LiPo battery care and basic information

[liveforphysics]

If you put a LiPo pack in the oven and over-voltaged it to blow it up, it would be fine. Oven would be a great place to charge, good idea.

You mentioned a Ping pack. For energy storage, it's fine. About twice the weight and bulk of LiPo for the same energy storage, but still fine. Now, lets talk about POWER differences. This is what LiPo is all about.

Let's choose Ping's biggest battery, the 48v 20Ah. This is a 2c battery, which tells us that this pack can discharge at 40amps. This battery weighs 20lbs, and can discharge at 1920w.

How much weight in LiPo do you need to match that?
Not picking anything fancy, just economical 30c zippy LiPo packs from hobby city, we can work out what it takes to equal the power of the biggest Ping pack in LiPo. What does it take? It just takes a single tiny 4cell 5Ah zippy pack, and it can all ready sustain 2200w VS the Ping battery 1920w, but the big difference is weight. The LiPo battery is just 1.2lbs vs the 20lbs of Ping battery! Yup, that's about 17 times the power density. It's also about the size of a regular non-flip-type cell phone, VS the size of a couple stacked shoeboxes. If you are looking for energy storage, lead-acid, LiFePO4, NiMH all offer energy storage at low prices if you don't mind a lot of weight and bulk. However, if you are looking for performance and power with a reasonable cost, nothing matches LiPo.

Just incase anyone wanted more specs on the battery I choose to compare power to the biggest Ping pack, here is a link. It's not anything special, just the upper model of zippy LiPo.



http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=8588&Product_Name=ZIPPY_Flightmax_5000mAh_4S1P_30C_

I'm lost, .... 14volts X 3 = 45 volts. 5AH X 4 = 20 AH. That means 12 of these units roughly equals a ping 48 V 20 AH. Each of these 12 units weighs over 500 grams. About 15 lbs. or so? Or did I miss something mighty big?

Power density and Energy density are very different things. If you are involving Amp hours in your calculation, you are confusing energy and power.

 

[liveforphysics]

17 times the energy density?

I think you have miscalculated or you are onto one of the greatest discoveries in battery tech yet.

You would need 4 packs, of the one's you suggested, to equal a ping 48 (56v actual)

And for capacity 4 times that. 5000mah = 5ah x 4 = 20ah

I believe that totals 16 packs with a total weight of 8416g. Ping battery is 9900g.

A battery that can burst all of it's power at once is not that useful on a machine made to stretch that power over hours and not risk burning your 3 decker home down at the end of the day.

Correct me where I am wrong because I will fire proof my kids playhouse if you are correct :wink:

Re-read my post. 17 times the power density. Very different than 17 times energy density.

 

[gunthn]

But I have to give up my 900d oven every time I make a mistake?

 

[gunthn]

p=W/T

time is the key factor here.

If were talking horses well lukes lipo can lift a 12650 lb.horse for one second(or minute or whatever the discharge rate boils down to)
while pings phosphate can lift a 1650 lb. pony for one hour

Who can lift more?

a)ping b)luke c)pings pony with lukes battery attached to its ass d) lukes horse with pings pony attached to its ass or fill in the blank

 

[Thud]

I am wondering about the durability of the prismatic lipos.
I just recieved a couple 6 cell packs &they were abused during shipping I havent put a volt meter to them yet & I doubt that I will get any warrenty satisfaction from hobby city.(the package had crush damage on both ends) I guess I should have never signed for it.....but Ive been waiting soooo looong...

Anywho..you helio guys surly have crashed these packs & dented/twisted and other wise "impact" modified a pack or two. so...

What constitutes a damaged pack?

Is there a rule of thumb on dents or gouges?

If a pack shows signs of abuse is their a safe way to test it...

I fear I may have to disasemble these & salvage the good cells....& you tube the damaged ones adding to the fears of the general public. (not)
any opinions are welcome.

 

[steveo]

I am wondering about the durability of the prismatic lipos.
I just recieved a couple 6 cell packs &they were abused during shipping I havent put a volt meter to them yet & I doubt that I will get any warrenty satisfaction from hobby city.(the package had crush damage on both ends) I guess I should have never signed for it.....but Ive been waiting soooo looong...

Anywho..you helio guys surly have crashed these packs & dented/twisted and other wise "impact" modified a pack or two. so...

What constitutes a damaged pack?

Is there a rule of thumb on dents or gouges?

If a pack shows signs of abuse is their a safe way to test it...

I fear I may have to disasemble these & salvage the good cells....& you tube the damaged ones adding to the fears of the general public. (not)
any opinions are welcome.

that freaking SUCKS MAN!!!

-steveo

 

[ZapPat]

I am wondering about the durability of the prismatic lipos.
I just recieved a couple 6 cell packs &they were abused during shipping I havent put a volt meter to them yet & I doubt that I will get any warrenty satisfaction from hobby city.(the package had crush damage on both ends) I guess I should have never signed for it.....but Ive been waiting soooo looong...

I would remove the rest of the blue shrinkwrap and closely inspect each cell pouch for punctures and/or excessive dents. Also check all the cell voltages for ones that are too different from the others (like over a 0.2-0.3V difference could indicate a problem, specially if the cell in question also has had some physical abuse).

If all is OK with these tests, put the pack on a slow non balancing charge mode using a good lipo charger such as ichargers or turnigys or whatever (but DO use the balance wires so the charger can cut off the charge for the first full cell). "Slow" for a 5000mAh pack might be something like 0.1A-0.25A or so and make sure you keep a close eye on it during this initial charge to check for puffing. Use your charger's cell monitor function to once in while check out the cell voltages to see if they are keeping together closely enough.

If all goes well with the inital charge, then a slowish discharge using the charger can then be done, again checking for any cells drifting too far away from the others or puffing. At the end of the discharge you will now know the weakest cell's capacity and it should be close to the specs (5000mAh), else there might be a problem.

Also, for added safety you might use your charger's temperature sensor input to check your pack's temperature (remember to configure the charger to use the sensor and set it quite low, like to 45oC or so depending on your room temperature). Probably not needed for the low rate charge/discharge test, but if all goes well and you want to charge/discharge at higher rates after, then the probe becomes a potentially usefull safety feature.

That's all I can suggest, but I'm not a long time user of these things yet either. Good luck!

 

[Thud]

report.

I did un-wrap the severly twisted one. gave it a thourough look over & pluged it into the I charger1010 to see where it was at.
All 6 cells were at 3.85(typical) I set it for a ballence charge & it finished with all cells reading 4.15 (my cut off point). no swelling, no heat, hmmnnn. I will cycle it couple times without ballancing & see what happens.
I figured if it had been punctured there would have been a fire during the shippment.
The 2nd pack with the crunched corner was superficial just a small flat spot in the foam tape inside the blue shrink.
If the super twisted pack holds up I will be quite impressed (I have a bunch of smaller packs I use on my park flyers)I have never had a pack fail, but again Ive never had one with that kind of damage.

 

[OneWayTraffic]

I have a question. If one got a prebuilt LiPo pack from a reputable supplier, what would be the actual chances of this over voltage->boom occuring?

Asking because ebikes.ca now has LiPoly options for their Ezee kit. I'd assume that that pack has a BMS to ensure proper charging, so I shouldn't need to worry about it, provided I don't do anything stupid, like shoot it with a shotgun or unwire the BMS?

 

[The Mighty Volt]

I have been looking for an advanced battery charger/balancer for Lifepo but all I find is small charger for 6s units.


Is there a good advanced charger/balancer for much bigger 36v type units that have a lot more than 6 cells?

Thanks.

 

[gilnet]

do you mean lipo? or lifepo4?

 

[gwhy!]

When using lipo's what is a exceptable sag voltage whilst being used if the lipo are fully charged. If I have a 44.4v set when fully charged read about 50ish v is there a absolute minimum voltage I should not pull them down to, I understand about the STOP using the pack if the recovered voltage is less than ~3v per cell but how low can they be safely pulled down to or is this dependant on the C rating of the cells. Thanks in advance.

 

[liveforphysics]

The dynamic voltage of the cell makes no difference to the cell for everything except heat. If you're pulling a volt of drop, and 100amps, then you've got 100w of energy working to heat that cell inside. If you're keeping the thermal issue in check, then there is no risk to the cell by having the loaded voltage drop.

The amount it drops is of course determined by the Ri of the cell, and Ri is what determines the C-rating. If you can cut the Ri in half, you cut the heating in half, and you can double the C-rate.

Ri = cell heating = C-rate

 

[gwhy!]

The dynamic voltage of the cell makes no difference to the cell for everything except heat. If you're pulling a volt of drop, and 100amps, then you've got 100w of energy working to heat that cell inside. If you're keeping the thermal issue in check, then there is no risk to the cell by having the loaded voltage drop.

The amount it drops is of course determined by the Ri of the cell, and Ri is what determines the C-rating. If you can cut the Ri in half, you cut the heating in half, and you can double the C-rate.

Ri = cell heating = C-rate

Thanks for the reply Luke, This is what I was hoping for

 

[jmygann]

Increasing Large Li-Ion Battery Pack Energy Delivery with Active Cell Balancing


http://www.automotivedesignline.com/showArticle.jhtml?articleID=220600788

 

[vanilla ice]

Thanks for the reply Luke, This is what I was hoping for

That is so simple even I can understand it.. Wow much simpler than I thought itd be before reading it! Now I can figure how many watts of heat my lipo is getting.

 

[jondoh]

I'd like to make a lipo pack using 8 of these (4s2p):

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=9176#


I would also like to use a bulk charger-- I know there's the risk of fire BUT let's say I'm able to specify a bulk charge of 47 volts? This way, if one cell dies, the rest get a max of 4.27 volts which is below the overcharge limit. It also means that when all cells are operating properly, the max charge is only 3.93v.

My question is, would this strategy prevent overcharging fires and what capacity (90%?) do I get charging to just 3.93v?

 

[mwkeefer]

Your best bet would be to use 2 or 3 CellLog8 with the High Voltage Alarm trigger set to Cell Count in Series * 4.16.

Now set your bulk charger for series count * 4.15 output voltage.

Then you collect the output of these via relay and use them to interrupt the connection between your battery and the charger (only need to disconnect the gnd or positive side) via relay...

Now when a cell hits 4.16v the alarm disconnects the charger until the resting voltage is again below 4.16v

This will occour durring the normal taper to 4.15v and yes it does work better with 2 or more in parallel but it will still work on a single P pack and is how I charge my 15S packs (1 and 3P)...

I also have the hobby king balancer / analyzer / dischargers which I turn on at the start of a charge manually but really even without them I get within 10mv of pack balance using this toggle on / off method... remember once the pack has reached full charge (4.15 * Cell Count) there will no longer be current flowing into the pack even when the charger is live and connected. This causes the charger to basically disconnect until the high cells fall down and again the battery pack voltage is below the charger set voltage.

Hopefully that isn't too complicated (or convoluted since it's tired and I'm late) {lol}

-Mike

 

[jondoh]

keefer,

using cell-logs is well and good. i have used one and they're great but i don't want the complication of adding relays. even with a HVC system in place, it wouldn't take much for it to go wrong. I'm still wondering how charging lipos to 3.93v per cell compares to 4.15v per cell. on paper, it looks like 90% charged.

 

[kZs0lt]

I'm still wondering how charging lipos to 3.93v per cell compares to 4.15v per cell. on paper, it looks like 90% charged.

I have no experience with Turnigys, but I don't think you'd get 90% capacity charged @3.93v, that is pretty low for a LiPo. More like 60-70%. See Usable Capacity vs charging voltage
To be sure, you should ask the guys in the Turnigy thread. But I don't think it worth charging to 3.93v.

Zsolt

 

[999zip999]

Hay 999zip999 I'm new, I have a 48v20ah ping slim line bat. with a 600w high speed BMC motor,36v-72v crystalye controller. I blown my battery #16 cell pos. red wire end cell in parelle of 4 packs of 3.2v-5000mha of aliumn puch cells. Where is spell check? Replaced the 4 puches to complete the cell change , then I charged up #16 low 3.2v rest were 3.7v Had a friend charge the one cell on the truney ? charger. NO GOOD! LOOK! no solder between #15 cell and #16 cell ONE BIG BLOB of solder. Where's spell check? A OK 53.4V WOW! Runs good # 16 light always on ? new cell. Ping told me to use a 60 amp. BMS insend of the 30 amp. BMS that came with it. The one black r2rr black thing under the #16 light had melted,on the new 60amp BMS the red light still works but changed back to old 30a. BMS NOW but what I do NOW?
?

 

[Bobocop]

I'm thinking of switching to lipo's, I do need to keep my 48 volts so i was thinking of getting a 5S and a 2S pack and hook them together to give me a 7S pack (25.9v) and then a 6S (22.2v) which then in series would give me a 48.1v pack,
I want to get 3 in this configuration and parallel them so i will have a 48v 15amp pack (7S3P and 6S3P)

untill i find a way to charge the complete pack at ounce, i will be charging both packs in parallel separately, the 7S3P with one charger and the 6S3P with another.

My question is, can i leave the packs balancing wires of each parallel pack connected wile i ride (discharging)
in other words, i need to hook up the 7S3P pack balancing wires together for parallel charging, can these wires always stay connected (in parallel) even if i put this packs main leads in series with the other 6S3P pack ?

 

[deronmoped]

From what I hear, if you want 48V you need 3-5S packs to be equivalent to other 48V packs, like the Headway packs.

I'm looking at doing a 48V pack too, kinda hoping someone will have a solution in the near future for a complete turn key pack.

Deron.

 

[Bobocop]

From what I hear, if you want 48V you need 3-5S packs to be equivalent to other 48V packs, like the Headway packs.

I'm looking at doing a 48V pack too, kinda hoping someone will have a solution in the near future for a complete turn key pack.

Deron.

3 x 5S would be 55.5 volts (more then that when fully charged) I don't think my controller can handle that

 

[amberwolf]

If you had SLA before, then while charging they'd be up around almost 60V (assuming 14.5V+ charge voltage). Even at a nominal full charge of 13.6V each, 4 SLAs would be 54.4V.