# nov. 07 update



## ElectriCar (Jun 15, 2008)

Nice job. I need to install a voltmeter as my PacTrakr is a POS. I like the idea of the PakTrakr but do not recommend it necessarily as it has some serious issues with noise. I've improved it somewhat but it still has issues and is unstable, jumping to different screens at random.


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## Lee Hart (Oct 16, 2009)

Nice work, Lou-ace. A couple things occurred to me.

Try one of your digital meters with its own battery. If that works, the problem is that your DC/DC is bad or is not isolated.

If your analog meter measures 518 ohms, it draws I = 12v/518ohms = 23ma at full scale. That's a lot! It will run your pack dead if left on a long time. And, your 4.7k series resistor will be dissipating (120v-12v)^2/4700ohms = 2.5 watts! The Radio Shack resistor is probably 1/4w or 1/2w and won't last long.

Analog meters that draw less than 1ma full scale are pretty common. That would solve these problems.

Another thing: Cheap meters aren't very accurate. Battery voltage doesn't change much between full and dead (like 12v=dead, 13v=full). So, what you want is an expanded scale meter, where the bottom end is around 100v and the high end 150v (for a 120v lead-acid pack). To do this, pick your resistor so the meter reads 0-50v, and then put a 100v zener diode (or string of zeners that add up to 100v) in series.


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