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Author Topic: Car Voltage Monitor / DC Voltage Level  (Read 3934 times)

Posts: 14


« on: September 21, 2002, 09:46:10 AM »

Hello all,

I looking for a Digital Voltage Display that is small enough to mounted on or around the dash board of a car. I would prefer a LED design because it would be easy to see at night.

The reason I looking for this is I have an older car with fog lights and day time driving lights. With the day time lights if my altinator fails it will drain my battery very quickly. With this I will be able to tell if the chatge rate is stable to maintain the battery charge.

I am not against building my own if someone has a design they can send me but I would prfer to by and install it in my car. I have surfed around a little but I have not had much luck. What I have found is bulky. Something like a small flat panel display LED or digital display with a back light for use at night.

Thanks for your help and 73 Moe KE4CQW /

Posts: 10248


« Reply #1 on: September 21, 2002, 09:20:03 PM »

Once upon a time, all cars had amp gauges, oil gauges, temp gauges, and fuel gauges, and some even had oil temp gauges. Problem is (was) no one really knew what all of the stuff meant. Of recent, car engines run at temps as high as 280° F, and to those uninformed, this is too hot! Amp gauges are no better. Who really knows nowadays just how much thingies on your car are drawing? Well, in their infinite wisdom, some corporate weenie decided voltmeters were the new rage. Heck, most folks think a 12 VDC car should have 12V. Well, if the gauge reads 14.5 they panic, just like they did when the temp reached anything over 200°. Now you know why they call those little read lights "Idiot Lights".

But if you REALLY want to know what's going on, fine. So, what to do? Build an expanded range volt meter using a diode, resistor, and a known meter movement of about 1 to 5 mils full scale. Follow the plans in the ARRL Handbook and you are home free.

But... regardless of what you do, that little red light is about as reliable as any gauge on your car. One thing is for sure, it is a lot more reliable than the person behind the wheel in most every case.

Alan, KØBG


Posts: 149

« Reply #2 on: September 23, 2002, 10:27:10 AM »

Moe, go to radio shack and buy #22-112 $5.99
vehicle voltage tester/uses LEDs page 238 2002 catalog
remove the test probe and alligator clip install an on/off switch and say an inline 1/2 amp fuse to be safe and connect to the battery or even your acc terminal in the car's ignition switch that way it will turn off if you forget.
it has 6 leds to tell you battery condition and various charging conditions.
It's small fairly accurate, cheap the auto supply store sells this for $10.00+
it has a magnet built in so it can stick to your dash or do double stick tape or velcro..whatever
I use this in my vehicle and even on the motorcycle as a voltage monitor

regards, Marty


Posts: 2198

« Reply #3 on: October 04, 2002, 01:31:27 AM »

Be wary of trying to use a "Test meter" to monitor your Auto Battery voltage unless you run the meter off a separate battery!  Most meters do NOT have a common connection between the negative test terminal and the negative supply to the meter circuit!   Doing so may have dire consequences, not the least of which are inaccurate readings.

Posts: 13

« Reply #4 on: October 11, 2002, 04:39:07 PM »

 I, too, had the same concern and I ended up wiring both a voltage AND an ammeter to my car's electrical system. The voltage guage can be connected just about anywhere in the vehicle's 12V system. The ammeter is wired up just after the alternator in series. That way, the more power I'm using, the more I must "pull" from the alternator. It lets me lnow if I'm pushing my luck while TX'ing at 100W on HF or something like that.
 Good sourced of meters are quality auto parts stores (I use the Autometer brand) or J.C. Whitney.

    Scott Heath   (AF4KK)    Smiley

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