# logic behind operation of fuel gages



## Dave Koller (Nov 15, 2008)

One question is do you have it hooked to the pack always - as I think it should pick up the time and current as you charge even if topping off.. Or Not - MY processor controlled monitor does that (DIY of my design and algorithm) .. And I really don't know much about yours (I am gonna look it up - as I have to know ) but I thought Curtis fuel gauges work that way also......


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## Dave Koller (Nov 15, 2008)

Well I gleaned this from a manual:

Features
1. All principal circuits are integrated in a single chip for long-life and reliability.
2. A 10-bar LED displays the state of charge successively, bar by bar, from full to empty. 
3. At 70% depth of discharge (30% S.O.C.), a flashing LED signals energy reserve alert. 
4. At 80% discharge, alternately flashing LEDs provides an "empty" status warning. 
5. The TCDL recognizes an improperly charged battery. 
6. High Voltage Reset-HVR Gauge must measure 2.35 volts per cell for 6 continuous minutes during charging. 
7. The key switch drives the LED and control pin #3. The LED does not display when the control pin #3 outputs 0V, so when pin #3=0V to shut off the electric equipment, the LED will also not display.

It looks like it needs to reach perhaps 70 % to trigger some reset to read charge --- 
Wonder if it WAS disconnected briefly before charge if it would reset - or  loose everything...

Perhaps someone is using one - and can tell us.. I was thinking of the same thing for my analog (ugh) gauges ( I thought it would make another way to see results than my digital!)


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## EVfun (Mar 14, 2010)

If it is the unit I think it is only connected to the traction pack to read voltage and there is not shunt input. It is basically an expanded scale volt meter with time averaging and some intelligence. A lead acid cell is about 1.95 volts when dead and about 2.15 volts at full charge (no load.) These kinds of meters used to be analog, but digital is easier now.


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## drdonh (Aug 8, 2008)

The gage monitors only pack voltage, and is always connected, other than a switch to turn the display off. I suspect there is some sore of time averaging algorithm, with perhaps programming to always calculate a decrease from the last reference point, other then the reset condition. 

That why knowing exactly what processing is going on in there would be helpful to understanding what the gage is actually indicationg. 

Don


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## DONEAL (Sep 10, 2008)

drdonh said:


> The gage monitors only pack voltage, and is always connected, other than a switch to turn the display off.
> 
> Don


I couldn’t find any thing in the manual either. One option may be to hook it to the contactor? Then it would reset when the contactor closed (energized) just not sure, since the Elcon is a “knock off” of the curtis there may also be specific wiring for it. Could you hook it to the contactor?


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## Dave Koller (Nov 15, 2008)

I am sure it is a voltage only monitor with some time algorithm as EVfun has stated. I use the shunt to monitor current and internal time clocking.. 

Something to try would be another switch (dpdt) with a resistor set to drop over-all (pack) voltage that resets the internal voltage monitor as would be the case in a low pack. BUT - that may start it at Zero and only add from the opportunity charge and you have screwed it up some more ... Hmmm, not an easy thing but even the Curtis probably works that way. Since it does NOT monitor current in and out - it is limited in its ability to be a decent "fuel" gauge!


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