The "Brave Combo" Lithium Pack

[safe]

That's a subtle joke about the music band:

http://brave.com/bo/

...but the real point is to walk through the REAL dangers about Lithium batteries verses the not-so-real dangers that people over react about.

The "official" way to build a Lithium pack is to use the "PCB" circuit that makes sure that the batteries can't be overcharged or over discharged. This is very complicated and expensive to do.

The "Brave Combo" approach is to go "naked" and with proper knowledge to manually avoid the pitfalls that can turn your battery pack into an imitation of "Three Mile Island". Like nuclear power itself, if you manage things correctly it's the best thing going.

So I'll start by asking about charging. What battery configuration is best to use for charging and which chargers are the best way to go about making it work?

If series is "bad" (dangerous) for charging, then would it be possible to design a pack so that it had all the sub-packs in parallel and when you charged it you could run everything through a parallel connection. When it came time to use the bike you unplug all the parallel packs and reconnect all the wires into series.

I ask that because that's how I do my SLA bike right now, I charge at 12 Volts and run at 36 Volts.

 

[xyster]

After see the above pics about the band "brave combo", perhaps Safe, lithium carbonate is the type of lithium you really need
http://www.rxlist.com/cgi/generic/lithium_ids.htm

 

[safe]

After see the above pics about the band "brave combo", perhaps Safe, lithium carbonate is the type of lithium you really need

You caught one angle on my joke... very impressive...

And what about my question... what if you charged EVERYTHING in parallel?

(Brave Combo is to music as we are to invention... we are always experimenting with new ideas even if they aren't mainstream)

 

[xyster]

The "official" way to build a Lithium pack is to use the "PCB" circuit that makes sure that the batteries can't be overcharged or over discharged. This is very complicated and expensive to do.

Just to note that there are now many good lithium packs pre-built with a BMS and all that. But this thread, as I understand it, is about DIY lithium solutions.

The "Brave Combo" approach is to go "naked" and with proper knowledge to manually avoid the pitfalls that can turn your battery pack into an imitation of "Three Mile Island". Like nuclear power itself, if you manage things correctly it's the best thing going.

Well, there are those niggling little issues with nuclear waste, mining uranium, and diversion of material to terrorists and rogue states...but I'll stay on-topic and not mention any of that....

So I'll start by asking about charging. What battery configuration is best to use for charging and which chargers are the best way to go about making it work?

Assuming we consider battery balancing as absolutely necessary, offhand I see four practical charging methods:

1)Single RC-type charger with associated balancer like Patrick Mahoney employs for his lithium pack.

2)Multiple single-cell chargers each connected to a single parallel subpack, and operated simultaneously ( my method ). These requires each charger be electrically isolated from every other, which in practice usually means NO three-prong grounded chargers (or the ground prong can be broken off).

3)Single, multi-cell charger with on-board BMS to do the pack balancing. Not all BMS's do pack balancing, which will sooner or later lead to apparent loss of pack capacity as the BMS will cut out when the lowest-voltage subpack goes below the LVC, while the other subpacks may have plenty left.

4)The "switch to parallel for charging" technique you asked about below.

If series is "bad" (dangerous) for charging,

Series is not necessarily bad for charging. But it depends on what you mean by series, and if the BMS is balancing the cells actively or not.

-Individual cells only "know" their buddies that are physically connected in parallel, they don't see the other subpacks or their cells. So long as the multiple chargers are isolated, and each charger connects to one and only one subpack, then the system continues in this manner, and no short or other untoward effect occurs.

-Now if you mean "series", charging the entire pack with one charger, or multiple chargers themselves wired in series AND THEN connected to the entire pack via a single jack, then dangerous overcharge is a real possibility if the cells are not simultaneously balanced somehow (like by an onboard BMS). Think about it: a subpack starting at 4.0 volts will get to 4.2v before a subpack starting at 3 volts. If your two-cell charger shuts off when the string equals 8.4 volts, then the higher voltage pack will be overcharged, perhaps with catastrophic results including fire.

then would it be possible to design a pack so that it had all the sub-packs in parallel and when you charged it you could run everything through a parallel connection. When it came time to use the bike you unplug all the parallel packs and reconnect all the wires into series.

Yep, it'd take a lot of relays for, say, a 20-series lithium pack (n-1) or 19 relays I think (been awhile since I drew myself a schematic looking at the same choice). I believe it's generally A-OK to wire lithium chargers in parallel so as to increase their amp output. However, unlike other chemistries charging, charging lithium at double the rate does not halve the time -- less effect than that.

Batteryuniversity.com has excellent info about all this.

 

[safe]

The Balancer

It took a search to find what Patrick Mahoney posted about the balancer he was using. It was in the "True Cost of Batteries" thread. He wrote that he was using a "Hyperion LBA10 balancer" - $39.95 :

The literature on this stuff might as well be in chinese because it makes no sense to me. How many Lithium batteries would you be able to "balance" with this thing? Could you buy one for the whole pack and make charging easy?

 

[xyster]

The name says it:
"6s" or 22.2V nominal.
It also says in that pic it can be networked with another balancer (to one charger I assume) for 7s - 12s balancing (25.9-44.4 nominal volts).

But you actually asked how many lithium batteries it could balance. The answer: infinite because any number can be wired together in parallel.

 

[xyster]

Chargin'

I just plugged all 20 subpacks into the 20 chargers for the first time a few minutes ago. I'm still tickled pink charging in this manner works! While researching pack construction some months ago, I could not find anyone, anywhere, who could verify beyond a shadow-of-a-doubt, or who had tried it themselves, that ungrounded, isolated lithium chargers could charge batteries strung in series simultaneously without shorting as it's well-known and shown lead-acid chargers can. Fechter and Aerowhatt, two of the wise EV wizards at the old V, couldn't think of a reason there'd be a problem, and much-less-EV-wise me couldn't either. So I crossed my fingers, bought enough batteries for a 19s12p pack and 21 single-cell chargers. Now about 100 partial charges later, and the pack reconfigured to 20s15p with 300 batteries, I'm very, very pleased. I don't have money to burn, so charging the pack with single-cell chargers was a major, but calculated and very well researched risk that (knock on electrons) appears to have paid dividends.

In the pic below, two charger plugs into the bike are hidden beneath the midframe nylon roll.

 

[patrick_mahoney]

A list of all safety-related issues with lithium ion batteries that I am aware of - at least every one that doesn't involve manufacturer problems (like the Sony's that were recalled) are:

overcharging - charging to a voltage in excess of rated voltage (4.2V, usually)
overdischarging - discharging to a voltage below the rated discharge voltage (3V usually)
high discharge rate - discharging at a rate above the specifications (1.5C for lithium-ion, 2-40C for lithium polymer, where "C" indicates the capacity in "ampere-hours" usually, so 1.5C on a 2Ah would be 2Ah * 1.5 = 3A)
high charging rate - charging at a rate above the specifications (1C usually for both lithium ion and lithium polymer)
puncturing - like drilling a hole in the cell wall. Or sticking a nail through it.
high temperature - letting the cell get above the specified rate (usually >45 Celsius).

And then add to this list two things that are a subset of the list above:
balancing issues - leads to a subset of overcharging or overdischarging.
short-circuiting the battery - a subset of high discharge rate.

Here's the datasheet for an LG 3.7V 2.6Ah 18650-sized lithium ion cell:
http://www.all-battery.com/datasheet/18650B2%20TI.pdf

The list above is, to the best of knowledge, a complete list. So if you can guard against these problems, the cells should behave in a safe (and non-pyrotechnic) manner. You can use whatever method you want to guard against these problems - I don't agree with the terms "official" and "brave". I am not using the PCB and I am convinced that my solution solution is superior to the PCB in several respects.

There's a description of my charging and discharging system in this thread, 6 posts down: http://endless-sphere.com/forums/viewtopic.php?t=127&start=0

overcharging - the PCB checks against a limit of 4.235V per cell, my balancer, the LBA10 checks against a limit of 4.3V per cell. 4.3V is higher than the specification but not high enough to cause problems. I call this a tie - both systems check this equally well.
overdischarging - The PCB checks against a limit of 2.3V - which is well below specification and is so low that this setting risks permanent damage to the cell. On the other hand, I monitor the pack voltage using a Hyperion E-meter, but I don't monitor individual cell voltage. I rely on the pack voltage to indicate a problem - which is not a good check but I try not to discharge below 40% charged and rely on the voltage of the pack to make sure that I stay within that range. I declare that neither the PCB or my system is very good, but the winner is the PCB because it monitors individual cells
high discharge rate The PCB checks against a set limit and trips a FET. I use two one-time fuses (and carry spares). I declare this to be a tie - we both guard against this equally well.
high charging rateNeither the PCB nor my system checks for this issue. My charger, however, is not capable of providing greater than 0.25C, and if it were to malfunction, my power supply isn't capable of providing more than 0.5C and is doubly fused (two separate fuses). The PCB doesn't care what you plug into it as long as it's below the discharge rate. My system isn't capable of exceeding 0.5C. I call this a win for my system.
puncturing neither the PCB nor my system prevent this issue. However, the cell walls on lithium ion cells are pretty thick steel. It takes a lot of effort to attempt to puncture them. This is a fairly low risk in my opinion. Plus the cells that I use are supposedly rated to withstand puncturing
high temperature I am using a Radio Shack thermometer to monitor pack temperature. The PCB doesn't check for this. I call this a win for my system.

and

short-circuiting - I have 2 fuses on the pack and each cell is individually fused. The PCB has the equivalent of two fuses on each cell. The PCB wins, but I think mine is pretty good.
balancing - this is the one area that I find the PCB to be deficient and the main reason that I did not use the PCB. Capacities on cells are not the same and over time certain cells will be drained more than others, and then in charging, they will receive differing amounts of charge before the voltage cut-off hits. Over time, this will lead to insufficient charging on some cells. The PCB guards against undervoltage in use, and overcharge during charge, so the PCB keeps the cells safe in the face of this issue, but that just means that your pack will appear to "wear out" over time and you'll have no way of knowing what's wrong with it. It will just take less current in than it used to. An expensive lithium ion or lithium polymer pack deserves a balancing system in my opinion to preserve the investment and insure longevity. My system balances all cells constantly during charging to within +/-5mV.

Overall, I believe that my charging and discharging system is safe, I don't think what I'm doing requires bravery; I think what I have is as good as, or better than the PCB system. I spent a long time considering the PCB systems available. The lack of a method for balancing was the problem. Otherwise rather than getting 500 cycles before I drop below 80% of the rated capacity, I might be looking at something more like 120 cycles before I hit the 80% capacity limit. The more cells in series, the more stastically likely this is to happen sooner. I even looked up the chip codes and considered making my own PCB to get the 44V that I wanted (because I couldn't get a commercial PCB that did this), and figured out how to do it. I also looked at more advanced IC's from, for example, Texas Instruments, than the Seiko S8254's used on the Batteryspace and All-battery.com PCB's. But I couldn't find an option that I liked that looked easy enough to justify the expene - especially over the LBA10 which did what I wanted and was cheaper.

I am completely receptive to anyone who thinks that there's a major problem in what I'm doing - if anyone has a good reason why this is unsafe, I honestly would be grateful to hear it. I have no desire to have a fireball go off in my garage, or while I'm cruising on my way to work.

That said, so far, it's been fine. The thermometer records max and min temperature during use and during charge and the numbers look great. I have hand-checked with a voltmeter all of the balanced voltages and they check out. I shorted the pack on purpose one time and nuked a fuse - the fuses work. I shorted a cell one time by accident and the cell fuse worked fine too. I have about 30 cycles on the pack and love the weight of the thing (10lbs) and the voltage and capacity 44V and 18Ah.

 

[xyster]

Excellent post, Patrick -- way to make the no-BMS case or at least help us not seem like risk-baiting daredevils and pyromaniacs.

A couple things....

overdischarging - discharging to a voltage below the rated discharge voltage (3V usually)

3.0V is far too low in highly parallel packs of 18650s under heavy amp draw, IMO. The cells in each parallel subpack don't balance immediately, and when power is over 1C or so, one lesser cell's PTC can get tripped, which sets up a chain reaction leading to very fast overdischarge of the entire subpack. This is, I think after much study, how I ruptured two cells and killed two subpacks when resting voltage had just been 3.65 or so (a couple minutes of hard riding later one subpack was like 2.35V and another was 0 volts. Two cells were melting, smoking as I rushed them to a pyrex container. 24 cells in those two subpacks died because I thought I could safely discharge the pack to 3.3 volts or so).

From this excellent thread you sent me from rcgroups.com:
http://www.rcgroups.com/forums/showthread.php?t=209187
"IA-Flyer posted this information:

4.20v = 100%
4.03v = 76%
3.86v = 52%
3.83v = 42%
3.79v = 30%
3.70v = 11%
3.6?v = 0%

These are resting voltages - not under load voltages."

These numbers jive very well with my experience. 3.6v (resting) seems to be it for lithium ion batteries. The voltage tanks so fast from then on, perhaps it's enough to land an airplane, but in multicell PTC-fused packs a runaway reaction seems to occur before 3.6. I do not go below 3.75V (~80% DoD) as read at a charging port, or marked on my bike's handlebar voltmeter for the whole pack. This gives me I think a little breathing room should one pack be a little less (typically they're within 0.02V), or if I need to ride a little further. With about 2.5kw-hours on tap, mostly I don't go below 3.9V (~40% DoD), recharging back up from there most every night. For longest life, lithium batteries prefer shallow discharges and regular recharges, but almost paradoxically do not like hangin' around at full charge above 4.15V (this from Tesla motors blog and batteryuniversity) So most of the time I run my pack from 4.15 --> 3.9.

Otherwise rather than getting 500 cycles before I drop below 80% of the rated capacity, I might be looking at something more like 120 cycles before I hit the 80% capacity limit. The more cells in series, the more stastically likely this is to happen sooner.

You do mean when no balancing system is used?

 

[safe]

Excellent Posts!

Some really good information and a good review of the "alternative techniques" that you don't read about in the "official" battery literature. The arguments appear sound... if you monitor things yourself (having enough knowledge about what you are doing) there's no reason to go with all the PCB's to keep your pack protected.

I'm still a little confused about how the balancer works. If this is something that is connected in parallel to a whole bunch of cells that are being charged how does the balancer make sure that all the cells are balanced?

What are the physical principles at work at the level of the balancer?

Or are people using the balancer without really understanding the possible "trade secrets" that make them function?

I'm hoping to go item by item in a thorough manner to be certain that I fully comprehend all aspects of these "manual observation" battery techniques. (Lithium is so much lighter it's hard to pass up)

Another separate question:

My "pet project" is the idea of "tubes and paste" as a way to assemble battery packs. One thought would be that if you use the "tubes and paste" approach you could periodically disassemble your tubes and measure the charactoristics of individual cells and possibly overt the problems of a "declining cell" before it went "terminal" on you. So you could think of it as a "regular checkup" for your battery supply. Any comments on this idea "in theory"? (don't talk about the paste verses soldering issue, because that's separate, just the "test for problems" issue)

 

[Leeps]

Im not sure what the official method of battery balancing is but i would do it using switched capacitors. The capacitors would charge to one cells voltage and then be switched to an adjacent cell. If there is a difference in voltage then a charge would be transferred and eventually everything would balance out.
I suppose relays could be used for the switching you would the same number of spdt relays as there are cells in the pack, but the switching element has to be constantly switching in order to equalize, you would wear out the relays very quickly. The best way would be to make a spdt switch with two mosfets and some pulse transformers to drive the mosfets in the switch connected to the top most battery in the pack. This is probably outside of what most people here would want to do.
Joe

 

[xyster]

One thought would be that if you use the "tubes and paste" approach you could periodically disassemble your tubes and measure the charactoristics of individual cells and possibly overt the problems of a "declining cell" before it went "terminal" on you. So you could think of it as a "regular checkup" for your battery supply. Any comments on this idea "in theory"? (don't talk about the paste verses soldering issue, because that's separate, just the "test for problems" issue)

I leave the balancer questions to Patrick or other balancer-experieced people.
Tube and paste could work quite well with tab-less batteries that have at least one end cap, usually the +, raised above its edge. Safe: I'd urge you to consider lithium-manganese and lithium-iron-phosphate chemistries first. Were it not for the added cost, I would have opted for lithium-mangenese emoli's:
http://www.bigerc.com/
http://www.m2energysolutions.com/products2.html (has bulk discounts)
http://www.rcgroups.com/forums/showthread.php?t=508443 (disassembly of V28 packs).

because at 15C their power output is so much higher, and they can be run down to zero with apparently little or no damage (no overdischarge risk though the cell can still be reversed if in a hybrid chemistry pack). The emoli's can be charged with any lithium-ion or lipoly charger, has a little higher voltage and greater capacity than the lithium-iron-phosphate a123 cells. These also don't have the 3-5 year "ticking clock" lifespan of lithium cobalt cells, and like a123's are designed to last 10 years or 2000 charges (in v28 packs they are guaranteed for 5 years or 2000 charges I believe.) All the alternate lithium chemistries currently available *appear* to weigh about 1/3rd more than lithium cobalt. But in real life since they can safely be run down much further, the difference in energy density is much less.
You can get emoli cells for $13/per if you look hard.
A123's can be had for $10/per off ebay in DeWalt powertool packs, or from the company directly for more money:
http://a123racing.com/html/rcdevkits.html

cell type       voltage peak             C-rating       AH        weight            chemisty
emoli                4.2                   15         2.9     100 grams    lithium-manganese
a123                  3.6                  30          2.2     70 grams    lithium-iron-nanophospate

Cheaper chinese pseudo-a123:
http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=3071

 

[safe]

I like the idea of "no-explosion" Lithium.

The price runs about triple that of NiMh/NiCad for the same energy, but the weight savings is, of course, there. (I ran a quick price/power comparison)

It seems more expensive since it's better... which is to be expected...

Good to know!

 

[xyster]

Safe: along with weight, calculate total lifetime cost of ownership, not just upfront cost, and I bet the 5-10 year 2000 charge lithiums will look much more affordable.

Unless of course you've also calculated the world will end before then

 

[safe]

Safe: along with weight, calculate total lifetime cost of ownership, not just upfront cost, and I bet the 5-10 year 2000 charge lithiums will look much more affordable.

Unless of course you've also calculated the world will end before then

These run just about exactly four times the price of NiMh/NiCads.

And the world doesn't "end" if you know your Nostradamus. The war against the Muslims ends when Chiren (the right wing "great king" of the West a decade or more from now) orders the death of all Muslims in a "Holocaust" kind of way. WWIII does go nuclear, but a third of the world will still survive.

The world doesn't end... geez... :lol:

 

[xyster]

Safe, those go for about $13/per, not the $20 listed on the website from whence you got the pic.
Did you calculate total cost of ownership? Your results look the same. Show yer math, man! There's little to be gained by a "yes it does"/"no it doesn't" debate.

 

[patrick_mahoney]

These run just about exactly four times the price of NiMh/NiCads.

How'd you calculate that?

Looking for common denominators and ignoring volume discounts at Batteryspace:
A 3s23p 3.2V 1300mAh Li-Fe-PO4 pack is 9.6V 29990mAh for $465.75
A 8s3p 1.2V 10000mAh NiMh pack is 9.6V 30000mAh for $166.80.

I get a ratio closer to 280%, not 400%.

I'll post up abouth balancing later tonight hopefully, when I have more time.

 

[safe]

The "Lithium2" is the one from "batteryspace".

The "Lithium3" is the one with what is now $13 pricing. (updated)

I've got a little calculator thing setup in the spreadsheet that figures it all out. We could attempt to go through it if you want. All it does is adds and multiplies different pack configurations and then arrives at a battery count. You then multiply the battery count by the price at that volume level. I'm pretty sure it's correct... I've been over it many times.

The $13 helps improve the situation a lot over the $20 as listed.

In this revised scenario the NiCad "D" batteries seem to roughly equal the lithium in every way except they are half the price... and probably double the weight. So maybe it's not so bad... :wink:

 

[patrick_mahoney]

I see. Thanks for the clarification and the chart.

Too many lithiums to keep track of.

 

[safe]

Watt Hours?

Just out of curiosity how many watt hours are people running?

We can get into all the various pack configurations, but the true "bottom line" is the number of watt hours that the pack can hold. There are factors about discharge rates compared to your controller which tilt the equations sometimes, but for range estimates it's all about watt hours.

My last bike had (if you factor in the Peukerts Effect) about 700 watt hours in total and I could get a solid hour of riding at full speed. (I have no pedals) My next one will likely go up to the 1440 watt hour mark so that I can ride longer and/or faster. (120 "D" NiMh for $600)

 

[xyster]

Just out of curiosity how many watt hours are people running?

2500.

In this revised scenario the NiCad "D" batteries seem to roughly equal the lithium in every way except they are half the price... and probably double the weight.

That sounds about right. However, in both cycles and calendar-life, nicad and the non-cobalt lithium chemistries should last about twice as long as a similar pack of NiMH batteries -- especially the lower quality, cheaper NiMH like the batteryspace D cells.

 

[safe]

...2500 watt hours... in both cycles and calendar-life, nicad and the non-cobalt lithium chemistries should last about twice as long as a similar pack of NiMH batteries -- especially the lower quality, cheaper NiMH like the batteryspace D cells.

That's one awesome battery pack. I'll bet all the girls come up to you and say:

"You know size really does matter."

But seriously, you are right, the NiMh aren't as durable as the NiCads, but for getting lot's of power at the lowest price the NiMh seem the ticket. So I might buy some NiCads for the first bike and then after six months buy some NiMh for the second or maybe even go to Lithum later on. (the topic of this thread) If I go NiCads then I'm buying myself some time and keeping my up front cost low. My range will be poor, but the ability to test for peak power will be there since the NiCads can go 15C. (only $366 to get started)

So let's remember to get back to the prior question of:

"How the heck do those balancers balance the cells?"

 

[xyster]

the NiCads can go 15C.

You're going to be in for a severe disappointment if you plan a nicad pack based on that. Good nicads may get 15C -- the one's in powertools most likely. The nicads found at battery shops get nowhere near that. Justin's nicads are rated for 5C, and a member of the old V pulled 38 amps out of an 8ah pack with the pack temp rising quite a bit. But Justin retagged them as 3C batteries because he wrote cycle life would be cut short at 5C.

http://www.ebikes.ca/store/
"24V 8Ah NiCad, 3C Max Rate
4.15 kg (9.15 lbs)
$110.00"

http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=2533
"tion
• 12.0 V 7000mAh Powerful Battery Pack made of 10 x F Size High Quality Ni-Cd Cells with 14 Gauge wire.
• Standard Charge Rate:  1 Amp Max.
• Standard Discharge Rate:  7 amp
• Max. Discharge Rate: Â Ã‚ Ã‚ Ã‚ 10 Amp Max.

"

 

[Lessss]

OT
Ever look at a 40Meter flooded map? The only terrain not flooded is Iran, Iraq and China.

 

[fechter]

If you run Ni-cd, you will probably need to use parallel strings, so the discharge rate on each string will be divided by the number of strings.
You will also need some kind of string isolator to separate them during charging. This could be just a big jumper plug or you could do something with diodes or FETs. You cannot charge ni-cd's in parallel. You would need a separate charger for each string or some kind of BMS that handles that. I've never seen a BMS for ni-cd's in parallel - but I could probably make one.

I would also recommend sub-C batteries only. The larger sizes really suck at high discharge rates. Sub-C should be the most cost effective.

One thing about Ni-cd is that you will get nearly the full rated capacity out of the pack, unlike lead-acid, which will Peukert out at about half the rated capacity if you drain fast like me.