Tripling battery life span

[DIY_Quad]

[Originally posted on DJI forum, but for obvious reason, DJI didn't like it and so I moved the discussion here]

So I made some modification to the MA2 charging hub to help my batteries last longer…a lot longer, supposedly like 3X longer.
I added a micro controller that monitors charging voltage and stops charging when it hits a preset level and then moves on to the next battery until all 3 batteries are charged to the preset level.
When I am charging to fly, the modified hub would charge to 90% (about 4.25V/cell) only instead of 100% (ie. 4.4V/cell).
It would cut flying time by that much each time I fly but if that translates to increasing number of discharge cycles by about 3X (source: batteryuniversity.com), that's a tradeoff worth taking.
Also, when storing batteries, instead of waiting 10 days for the intelligent self-discharge to kick in, I can set the modified charging hub to charge all 3 batteries to 50% only and stop.
Because I don’t like the idea of leaving batteries fully charged even for 10 days since irreversible damages however small will take place during that time and if repeated over time, it will further shorten life.



The added tactile switch cycles through 50%, 90% and 100% charging modes and the LED lets me know mode selected.



*edit* Adding this table from batteryuniversity.com for those skeptical bunch.
The table is for normal LiPo cell with rated max voltage of 4.2V.
MA2 batteries are high-voltage LiPo with rated max of 4.4V.

 

[slup]

Nicely done, for sure a pleasant feeling to enhance things by your self ... but have you considered the Hanatora parallel charger, will add all (up to 4) batteries charged in parallel + RC, & also discharge to storage level.

Here --> https://www.amazon.com/dp/B08J7M1MPL/

Have one for the previous MA1 & works as advertised ... may be worth the money for the additional features & no need for any DIY.

*EDIT*

Copy & paste in the link above ... don't know why the "insert link" function goes to another place ..?

 

[msinger]

no need for any DIY

But, isn't that the fun part?

 

[DIY_Quad]

Nicely done, for sure a pleasant feeling to enhance things by your self ... but have you considered the Hanatora parallel charger, will add all (up to 4) batteries charged in parallel + RC, & also discharge to storage level.

Here --> https://www.amazon.com/dp/B08J7M1MPL/

Have one for the previous MA1 & works as advertised ... may be worth the money for the additional features & no need for any DIY.

*EDIT*

Copy & paste in the link above ... don't know why the "insert link" function goes to another place ..?

Certainly a nice charger that allows you to charge up to 4 batteries at the same time plus the controller.
But it does not offer the option to charge to 90% and stop.
Limiting maximum voltage seen by each cell to 4.25V (or approximately 90%) is the key to tripling number of discharge cycles.
And that is the main benefit of this mod.
50% charging is added convenience to keep batteries in their most relaxed state between flights.

 

[dirkclod]

But, isn't that the fun part?

Used to be Mike but after all we have done over the years I’m ready
to let someone else do it and just buy it.?

 

[Kilrah]

It's never going to "triple your life span". Make a small difference maybe, but not even enough to bother.

 

[Deleted member 114292]

It's never going to "triple your life span". Make a small difference maybe, but not even enough to bother.

Correct - It's the high current draw of a flight that wears batteries.

 

[StantonZ]

Correct - It's the high current draw of a flight that wears batteries.

Yes: and the heat that it generates. If you could/would monitor battery temps during the charge cycle, you would see they come no where near those 'in flight'. It has to do with 'C' rates (just like when I drive my Leaf at high speeds)...

 

[DIY_Quad]

Kilrah, Done and StantonZ, care to share any data to support your claims?​

Here is the data I am basing my claim.

BU-808: How to Prolong Lithium-based Batteries

BU meta description needed...

batteryuniversity.com

 

[DIY_Quad]

Correct - It's the high current draw of a flight that wears batteries.

True, high current draw or charging current do cause wear on batteries.
That's why batteries will still deteriorate after large number of discharge cycles.
But reducing high-voltage stress alone reduces the wear significantly enough that discharge cycle increases dramatically.
See the data posted above.

 

[DIY_Quad]

Yes: and the heat that it generates. If you could/would monitor battery temps during the charge cycle, you would see they come no where near those 'in flight'. It has to do with 'C' rates (just like when I drive my Leaf at high speeds)...

All else being equal (ie heat during charge/discharge), data shows reducing high-voltage stress alone prolongs battery life dramatically.
See the data above.

 

[DIY_Quad]

It's never going to "triple your life span". Make a small difference maybe, but not even enough to bother.

You must have some solid data to be that confident in what you are saying.
Please share your data/source.

 

[dawgpilot]

Is your circuit letting the charger still balance the cells? I thought that occurred during the final steps of the charging process. Seems like cutting off charging at only 90% could possibly leave you with unbalanced cells.

 

[Kilrah]

You must have some solid data to be that confident in what you are saying.
Please share your data/source.

All else being equal (ie heat during charge/discharge), data shows reducing high-voltage stress alone prolongs battery life dramatically.
See the data above.

That data is as you mentioned but ignored for different chemistries than what DJI is currently using, assuming it's also valid for them in the same proportions is as good as nothing.

Also, the base cycle count quoted on BU already exceeds what most people will ever do with their drone batteries... With all of my aircraft and those of colleagues and friends I don't think I've ever seen a battery with more than 100 cycles.

 

[DIY_Quad]

That data is as you mentioned but ignored for different chemistries than what DJI is currently using, assuming it's also valid for them in the same proportions is as good as nothing.

Also, the base cycle count quoted on BU already exceeds what most people will ever do with their drone batteries... With all of my aircraft and those of colleagues and friends I don't think I've ever seen a battery with more than 100 cycles.

I would say your assumption for saying LiHV batteries do not benefit from reduced voltage stress is as good as nothing.
Sure, the BU data is not a direct measurement of LiHV cells that DJI is using in their drones, but it is more than reasonable to assume the same tradeoff exists for LiHV cells because if you read the text, it is talking about 'Lithium-based Batteries', not just one particular type of Li-based cell.
And guess what? DJI batteries are Li-based.
Also, you are neglecting the fact that not all lithium-based batteries are created equal.
Some are designed for higher discharge cycles, some are designed for high discharge/charge currents and some with different energy density to accommodate different characteristic they need for their specific applications just to give you few examples.
The BU data is taken from one of many different lithium-based batteries and not necessarily based on the lithium cell you are using in your particular drone.
Hope you understand that there are different Li-based cells out there and that the max voltage vs discharge cycle tradeoff is not limited to just one specific type of Li-based cells.
Again, if you still believe reducing voltage stress on the LiHV won't do any good for increasing discharge cycles for DJI batteries, pls provide actual measured data to back your claim.

 

[lee82gx]

Hi @DIY_Quad I was the one asking you to come over here instead of DJI forums, welcome. I'm glad you got sorted out and can start posting.

I too have some doubts on whether it will really triple the battery life time expectancy, by reducing the maximum charging stress. One thing I am guessing (Stress - Guessing) is that the life cycle limit is also likely limited or mostly affected by the thermal stress from discharge.

Nonetheless a cool mod. Can I know how does your mod works actually? Are you just detecting the battery voltage and applying a hard disconnect to the affected port? Or are you communicating to the charging IC and instructing a stop at your desired voltage? For the purpose of storage and actual flight for max performance, can we have some presets for like 3.9V and 4.4V per cell?

 

[msinger]

Used to be Mike but after all we have done over the years I’m ready
to let someone else do it and just buy it.?

Haha... oh, of course. I was thinking it would be fun for @DIY_Quad. I'd have no idea where to start with a project like this.

 

[Kilrah]

if you read the text, it is talking about 'Lithium-based Batteries', not just one particular type of Li-based cell.

That is not correct, it specifically mentions cobalt-based batteries and precises that not all batteries behave the same.

 

[DIY_Quad]

That is not correct, it specifically mentions cobalt-based batteries and precises that not all batteries behave the same.

View attachment 118778

Precisely!
As I said, not all batteries are made equal.
This means not all batteries will have the same number of discharge cycles, same charge/discharge currents, same energy density, same capacity and so on.
Like I said, the table from BU is an example based on one type of Lithium-based cell.
It is saying 'Not all batteries behave the same' just to inform people like you who claim that they get far less discharge cycles than what's shown in the table.
You are reading it the wrong way dude.
Let me know if you find any article or data showing that LiHV batteries do not trade between max voltage and discharge cycle, which is your claim.

 

[Kilrah]

Let me know if you find any article or data showing that LiHV batteries do not trade between max voltage and discharge cycle, which is your claim.

Not at all, I never said that wasn't a trade for LiHV, what I said is that the 3x claim doesn't hold. With this battery type it could be 1.5x or 5x, but you said "tripling" and nothing you have shown backs this up for that particular battery chemistry. It's just clickbait.