here is some info on 20v yardworks lithium ion

[drunkencat129]

just go the last packs in woodbridge and maple stores

 

[29a]

Have you guy's found out if the YW chargers do cell balancing or not
Is parallel charging OK If so what if any extra protection is needed
do the leds on the packs actually give a real indication of state of charge
Are the YW chargers still operating normal after doing the increase amperage mod

It would be very appreciated if one of you guy's did a summary of the fact finding so far
Ive read and been following the thread but its getting long and difficult to find the facts from the testing.

 

[mikereidis]

So that'll be 5 virgin batts and 9 damaged ones...

And over $1,400 that could been used to buy a lot of PSI or a123. :wink: Tinkering is definitely an expensive hobby!

It's a business expense, gosh-darn it ! So it's only $700 out of my pocket or whatever the rate is these days in Quebec+Canada. And it's supporting at least 2 Canadian companies so I'm doing my patriotic part in supporting Cdn companies (with 50% taxpayer funding) in these difficult economic times.

And once I return some of these clearly factory defective units, I presume I can just collect a refund if the store has no stock.

Bike is down to 14s1p now. I got tired of the 3 surviving cells in the front battery slowly top-up charging to a crawl, so I repurposed it for bike lights. Also, climbing up my street hill on a full charge the other night at 30 KMH put my worst cell under 3 volts, so those cells weren't good enough for ebiking anymore. Now my new "sacrificial cell" is the one just above the low bypassed dead cell in my "should be 15s YW 3s pack".

Hope the virgin batts arrive soon, and no they will not be sacrificed to the dangerous charger volcano... )

 

[mikereidis]

Have you guy's found out if the YW chargers do cell balancing or not
Is parallel charging OK If so what if any extra protection is needed
do the leds on the packs actually give a real indication of state of charge
Are the YW chargers still operating normal after doing the increase amperage mod

It would be very appreciated if one of you guy's did a summary of the fact finding so far
Ive read and been following the thread but its getting long and difficult to find the facts from the testing.

YW chargers do not and can not balance. BMS IMO, SHOULD balance, but I think it doesn't. My tests indicate it does not. I saw one cell at 4.23v and others around 4.1 or so. It IMO can't balance with the super-thin 20-22 gauge wires it uses for cell voltage LVC monitoring.

I think parallel charging should work, but haven't tried it, and the risk is up to you. I'm not sure it would work with YW charger when batts are highly discharged, but it might. Main protection required IMO is to ensure both batts are at almost exact same voltage when connected in parallel. Diodes I think might avoid this issue, but will drop your charging voltage a bit.

Yes, I think the LEDs are reasonably accurate. Percentage charge is listed in manual for LED readings. Lithium batts in general tell you state of charge by their open circuit voltage, if undamaged and with a known AH capacity. That's all the LEDs do, they check batt voltage. A DMM will give you a better idea, if you have a cheat sheet listing voltage versus capacity.

I'm the only one who has tried to increase current from YW charger. No it does not act normally after that mod. Don't try it.

What DOES work IMO, is trimming to voltage setting pot to exactly the voltage you want, for example: 21.00 volts.

I'll post a quick summary in the next post.

 

[mikereidis]

Quick Summary on YW batts etc.:

BTW, I'm "putting together" a BMS and charging solution for these batts (but should work with any lithium batts). Just watch this thread and I'l keep you updated. I'm expecting to have something decent together by Halloween, just in time for the snow to start threatening.

Pro:
IMO, these are great batteries for the price.
LiMn does not seem to explode or burn when stressed. (I think my meltdown helped prove that.)
LiMn has some nice advantages over LiFePo, IMO.
1 year over the counter warranty.
Easily available anywhere in Canada, from a zillion stores or online and shipped.

Con:
Cells are better, out of the cases, and with a better (and charge balancing) BMS than the stock one.
IMO the batts are designed to fail eventually with no balancing.
YW Charger is slow, it takes about 3 - 3.5 hours from full discharge to fullish charge (20.8v).


From http://endless-sphere.com/forums/viewtopic.php?f=14&t=6586#p99678

Batteries labeled as "Canadian Tire Yardworks LiMn 20v 6ah batteries":

ES Topic: viewtopic.php?f=14&t=4908&start=0
Availability: Only in Canada at Canadian Tire stores or delivered to anywhere in Canada.
Current price: $109.99 Canadian plus taxes as of Sept. 2008.
Warranty: 1 year over the counter exchange.
Includes: BMS and casing but can be reduced to 5 banded cells.
Intended usage: Smallish Grass Trimmer, leafblower, polesaw, chainsaw, etc.
Ebike/technical support: none.
Charger: $29.99, rated 2 amps but measured 1.8amps; takes 3-3.5 hours for full charge.
Charge-ability: Charge-able in 1 hour at maximum current I tested of 12 amps.
Chemistry: Lithium Manganese / Spinel.
Form Factor of 5 banded cells: prismatic, 65 mm x 65 mm x 140 mm
Voltage: Per cell: 3.7 V nominal, 4.2v max, 3.0v minimum normally but LiMn good to 2.5v.
Capacity: rated 6Ah; observed 5-6Ah, about 5AH at 16-20 amps.
Mass: about 1600 grams with case and BMS, about 1230 grams for 5 banded cells; 245 grams per cell,
Internal DC impedance: measured about 125 milliohms at 16 amps for 5 cells; 25 mO per cell.
Max Current: BMS limits to 31 amps.
Power Density (5s pulse) about 440 W/kg ? (at 30a, 18v for 5 cells)
Energy Density: ~90 wh/kg

Voltage sag at full throttle, 20amps: 84v open circuit off charge to 75v = 9 volt drop (about 450 milli-ohms for 20 cells)

My range with 2 batteries/10 cells has been as high as 25 km or 16 miles on recumbent. With 4 batts/20 cells I can get up to 40 KM (25 miles) at 20 KMH (12 MPH) on small upright bike weighing 64 pounds and me 176 equipped for total of 240 lbs.

At average 32 KMH (20 MPH) I get about 20-22 KM up and down my street with max incline of 2-3%. At max throttle I think I can get 10 KM or 6 miles and max speed on flat in 50 KMH or 30 MPH area. Ranges with me sitting upright, not aero.

 

[mikereidis]

EDIT: 5 more ordered, 23.99 for express shipping; guess I got bit by Quebec PST since they use my shipping address, unlike when I pick up in Ontario stores.

Stupid Canadian Tire/RBC Visa.

Got an "URGENT" voice-mail this morning from Can Tire fraud department. Oh noes !

After 10 minutes of fussing around with her computer etc. she tells me it was over $600 (not that that is a threshold) and my shipping address didn't match my RBC Visa address. Yes it did ! Precisely, except perhaps for French "Chemin" for English "Road".

Whatever, <sigh>...

 

[drunkencat129]

Have you guy's found out if the YW chargers do cell balancing or not
Is parallel charging OK If so what if any extra protection is needed
do the leds on the packs actually give a real indication of state of charge
Are the YW chargers still operating normal after doing the increase amperage mod

It would be very appreciated if one of you guy's did a summary of the fact finding so far
Ive read and been following the thread but its getting long and difficult to find the facts from the testing.

no it dosent it just puts a charge and the crapy bms drains the cells to even them out but its crap

 

[ZapPat]

Have you guy's found out if the YW chargers do cell balancing or not

no it dosent it just puts a charge and the crapy bms drains the cells to even them out but its crap

Seems to me that this is pretty much the way all BMS's do charge balancing, including Ping's and Gary's too.

Does the YW's BMS use FET(s) to cut off charge current when the first cell reaches the high voltage cutoff, then drain it down a bit, then turn charge current back on, etc, until all cells are equally charged? This is what I've heard every BMS does so far.

 

[mikereidis]

Have you guy's found out if the YW chargers do cell balancing or not

no it dosent it just puts a charge and the crapy bms drains the cells to even them out but its crap

Seems to me that this is pretty much the way all BMS's do charge balancing, including Ping's and Gary's too.

Does the YW's BMS use FET(s) to cut off charge current when the first cell reaches the high voltage cutoff, then drain it down a bit, then turn charge current back on, etc, until all cells are equally charged? This is what I've heard every BMS does so far.

I've never seen any evidence of cell balancing in BMS. drunkencat129 MAY be correct; perhaps there is some very low current balancing; it would have to be very small current to work over 22 gauge wires especially when trying to measure a loaded voltage over the same wires. But I haven't seen this, although I haven't tried an mA meter on the sense leads.

I'm not 100% sure, but AFAIK, the BMS does nothing to protect the cells during charging. The "protection" is in the charger which never goes above 21v, and severely limits current in a "pseudo CV phase" which causes the batt to slowly approach 21v.

It's up to the cells to all be good/undamaged and split the voltage equally to 4.2v per cell. I think it works OK-ish with new undamaged cells if you are OK with the extra long charge time for a 0.3C (1.8 amp) charger. (I.E. a 0.3C charger with a full, proper CV phase would charge faster.)

Once the cells get "worn" by age/cycling however, bad cells will go above 4.2v (I saw 4.23v on one with BMS) and it will soon be time for Canadian Tire to get "replacement battery" revenue from you, designed to be between 1W and 2W of course, where W is the Warranty period.

Way back when, they gave away the razors and sold the blades.

These days we get an inkjet printer for "free" and make the companies money on ink refills.

CTire, IMO, is selling the trimmers etc. cheap (expect sales this winter), and looking to make money on batts.

AFAIK, the BMS does just two things:
- Triggers LVC if any cell goes below 3v under load.
- Triggers OC if current goes over 31 amps.

Maybe it triggers LVC if battery goes under 15v (on load side) also. I noted 15v being a magic number in many discharge sessions, even at high 16 amp currents that were dropping voltage by 1-2v in the BMS.

 

[ZapPat]

Thanks for the BMS info, Mike.

You're probably right about the warranty period vs life span being one of yardworks variables in their decision not to add any individual cell OV protection. One of the sad signs of an economy based all too much on consumable products.

I guess this means slow charging (relatively low current) is the best way to go for these cells with the stock BMS.

On another note, has anyone checked out the mastercraft li-ion packs such as the one that comes with the drill for 99$ on sale this week? (Front cover item) If the mastercraft brand contains good lithium cells, it might become a good place to snag good cells. I'm thinking this because mastercraft brand comes on sale much more than yardworks, although this might not be true of the battery packs themsleves.

 

[mikereidis]

On another note, has anyone checked out the mastercraft li-ion packs such as the one that comes with the drill for 99$ on sale this week? (Front cover item) If the mastercraft brand contains good lithium cells, it might become a good place to snag good cells. I'm thinking this because mastercraft brand comes on sale much more than yardworks, although this might not be true of the battery packs themsleves.

Is 18v made of 5 cells at 3.6v each ?

Yardworks is yard products; mastercraft is tools.

PowerXchange is Nickel or Lithium choice.

The Li-Ion battery is apparently 2 AH (or 2.2 ?) and costs $130. Funny the drill includes battery and is on sale for less than battery alone. But there is a variant battery with different connector thats only $100 ??

The button and four LEDs on that batt look familiar.

Black and Decker VPX line is discontinued, but you couldn't tell that from lack of sale prices at CTire. I expect they will go on clearance here eventually, like they've done in the US already.

So, IMO it's still pretty hard to beat 5 cells prismatic of LiMn/Spinel for $110 for 6 AH, here or in the US.

I'd hate to have to wire 3 of the 2 AH cells in parallel to get the 6 AH from these cells without wiring. As it is I'm looking to try 5s4p (esp. for my damaged batts) and that's only 4 cells in parallel, not 20 like 5s20p !

I'm starting to think of ThunderSky 90 AH cells or similar, never mind some wimpy 2 AH power tool cells.

 

[mikereidis]

You're probably right about the warranty period vs life span being one of yardworks variables in their decision not to add any individual cell OV protection. One of the sad signs of an economy based all too much on consumable products.

I guess this means slow charging (relatively low current) is the best way to go for these cells with the stock BMS.

Yes, and I'm thinking that is why the YW charger does not have a true CV phase; it slowly tapers off to no current and if you wait long enough, like several days, your batts will eventually top off to just about 21v or whatever the pot on the board is adjusted for.

I've heard that Lithium batteries tend to be self balancing, and I'm wondering if there is a mechanism by which the fuller cells turn more of the current into heat than the less full cells. Since the same current flows through all cells, this is the only way to explain self balancing. This would imply a full cell has higher internal resistance then a less full cell when charging near high voltage and at low current.

In my next post I'll expose the front end voltage monitor circuitry for the BMS...

 

[mikereidis]

OK, let's put this YW BMS balancing thing to bed.

YW BMS does not balance, it only measures voltage through the thin 22 gauge cell wires.

I'm charging a battery with first 2 cells near full and rest much less full. If there was balancing, there would be some noticable current going through these wires. My DMM shows 0.1 micro-amps of current, about what you'd expect with 4 volts going through 40 megohms of resistance.

I've traced out all of the BMS circuitry from the voltage monitor connector through the 10 diodes at middle of BMS. Five diodes are like a 5 input OR gate controlling over-voltage, and 5 are for under-voltage. So, yes, the BMS should detect over-voltage at some point, but the best it can do is throttle or stop charging; it can't balance, unless it's the very low current self balancing Lithium trick.

Input resistors are 470 ohms. They go to a "G3PL" 6 pin IC:

BATTERY PROTECTION IC FOR SINGLE-CELL PACK S-8261 Series
http://datasheet.sii-ic.com/en/battery_protection/S8261_E.pdf

I beleive the specs are, or are very similar to:

Model No. S-8261ABPMD-G3PT2G 4.200 V 0.10 V 2.80 V 0.1 V 0.15 V Unavailable (1) Yes
Overcharge detection voltage VCU: 4.200v
Overcharge hysteresis voltage VHC: 0.10v
Overdischarge detection voltage VDL: 2.80v
Overdischarge hysteresis voltage VHD: 0.1v
Overcurrent 1 detection voltage VIOV1: 0.15v (but this func not used)
0 V battery charge function: Unavailable
Delay time combination *1: (1)
Power down function: Yes

*1. Refer to the Table 2 about the details of the delay time combinations (1) to (9).


Further evidence of no balancing is that there are NO power resistors on the BMS, except for the all cell current sensing shunt. There are 3 big semiconductors on heat sink, and 2 smaller ones on board, plus a bunch of tiny SMD devices.

But no power resistors means no balancing because almost nobody uses semiconductors to waste power purposely, and there aren't even enough semiconductors big enough to balance more than a few millamps anyway.

It's possible the circuitry on the BMS could be modified to make it charge balance by tying FETs to power resistors triggered by the HV detection. I might try this.

Over-current issues are not handled per cell, they are handled for all series cells.

I'm a little surprised to see HV detection; I had presumed YW BMS would just keep going to 4.3v and up, but maybe not; I'll have to test. At best I think it disconnects battery or at least drops current to miniscule value.

So that's it and that's my final word. YW BMS does NOT balance, but it might help self-balancing (if such a possible unicorn exists) if low current helps that happen.

 

[GGoodrum]

I would agree, it doesn't look like this unit does any sort of balanced charging. You would need either power resistors, or heatsinked FETs on each channel, and wires capable of passing at least 50-100mA.

I'm not entirely sure how the Ping, and other Chinese BMS variants, do balancing, but with our BMS design, it doesn't balance the cells, in relation to each other, which is what most RC balancers do. What ours does is allow each cell to reach a 100% charge level, whatever that is. The cells don't have to be the same exact capacity, which they almost never are. With RC-type balancers, the high cells are dragged down to the level of the lowest capacity cell.

With all Lithium-based cells, a proper charger will start in a current-limited (CC) mode, which pumps as much current as the charger can put out, into the cell. While this happens, the cell voltage slowly rises at a pretty steady rate, as it becomes harder and harder for the cell to accept current at the same rate. When the cell gets to about the 80-85% full level, It suddenly becomes a lot harder to pump the current in at the same rate, and the voltage starts to rise at a much quicker rate. For LiFePO4 cells, this "knee" in the voltage curve, happens at around 3.65-3.70V. For LiMn, it is around 4.1-4.2V and for LiCo-based "LiPo" cells, it is 4.20V. SLA cells actually have the same sort of "knee", which is around 2.40V per cell. Anyway, in order to get the last 15-20% into the cell, what the charger needs to do is to limit the voltage to the required cutoff point (i.e. -- 3.65V/4.10V/4.20V/etc...), and since the cell can't keep accepting current at the max rate, the current will start dropping. It will do this reduction at roughly the same rate-of-change as when the voltage was rising. Generally, when the current drops down to under 50-100mA, the cell is about as full as it can get.

With all Lithium-based cells, the current will eventually drop to zero. This is a problem when you are trying to bulk charge multiple cells in series, because unless the cells all start out at exactly the same levels, and have the same exact capacities, and have the same internal resistances and have the same thermal characteristics, some cells will get full quicker than the others. When this happens, the fullest one drops the current down and since all the current has to go through all the cells, the lower level cells never get a full charge. What ends up happening is that the cells drift farther and farther out-of-balance with each other. Without a proper, cell-level, LVC function, you can eventually get to the point that one, or more cells are below their "danger" points (2.0V for LiFePO4, and 2.70-2.80V for LiMn/LiCo...), but the overall pack voltage is still above a pack-level LVC value.

SLA cells have one very handy characteristic. They have the ability to absorb a bit more current, even when they are completely full. This built-in "shunt" capability allows enough current to pass through all the cells so that the low ones can "catch up". That's why most SLA chargers have a trickle charge, or balance mode. Lithium-based chemistries don't have this capability, and when they get full, current stops flowing. The BMS board that Richard and I are developing simply adds a small power transistor and a big power resistor to each channel so that if the cell is full, the shunt will bypass current so that the low cells can catch back up. The amount of current bypassed is controlled by the size and value of the shunt resistor. With a 15 ohm resistor, about 250mA of current can be bypassed, and with a 6.8 ohm value, this goes up to about 450-500mA. Obviously, the higher the current, the less time it will take for the low cells to reach their 100% level. With most of the Chinese BMS boards, the bypass current is only 50-100mA, which is why it can take hours for a new "duct tape" pack to have each cell fully charged, or balanced. In any case, shunt-based balanced charging is equivalent to using individual cell CC/CV chargers, like the 2A Voltphreaks units popular with many here, but can be done with a standard SLA-type CC/CV charger, like the Soneils and the Zivans.

I read through all 20-some pages of this thread, initially to see if these packs could be used with the supplied BMS with any greater success than many of us have had with the DeWalt packs. I think the general consensus now is that no, the YW BMS is not going to work any better in a bike application than the DeWalts. The big problem I had with the DeWalt BMS is that it was insanely easy to discharge the packs to the point the DeWalt charger would not work. You'd get the flashing LEDs that indicate a faulty pack. The reality is that because on a bike, the average current pulled out of the pack is less than what it might see in a drill, or a saw, so the "resting" voltage of the pack ends up below the charger cutoff, which I think is 29-30V, if you drain the packs down too far. The other problem is that even if you don't drain the packs too far, the cells still get out-of-balance, and the charger/BMS combo does a piss-poor job of balance charging the pack. Eventually, this causes pretty significant drifts in the individual cell voltage levels/SOC.

The only "good" news about this is that even with the tools, packs can get to the point that the charger will fail them, so there ends up being a lot of service center returns. In most cases, almost all of the cells are fine, with at worst, one or two that are below 2.0V. Many of the returned packs have all the cells above 2.5V, which means they are all 100% recoverable. The good Doctorbass now has an excellent relationship with his local DeWalt service center, and he gets returned packs for free. All he did was go there, show them his ebike, and offered to let them ride it. Obviously this won't work at every, or even many, service centers, but it is definitely worth trying. You might look for equivalent YW/CT service centers, and see if you might use the same tactic to get them to cut loose with some "rejects".

-- Gary

 

[mikereidis]

The only "good" news about this is that even with the tools, packs can get to the point that the charger will fail them, so there ends up being a lot of service center returns. In most cases, almost all of the cells are fine, with at worst, one or two that are below 2.0V. Many of the returned packs have all the cells above 2.5V, which means they are all 100% recoverable. The good Doctorbass now has an excellent relationship with his local DeWalt service center, and he gets returned packs for free. All he did was go there, show them his ebike, and offered to let them ride it. Obviously this won't work at every, or even many, service centers, but it is definitely worth trying. You might look for equivalent YW/CT service centers, and see if you might use the same tactic to get them to cut loose with some "rejects".

-- Gary

I don't know for sure, but I suspect there is no Canadian Tire service department to fix or "re-build" failed batteries. At best, they might send them to a recycler or perhaps the Canadian company that builds the cells (built in Asia) for examination or rebuilding or whatever (here in Canada; they wouldn't ship these back to Far East IMO). Even if the cells are in good shape, I don't think anyone could legitimately sell such cells/batts as new; they'd have to call them refurbished at least. With little assurance of life/cycles left, there probably aren't many who would want these batts/cells IMO (Except us, at drastically lower prices or free of course.)

I wouldn't be surprised if failed batteries are just dumped/crushed like many things these days. Of course they'd have to pay to dispose of them properly; AFAIK you are not supposed to just throw Li-Ion in garbage. So, hmmm, time to consider contacting the cell manufacturer again for info. If they paid to dispose of them, they might be happy to give away for free. They could be concerned that bad cells would just end up in normal garbage though.


BTW, the 5 cells are tied together pretty good in these batts. I've seperated a few failed cells out, and hacked together the half decent ones, but it looks awful and is certainly not a "professional inter-battery connection". Also, the compression bands go around all 5 cells. So, IMO a failed batt with only one bad cell is still a failed batt. You can't make the batt like new again by just replacing a cell, unless you have the time and equipment to do it properly.

Shorting a bad cell to bypass it works OK, but that bad cell is now dead weight.

 

[GGoodrum]

DeWalt just disposes returned packs as well. They don't do any sort of repair on these, and they don't sell "refurbished" packs. That's why, in the case of Doc's service center, they don't mind giving them away, at least on the QT. The trick is finding a guy who likes what you are doing with them. Some will not get it, at all, and others might get it too well, and may keep the cells/packs for themselves, but I think there has to be more guys out there that are like Doc's new-found friend(s), and who will be cooperative.

The point is that if you can get packs for nothing, there's probably lost of salvagable cells. From what I've read about your experiences and the those of others here who have used these, the cells themselves are quite robust. Plus, they are in a very handy packaging format. All that is needed is a better BMS, or at least a cell-level LVC capability and a bulk charger with external balancers, or maybe a set of individual chargers.

 

[mikereidis]

DeWalt just disposes returned packs as well. They don't do any sort of repair on these, and they don't sell "refurbished" packs. That's why, in the case of Doc's service center, they don't mind giving them away, at least on the QT. The trick is finding a guy who likes what you are doing with them. Some will not get it, at all, and others might get it too well, and may keep the cells/packs for themselves, but I think there has to be more guys out there that are like Doc's new-found friend(s), and who will be cooperative.

The point is that if you can get packs for nothing, there's probably lost of salvagable cells. From what I've read about your experiences and the those of others here who have used these, the cells themselves are quite robust. Plus, they are in a very handy packaging format. All that is needed is a better BMS, or at least a cell-level LVC capability and a bulk charger with external balancers, or maybe a set of individual chargers.

Hmm, maybe there is a Cdn Tire service centre in Toronto, where they test the batts at least to see if there is nothing wrong with them.

I see the Doc is reselling these batteries; I'm trying to get a few from him.

My Arduino micro-controller charger/BMS/Super CA project is going well. I have a prototype that works for 2 cells; seems to balance well.

My build thread is here: http://endless-sphere.com/forums/viewtopic.php?f=14&t=6650&start=0&st=0&sk=t&sd=a

I'm on track to have this ready by Halloween, for myself and whoever wants to be my first beta tester... I'd prefer if the first tester was at least comfortable checking voltages at the cell level; any volunteers ?

I'm still considering the "battery option" for those who don't want to mess with things at the cell level. Regardless, I'm convinced you will eventually have problems if you don't balance & monitor at the cell level.

I thought it would be faster to buy the TME balancers than build my own, but due to an alleged shipping snafu I still don't have them 8 days after ordering, and probably won't until next Tues or Wed. ! Will be interesting to compare with my own anyway. Anyone want to buy some TME balancers after I'm done testing with them ?

 

[drunkencat129]

ill volunteers my YW battery packs for the bms ur makeing also do u got a setup thats a 5 sell at least me and steveo will test and post results so far for my 3s2p pack it gets about 2.26km per AH at 40a peak avrage is about 10amp draw load is about 26 to 30amps and im doing about 55 km\h on my e scooter with a 16 inch wheel

 

[29a]

I stuck a astro lipo blinky between bms and pack using the from cells plug (blue is negative to blinky) and according to the blinky they were already balanced.
The same result on another two packs !
Ive only cycled these batts twice using the YW charger but I think they must be self balancing as i can't see them matching cells and balancing during manufacture.

Of the six packs i have, only the one bought with weed eater has security torque screws are you guy's the same ?

 

[mikereidis]

ill volunteers my YW battery packs for the bms ur makeing also do u got a setup thats a 5 sell at least me and steveo will test and post results so far for my 3s2p pack it gets about 2.26km per AH at 40a peak avrage is about 10amp draw load is about 26 to 30amps and im doing about 55 km\h on my e scooter with a 16 inch wheel

OK, will let you know. I'm very happy with project progress; still on track to have two prototypes built by Halloween.

Prototype schematics/layouts/physical design almost completed. Expect prototypes to be about 3.6" x 2.4" x 2" high with a few FETs vertical. Perhaps 1.5" high with FETs bent down. Possibly as little as 0.7"-1" high for compact production version; small enough to fit in large 25 cigarette pack.

Size does not include AC power supply but that could fit into a cube as small as 1"x1"x1" for a simple bridge rectifier pulsating DC supply.

Balancing resistors, and voltage divider resistors will be external, connected to battery lines.

Components/device will be generic enough to use for many purposes, like robot or RC model control, etc. Anything you can think of that doesn't take too much intelligence and uses up to 32 analog inputs resolved to 12 bits, and can control up to 32 digital/PWM outputs that can handle up to 1 Amp, or 100+ amps on all output channels using 32, 4110 FETs.

Project has me pumped... It WILL/MUST be done...

 

[mikereidis]

I stuck a astro lipo blinky between bms and pack using the from cells plug (blue is negative to blinky) and according to the blinky they were already balanced.
The same result on another two packs !
Ive only cycled these batts twice using the YW charger but I think they must be self balancing as i can't see them matching cells and balancing during manufacture.

Of the six packs i have, only the one bought with weed eater has security torque screws are you guy's the same ?

Thanks for the report. Yes, of my first 9 batts, only the weed-wacker package batt had the security torx screws. I strongly suspect torx was in the first shipped batts and they later changed their mind about using them.


Yes, if your lithium cells are in good shape, they should be reasonably self balancing. I think the manufacturer has decent tolerances that make all cells decently matched at manufacture.

It's when one of your cells gets damaged (or ages faster than the others) that the problems start. High voltage when charging and low voltage when discharging are the biggest threats. If you use properly functioning YW charger for charge and properly functioning BMS for discharge, you should be good, in theory.


For practice versus theory, I'm interested in hearing all reports of cell balance condition.

One concern I've developed is heat related. Next time I build a pack, I will put some ventilation space between batteries. Would be nice if the "Tunnels" created pointed forwards for bike driven air cooling, but I would consider one or two micro controlled fans also.

TylerDurden's idea to harvest velcro from weight or sports equipment at thrift stores has been fruitful. Next pack I install will be velcro'd to the bike.

 

[29a]

Am I correct in thinking the weed whacker is 9 amp so as long as i'm drawing more than that per parallel pack low voltage discharge shouldn't be a problem.
I also think the leaf blower is 12 amp so we should be good for at least 12 amp with no problems per parallel pack.
Anyone know what the amp rating's on the hedge trimmer and chain saw are ?

excellent thread lots of good info helped me a lot, im looking forward to the completion of the bms hopefully before i trash the YW ones.

 

[mikereidis]

Am I correct in thinking the weed whacker is 9 amp so as long as i'm drawing more than that per parallel pack low voltage discharge shouldn't be a problem.

The BMS seems designed for 31 amps, so I'd say these cells are good for 30 amps (5C) without immediate damage. It's up to you how much you want to derate that for the cycle life you desire.

My wacker tripped the BMS just once, in VERY deep heavy wet grass (with close to full charge so I don't think it was LVC). So the stall current of the motor is IMO 31 amps or more.

In general, Lithium will always last longer/more cycles with lower charge and discharge currents. I think the lowest you'd want to consider is 1C or 6 amps. At that rate I think cells should last at least 1000 cycles before losing maybe 10-20% of their capacity. I think that graph at battery university showed perhaps 500 cycles at 2c charge and discharge.

Maybe charging at a mere 0.3c like the YW charger does could double your cycles to 2000 at 1C discharge.

For my conservative maximum life test batteries, I'm expecting to go 4p and limit total current to 20 amps which should keep me under 5 amps or 0.83c per battery/cell. I think that's too conservative for the average thrill seeking ebiker though; perhaps 10-12 amps or up to 2c would be more appropriate/fun/easy, but battery life might decline a bit.

IMO, high currents do not kill or damage these batts immediately; they just lower cycle life. (This assumes battery temperatures remain reasonable which they normally do with low internal resistance when undamaged.) That's one of the beauties of these LiMn cells; they are good for at least 5C, unlike cheap LiFePo which may only be good for 1C or so and thus requires lots of wiring and work to parallel the cells.

 

[mikereidis]

Status update:

- I'm expecting 3 "36v" (actually 33v nominal) refurbished DeWalt packs from Dr Bass soon. They are 2.3 AH each, I guess 123 cells (M1 ?). They are almost exactly the same price per watt hour from the Dr as these YW batts. 3 packs almost (33v, 6.9AH) exactly same price as 2 YW batts. Will be interesting to see how they compare.

Yes, my BMS will be able to handle multiple chemistries in series.

- 15 days from order and I haven't seen my TME balancer package yet. Hmmm... I may have to dispute my CC charge if there is no product forthcoming in a reasonable time.

- 5 new YW batts arrived Friday so they took about 1 week after order. They sit in the corner until I complete my BMS etc design and order parts for first production prototypes.

- My first prototype BMS, with Blinky LEDs and "Clicky" relays is still running, over 1 week after I loaded the very simple version 3 of my test balancing code. Every few days, I check the 2 cell voltages and recharge with a Nintendo 9v, 2 amp power supply if they are 3.20v or less.

One night I forgot and left the charger running. Oh, no the relays aren't clicking anymore ! But that was OK, they were 100% on and shunting at least 400 mA of the excess current. Cell voltages were right around 4.2v. As soon as I disconnected charger much clicking ensued to try and get them back down to 4v or whatever I set it for.

So, cool, my original prototype actually succeeded at exactly what it was supposed to do. My "Cell Saviour".

 

[steveo]

ill volunteers my YW battery packs for the bms ur makeing also do u got a setup thats a 5 sell at least me and steveo will test and post results so far for my 3s2p pack it gets about 2.26km per AH at 40a peak avrage is about 10amp draw load is about 26 to 30amps and im doing about 55 km\h on my e scooter with a 16 inch wheel

OK, will let you know. I'm very happy with project progress; still on track to have two prototypes built by Halloween.

Prototype schematics/layouts/physical design almost completed. Expect prototypes to be about 3.6" x 2.4" x 2" high with a few FETs vertical. Perhaps 1.5" high with FETs bent down. Possibly as little as 0.7"-1" high for compact production version; small enough to fit in large 25 cigarette pack.

Size does not include AC power supply but that could fit into a cube as small as 1"x1"x1" for a simple bridge rectifier pulsating DC supply.

Balancing resistors, and voltage divider resistors will be external, connected to battery lines.

Components/device will be generic enough to use for many purposes, like robot or RC model control, etc. Anything you can think of that doesn't take too much intelligence and uses up to 32 analog inputs resolved to 12 bits, and can control up to 32 digital/PWM outputs that can handle up to 1 Amp, or 100+ amps on all output channels using 32, 4110 FETs.

Project has me pumped... It WILL/MUST be done...

well for me i dont care about the size of the bms due to the amount of lead that my bike had lol i got battery space coming out my a$$ lol