Solar Tracker Help pt.2

[jmarmontgomery]

First off, thank everyone for your continued help
So I did some webcrawling and came across this circuit...im just havin a little trouble picking the correct components.
i 'm changing certain components, however the changes have not been reflected on the diagram... I will list them...
V1=3.0V
V2=1.5V
V3=3.0V
Small DC Motor running off of 600-800mA..
LDR provide 300K ohms in total darkness
LM339 op amp...max Input current of 50mA and max ouput is 20mA..

Self Constructed H-Bridge
NPN 2N2222
1) hfe=200
2) max Ic=800mA Ib=200mA
PNP 2N3906
1) hfe at 10mA > 50
2) max Ic=200mA Ib=100mA


I tried building Boncuks circuit, however, I burned up a transistor, but the motor ran.. and the circuit was just a lil too complicated for my purposes and for me to explain.

To my understanding the transistors are just acting as switches.. being that the motor is receiving its power from V3, and the output of the op amp is small, do I have to worry about my transistors burnin up because of the power demands of my motor?

 

[Boncuk]

Hi jmarmontgomery,

the circuit I provided for you allows only unidirection motor control. For bidirectional motor control the circuit requires a full H-bridge or two relays.

A transistor rated 200mA collector current won't suffice to drive a 800 - 1,000mA rated motor. It will fry very quickly.

A transistor rated 800mA collector current will be killed if you apply 200mA of base current. A beta value of 200 requires 4mA of base current for 800mA collector current.

To drive the motor safely without frying the driver transistor BD139/BD140 are a good choice.

Boncuk

 

[jmarmontgomery]

Ok, now im starting to understand transistor selection. I wasn't able to find the transistors you were talkin about; however, I think I got the idea. I picked up these.

TIP42 PNP
1) MAX Ic=10A
2) hfe > 20
3) max emiiter base voltage 5V

TIP3055 NPN
1) MAX Ic=10A
2) 20<hfe<70
3) max emitter base voltage5V

Once again, I really appreciate your help..

 

[Boncuk]

TIP42 PNP TIP3055 NPN

1,000% overkill!

OK, I'll make a schematic for uni-directional control. It will use small transistors and a relay to keep the wiring simple.

Boncuk

 

[jmarmontgomery]

ok pha sho...but damn, this parts selection is a task lol...I appreciate it tho...I have a SPDT 5vDc Relay on hannd..
nominal current is 89.3mA
pick up voltage is 3.5v
drop out voltage is 0.25V

 

[Boncuk]

Solar tracker

Hi jmamontgomery,

this circuit is made for uni-directional motor control. You might omit the limit switches and connect the opening relay terminals directly to ground.

Only one relay can activated at a time and makes the motor rotate in either direction. When both relays are deenergized the motor "sees" just ground on each terminal, meaning the motor is shorted which takes care of braking action and immediate motor stop.

If the realys don't switch properly you might decrease the zener voltage down to 3V9.

Boncuk