How do I not suck at lipos?

So, since getting into this, I’ve probably ruined at least 2 or 3 lipo packs. Some had dead cells and some have died through neglect. I was wondering if any of you guys with more experience could give me some advice on how to properly take care of these.

Things I know:

  • Take C ratings with a grain of salt and only use half of what the battery is rated for
  • Don’t charge over 4.2V
  • Don’t discharge under 3.0V
  • Discharge to 3.7V for storage

If I do happen to over discharge a cell, what’s the lowest “salvageable” voltage I should look for? Also, I’ve heard that internal resistance plays a large role in the health of a cell. How do I measure this and what kind of numbers should I be happy or concerned with? Thanks.

Lipos are much pickier about low voltages than Li-ion. I don’t use them myself but from the discharge graphs I’ve seen I wouldn’t discharge a lipo lower than 3.5v

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Agreed! Given sag when in use, i set my alarm for 3.7/3.6v and just make sure i’m going easy at the end not to over-discharge. Example - it’ll beep going up a hill, but then back to 3.8v+ on the flats - if i’m squeezing range i’ll ride on the flats until it beeps again w/o high draw like hill or hard accelerating.

Gives some warning this way and i can moderate my acceleration or walk up a hill to make sure i can get where i need to go. Instead of only beeping at 3.5v or similar when it’s effectively “empty”.

Overcharging and over-discharging - best way to kill a cell/pack/battery!

my iCharger has a measure IR feature. I think the legit iMax B6ACV2 does as well?

checking good 'ol Amazon:

[quote] Product description

The B6AC V2 is the upgraded version for well-known iMax B6AC. Compared with B6AC V1, it is more accurate and stable and also has some new features and functions. Users could set the terminal voltage by themselves and connect it to PC for PC control and firmware upgrade. What’s more, users could also use it as Lithium Battery Meter and Battery Internal Resistance Meter. There are Automatic Charging Current Limit, Capacity Limit, Temperature Threshold and Processing Time Limit which makes the charger safer than V1. B6AC V2 is a high-performance, micro processor control charge/discharge station with battery management suitable for use with all current battery types, with integral equalizer for six-cell Lithium- Polymer (LiPo), Lithium iron phosphate(LiFe) and Lithium-Ion (LiIon) batteries; maximum 6A charge current and maximum 50W charge power. [/quote]

My recipe for success has been:

  1. Use guality Lipos with high C rating (60C+)
  2. Balance charge every Cycle
  3. Try to not discharge below 3.6v at rest and never go below 3.2v under load.
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Any good charger can do this. Its called a IR measurement, (internal resistance). Good numbers range in various conditions. You would take the resistance and times it by the average amperage to get your voltage drop. If you look at the example under Internal Resistance: The Mystery Number https://rogershobbycenter.com/lipoguide/

I have my lipo alarm set to 3.7, conveniently placed at the storage voltage. I have only once in the last 3 weeks had my alarm go off from voltage sag (was from flooring the throttle). I could go lower but that would mean once I’m done using the lipos I would have to recharge them.

One thing I forgot to mention. You should let your Lipo batteries rest for at least 15 min after charging them before running them. And, you should let them rest for 30 min after running them before charging them. I read that somewhere but I can’t remember where.

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Yea this is pretty standard practice, I think battery university says something on their site as well.

Is there a battery capacity meter that will display the voltage in a cell (or the average) instead of a cumulative measurement or a percentage? What is this voltage alarm you speak of?

@evoheyax did exactly this with his board, he has like 12 LCD’s that display the voltages of each cell group. You’ll pretty much have to do that if you want readings from every cell group.

Yea, theres not really a better solution than that at this moment. I am looking into using the bms to feed individual cell data to the vesc, and modifying the vesc firmware to take in this extra info and pass that along to my iphone app. However, the issue with this will be you’ll have to use certain or maybe even one particular bms.

So is there anyway to get some indication while riding that things are getting perilosly low, aside from performance degradation? This will be my first time with lipos to care for as well and I had intended to ask this same question so I am glad it was posted.

If you’re using a VESC you can set a battery cutoff start in which you’ll notice performance degredation but not harm the battery if the value is sufficient. Otherwise voltage alarms will scream like a banshee when you’re voltage is too low.

Yes, you would need some sort of wireless protocol from the bms to get that info I would think

My first build I am using the x-car beast. Hoping that by the time I am ready for another build the vesc-6 will be out and tested (and the other “stuff” currently surrounding the vesc is sorted out)

I wouldn’t hold my breath. I’d say just pick up a VESC4 as it’s tried and true as long as you get it from a reputable source such as Ollin, Axle, esk8.de, Enertion, and others

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Well I have a vesc to iphone system, so if I could modify the firmware to add that data to the vesc’s data structure, and then pass it off with the COMM_GET_VALUES. But the bms needs to communicate to the VESC and vice versa.

I got these, you can also set a voltage for the alarm to beep at. https://www.amazon.com/Readytosky-Battery-Checker-Voltage-Indicator/dp/B01FHIMU0M

You might get the data from the bms to feed into an off board BT xmitter but then your app wouldn’t be able to talk to anything else and it might interfere with your remote receiver…,it would be an interesting project.

@wmj259 that’s great, thanks!