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Difference between revisions of "EMeter"
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In a nutshell, it measures the current flow into and out of the battery pack. The thing is that the effective capacity of a leadacid battery is dependent on the rate at which it's discharged. A simplified example:  In a nutshell, it measures the current flow into and out of the battery pack. The thing is that the effective capacity of a leadacid battery is dependent on the rate at which it's discharged. A simplified example:  
−  A 100 Ah (amphour) battery can provide 1 amp for 100 hours, or 2 amps for 50 hours, or 5 amps for 20 hours. That's the theory. In actuality, the more current you draw, the lower the actual capacity you get out. So, you may get 1 amp for 100 hours, but 5 amps for only 19 hours, and instead of 50 amps for 2 hours, you'd only get 50 amps for 1 hour. This is known as the [[Wikipedia:Peukert's Law]].  +  A 100 Ah (amphour) battery can provide 1 amp for 100 hours, or 2 amps for 50 hours, or 5 amps for 20 hours. That's the theory. In actuality, the more current you draw, the lower the actual capacity you get out. So, you may get 1 amp for 100 hours, but 5 amps for only 19 hours, and instead of 50 amps for 2 hours, you'd only get 50 amps for 1 hour. This is known as the [[Wikipedia:Peukert's LawPeukert's Law]]. 
Anyhow, an emeter not only measures the total amps that go into (charging) and out of (discharging) a battery, but takes into account the rate that it's used, and uses Peukert's empirical formula to calculate the effective charge, giving a more accurate indication of the battery's true state of charge (SOC).  Anyhow, an emeter not only measures the total amps that go into (charging) and out of (discharging) a battery, but takes into account the rate that it's used, and uses Peukert's empirical formula to calculate the effective charge, giving a more accurate indication of the battery's true state of charge (SOC). 
Revision as of 01:05, 29 January 2007
An Emeter measures the state of charge of batteries.
In a nutshell, it measures the current flow into and out of the battery pack. The thing is that the effective capacity of a leadacid battery is dependent on the rate at which it's discharged. A simplified example:
A 100 Ah (amphour) battery can provide 1 amp for 100 hours, or 2 amps for 50 hours, or 5 amps for 20 hours. That's the theory. In actuality, the more current you draw, the lower the actual capacity you get out. So, you may get 1 amp for 100 hours, but 5 amps for only 19 hours, and instead of 50 amps for 2 hours, you'd only get 50 amps for 1 hour. This is known as the Peukert's Law.
Anyhow, an emeter not only measures the total amps that go into (charging) and out of (discharging) a battery, but takes into account the rate that it's used, and uses Peukert's empirical formula to calculate the effective charge, giving a more accurate indication of the battery's true state of charge (SOC).
Short version: Battery Fuel Gauge.
A commonly used EMeter for electric vehicles it the Xantrex Link10. http://www.xantrex.com/web/id/237/p/1/pt/5/product.asp The Link 10 is a stateoftheart battery bank monitor that uses sophisticated microprocesor technology to report all significant battery information.
Xantrex also make the Link20 and the XBM emeters.
 Build it yourself battery monitor for multibattery packs http://home.earthlink.net/~evtkw/ Includes plans schematics and details  by Tim Wong
 Gordon Stallings battery monitor with schematics http://genki.home.ionet.net/BattMon/BattMonArticle.html
 Smart Gauge (UK) http://www.smartgauge.co.uk/ Great technical info on how battery monitors work.