Hi Guys!
OK I'm not a real newbe but lets say I'm not skilled to built regulators with transitors...
I' building a a regulator for my boss's
oldtimer. Its an old Chevy which did use 6V battery supply. Now its rebuilt to a modern 12V system.
Problem the ventilation fan still is a (very special) 6V motor. The fan motor shall stay in the car and so I looked how to regulate the supply down to 6V. The current demands are high: between 3 - 5 A. I can't use a LM317/350 it too much for them. I did not find a PWM module which is cheap enough.
So I chose to built a "Series Regulator" controlled by a Z-Diode. I thought that really simple....
Attached is my schematic. I use a TIP 3055 and Z-Diode 7,4V (500mW).
The Tip is mounted to a heat sink. The diode get a voltage by the 470Ohm resistor.
Input and output side is stabelized by 100µF cap.
NOW MY PROBLEM: I expected appr. 7.4V - 0.7V = 6.7V on the motor. (It may drop a bit due to the load etc..)
BUT !! I get 2,7V.
What would you check? What do you expect? Is the TIP 3055 maybe not the right choice or is Base- Emmitter leakage problem present? What I can say is that I have plenty of current available and the input voltage is not dropping down
OK I'm not a real newbe but lets say I'm not skilled to built regulators with transitors...

I' building a a regulator for my boss's
Problem the ventilation fan still is a (very special) 6V motor. The fan motor shall stay in the car and so I looked how to regulate the supply down to 6V. The current demands are high: between 3 - 5 A. I can't use a LM317/350 it too much for them. I did not find a PWM module which is cheap enough.
So I chose to built a "Series Regulator" controlled by a Z-Diode. I thought that really simple....

Attached is my schematic. I use a TIP 3055 and Z-Diode 7,4V (500mW).
The Tip is mounted to a heat sink. The diode get a voltage by the 470Ohm resistor.
Input and output side is stabelized by 100µF cap.
NOW MY PROBLEM: I expected appr. 7.4V - 0.7V = 6.7V on the motor. (It may drop a bit due to the load etc..)
BUT !! I get 2,7V.
What would you check? What do you expect? Is the TIP 3055 maybe not the right choice or is Base- Emmitter leakage problem present? What I can say is that I have plenty of current available and the input voltage is not dropping down