Car Ammeter

[barry wilkins]

Just wondered if any of you seen any of the designs for reading the amperage of a battery in a vehicle ?
Its is done by measuring the voltage dropped by earth strap from the negative terminal to the chassis .

Barry Wilkins

[eccerr0r]

Re: Car Ammeter

It's frequently done actually, but calibration is a problem - how many amps is that voltage drop equal to?

The alternate method is using hall effect sensors on those wires and those can be somewhat calibrated, but there are inaccuracies in that due to orders of magnitude from standard power draw versus starter current draw.

[Curious.George]

Re: Car Ammeter

Just wondered if any of you seen any of the designs for reading the amperage of a battery in a vehicle ?
Its is done by measuring the voltage dropped by earth strap from the negative terminal to the chassis .

You can monitor "low side" or "high side" -- low side is usually easier. But, a lot depends on what else you're interfacing with.

And, the range of values you want to be able to measure -- along with the accuracy and precision of those measurements.

The more demanding you become, the more adventurous the circuit topology needs to become. E.g., you can measure big starter currents easier with a Rogowski coil than you could with a shunt -- esp if you also have to monitor very small currents that a suitably SMALL shunt would drive into the noise floor! (because the shunt would want to be a very low value in order not to impose a large voltage drop in the starter lead). Likewise, you can adopt different measurement strategies for different circuit components -- if you can alter the circuit to accommodate your measurement!

[petehall347]

Re: Car Ammeter

it all sort of depends on what you you are trying to measure .like ammeters are are generally to measure charging current . ah is normally on the tag . and cranking amps .

[redwire]

Re: Car Ammeter

OP I think you've asked the same question before:
https://www.badcaps.net/forum/showthread.php?t=68684
https://www.badcaps.net/forum/showthread.php?t=45512

I remember seeing a circuit in an electronics magazine years ago, but can't find it. I was looking here American Radio History
It's just an op-amp you need biased at 1/2Vcc to read + or -.

This pic appears to be from Silicon Chip magazine 2002, where you make your own hall sensor.
There are some cheap chinese car ammeters on fleabay and ali. They are all hall-effect sensor based.

[barry wilkins]

Re: Car Ammeter

Hi guys thanks for your posts
Attached a pictures of the ferrite txr I made ,the output varies by about 3mV at a current of 3 Amps.
Barry Wilkins

[redwire]

Re: Car Ammeter

How did you cut the air-gap in the ferrite, it looks very well done.

You are using Allegro UGN3503 analog hall sensor? They are discontinued many years ago and the newer versions look interesting. F.W. Bell also has some I've used.

1mV/A into the LM358 or OP-07 should work to make an ammeter.

[barry wilkins]

Re: Car Ammeter

Sorry about the delay in answering
I used a Dremel with disc looks like a normal abrasive wheel to me.
The txr works OK not sure if there is some remance in the core ,having a slight zero drift ?
Anyway I have not done any more at the moment ,waiting for an LCD ammter to come on ebay .Looks like it has got a shunt on it which I intend to remove as it is 100 Amps
On my Car which is a Citreon there is large lead from the battery to a sort of distributing assembly with fuses on it.
It might to be possible to read the current drawn on different cables ,so it may be possible to dismiss the large current drawn by the starter motor.
I built my own amplifier circuit for the txr core to read with adjustable gain.

Barry Wilkins

[sam_sam_sam]

Re: Car Ammeter

Anyway I have not done any more at the moment ,waiting for an LCD ammter to come on ebay .Looks like it has got a shunt on it which I intend to remove as it is 100 Amps

You do not have to reinvent the wheel you could use something like this

https://www.ebay.com/itm/Hall-Voltme...53.m1438.l2649

On my Car which is a Citreon there is large lead from the battery to a sort of distributing assembly with fuses on it.

If you are wanting to see your alternator output the wire that is on the back of the alternator marked (“+”) terminal and this give you this information

It might to be possible to read the current drawn on different cables ,so it may be possible to dismiss the large current drawn by the starter motor.

If you are wanting to read this then you have to do on the positive terminal on the battery

I built my own amplifier circuit for the txr core to read with adjustable gain.
Barry Wilkins

What reason do you have for wanting to do this