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Hi Guys/Gals,

Anyone know how the curtis fuel gauge works? Does it use the sag in the
voltage of the battery pack to somehow determine the Ah removed?

Cheers
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To your point about the single battery connection: I just wrote to
Curtis about that issue, is it the first battery or the whole pack.

Curtis responded: You are correct in your assumption. In our industry
a battery is referred to as the entire string of individual cells
making up the 'battery'.

-----Original Message-----
To: [email protected]
Subject: CURTIS Model 900 R Installation Question

This is taken from the installation section of the manual on your web site:

Document number "WEB 53006B pdf.pdf"

>Connecting Model 900R
>CURTIS Model 900 R fits into a dash-panel cutout
>measuring 2 1/16 " (52 mm). The unit's positive (+)
>terminal connects to the first battery positive (+) terminal
>closest to the battery. The unit's negative (-) terminal
>connects to the first battery negative (-) terminal closest
>to the battery.Wiring must go directly to the battery.
>Do not route through the key switch or contactors.
>The LED display will always be "ON."

The connection reference to the "first battery" positive and negative
makes it sound like your only connecting to ONE battery. But, I assume
you need to connect to the very most positive and most negative to
measure the total traction battery pack voltage.

Can you help me understand this please?
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Robert Chew wrote:
>> Anyone know how the curtis fuel gauge works? Does it use the sag
>> in the voltage of the battery pack to somehow determine the Ah
>> removed?

James Massey wrote:
> To the best of my knowlege, there are three types of Curtis "fuel
> Gauge":
> 1) The true Ah counter type with a 'sample cell' that connects in
> parallel to a single cell of the traction pack, that counts the
> Ah's in and out of the sample cell to determine the pack's
> representative state of charge.
>
> 2) The later version that uses an electrolytic capacitor in place of
> the cell, a bit less accurate.

1) and 2) describe the Anderson SOC gauges. They patented these
techniques, so I doubt Curtis has used them.

> 3) an expanded-scale voltmeter type.

This is how the Curtis gauges I've seen have worked. Basically, they are
an expanded-scale voltmeter. Additionally, there is circuitry so they
only move downward, so in effect they read the minimum battery voltage
seen. The gauge "sticks" at this lowest-voltage reading until the
charger takes the pack voltage high enough for long enough to "reset" it
to full (i.e. pack voltage exceeds about 2.5v/cell).

--
"Never doubt that the work of a small group of thoughtful, committed
citizens can change the world. Indeed, it's the only thing that ever
has!" -- Margaret Mead
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net


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