Ammeter help

[DanLXIX]

I've recently fitted a KUS ammeter to be able to see the alternator charge, but for the life of me I can't work out why it's reading what it does. Turning on the ignition, it reads 0A as you would expect, but once the engine is running it just shows -80A. I've checked the voltages on the shunt and the sensor output is about 0.5v which tallies with it reading max consumption, but the voltage on the battery is 14v so it's clearly getting a charge. The wiring diagram below shows how things are set up, and I get the same reading from the ammeter whether I turn the DC-DC on or off. The shunt is installed as per the instructions so it's the first thing after the cutoff switch on the starter battery. Any clues to this would be very welcome.

 

[wonkywinch]

If you're trying to measure total alternator output rather than charge of the starter battery, then it should be in series between the alternator output and the positive bus bar.

The circuit diagram you've posted, assuming the shunt on the right side of the drawing is the ammeter one, then you are only measuring the charge to the starter battery. What happens after 10-15 mins when the starter battery has recovered?

 

[DanLXIX]

If you're trying to measure total alternator output rather than charge of the starter battery, then it should be in series between the alternator output and the positive bus bar.

The circuit diagram you've posted, assuming the shunt on the right side of the drawing is the ammeter one, then you are only measuring the charge to the starter battery. What happens after 10-15 mins when the starter battery has recovered?

Yes you are correct on the shunt location. I have to admit I've not run the engine long enough to see what happens after the starter battery recovers, I'll have to try that. I assumed from the ammeter instructions that it would monitor charge and/or consumption - this is the installation guide:
I'd not thought to just put it on the alternator outout!. I fitted it to show that the alternator was charging, so that would do it.

 

[wonkywinch]

The "load" is the busbar as this then feeds the starter, it's battery and house battery system. The "batt+" in the installation diagram is really your "alt +" since that is what you are trying to measure. The starter will draw a lot more current than the 100A limit of the meter but this will be OK since it will be drawing from the starter battery via the bus, not the alternator output.

It is measuring current but only the starter battery charge/discharge. I'm surprised it didn't burn out trying to start the engine with it in the config you have at the moment since cranking amps are in the hundreds.

You don't indicate in your schematic which way round you wired the meter shunt but I guess you put the "batt +" to the starter battery and "load +" to the bus bar, hence it's reading backwards, ie -80A flowing through it to recharge the starter battery.

 

[DanLXIX]

Got it, thank you - and yes you are correct in how I'd wired up the shunt. Now I need to go and rejig things!