RC Lipo pack inspection, series/parallel charging, and lifespan/safety tips

[cycleops612]

Ha. You thought you were rid of me.

I am not quite there?

discussion on lipo all seems about hardcore fussing about with RC sub paks that have to be laboriously and meticulously charged and balanced. Its not for those who have a life. Perhaps i have been misled. Hi drain also has limited appeal for ebikes, as per the goldenmotors link below.

I didnt know lipo came in pouch cell form.

i wasnt aware, & nobody explained, & i got the impression, nobody used

further, the chinese seem to make it a major puzzle finding out what exactly is in a pak; wrong/ambiguous terms (lipo/polymer/li-ion,cannister/pouch/bms/c-rate,,...???), vague, ...

eg.:

http://gebattery.en.alibaba.com/product/1572634111-802657727/high_capacity_lipo_battery_3_7v_20ah_single_cell.html

"Product Description:
Dimensions: 8.7*150*180mm
Nominal capacity:20Ah
Nominal voltage:3.7V
Operation VoltageCharge)3.9V,(Discharge)2.5V
Charging ways:Constant-current/constant voltage
Max Charge Current:≤1CA
Max Discharge CurrentConstant Current)≤100A,(Impulse Current):≤400A
Standard Charge/Discharge Current:0.3 CA
Cycle Life 80DOD%)≥500Times
Operating TemperatureCharge)0°C~45°C, (Discharge)-25°C~60°C
Self-discharge Rate:≤3%(Monthly)
Weight:less than 400g"

i like general rules of thumb, so the above means; a 36v 20ah, 5c (am happy with 2-3c, but 5c is good so its not straining) discharge using 10 x 3.7v nominal?? cells at 400g ea. for a total of 4kg for 20ah, or ~100amp (3.6kw) burst.

AND BMS

that is pretty awesome.

500 cycles - meh. hang the expense, tho i hear these numbers are optimistic.

A similar lipo pouch cell
http://gebattery.en.alibaba.com/product/796643885-802657727/10059156_11Ah_5C_lithium_polymer_battery_3_7V.html

an example of a similar finished product:
http://www.alibaba.com/product-detail/Factory-price-36V-china-10AH-rechargeable_60402851552.html?spm=a2700.7724857.0.0.Wfi9uF


So, is this as convenient as a bottle battery - is recharge as safe and simple? Whats the catch?

seeking wisdom on this. pls help?

incidentally, gary salo of goldenmotor expresses similar views to mine about lifepo4, but better:

http://www.goldenmotor.ca/news/184/LiFePO4-vs-LITHIUM-ION.html

NB, yes, a 12x cell 36v lifepo4 is heavier than a 10 cell lipo 36v pak, but they are a very steady 38.4v vs 37v diminishing?.

OTH

am thinking, if the 15ah lifepo4 is too big and heavy, maybe its my estimate is the problem. Get a sturdy lifepo4, but smaller.

an hour and a half is all i want to be in the saddle, and am thinking 250w ph average use, a generous allowance w/o no pedaling on my mid-drive, - 25-30kph, with 500w on tap if needed.

10ah lifepo4 does that at a liveable ~3.5kg, tho 12ah (~4.2kg) seems sound for some wiggle room as it ages.

Pouch brands seem a well kept secret by pak makers. What gives? Ought one be wary?

all the fakes and lies of 18650s seem absent in the pouch world.

i have heard of crap quality tabs to work on, but not poor function or fraud or mislableing?

any advice?

ta in advance

 

[bionicon]

Don't know if i am right here I want to make a 12s 90ah pack out 3x ( 2x30ah) tattu lippo's. How can i balanced charge this as a complete pack......what do I need
What kind of charger and balancer?

Thx

 

[MrDude_1]

Don't know if i am right here I want to make a 12s 90ah pack out 3x ( 2x30ah) tattu lippo's. How can i balanced charge this as a complete pack......what do I need
What kind of charger and balancer?

Thx

Theres only 2 ways to do it.

1. get a BMS that works for 12s... this makes it easy as the OEM stuff, just feed it a bulk charge.

2. split the pack balance leads into 8s groups or less. You can then monitor everything with RC vehicle tools... you can still bulk charge, but keep an eye on the balance and run it through an RC balancer when needed.

to do #1 you need a BMS and a bulk charger.
to do #2, you need a RC balance charger... but to bulk charge you need a bulk charger and some cheap cellogs or other cell monitor. They're a couple bucks and they let you see the voltages as it charges.

 

[neptronix]

easy..

Buy a nice high quality 6s charger, use it to weed out the funky packs ( guaranteed you will get shipped at least 1 ), then bulk charge the pack for 99% of it's life. Charge to 4.15v average, discharge to 3.6v average ( or whatever the lowest common denominator is for all packs once you've created the graphs ).

With a little monitoring here and there, you can get away with this.. you just want to cut off the top 5-10% and bottom 5-10% of the pack's capacity. As long as the packs in question remain balanced over lots of cycles, this works.

If they don't remain balanced, you can always break apart the pack and do a balance on the 6S charger when needed.

12S BMS would certainly be a lot nicer though. If you can find one with the appropriate amperage output, that doesn't drain cell #1 and kill your battery early, and has the right voltage cutoffs etc.

 

[bionicon]

....euh did a quick search and did not found a 12s bms that has a continue discharge of 350 amps. My battery's are 3X2 30000mah with 25C continue ...so 90X 25 =2250 AMPS continue!(tell me if i am wrong)
So can I use the bms just to charge the pack? And to discharge disconnect the bms?

 

[wesnewell]

You don't even have to disconnect the bms to bypass it for discharge. Just use a separate main ground wire for the discharge and leave the bms connected all the time if you want to. But yes, you could just unplug the bms if you designed it that way.

 

[neptronix]

If you do that, the BMS will not cut off when a cell goes too low though.

Which is one of the main things you wire up a BMS for, ya know.

 

[bionicon]

and if i will use regenerative braking.....wihout bms? Will that work?

 

[MrDude_1]

and if i will use regenerative braking.....wihout bms? Will that work?

of course.
Just dont fully charge it at the top of the mountain and regen brake the entire way down.

 

[Wheazel]

and if i will use regenerative braking.....wihout bms? Will that work?

of course.
Just dont fully charge it at the top of the mountain and regen brake the entire way down.

Sorry for no constructive post, but this was hilarious and put funny images in my head

 

[Dylancoffin]

Hi, I'm planning my first ebike. I have a 26 in steel frame bike and I'm thinking of a 350-500w front hub. My commute is a flat 5 miles. I have years of flying rc planes with lipos. These batteries from hk seem like a good fit:

https://hobbyking.com/en_us/multistar-high-capacity-4s-10000mah-multi-rotor-lipo-pack.html

Huge capacity, light weight and a screaming deal. They are 10C, which is really low compared to my airplane lipos, but at 10Ah should be capable of 100 amps. The bike load should be more like 10 amps or only 1C, right?

 

[Ykick]

Hi, I'm planning my first ebike. I have a 26 in steel frame bike and I'm thinking of a 350-500w front hub. My commute is a flat 5 miles. I have years of flying rc planes with lipos. These batteries from hk seem like a good fit:

https://hobbyking.com/en_us/multistar-high-capacity-4s-10000mah-multi-rotor-lipo-pack.html

Huge capacity, light weight and a screaming deal. They are 10C, which is really low compared to my airplane lipos, but at 10Ah should be capable of 100 amps. The bike load should be more like 10 amps or only 1C, right?

3qty of those series wired for 12S1P would be a nice voltage for majority 48V systems. 500W @ 48V would be about 10A, plenty of headroom for those packs.

$/Wh is a very good deal although you may have to install different connectors or hardwired to series them. Have you checked prices on 6S packs? if similar price that would require one less series connection.

 

[Dylancoffin]

Thanks Ykick. The 4s 10 Ah are $37 and the 6S are $90. I don't know why the 4S are so cheap. Maybe they made a bunch. My experience with Turnegy batteries has been problem free, although I've never used these 10C packs. I like the XT connectors. It would be easy to make up a series connector.

 

[Ykick]

Pricing is just one of those HK mysteries. When they wanna move stuff they price it to move.

I believe these 10C packs are intended for AP multi-rotors? Slow and steady with long flight times but well within modest eBike needs.

I like XT’s and use them for all my aircraft but for series wiring packs 4mm Bullets have spoiled me. I’ve been using 4S Turnigy Hardcase with bullets for several years on my bikes. That was before these MS (multi star) packs became more prevalent.

 

[rguy56]

I was measuring internal resistance in some packs I just bought. I believe that's measured in micro-ohms?

One cell was showing 3x the resistance of all other cells. I remeasured, and it's consistently off. I'm getting .001 in the other 63 cells, but .003 in that one cell.

Is that measurement meaningful enough that I should use that pack for "utility purposes" or spare cells, is it something I should be returning as faulty, or is it truly no big deal at all?

 

[MrDude_1]

Thanks Ykick. The 4s 10 Ah are $37 and the 6S are $90. I don't know why the 4S are so cheap. Maybe they made a bunch. My experience with Turnegy batteries has been problem free, although I've never used these 10C packs. I like the XT connectors. It would be easy to make up a series connector.

The 4s hardcase are so cheap because HUGE numbers of RC racers buy them. The non-hardpack ones are the same, except for the shrinkwrap instead of the case.. so the huge volume lets them be cheaper.

 

[CobraJet]

So what charger out there now does 14S Lipo packs and balances at the same time?

 

[Jon NCal]

So what charger out there now does 14S Lipo packs and balances at the same time?

thunder power, adaptto

 

[Quinc]

Please school me on why I can charge my 4S lipos more after they have been balanced charged to "Full"

45a charger charging 6x turnigy 4S 5000mah 25C batteries in parallel.(30ah total charging them at .5C) Charger completes says they are full. But if I hit stop and start again they will take another 3-4000ah. Is this normal? An issue with my charger?

Charger:EV-Peak C6 High Power LiPo/LiHV DC Battery Charger (6S/45A/1140W

Full build thread: https://endless-sphere.com/forums/viewtopic.php?f=34&t=91687

 

[neptronix]

What's the difference in resting voltage for the whole pack between balanced and full?
Maybe 'balanced' means something else to your charger than 'full'.

Important to know these things so that things don't go on you.

 

[tomjasz]

My neighbor bought some Lipo off eBay. They won’t charge and in balance mode they show 1.3xV per cell 3s1p.

Trash battery?

 

[amberwolf]

Below 2v I wouldn't use them, myself.

 

[tomjasz]

Below 2v I wouldn't use them, myself.

Thanks. That’s what I thought I learned here but have zero experience. I wanted to hear a repeat of what I surmised was the best advice. A shame. The fella paid more than double the hobbyking price on eBay, and made modifications before ever testing/metering the packs. A sad lesson.

Thanks for confirming.

 

[GordonFreeman]

Got an e-bike for cheap at a garage sale...however...no battery. I've been doing RC stuff for years so I figured I could handle it. The bike says "48V", but I have no idea if that is "nominal" (3.7v) or max. I decided to get a total of 15 Lipo cells (5 x 3S)

I purchased 5 3S 5000mAh hard packs (lipo) hoping they'd fit (they did) and charged them up with an RC balance charger.

Hang on, this is totally ghetto:

I wanted to charge the whole pack at once so I needed 62+ volts.

I had a variac and some big caps laying around and obviously a rectifier. I set that to about 65 volts out. I charge it through a watt meter that shows me the voltage. Now if I let it go forever it will overcharge them a bit, so I'm always watching it. I go to about 63 volts (4.2v per cell).

I hadn't checked the balance on it over the winter and when I did, there was a bad (dead shorted) cell. So I figure I need to get a better way to balance them. I threw out that whole 3S pack and put a new one in it's place (not ideal, but).

I've been looking online for a "BMS" but maybe that's not what I need. I think I just want a balancer. But I'm worried about spending $50 and getting the wrong thing.

So now I'm thinking I could "split" the packs into 2 6S packs and a single 3S. My charger has dual 6S. So I could balance charge the two 6S packs at the same time and charge the other 3S with another charger or wait and do it on the same charger.

If any of that make sense or not, please advise. I'd like to charge it like I have been as one 15S pack, but it clearly needs a balancer to keep it in check.

Thanks

 

[neptronix]

Sir, this makes my hair stand on end to think about.

If you have not cycled those lipos and found the weak cells then at 4.2v you are 100% overcharging some of the cells and overcharged cells eventually catch fire from internal damage.

I would only suggest charging even up to 4.15v average even if you know you have a pack that keeps a very nice natural balance and never goes out of line.

If you add a BMS it needs to have an adequate rating.

Buy an iCharger and use it to cycle the lipos and find out what the weak packs are. Design your pack so that it can be broken into series units and be occasionally.

Your charger also absolutely needs current limiting also or it could internally damage/blow up the pack during charging itself. You need to current limit to 1C for most lipos, some specialized ones tolerate up to 5-10C


Please know that you are playing with the most flammable chemistry money can buy and we've seen hundreds of fires on this forum over lesser offenses to lipo management ( i once had one nearly ignite on it's own from very minor physical drama during shipping. )