Circuit for converting vintage ammeter to voltmeter.

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Thread Starter


Joined May 10, 2012
I have a vintage car that has a shunt ammeter. The needle sits in the middle and fully deflects in either direction for about 2A of current.

I want to convert it to a voltmeter with an 8 to 16V range. A 12V reference power supply came to mind using a SEPIC DC-DC converter. The SEPIC supply is connected to one side of the ammeter and a current limiting resistor and the battery is connected to the other side.

When the battery voltage is +/-4V different that the 12V reference and with 2 ohms of circuit resistance, 2A would be flowing and the ammeter would be fully deflected in one direction or the other. Current and subsequent ammeter deflection would be linear for < +/-4V.

Problem here is that a SEPIC converter can't sink current. I could add a current sink transistor switch and resistor possibly that turns on only when 12V < battery voltage.

4 switch Synchronous DC-DC converters can sink current, but this solution is expensive and i'm trying to find the lowest cost solution.

What do you guys recommend? I thought of using a Power Op Amp, but I think it would require a V+ and V- power input. I'm a bit rusty on Op Amps so I can use some help though.


Joined Apr 5, 2008

Sorry, but we do not allow any automotive modifications here.
I am closing this thread as it violates AAC policy and/or safety issues.

6. Restricted topics. The following topics are regularly raised however are considered “off-topic” at all times and will results in Your thread being closed without question:

  • Any kind of over-unity devices and systems
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PS @ tshuck, please do not do any recommendations to conceal a violation of the ToS
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