LiPo battery care and basic information

[Bobocop]

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.

I must be missing something then, because at 13.5 or as you say 13.6 = 54.4v for sla's charged,
and lipo 13"s charged (4.2v) would be 54.6, that's pretty even.
3x5's fully charged (4.2) would be 65v, discharging down to 3.0 volts 45.v (to be safe) would not work with my controller,
one, because i think it's to high a voltage (blow the controller)
and second since the my controllers cutout point is 41.5v, i would be discharging them down to far (below 3.0v before the controller cuts out.

From the few posts i read about people switching to lipo's with a 48v system are using 2x6S to get 44v, i haven't read (yet) about anyone going with 3x5S, but i'm still reading

I'll read up more on this voltage thing, but either way weather i get 3x5's or a 7's and 6's I still need to know if i can always leave the balance wires connected in parallel, or do i need to disconnect them after charging ?

 

[amberwolf]

That 4.2V is not going to stay that high for very long, though. 3.6V is more like the nominal flat part of the discharge curve on most of the LiPo cells I have seen spec sheets for, so it will only be at that voltage when under load for most of the time, dropping down to about 3.0-3.2V just before the LVC cliff.

Perhaps you could setup your charger to not charge the cells to 4.2V, as you won't typically get that much more capacity out of them that way (and it could shorten their life, in theory, to be charged to "full" capacity).

The parallel balance wires must be disconnected before reconnecting the packs in series. I recall a recent post in another thread describing exactly why, which involved fire, vaporized metal, melted connectors, etc.

I am still learning about Li as I test a bunch of cells to build packs from them. They'll probably be built as 12V packs simply because it makes it easier to replace SLA stuff I already have, while still keeping the SLA around as spares. I intend to only charge them up so that they match the SLA surface charge voltage, which won't get quite the max Ah out of them that way, but it will probably make them last longer and it will be easier to ensure they stay at voltages in system that I need during the long flat part of the discharge curve.

 

[Bobocop]

I found my answer, and for anyone else wondering the same thing, Yes you can always keep the balance connectors connected to the other packs, since the main pack wires are always connected also when paralleled, unless (of course) you want to balance each pack separately, which i don't see a need to do at every charge.

 

[Bobocop]

That 4.2V is not going to stay that high for very long, though. 3.6V is more like the nominal flat part of the discharge curve on most of the LiPo cells I have seen spec sheets for, so it will only be at that voltage when under load for most of the time, dropping down to about 3.0-3.2V just before the LVC cliff.

Perhaps you could setup your charger to not charge the cells to 4.2V, as you won't typically get that much more capacity out of them that way (and it could shorten their life, in theory, to be charged to "full" capacity).

The parallel balance wires must be disconnected before reconnecting the packs in series. I recall a recent post in another thread describing exactly why, which involved fire, vaporized metal, melted connectors, etc.

I am still learning about Li as I test a bunch of cells to build packs from them. They'll probably be built as 12V packs simply because it makes it easier to replace SLA stuff I already have, while still keeping the SLA around as spares. I intend to only charge them up so that they match the SLA surface charge voltage, which won't get quite the max Ah out of them that way, but it will probably make them last longer and it will be easier to ensure they stay at voltages in system that I need during the long flat part of the discharge curve.

Sorry amberwolf, I must have been posting as you were posting

Yah, i think charging to 4.0 or 4.1 would be best, but i still like the 7S and 6S idea better then 3x5S
I know i'll have more power then i have now with my SLA's, as the lipo keep their voltage up better then then SLA's. You can feel the SLA's dropping as you ride (a few minutes after you start), supposedly lipo's don't do that

I placed my question on the RCGroups forum and according to them, it is totally safe to keep the balance wires connected, from what i understand, when packs are paralleled through their main wires, there is no reason to disconnect the balance wires after charging.

Luke and Methods (and others) here seem to have a lot of experience with lipo's (from what ive been reading) but i haven't seen any threads yet about my question above.

There is actually very good info on Lipo's on the RCGroups forum as these people use these every day for their planes, cars,etc.
If you look under the Battery section, 90% of the posts are on Lipo's and the connections, charging and discharging of them.
Mind you, they do use smaller packs then we do, but the info (about the batteries) is the same.

 

[amberwolf]

Yah, i think charging to 4.0 or 4.1 would be best, but i still like the 7S and 6S idea better then 3x5S
I know i'll have more power then i have now with my SLA's, as the lipo keep their voltage up better then then SLA's. You can feel the SLA's dropping as you ride (a few minutes after you start), supposedly lipo's don't do that

Yes. That's what I meant about the flatter discharge curve--most of their cycle is spent around 3.6V. Once it starts dropping from there, it isn't long before it's at LVC (3V typical).

As long as you get the power and performance you need, it doesn't matter how many cells you use, or in what type of pack, except that having symmetrical packs makes it easier to parallel charge them if you wanted to do that.

I placed my question on the RCGroups forum and according to them, it is totally safe to keep the balance wires connected, from what i understand, when packs are paralleled through their main wires, there is no reason to disconnect the balance wires after charging.

Well, I must be misunderstanding how you meant to setup the packs. I thought you meant you would charge all your packs in parallel, then put them back in series to get the voltage for the motor to run from.

If you leave any wires connected from one pack to the other (in parallel) then when you series connect them again you will be directly shorting across every cell between those points.

If you are disconnecting all the inter-pack connections from parallel charging before reconnecting them as series, then it is ok.

If you instead are using a balancer that measures the cells while still wired *in series*, and are not disconnecting the packs from series connections to charge them, then that's ok too.

Mind you, they do use smaller packs then we do, but the info (about the batteries) is the same.

Generally, yeah. Only big difference is the length of time we use the packs at high discharges is much greater than most RC stuff does, since we might be riding for up to several hours on one pack charge, and most RC stuff is minutes at a time.

 

[Bobocop]

Well, I must be misunderstanding how you meant to setup the packs. I thought you meant you would charge all your packs in parallel, then put them back in series to get the voltage for the motor to run from.

If you leave any wires connected from one pack to the other (in parallel) then when you series connect them again you will be directly shorting across every cell between those points.

If you are disconnecting all the inter-pack connections from parallel charging before reconnecting them as series, then it is ok.

Maybe i didn't explain myself right, and i would like to get more info before i blow my new batteries up

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.

What i want to do is get a 7S pack and a 6S pack and hook them up in series for my application.
but i also want more amps, so the 7S pack will be paralleled with 2 other 7S packs to give me 15ah (7S at 5000ma x 3 = 15ah)
The 6S will also be connected this way (6S at 5000 x 3 = 15ah)

But they will be charged as 2 different packs, The 7S3P will have the main leads and the balance wires connected in parallel, for charging with one charger, and the 6S3P will be connected the same, but charged with another charger.

The 7S3P pack will be connected in series (by the main leads) with the 6S3P pack to give me 48v while in use.
My question was, do i need to disconnect all the parallel plugs from the 7S3P pack (and the 6S3P) before putting the main leads in series ?
Or can i leave all the 7S3P's pack balance wires connected in parallel (to each other) and the 6S3P's pack balance wires connected in parallel (to each other), while hooking up both main wires in the 7S3p and 6S3P packs in series.

But from the answer i got from RCGroups (and makes sense) the 7S3P packs main wires need to be connected to each other in order to get 15ah out of 3 x 5ah batteries, so why can't you also leave the balancing wires connected at all times.

 

[amberwolf]

Ah--I missed the actual way you were going to connect them.

Doing it that way is perfectly fine, and as far as I know would actually be preferred. No reason to disconnect the balance wires I'm aware of.

The way I intend to build my packs is to actually wire cells up in parallel first, and then wire those parallel sets in series, rather than to take series sets wired in parallel.

In theory that should both be better for the charging and discharging of them. It's how a number of longer-life dead laptop batteries I've taken apart have been wired, where they use more than one string of cells for more capacity.

I'm considering using individual chargers for each parallel set of cells, built from celphone battery BMS boards and the celphones and their chargers. It'll be big, very ugly, probably not safe, not portable, and only cost my time.

 

[Bobocop]

The way I intend to build my packs is to actually wire cells up in parallel first, and then wire those parallel sets in series, rather than to take series sets wired in parallel.

Are you getting cells separately (a 3.7v cell) to wire them in parallel, or do you mean packs to wire in parallel.
If you meant you are getting cells, where are you buying single cells ?
I've seen single cells for sale, but they cost as much as a pack does.

 

[amberwolf]

I got lucky with a for sale post here on ES; someone planning a conversion for a bike or motorcycle (forget which) had a bunch of 18650 size Li-Ion (LiPo, I guess it is) pulled from new/unused equipment batteries, Advertised as tested that most were fine and some were questionable or dead. Great deal at around 30 cents a cell, once I get the whole thing setup to actually use. So far all the ones tested at their end as working have worked, of the handful I have had time to test. I've not dealt with any of the ones tested as bad, but suspect they all really are. I'll be practicing my pack assembly techniques with those.

I have a thread about it linked in my sig; I just haven't had enough uninterrupted time to deal with it so have gotten almost nowhere so far.

 

[nomad85]

3x5's fully charged (4.2) would be 65v

I currently have a 48v controller, I am planning to use a 15s pack(3 5s packs). Your controller may be different, but most have 63v rated caps. a fully charged 15s pack would be at 63v (15x4.2= 63) I have run 5 sla batteries at 65-70v(it quickly went below 60v) before and it has worked, so I think this configuration will work. I haven't tried it so I cant be sure, just thought I would share what I know from where I am in the process.

 

[Bobocop]

I haven't tried it so I cant be sure, just thought I would share what I know from where I am in the process.

If that's what you believe, Try it, And then let us know. If your right, you will become a GOD

 

[Arlo1]

3x5's fully charged (4.2) would be 65v

I currently have a 48v controller, I am planning to use a 15s pack(3 5s packs). Your controller may be different, but most have 63v rated caps. a fully charged 15s pack would be at 63v (15x4.2= 63) I have run 5 sla batteries at 65-70v(it quickly went below 60v) before and it has worked, so I think this configuration will work. I haven't tried it so I cant be sure, just thought I would share what I know from where I am in the process.

One thing you will find is they are almost never perfactly ballanced. I charge my 24s pack as a pack and ballance with a 6 s balancer on the highest charged pack every time. The math says 24s x 4.2 v = 100.8 But my beepers warn me usualy ~97-100 volts when the first cell hits 4.22 so unless you have a great balancing system you likely wont charge to 63 v very often. The other thing is if you charge to 4.1 volts a cell they last alot longer (i think its 10x the cycles) there is a chart I can find a link for if you like to see it. But that only puts you to 61.5 So that may help.
: Edit I see the chart was linked on the last page and it looks that at 4.1 volts charge you still get >90% charge capacity! I was realy concidering making my setup a 25s system and only charging it to a little less to let the batterys last longer (in terms of charge cycles) and to get a higher nominal voltage for a more consistant higher top speed!

 

[The Mighty Volt]

Is it a good idea to leave the battery plugged into the charger even though it is fully charged? I have been told that the BMS allows a trickle into the battery which helps balance it all out nicely.

 

[Arlo1]

Is it a good idea to leave the battery plugged into the charger even though it is fully charged? I have been told that the BMS allows a trickle into the battery which helps balance it all out nicely.

Uhm If I am understanding what you are asking no. I never charge any one cell over 4.22 v where my cell moniter starts beeping. So if you ceel gets to 4.22 volts and you keep chargine it its not a good thing. But we should let some one chime in who has your bms and understands how it works. but basicly rule of thumb NEVER CHARGE any one cell OVER 4.3 VOLTS EVER! The lower you charge each cell ever time the more cycles you can get out of a pack as well.

 

[liveforphysics]

Is it a good idea to leave the battery plugged into the charger even though it is fully charged? I have been told that the BMS allows a trickle into the battery which helps balance it all out nicely.

A LiPo charger will not and can not trickle charge. Charging from a CC/CV power supply will not and can not trickle charge LiPo. The only way LiPo can continue to accept current is by raising the voltage, which = fail.

 

[BikeFanatic]

Is it a good idea to leave the battery plugged into the charger even though it is fully charged? I have been told that the BMS allows a trickle into the battery which helps balance it all out nicely.

I think you are referring to your Lifepo battery correct? Don't you have a lifepo from cammy or ping? And this thread is lipo.

If I am mistaken, sorry, and would be interested in your lipo BMS source.

 

[damcard]

So I have 18 of these Zippy Flightmax 6s 5ah packs.
View attachment IMG_0827.JPG

I will be using two packs of 9 in series and parallel them together for a total of 12s9p.

First, I just need to parallel the cell taps together right? And then I should be able to use a 12s charger to charge them all together right?

If I got this right, Matt recommended charging/balancing each individually and then parallel two packs together overnight. Afterwords, I can solder together all the main power leads, correct?

Also, I am lost trying to find a good 12s charger. I am looking for a quality charger at a good price-point, not necessarily the best. Is the Hyperion duo charger the way to go?

Eventually I want to build my own solution, but I am looking for an in between option. -damcard

 

[jondoh]

I guess i should have jumped onto this thread instead of starting my own.

Here's my attempt at a 2s3p using 6s5000mah turnigy cells:

http://www.youtube.com/watch?v=2KOmPAZqhnw

http://www.youtube.com/watch?v=5rPakXuia5U

I too am looking for a bulk charging solution.

 

[markcycle]

I got to say seeing all this Lipo being used in basically unprotected rack bags is really scary. If you should drop your bike onto a curb or any hard object and the cells get damaged the chance of fire is very real. There are examples of people just dropping a pack and it starts to smoke and flame.

I made this frame out of wood and I'll send the plans to any one who asks. Its simple and should protect the cells from a falls as well as impact damage. Remember a bicycle rack sees impact loading on every bump, RC airplanes do not except on landing and crashes. The soft pouch cells are going to fatigue from constant impact loading and vibration which can result in a terrible fire.

The power to weight and low cost of these Lipo cells are amazing but just putting them in a rack bag is going to result in some bad outcomes.

I'm also working on a activly cooled version, cooling tubes in the walls of the frame, using water or oil.

Mark

 

[jondoh]

the bag has a lot of foam padding. It's not like just a flap of nylon. you think this is still a problem?

 

[markcycle]

the bag has a lot of foam padding. It's not like just a flap of nylon. you think this is still a problem?

I can't say but
I would recommend placing the cells in a hard walled box to group them together as a brick (so to speak) to prevent them from vibrating against each other and prevent a puncture in the event of a fall or crash. At least tape them together so they don't bang against each other (you may be doing this I can't tell from the video's)
You know at some point in the life of the bike it's going to fall every bike does so you have to think about how the batteries will be impacted when this happens, also think about the worst real world situation the batteries may experience such as a accident. A major fire in the middle of a interestion is going to draw alot of attention. A box of half inch plywood to prevent puncture damage is cheap insurance.

Then foam under and around to reduct impact vibration is good. Every bump is a spike of vibration so the foam your doing is the right thing to do.


Mark

 

[liveforphysics]

Mark- You buy 30C LiPo, and I promise you that a cooling system is no concern at all.

Ask anyone here with quality LiPo, you can't get the cells to warm up no matter what you do to them.

 

[markcycle]

Mark- You buy 30C LiPo, and I promise you that a cooling system is no concern at all.

Ask anyone here with quality LiPo, you can't get the cells to warm up no matter what you do to them.

good to know thanks

The 20C cells I have got just a little warm a few degrees above room temp. at a constant 100amps for 8AH usage of a possible 10AH pack.

so I was thinking maybe cooling of these cells (20C) may be needed If i pulled much more than 10C from them

A better solution to cooling is to use 30C cells
Mark

 

[damcard]

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

 

[CamLight]

The carbon fiber tubes will certainly stop some of the heat from spreading but the resin used to make the fabric rigid might be rated for a much lower temperature than the fabric itself. I'm not sure it will just char or would soften and let the packs sag (which could be very bad).

Not sure if it will work for you, but, how about fiberglass or carbon fiber fabric? The fiberglass at Mcmaster-Carr (http://www.mcmaster.com, catalog pages 3478-3480)is rated up to 1500F and the carbon fiber is rated up to 800F. The crazy high temperatures you see for carbon fiber are when there's no oxygen. The fabric lets you mold it where you need it, stack it up where you want more protection, and will let the smoke out where you want it to leave. You'd still need a hard case but with the insulation the fabric supplies, it could be made out of anything.