# i need someone to look at this circuit before my teacher will get it

Discussion in 'Electronics Homework Help' started by nathansmith2611, Oct 15, 2018.

1. ### nathansmith2611

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Oct 15, 2018
my teacher doesn't know much about electronics but is willing to get this circuit for a class project i am doing.

I have been building a constant power circuit to drive a motor on a solar powered car, and was after someone to have a look at it to see if there is any problems with its design.

The circuit is powered by a 6ish watt solar panel being fed into an MPPT that outputs 12 volts. The circuit uses an arduino uno to control a buck converter that feeds the motor a constant amount of electrical energy. The output of the buck converter is shunted, the voltage drop from the shunt is amplified by the LM158 which in turn feeds into the arduino. Also the output voltage is measured by the arduino after being divided by 5.

Note- R6 should be 10k, had editing problems

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,419
2,790
Jan 21, 2010
Your circuit may be fine, but let's tidy it up. Drawing things in a standard way assists readability.

Firstly, eliminate crossing lines where they're not necessary:

Next, make sure that identifiers are not obscured by lines running through them:

Move isolated parts of the circuit away from the rest

Remove unnecessary bits of wiring:

Remove unnecessary deviations in your wiring

Add more whitespace inside your drawing. You've got plenty of room, spread things out a bit more.

Remove a connection shorting Vcc to ground (or is that just another of those additional unconnected segments near the Vin pin?)

Decide which way you'll draw your connectors and stick to it. I would generally face inputs to the left, outputs to the right.

Decide which way you'll draw voltage dividers, and stick to it.

vs.

On ICs, only show the pins you need, and order them as necessary to simplify the diagram.

Give your schematic a sensible title

And wherever possible, try to make the circuit flow from left to right.

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3. ### Ratch

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Mar 10, 2013
I don't understand the "constant" power concept. Is the motor going to "starve" if it needs more power than the limits of the output supply provides? If it does not need what the supply can provide, is the extra powe going to be shunted into a heat dissipating element (resistor)? Wouldn't it be better to make a power supply that provides what the motor needs for light and heavy loads?

Ratch

4. ### nathansmith2611

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Oct 15, 2018
if the motor tries to draw more current than what the panel can provided the voltage will be dropped so that there is enough current available. If there is motor is not using all the power that panel supplies the voltage will increase till the motor is drawing all the available energy.

5. ### Ratch

1,088
331
Mar 10, 2013
Increasing the motor current by increasing the load risks burning out the windings. You want to keep the voltage up so that the motor will demand less of a current increase. If the motor needs more power, it has to be supplied, or the motor will not perform according to its specfications.

Ratch

6. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,419
2,790
Jan 21, 2010
Clearly Dave has been reading our forums and has posted a video on this topic.

Watch him complain about all the same stuff :-D