Batteries So ... I almost averted a fire last night. Lesson learned

[coolgabsi]

Had put 2 12s packs to balance charge . Was in sight but I couldn't see details and was rebuilding the warp. Well watched a full movie and still the packs didn't say completed charging. Still balancing. I go over and all packs are cool nothing wrong.

Well I start inspecting things. And one pack, outer shell is hard is it is supposed to be, but one of the 6 cells looks a bit deformed.. Wierd. Pull all batteries from charge and start checking internal resistances. This one 6s in the 12s duo, gives 140 mOhm and doesn't wanna give any cell wise reading.

I inpecr it further and it seems like there is moisture on the inside of these packs. Inside like two layers of clear heat sshrink in. Wierd..

Then turn the pack around for closer look, one cell right in the middle has lost it's seal.. Opened , I can see black on the inside.. And hold the battery eye level, I can see there is a little deformation in the outer shape!! Wow!

If I hadn't noticed this would have turned into a fire!

Why this happened? Cells were not on storage charge for over two months sitting in a cool place with no checking.... I preach it but I didn't follow.

Please make sure your cells are on storage charge (3.8v/cell) on storage for long times and monitor them every once in a while! Please balance charge big capacity packs when possible.. And check IR often

Good packs iR --- 1---5mOhm

Weak pack ---6---12mOhm

Higher... Is low low power and after 20.. Heli probably won't lift off easy

Please be safe

Will post a pic of the pack which is now sitting out on te concrete patio

 

[Tony]

Yup, you got lucky there. Gotta love the 306 though for being able to read those readings.

 

[xokia]

Please make sure your cells are on storage charge (3.8v/cell) on storage for long times and monitor them every once in a while! Please balance charge big capacity packs when possible.. And check IR often

Good packs iR --- 1---5mOhm

Weak pack ---6---12mOhm

Higher... Is low low power and after 20.. Heli probably won't lift off easy

I've ALWAYS put my batteries in storage charge and ALWAYS balance charge them. I've just always purchased multi port chargers such that I can charge each battery individually at high rates of speed. For 3S and below I have a 4 port 100W per port charger. For above 3S I have a 2 port 400W per port charger. The only batteries I have ever parallel charged is the 1S batteries I had for my mcpx.

Glad you didn't start a fire!! That would really suck if that was inside your house.
And those IR/ESR reading will depend on the C rating of the battery.

6-12 mOhms per cell is perfectly normal for a 45C battery. To high for a 65C which should be around 2mOhms.
My understanding though which I haven't measured this myself yet is that Pulse 40C 6S 5000mAh batteries are actually 65C batteries just with a 40C label. So the extra money you are paying for a 65C Pulse is just for the label

 

[coolgabsi]

Btw this was written half awake so heading makes it look like I burnt something.
I didn't though. Lol I saved it all ..

You are right xokia

The one rule of thumb I just read is actually anything under 10 is good .. I am not sure about what you said about lower C rated battery with 12mOhm is ok... But I will have to look into that.

Usual rule of thumb

1-10 good actually great

10-20 sport fliers ... Lower your timer down..

Over 20... Usually useless

 

[xokia]

If you start measuring different C rated batteries you will find varying mOhm ratings for the different C ratings. That's really what is determining the C rating for a particular battery. C rating itself IMO is hocus pocus. The ESR is going to determine what the voltage drop under load will be. In a higher end battery the ESR will be really low such that large current draws results in minimal voltage sag. ESR should be essentially the same throughout the entire charge but will increase drastically when the battery is depleted. When you start talking about 6S and higher batteries having a really low ESR becomes more important because its like a bunch of resistors in series ands the resistance adds.

What ads to the confusion is that it's really up to the manufacturer to place the right C rating on the battery. So a 65C from one manufacturer may be 40C for another manufacturer. So you might measure the ESR and be confused. When really these two batteries should probably be rated the same.

I added extra info here so that other people that might read this and can follow along. I know you know some of this stuff already so don't get offended