Digital AmMeter Schematics

Thats because electron and current flow from the negative to the positive .

The other way you can do it is get an inductance pickup type that can go on the positive.

Silicon Chip magazine sept 2003 had a Current Clamp adaptor for DMMs. Measured current upto 900 Amps DC @630 Amps AC uses a hall sensor & toroidal core over lead for sensing. I have built one some time ago.The Kit was Jacar-KC5368 dont know if its still avalable.

I found my solution .. had to dig a bit in my memory ...
It is not about just to measure the high current .. it is about having
a small a cheap panelmeter installed for permanent reference.

The signal conversion from the + shunt to the measure voltage against ground
is done by a difference amplifier.

here is a link if somebody is interested
http://www.play-hookey.com/analog/difference_amplifier.html

Also just 2 transistors will do with a few resistors.
I will put a little board together and test it. It's a matter of the right resistor dimensions.

have fun
gmd

Like I said........ "Interesting answers"

Clay S: Voltmeter versus ammeter ........ Good point.

_gmd_pps: Why should I educate you ?? ....... That's a neat way to evade the issue.

Kiwi Kia: Just off the top of my head ..... errrr..200amps? But so what? "Sorry guys, my ammeter is reading a bit high, just have to let the tide take ya."
If you are concerned for the safety of your winch you would do much better to monitor its temperature than its current.

Phil G: If it's reading amps it IS an ammeter, no matter how you derive the measurement.
"As the current drops towards zero, I know the battery is approaching full charge. Useful info IMO."......... How is it useful information? When its time to make camp you stop, even if the battery is not at full charge. Huh?
"A single digital voltmeter can do everything I need, including telling me how many amps are going into the aux battery." .......... And if the indication is that not as many amps are "going in" as you expected, what do you do then?
By the way, using existing cable sections as shunts for current measurement is an easy and economical method but it is less than accurate. The temperature coefficient of copper resistivity is such that the measurement error will increase with temperature to the tune of 0.393% per degree C. This means that from a 20C start the current will read 10% higher as the cable warms to 45C from engine heat and cable self-heating. Still reasonable but don't perform any higher-order maths using data obtained this way. Proper shunts are made of alloys such as Manganin which have almost zero temperature coefficient of resistance.

The use of a (+/-) ammeter will show the total LOAD or CHARGE amperage on the battery
The ammeter will give you an accurate reading of what current is going in or out of the battery at a glance

When a Voltage meter is installed nearby you can also see the battery Voltage reading at the same time
however it shows CHARGING/DISCHARGING Voltage of the battery, as indicated below, which is not the true rested battery Voltage
the two meters have to be read in unison to get the correct picture of the health of your battery system

Image Could Not Be Found
It's very obvious looking at the picture above there is <1 Amp charging a 13.8 Volt battery system

Maîneÿ . . .

Phil, you have hit the nail on the head with your:
"There are more interesting things to think about when I go bush"

I have spent a lot of my career monitoring meters to ensure that processes are behaving themselves and the last thing that I want to do in the bush is stare at meters and consider if "things" are going right.

Sure, I have alarms to alert me to the essential parameters such as engine temperature and oil pressure but I can live without knowing if my auxiliary battery is fully charged or not. It should be charged, given the driving time, but if its not then I'll know soon enough and do something about it then. I would much prefer to know my wheel bearing temperatures whilst mobile than worry about a few millivolts of battery state.

After reading many postings on this site I really do believe that there is a dedication to the mystique of electricity and a preoccupation with matters of batteries, volts and amps. Apart from cranking your engine when you need to, the rest is simply domestic convenience and not exactly essential for human survival. But if determining the state of your amps & volts is what "lights your lamp" (pun intended) then so be it. Maybe because I know I can fix electricals when they go wrong, I tend to not be preoccupied by them and turn my attention to those things that I went bush for. But then, we are all different.

Oh, and your meter indicating current on the dashboard....... do you gesture to it and say "and this is my digital millivolt meter that is really indicating amps"? Of course not, you refer to it as your ammeter. Believe me, virtually every indicating instrument is an inferential device. The needle of a Pressure Gauge is not moved directly by pressure, it reacts to the deflection of a bourdon tube which is acted upon by the pressure. But we call it a Pressure Gauge because it indicates the value that we are interested in. If a meter reacts to an electrical current and the scale is graduated in amperes then it IS an ammeter regardless of how the signal is transmitted and processed before being indicated. So what is your REAL ammeter? I do have a type in mind but don't see many of them these days.

Yep, healthy debate. And absolutely no offence intended.

Geeez gmd,

I'll bet you're glad you asked that question!!

Have fun

;-))

Warning - you will be wasting your time reading this thread if you don't understand how to use Current Readings.

Oatley electronics sell this Dual Current Monitoring Kit for $30 that allows you to monitor the voltage across two shunts that are at ANY voltage.

It does this by generating two low-power isolated voltages that power the Digital Panel Meter so you can connect their reference point anywhere.

For example, you could have one shunt in the Alternator lead (or use the Alternator lead as the shunt for more reliability !) to show total output current and one acroos the Battery Earth lead to show current going in or out of the battery.

With so many wires connected to the Positive post of a battery, it's very hard to monitor the current going to the Loads without installing a shunt, and that will reduce reliability.

Oatley sure come up with some brilliant innovative designs at great prices.

Has anyone else come up with a Battery Isolator or a Low Voltage Cutout using a Latching Relay so it wastes no current when closed ???