Lipo IR's. Might retire some batteries soon

[DavidB1126]

Are these IR's good? These are on the 2 SMC batteries my uncle gave me. Might retire these soon.

 

[Greywolf74]

Those IRs are OK in and of themselves but keep an eye on them (especially the first pack) and see if the gap in IRs gets bigger. If they get to far apart then the battery becomes unsafe. make sure your LVC is set to at least 3.4V/C. The second one isnt as bad.

 

[Bogda89]

I would not worry about it for bashing, run until they puff or don't hold a charge properly.

Make sure charger is able to balance them properly while charging

 

[Slick2500]

Gap aside those numbers are good for used packs. Once the ir gets too far apart between cells or get to be about 20 is when you want to worry.

 

[RustyUs]

Packs are fine in my book. I would just keep an eye on readings and when taking IR readings do it the same way every time to keep things consistent. Here is a good read... LiPo Internal Resistance - Is your battery still healthy?

 

[bill_delong]

I don't particularly like it when any 2 cells go farther than 2mΩ apart as that tends to make the battery take longer to charge.

Not really sure if there is any danger unless you see signs of swelling.

I noticed performance start to degrade with loss of capacity and punch when any individual cell goes past 7mΩ and that's typically the point where pack swelling begins to appear. That's about the time it would be a good idea to start looking for a replacement. Once a cell goes past the 15mΩ mark is when I start to question the integrity of the pack and would consider discarding it at that point.

These readings are based on modern LiPo packs in the 5Ah+ range

There are smaller capacity packs in the 2Ah range that will start with poor IR readings and I have no experience on IR to make recommendations with those packs... use your best judgement by inspecting the pack for any signs of swelling and decide for yourself when you think is the best time to retire it.

Of the handful of LiPo fires I've seen at the track, not a single owner knew what their IR readings were, almost every pack was over a year old and already had significant signs of swelling before the fire occurred, in the cases where newer packs caught on fire were attributed to the owner "boosting" their pack in NiMh mode to get voltage above 4.2V/cell then walking away or forgetting they left their charger in NiMh mode with a subsequent charge.

I prefer to charge my packs at 40A where the average charge time is between 8-12 min.... if a pack takes longer than 15 min to charge, then I start looking for a replacement... where the IR is undoubtedly greater than 7mΩ at that point anyway.

More info here:

• Which charger is the best?

 

[DavidB1126]

On all of my lipos, I dont notice any swelling so that's good. These 3 of these lipos were bought in last June, my 2 mini b ones were in April, andy 2 SMC stick packs from my uncle are about 7 years old. Don't know about my maclan shorties since I bought them second hand. I charge the SMC and maclans on 10A. I charge the mini b packs on 2A and the 3 basher packs on 8A. My charger can only charge up to 12A on regular wall outlets. Seems like the lipos are all good for now. We will see on how ny basher packs do this June since they will be a year old. When I used to run nimh, the cells will have less run time about owning the batteries for a year. (Back then I didn't know much about batteries and I had a cheap charger)
For the past couple of weeks I had been checking the IRs after fully balance charge and after storage charge and IRs still look good. I had noticed that after fully balance charge the IRs are at 1.0 on both cells.

 

[bill_delong]

The first charge of the day will always yield the worst IR readings, to get the best IR readings you want to charge the pack almost immediately after being discharged which is similar to the "Pack Cycling" method which will boost the performance of your pack to increase punch (speed), you know how well your pack is going to perform when you measure the significantly lower IR after a cycle or two

 

[Bogda89]

The first charge of the day will always yield the worst IR readings, to get the best IR readings you want to charge the pack almost immediately after being discharged which is similar to the "Pack Cycling" method which will boost the performance of your pack to increase punch (speed), you know how well your pack is going to perform when you measure the significantly lower IR after a cycle or two

From your experience how long do batteries last when charged at 40 amps? Do you just charge them after race when voltage is like 3.9, 3.8v or you discharge it all the way down and then charge?

 

[bill_delong]

From your experience how long do batteries last when charged at 40 amps?

All depends on the brand... most budget brands will last anywhere between 6 months to a year and a high end brand might last a year or longer.

Main issue with batteries is heat... doesn't matter what brand I've ran (close to a dozen I've tested over the years) they all start swelling and IR fade in the heat of summer typically when ambient temps are above 110°F+

Do you just charge them after race when voltage is like 3.9, 3.8v or you discharge it all the way down and then charge?

For Open Mod classes yes, after a 5 min qual + 2 min of practice (close to 7 min run) of hard racing which tends to pull a lot more current than bashing around in the yard my 4S-5.2Ah pack in my eBuggy will typically be in the 3.8v/cell range and I will put about 3.5Ah back into the pack

For Stock Racing on 2S I will do the same thing unless I'm on the bubble in the B-Main, then I will cycle to 3.4v/cell just before each race... and I typically cycle before every main regardless in stock.

Note that 40A charge rate is not constant, it might spend a few seconds at 40A and it quickly drops in a reverse exponential curve through the CCCV process. The bulk of the time in a typical 10 min charge is under 10A.

I believe the damage caused by charging 40A is no worse than the high rate discharge where my packs are averaging the same lifespan of the packs I used to charge at 10A many years ago when I had a lower limit charger back then.

Yes, charging at 1C is safer and causes less damage, but it's a moot point if you're gonna drive in extreme conditions on a race track.

For a casual basher who doesn't need peak performance, then 40A charge is not necessary, just a convenience where I only race 1 pack per car and keep a spare pack only for bumps and when the IR starts to fade on the primary pack.