This is kind of off topic, yet it's on topic. It's not AT ALL addressed at any one or any thing that has happened with this project. It's merely a rant against shotty workmanship and allowing the accounting department to make critical decisions...
It's on topic because recently we had a conversation about necessary capacitance, and because I have been spec'ing components for the resolver decoder.
For a while now, I've noticed various electronic gadgets fail because of a power supply failure. They will inexplicetly not power up, or cycle on and off rapidly.
I've had a bunch of LED lights do this, which for an ecologically minded person is pretty frustrating. They are supposed to be ecologically friendly because they use little energy and because they're supposed to last a long time - virtually indefinitely. The LED lights will fail by blinking at about 60hz. Sometimes they warm up and stabilize, but eventually, they will just blink.
This is about after one year or even shorter. Not good for something that's supposed to have a 10yr + life span. Especially not good because there are obviously a lot more resources involved with one of these light bulbs when compared to an incandescent light.
I've suspected these devices have failed because they underspec'd a critical capacitor in the power supply. It's very easy to do this with cheap electrolytic capacitors.
To test this, I tore apart one of those LED lights. Unfortunately, the way it was made, you couldn't take it apart without breaking the case. BTW, the case had a very impressive heat sink/fin setup so the LED's could stay cool and not fail prematurely.
Inside this light bulb was a TINY switch mode power supply. The power supply had no way to dissipate heat. It was not connected AT ALL to the heat sink and was wrapped in tape and covered with a case that allowed no air movement. The workmanship was a little shoddy, especially when compared to the heat sink. As I suspected, there was a relatively large 4.7uF electrolytic capacitor. Upon further inspection, I found the Mosfet (the main power switch) with no way to connect its heat sink to anything..... -no I can't believe this - except the bottom of the electrolytic capacitor!!
What a bunch of idiots - the main heat generating device in the power supply is directly connected to the ONE thing that needs protection from excess heat....
Just to see if I was right, I grabbed a giant 470uF capacitor out of my parts bin and replaced the 4.7uF capacitor with it.
la LA la la - - the light works! Too bad I destroyed it while taking it apart.
So, back to our project. What brings this up is I was spec'ing a 10uF capacitor for my circuit. For $1.00 you can purchase a ceramic surface mount capacitor with an infinite life. For $0.44 you can spec the cheapest electrolytic option, with a 100C maximum temperature and a 1000 hr. life.
Is saving the $0.56 worth it? Not in my opinion. It's annoying for your kitchen lights to fail, but if this circuit fails, you'll be sitting by the side of the road, wondering what happened...
It may be tempting when spec'ing parts for your car ( say this motor controller ) to save money on each little part, adding up to perhaps some significant cups of coffee. On the other hand, you might consider the reliability of your transportation as more important.
MIL spec? A little over the top. OTOH, automotive & high reliability parts are definitely worth it.
- E*clipse