How to choose the right Lithium Ion battery for your project?

Thread Starter

nikolasgioannou

Joined Aug 3, 2019
12
Hello,

Project description: I am building a project that uses two 12v 1Amp DC motors (link) as well as a small controller circuit that has an LCD display and some buttons. I want the motors to run for about 2 hours before needing a charge.

Question: What batteries should I use and, for the future, what should be my thought process in choosing batteries for a project.

Thank you, any help much appreciated.
 

KeithWalker

Joined Jul 10, 2017
413
Hello,

Project description: I am building a project that uses two 12v 1Amp DC motors (link) as well as a small controller circuit that has an LCD display and some buttons. I want the motors to run for about 2 hours before needing a charge.

Question: What batteries should I use and, for the future, what should be my thought process in choosing batteries for a project.

Thank you, any help much appreciated.
What you need to consider in future is:
What is the maximum current required? You will need a battery that can supply at least enough peak current under maximum load.
Is the load constant or does it change a lot? You will need to estimate the average current the device will require. Allow between 25% and 50% extra capacity for aging and unusual conditions.
How tolerant is the circuit to voltage variations? This may dictate that you use a higher voltage battery with a voltage regulator.
What space is available for batteries and is weight an issue? This will affect the choice of battery type.
What recharging facilities are required? This could significantly affect the choice of batteries and the cost of the project

If the motors are running all the time, under constant load you will need a battery that has the capacity of a little more than two ampere hours. You could use three 18650 3500maH lithium ion cells if you can tolerate the voltage variation with the discharge of the cells. The voltage would start at about 11.4 volts and drop to 9 volts before a recharge is needed. The best choice would probably be a sealed lead/acid 12V battery with 3AH capacity. The voltage would vary much less but it would be considerably larger and heavier than lithium ion.
 
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Thread Starter

nikolasgioannou

Joined Aug 3, 2019
12
What you need to consider in future is:
What is the maximum current required? You will need a battery that can supply at least enough peak current under maximum load.
Is the load constant or does it change a lot? You will need to estimate the average current the device will require. Allow between 25% and 50% extra capacity for aging and unusual conditions.
How tolerant is the circuit to voltage variations? This may dictate that you use a higher voltage battery with a voltage regulator.
What space is available for batteries and is weight an issue? This will affect the choice of battery type.
What recharging facilities are required? This could significantly affect the choice of batteries and the cost of the project

If the motors are running all the time, under constant load you will need a battery that has the capacity of a little more than two ampere hours. You could use three 18650 3500maH lithium ion cells if you can tolerate the voltage variation with the discharge of the cells. The voltage would start at about 11.4 volts and drop to 9 volts before a recharge is needed. The best choice would probably be a sealed lead/acid 12V battery with 3AH capacity. The voltage would vary much less but it would be considerably larger and heavier than lithium ion.
Hello,

Thank you for your detailed response. I am building a tennis ball machine, so weight will not be an issue. However, this does mean that I want to consistently hit speeds throughout the duration of the session. Could this be achieved if the voltage drops from 11.4 to 9, like you said?

Regarding lead/acid vs. lithium ion, what are the pros and cons? I want to be able to charge with a simple plug in, could this be achieved with both? Thanks.
 

jpanhalt

Joined Jan 18, 2008
7,863
If you want consistent (or controlled) speed. You could design for a little under your minimum voltage, then use PWM (pulse width modulation) to keep the speed at the desired value. Feedback to keep current constant would probably be sufficient. Speed controllers for models that will handle that current are cheap and can be controlled with a potentiometer and simple circuit.
 

Thread Starter

nikolasgioannou

Joined Aug 3, 2019
12
If you want consistent (or controlled) speed. You could design for a little under your minimum voltage, then use PWM (pulse width modulation) to keep the speed at the desired value. Feedback to keep current constant would probably be sufficient. Speed controllers for models that will handle that current are cheap and can be controlled with a potentiometer and simple circuit.
Thanks for your response! What do you mean by "You could design for a little under your minimum voltage". I am planning to use PWM as I need to control the individual speed of each motor to the nearest x rpm.
 

KeithWalker

Joined Jul 10, 2017
413
Hello,

Thank you for your detailed response. I am building a tennis ball machine, so weight will not be an issue. However, this does mean that I want to consistently hit speeds throughout the duration of the session. Could this be achieved if the voltage drops from 11.4 to 9, like you said?

Regarding lead/acid vs. lithium ion, what are the pros and cons? I want to be able to charge with a simple plug in, could this be achieved with both? Thanks.
If you use lithium ion batteries, the speed of the motors would vary significantly with the state of the charge, You would need to add an extra cell and a voltage regulator. The regulator would need to be able to handle the peak current of the motors.
The voltage of lead/acid batteries varies much less and the variation would probably not make a enough of a difference to the speed of the motors to be noticeable. For very little increase in cost you could increase the capacity of the battery by 50%. Then the voltage will drop even less over the two hour period.
You plan on monitoring the batteries so there would be little difference in which choice you made.
For storage when not in use they will need to be recharged occasionally:
Lithium ion batteries do have an excellent shelf-life. Self discharge rate is 5% in 24h, then 1–2% per month
A sealed lead/acid battery generally discharges 3% every month.
Battery chargers are readily available for both types of battery. Those for lithium ion batteries are a little more expensive because they monitor the state of each cell and make sure the charge is even.
 

jpanhalt

Joined Jan 18, 2008
7,863
Thanks for your response! What do you mean by "You could design for a little under your minimum voltage". I am planning to use PWM as I need to control the individual speed of each motor to the nearest x rpm.
If your voltage is, say, 11 V to 13 V, design so you get the highest speed needed at ≤11 V. As for speed speed control, doing it based on rpm will be more difficult, probably not respond as quickly, and may not be necessary.

Note, the strength of an electromagnet is related to current, not voltage: https://www.electronics-tutorials.ws/electromagnetism/electromagnets.html Although, with a fixed resistance, voltage controls current.
 

Thread Starter

nikolasgioannou

Joined Aug 3, 2019
12
If your voltage is, say, 11 V to 13 V, design so you get the highest speed needed at ≤11 V. As for speed speed control, doing it based on rpm will be more difficult, probably not respond as quickly, and may not be necessary.

Note, the strength of an electromagnet is related to current, not voltage: https://www.electronics-tutorials.ws/electromagnetism/electromagnets.html Although, with a fixed resistance, voltage controls current.
I see. Thank you for the clarification. How does mAH come into play? Also, will using this motor controller (https://www.adafruit.com/product/2448) work? I apologize for all the questions, I am learning through this project. I appreciate the help!
 

Thread Starter

nikolasgioannou

Joined Aug 3, 2019
12
If you use lithium ion batteries, the speed of the motors would vary significantly with the state of the charge, You would need to add an extra cell and a voltage regulator. The regulator would need to be able to handle the peak current of the motors.
The voltage of lead/acid batteries varies much less and the variation would probably not make a enough of a difference to the speed of the motors to be noticeable. For very little increase in cost you could increase the capacity of the battery by 50%. Then the voltage will drop even less over the two hour period.
You plan on monitoring the batteries so there would be little difference in which choice you made.
For storage when not in use they will need to be recharged occasionally:
Lithium ion batteries do have an excellent shelf-life. Self discharge rate is 5% in 24h, then 1–2% per month
A sealed lead/acid battery generally discharges 3% every month.
Battery chargers are readily available for both types of battery. Those for lithium ion batteries are a little more expensive because they monitor the state of each cell and make sure the charge is even.
Thank you for the clarification. Though a lithium ion battery would cause variability in the speed of the motors, would using a motor controller help? Like this one listed: https://www.adafruit.com/product/2448. Thank you.
 

jpanhalt

Joined Jan 18, 2008
7,863
I see. Thank you for the clarification. How does mAH come into play? Also, will using this motor controller (https://www.adafruit.com/product/2448) work? I apologize for all the questions, I am learning through this project. I appreciate the help!
That Adaftuit controller is for stepper motors. The motors you show in your first link are not stepper. I do not think it will work with them. For what you are doing, I think a non-stepper DC motor, rather than stepper, would be best. Among DC motors, you have those with a field and those with permanent magnets (PM) and brushed versus non-brushed ("brushless"). A series-wound brushed motor (e.g., starter type), PM brushed, or PM brushless motor would be my top choices. The latter requires a different type controller than the former two require.

"mAH" is the maximum capacity of the battery. 1000 mAH = 1 AH, which in theory can supply 1 amp for one hour. In practice, one tries to avoid completely discharging a battery. Complete discharge is very hard on batteries.
 

Thread Starter

nikolasgioannou

Joined Aug 3, 2019
12
That Adaftuit controller is for stepper motors. The motors you show in your first link are not stepper. I do not think it will work with them. For what you are doing, I think a non-stepper DC motor, rather than stepper, would be best. Among DC motors, you have those with a field and those with permanent magnets (PM) and brushed versus non-brushed ("brushless"). A series-wound brushed motor (e.g., starter type), PM brushed, or PM brushless motor would be my top choices. The latter requires a different type controller than the former two require.

"mAH" is the maximum capacity of the battery. 1000 mAH = 1 AH, which in theory can supply 1 amp for one hour. In practice, one tries to avoid completely discharging a battery. Complete discharge is very hard on batteries.
For the first part, the adafruit controller also works for DC motors, but the video only shows a stepper. Should it work?

Ok, to power the two DC motors for two hours, would I need 4 amps (1 for each motor for each hour)? It says that for each motor, the no load current is 1 amp.

Thanks again for your help!
 

KeithWalker

Joined Jul 10, 2017
413
I see. Thank you for the clarification. How does mAH come into play? Also, will using this motor controller (https://www.adafruit.com/product/2448) work? I apologize for all the questions, I am learning through this project. I appreciate the help!
"mAH" is the capacity of a battery in milliamperes per hour. It is how much current the battery can supply and for how long. e.g. a 3000mAH battery, when fully charged, can supply 3 amps for one hour, 1 amp for three hours or 100 mA for thirty hours.
The motor speed controller you mentioned can control one stepper motor or two DC motors. I would recommend that you measure the current through the motors and use the result to control their speed using PWM. That way, your speed will not depend on the battery voltage.
http://www.vwlowen.co.uk/arduino/current/current.htm
 

Thread Starter

nikolasgioannou

Joined Aug 3, 2019
12
"mAH" is the capacity of a battery in milliamperes per hour. It is how much current the battery can supply and for how long. e.g. a 3000mAH battery, when fully charged, can supply 3 amps for one hour, 1 amp for three hours or 100 mA for thirty hours.
The motor speed controller you mentioned can control one stepper motor or two DC motors. I would recommend that you measure the current through the motors and use the result to control their speed using PWM. That way, your speed will not depend on the battery voltage.
http://www.vwlowen.co.uk/arduino/current/current.htm
I see. Thank you for the explanation on mAH.

Now that I am using the motor controller to control my two DC motors and thus the variability is mitigated, would you still recommend a lead/acid battery?

Also, say I use the three 18650 3500maH lithium ion cells that you referenced earlier, how long would this run for?
Is it the mAH that controls how long the battery can operate the motors?

Thank you so much for your help! I have learned so much and I am very grateful for your patience!
 

jpanhalt

Joined Jan 18, 2008
7,863
For the first part, the adafruit controller also works for DC motors, but the video only shows a stepper. Should it work?

Ok, to power the two DC motors for two hours, would I need 4 amps (1 for each motor for each hour)? It says that for each motor, the no load current is 1 amp.

Thanks again for your help!
Well, yes, you need 4 AH (amp-hours), not just 4 amps. But as I said, the usable capacity will be less. An 8 to 10 AH battery would would work, but since weight is not an issue, I would go with a garden tractor lead acid battery for cost or your Li battery if cost is not that important.

I am suspicious that a 12W motor (1A @ 12V) will be sufficient. Do you have reference designs that use such small motors?
 

BobTPH

Joined Jun 5, 2013
2,019
Two more things to consder.

A battery rated for 1Ah will generally not be able to supply 1A for 1 hour. The battery rating is for a discharge over a much longer period, often 20 hours. When discharging at a high rate, it will mot have the same capacity, so it might last 1/2 hour or even less at a 1A discharge rate.

Secondly, the stated no load current is just that, the current at no load, When heavily loaded, the current might be twice that or more.

Bob
 

Thread Starter

nikolasgioannou

Joined Aug 3, 2019
12
Well, yes, you need 4 AH (amp-hours), not just 4 amps. But as I said, the usable capacity will be less. An 8 to 10 AH battery would would work, but since weight is not an issue, I would go with a garden tractor lead acid battery for cost or your Li battery if cost is not that important.

I am suspicious that a 12W motor (1A @ 12V) will be sufficient. Do you have reference designs that use such small motors?
I see. No I do not have any reference designs but, to provide more information, the two motors will each be spinning two of these wheels via two pulleys. The wheels will be setup like this

Do you think the motors will work? If not, what would you recommend?
 

Thread Starter

nikolasgioannou

Joined Aug 3, 2019
12
Two more things to consder.

A battery rated for 1Ah will generally not be able to supply 1A for 1 hour. The battery rating is for a discharge over a much longer period, often 20 hours. When discharging at a high rate, it will mot have the same capacity, so it might last 1/2 hour or even less at a 1A discharge rate.

Secondly, the stated no load current is just that, the current at no load, When heavily loaded, the current might be twice that or more.

Bob
Right, thank you for the information. I have been considering using 3 18500 3.7v 3500 mah lithium ion batteries run in series. Would this work? Thank you for your response!
 

KeithWalker

Joined Jul 10, 2017
413
Right, thank you for the information. I have been considering using 3 18500 3.7v 3500 mah lithium ion batteries run in series. Would this work? Thank you for your response!
Three 3500mAH batteries in series will give you nominal 10.8 volts but will supply 2 amps for a maximum of one and three quarters of an hour.
If you are using pulse width modulation to set the speed of the motors, the speed will still reduce as the battery voltage drops unless you monitor the speed and provide some feedback to vary the pulses to maintain the speed.
The best thing you can do is to measure the current of the motors when they are running under load at the required speed. It may be more or less than one amp each. Then you will be able to pick a suitable battery.
 

Thread Starter

nikolasgioannou

Joined Aug 3, 2019
12
Three 3500mAH batteries in series will give you nominal 10.8 volts but will supply 2 amps for a maximum of one and three quarters of an hour.
If you are using pulse width modulation to set the speed of the motors, the speed will still reduce as the battery voltage drops unless you monitor the speed and provide some feedback to vary the pulses to maintain the speed.
The best thing you can do is to measure the current of the motors when they are running under load at the required speed. It may be more or less than one amp each. Then you will be able to pick a suitable battery.
Ok, thank you for your feedback. How can I do this?
 

KeithWalker

Joined Jul 10, 2017
413
Ok, thank you for your feedback. How can I do this?
You will need some way of generating the pulses to control the speed of the motors. I would recommend an Arduino microprocessor module. It is fairly simple to use and there are lots of application examples on the internet. It will interface directly to the motor controller you have chosen.
There are a couple of ways to measure the speed of a motor. You can use an optical tachometer circuit or you can measure the back EMF of the motor which is proportional to its speed. Once you have a signal that is proportional to the motor speed, you can compare it to a reference and program the microprocessor to change the ratio of the pulses to maintain the correct motor speed.
If you do not feel confident enough to tackle a project like that, I would recommend that you use a simple speed controller and voltage regulator to compensate for changes in the battery voltage.

Here is a suitable motor speed controller:

https://www.aliexpress.com/item/32840532022.html?spm=a2g0o.productlist.0.0.4e1b253d9nAQri&algo_pvid=d7ff858e-a43d-43f5-ae34-029fa39f9d8e&algo_expid=d7ff858e-a43d-43f5-ae34-029fa39f9d8e-4&btsid=d6b99bed-d4f2-4008-92f4-4d6e210eeadf&ws_ab_test=searchweb0_0,searchweb201602_4,searchweb201603_52

Here is a voltage regulator:

https://www.aliexpress.com/item/32980241746.html?spm=a2g0o.productlist.0.0.3d5141c0F8xmHU&algo_pvid=33bddf2f-7ecc-41af-a375-adcb6e6be9eb&algo_expid=33bddf2f-7ecc-41af-a375-adcb6e6be9eb-32&btsid=a2332041-c53a-464b-b305-8bb759f3b670&ws_ab_test=searchweb0_0,searchweb201602_4,searchweb201603_52
 
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