Why Circuit not outputting max voltage?

[Guest roineust]

Hello!

I am using the following circuit, with a LiPo 3S 11.1V (which charged, outputs 12.5V), with a split from the bat, one side to a regulator, that converts to 5V towards the Arduino and rest of chip legs, that need 5V and the other split side, stays 12.5V, for the motor that is switched on/off, by the chip via the Arduino, here is the schematics (in case you can't see the link, a picture is attached) :

http://fritzing.org/projects/drive-m...l293d-sn754410

I have 2 questions, regarding this circuit:

1. Why when bat is fully charged (12.5V), still, the motor gets only about 10.5V? Is it the grade of the pot i am using? should i use a higher quality pot? What would happen, if i used instead of that 10k pot a 5k pot? How can i get the full 12.5V?

2. If i want to have this circuit without a pot, just switch the max 12.5V on/off, without changing the voltage, what should i change in the circuit?

Thanks a lot!

[Guest roineust]

Meanwhile, more questions popped up:

Attached is a circuit i found with a mosfet.

Will this circuit do the exact same thing, as the circuit with the chip and pot, just without the pot function (which i don't need anyway), and give me switching for max voltage? If so it is good for me, but a few more questions:

1. Will it work also with 12.5V battery and motor or just with up to 9V bat and motor? The mosfet type is: irf540n, mofet weight: 3 grams.

2. Can i find a mosfet that will do the same thing, but weight less? Do you know that mosfet model number? If there exists such a mosfet, should the circuitry be just the same, just replace the mosfet model?

3. i intend to switch it once every 2-10 seconds.

Thanks.

[audioguru]

I explained your problems a few minutes ago on another website forum:
1) No schematic.
2) I do not know the maximum current of the motor.
3) The first breadboard photo shows an L293 driver. Look at its high voltage loss in its datasheet.
4) The second breadboard photo shows an IRF540 Mosfet. Its datasheet shows that it needs 10V input to fully turn on but is getting only 5V from the Arduino. Use a "logic level" IRL540 Mosfet instead.

Find a small Mosfet yourself.

[Guest roineust]

Thanks a lot for responding.

BTW, as a beginner in electronics forums, i can see the problem in posting, at the same time, in several categories of the same forum. What seems to be the problem with posting the same questions, at different forums?

[audioguru]

With the same questions on different forums then it gets confusing because we do not know which forum an answer was given which might be wrong.

On the other forum you said the motor draws 3A but you did not say at what supply voltage and if that is its running current or its maximum starting or stalled current.
Over there a TIP31 transistor was suggested that will burn out and a 20k pot biased it which will also burn out.

On one of these forums I asked, "What is the Arduino for?" but an answer might come here or there from you.

[Guest roineust]

Hey Audioguru!

The Arduino is for switching the motor on and off from a bluetooth.
The continuous current of the motor is around 3 Amps and the stall current is somewhere between 40-60 Amps, but i don't believe it will get any close to that, since it will run a liquid pump and either pump the liquid or be shut off. But, maybe i also don't understand well enough the term 'stall'.