Help needed with a simple project

sunny32_1967

Joined May 11, 2017
9
I am stuck with a project which requires the following:
1. 12 Volt DC Power (I am using four 3 volt button cells to produce 12v)
2. 12 Volt 1 meter long LED Strip by 3M (5 meter length as per Amazon uses 1.5 amp)
3. A micro-motor which according to the instructor works optimum at 3v.

Problem: Using parallel circuit, when I connect LED strip, it lights up just fine. The moment I introduce mini-motor in the circuit the LED goes off, and the fan runs. Knowing that I need to use a resistor in front of the mini-motor (3v), I subtracted 12v - 3v which gave me 9v which I divided by 1.5 amp of fan, and the resulting number was 6 ohms Resistor. I can't find 6 ohms resistor and the value which I currently have is 15 ohms. When I try to use 15 ohms infront of the mini-motor, the fan doesn't work however the LED's stay lighted.

What am I doing wrong? Is there a way to make it work by increasing the voltage of DC power supply or some other idea's? I am completely bummed and not able to work this out. Kindly help.

WBahn

Joined Mar 31, 2012
26,398
What kind of current are these button cells supposed to be able to provide? 1.5 A sounds like quite a bit.

A schematic of how you are hooking things up would be very helpful, too.

dl324

Joined Mar 30, 2015
12,258
Welcome to AAC!
12 Volt DC Power (I am using four 3 volt button cells to produce 12v)
Are you required to use button cells? LR44 type batteries are rated at about 120mAh and discharge characteristics are typically given for loads of 0.1C, or so.

You're not going to get 1.5A from that type of battery for very long.

What current does the motor require at 3V?

These look more like coin style batteries. CR2032 has twice the capacity of LR44...

EDIT: And Panasonic seems to call LR44 coin style...

Last edited:

Joined Feb 20, 2016
3,658
You will not be able to use the button/coin cells. It is like trying to put a model car engine in a real car. They are just way too small for the job.
What is the fan you are referring to? If it is the Micro motor, it will be drawing WAY too much current for those batteries.
It will be better to get a 12V motor if it is all running on 12V anyway. Using a 3V motor will waste a lot of power. You cannot really just put a resistor in line with a motor to drop the voltage as the current drawn by the motor will vary greatly with load changes. At least a voltage regulator is needed, preferably a switch mode on for power savings.
Oh, a good source of fan motors is from old PCs. They are usually 12V. And if you want them to drive something else, no doubt a pulley cold be grown onto the front of the fan.
Yes, a circuit is needed as your description of what you are trying to do is pretty vague.

Last edited:

sunny32_1967

Joined May 11, 2017
9
Thanks everyone for the replies. In the project I have to use 3v motor with a 12v LED strip. Similar motor specifications are:
• Nominal voltage: 1.5/ 3V
• Rotation: anti-clockwise
• Current (@ maximum efficiency): 0.81/ 1.15A
• Efficiency: 33.9/ 35.6%
• Stall torque: 24/ 44g/cm
I thought about getting a 12v motor but that defeats the purpose. The whole idea about this school project is: once all the pieces are working together, I have to insert the LED Strip in the wand along with the motor to create vibration on the LED's (please see the attached thumbnail). I am using CR2032 coin cells. I am also attaching the Duracell specifications for CR2032 coin cells. I am not worried about Coin batteries not lasting much longer. As long as the whole circuit works and if the battery lasts even 10 - 15 mins, it is ok. The reason for me to use coin cell was due to ease of inserting them in the wand. I was earlier trying 9V battery x 2 with 18 volt current but then realized it was not going to fit in.

If you prefer schematic, I can do so, however I thought that providing the pictures will be faster. If that doesn't work, i will work on providing the schematic.

FYI: Only the positive of the micro-motor is connected to C10 and the moment i connect the negative to H10 or I10, the LED goes off and the fan starts working. Ideally I will like to connect the red cable to C15 after the resistor but my resistor is 10 ohms. When I connect the micro-motor after the resistor, the fan doesn't work however the LED works.
Please let me know if you need more information and/or schematic after what I have provided below.

Thank you so much guys...

Attachments

• 358.9 KB Views: 3

Joined Feb 20, 2016
3,658
The example rating they have for those batteries is talking about .000019 amps, and you are using 1.5 amps. These cells are designed for long life at low current. They will have significant internal resistance but that may work for you in limiting the LED current to lower levels so extend the cell life a bit.
Surely there is enough room in the handle for 8 x AAA cells, or make an external battery pack and have a cable?
What you are doing is not the best way. You need to look into bigger capacity batteries. Using those cells is just a no no.
Do you have a multimeter?
One thing you could try is a single AAA or AA cell ( or C if it will fit) for the motor and see if it works ok on 1.5V. Then have a separate supply for the LEDs. That will extend the life a little too.

sunny32_1967

Joined May 11, 2017
9
The example rating they have for those batteries is talking about .000019 amps, and you are using 1.5 amps. These cells are designed for long life at low current. They will have significant internal resistance but that may work for you in limiting the LED current to lower levels so extend the cell life a bit.
Surely there is enough room in the handle for 8 x AAA cells, or make an external battery pack and have a cable?
What you are doing is not the best way. You need to look into bigger capacity batteries. Using those cells is just a no no.
Do you have a multimeter?
One thing you could try is a single AAA or AA cell ( or C if it will fit) for the motor and see if it works ok on 1.5V. Then have a separate supply for the LEDs. That will extend the life a little too.
Dendad, I can try all what you mentioned above but one last piece of information which I didn't thought was useful earlier is: LED's and micro-motor both need to be turned on with a single switch, which means there can only be a single power source....right?

In the meantime I will test if the micromotor works with AAA or AA or C battery and reply shortly.

sunny32_1967

Joined May 11, 2017
9
Dendad, If I hook up the micro-motor directly with AAA or AA or C battery, the motor runs slower compared to when two of those batteries are connected, the motor runs faster due to optimum voltage of 3v which is necessary to create vibration in the LED's when packed inside the wand.

sunny32_1967

Joined May 11, 2017
9
The example rating they have for those batteries is talking about .000019 amps, and you are using 1.5 amps. These cells are designed for long life at low current. They will have significant internal resistance but that may work for you in limiting the LED current to lower levels so extend the cell life a bit.
Surely there is enough room in the handle for 8 x AAA cells, or make an external battery pack and have a cable?
What you are doing is not the best way. You need to look into bigger capacity batteries. Using those cells is just a no no.
Do you have a multimeter?
One thing you could try is a single AAA or AA cell ( or C if it will fit) for the motor and see if it works ok on 1.5V. Then have a separate supply for the LEDs. That will extend the life a little too.
I have ordered multimeter which will be delivered on Saturday this week.

sunny32_1967

Joined May 11, 2017
9
Welcome to AAC!
Are you required to use button cells? LR44 type batteries are rated at about 120mAh and discharge characteristics are typically given for loads of 0.1C, or so.

You're not going to get 1.5A from that type of battery for very long.

What current does the motor require at 3V?

These look more like coin style batteries. CR2032 has twice the capacity of LR44...
View attachment 126515

EDIT: And Panasonic seems to call LR44 coin style...
View attachment 126516
DL324, Button cells so they can fit in the wand. The motor requires about 1.15 amp at 3v. Life of the battery is not an issue. Even if the whole thing works for 10 minutes and then dies, so be it. The challenge has been to get it to work at the least.

Joined Feb 20, 2016
3,658
Here is a quick circuit to show you how to hook up a switch to control both.

If you want, you do not need to have both battery -ve pins connected together. They can be completely separate.

WBahn

Joined Mar 31, 2012
26,398
If you look at the specs for the CR-2032 that you provided, you will see that the nominal internal resistance is 20 Ω (with a typical range from 10 Ω to 40 Ω). So even with a dead short that 3 V cell is only going to produce something on the order of 150 mA, or about a factor of ten less than what you say you need. It has a 240 mAh capacity (at a draw of 0.19 mA, or about a factor of 5000 less than what you say you need) and even if it could produce 1.5 A and deliver that same capacity (which it can't), you would drain it in completely in less than ten minutes. At that much over the rated current draw, you will be lucky a fraction of that.

What is it going to take to convince you that these coin cells are not adequate for the demand you claim you need to place on them?

sunny32_1967

Joined May 11, 2017
9
Here is a quick circuit to show you how to hook up a switch to control both.

View attachment 126526

If you want, you do not need to have both battery -ve pins connected together. They can be completely separate.
Dendad, The time you put in for me to provide me with the details, helped me succeed.......yay. I can't be more thankful to you for all the assistance and time you poured in for me. My project was a success and this weekend I will be able to put all the things together. Thank you so much. BTW I am from US. Once again thank you.

sunny32_1967

Joined May 11, 2017
9
If you look at the specs for the CR-2032 that you provided, you will see that the nominal internal resistance is 20 Ω (with a typical range from 10 Ω to 40 Ω). So even with a dead short that 3 V cell is only going to produce something on the order of 150 mA, or about a factor of ten less than what you say you need. It has a 240 mAh capacity (at a draw of 0.19 mA, or about a factor of 5000 less than what you say you need) and even if it could produce 1.5 A and deliver that same capacity (which it can't), you would drain it in completely in less than ten minutes. At that much over the rated current draw, you will be lucky a fraction of that.

What is it going to take to convince you that these coin cells are not adequate for the demand you claim you need to place on them?
Wbahn, It was continuous failure to run both components with the coin cell batteries, that convinced me that I really need to move on to different battery type and I ended up using two 9v batteries. Now when I have the circuit functional with both components working fine, I am going to change the hilt to a wider one, to be able to put everything inside the Wand.

You guys have been nothing but simply awesome. I hate engineering to be honest and couldn't be more glad that by next school year, I will completely focus on medical school.

Once again, thank you so much folks. I couldn't have done it without you guys talking about the intricate details which I had no clue about.

Cheers...

WBahn

Joined Mar 31, 2012
26,398
Wbahn, It was continuous failure to run both components with the coin cell batteries, that convinced me that I really need to move on to different battery type and I ended up using two 9v batteries. Now when I have the circuit functional with both components working fine, I am going to change the hilt to a wider one, to be able to put everything inside the Wand.

You guys have been nothing but simply awesome. I hate engineering to be honest and couldn't be more glad that by next school year, I will completely focus on medical school.

Once again, thank you so much folks. I couldn't have done it without you guys talking about the intricate details which I had no clue about.

Cheers...
If you hate engineering, then you are probably going to hate medical school. Both are first and foremost about problem solving and both rely very heavily on deductive reasoning skills.

sunny32_1967

Joined May 11, 2017
9
If you hate engineering, then you are probably going to hate medical school. Both are first and foremost about problem solving and both rely very heavily on deductive reasoning skills.
Actually I am loving the medical science and have been getting GPA of 4.3 so far. I am determined to become a Surgeon and everything is falling in place so far. I am really looking forward to it. As to hating engineering I used strong words and should not have put it that way. What I meant (choice of wrong words) was that I didn't even have basic tools (e.g. Multimeter, Soldering iron) etc at home. My father ended up ordering tools worth USD 400 approx. which will be getting delivered by end of this week. Hopefully positive experience after getting the tools will make me less nervous about engineering.

WBahn

Joined Mar 31, 2012
26,398
Not having the proper tools definitely makes a difference, in any field. Imagine having to do surgery with only what you can find in your kitchen!

Best of luck to you.