The care and feeding of a123-based packs...

Batteries, Chargers, and Battery Management Systems.
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silicium   10 W

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Post by silicium » Dec 04 2007 4:57pm

Hi,
News of BMS for 12...15 cells A123M1
I progress... Slowly but surely
The board isn't finish, remain 30 components to place...
Attachments
BMS A123 x15V4c.pdf
(72.04 KiB) Downloaded 414 times
Last edited by silicium on Dec 05 2007 3:30am, edited 1 time in total.
RH205, A123 4P12S with BMS http://vae-tech.forumactif.org/t8-un-bms-home-made (in french)

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Post by Doctorbass » Dec 04 2007 8:38pm

Wow great job Silicium!

Let us know when the first unit will be tested!

You could get alot of demand about it!!

Prepare your production!
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silicium   10 W

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Post by silicium » Dec 06 2007 4:39pm

Hi,
Good news of BMS 12...15 Cells A123 !
Board is ready and start prototype tomorrow.
Size board for 15 cells is 245x96 (milimeter) :wink:
Silicium,
Attachments
BMS A123 x15V5.pdf
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RH205, A123 4P12S with BMS http://vae-tech.forumactif.org/t8-un-bms-home-made (in french)

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Post by steveo » Dec 11 2007 4:32pm

silicium wrote:Hi,
Good news of BMS 12...15 Cells A123 !
Board is ready and start prototype tomorrow.
Size board for 15 cells is 245x96 (milimeter) :wink:
Silicium,
How much are you asking per bms... what charger would we be needing to charge ?


fill us in we are waiting :lol:
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Post by GGoodrum » Dec 11 2007 9:03pm

I'm still not clear why this thing has to be so incredibly complex (380 parts? Yipes! :shock: ). Also, I think it is still a shunt-based design, which means each cell is cutoff when it reaches 3.7V. This will only allow each cell to charge to about the 85-90% level.

Most chargers have constant current (CC)/constant voltage (CV) charging profiles. During the initial CC mode, the current is held, and the voltage is allowed to float. It will rise, steadily, until it reaches the cutoff. At that point, the charger switches to the CV mode, which holds the voltage at the cutoff, and lets the current gradually taper off, usually until it gets down to about 200-300 mA. With these shunt-type regulators, the cell misses the whole CV side of the charging process.

I also don't think we need an absolute cutoff for low-voltage protection, for use with Crystalyte controllers, when the controller can do this function and all it takes to activate it is by grounding one signal. The LVC circuit that Bob Mcree came up with has two extremely low-power chips and a resistor, per channel, that's it. If somebody came up with an effective way to handle the CV part of the process that was simple enough to be co-located with the cells, I think this would be a worthwhile thing to do. Until then, I think it is still best to bring out the cell junction wires, and either do external balancing or individual cell charging.

-- Gary

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Post by Snickers » Dec 12 2007 7:50am

@Gary, for sure. You have the possibility to charge and discharge without BMS…
But in order to expect specification about numbers of cycles, max capacity over life cycles, no risk of elements damaging, no need to test each element capacity before assembly,….I think there is not so much alternative…We must manage each element separatly.
I'm ready to add 20-30% of battery price to have this.

I would like to charge battery with solar panel, I have allready (2xBP7170- 36V -170 Wp) with this BMS. It will be possible without complicated electronics between solar panel and battery. I just need to limit the maximal voltage of solar panel arround 60 volts.

For a standard charger, we need one with 56V-60V output with xxA
For starting of charge arroud 45V, I will check if my power supply can support this without external current limiter…
If not, I will add current limiter based on transitor or some small resistor. It will be used in serie to reduce the current output for the charger at appropriate value.

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Post by GGoodrum » Dec 13 2007 2:30pm

Snickers wrote:@Gary, for sure. You have the possibility to charge and discharge without BMS…
But in order to expect specification about numbers of cycles, max capacity over life cycles, no risk of elements damaging, no need to test each element capacity before assembly,….I think there is not so much alternative…We must manage each element separatly.
I'm ready to add 20-30% of battery price to have this.

I would like to charge battery with solar panel, I have allready (2xBP7170- 36V -170 Wp) with this BMS. It will be possible without complicated electronics between solar panel and battery. I just need to limit the maximal voltage of solar panel arround 60 volts.

For a standard charger, we need one with 56V-60V output with xxA
For starting of charge arroud 45V, I will check if my power supply can support this without external current limiter…
If not, I will add current limiter based on transitor or some small resistor. It will be used in serie to reduce the current output for the charger at appropriate value.
You are missing my point. I'm not talking about bulk charging a series connected pack without any sort of BMS. What I'm saying is that if you don't have a BMS design that holds the voltage at around 3.7V and allows the current to gradually reduce to somewhere around 200-250mA, the cell will not get a full charge. If you simply use a FET to cutoff current when the cell first hits 3.7V, that cell will only be charged to the 85-90% level. I'd love to have a configuration that would not have to have the individual cell junctions brought to the outside of the pack, but not if it means I can only get the cells charged to an 85-90% level.

What I'd like to see is a circuit design that simply "capped" the voltage at 3.7V, while still allowing it to accept as much current as it will take. Then, the external portion of the charging "system" can be a just a constant current supply.

My true desire is to have whatever is needed in the pack so that it "looks" like an SLA battery to the charger. There are a whole slew of affordable SLA charging solutions that have the exact CC/CV charging profile that is optimum for an a123-based setup. All you have to do is use a pack configuration that is a multiple of 4 cells in series. Anyway, until I find this, the "holy grail" of BMS solutions, I will continue to use my individual cell CC/CV chargers to make sure my packs are full, as as balanced as they need to be. :)

-- Gary

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silicium   10 W

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Post by silicium » Dec 13 2007 4:34pm

To ensure a full charge when the last cell reaches 3.6 V, there is a timer that allows you to wait until the last cell is fully charged.
The current is reduced to 500mA during the balance to reduce dissipation power.
RH205, A123 4P12S with BMS http://vae-tech.forumactif.org/t8-un-bms-home-made (in french)

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Post by fechter » Dec 14 2007 9:25am

If you bump the current down when the first cell hits max voltage, will the voltage on that cell drop at the lower current for a while?


A dissipative voltage clamp like the one Victor drew may not be as bad as you think. If the cells are all balanced perfectly, then there should be practically no dissipation. A cell would have to be way out of whack before the voltage clamp would need to dissipate the full charging current.

That switching mode current limiter circuit from 4QD could be switched in series with the charger input to drop the current below the normal current limit to do the balancing phase. This would be more expensive than just tweaking the charger circuit, but would allow a standard SLA type charger to work as is. At a fairly low current, the parts for the switcher wouldn't need to be to big or expensive. I suppose a big resistor would work too.
"One test is worth a thousand opinions"

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Post by silicium » Dec 18 2007 12:18pm

News of week for my BMS...
I progress:
only 5 components to placed and tests tomorow !
Attachments
P1060302.JPG
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RH205, A123 4P12S with BMS http://vae-tech.forumactif.org/t8-un-bms-home-made (in french)

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Re: The care and feeding of a123-based packs...

Post by fechter » Dec 20 2007 11:46pm

Wow! Nice board!

It will be interesting to see how it works.


I had one of those dumb ideas the other day:
Say you use separate chargers for each cell and are only concerned with discharge protection.
You can monitor every cell's voltage to have good protection.
But what if you monitor every two cells (or 3 cells)? If you measure two cells, one might assume that one cell will go flat before the other, and you could determine a good cutoff voltage for the pair that would guarantee that neither cell gets overdischarged before it triggers the cutoff.

The advantage of this approach is it uses half the parts :wink:

In hybrid car batteries (Nimh), they monitor every 6 or 8 cells, not every cell.
"One test is worth a thousand opinions"

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Re: The care and feeding of a123-based packs...

Post by Malcolm » Dec 21 2007 4:00am

fechter wrote:I had one of those dumb ideas the other day:
what if you monitor every two cells (or 3 cells)? If you measure two cells, one might assume that one cell will go flat before the other.
I've been thinking along the same lines (convergent dumbness?). I think this would work very well if you had single cells connected in series or maybe pairs of parallel cells wired in series (e.g. LifeBatt cells). It would be less reliable for multiple parallel strings wired in series (e.g. A123), as faults in individual cells would have less overall effect on the average voltage.

The advantage with lithium phosphate is that because the voltage drop-off is so sharp, a weak cell will significantly lower the average voltage of a group of two or three cells, so if you set the cutoff or warning at, say 2.9V, it will trigger before any single cell has dropped below the point of harm – say 2.5V. A while back I posted a little circuit that the RC crowd use to sound a buzzer when the voltage drops below an adjustable level. I'm sure this can easily be adapted to cut off power or trigger a warning light on handlebars, etc.
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Re: The care and feeding of a123-based packs...

Post by silicium » Dec 21 2007 5:52am

There is only one charger for all cells.
The cells is arranged with 4P12S for my battery. The BMS up to 15 cells.
The complet schematic is down:
BMS A123 x15V5complet.pdf
(84.15 KiB) Downloaded 266 times
The schematic for one cell (sub-circuit) is down:
BMS A123 Cell.pdf
(21.1 KiB) Downloaded 245 times
First test:
Voltmeter display 3.63V (voltage cutoff cell1)
Image

We must wait for the circuit test results...
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Re: The care and feeding of a123-based packs...

Post by efreak » Jan 01 2008 12:25am

Happy new year


I am trying to decide the best and easiest and most reliable set up for my charging plans a123 cells.
I need to gather 80 good cells. i was hoping to use them as is like most of the folks who have gone that route but not entirely without problems ( i am going to use them witha 72/40 controller on a 5304 hub motor) this sounds do able for me ala Dean or emf or ross and all the other good folks. or... bypass the bms for discharge and keep bms for charging again i think the majority are using a 40x motor not a 530x. this also easy but what i suspect will happen (murphy old buddy) after investing in say 4 chargers and all of the mod you end up having to go ahead with the surgery and implants
!! which Is still in the realm of things i am comfortable attempting.

but at that point you have to pull the packs apart and possibly do a Gary's style (keeping the alot of the cell protective plastic and the existing wiring) set up of i guess 10s 4p and the x2 i am not to good at that yet to get like 66 8ah usable

by doing that i need to configure what charging set up to use single cell do-able and reliable. $150~$300
or a megapower or two for like $500like the doc (hey doc what do use to feed that charger ? good luck with the current charger project. cool video)
i still have 2-3 months before all peices come together.

I pulled the trigger on those m1's the week befor ethe big lifebatt announcment figures Murphy @ work. o well someone else have to be the first to test those mind you depending on my my futre experinces and others here I be more that happy to test those on my second set up. I still gonna need those lvcs

thanks for this
good year to all
efreak
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Re: The care and feeding of a123-based packs...

Post by EMF » Jan 06 2008 11:18am

I wonder if this current monitor relay could be used to monitor a charge cycle and cut the charge with a generic power supply, such as the Mastech 2050? I am trying to figure out a way to make sure I don't overcharge my batteries, or be able to charge unattended.

Check out the EMD-FL-C-10 2866022 on this page (third item down from the top) : http://www.phoenixcon.com/shared/framer ... %23current.

I am not sure how far down it will go on current, but even 1 amp would be ok. Then I could top off with a much slower charger if needed.

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Re: The care and feeding of a123-based packs...

Post by green hornet » Jan 07 2008 10:46am

Big Q - Do people who pay $11 per M-1 cell really NEED 40C discharge for their e-bikes....No

Then why do they pay too much for them when it's not necessary ???
Maybe it's the joy of tearing apart a power tool pack ( a primordial urge perhaps..? )
Maybe people really love the paper cover on the a123 cell... ??

Note...to those tearing apart dewalt packs ;

the a123 cell is 2.3Ah. cost is $11 each
SO - If $ 11 / 2.3Ah = $ X / 2.7Ah...then the equivalent is $12.91. The price a 2.7Ah cell should cost ! !
Anything less will be cheaper than an A123 cell

Please, Let's hear a really good reason for this from all the brainiacs out there.
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Re: The care and feeding of a123-based packs...

Post by Ypedal » Jan 07 2008 11:14am

Because the M1's have a proven track record.. with millions sold and in use.

the High-C rate means you can load them with little V sag.. and no heat.

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Re: The care and feeding of a123-based packs...

Post by green hornet » Jan 07 2008 11:47am

right, OK, I guess somebody should tell all the other producers to close their doors, and shut down.
Bye Bye life batt
Bye Bye phostech, PHET
too bad valence, Bye
Proven Track record ?
Is that why so many people on this board are buying no-name chinese packs ?
Load them ?...yea, an ebike 40,50 amp controller really loads it up all right

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Re: The care and feeding of a123-based packs...

Post by Ypedal » Jan 07 2008 12:00pm

Not sure i understand what you are getting at.. but I bet there are WAY more people buying A123's than cheap chinese packs in general.

Self included, packs wrapped in duct-tape are not my idea of quality packaging..... there is a market for that from the looks of it..

But those who want quality and are willing to pay for it, won't buy anything wrapped in duct tape.
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Re: The care and feeding of a123-based packs...

Post by TylerDurden » Jan 07 2008 12:03pm

green hornet wrote:right, OK, I guess somebody should tell all the other producers to close their doors, and shut down.
Bye Bye life batt
Bye Bye phostech, PHET
too bad valence, Bye
Proven Track record ?
Is that why so many people on this board are buying no-name chinese packs ?
Load them ?...yea, an ebike 40,50 amp controller really loads it up all right
Uh... "so many people" being a handful for testing. :roll:
Have a Nice Day,

TD

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Re: The care and feeding of a123-based packs...

Post by fechter » Jan 07 2008 12:18pm

green hornet wrote:Big Q - Do people who pay $11 per M-1 cell really NEED 40C discharge for their e-bikes....No

Speak for yourself, I could use 40C discharge :twisted: It's nice to have a little headroom too.

What's your point? A123's are too expensive?
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Re: The care and feeding of a123-based packs...

Post by GGoodrum » Jan 07 2008 1:36pm

The only cells I've found that have come close to holding the voltage up under load are the LiFeBatts, which are rated about 10-15C. Most of the bag-type Chinese cells I've seen have much lower C ratings so in order to be able to handle 40-50A without the voltage sagging so much, you have to use much higher capacities, like 20-25Ah. Even then, they just don't seem to perform as well. The a123-M1s are so strong, that you could use fairly small capacity packs, like a 2p/4.6Ah version and it will still outperform most everything out there. Granted, a 4.6Ah isn't going to get you very far, but I think most people only need about 10Ah for most running around. It is for me, at least, so I'd prefer to not have to carry around more battery than I need.

-- Gary

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Re: The care and feeding of a123-based packs...

Post by DeeL2003 » Jan 07 2008 2:28pm

green hornet wrote:Big Q - Do people who pay $11 per M-1 cell really NEED 40C discharge for their e-bikes....No

Then why do they pay too much for them when it's not necessary ???
Maybe it's the joy of tearing apart a power tool pack ( a primordial urge perhaps..? )
Maybe people really love the paper cover on the a123 cell... ??

Note...to those tearing apart dewalt packs ;

the a123 cell is 2.3Ah. cost is $11 each
SO - If $ 11 / 2.3Ah = $ X / 2.7Ah...then the equivalent is $12.91. The price a 2.7Ah cell should cost ! !
Anything less will be cheaper than an A123 cell

Please, Let's hear a really good reason for this from all the brainiacs out there.

Are you Mr. Forsen USA himself?

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Re: The care and feeding of a123-based packs...

Post by green hornet » Jan 07 2008 3:32pm

Shhhh,
I don't want to break anybodies love affair w a1234....
but this whole a123 lovefest was out of control,
just do the math.
If LifeBatt can do it, I can do it 8-)
I'll put my cell up against a123 anytime.
I'll even do a one time offer for group purchase ~9+ each

end of posting on this

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Re: The care and feeding of a123-based packs...

Post by GGoodrum » Jan 07 2008 4:42pm

green hornet wrote:Shhhh,
I don't want to break anybodies love affair w a1234....
but this whole a123 lovefest was out of control,
just do the math.
If LifeBatt can do it, I can do it 8-)
I'll put my cell up against a123 anytime.
I'll even do a one time offer for group purchase ~9+ each

end of posting on this
What are the specs for these 2.7Ah cells you have? What is the C-rating you are claiming? Is there any sort of guarantee/warranty offered?

The LiFeBatts are not quite as strong as an equivalent a123 setup (Xs4p...) but close enough, and they have one huge advantage, in my opinion, which is the form factor, with the studs. Making packs is much easier. Actually there is another significant benefit, and that is the two-year warranty, if you use an approved LVC/BMS/CMS, and 90-days for the cells-only.

Actually, maybe you should start a new thread/lovefest for these, if they are as good as you say they are. :)

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