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R1& R2 are 220k ohm in my setup. No trimpot now though. ebay a 20 Volt DC auto polarity sensing meter. My pack is 160V. A shorted cell will display half the voltage or about 1.65V. Good luck. Dang spell check!
i guess the trim pot is to zero out the display, which should be zero anyway. Can you give me an ebay example of the meter. I am only finding LED panel meters from 7.5-20v and analog 0-15v meters.

thanks
francis
 

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i guess the trim pot is to zero out the display, which should be zero anyway.
If you buy %5 resistors they could be at either extreme of their specification range which would give you a difference. The trim pot fixes this. Your other option would be to buy precision resistors which I understand are very expensive. Alternatively, you might be able to by a sample of the 5% variety and the measure their resistances until you find two with the same value.

ElectriCar, with using a volt meter, as opposed to an ammeter, in the megaohm range of resistance wouldn't the resistor values be of less importance? For example, in your setup couldn't you go with 440kohm and have the same results with the benefit being lower current drain from the device?
 

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I chose those values to keep current drain to a minimum. Megohm would be ok too. I plan to use zener's back to back to limit voltage to the meter but not so sure it will work properly if the resistance in the circuit is so high the zener can't conduct properly. They will be wired with a 1k resistor like this
-----l<l----l>l--/\/\/\----- with one forward and one reverse biased all the time. Once the voltage exceeds about 21V the reverse biased one should conduct and shunt the over voltage. I think this will work.
 

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I have a couple of the panel mount led displays that are 0-200v. Would i not achieve the same results of 1/2 pack monitoring of 46 cells =23 @73.6v each? If i notice one is 72v and the other is 70.8, then i have a problem.

Francis
 

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The meter displays both negative and positive values, that's how you determine which half of the pack it's on. Not sure how your led could do that.

I was at first wanting to use a bar led with the center led lit up at 0V. Each led right and left of center would represent a voltage value like .5V or such but I couldn't figure out a way to make that work.
 

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Aloha, y'all. I see an advantage of the one gauge and seeing + or- 1.5v as a quick and understandable visual, but is there any other advantage over seeing two gauges, one being 72.5 and the other possibly 74v. The LCD @ 0-200v are the same as the ones described before at 0-20v, but they only go down to .1 not .10 decimal places.
Since i like lots of visuals, I am going to use one LCD for total pack voltage, 2 for 1/2 pack and one for the 12v side. And leave the Link10 on amperage. Now to find a good place to put them.
Francis
 

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I ordered an LCD volt meter from eBayer clinia and he will be setting the meter to display twice the voltage it reads. It will display from -19.99V to +19.99V with a -10V to +10V input. This should be ample. If my 20 cell pack is 10V off there is definitely a problem!

He said the meter could handle 100V input without damage so I should be just fine with my 64V nominal pack.

The listing was http://cgi.ebay.com/LOW-COST-LCD-PA...110?pt=LH_DefaultDomain_0&hash=item588b92e986

Oh, this runs off of a 9V battery so it definitely has an isolated PS. I have one from him on a 50A shunt and it ran for several months with an old 9V battery out of a smoke detector.
 

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I really like this thread. This battery bridge principle is just genious.

I have the feeling that some kind of alarm, buzzer or warning light would be better suited for getting the driver's attention rather than a digital voltmeter. However the DVM would be useful to analyze the situation once an alarm has appeared.

I am planning to build an electronic alarm, based on this principle. It will have hold/reset function and not draw any significant amount of current from the battery pack (which some of the designs/suggestions in this thread unfortunately do).

I do not own an EV myself but I have a friend who might be tempted to test it out for me.
If it turns out well I will post the results here.

Agust
 
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