I have a DC motor connected to a 12V DC power supply from rectifier. Sometime the load increases than usual and motor RPM reduces. This in turn makes a voltage drop in the power supply something 11.97 to 11.89 volt. Then the Motor stops. Any idea why the motor stops.

 

winding resistance limits current, limiting torque, superseded by load. In other words, it stalls.

 

We need more detail, such as: What kind of over current protection does your power supply have?

 

24V supplied into the L7812CDT regulator that output to the 12 V DC power supply.

 

Hello,

Are there details on the motor, like a datasheet.
It could be that the motor takes to much current and the regulator shuts down.

Bertus

 

Hi c85,
The 7812 can dissipate approx 2Watts without an heat sink.
From a 24V supply, this means the maximum allowed current would be 2W/12Vdrop = 0.165Amps.

So I suspect the 7812 is going into thermal shut down as the motor current draw is exceeding say 0.2A.
E

 

It is entirely possible that as the load on the motor increases and the resulting power draw current rises, that the current exceeds the capability of that " 12V DC power supply from rectifier", and that supply voltage switches off.
Since we have no description of that power source or it's capability, I have no basis for any additional comments about it.

 

I think that the 7812 going into thermal shutdown is an excellent candidate. After the motor shuts down, how hot is the 7805 (actual degrees C would be helpful too, but a subjective evaluation may be enough "It is hot enough to fry spit" to "It hurts to keep my finger on it" to "about room temperature, etc.)

 

It would also help to have a complete, detailed description
of the Mechanical-Load that the Motor is expected to deal with.

~12-Volts is entirely too much Voltage to be dropped across any Linear-Regulator.

A PWM-Current-Regulator would be the best way to control and protect the Motor at the same time.

More details are needed on the Power-Supply, even if not using a Linear-Regulator.
How big are the Filter-Capacitors ?,
if practical, a Choke-Input-Filter on the Power-Supply would be even better.
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.
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Hi c85,
The 7812 can dissipate approx 2Watts without an heat sink.
From a 24V supply, this means the maximum allowed current would be 2W/12Vdrop = 0.165Amps.

So I suspect the 7812 is going into thermal shut down as the motor current draw is exceeding say 0.2A.
E

But, I looked at the datasheet of the L7812CD2T-TR, it can handle of up to 1.5A. Attached the data sheet of L7812CD2T-TR. The motor part number is MG16B-060-AB-00 (DC 12V). I dont think it is not capable of handling the motor current draw. What do you think about this.

 

It would also help to have a complete, detailed description
of the Mechanical-Load that the Motor is expected to deal with.

~12-Volts is entirely too much Voltage to be dropped across any Linear-Regulator.

A PWM-Current-Regulator would be the best way to control and protect the Motor at the same time.

More details are needed on the Power-Supply, even if not using a Linear-Regulator.
How big are the Filter-Capacitors ?,
if practical, a Choke-Input-Filter on the Power-Supply would be even better.
.
.
.

Datasheet of the L7812CD2T-TR (12V Voltage regulator), it can handle of up to 1.5A. Attached the data sheet of L7812CD2T-TR. The motor part number is MG16B-060-AB-00 (DC 12V). What do you think about this.

 

Hi c85,
The motor start current is ~0.8A, so with a 24V input to the 7812 regulator, that gives for the 7812 dissipation 12V* 0.8A =9.6Watts!!!
Look through these clips from the datasheets, I would say again the 7812 is going into thermal shut down at motor start up.

E


E

 

What you also need to take into account is the temperature of the die.

The fact that you can get the motor started but it cannot recover from a stall strongly suggests that, as ericgibbs noted, the problem is thermal shutdown.

Without going through more math exercises it seems quite clear that when the motor stalls it draws more current, causing the power dissipation of the die to increase, pushing the die temperature to the point that the chip goes into termal limiting.

Some things you can try are:

Reduce the voltage going into the 7812,

Difficult but often effective is to shunt some current around the 7812, such as by placing a resistor from the input to the output. You need to pay attention to the power rating of the resistor because you will be moving some power dissipation from the 7812 to the resistor.

Improve the heatsinking buy using a more efficient heatsink and/or fan.

Those are your best choices. A poor solution would be to add an external pass transistor, because that brings in complications such as current limiting but you might end up doing that because of circumstances not noted here.

Try reducing the temperature of the 7812 and you will probably be able to move beyond this problem of a motor stall locking the motor even after the cause of the stall is removed.

 

Motors aren't driven by voltage, they are driven by current- you have insufficient current. When motor stalls, you're shorting the battery through the motor

 

Hi c85,
The motor start current is ~0.8A, so with a 24V input to the 7812 regulator, that gives for the 7812 dissipation 12V* 0.8A =9.6Watts!!!
Look through these clips from the datasheets, I would say again the 7812 is going into thermal shut down at motor start up.

E

View attachment 343573View attachment 343574View attachment 343575
E

Yes, I agree with you but on the data sheet mention about, load regulation. Does it not can handle up to 1.5A.

 

Hello,

It can only handle 1.5 amp when very well cooled by a very large heatsink.
It says Tj = 25 °C.

Bertus

 

Datasheet of the L7812CD2T-TR (12V Voltage regulator), it can handle of up to 1.5A. Attached the data sheet of L7812CD2T-TR. The motor part number is MG16B-060-AB-00 (DC 12V). What do you think about this.

.
What is the Mechanical-Load on the Motor ?
What is it expected to do, and how fast ?
What is the Weight of the Load, and how BIG is it ? , a picture would help a lot.
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.
.

 

and of course, does the voltage persist once the motor stops?

 

and of course, does the voltage persist once the motor stops?

Yes, the voltage exist even after the motor stops.

 

but on the data sheet mention about, load regulation. Does it not can handle up to 1.5A.

Current is likely not the problem but power dissipation is, which has been mentioned several times.

What is there about excess power dissipation that you seem to not understand?