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Help with mc34063a

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mvictoras

New Member
Hi,

first of all let me say that I am a software engineer and have no experience in electrical engineering, so some of the below questions may sound stupid. I am learning electronics for some of my side projects and would need a little help!

I am powering up 13 vibration motors (28822) from a Lithium Ion battery (https://www.adafruit.com/products/354) and need to keep the voltage steady at 3.6V as the batteries discharge. The reason is that I want the perceived amplitude to be steady at all times.

Somebody recommended using the mc34063a to do that, but I am having difficulties wrapping my head around it.
So basically my specs are the following:
Vin(min) 3V
Vin(max) 3.7V
Vout 3.6V <--- Needs to always be 3.6V regardless of the input, until the last drop of the battery
Iout 1.5A

I have used the following calculators:
http://www.nomad.ee/micros/mc34063a/
and
http://www.rau-deaver.org/MC34063_boost.html

to figure out the values for the inductor, capacitors, etc., however I am getting errors when running them.

Any clue what I am doing wrong?
Any better/smarter/easier way of doing this?

Thank you!
 

ronsimpson

Well-Known Member
Most Helpful Member
It is hard when Vin is about the same as Vout.
It is much easier when Vin>>Vout or Vin<<Vout. (buck) or (boost)
So you need a (boost buck) which I have not done with the 34063.

I need to run do a chore. I can get back in a while or some one else can help.
------------edited------------
I just looked at the two links. Those simple calculators are for buck only. (or boost only)
-----edited again------
1.5A out is much more than the little 34063 will do. It can take 1.5A peak and in some modes it will meed more like 3A to make 1.5A.
 
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ronsimpson

Well-Known Member
Most Helpful Member
Wait:
13 motors at 0.25A each = 3.25A total
AND
At start up they pull 0.68A each. You don't need 13x0.68 but......
 

ronsimpson

Well-Known Member
Most Helpful Member
As long as I am commenting:
Your battery is designed for 1A or less output. 2A peak for short periods of time. The connector/wire is only good for 2A.
How much bad news do you want? lol
 

spec

Well-Known Member
Most Helpful Member
Hi,

first of all let me say that I am a software engineer and have no experience in electrical engineering, so some of the below questions may sound stupid. I am learning electronics for some of my side projects and would need a little help!

I am powering up 13 vibration motors (28822) from a Lithium Ion battery (https://www.adafruit.com/products/354) and need to keep the voltage steady at 3.6V as the batteries discharge. The reason is that I want the perceived amplitude to be steady at all times.

Somebody recommended using the mc34063a to do that, but I am having difficulties wrapping my head around it.
So basically my specs are the following:
Vin(min) 3V
Vin(max) 3.7V
Vout 3.6V <--- Needs to always be 3.6V regardless of the input, until the last drop of the battery
Iout 1.5A

I have used the following calculators:
http://www.nomad.ee/micros/mc34063a/
and
http://www.rau-deaver.org/MC34063_boost.html

to figure out the values for the inductor, capacitors, etc., however I am getting errors when running them.

Any clue what I am doing wrong?
Any better/smarter/easier way of doing this?

Thank you!
Hi mvictoras,

Welcome to ETO,

I don't like to be a kill-joy, but you really need to start again. If you would like to do that let us know and a solution should be quite simple. Perhaps you could use the battery pack for something less demanding.

spec
 

mvictoras

New Member
ronsimpson: Thank you for your quick reply! Your answer actually created a ton of questions from my side, see below!
spec: What do you mean to start again? Replace the battery with something else or design the circuit again? I am fine starting again from scratch, am not constrained with the above hw.

I was looking at the specs of the motor (https://www.parallax.com/sites/defa...822-Vibration-Motor-Capsule-Documentation.pdf) and do not really understand the difference between rated and operating voltage? If I want to get the maximum amplitude, do I power at the rated (3V) or max operating voltage (3.6V)?

Full disclosure: In reality I want to power 40 vibration motors. I bought 3x of the above battery packs and 1x 2200mAh battery and the plan was to connect groups of 13 motors to each big battery and the rest to the smaller one but I can now clearly see that that is not possible. Any idea what to do instead?
 

spec

Well-Known Member
Most Helpful Member
spec: What do you mean to start again? Replace the battery with something else or design the circuit again? I am fine starting again from scratch, am not constrained with the above hw.
Hy mvictoras,

As ronsimpson has implied there are difficulties with your present approach. The first is making an efficient inverter where the input voltage traverses the output voltage. Also, given a free choice, I would not have gone for that battery pack for any job (sorry). I am afraid that choosing batteries is a minefield and the only way to ensure that you get a good product with a fully defined specification that you can design to, is to buy the main manufacturer's products from a reliable source.

I haven't done a detailed and practical design analysis of your requirements but it seems to me that your best approach would be to connect two 18650 LiIon batteries in series to give a nominal voltage of 3.6V * 2= 7.2V and then step that down with a ready made buck switch mode power supply board to the constant voltage (3V to 3.6V) that you require. The voltage would be adjustable anyway

My feeling is that this approach will be more flexible, cheaper, easier, and will also enable you to extract the most power from the batteries. To ensure good performance and long battery life, a good charger must be used- afraid there are also a lot of suspect chargers on the market too.

Something we would need to know is how accurate and stable you require the output voltage to your motors to be. If you need very high accuracy, you may require a post switch mode power supply linear regulator. But that can always be added later if necessary.

The three batteries that I have in mind each have a nominal voltage of 3.6V (which is the case for nearly all LiIon batteries) and a capacity of 3 amp hours or 3.4 Ahrs (if they were put in parallel like your present pack they would thus give 6 Ahs or 6.8 Ahs) and they would have a much more consistent voltage during their discharge. They would also be capable of providing 10A, 15A, or 20A depending on specific battery chosen.

I don't think you have said where you are from so I don't know what markets are open to you, but in UK terms the batteries would be around £7 each and the power supply boards about the same.

If you favor this approach, please let us know and we can then look at a detailed design for you. You could even roll your own buck switch mode power supply if you wished. What normally happens on ETO is that you will be offered different designs to meet the requirement by different ETO members- there is more than one way to skin a cat.:)

spec
 
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ronsimpson

Well-Known Member
Most Helpful Member
rated and operating voltage
Probably:
All the numbers are taken at 3.0V. RPMs, current, noise level, etc (this is where they did all the testing)
The motor "works" from 2.2 to 3.6V. (it works but the noise is not rated, current is not written down, etc)
The motor starts under 1.7V. (All the motors will start by 1.7V, probably some started at 1.5V but...)

If the data sheet was 10 pages long they would show curves of voltage verses current, RPM, noise,......
You know at 3.0V the RPM is 12,000 +/-2,500.
You are missing the data for 2.2V. and 2.3V and 3.4V etc.
They do this because, now they have to prove 12,000 RPM at 3.0V and they do not have to stand behind the warranty for all cases.
You can use it at 2.5 or 3.5 but the company does not really know what it will do.
----------------------------------------
When I got my last truck, GMC said it will do 17.5mpg. They did not say at what speed. It turns out that it will do 17.6mpg at 35mph (down hill LOL) Some companies do not want to stand behind their numbers. In part because the prototype and production parts are slightly different. Parts make in 2007 are slightly different than those in 2016. So often the numbers are given so all parts will pass the test. Example 12,000 RPM +2500 or -2500 will pass all the parts.
---------------------------------------
I do not really know what you are doing but if you could get a 6V battery, I can find a simple 6V yo 3V buck power supply that will work. Search ebay for this:
"5pcs Re DC-DC 3A Buck Converter Adjustable Step-Down Power Supply Module LM2596S"
This supply will input 6V at 1A and output 3V at 2A.
OR
This supply will input 12V at 0.5A and output 3V at 2A.
----------------------------------------------
"DC-DC, 12A adjustable buck-board module"
This should work for 8A, 10A. I would not count on it doing 12A. Here is another example.

 

ronsimpson

Well-Known Member
Most Helpful Member
Our posts crossed RS
Well I wrote and thought it posted. But nothing happened. So when I came back to the computer there it sits.
Operator error. I have been blaming my tools all day. No me! lol
 

spec

Well-Known Member
Most Helpful Member
Well I wrote and thought it posted. But nothing happened. So when I came back to the computer there it sits.
Operator error. I have been blaming my tools all day. No me! lol
:) Happens to me too.

spec
 

spec

Well-Known Member
Most Helpful Member
Hy mvictoras,

Can you let us know how long you want the motors to run from the batteries?

Is this a portable application where size and weight are important or is it stationary where size and weight are not paramount. If the later, 1 to N, 12V lead acid deep discharge batteries (size and weight of an automobile battery) may be your best option for the power source.

On the other hand, can the vibration motors be powered from your mains supply via an appropriate power supply unit (PSU).

spec
 
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dr pepper

Well-Known Member
Most Helpful Member
How about 2 batteries, 2 power converter circuits, and split the motors into 2 groups, then your not draining a single battery too much.
 

mvictoras

New Member
I haven't done a detailed and practical design analysis of your requirements but it seems to me that your best approach would be to connect two 18650 LiIon batteries in series to give a nominal voltage of 3.6V * 2= 7.2V and then step that down with a ready made buck switch mode power supply board to the constant voltage (3V to 3.6V) that you require. The voltage would be adjustable anyway
This sounds really easy!

Something we would need to know is how accurate and stable you require the output voltage to your motors to be. If you need very high accuracy, you may require a post switch mode power supply linear regulator. But that can always be added later if necessary.
Not too accurate, I will be driving the motors from this: https://www.adafruit.com/product/815 and then use a NPN so I can power them from the battery pack. So for the PWM 0 would be no vibration, 1023 would be 3.6V.

The three batteries that I have in mind each have a nominal voltage of 3.6V (which is the case for nearly all LiIon batteries) and a capacity of 3 amp hours or 3.4 Ahrs (if they were put in parallel like your present pack they would thus give 6 Ahs or 6.8 Ahs) and they would have a much more consistent voltage during their discharge. They would also be capable of providing 10A, 15A, or 20A depending on specific battery chosen.

I don't think you have said where you are from so I don't know what markets are open to you, but in UK terms the batteries would be around £7 each and the power supply boards about the same.
I think that would work for me. I am located in Chicago, IL.

If you favor this approach, please let us know and we can then look at a detailed design for you. You could even roll your own buck switch mode power supply if you wished. What normally happens on ETO is that you will be offered different designs to meet the requirement by different ETO members- there is more than one way to skin a cat.:)
Yes, I would be very interested to seeing this design!

Hy mvictoras,

Can you let us know how long you want the motors to run from the batteries?

Is this a portable application where size and weight are important or is it stationary where size and weight are not paramount. If the later, 1 to N, 12V lead acid deep discharge batteries (size and weight of an automobile battery) may be your best option for the power source.

On the other hand, can the vibration motors be powered from your mains supply via an appropriate power supply unit (PSU).
1 hour should be enough. Yes this is a portable application, so a battery pack would be preferable. If this is not feasible, I will go with the PSU.

PS: All the motors won't be working at full 100% all the time. Most probably around 50% of the motors will be working at 75% capacity on average, the rest being idle. So when I say 1 hour max, I don't mean 1 hour of 40 motors vibrating at 3.6V for 1 hour. That would be crazy! Sorry for the confusion!
 

spec

Well-Known Member
Most Helpful Member
This sounds really easy!

Not too accurate, I will be driving the motors from this: https://www.adafruit.com/product/815 and then use a NPN so I can power them from the battery pack. So for the PWM 0 would be no vibration, 1023 would be 3.6V.

I think that would work for me. I am located in Chicago, IL.

Yes, I would be very interested to seeing this design!

1 hour should be enough. Yes this is a portable application, so a battery pack would be preferable. If this is not feasible, I will go with the PSU.

PS: All the motors won't be working at full 100% all the time. Most probably around 50% of the motors will be working at 75% capacity on average, the rest being idle. So when I say 1 hour max, I don't mean 1 hour of 40 motors vibrating at 3.6V for 1 hour. That would be crazy! Sorry for the confusion!
Hy mvictoras,

Thanks for your answers to my questions- I get the impression that you have a scientific mind which is always a great help when trying to do a design remotely.

From your answers, I now feel that we can arrive at a good approach to meet your requirements. I will give this some thought and get back to you. Ronsimpson has already done a lot of the ground work so I will be mainly concerned with the battery side of things.

spec
 

spec

Well-Known Member
Most Helpful Member
Issue 2 of 2016_06_11

Here is an outline schematic illustrating one approach for controlling your vibration motors. You would need three of these circuits to provide the capability of driving 3 x 16= 48 vibration motors which will meet your requirement for driving 40 vibration motors.


2016_06_07_ETO_VIBRATION_MOTOR_CONTROLLER_VER1.png
ERRATA
(1) Fit rectifier diode (to be defined) cathode to drain and anode to 0V for each PMOSFET (catching diode to catch voltage under swing caused by motor inductance when PMOSFET turns off).



NOTES

(1) The basis of the design is from ronsimpson's summary of the vibration motor current consumption: start current = 680mA, run current = 250mA.
(2) Two LiIon batteries, connected in series, and one PCA9685 chip or module to drive 16 vibration motors via a PMOSFET for each motor.
(3) At a first approximation, the battery duration will be an hour with all sixteen motors running at full power.
(4) The capacitors play no part in the basic operation of the circuit, but are decouples to help eliminate frequency instability.
(5) The 10 Ohm resistor plays no part in the basic operation of the circuit but is a gate stopper to stop the PMOSFET from oscillating and to improve the gate drive. The 10 Ohm resistor should connect directly to the PMOSFET gate terminal.
(6) The batteries under consideration are:
(6.1) Panasonic, NCR18650GA, 3.4Ah, 10A max
(6.2) Samsung, INR18650-30Q, 3Ah, 15A max
(6.3) LG, INR18650-HG2, 3Ah, 20A max
(7) The Switch Mode Power Supply (SMPS) is as described in ronsimpson's post #10, or similar: "DC-DC, 12A adjustable buck-board module"
(8) The non polarized capacitors are ceramic types with X7R dialectric
(9) C2, 2m2F (2200 uF), is an aluminum low-loss type.
(10) All capacitors are minimum values. Higher values will also be suitable.
(11) The PMOSFET under consideration is, ON, DMP4015SK3
(12) R8 (470 Ohms) speeds the PMOSFET turn-off, as the PCA9685 outputs have very low source current capability.

Data Sheets
(1) NXP PCA9685 (gives function of module)
http://cache.nxp.com/documents/data_sheet/PCA9685.pdf?pspll=1
(2) Panasonic, NCR18650GA, 3.4Ah, 10A max
http://www.nkon.nl/sk/k/ncr18650ga.pdf
(3) Samsung, INR18650-30Q, 3Ah, 15A max
http://www.nkon.nl/sk/k/30q.pdf
(4) LG, INR18650-HG2, 3Ah, 20A max
http://www.nkon.nl/sk/k/hg2.pdf
(5) PMOSFET ON, DMP4015SK3
http://www.diodes.com/_files/datasheets/DMP4015SK3.pdf
 
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