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Hi from Australia - Why globes and resistors keep continually blowing

486 views 0 replies 1 participant last post by  PawRocks 
#1 ·
Hi Everyone,

I'm new to the forum. I was looking for a repair manual for my Nissan Terrano Diesel - Manual 5 speed. Haven't used it for a while and I needed to move it but couldn't engage the clutch today :( the pedal just went all the way to the floor. I've read the forums on this issue and it mentioned that I had to bleed the nibs in three different places, check for corroded lines and top up the fluid in the clutch master cylinder.

This is probably a stupid question but do you use brake fluid in the clutch master cylinder or is there a specific fluid (different specifications) for the clutch master cylinder?

BTW my background is in electronics and computers, a bit of car maintenance, model making, welding and metal fabrication. I'm really a hands on person and like to make things, fixing is kinda an off shoot to all of this :)

OK, now for the good bits. On my old car, I've found that partially corroded connectors or poor contacts were causing the same globes to keep blowing nowhere near the expected globe life (compared to the same globe in another socket). Even though the globes appear to work normally, the contact is sufficient enough to allow an initial current for the globe to work. What is actually happening is that when the car is running, the vibration effect is causing arcing inside the corroded contacts sending spikes to the connected globes. The instantaneous voltage and current produced due to the spike can well exceed the rating of the globe. Even though the globe can absorb this spike due to its short burst (or duty cycle) it places excessive stress on the material in terms of both heat and in some cases movement as well, thereby reducing its working lifespan. It's a bit like having a clunk in the motor, if you don't fix it and make it run smooth, it will eventually cause the motor to break much sooner than it's usually expected to last.

In a nutshell, the life of the bulb is reduced, in some cases drastically, due to arcs caused in poor or corroded contacts. These may be either connectors delivering the power to the globe or the globe sockets themselves.

This is also the case for the blower resistors mention in one of the threads. Besides having to have the resistor in the air stream to keep it cool, some people have soldered the resistor in, thereby eliminating the poor contact that may have damaged the resistor in the first place. It also sounds like the blower resistor is exceeding its power rating at ambient temperature and needs airflow to keep it from failing.

If you are replacing the blower resistor with a DIY, you can use two in series or two in parallel or combinations of these, but before replacing it, it's important to know what the value of the original resistor is and its approximate power rating.

Note: Running the resistor at a much lower power consumption than its rated value will keep it cooler because it can dissipate the heat much easier.

2 resistors in series (identical values)
Total resistance is twice the resistance of one resistor (due to identical values)
Total power rating is twice the power rating of one resistor (due to identical values)

3 resistors in series (identical values)
Total resistance is triple the resistance of one resistor (due to identical values)
Total power rating is triple the power rating of one resistor (due to identical values)

2 resistors in parallel (identical values)
Total resistance is half of the resistance of one resistor (due to identical values)
Total power rating is twice the power rating of one resistor (due to identical values)

3 resistors in parallel (identical values)
Total resistance is one third of the resistance of one resistor (due to identical values)
Total power rating is triple the power rating of one resistor (due to identical values)

Power dissipated in the resistor is approx = measured current * measured current / resistor value. (it's approx due to motors generating a fair bit of noise when running).

PWM (pulse width modulation) circuits are normally used these days to control DC motors to make the power consumption more efficient. They are used to speed control the fans on the CPU heatsinks in all the new computers and laptops.
BTW you can't just wack any PWM circuit on any DC motor and hope that it will work. It's quite dangerous if you haven't designed or spec’d it correctly and you can have switch mode components exploding through sheet metal like bullets. Even if it appears to work initially, poorly designed or spec’d PWM may fail at any time with catastrophic results. So for all the Arduino fans, be careful!

That's it 4 me :)

Say hi if you like >:D
 
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