#### stspringer

- May 10, 2019

- 116

- Joined
- May 10, 2019

- Messages
- 116

I watched this video and I have an electric motor 12 volt 7.2 watt .06 amps "load amps". I did the math for my motor copying the tutorial example for his "load" is solenoid valve spec .67 watts at 12 volts. His device had really low watts .67

Question 1: did I get it right, the math? I came up with a 220k resistor for the base on the transistor.

Question 2: can this transistor handle 600ma?

Please advise

Thank you for any help

Tutorial: How to design a transistor circuit that controls low-power devices
pn2222a transistor beta "gain" of 100

load is solenoid valve spec .67 watts at 12 volts

what is current? .67 /12 = .0558 amps x 1000 = 56ma

the transistor must handel 56 ma

transistor beta "gain" of 100

IB the base current Ib = 56ma/100 = .56ma

.7 is an intrinsic value to silicon transistors this is an NPN

Ib = 5v - .7 / rb

.7 - 5 = 4.3

now we are going to increase the ma to be safe so instead of .56ma we will use 1 ma

change 1 ma to amps 1 /1000 = .001

4.3 /.001 = 4300 ohm resistor

they dont make 4300 ohm resistors so use a 4.7k resistor

=============================================================

12 volt electric motor 7.2 watts

load is motor valve spec 7.2 watts at 12 volts

what is current? 7.2 /12 = .06 amps x 1000 = 600ma

the transistor must handle 600 ma

transistor beta "gain" of 100

IB the base current Ib = 600ma/100 = 6ma

.7 is an intrinsic value to silicon transistors this is an NPN

Ib = 12v - .7 / rb

12 - .7 = 11.3

now we are going to increase the ma to be safe so instead of 6ma we will use 6ma x10 = 60 ma

change 60ma to amps 60/1000 = 0.06

11.3/.06 = 188.333333333 = they don't make 188k resistor so use a 220k resistor

could this be a 220ohm resistor and not a 220k resistor? not clear

Question 1: did I get it right, the math? I came up with a 220k resistor for the base on the transistor.

Question 2: can this transistor handle 600ma?

Please advise

Thank you for any help

Tutorial: How to design a transistor circuit that controls low-power devices

load is solenoid valve spec .67 watts at 12 volts

what is current? .67 /12 = .0558 amps x 1000 = 56ma

the transistor must handel 56 ma

transistor beta "gain" of 100

IB the base current Ib = 56ma/100 = .56ma

.7 is an intrinsic value to silicon transistors this is an NPN

Ib = 5v - .7 / rb

.7 - 5 = 4.3

now we are going to increase the ma to be safe so instead of .56ma we will use 1 ma

change 1 ma to amps 1 /1000 = .001

4.3 /.001 = 4300 ohm resistor

they dont make 4300 ohm resistors so use a 4.7k resistor

=============================================================

__my electric motor 12 volt 7.2 watt .06amps load amps__12 volt electric motor 7.2 watts

load is motor valve spec 7.2 watts at 12 volts

what is current? 7.2 /12 = .06 amps x 1000 = 600ma

the transistor must handle 600 ma

transistor beta "gain" of 100

IB the base current Ib = 600ma/100 = 6ma

.7 is an intrinsic value to silicon transistors this is an NPN

Ib = 12v - .7 / rb

12 - .7 = 11.3

now we are going to increase the ma to be safe so instead of 6ma we will use 6ma x10 = 60 ma

change 60ma to amps 60/1000 = 0.06

11.3/.06 = 188.333333333 = they don't make 188k resistor so use a 220k resistor

could this be a 220ohm resistor and not a 220k resistor? not clear

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