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NPP Reverse-Engineered - Full Open/Close, Non-Factory-NPP Retrofit

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NPP Reverse-Engineered - Full Open/Close, Non-Factory-NPP Retrofit

 
Old 03-10-2019, 05:19 PM
  #221  
ttk53
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I got my board installed it worked great on first tests. But today on a longer drive it stopped working twice. I'm not sure if its because it's still new and I played with it a little to often or if I have a problem. I do not use the switch attached to the board I leave it in the 80%/closed position and switch the 12volt source feeding the board and valves and let the spring open the valves.
1.The switched 12 volts goes to both the board and valve do I need to wire the valve 12 volt separate? 2. The LED's on my board do not light up should they?
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Old 03-12-2019, 07:13 PM
  #222  
fryfrog
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As the components on the board heat up, it causes the signal it generates to change a little bit. The valves are expecting a *very* specific signal to hold themselves closed, when they no longer get it... they open up. My board is mounted near the CPU, in the trunk, under the board and over the exhaust. After a drive, it doesn't work anymore. On hot days, it also doesn't work anymore. I haven't bothered to try and fix it, but if the board were somewhere cooler it'd help. Or maybe a little fan on it?
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Old 03-12-2019, 08:14 PM
  #223  
FYREANT
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Originally Posted by fryfrog View Post
As the components on the board heat up, it causes the signal it generates to change a little bit. The valves are expecting a *very* specific signal to hold themselves closed, when they no longer get it... they open up. My board is mounted near the CPU, in the trunk, under the board and over the exhaust. After a drive, it doesn't work anymore. On hot days, it also doesn't work anymore. I haven't bothered to try and fix it, but if the board were somewhere cooler it'd help. Or maybe a little fan on it?
mine did something similar and I disconnected them a while back when I finished my big horsepower build. I need to hook them back up and try and fix it.
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Old 03-12-2019, 09:47 PM
  #224  
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I just found a read this entire thread (I have a 2014 C7 Z51 w/NPP and various nice bits).

I have to give credit to Theta for a nice progression of versions of the design, going to the trouble of finding the right connector, clean layout, etc.

But I would also point out two issues I see: i) the use of an LM317-class regulator when an LM2940-class (automotive) regulator (with all sorts of additional protections) would have been a better choice, and ii) the use of RC components to achieve the right duty cycle. I saw that Theta had arguments against using an Arduino (I'm no fan of Arduinos), and that's OK, but using a good modern microcontroller with a stable (internal) oscillator over temperature will likely yield much better results in terms of ease of manufacturing (no tuning required) and temperature stability.

I don't have the bandwidth to tackle this project right now, but if there is someone who does, please consider the above for a next-generation design.

I suspect messing with the exhaust system and legal ramifications may be one reason why this hobby-level solution hasn't gone further.
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Old 03-13-2019, 01:56 PM
  #225  
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Since I'm sick today and working from home, I'll elaborate a little on my post.

I suspect (but do not know for certain) that the NPP valve controllers are much more sensitive to duty cycle, than to frequency. Why? Because having an accurate frequency reference costs money, and GM knows how to pinch pennies. Yes, an el-cheapo 32kHz crystal (which is actually not that cheap, in the overall scheme of things) might work, but over the temperature range in that area of the car, the frequency drift is going to be pretty awful, you still need other components that take that base frequency and do something with it. This adds many pennies (or even, dollars) pretty quickly to the cost of the valve controller.

Now, if this DIY project used a microcontroller instead, there would never be any duty cycle drift, over temperature. Yes, the frequency stability of the signal might move around a bit (e.g., the 200Hz signal might be 199Hz or 201.5Hz), but the duty cycle would remain rock-solid (e.g. at 80%), independent of the temperature of the circuit. Simply because the duty cycle is set by registers in the microcontroller, and the register values do not change over temperature.

Anyway, if I were chasing down temperature-related problems in these designs, this is the approach I would take to fix it.
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