<VV> Thermister Swap
MarK Durham
62vair at gmail.com
Tue Sep 2 16:57:31 EDT 2014
Guys, keep in mind that there are companies out there that can add the
Rochester gauge to the same instrument cluster and repaint it to be exactly
stock. Keep in mind the working bits are behind what you see, all they
would need to do is attach the new unit so the needle pointer is in the
correct spot. That isn't that hard to do. So, if the resister thing does
not work or ends up being unsatisfactory, that option is available as well.
Usually, all it takes is drilling a few screw holes and mounting the gauge,
so may not even need a paint touch up.
I know Ted Brown used a resister in line with a temperature probe in the
EFI kits sold through Clarks to compensate for the differing temp curves of
the air cooled motor versus the water pumper the computer came off of. I
saw the temperature curves at the full range of OHM's cold to hot, and
while not as good as would be expected for a gauge reading (hence my
comment above), it was good enough at the proper time and proper resistance
reading to get the computer to switch from its cold to hot/run setting for
mixture at the right time.
I know this changes the original look, but the EM dash's speedo's are
nothing more than a 90 degree sweep stretched out over a stretched flat
face, and a long enough needle to read over it all. My thought was to have
the speedo face redone in the exact same style lettering, in a circle arc
instead of stretched out like it is, then add the VDO oil pressure and CHT
guages, again, in the same style lettering, tucked up to and on either
either side of the speedo. Then, since I would no longer need the
temp/press idiot lites, I would add a digital tach in that lower window.
They have tiny LED lites that would not show unless on I would add for the
low voltage lite, in case the belt flipped off.
Mark Durham
Hauser, Idaho
62 Monza coupe Red/Red 4 speed
On Mon, Sep 1, 2014 at 4:13 PM, Patrick via VirtualVairs <
virtualvairs at corvair.org> wrote:
>
> 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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