LiPo battery care and basic information

[mwkeefer]

I have been looking all day at how to contain the fire between my legs (lipos) on my race-link build. I am leaning toward some rectangular carbon fiber tubes such as these. http://dragonplate.com/ecart/product.asp?pID=4309&cID=54 Its pricey, but if I cut them in 6" lengths and milled some simple end caps with an o-ring for weather proofing, I thought that would work. So, two per 6" enclosure. That would be a little over 6.5" x 2" x 4" per enclosure. I could still assemble the pack the way I pictured above, except for the center cells, which I could put two cells end to end in a 2" x 2" x 12" tube. Glue, screw, rivet them all together. I wonder if that would be enough to stop one pair of flaming packs to cause the others to flame up. I would guess no. If I go this route, I will have to sacrifice a couple packs just to see. I assume the carbon fiber tubes would insulate or trap the heat though as opposed to Matt's machined aluminum boxes (again, not sure). Not having run these batteries before, I am relying on them not getting hot. That is another reason I decided to keep my pack together instead of making swappable smaller packs, to limit how much draw any one pack will get. Mine are 25C. -David

Dont forget the exhaust venting away from you and the frame in case of a flame out... a nomex lining would serve as padding but also would contain the flames and heat protecting your ride and your legs.

Probably not needed though!

-Mike

 

[rodgah]

Hi Gurus of LIPO,

I have a few questions myself that I have not found the answers to. I plan on running a 12s4p pack of 6s 5ah turnigys making 20ah....

charging is a hyperion eos1210i...with 2 lba10 ballancers(capable of balance charging 12s when using 2 balancers).

Am I able to make my pack so that I have 2x 6s 20ah (4x 6s packs in parallel at both discharge wires and balance tabs) so that I can balance charge both of these at the same time, then series the 2 packs to make 12s for discharge, while still keeping the balance tabs in parallel. I hope this makes sense, I know its a mess of words.....essentially i want to just unplug the series adaptor on the discharge wires then plug in both sets of discharge wires and balance tabs, for a balance charge.

Secondly the charger is capable of 10amp 180watt ....its my understanding that charging a pack past 1C gives little reduction in time and an increase in chances of overcharging. So 20 000mah pack at 1C is 20amp right? So if the charger can only do a max of 10amp that makes it a 0.5C charge? Is there a mathematical way of predicting how long a charge will take? I know balancing takes a fair bit of time, and I have also read that charging to 95% will shorten charge(balance) time considerably with added byproduct of making the cells last longer. Also since the 2 x 6s 20ah packs will be charging at the same time in series on the charger, how does this effect the rate at which they charge. Im kind of lost since Im mixing so many different techniques together(series,parallel, C rates ).....oh yeah im a dumbass so nice and slow with the details 8)

Cheers guys

 

[recumpence]

OK, a few details to bring out;

#1 The charger will not charge in a linear fassion, IE it does not charge in one hour even if set at 1C. The reason for this is because the charger will pulse the pack. If you watch the readout, you will see (for instance) 1 amp, 1.5 amp, 2.6 amp, 1.8 amp, 1 amp, 0 amp. This will occur throughout the charge cycle, but predominantly near the end of the charge. I have found a 1C charge rate will require about 90 minutes to complete if the pack is down at or near 20% SOC (State Of Charge) when charging began.

#2 You cannot parallel the charge leads with the packs in series. You will blow the ballance leads. You can, however, run separate ballancers for each 6s pack even while they are seriesed.

#3 Do not stress over constantly ballancing your packs. Lipo cells tend to stay in ballance. I have never seen more than 1% out of ballance state in many dozens of packs I have run over the last 6 years, NEVER! I suggest ballancing them (or at least checking them) when they are brand new. Then you really only need to check them if you are regularly dropping them down below 30% SOC. If kept above that, Lipo cells will almost surely remain in ballance.

Matt

 

[GGoodrum]

I agree with everything Matt says, but I would add one more thought. Although I agree, if you aren't running packs down to LV cutoff, LiPo cells stay fairly well balanced, that's not the only function the LBA10 balancers perform. They also provide individual cell voltage info to the 1210i, which it will use to shut down the charge process, if a cell goes over a safe limit. This is a very important safety feature. Occasionally, LiPo cells still fail (see what happened to AussieJester, in his cruiser build log...), and when they do, the voltage goes to zero. If you don't have cell-level HV protection, the rest of the cells can become overcharged, which can have disastrous results.

-- Gary

 

[recumpence]

Absolutely great additional information!

AJ was using a nonregulated charge method. That is what did his lipos in. If charged properly, they are stable.

Matt

 

[GGoodrum]

Absolutely great additional information!

AJ was using a nonregulated charge method. That is what did his lipos in. If charged properly, they are stable.

Matt

Yes, but had he charged with a 1210i, without the LBA10s, the result would've been exactly the same. Without the cell info from the balancers, the 1210i is simply a CC/CV supply, that runs off 12-15VDC instead of 110/220VAC.


-- Gary

 

[recumpence]

Not exactly. It would not overcharge a pack unless you had one cell (or more) that were completely bad because it looks at the total pack voltage. These things are very precise in their voltage monitoring. AJ had a few cells that were VERY overcharged! He has several that were 4.8 volts and even higher! That is insane. I do not see how that could happen with his 1210i even without cell monitoring while charging.

I totally agree that a BMS is the best way to go. However, if you check your packs periodically with any decent hand-held cell level tester or ballancer, charging without cell monitoring is a non-issue.

Matt

 

[GGoodrum]

Not exactly. It would not overcharge a pack unless you had one cell (or more) that were completely bad because it looks at the total pack voltage. These things are very precise in their voltage monitoring. AJ had a few cells that were VERY overcharged! He has several that were 4.8 volts and even higher! That is insane. I do not see how that could happen with his 1210i even without cell monitoring while charging.

I totally agree that a BMS is the best way to go. However, if you check your packs periodically with any decent hand-held cell level tester or ballancer, charging without cell monitoring is a non-issue.

Matt

This is exactly what happened. One cell went bad, going to 0V. This pulled down the other four cells in the same paralleled group to 0V as well. When a cell goes to 0V, it is like a dead short, so his 12s setup became an 11s pack, 4.2V x 12 = 50.4V, so if you take 50.4V and divide that by 11, you get an average voltage per cell of 4.58V. It is quite possible to have some cells as high as 4.9V, and still have an average of 4.58V.

 

[recumpence]

Ahh, I see.

Man, that really sucks. I feel bad for him because his does not have much money to work with.

Anyway, I am also a big fan of charging to 95% max. I know it reduces my range, but it is also much better on the cells. Of course in his case, he would have had to stop at 46 volts to prevent his problem.

That truely stinks.

Matt

 

[rodgah]

You guys are dedicated, thankyou both.

#1 The charger will not charge in a linear fassion, IE it does not charge in one hour even if set at 1C. The reason for this is because the charger will pulse the pack. If you watch the readout, you will see (for instance) 1 amp, 1.5 amp, 2.6 amp, 1.8 amp, 1 amp, 0 amp. This will occur throughout the charge cycle, but predominantly near the end of the charge. I have found a 1C charge rate will require about 90 minutes to complete if the pack is down at or near 20% SOC (State Of Charge) when charging began.

yeah Im only really worried about total charge time if its something crazy like 9 hours.......long time to supervise. It seems though that I can max out the charger without getting close to charging the pack at its limits.

#2 You cannot parallel the charge leads with the packs in series. You will blow the ballance leads. You can, however, run separate ballancers for each 6s pack even while they are seriesed

View attachment charge.jpg
View attachment discharge.jpg

so this setup will work for me Matt?



The reason I am worried so much about this is my friend with the other build is technically challenged....more so than I. I think for the extra time it costs for balancing it is probably alot safer for him as he would not know/understand/care about how to check individual cells V, and the thought of 20ah of lipo 2x3220s and the rest burning to the ground worries me.

 

[recumpence]

Yes, that looks correct to me.

Remember, even IF you wired the ballance leads incorrectly, the wire will blow like a fuse. It will scare the **** out of you. But, it should not affect the cells.

Matt

 

[gwhy!]

Sorry if this has already been asked or talked about before but I would like to know from peeps with a lot more experience than myself ( I'm still on that learning curve ) about acceptable levels of cell balance within a 6cell lipo i.e would a range of say 4.15v to 4.20v be acceptable or do it have to be tighter than this.
Thanks.

 

[vanilla ice]

That should work fine if you have cell level lvc warnings. Like it was stated, there is not much capacity difference between a 4.2v cell and a 4.1v cell.

If you're using something like those 6s $3 lvc buzzers like I am, it may cause the low cells to fall a little too low.

 

[recumpence]

No worries about that. As long as you are that close, your packs will be fine.

I normally set my charger to stop charging at 4.1 volts per cell anyway for safety factor.

Matt

 

[gwhy!]

Thanks guys.

 

[Ykick]

Hello - I've been getting some great answers for my battery quest in a thread I authored and the responses have confirmed that I should explore Lipo chemistry.

I've read most, if not all of this topic and wanted to know what's up with those $40 15C 5S 5000mAh Zippy packs from Hobby King? I'm thinking 3qty in series for 50-55V x2 for 10Ah total? I only need about 4-5Ah at less than 10C drain. Which charger(s) and what type of monitoring would y'all suggest?

Thanks!

 

[wasp]

i bought 8 of those 5s 15c 5000mah lipo's my only complaint is 1 cell in 1 pack was 0v
i was also using them in 15s config but blew my controller(my fault i attempted a shunt mod)
have a lyen 18fet coming and can't wait to see how they handle 65amp loads
as for a charger i think the 4x6s look very nice
i have a imax6ac and it takes a while to go through all my bats
one more thing is the battery medic is a really useful tool and is more accurate than my imax for balancing

 

[Seriousknot]

For battery enclosures carbon fiber would be cost prohibitive unless you just like to spend money. A very much less expensive material (and easier to work with) would be Normal fiberglass 1 1/2 oz. chopped strand mat with Vinyl-Ester resin. This was used to make bullet and fire resistant composite doors at a place where I used to work. Here is one source for materials
http://www.fibreglast.com/product/General_Purpose_Vinyl_Ester_Resin_just_resin_1110/Vinyl_Ester_Resins
The chopped mat will not burn, the Vinyl-Ester is very heat resistant. A piece of plastic rain gutter would make an excellent mold.

 

[bart_dood]

Hi Guys, I should have asked this question in this thread, so I'll copy and paste below. Hopefully someone knows the answer to my question:

"On a side note, when a lipo cell goes bad, during recharge they balloon up right? is this accompanied by an increase in temperature? or do they stay at the same temp as the good cells until they really fail and turn into a ball of flames?

I was working on a safety system based on temperature monitoring, if bad cells don't show themselves up with increased temps my system won't work.

thanks"


If the cell temps aren't a good indicator of a bad cell about the go FUBAH, is some kind of sensor to detect the ballooning of the cell a better method?

Thanks

 

[gwhy!]

Hi Guys, I should have asked this question in this thread, so I'll copy and paste below. Hopefully someone knows the answer to my question:

"On a side note, when a lipo cell goes bad, during recharge they balloon up right? is this accompanied by an increase in temperature? or do they stay at the same temp as the good cells until they really fail and turn into a ball of flames?

I was working on a safety system based on temperature monitoring, if bad cells don't show themselves up with increased temps my system won't work.

thanks"


If the cell temps aren't a good indicator of a bad cell about the go FUBAH, is some kind of sensor to detect the ballooning of the cell a better method?

Thanks

There will always be a problem temp monitoring charging battery's unless you use at lest 2 temp monitors 1 to monitor ambient temp and the other to monitor cell temp ( I made a temp sensor charger for nicads when I used to race off road rc cars years ago that allowed me to fully recharge them in around 5-10mins ) this worked very well and was more reliable than commercial temp fast chargers ( I seen quite a few nicad fire balls at race meetings ) IMHO the ultimate way in safely charging any battery chemistry would be to monitor temp and pressure ( this would be for fast charging ) but lipos do ballon well when about to fail( I have seen the vids ) so I would have thought it would be so much easier to make a pressure sensor emergency cut off rather than a temp cut off as there are normally more than one cell to monitor the temp of.

 

[bart_dood]

Hi Guys, I should have asked this question in this thread, so I'll copy and paste below. Hopefully someone knows the answer to my question:

"On a side note, when a lipo cell goes bad, during recharge they balloon up right? is this accompanied by an increase in temperature? or do they stay at the same temp as the good cells until they really fail and turn into a ball of flames?

I was working on a safety system based on temperature monitoring, if bad cells don't show themselves up with increased temps my system won't work.

thanks"


If the cell temps aren't a good indicator of a bad cell about the go FUBAH, is some kind of sensor to detect the ballooning of the cell a better method?

Thanks

There will always be a problem temp monitoring charging battery's unless you use at lest 2 temp monitors 1 to monitor ambient temp and the other to monitor cell temp ( I made a temp sensor charger for nicads when I used to race off road rc cars years ago that allowed me to fully recharge them in around 5-10mins ) this worked very well and was more reliable than commercial temp fast chargers ( I seen quite a few nicad fire balls at race meetings ) IMHO the ultimate way in safely charging any battery chemistry would be to monitor temp and pressure ( this would be for fast charging ) but lipos do ballon well when about to fail( I have seen the vids ) so I would have thought it would be so much easier to make a pressure sensor emergency cut off rather than a temp cut off as there are normally more than one cell to monitor the temp of.

I have already written software for a microcontroller to pick out a bad cell temp from the others while charging so this isn't a problem. So are you saying bad lipo cells do undergo a temp rise before/during the ballooning when they fail??

 

[gwhy!]

All battery's get warm when charging, but how warm depends on how fast your charging them (this may be minimal warming on the newer chemistry's i have always charged my lipos at the recommended rate upto now and have never really noticed if they get warm or not ). I cant say for sure that the temp of a ballooning lipo rises any faster than any other cell in a pack but I would have thought so.

 

[bart_dood]

All battery's get warm when charging, but how warm depends on how fast your charging them (this may be minimal warming on the newer chemistry's i have always charged my lipos at the recommended rate upto now and have never really noticed if they get warm or not ). I cant say for sure that the temp of a ballooning lipo rises any faster than any other cell in a pack but I would have thought so.

I would have thought so too, but before I plough ahead with stuff I need to confirm with someone in the know.

 

[The Mighty Volt]

I recently acquired a job lot of LiCoO2 18650 cells. 3.7v and 1500 mAh.

Do these fall under this broad category of LiPo?

How would I wire these into a 36v 20Ah pack {i.e. XsYp}, and what BMS do people recommend.

Thanks.

 

[amberwolf]

Broadly, yes, they are LiPo; the most "dangerous" kind. :lol: That's what I have here.

I have not built my pack yet but I am highly likely to use the method that doesn't require soldering to them. Build a containment box of wood, screw down brass bars across the tops of each parallel row, attach battery spring contacts to the bars at each battery pole point. Wire up balance wires to each brass bar, and the main input and output wires to the two end bars. Enclose it all in whatever is appropriate for your use. There's a thread specifically about this method, but I dont' remember what it's called.

If you have that cell welder built you can also use that to put them into packs.

Basically any method that gets you the pack shape you need that works for any cylindrical cell is ok.

Actual configuration depends on final nominal voltage you want. 3.6/3.7V per cell. Ah and C rating depends on the manufacturer, thus parallel amounts needed depend on how much current peak and continuous you need out of the pack, and how many Wh, vs what each cell is capable of.

BMS can be anything that supports the 3.7V max and ~3V min of these cells. I'll be using a F/G v2.6.

If yours are marked with a specific manufacturer, get their datasheet and go by whatever that says for max rates/etc. Most of mine are Sanyo URF18650 I think.