LiFeBatt Battery Woes

[BatteryKing]

I am regularly going 20 km one way at 50 kph much of the way. I normally use around 10 Ah on a 48V HPS pack, but sometimes use 12+ Ah. (I am a big dude.) I also live in a Republican town, so of course the roads are in horrible shape and I have actually been having problems breaking 12G spokes. (Frequent tune ups are a must.) I figure for a real configuration, you need to calculate for loss of capacity over time, avoidance of 100% discharge on the normal route, and buffer space if you need to take a detour (a likely detour for me is an additional 7-8 km away up a hill), so 48V and 20 Ah seems proper for my purposes. Peddling this thing back the other way is quite a workout!

It seems in order to go to a lower CG with this pack like what Micro Car is doing would be quite an endeavour for me because I would need to have cells all over the place. Trying to go around this by lower voltage would mean less speed, but 20+ km can be a long ways at lower speeds when I have somewhere I need to be (like work). Then Ah goes in 10 Ah increments with these cells and I am already doing 10+ Ah on a trip, so it seems unwise to scale this back.

A thought to cross my mind is to double saddle batteries on either side of the luggage rack and have padding because smacking batteries into concrete isn't the best of ideas as I have noted before and padding would at least mitigate the shock. I also like the idea of using a recumbent bike because in theory at least you should be able to free up the space under the bike for a battery pack and you should be more aerodynamic granted that you could get the right frame configuration and route the chain around the battery or something.

 

[miro13car]

O yes,
if you want to go over 40km/h , I hope you don't try to reach over 40km/h on bike path , because that is asking for trouble.
your broken spokes is a proof that mechanical stress on the bicycle is quite big.
It /frame/ was never designed to go 50km/h with all the weight of kit and yours and it is for sure illegal to go 50km/h on not registered bike. Plus crappy Chinese workmanship
The thing is that you buy battery BEFORE deciding on frame to install kit.
You buy frame/bike AFTER you figured out how to place cells and electronics in new enclosure and where on frame.
MC

 

[BatteryKing]

I figured out placement, it is just thoughts occurred after the fact. I ride by cops all the time at full speed, they don't know which regulation to site, so they don't stop me. Of course if I were to do things now with all of the knowledge and experience I have gained since I started this adventure, I think I would have a substantially different setup. Here are some things I would opt differently:
1. I had initial worries about properly supporting the battery on the rear without bending something, so I went for front suspension only so that I could have direct supports for the battery to the rear axle. However with 1920W and 45+kph speeds rims warp and spokes subsequently break, so I just moved super-critical stress from the frame to the wheel.
2. 1920W is nice for long commutes, but on a bicycle it is really more practical to have half of that power or less and lower speeds because then you are more in the realm of what bicycle parts can handle. Plus with lower speeds, you can use less batteries as long as you are not climbing steep hills all of the time.
3. With lower speeds comes smaller batteries that can have lower power ratings. The more ideal configuration seems to generally fall along the lines of split packs that can either go into side panniers or along the frame or a specialized frame battery pack. The LifeBatt / BMI / PSI cells seem kind of voluminous for this task.
4. For higher rates of speed, it seems you start to really get into the range of setups dedicated to motorized transport as opposed to hybrid peddle electric. My particular configuration is reasonably low resistance on flat and level ground while peddling, but it is a fair amount of weight to lug up hills.
5. Getting into 40+kph range seems to generate a fair amount of wind drag on a typical bicycle configuration. It seems in this range aerodynamic considerations should have a significant effect on battery life.

 

[BatteryKing]

I just ran a full cycle on the battery and re-calculated average usage under no peddling conditions. At the time of this writing the cycle computer odometer is at 439 miles and this is combined peddling and motor use. For full motor trips one way to work with a ~100 foot net elevation drop (mostly in one small spot with a light at the bottom of the hill) going 12.29 miles running at full speed, averaging around 45 kph when acceleration levels off and having 9 lights and 2 stop signs along the way I use 12.25 Ah on this LiFeBatt HPS4820 battery and Crystlyte 5304R motor. On the particular trip this morning I went 18.70 miles and used 19.50 Ah before the battery beeped at me right as I was pulling up to work. Both OHV and OLV (over high voltage and over low voltage) lights were off and power was still being produced. So far I have used 378.35 Ah, most of the time of which the battery was running between 51-54V and the battery was originally delivered last November.

 

[miro13car]

It is outmost importance that the cells are balanced well if you want to get over 20AH AND FOR SURE YOU CAN GET ON WARM DAY, CELLS BALANCED.
On my pack I checked few times that I can get over 10Ah on over 20Celsius day and with really good balanced cells.
Do you get any beeping at the end of charge?
It is indication that the pack is still not balanced. LBatt charger turns itself off but it should stay longer on at the laast stage of charging to allow cells to balance.
REMEADY IS TO RESTART charger several times, balancing takes place only when LEDs are active.
I woulkd not allow to discharge my pack until LV BEEP , it happend only once on my pack - it is generally and universally agreed that doing more than 80%DOD shorten life of any Lithium pack. LBatt pack is no different.
Way to go is to charge as often as possible.
Miroslaw

 

[BatteryKing]

I long ago gave up on getting intelligible charging information out of the owners of LBatt. I have been charging until hearing first three beeps in rapid succession and just once yesterday stopping after hearing more beeps at the end of a long ride. I charge after every ride in order to keep the battery as charged as possible only stopping when I can't be around to hear the beeps at the expected completion time (which is kind of annoying actually). Are you also suggesting that I go beyond the three beeps while charging and wait for the red OHV (over high voltage) light to come on before turning off the charger? Looking up the online specs for the Soniel charger it looks like by default the charger goes up to 57.6V before cutting off the charge, but the HPS4820 beeps a couple of volts before that point when the charger is still going full steam ahead. LBatt's own posted specs suggest that with perfect balance the cells should be able to get up to 58.4V, so one would think there would still be a little head room even if the balance wasn't quite perfect for the charger to reach the cut-off point.

 

[ejonesss]

as long as the lvc works properly you should not ruin the cells.

you probably left the battery in it's fully discharged state and it slowly went down or you blew 1 or more tc54 so the low cells are not stopping the load and ruined a cell.

it may be a good idea to bring the battery in the house if you can and maintain it as needed.

it would be neat to study them over time and see how they perform in comparison to yours.
the big difference is the BMS, so you guys should keep track of the charging, what size charger and voltage and current levels over time, that would be really informative.

I'll be charging my PSI cells with a 4812sr Soneil charger which is 6amps according to the site.

My last 48 volt LIFEPO4 pac failed miserably after one season. Might have been because I left it in the cold garage witch never went below -15 C, or running to LVC too often, either way it's for sale super cheap, but only gets about 6amp hrs from the original 12. I'm going to post my sad results on Fechters lifepo4 thread.

 

[miro13car]

enjoness,
HPS packs from LB or BMI /again they are identical/ do NOT have any LVC - another reason not to deplete untill you hear any beep. Why to take the risk of bringing even one cell to 2V??
In general any beep coming from HPS pack is bad, shortly you should do everything NOT to get any beep.
I was getting 3 long beeps at the end of charging everytime and it was clear indication that pack was not balanced - bad.
I was making mistake of disconnecting charger right after I saw green end of charge light. You must keep applying
41-42V/on 36V pack/ across string of cells for hour or two so VMSes are active/LEDs are on/ and have a chance to level voltages of cells. Sometimes I was getting short continous beeps after 3 long beeps so I waited out until they disappeared and again gave VMSs time to level voltages of cells. Now I never get any beeps at the end of charging - means all cells reach voltage at almost the same time - good balanced pack. Pack feels stronger like any balanced pack, less voltage sag.
Max after charge voltage means little, because it says nothing if pack is balanced. One cell can be at 4.4V and another 4.2V and you still get max voltage on terminals. Only lack of beeping at charging is sure indication that all cells reach top volts at the SAME time - balance achived.
MC

 

[BatteryKing]

The capacity I am seeing now is still well within margin of error for full capacity, so I am rather reluctant to dork around with potentially over-charging individual cells within the pack. The notion of any beeps are bad is also nonsense because a cap cap halt! strategy would generate too many returns just as the sequel police in Space Quest IV caused many game reloads and the general protection faults in Windows 95 caused many cascading application / system crashes from lack of real memory protection.

Green light on the charger would mean the charger reached the cut-off voltage, but the battery beeps before that ever happens in my case, so it would not make sense for that to be the first indicator of the pack being charged and then the beep coming later. I have noted that voltage does drop a little over a few minute time span after the charger is disconnected, so I would think this is the pack balancing itself out as it settles from 56V down to 53.5V or so when I took measurements last. It would be nice to have the charging cycle automatically stop and I hope this gets properly integrated into future revisions of the product.

 

[BMI]

It would be nice to have the charging cycle automatically stop and I hope this gets properly integrated into future revisions of the product.

I am rather confused here?!

If you use the proper, high quality, fully automatic battery chargers supplied/approved by the BMI/Lifebatt factory (either the regular charger or the fast charger) your battery will be fully charged to capacity and will automatically switch itself off as soon as the battery is 100% fully charged. This is just before the point where the first warning buzzer sounds so if you use the approved charger you will never hear any beeps. If you are using a Sonneil charger or other charger which is not an approved factory charger this is probably why you are hearing beeps. The approved chargers (48V versions) look like this-

Therefore if you are hearing "beeps" and are overcharging your battery to the point where overcharge errors are recorded in the VMS memory this will give the factory every reason to void your warranty if you make a claim in the future due to use of a non-approved charger.

 

[miro13car]

Again,
I do not get any beeps at the end of charge anymore. I use Soneil approved by LifeBatt. Soneil knows exactely what it will bw used for.
BatterKing,
just more understanding of how 12 cells kin series work.
VMSs ARE THERE in your pack to make voltage the same on all cells.
Beep does not mean pack is about to be destroyed or something like that, but means that one cell reach max voltage before , maybe moment before other reached that voltage and this means not perfect balance and it means you leave pack not perfectly balanced.
You can get 3 beeps for months and months, but pack will not be in top shape, be3cause experience tells me you should exceed your rated Ahours at least by 0.5Ah on hot day.
Again read my post, VMS only balance when LEDs are on.
If you understood how charger , VMS and balancing worked you would know that lack of beep is what you need.
No doubt in my mind - lack of beep means pack in top shape.
Leave it on longer, restart charging untill next time 3 long beeps dissapear.
Obviosly you do not want to hear LV beep also, why, answer yoursef.
MC

 

[BatteryKing]

After going through 5 cycles where I charged to the first three beeps and let it settle for a while while doing other things (including sleep at night), I found that every time the voltage went higher before the beeps occurred and the fifth time around the beeps occurred around 58V, but before I could turn off the charger, the light went green on the charger. When I checked this voltage, it was at 58.4V and started dropping down, meaning the charge cycle was complete.

I take it this is what a balanced pack is supposed to look like?

 

[BatteryKing]

The best I seem to be able to get is the three beeps in the 57.6V to 58V range and then the light goes green on the charger at 58.4V, which happens soon after. I have been informed that the max voltage before damage occurres on a single cell is 4V and according to LiFeBatt's own literature the charging voltage is 3.65V per cell, so it makes sense the the charging cut-off voltage is set to 58.4V which equals (3.65V per cell) * (16 cells in series). It seems that perfect balance is not achievable however one should be able to come reasonably close without causing damage to any cells with the play room allowed in the specs.

 

[miro13car]

my charger doesn`t turn itself off , but hold 42V at the last stage meaning 3.5V for cell if perfectly balanced , nowhere near dangerous 4V per cell.
With our chargers there will never be 4V!!
From what I figured and it took me some time to figure this out:
42V should be held against string of 12 cells untill all LEDs go dark.
Shunts allow only 200mA to bleed , especially after deeper discharge they need time to equilize cells voltages.
Don`t even start me on technical " desinformation" from LifeBatt, it was nightmare , I got damaged charger, next I got better charger from them lasted less than a year. IF they sit there why they did`t demanded tech literature from Taiwan and educated themselves. To be just factory is pretty scimpy on info also mainly ,because they don`t make VMSes are contracted from other compny called All New Energy.
Armin is so much better in technical info .
there was macstar with 48V built from grey BMI/LB cells member on this forum who connected special circuit parrarel to charger to make it cycle CHARGER several times to allow VMSs to work.
Miroslaw

 

[BatteryKing]

My charger seems to drop to 57.6V after turning green at 58.4V. Will the shunts bleed more at higher voltages so that the cells will eventually balance out at 57.6V / 16 cells = 3.6V per cell or do you think it will take multiple cycling? I also don't like the idea of leaving the battery on the charger for long periods of time because I never saw any sort of added cooling for the shunts in factory pics, though I suppose a 3.6V drop * ceil(0.2A) current per shunt should be a reasonably small <= 0.72W dissipation with a total of 11.52W max for 16 shunts.

 

[miro13car]

Voltage of my charger also drops of course at the end of charge.
what makes shunts work more or less are voltage differences between cells.
the bigger voltage diff between cell the harder they must work to level voltages.
Take look at one VMS.
AS I understand that if you have voltage applied across 4 cells and microcontroller monitors volage diff between cells, as soon as there is diff. big enough it activates shunts. This does't work like analog BMS.
I would not worry about shunts getting warm on not severly unbalanced pack.
All shunts rearly work all at the same time.
I found out VMS es work independent of each other.
Beauty of this intelligent system, I very like how it is designed.
But if cells are severely unbalanced shunts get hot like crazy.
I was riding on unbalanced pack for months, 3 beeps and next continous beep I was pulling charger plug
before I found out that I should give shunts a chance to work.
Now I have 0/zero/ beeps and LEDs go off pretty fast after charging - clear indication that shunts barely work. They don`t need pack is balanced.
Now when I go steep uphill LEDs drops 1 off almost at the same time and they come back after hill back on at the same time, not like before.
You need lowered voltage applied to string of cells during balancing so good that charger lower volts at the end.
When I had my LBatt charger I never check if charger once shut itself off would stay like that or would it restart once volage of all pack drops below certain level. What happens with your LBatt charger if you leave it connected like for longer?
Taiwan factory literature says that it takes several charging cycles to balance but they don`t say on what pack how deep discharged.
AS I said other company makes VMSs , explaination how they work is very limited.
If you understand what 3 long beeps really mean you know that pack is not balanced if they sound.
they sound for the reason.
MC

 

[ejonesss]

i have seen mention of settling effect.

what does that mean?

 

[BatteryKing]

The VMS on these LiFeBatt / BMI / PSI battery packs have voltage triggered shunts between cells that discharge the cells so that no single cell becomes overcharged (at least in theory). Actually with my pack it seems to take a couple to a few days for the pack to really settle below 53V, but once this happens, the pack seems to be really unbalanced. I suspect this value is too low and too far into the flat part of the discharge curve and this is why I am getting the lumpyness. The pack seems to drop down to 54V within a few hours and over one night goes down to 53.5V, but when riding it takes a while to get to 52.4V, so I suspect a smarter cut-off voltage setting would have been around 3.34V per cell, not 3.3V as what seems to be the case.

 

[miro13car]

I don`t know if I understand correct but you don`t think shunts do anything when VMS is not active LEDs lit up?
I would be very surprised if shunts worked when there is no charger voltage applied across string of cells.
no LEDs lit up = VMSs not activated = no balancing.
Again votage on batt terminals says not much if cells balanced.
MC

 

[dnmun]

doesn't make sense to me either. the shunt resistors are there to allow the charging current to flow around the cell when it is fully charged, and is carrying current only when the charger is active.

i have never even heard of settling, not sure where that came from.

 

[TylerDurden]

i have never even heard of settling, not sure where that came from.

Source: battboy, aka don harmon, aka mr. truth in advertising. http://endless-sphere.com/forums/viewtopic.php?f=1&t=593&p=168077&hilit=settling+effect#p168077

 

[BatteryKing]

The fundamental rendering of what's going on that I see here is once a cell is charged, is current shuttled over the cell at charging current rates or not. Everything else can be derived from that. One established fact is LiFePO4 cells do not self discharge like lead-acid cells do. This is the principle reason why a VMS is required. An observation I made is once charging power is disconnected and the the circuit is open, the voltage at first drops quickly, but then slows down at a logarithmic rate. Seeing that this product a) way outperforms any lead-acid I know of, it is unlikely to be that, b) is advertised to have a BMS (though really sounds like a VMS), and c) is claimed to have the voltage settle (totally different than cell orientation) to 52.8V by the LiFeBatt representative and this basically concurs with what I see over the period of a few days, it stands to reason this initial voltage drop is caused by the VMS trying to balance the cells to some preset voltage.

As for safe charging, a.k.a shuttling current over charged cells, there are only so many ways this is economically possible. Just turning off the cell wouldn't work economically because a) that is a lot of current to redirect and b) how do you cheaply manage the voltage differential the cell was creating? Managing the cell by having a huge resistive load balanced with the charging current would be expensive and generate a whole lot of heat. (In this case upwards to 200W of heat to reject.) The logical solution would be to use small transistors coupled to fixed resisters (basically) across each and every individual cell that switch on at a specific voltage due to field effects in the transistor (where do think the name transistor came from?) and allow each cell to gradually bleed down through this circuit to a preset voltage. To remain cheap something like this would only discharge a small amount (in the 1mA to 200mA range from what I hear) and rely on the notion that things only need relatively small corrections on each charge cycle to stay balanced.

Considering the aforementioned model it stands to reason that if 3500mA is going through the cells continuously while charging and the VMS circuits only bleed off upwards to 200mA, that one fully charged cell will continue to get at least 3300mA of current until the charger shuts off with a constant current charger like what I have. If you for some reason you have 15 cells at 3.1V on the flat part of the charge curve and one cell at 3.65V pretty much at the vertical part at the end of the charge curve, then unless power is immediately disconnected, that one cell will undergo a rapid voltage change. Rapidly going into the 4V+ range is supposed to be bad, so I am trying to avoid that by developing a better understanding of how to properly balance the cells. Properly balanced cells mean that all cells get near the vertical end of the charge curve at the same time and the balanced voltage increase triggers the charger to stop charging at full rate.

 

[GGoodrum]

Wow, you have several total misconceptions on how this actually works. First of all, the VMS is not really too much different than any other shunt-based BMS circuit. It does nothing until the cell voltages reach about 3.65V, at which point they start conducting, bypassing a small amount of current. The early VMS versions only bypassed 100mA, but I think the later ones now do about 200mA. the whole point of why the shunts are needed is because once a cell starts getting full, it becomes harder and harder for that cell to accept current at the same rate, so the voltage goes up. In the constant current mode, the current is maxed out, but the voltage is allowed to rise. Once it gets to the crossover point (usually 3.65-3.70V...) the voltage is held there, which causes the current to start dropping. The problem with having cells in series is that once one cell gets full and starts limiting the current, it is limiting the current for all the cells. that's because all the current has to go through all the cells, all the time. Anyway, what the shunts do is bypass at least some current, so that the cells not full yet will at least have some current available to continue charging, and catch up.

One thing about all the BMI/PSI/LiFeBatt cells that is unique among all other LiFePO4-based cells is that they don't hold the surface charge. With other versions, like a123s, for instance, the surface charge will be held pretty much indefinitely, as long as the cells are healthy. Once any load is put on the cell, the surface charge burns off, and the voltage drops to the real "full" level. For some reason, the BMI/PSI cells will burn off the surface charge on their own, within minutes of coming off the charger. The "full" voltage seems to be around 3.36-3.38V. This is not an indication of the quality of the cells at all, just a weird quirk of sorts.

-- Gary

 

[BatteryKing]

I have taken and done well in three semesters of calculus based physics including motion and inertia, electro-magnetism, optics, and digital circuits. What the LiFeBatt representative told me was wholly inadequate and demonstrated to me a total lack of a mathematical and conceptual understanding of their own product, but there appeared to be engineers inaccessible to me who did understand what they were doing when they designed this product. I did some digging around for some base knowledge and then built models that I described to you in generalized terms. Based on these models and observations I have been accepting and throwing away knowledge based on whether it can fit into these models and have been giving a low priority unlikely but plausible configurations. Considering this, here are a couple more things:

1. Near 100% charge a jump of 400mV has been observed when charging current is applied. Some sort of slight memory effect can be suggested for this when considering the incredibly low internal resistance of this pack.

2. A constant current charger charges at a constant current until a cut-off voltage is reached. In this case it is 58.4V according to my volt meter. Each working cell (shorted cells don't count) creates a particular voltage drop all of the time (unless you destructively use the pack) and the voltage drop is greater when storing more charge and less when storing less charge. Constant current (and variable voltage) charging means just that the current is held constant as the voltage drop across all cells rise. In this case in a basically series circuit, particular cells can have a larger voltage drop across terminals than others and more charge you have, the larger the voltage drop across the particular cell, however this constant current charge will continue to raise the voltage in order to maintain the 3.5A current through all the cells (actually in this case all the cells divided by two with two sets of cells in parallel) until that 58.4V is reached, which is much greater than the impedance any one cell will put out. These are just basic electrical laws applied to this system. Having a constant voltage in constant current system like this does not make any mathematical sense unless you either bypass 100% of the current into a resistive load or something or the charger reaches its cut-off voltage or is disconnected from the circuit.

 

[BatteryKing]

So when is somebody going to have a battery charger that plugs into the serial port to monitor the charge levels of every cell and adjust accordingly as opposed to potentially dangerous approximations for these HPS packs?