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motor driver 12v .. 2a... fail~

kamarul

Sep 27, 2015
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here my schematic..i got from website... it seems this circuit not operates well... for first time i try to run the motor .. which 12 v 1.8a.... the mosfet will heat up so much.... until i knew that the mosfet is not function anymore
after then i change a new mosfet..same model...tip 147... until i know that..the voltage will rises up from 6v to 24v automatically until my power supply will blinked which shown an abnormal state...
 

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BobK

Jan 5, 2010
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Welcome to the forum!

First of all, that is not a MOSFET, it is a Darlington pair.

Second, you need to heat sink it. What is the input voltage? Assuming 15V, which is the minimum needed to get 12V out, the pass transistor will dissipate 5.4 Watts, which would require a hefty heat sink. If the input voltage is more than 15, it will dissipate even more power. The formula is:

P = (Vin - 12) * 1.8

Third, if the motor runs at 1.8A, it needs quite a bit more to start and if it is heavily loaded. I would use at least a 3A supply.

Bob
 

kamarul

Sep 27, 2015
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Welcome to the forum!

First of all, that is not a MOSFET, it is a Darlington pair.

Second, you need to heat sink it. What is the input voltage? Assuming 15V, which is the minimum needed to get 12V out, the pass transistor will dissipate 5.4 Watts, which would require a hefty heat sink.

Third, if the motor runs at 1.8A, it needs quite a bit more to start and if it is heavily loaded. I would use at least a 3A supply.

Bob


i already put heat sink...and it does heat up easily... in one minutes...the voltage will rise up to 24v and the heat is really hot...my input voltage is 24v 5a power supply..scheider..i use pot 2kohm at r2.. and 320 at r1....
 

Alec_t

Jul 7, 2015
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Your motor probably has a starting current well above 5A, so not surprising your power supply blinks.
If R1 = 320Ω, the maximum setting (2k) of the pot R2 will give an output voltage of ~ 9V. That means the motor is under-powered and will start slowly, prolonging the time at which it draws a lot of current.
With 9V out and 24V in, the regulator + TIP147 (mainly the latter) will be dissipating 24-9=15 Watts per Amp the motor draws. That will require a LARGE heatsink.
 

kamarul

Sep 27, 2015
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Your motor probably has a starting current well above 5A, so not surprising your power supply blinks.
If R1 = 320Ω, the maximum setting (2k) of the pot R2 will give an output voltage of ~ 9V. That means the motor is under-powered and will start slowly, prolonging the time at which it draws a lot of current.
With 9V out and 24V in, the regulator + TIP147 (mainly the latter) will be dissipating 24-9=15 Watts per Amp the motor draws. That will require a LARGE heatsink.


last question..do will the tip147 automatically lost control and automatically given 24v mainsource voltage to motor when it overheat?
 

Alec_t

Jul 7, 2015
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Possibly. It depends whether the TIP147 fails open-circuit or short-circuit.
 

kamarul

Sep 27, 2015
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Usually

Usually, transistors fail open-circuit. MOSFETs tend to fail short-circuit.
so do u said that my wiring is wrong...? k just let it be...i will check it for the fifth time.. can i ask something? as i know that lm 317 can max up to 1.5a... will the cap in the schematic will help boosting the current ?
 

Old Steve

Jul 23, 2015
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so do u said that my wiring is wrong...? k just let it be...i will check it for the fifth time.. can i ask something? as i know that lm 317 can max up to 1.5a... will the cap in the schematic will help boosting the current ?
No, I didn't say that. I said "Usually, transistors fail open-circuit" . Nothing more.
Now that you mention it, though, it is a distinct possibility that something is connected wrongly, if the voltage goes up to 24V. Measure the transistor and see if it is short-circuited internally first.

Normally, but not necessarily always, the transistor would fail open-circuit, then the regulator would 'lower' it's output voltage with temperature due to it's inbuilt over-temperature protection.

And the caps make no difference to the amount of current the circuit can pass. They merely smooth the voltage and provide stability.

I'd recommend that you get rid of the linear regulator altogether and use a switching DC-DC converter. They don't have the same overheating problems.
 

kamarul

Sep 27, 2015
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No, I didn't say that. I said "Usually, transistors fail open-circuit" . Nothing more.
Now that you mention it, though, it is a distinct possibility that something is connected wrongly, if the voltage goes up to 24V. Measure the transistor and see if it is short-circuited internally first.

Normally, but not necessarily always, the transistor would fail open-circuit, then the regulator would 'lower' it's output voltage with temperature due to it's inbuilt over-temperature protection.

And the caps make no difference to the amount of current the circuit can pass. They merely smooth the voltage and provide stability.

I'd recommend that you get rid of the linear regulator altogether and use a switching DC-DC converter. They don't have the same overheating problems.

the motor is 1.8a load...and the lm317t is 1.5a max... so i use the steel type lm 317.... will this cause the problem? and how to measure the transistor? to know if is there any miss requirement to turn on the transistor
 

Old Steve

Jul 23, 2015
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the motor is 1.8a load...and the lm317t is 1.5a max... so i use the steel type lm 317.... will this cause the problem? and how to measure the transistor? to know if is there any miss requirement to turn on the transistor
Just measure across from collector to emitter and see if it's short-circuited.

That LM317 is fine - the problem is that you're trying to dissipate too much power. Bad circuit design.

I've answered enough questions on this. Go and buy a DC-DC converter.
 

kamarul

Sep 27, 2015
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Just measure across from collector to emitter and see if it's short-circuited.

That LM317 is fine - the problem is that you're trying to dissipate too much power. Bad circuit design.

I've answered enough questions on this. Go and buy a DC-DC converter.
will be tested in next 5 hours..will be updated
 

kamarul

Sep 27, 2015
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Just measure across from collector to emitter and see if it's short-circuited.

That LM317 is fine - the problem is that you're trying to dissipate too much power. Bad circuit design.

I've answered enough questions on this. Go and buy a DC-DC converter.


i bought transformer 12v .. 25va = 2a ?... if there is no load ...the output can give 13v.... and when i connect to load... it will drop to 5.8 v - 6v some like that..? any idea? huhu
 

kamarul

Sep 27, 2015
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duke37

Jan 9, 2011
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With 2V across the 317 and at least a volt across the Darlington, you are lucky to get 9.5V.
 

kamarul

Sep 27, 2015
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With 2V across the 317 and at least a volt across the Darlington, you are lucky to get 9.5V.

i see.. so that totally 3 volt loss for passing through the lm317 and transistor right...thx all for helping ...;)

anyway... how can i obtain the load of amp at the motor...i tried already by series the +ve terminal of the output circuit....but i failed...pls ..need some advice
 
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duke37

Jan 9, 2011
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anyway... how can i obtain the load of amp at the motor...i tried already by series the +ve terminal of the output circuit....but i failed...pls ..need some advice

Why did you fail? What did you get? You seem to have done things correctly by putting a current meter in series with one of the motor leads. Did you have the meter set to current at a range of about 5A?
 

kamarul

Sep 27, 2015
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With 2V across the 317
Why did you fail? What did you get? You seem to have done things correctly by putting a current meter in series with one of the motor leads. Did you have the meter set to current at a range of about 5A?

im using fluke meter...it will automatically ranging it self.. im sure this is correct setting... besides im using other multimeter... ane series at +ve..the motor will not run...huhu
 

Old Steve

Jul 23, 2015
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im using fluke meter...it will automatically ranging it self.. im sure this is correct setting... besides im using other multimeter... ane series at +ve..the motor will not run...huhu
Are you setting it to the current setting? And are the leads in the correct multimeter jacks for current measurement?
 
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