<VV> Thermister Swap
RAMBLERPAT at aol.com
RAMBLERPAT at aol.com
Mon Sep 1 19:13:42 EDT 2014
J. B.,
Sounds interesting, I will study the situation. I was mindful of
keeping the stock appearance of course, I forgot to add that earlier. So, in so
many words, the key to utilizing the Rochester unit appears to find the
correct capacitor in order to use the stock gauge. Like I mentioned earlier, I
initially was searching for an affordable AC thermister used or otherwise,
and then I stumbled upon this. My need for a head temp reading is still my
priority at this point, however, I would like to address the gap for
available and affordable thermisters for both future and present Spyder and 140
Corvair owners. It is too bad AC or someone else never continued
production, but I can see a small market for them as a possible reason. However, they
seem rather simple in design, and they use a small amount of materials.
Patrick
In a message dated 9/1/2014 2:51:49 P.M. Eastern Daylight Time,
jb30343 at windstream.net writes:
Patrick, Talk with your brother. This stuff is not rocket surgery. I
have no formal training in electronics but I have managed to design many
simple circuits to deal with various needs where off the shelf solutions
were either unavailable or expensive. You will need to do a little
algebra but nothing scary. Parts like op amps, resistors, small
capacitors and small transistors are insanely inexpensive. You can burn
a lot of them up without any real impact on your wallet. There are some
good cookbooks and websites that will give you basic schematics that you
can adapt to fit your needs. You can do this.
The Rochester part you're looking at is just a thermistor in a proper
housing. The thermistor is just a resistor that changes value with
temperature. The problem you're trying to solve is that the values and
the curve of the new part is way different than that of the old part.
Here's a little of what I remember thinking 15 years ago. I do not have
a great memory. The circuit in the Corvair is just car's nominal 12
volts fed through the thermistor and the gauge. My thought was to
essentially put an op amp circuit in place of the gauge and use that
circuit to feed the stock gauge. An op amp is just a tiny integrated
circuit amplifier. Using two or more, working together and against each
other it should be possible to bash the output into something closely
resembling the stock thermistor. If I got any farther than that, I
don't remember the details.
The Arduino in an off the shelf microprocessor that is designed for
hobbyists and experimenters. It's like a digital erector set. To use
it in an application like this, you would put an Analog to Digital (A to
D) converter in place of the stock gauge. The converted digital signal
gets fed into the processor. You write a program for the processor that
would basically be a Look Up Table (LUT) the processor then tells the
Digital to Analog (D to A) convertor what voltage to feed the stock
gauge. The Arduino route would be a lot bulkier and more expensive than
a "roll your own" solution made out of a few Op Amps. It would also be
more accurate. The really intriguing part is that you would then have a
computer riding around in your Corvair which could be used for all sorts
of other applications. --J.B.
RAMBLERPAT at aol.com wrote:
> J. B., My oldest brother is the electrical engineer in the family and
> he is retired in a different state, on the other hand I am a social
> worker with little electrical trouble shooting knowledge. I was
> thinking that the Rochester unit is already DC because it can be used
> in light aircraft (if that is what you were referring to). Not sure
> what the voltage would be in those though. The rest of what you were
> saying make as much sense to me as algebra which is close to none. At
> some point I may try to purchase one of these Rochester units and see
> which direction it leads me, and perhaps learn a few things along the
way.
> Thanks!
> Patrick
> In a message dated 9/1/2014 12:29:15 P.M. Eastern Daylight Time,
> virtualvairs at corvair.org writes:
>
> Sounds like you might want to take on this project, Patrick. I
> started
> down a similar road about 15 years ago. It's a worthwhile project
> but
> it wasn't anything I wanted to pursue. Here's more or less where I
> left
> it. A few things have changed. There were no bare thermistors on
> the
> market that were close to following the curve of the one used in the
> Corvair. I had not considered replacing the gauge nor was the
> Rochester
> unit you found available when I was looking. Replacing the gauge
> might
> be a good option but it will likely mean sacrificing stock
> appearance.
> I don't think you'll be able to match the Rochester sensor to the
> stock
> gauge with just a resistor network but you should be able to get
> close
> with an op amp or two. That's the direction I was going before I
> decided not to proceed. If I were taking on that project today, I
> would
> think about using an Arduino processor, an A to D converter, a D to A
> converter and a LUT. The Arduino is major overkill for a job like
> this
> but once it's in the car I'm sure you could think of numerous
> other jobs
> for it. If you have the time, you might enjoy working out a
> solution.
> Have fun. --J.B.
>
>
>
> Patrick via VirtualVairs wrote:
> > To all, I have been reading the feedback on the ROCHESTER 3080-38
> > TEMPERATURE PROBE that I happened upon while trying to save a
> few dollars
> > on the unfortunate shortage of affordable thermisters
> situation. It is true
> > that the $300 - $400 needed to purchase an NOS AC thermister is
> > prohibitive for many Corvair owners, and the $80 or so
> necessary for a used one is a
> > risk as well. In addition, I well aware that this is the way it
> is in the
> > old car business world and hobby. For theses reasons, and
> others, I was so
> > excited when I discovered the new Rochester temp probe for $80
> in the 2015
> > Spruce Aircraft catalog and I recognized the possibilities that it
> > represents.
> >
> > It appears that no one here knew of this so the Rochester
> 3080-38 is
> > untested in a Corvair auto application as of today of course.
> However, the
> > good news is that there is VV confirmation that this unit it is
> essentially
> > the same dimensions including the thread size as the AC
thermister.
> > Perhaps, this is half the battle right there. It is also my
> understanding is that
> > this thermister will work for us if we match it to a compatible
> gauge,
> > after all it is designed to measure head temps in an air cooled
> engine. This
> > discovery may help some of us save some dollars and give us an
> upgrade to
> > more efficient and reliable equipment too. Though I have not
> researched any
> > head temp gauges yet I am hopeful the someone out there will
> try this set up
> > and let us know how it works, provide us with the costs, and
> let us know if
> > it was worth the efforts.
> >
> > Patrick Laus
> >
> > 64 Spyder Coupe
> > Metro Detroit area
> >
> >
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