shunts for testing things like the entire draw from everything on the battery at once.

jaschrumpf · #6 (**permalink**) 07-31-2007

The ammeter is not one of the hand-held type, but is a gauge in the instrument panel, just like the oil pressure and engine temp gauges. How does one of this type get connected up so that it shows the flow of current? The gauge is designed to show flow to and from the battery, so I presumed that this would be a straightforward installation.

Seems not to be so. Do I really need an ammeter at all, or is a voltmeter enough to determine battery health and recharging ability?

jaschrumpf · #7 (**permalink**) 07-31-2007

I think I've found my error. If I run the DC panel lead off the common terminal on the battery switch (or even the battery terminal on the starter solenoid), anything that draws power through that panel will be "seen" as a current drain on the system just like charging the battery would be -- in essense, it would be a current "sink" just like the battery.

The current to the DC distribution panel doesn't have to pass through the ammeter, as the current from the alternator already is, and anything connected to the panel will pull current from the alternator through the ammeter and provide the reading.

I knew I was overlooking something simple. I always did have trouble visualizing electrical current flow in my college physics courses.

jaschrumpf · #8 (**permalink**) 07-31-2007

Rats! My circuit above would work while the alternator is charging the battery, but not for loads off the battery itself while the engine is not running.

Back to the drawing board!

stevemac00 · #9 (**permalink**) 07-31-2007

Assuming you have a 1-2-Both switch with two inputs and a single output (common) then just go from your common out to your ammeter on to your loads. I.E. Disconnect your loads from common and connect to ammeter. Then make a jumper of battery cable (probably 1/0) to connect from common to ammeter.

jaschrumpf · #10 (**permalink**) 07-31-2007

I don't think I'm expressing myself clearly on this subject; let me try again.

What I'm shooting for is an ammeter permanently mounted in my instrument panel that will, when I set the battery switch to 1/2/Both and turn on (for example) the blower show negative amps going from the battery. Then, when the engine is running it will show the charge going into the battery and reflect any additional load placed on the system by turning on cabin or running lights, etc. I'm not looking for a temporary jumper between the battery and the ammeter or a hand-held solution.

Here's the drawing from the ammeter instructions:

The part inside the red box is my proposal for powering the DC panel so that the ammeter will read it. Presuming I use a proper gauge wire (8 or 10G), is there any other problem with this setup?

Thanks!