Your thoughts on my college project

Thread Starter

gogo00

Joined Oct 28, 2023
37
Hey there,
I've been exploring ideas for a college project and came across something interesting. We often check our laptop or mobile battery life, right? I thought it'd be cool to create a system that monitors and displays battery life.
I'm really intrested by this and would like to develop something similar that can monitor battery life and display it. After researching online, it seems I'll need a a battery, microcontroller, and an LCD display. The problem is picking the right battery type lead-acid or lithium-ion battery , specifications voltage, capacity, along with choosing the appropriate microcontroller 8051/ AVR/PIC/ ARM and display?

Any advice on what specifics I should aim for?
Thanks!
 
Last edited by a moderator:

Thread Starter

gogo00

Joined Oct 28, 2023
37
The real problem is how to determine battery life.
Displays and choice of processor is of minor consideration.
Thank you for highlighting that! So selecting battery should in higher priority

Which battery would you recommend?
 

Ian0

Joined Aug 7, 2020
9,497
First, decide on exactly what you mean by "battery life". The term is ambiguous, as it can mean the time remaining before the battery is flat and needs recharging, or it can mean the time before the battery is no longer serviceable and needs replacing.
Neither is particularly easy to determine for any type of battery.
Have you looked at Battery University? That is probably your best source of information.
 

Thread Starter

gogo00

Joined Oct 28, 2023
37
First, decide on exactly what you mean by "battery life". The term is ambiguous, as it can mean the time remaining before the battery is flat and needs recharging, or it can mean the time before the battery is no longer serviceable and needs replacing.
Neither is particularly easy to determine for any type of battery.
Have you looked at Battery University? That is probably your best source of information.
I'm looking for a way to track the estimated time remaining before the battery runs out and needs to be recharged.
 

Ian0

Joined Aug 7, 2020
9,497
I'm looking for a way to track the estimated time remaining before the battery runs out and needs to be recharged.
There's an awful lot of silicon available these days that does exactly that. (Anything made by Texas Instruments that starts "BQ" for instance)
It's easier for Lithium than Lead Acid as there is no Peukert effect with Lithium.
The basic principle is the "coulomb counter" - a numerical integration of the current.
But for it to work you need an accurate knowledge of the battery capacity, and that reduces as the battery ages.
Search for "gas gauge" ICs, and read the datasheets to see how they work.
 

Thread Starter

gogo00

Joined Oct 28, 2023
37
I'm feeling a bit lost about where to start and what steps to take next for this project. I believe breaking it down into smaller functional tasks could be more manageable. Right now, I'm seeking guidance on planning these tasks into several modules. What are the various modules I should consider for this project?
 

Ian0

Joined Aug 7, 2020
9,497
1. Measure the current (what hardware is needed, what accuracy and precision is required?)
2. Do the maths (how much capacity has been used?)
3. Take the decision (does it need recharging?)
 

Thread Starter

gogo00

Joined Oct 28, 2023
37
1. Measure the current (what hardware is needed, what accuracy and precision is required?)
2. Do the maths (how much capacity has been used?)
3. Take the decision (does it need recharging?)
I believe a fundamental system should include a battery, charger, microcontroller, display, and a load, with the load being assumed as a motor. The battery is only utilized to power the motor. It's important to determine the type of battery first. Once we know the battery type, we can know its specifications like voltage and capacity, and then need to understand the type of motor connected accross battery. as this information will help calculate the battery life
 

Irving

Joined Jan 30, 2016
3,794
I think you need to go back to first principles. The fundamental aspect is 'State of Charge' or SOC as measure of remaining battery capacity in Ah. The available run time is a direct measure of immediate SOC less the lowest SOC allowed (which will vary by battery technology but typically between 5 and 20% of capacity) divided by the time-averaged discharge current. Battery voltage is not a measure of SOC unless the system has been calibrated as for most technologies the relationship is highly non-linear. Detemining 100% SOC when charging again varies by battery technology, as a rule you put more in than you get out - often by as much as 10% - but the end point is typically when charging current drops to a low value relative to battery capacity.. So your first task is to figure out how to measure the energy going in to, or out of, the battery - so called 'coulomb counting'. Once you know how to do that the rest of the decisions of MCU, display, etc is down to what you already have, can borrow or, worst case, can buy (but my advice to you is stick with something easy to use - a basic Arduino is perfectly capable for this and cheap)

Last thought - a motor is a bad choice of load, at least in the first place. A simple constant current sink or electronic load will make life much simpler.
 

Thread Starter

gogo00

Joined Oct 28, 2023
37
I've downloaded a Lithium battery datasheet, which I've attached for our discussion on capacity. I'm trying to understand the ratings provided in the datasheet. Could you clarify what the voltage value would be when the battery is fully charged and what it would be when the battery is discharged? Thank you!
 

Attachments

Sensacell

Joined Jun 19, 2012
3,399
I've downloaded a Lithium battery datasheet, which I've attached for our discussion on capacity. I'm trying to understand the ratings provided in the datasheet. Could you clarify what the voltage value would be when the battery is fully charged and what it would be when the battery is discharged? Thank you!
You are totally missing the point here - the battery voltage alone is not viable to determine the state of charge.

Think of it this way, you have a water tank, you cannot see inside the tank.
Keep track of how much water goes in, and comes out.
It's like accounting, only less precise.
 

Ian0

Joined Aug 7, 2020
9,497
You are totally missing the point here - the battery voltage alone is not viable to determine the state of charge.

Think of it this way, you have a water tank, you cannot see inside the tank.
Keep track of how much water goes in, and comes out.
It's like accounting, only less precise.
It’s like filling a tank with a leaky hose. The tank has no gauge so you only know it is full when it overflows, and if it gets completely empty, it fails and you can’t use it again. Not the sort of tank you’d buy if you had a choice, but you don’t have the choice with batteries.
Having said that, my father owned a photographic flashgun with a small lead-acid battery, which was in a transparent case, and a little float went up and down a small tube within the battery and indicated the specific gravity, akin to a Galilean thermometer)
 

Ya’akov

Joined Jan 27, 2019
8,973
Battery SoC is one of the great mysteries.

It’s like a cat. If you watch it constantly and continuously you will be able to understand it, within limits. But if a cat walks into the room, looking at it will tell you nothing about what is has been doing or will do—even a few moments from now.

Watching a battery, from the beginning of it being charged to the end of it being discharged, you will be able to speak about its SoC with a least some authority. But, take a battery of unknown state and nothing you can measure about it is going to let you claim convincingly that you can speak about its SoC.

That’s why a Coulomb Counter, basically total surveillance of all the charge going in and all the charge going out is the way anything that needs better than a guess at SoC works it out.
 

Thread Starter

gogo00

Joined Oct 28, 2023
37
So The State of Charge (SOC) refers to the amount of energy remaining in a battery compared to its total capacity, usually represented as a percentage. It indicates how much charge the battery has left to deliver. When expressed in Ampere-hours (Ah), SOC signifies the remaining capacity in terms of the total charge the battery can hold, measured in ampere-hours. For instance, if a battery has a total capacity of 100Ah and it's currently at 50% SOC, it means there's around 50Ah of charge remaining.
 

nsaspook

Joined Aug 27, 2009
12,778
Use a linear battery type like LiFePO4 for your project. Lead-acid is a State of Charge tracking nightmare that can't be solved by simple coulomb counting because it's a non-linear energy tracking parameter.
For a LA battery, coulombs at 50% SoC mean more energy-wise than coulombs at 90%.

https://forum.allaboutcircuits.com/...rge-controller-datalogger.194146/post-1830877
It's so nice to have a battery that's linear in the charge and discharge energy profile from near zero to 100%. It makes writing the energy tracking algorithm so easy, I'm done with lead-acid for energy storage.
Day one full battery charge profile. LiFePO4 is a near perfect energy sponge that's worth the extra money.
I don't track current IN/OUT for my SoC/energy storage calculations. You do need to measure current and voltage (I use external components for that but a controller can easily handle it) to generate the energy parameters needed.
 
Last edited:

Irving

Joined Jan 30, 2016
3,794
Use a linear battery type like LiFePO4 for your project. Lead-acid is a State of Charge tracking nightmare that can't be solved by simple coulomb counting because it's a non-linear energy tracking parameter.
For a LA battery, coulombs at 50% SoC mean more energy-wise than coulombs at 90%.
Not sure I fully understand/agree with that...

I have used coulumb counting for tracking SOC on my wheelchair for over 10y, initially with 40Ah then 80Ah SLA and, more recently, 200Ah LiFe batteries. The thing with LiFe is I can safely discharge to 10% SOC and use the full 90% capacity whereas with SLA, 50% SOC means the on-load voltage has dropped low enough (or internal resistance has increased) to the point where the chair no longer functions reliably making a 80Ah SLA effectively only 40Ah usefully.
 
Top