Date:         Fri, 21 Apr 2000 08:26:51 -0700
Reply-To:     David Greenland <dave.g@MINDSPRING.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Greenland <dave.g@MINDSPRING.COM>
Subject:      Re: LP tank level detection proposal, its Friday..
In-Reply-To:  <005901bfaba3$304af160$8813a0d1@default>
Content-type: text/plain; charset="US-ASCII"

Doesn't the Eurovan have a propane level sensor in it's tank ?

I had a quick tour of this guys EV Westy a few months ago while camping.
He borrowed my shore power cable to make Margaritas, so I'm still a little
fuzzy on some of the things from that evening.

Dave.
'91 Westy.

on 4/21/00 8:05 AM, Mike Miller at mwm@LANSET.COM wrote:

> I went camping earlier this week.  Fired up the stove for dinner and, yup,
> was out of propane.  Had to drive to town and fill up [?, it took 1.75
> gals...very slowly.  Something wrong?] so I'd definitely be interested in
> some way to tell what the level is.
>
> Mike
>
> ----- Original Message -----
> From: "Ezra Hall" <ehall@TOGETHER.NET>
> To: <vanagon@GERRY.VANAGON.COM>
> Sent: Friday, April 21, 2000 5:40 AM
> Subject: LP tank level detection proposal, its Friday..
>
>
>> Given that it is Friday now, I will start another thread..
>>
>> I searched the archives for info on detecting Liquid Propane level in the
>> Manchester tank. It seems there are no elegant solutions. Pressure is not
>> an indication of propane level until there is no liquefied propane left in
>> the tank, too late unless you happen to be near a filling station, plus
>> pressure is temperature dependant. A mechanical float would require
> welding
>> and re-certification of the tank, I am not interested plus I couldn't find
>> a sensor to weld on! That leaves thermal methods. Detection of difference
>> in temperature along the outer surface of  the tank requires high flow
>> rates to cool the liquid through adiabatic expansion, we don't flow a lot
>> of propane with Westy appliances, so this doesn't work well. The only
>> practical method remaining (sure you could use acoustical waves or RF, but
>> that gets expensive and complicated) is detection of thermal resistance
> and
>> mass. Presence of LP on the other side of the canister wall decreases
>> thermal resistance and increases thermal mass to absorb heat whereas
>> portions of the tank with only gas have a relatively higher thermal
>> resistance and smaller thermal mass. Liquid crystal level gauges take
>> advantage of this by measuring temperature at the surface of the tank when
>> heat is applied to the surface. This elegant solution is described in the
>> archives as the "fling the boiling water" method. Ok, as you can guess by
>> now, I want some sort of electronic warning that tells me the tank is low.
>> Unlike my recent thread on towing a wheelbarrow sized motor to power
> you're
>> A/C system while camping, I think this concept is actually fairly straight
>> forward to implement, the question is, how much interest would there be
> for
>> such a system? Well, here goes:
>>
>> - To apply heat to the tank, an electrical heating element will be used (a
>> flat thin film strip)
>> - To detect temperature, inexpensive thermistors will be used
>> - A minimum of two sensors is required to detect that LP is below a
>> threshold, more sensors could be used for finer granularity
>> - In the two sensor scenario, one thermistor is placed at the desired
>> liquid level threshold, the second would be used to set the compare
>> temperature of a gaseous portion of the tank (near the top)
>> - A simple op-amp window comparetor would be used to compare voltage from
>> the level sense to the voltage from the reference sense. The window will
> be
>> set large enough to prevent false readings, ie. A certain temp delta will
>> be required. Of course, measurements are only taken during or after heat
>> application via the heating strip.
>> - Additional level sensors and comparetors could be added for additional
>> levels of granularity
>>
>> This really is a simple solution. The only difficult part will be affixing
>> the sensors to the tank, perhaps a stainless steel band around the tank
>> could hold them in place vs. an adhesive that could fail. The electronics
>> and LED(s) could be placed in the same housing with the batt and water
>> level sense. When you flip the switch, you would also get an LP reading.
> If
>> there is enough interest, I can develop this into a product and sell to
>> list members at a decent price. The above should be enough info for anyone
>> with the skills to fabricate and build such a device. Anyone interested?
>> Thanks,
>> Ezra (going camping this weekend, with full LP tank)
>> '88 Westy, 94K
>> '86 944, 260K