# Gas Gauge State of charge?



## CrunchTime (Feb 13, 2009)

Snakub said:


> I know that the Soliton does this but has it been discussed somewhere on here about how to make your stock fuel gauge represent your state of charge?


One option is the Fuel Gauge Driver+. It can also show Amps on the rev counter (I have a switch to choose between RPM and Amps)


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## Snakub (Sep 8, 2008)

That is a bit pricey for me I wonder if there is anyone who has a diy solution?


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## CrunchTime (Feb 13, 2009)

There is this article which describes a circuit to drive the bimetallic strip on the gauge in an "older Volkswagen", but I don't know if it would work for you (my electronics is nowhere near good enough to know ). If your gauge isn't bimetallic, I would assume you would need to change the output PWM period, voltage and/or current to suit, but could possibly use it as a starting point?


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## dougingraham (Jul 26, 2011)

Snakub said:


> I know that the Soliton does this but has it been discussed somewhere on here about how to make your stock fuel gauge represent your state of charge?


The Soliton does not do this.


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## frodus (Apr 12, 2008)

After all the time you spend with a microcontroller, isolating and filtering the voltage and current, powering it, building a board, and coming up with an algorithm that outputs a state of charge, you'd be better off just buying one of those devices IMHO. To accurately judge SOC, you need to measure Ah in and out of the pack, so it's not trivial.

There's a few others, but they're not much different in price:
http://webshop.evlithium.net/product_info.php?products_id=83
http://www.donrowe.com/accessories/me_bmk.html
http://evolveelectrics.com/E-Xpert%20Pro.html
http://minibms.mybigcommerce.com/products/EV-Display.html
http://ebikes.ca/drainbrain.shtml
http://www.emotorwerks.com/emw3/product/ev-dashboard-by-emw-basic-edition/


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## dladd (Jun 1, 2011)

i use the emotorwerks version, just a repackaged minibms Evdisplay with a bluetooth sender. I initially liked it mostly because it used a hall effect sender so it does not require added connections in the traction pack for a shunt. As it turns out, the sender is too small to fit over a 2/0 cable, so I used their bar anyway, so I'm still adding in two more connections in the traction pack. 

No matter what though, you will be needing to measure amps in/out. It can be done in the controller (my controller does have a fuel gauge output, but I don't use it), but you will miss any loads from the DCDC or heater (or other accessories). More significantly, the controller does not 'see' charging, so it is a digital reset to full when the voltage hits a set point. Makes it useless for partial opportunity charging measurements.


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