Maker Pro
Maker Pro

Battery charger power supply/circuit question...

I am using a battery charger for a power supply for a circuit i am
building to control the speed of a DC motor. here is my circuit (view
in notepad)

|
| +5 V
| |
| .-.
| 470 | |
| 1/2 W | |
| '-'
| |
| o---------> to MOSFET
| | Gate
|PRN ___ |/
| o-|___|-o-|2N3904
| 2.2K | |>
| .-. |
| 10K| | |
| | | ===
| '-' GND
| |
| ===
| GND
|



V+ from battery charger
(18.8 V, 10A)
|----.
| |
.-. |
Motor ( X ) -
'-' ^
| |
o----'
| D1
|
||-+
||<- PM
from 2N3904 -->-----||-+
|
|
|
Ground


Power MOSFET IRF510


Anyway, there are serious problems with this circuit. It keeps blowing
up, haha. Especially the 2N3904 transistor. Any ideas? Is a battery
charger suitable for a power supply? Are there modifications i need to
make? Any help would be great. Thanks, Lucas
 
J

James Thompson

Jan 1, 1970
0
I am using a battery charger for a power supply for a circuit i am
building to control the speed of a DC motor. here is my circuit (view
in notepad)

|
| +5 V
| |
| .-.
| 470 | |
| 1/2 W | |
| '-'
| |
| o---------> to MOSFET
| | Gate
|PRN ___ |/
| o-|___|-o-|2N3904
| 2.2K | |>
| .-. |
| 10K| | |
| | | ===
| '-' GND
| |
| ===
| GND
|



V+ from battery charger
(18.8 V, 10A)
|----.
| |
.-. |
Motor ( X ) -
'-' ^
| |
o----'
| D1
|
||-+
||<- PM
from 2N3904 -->-----||-+
|
|
|
Ground


Power MOSFET IRF510


Anyway, there are serious problems with this circuit. It keeps blowing
up, haha. Especially the 2N3904 transistor. Any ideas? Is a battery
charger suitable for a power supply? Are there modifications i need to
make? Any help would be great. Thanks, Lucas
You need a resistor from the 3904 to the irf510 . You are most likely
getting the current from the gate feeding back into the 3904 and burning it
up. Try adding about a 10K resistor there.
 
E

ehsjr

Jan 1, 1970
0
I am using a battery charger for a power supply for a circuit i am
building to control the speed of a DC motor. here is my circuit (view
in notepad)

|
| +5 V
| |
| .-.
| 470 | |
| 1/2 W | |
| '-'
| |
| o---------> to MOSFET
| | Gate
|PRN ___ |/
| o-|___|-o-|2N3904
| 2.2K | |>
| .-. |
| 10K| | |
| | | ===
| '-' GND
| |
| ===
| GND
|



V+ from battery charger
(18.8 V, 10A)
|----.
| |
.-. |
Motor ( X ) -
'-' ^
| |
o----'
| D1
|
||-+
||<- PM
from 2N3904 -->-----||-+
|
|
|
Ground


Power MOSFET IRF510


Anyway, there are serious problems with this circuit. It keeps blowing
up, haha. Especially the 2N3904 transistor. Any ideas? Is a battery
charger suitable for a power supply? Are there modifications i need to
make? Any help would be great. Thanks, Lucas

You need an entirely different circuit. When controlling
the speed of a small DC motor, you want PWM - pulse width
modulation. A sample circuit is attached:

+12 ------------------+--------------+
a| |
[D3] |
| |
+---+----------+ +-----+
| | | | |
[1K] | ---------- [D2] [MOTOR]
| | | 8 | a| |
| +-----|4 | | |
/ | | +-----+
25K \<---+----|7 555 | |
/ | | | /
| a| | 3|---[150R]---| TIP31
[1K] [D1] | | \e
| | | | |
+----+----|6 | |
| | | | |
| +----|2 5|---+ | Diodes: 1N4001
| | | | |
[C1] ---------- [C2] |
| .1uF | .01uF |
Gnd ---+------------------------+----------+

Also, the battery charger may put out DC with a good
deal of ripple. Add a hefty electrolytic, say 470uF,
from pin 8 to ground. D3 consists of 5 1N400x diodes
in series, to drop the 18 volts from the charger
down closer to 14 volts. If you had a regulated 12 volt
supply, D3 would be eliminated.

Ed
 
Sorry, i forgot to inform everyone i was controlling the PWM from my PC
with the printer port (thus the prn in my origonal circuit). Thanks
though.
 
Another thing, I used this same schematic with a homade power supply
(transformer, full wave rectifier, some capacitors, etc..) and it
worked fine. This is why I think the problem lies within using the car
battery charger (again 18v 10 amps). Anyway, ehsjr brought up a good
point with the ripple. Maybe this is causing the problem. And James
Thompson ill try to throw a resistor in there for safe measures. Here
is a more general question however, if I am using a power supply with
the same voltage but allows more current (10 Amps v. 2.8 amps from my
home-made power supply), but am powering the same motor with the same
circuit, the same amount of current should be running through the
circuit right? That is, just because the battery charger is rated at
10 amps, doesn't mean it is indeed supplying more current since im
powering the same motor, right? Anyway, I think the problem lies
withing the power supply, so any idea on what exactly the problem is
would help A LOT!!! Thanks so much everyone.
 
E

ehsjr

Jan 1, 1970
0
Another thing, I used this same schematic with a homade power supply
(transformer, full wave rectifier, some capacitors, etc..) and it
worked fine. This is why I think the problem lies within using the car
battery charger (again 18v 10 amps). Anyway, ehsjr brought up a good
point with the ripple. Maybe this is causing the problem. And James
Thompson ill try to throw a resistor in there for safe measures. Here
is a more general question however, if I am using a power supply with
the same voltage but allows more current (10 Amps v. 2.8 amps from my
home-made power supply), but am powering the same motor with the same
circuit, the same amount of current should be running through the
circuit right? That is, just because the battery charger is rated at
10 amps, doesn't mean it is indeed supplying more current since im
powering the same motor, right? Anyway, I think the problem lies
withing the power supply, so any idea on what exactly the problem is
would help A LOT!!! Thanks so much everyone.

Ok, your circuit diagram shows +5 to the collector of
the 3904 through 470 ohms. Is that the same when
you use the car battery charger as it is when you
use your homemade supply? (Implying a 5 volt
vr in there) If not, add a 7805. Filter out the
ripple. Make your battery charger supply equal to
your homemade supply.

Make sure you have common ground (prn and power
supply). Put a 100 ohm resistor between the
3904 and the gate.

Who knows if the current is the same? The circuit
between the load and the source may behave differently
when powered by a high ripple source. If that circuit
behaves the same, then it does not matter if your
source is capable of 10 amps or 2.8 amps, provided
the motor can draw no more than 2.8 amps. A supply will
provide only the amount of current drawn from it,
not its full current rating in excess of what is drawn.

Ed
 
Top