E-meter

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Tom Thomson
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E-meter

Postby Tom Thomson » Tue Jan 29, 2008 2:03 am

Well, here I am again, hat in hand, seeking enlightenment. What, exactly, does a fuel gage measure?
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ChrisB
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Postby ChrisB » Tue Jan 29, 2008 9:02 am

Ah well that depends on what vehicle/type of e-meter its fitted to :wink:

Some measure just battery voltage others are much more clever and measure charge and discharge rates.

Of course in a ICE it tells you how much petrols in your tank :P

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aminorjourney
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Postby aminorjourney » Tue Jan 29, 2008 9:48 am

My car will tell you how full or empty the car is using bars to represent charge remaining. It also will tell you how many hours the battery will last using instantaneous current drain as the predicted consumption.
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Tom Thomson
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emeter

Postby Tom Thomson » Wed Jan 30, 2008 12:19 am

Amino
Yes but - - how does it know how much charge is remaining? And then there is the fact that a battery contains no electricity. For lead/acid batteries it appears that one must measure the amount of sulphuric acid and I'm pretty sure the e-meter doesn't do that.
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ChrisB
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Postby ChrisB » Wed Jan 30, 2008 6:24 pm

Ah well it works it out by measuring the amount of charge recieved by the battery and the amount its discharged and hence you can work out how much stored energy you have.

The Blingo does this with its energy meter quite well, but can be fooled as with many batteries if you discharge a battery outside its calibrated Ah you will find it goes flat much quicker than you will expect.

The next bit applies to Lead Acids and Nicad, I'm not sure about Li-ions as I've not experianced these yet, but I suspect its similar ?
A battery is generally rated in Ah Ampers per Hour, for instance 12volts @ 20Ah , this does not mean you can draw 20Amps for an hour or 1 amp for 20 hrs as you need to know the batteries C rating.
On a decent battery you will find it labled like this 12volts 20Ah C20 or C5 etc etc
So to find the true discharge rate you divide the C rating into the Ah rating and that will give you the maxium calibrated energy that battery will give you per hour for a set number of hours.
A 12volt battery 20Ah @ C20 will give a output of 1amp for 20hrs
A 12volt battery 20Ah @ C5 will give a output of 4amps for 5hrs

Discharging outside these parameters generally wont do the battery too much good but most of us EV'ers do this all the time :oops:

Hope that sort of helps a bit

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