Help with DC motor driver circuit

Thread Starter

herher

Joined Oct 18, 2011
53
Hi,

I have found a place to purchase my power supply, but before I place the order, I would like to ask for you guys opinion.

What amount of wattage do the power supply suppose to have?

The link below shows the site that I am going to purchase the supply from, please refer to the model T-120C for the first site and QP-100F for the second site :

http://www.peaktopeakpower.com/ac-dc-power-supplies/enclosed/t-120c

http://www.peaktopeakpower.com/ac-dc-power-supplies/enclosed/qp-100f


I am thinking of buying this power supply, but is this wattage sufficient enough for my entire application that I have mentioned in my previous posts?

p/s: I need the +15V and -15V of this power supply to power up two OPA544 operational amplifiers which are used to
drive two 12V, 2A DC motor respectively. Besides, I want to use the +15V of the power supply to supply analogue
10V to two voltage divider (potentiometer) respectively. Thanks a lot.

Please advice. Thank you very much. Hope to hear from you soon. :)

Best Regards,
herher
 
Last edited:

SgtWookie

Joined Jul 17, 2007
22,221
Neither of those supplies are adequate for your project.

There isn't any point in asking us, when you can see by the datasheet specifications that they don't meet your requirements.

Since you didn't want to use a pair of power opamps as an H-bridge, you will wind up buying a power supply that will cost twice as much as you could buy otherwise.

So, do you want to spend a little more on some more opamps, or do you want to keep searching for more power supplies?
 

Thread Starter

herher

Joined Oct 18, 2011
53
Hi,

Thank you very much for your reply.

Certainly, if there is any other better ways, I am willing to try. And you are right, I just found out that the current generated from both power supplies are not sufficient for my application ( Because I have misunderstood that the 100 wattage is the power generated from the outputs respectively)

But, I have already purchased two OPA544 opamp. How can I do any modification from this? Please help.

Please advice, I am really sorry if there is any stupid question or concept as I am not that experienced on this. Thank you very much. :)

Best Regards,
herher
 
Last edited:

Thread Starter

herher

Joined Oct 18, 2011
53
Hi,

All the expert here, please give me some suggestions.

I am really willing to learn.

Thank you very much.

Best Regards,
herher
 

Thread Starter

herher

Joined Oct 18, 2011
53
Hi,

I have some questions over here...please ignore the previous two posts...I will try to figure out a way by myself but I hope you guys can guide me along the way. Because I have to solve this problem desperately. :(

Since I have already bought the OPA544T, I will use it as my dc motor driver. I would like to ask if I wanted to power up the OPA544T chip, does the current supply to the V+ and V- have to be equivalent??? I am asking this because I found out that most of the power supplies do not generate identical current from the + - supply port. As an illustration, the rated current at the +15V supply port is 3.5A and the rated current at the -15V supply port is 1A.

So, with the values above, does it mean I can't even drive a 2A, 12V DC motor driver?

Please advice. The information about the OPA544T is really insufficient in the network, please as least guide me to any link and I can study by myself.

Thank you very much.

Best Regards,
herher
 

ifixit

Joined Nov 20, 2008
650
A better choice would be two of the NES-100-15 model. Each output can supply 5 Amps, which is enough to handle the 4 Amps you need for two motors plus the resistor divider.

Regards,
Ifixit
 

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SgtWookie

Joined Jul 17, 2007
22,221
Sorry for the slow response from me; I've been rather busy this weekend.

I just downloaded the SPICE file for the OPA544; getting it set up, but have to update a few things first.
 

SgtWookie

Joined Jul 17, 2007
22,221
Gosh, I didn't bother to look at the datasheet before downloading the model.

#12, did you know that the OPA544, like the LM675, doesn't get within 4V of the power rails?
 

Thread Starter

herher

Joined Oct 18, 2011
53
Hi Everyone,


Thank you very much for the replies...I am really appreciate it...

Ifixit: Thanks for the circuit. It is indeed a wake up call, I never think of using that way before...but from the SgtWookie's reply, it seems like the OPA544 has some problems...

SgtWookie: Thanks a lot. You mentioned that the OPA544 doesn't get within 4V of the power rail, does it means that the output won't be able to generate voltage signal that is below 4V???

Please advice, hope to hear from you all soon.


Best Regards,
herher
 

ifixit

Joined Nov 20, 2008
650
You are using ±15V power supplies to have an output of ±10V. The extra 5V allows for the 4V of headroom needed by the OPA544 that sgtwookie referred to.

Your problems are more likely to be with power (heat) dissapation. Be sure to use a good heatsink and provide lots of airflow over the heatsink.

Regards,
Ifixit
 

Thread Starter

herher

Joined Oct 18, 2011
53
Hi,

Thanks for the reply.

Can I know what is the rated current limit of the power supply that I can buy? The NES-100-15 power supply can output up to 7A of current. Is it too much for my application.

Can I know also what is the usage of the 100 ohms at the non-inverting pin and the inverting pin of the op-amp in the first circuit that you have given me? Because, usually there is no resistor at the feedback in order to acquire uniity gain.

Once again, thank you very much...Ifixit, SgtWookie, Bennard.

Best Regards,
herher
 
Last edited:

ifixit

Joined Nov 20, 2008
650
Your circuit will only use what it needs (4 Amps). The NES-100-15 can supply 5 amps at 15 Volts, 1 amp more than you need, which is its maximum full load rating of 100 Watts. It will limit or shutdown at 7 Amps, which would be a fault condition, or a dead short in the load.

Watts = Amps X volts.

Regards,
Ifixit
 

SgtWookie

Joined Jul 17, 2007
22,221
Here is how you could do it using two opamps per motor in an H-bridge configuration; see the attached.

However, you mentioned early on that you have 0v to 10v in, and you want to simply amplify that to be roughly -10 to +10 out, right?

And use just one opamp per motor, right?
 

Attachments

Thread Starter

herher

Joined Oct 18, 2011
53
Hi,

Thanks for the replies.

Ifixit: So, you mean after considering the efficiency, the maximum current NES-100-15 can output is only 5A although the datasheet specify the current range is 0A-7A right?

SgtWookie: Thank you very much for the circuit. The input signal range to the OPA544 is -10 to +10 with low current. So in order to drive my dc motor I have to apply the OPA544 in between. My aim is to input -1V low current voltage and output -1V high current voltage, vice versa. The input signal to the OPA544 is controlled by PID algorithm, this is the reason why the signal has positive and negative. Can you please have a look at the circuit that Ifixit gave me? His circuit need only one OPA544 to drive the motor. So, if both of your circuit are working well, then his one should be cheaper. Please advice.

Please advice, thank you very much.


Best Regards,
herher
 

SgtWookie

Joined Jul 17, 2007
22,221
Sure, here you go... see the attached.

I left out the 100 Ohm resistor from the PID to the noninverting input, as it would introduce a slight error.

R1 is there in case you power it up without the PID connected; R1 will keep the input centered around ground so that the motor should not turn.

You may or may not need to add a Boucherot cell to the output. See this Wikipedia entry:
http://en.wikipedia.org/wiki/Boucherot_cell
There is an example of a power opamp wired with a Boucherot cell on each output in this datasheet:
http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00000055.pdf
The Boucherot cell is mentioned on page 5. Connections are shown on the 3rd schematic on that page (nearest the bottom).
 

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ifixit

Joined Nov 20, 2008
650
Your circuit will only use what it needs (4 Amps). The NES-100-15 can supply 5 amps at 15 Volts, 1 amp more than you need, which is its maximum full load rating of 100 Watts. It will limit or shutdown at 7 Amps, which would be a fault condition, or a dead short in the load.

Watts = Amps X volts.
To clarify my imprecise comments...

The manufacture implies the NES-100-15 can supply 7 Amps continuously, that's 7 x 15 = 105 Watts. Even if I believed them, I wouldn't operate the supply at full load for too long as it will get very hot and may be damaged if not cooled properly and its life will be shortened.

I recommend that you do not load it more than 5 Amps maximum, that's 5 x 15 = 75 Watts. It will be much easier to cool and will last much longer.

Your motor driver design needs only 4 Amps, that's 4 x 15 = 60 Watts. Therefore, the NES-100-15 can easily handle this 4 Amp maximum load.

I hope that is more clear.

What is the resistance value of the pot you spoke of earlier?
Is the pot being driven by the motors to provide rotor position feedback?
Can you post the motor spec?

Regards,
Ifixit
 

Thread Starter

herher

Joined Oct 18, 2011
53
Hi Ifixit,

Thanks for the reply.

So, my circuit will only use what it needs from this power supply right?

The potentiometer value I am using is 10k.

Yes the potentiometer is driven by the motor via shaft and coupling.

Here is the spec of my dc motor:
DC12V
Output Power: 1.1 Watt
Rated Speed: 58RPM
Rated Current: 410mA
Rated Torque: 254.8mN.m
Sample Application: lightweight mechanism such as: bank note machine, handling machine, educational robot, etc


Please advice. Thank you very much.

Best Regards,
herher
 

Thread Starter

herher

Joined Oct 18, 2011
53
Hi SgtWookie,

Thanks again for the great help. I will try to run your circuit and Ifixit's one asap...and I will constantly update my progress over here.

Thank you very much. :)

Best Regards,
herher
 

Thread Starter

herher

Joined Oct 18, 2011
53
Hi Sgtwookie & Ifixit,

I have get all the components ready already. But before I commence can i know what is the maximum current that can be input to the signal pin (+Vin)? Can I run the testing by inputing a 9V voltage, which is generated from a alkaline battery to the signal pin ( I just want to test it because currently the microbox is not with me)?

Please advice. Thank you very much.

Best Regards,
herher
 

SgtWookie

Joined Jul 17, 2007
22,221
That you can read in the datasheet.

You can use a 9v battery as an input, as long as you don't exceed the voltage on the rails. If the supply you are using to power the opamp is less than 9v, then don't use the 9v battery for an input.
 
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