Re: [DML] Auto Transmission Seal controllers

[Jeff Angwin <jangwin@xxxxxxxxx>]

Hi Marc:

My design is mostly the original, but I improved upon it in a few ways.

First, I added a component that conditions the power to the board. It
protects against reverse voltage, over voltage and voltage spikes. Info on
this component is here: http://www.circuitprotection.com/PolyZen/ Check out
the application note on Automotive Infotainment Peripherals.

I added this component because I have heard anecdotal evidence that the
original CG's could be destroyed by simply jump starting the car. Now,
evaluating the schematic I don't understand how that can happen, but Rob
Grady has confirmed in practice that it can and does happen. With the
voltage protection circuitry added, my governor shouldn't be adversely
affected by dirty power.

Also, I did not like the fact that the solenoids were switched by power
transistors. There is an inherent voltage drop across the transistors when
they switch on, and the power dissipation (ie heat) across the transistor is
proportional to the voltage drop times the current flowing. Having to heat
sync them is a pain, and extra heat and vibration in the enclosed box only
serves to hasten the degradation of the unit. So, I replaced the power
switching transistors with this optically isolated solid state relay:
http://www.clare.com/home/pdfs.nsf/www/LCA710_R07.pdf/$file/LCA710_R07.pdfIt
has a typical on resistance of 0.1 ohm, which is about an order of
magnitude lower than that of the power transistors. In fact, I mount all
components in an enclosed box and I don't have to worry about heat
dissipation.

Of course I implemented the circuit mods that are done when the old boards
are re-worked: changing electrolytic capacitors for tantalums, and adding
bypass capacitors and diodes. I also swapped out a few components just to
ease manufacturability. For instance, I use a single LM339 quad comparator
in place of the two separate op-amps (leaving 2 comparators unused), and am
using common 1N914 switching diodes throughout.

I hope that helps!

---Jeff---
VIN 3034



On Wed, Dec 2, 2009 at 5:01 PM, Marc Levy <malevy_nj@xxxxxxxxx> wrote:

>
>
> Jeff,
>
> I am wondering how the design is "improved"? The Renault design is quite
> simple and reliable. Most failures of these devices are due to blown
> capacitors or bad connections internal to the unit (assembly issues).
>
> While I have no idea how your device works, I can't imagine it could be any
> simpler than the original.
>
> I do agree, The "piggyback" idea is great for someone who does not want to
> crawl under the car to repair/swap the broken one.
>
> Marc
>
>
>  _
>


[Non-text portions of this message have been removed]



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