# [EVDL] EV Fuel Gauge Driver



## EVDL List (Jul 27, 2007)

And if you'd like to experiment with "rolling your own," you'll find a 
circuit in the EVDL library.

http://www.evdl.org/docs/ev_fuel_gauge.pdf

Thanks to Rod Hower for passing this along.

David Roden - Akron, Ohio, USA
EVDL Administrator

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## EVDL List (Jul 27, 2007)

Please note that the Honeywell EV gauge is a fancy way to make an
expanded scale voltmeter
with all its limitations - it won't display SoC accurately, just give
you a feel of the
pack's voltage level which is somewhat related to its SoC but nowhere
near accurately
especially while driving.
The promoted SoC display by Ian is actually measuring current in/out the
battery
and so it will display the SoC, no matter how much your battery pack
voltage varies or not.
Note that having a "hard" = non-varying pack makes it even more
difficult to get a feel
what is going on without current measurement, you see this with modern
battery chemistries that the voltage
will stay constant over most its operational range, then suddely you hit
the knee and
it falls to the floor and you end up stranded with a dead pack, if you
rely on a voltmeter...

Regards,

Cor van de Water
Director HW & Systems Architecture Group
Proxim Wireless Corporation http://www.proxim.com
Email: [email protected] Private: http://www.cvandewater.com
Skype: cor_van_de_water IM: [email protected]x
Tel: +1 408 383 7626 VoIP: +31 20 3987567 FWD# 25925
Tel: +91 (040)23117400 x203 XoIP: +31877841130

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of EVDL Administrator
Sent: Saturday, February 06, 2010 11:39 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] EV Fuel Gauge Driver

And if you'd like to experiment with "rolling your own," you'll find a
circuit in the EVDL library.

http://www.evdl.org/docs/ev_fuel_gauge.pdf

Thanks to Rod Hower for passing this along.

David Roden - Akron, Ohio, USA
EVDL Administrator

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Information: http://www.evdl.org/help/ = = = = = = = = = = = = = = = = =
= = = = = = = = = = = =
Note: mail sent to "evpost" an "etpost" addresses will not reach me. To
send a private message, please obtain my email address from the webpage
http://www.evdl.org/help/ .
= = = = = = = = = = = = = = = = = = = = = = = = = = = = =


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## EVDL List (Jul 27, 2007)

How do you know whether you have turned the pot to the correct setting? 

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of Ian Hooper
Sent: Saturday, February 06, 2010 1:16 AM
To: Electric Vehicle Discussion List
Subject: [EVDL] EV Fuel Gauge Driver

Hi folks,

Forgive the semi-commercial nature of this posting, I thought this 
might be of interest to everyone so I hope it's OK!

A couple of months back I designed a battery gauge for EVs which 
drives the vehicle's factory standard fuel gauge in the dash, avoiding 
the need to install any extra screens/gauges/etc. We (EV Works staff) 
have been testing prototypes in many of our own EVs for a while now 
and have found it to be a very elegant and intuitive way to keep an 
eye on your battery's SoC. So we've put it into production, check it 
out here:

http://www.evworks.com.au/index.php?product=INS-EVW-FGD

As always I'm open to any comments or suggestions! Some ideas for 
extra features which have already been suggested for version 2 are the 
ability to drive a Low Fuel light when there's say 20% left, and the 
ability to open the main contactor when the pack is empty (like the 
TBS units can).

Ian Hooper
--
"Never doubt that the work of a small group of thoughtful, committed 
citizens can change the world." - Margaret Mead
http://www.evworks.com.au

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## EVDL List (Jul 27, 2007)

> Rodney Cook <[email protected]> wrote:
> > How do you know whether you have turned the pot to the correct setting?
> 
> The pdf on their website says to drain the pack to 80% soc and then
> ...


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## EVDL List (Jul 27, 2007)

Nice bit of kit there!

One comment - the file name, download link, and web page text for the 
datasheet download all misspell "gauge" as "guage".

Let's see if I understand how to use the device.

1) Start with a full pack.
2) Reset the gauge by cutting and restoring the power. It resets to 
"Full".
3) Drive around until the pack is what you want to consider Empty.
4) Adjust the pot on the device until the fuel gauge says "Empty".
5) Charge up the pack again.
6) Reset the gauge to "Full".
7) Drive around for a while, and enjoy your fuel gauge.
8) Go to step 5.

Looking over the datasheet again, it occurs to me that the device 
might be counting coulombs both directions, so that it will gradually 
update the fuel gauge while the battery is being charged. This would 
eliminate step 6 above, until the gauge is no longer accurate.

Given that I felt it necessary to ask the above, perhaps you could 
add an "Operation" section to the documentation, or "Theory of 
Operation".

I'm also curious about how much current it draws when the car is off, 
so I could figure out how long it would be safe to leave it connected 
to the 12v system.

Again, very nice work! I hope it sells well. We need solutions like 
this one.




> Ian Hooper wrote:
> 
> > Hi folks,
> >
> ...


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## EVDL List (Jul 27, 2007)

oops! I hit send too soon.

Ian, or any one else. It is not obvious to me from the pdf but I
assume one should start out with a full pack before doing the
"calibration run." Is this right. Also, how sensitive is the coil? My
only 12V source is my DC-DC which has an unswitched side and a
switched side. Will it be able to "see" the mA level parasitic load if
I externally power the sensor to get it started?

-- 
David D. Nelson
http://evalbum.com/1328

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## EVDL List (Jul 27, 2007)

Could someone explain how knowing the current at a given battery pack voltage estimates SOC? 

Thanks,
Barry Oppenheim
Wrightstown, PA
www.JustAnotherEVConversion.blogspot.com 
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## EVDL List (Jul 27, 2007)

On Sun, Feb 07, 2010 at 03:46:05PM +0000, [email protected] wrote:
> Could someone explain how knowing the current at a given battery pack voltage estimates SOC? 

Integration.

-- 
Willie, ONWARD! Through the fog!
http://counter.li.org Linux registered user #228836 since 1995
Debian3.1/GNU/Linux system uptime 785 days 5 hours 32 minutes

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## EVDL List (Jul 27, 2007)

> Willie McKemie <[email protected]> wrote:
> > On Sun, Feb 07, 2010 at 03:46:05PM +0000, [email protected] wrote:
> >> Could someone explain how knowing the current at a given battery pack voltage estimates SOC?
> >
> ...


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## EVDL List (Jul 27, 2007)

On Feb 7, 2010, at 3:46 PM, <[email protected]> 


> <[email protected]> wrote:
> 
> > Could someone explain how knowing the current at a given battery
> > pack voltage estimates SOC?
> ...


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## EVDL List (Jul 27, 2007)

The question is somewhat confusing as the correct way to
measure SoC ignores the battery voltage completely (in theory)
and simply accumulated the current in/out integrated over time
to count the Ah still available in the battery.

Hope this clarifies,

Cor van de Water
Director HW & Systems Architecture Group
Proxim Wireless Corporation http://www.proxim.com
Email: [email protected] Private: http://www.cvandewater.com
Skype: cor_van_de_water IM: [email protected]
Tel: +1 408 383 7626 VoIP: +31 20 3987567 FWD# 25925
Tel: +91 (040)23117400 x203 XoIP: +31877841130

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Willie McKemie
Sent: Sunday, February 07, 2010 10:03 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] EV Fuel Gauge Driver

On Sun, Feb 07, 2010 at 03:46:05PM +0000, [email protected]


> wrote:
> > Could someone explain how knowing the current at a given battery pack
> voltage estimates SOC?
> 
> ...


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## EVDL List (Jul 27, 2007)

With this discussion of fuel gauges, I was wondering if most fuel gauges 
work like the one in my car. It has two inductors in parallel. One 
inductor has a fixed current going through it. The current through the 
second inductor varies depending on the fullness of the gas tank. 

Thanks.

Bill

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## EVDL List (Jul 27, 2007)

That is one of the more modern and popular gauge types, the "magnetic"
gauge.
Some background info with pictures of actual units here:
http://mgaguru.com/mgtech/electric/fg_05.htm
http://www.nls.net/mp/volks/htm/fuel_ga.htm
http://www.aa1car.com/library/fuel_gauge_diagnosis.htm


Cor van de Water
Director HW & Systems Architecture Group
Proxim Wireless Corporation http://www.proxim.com
Email: [email protected] Private: http://www.cvandewater.com
Skype: cor_van_de_water IM: [email protected]
Tel: +1 408 383 7626 VoIP: +31 20 3987567 FWD# 25925
Tel: +91 (040)23117400 x203 XoIP: +31877841130

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Bill Dennis
Sent: Sunday, February 07, 2010 11:05 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] EV Fuel Gauge Driver

With this discussion of fuel gauges, I was wondering if most fuel gauges
work like the one in my car. It has two inductors in parallel. One
inductor has a fixed current going through it. The current through the
second inductor varies depending on the fullness of the gas tank. 

Thanks.

Bill

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## EVDL List (Jul 27, 2007)

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