Even Newer 4 to 24-cell Battery Management System (BMS)

Batteries, Chargers, and Battery Management Systems.
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Re: Even Newer 16-cell Battery Management System (BMS)

Post by fechter » Jul 23 2008 9:26am

JB_EB wrote: So just to confirm, this board takes care of:
- Charging and equalising of the individual cells in the pack.
- And provides a Low Voltage Cutoff signal that can be connected to the e-brake switch on the controller to prevent over discharge?

In addition, all that is needed is a power supply that is a few volts greater than 3.65v x (Number of cells in series) and with sufficient Current to charge the pack in your required time, plus some high-current connectors. Is that correct?

JohnB
Correct. The connector to the charger needs two high current contacts, and two low current contacts (or an integrated switch on the BMS side).
"One test is worth a thousand opinions"

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Re: Even Newer 16-cell Battery Management System (BMS)

Post by GGoodrum » Jul 23 2008 10:28am

JB_EB wrote: So just to confirm, this board takes care of:
- Charging and equalising of the individual cells in the pack.
- And provides a Low Voltage Cutoff signal that can be connected to the e-brake switch on the controller to prevent over discharge?
That is correct.
JB_EB wrote:In addition, all that is needed is a power supply that is a few volts greater than 3.65v x (Number of cells in series) and with sufficient Current to charge the pack in your required time, plus some high-current connectors. Is that correct?
Actually, the charger/supply just needs to be a few millivolts above the sum of the individual cutoff voltages. The cutoff voltages are a function of the voltage divider resistors, so you can adjust the number by changing these values, if you needed to. With the 180k/75k 1% resistors supplied, the number ends up being somewhere between 3.65-3.69V per cell. To go lower than this, the 75K value can be lowered.

-- Gary

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Re: Even Newer 16-cell Battery Management System (BMS)

Post by slayer » Jul 23 2008 12:38pm

So are you saying for around 90.00 kit to be aasembled you get both the cms and lvc combined in this bms kit

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Re: Even Newer 16-cell Battery Management System (BMS)

Post by GGoodrum » Jul 23 2008 1:38pm

slayer wrote:So are you saying for around 90.00 kit to be aasembled you get both the cms and lvc combined in this bms kit
Hopefully less than $90, but yes, that is correct.

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Re: Even Newer 16-cell Battery Management System (BMS)

Post by deVries » Jul 23 2008 4:28pm

GGoodrum wrote: Actually, the charger/supply just needs to be a few millivolts above the sum of the individual cutoff voltages. The cutoff voltages are a function of the voltage divider resistors, so you can adjust the number by changing these values, if you needed to. With the 180k/75k 1% resistors supplied, the number ends up being somewhere between 3.65-3.69V per cell. To go lower than this, the 75K value can be lowered.
Four questions:

1) Anyone have links to the best ideas for chargers or dc converters for this?

For example: I want to use a total of 56 a123 DeWalt cells in a 4 parallel configuration. So it's a 14s4p set-up at the theoretical voltage of 14x3.65 = 51.1v So, I guess I would need at least a 50v DC converter that should work fine. Correct? Best Buy Suggestions are: ?

2) Also, will the above example work with the circuit board even if I'm only using 14s4p of the 16s connection slots that are available? Correct? In other words, I don't have to use all 16s cell slots on the circuit board for any lesser number of Xs lower voltage set-ups I use? I can use any number available. Correct?

3) Are these kits already pre-assembled w/soldering complete? What does the buyer have to do to complete the kit... like the old Heath Kits?

4) It's my understanding that one circuit board will work with several identical parallel packs of x# up to 16 cell packs in x# of parallel packs. As I think Gary put it simply, the bucket (each parallel pack) simply overflows from charging one parallel pack to the next until the entire parallel set is fully charged. Correct?

Thanks!

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Re: Even Newer 16-cell Battery Management System (BMS)

Post by GGoodrum » Jul 23 2008 8:41pm

deVries wrote:Four questions:

1) Anyone have links to the best ideas for chargers or dc converters for this?

For example: I want to use a total of 56 a123 DeWalt cells in a 4 parallel configuration. So it's a 14s4p set-up at the theoretical voltage of 14x3.65 = 51.1v So, I guess I would need at least a 50v DC converter that should work fine. Correct? Best Buy Suggestions are: ?
Since you are going for a "non-standard" configuration (i.e. -- not a multiple of 4 cells in series...), you are cutting out the possibility of using an existing CC/CV-type charger, so I would look on ebay for a variable supply. Awhile back, I picked up an HP 0-60V/0-15A supply on ebay for $125.
deVries wrote:2) Also, will the above example work with the circuit board even if I'm only using 14s4p of the 16s connection slots that are available? Correct? In other words, I don't have to use all 16s cell slots on the circuit board for any lesser number of Xs lower voltage set-ups I use? I can use any number available. Correct?
Yes, you can use this with any number of cells/channels, 4 or over. You just jumper across the unused positions.
deVries wrote:3) Are these kits already pre-assembled w/soldering complete? What does the buyer have to do to complete the kit... like the old Heath Kits?
Assembly is not included. You get the board, separate parts bags and a detailed set of instructions. If you can't do basic soldering, this kit is probably not for you. I suspect, however, that some here will be able to offer their assembly services. That said, it is not terribly difficult to put together. Testing is very simple as well.
deVries wrote:4) It's my understanding that one circuit board will work with several identical parallel packs of x# up to 16 cell packs in x# of parallel packs. As I think Gary put it simply, the bucket (each parallel pack) simply overflows from charging one parallel pack to the next until the entire parallel set is fully charged. Correct?
Not quite. You need to connect cells in parallel first, and then to the board. You don't connect multiple series packs in parallel.

-- Gary

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Re: Even Newer 16-cell Battery Management System (BMS)

Post by fechter » Jul 23 2008 9:21pm

I have my eye on some surplus switching power supplies. Since they have isolated outputs, I can put units in series to get the desired voltage. If I take about 3.7v x the number of cells, I get about 59.2v for 16 cells.
I should look for a power supply that runs at about 60v. Most have a trim adjustment for the voltage, which I could turn down a bit. I could use a 48v supply in series with a 12v supply also.
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Re: Even Newer 16-cell Battery Management System (BMS)

Post by deVries » Jul 23 2008 10:12pm

GGoodrum wrote:
slayer wrote:So are you saying for around 90.00 kit to be aasembled you get both the cms and lvc combined in this bms kit
Hopefully less than $90, but yes, that is correct.
From your website: Unique "stick pack" construction technique groups four blocks of four paralleled cells, one block in front of the other, with the LVC board on the top of the stack. Between blocks are G10 plates with nickel-plated springs, which are used to make connections with the cells. A threaded rod down the middle holds everything snugly in place. Should cells ever need replacing, this can be accomplished with a simple partial dis-assembly of the stack. No messy soldering is required at all. Multiple 12V/9.2Ah "stick packs" can be connected in series in order to be used in 24V, 36V, 48V and/or 72V setups.

Can you do a special ES member combo deal :D for a "limited time" where one can order the battery assembly stick-packs for 4sx4p x #needed for voltage choice (minus its LVC board) as an add-on for your new LVC-charging BMS system with the necessary mods to make it work? In other words, for example, 4 stick packs to assemble 48+v PLUS your new board?

OR

Does anyone know of good sources for battery assembly using solderless battery kits that can be purchased? I'm going to use 26650 batteries Dimensions: 26mm x 65mm for mine, and I have to avoid soldering tabs to these babies. Not possible for me to do that, spot weld tabs, so I need a solderless solution.

Thoughts and suggestions?

Thanks!

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Re: Even Newer 16-cell Battery Management System (BMS)

Post by shinyballs » Jul 23 2008 10:22pm

For this integrated LVC/BMS board, is it BAD to position it far from the battery? In my setup, all the batteries are mounted in the center frame and controller in the rear rack. And this board will be inside a box clamped in the seatpost.

btw, great work guys!
Sale section etiquette, pls be courteous to other members, if you know of a better deal or do not agree with the sale price, do not shove links to similar products being sold by someone else in another member's post.. it's just not nice. If you suspect a scam pls FLAG the thread for moderation and it will be checked out... i know this is a tough one to call but put yourself in the seller's shoes and imagine how you would like it.

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Re: Even Newer 16-cell Battery Management System (BMS)

Post by GGoodrum » Jul 24 2008 1:34am

I had a bit of a setupback today. It turns out the KSA931 PNP transistor that we picked for driving the shunt resistor, has the collector and base leads reversed, from the normal E-B-C configuration. I didn't know this before installing 16 of these on the new board. This caused the orange LEDs to come on too early, at about 2.6V. It took me awhile to find the problem, which was bad enough, but then it took me the next 10-1/2 hours to cut out the bad ones, clean out the holes, bend the leads around on 16 new ones, and then install/solder them. The good news is that the shunts come on at about 3.7V now, but the bad news is that six of the orange LEDs aren't coming on.

The bottomline is that the kits are not going to be ready this week, like I had hoped. I'm going to have to either pick another part, with the standard E-B-C piniout, or scrap these boards, and do a new one. In any case, Richard has all the parts and a board, so he will continue on with more testing. One thing we still need to get is a baseline on the amount of bypass current and heat that is generated. I did see that when I got the shunts working, the current it passed was close to an amp, and the big 5W resistor never got above about 150F. If that holds true with all 16 channels operating, that would be good news indeed. :)

-- Gary

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Re: Even Newer 16-cell Battery Management System (BMS)

Post by shinyballs » Jul 24 2008 1:51am

GGoodrum Is it critical that this board be very close to the batteries or it still works fine if farther by more than 4 feet of wire?
Sale section etiquette, pls be courteous to other members, if you know of a better deal or do not agree with the sale price, do not shove links to similar products being sold by someone else in another member's post.. it's just not nice. If you suspect a scam pls FLAG the thread for moderation and it will be checked out... i know this is a tough one to call but put yourself in the seller's shoes and imagine how you would like it.

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Re: Even Newer 16-cell Battery Management System (BMS)

Post by GGoodrum » Jul 24 2008 1:59am

shinyballs wrote:GGoodrum Is it critical that this board be very close to the batteries or it still works fine if farther by more than 4 feet of wire?
I think four feet is too much. I wouldn't have the leads longer than about 18 inches. I know someone here is using 30" leads, because he had me make them, but that's the longest I've seen..

-- Gary

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Re: Even Newer 16-cell Battery Management System (BMS)

Post by fechter » Jul 24 2008 8:39am

GGoodrum wrote:I had a bit of a setupback today. It turns out the KSA931 PNP transistor that we picked for driving the shunt resistor, has the collector and base leads reversed, from the normal E-B-C configuration.

Oops, yep, I screwed up. :oops: There are hundreds of transistors that are similar and I was paying more attention to the ratings than the pin configuration. This was real bad for Gary, since it resulted in a crapload of needless work and a big pile of transistors that won't work with the board.

One the one hand we're trying to hurry to get these out to people who need them, but on the other hand we need to make sure eveything works properly. I just got the newest version board in the mail, and I'll try building and testing it as soon as I can. At least I know ahead of time to reconfigure the leads on the transistors. :mrgreen:
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Re: Even Newer 16-cell Battery Management System (BMS)

Post by JB_EB » Jul 24 2008 10:26pm

Bad luck about the transistors. :( The joys of prototyping. Don't you just love the "standard pinouts"!

I have a low-tech question. I will be charging an 8s5p string so need ~ 30VDC.
I have a 240VAC to 24VAC 3A secondary transformer (240V, 50Hz mains here in Australia) and I was wondering if I added a bridge rectifier and a few thousand uF of capacitance, if I could use this unregulated linear power supply to drive the BMS? The output would be ~34V unregulated DC with some 100Hz ripple.
Or should we only use a regulated supply.
I would be happy to take 4-5 hours to charge overnight, so don't really need a high current power supply.
(Forgive me - it is my Scottish ancestry coming to the fore and looking at alternative cheap solutions. :roll: )

JohnB
26" Learsport BW3240 Dual Suspension MTB, Shimano Nexus 8-sp Hub gear, Cyclone 360W chain-drive, a123 8s5p battery.

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Re: Even Newer 16-cell Battery Management System (BMS)

Post by Jeremy Harris » Jul 25 2008 1:41am

I've been caught by the dreaded TO92 transistor pin out problem before now, so you have my sympathy - it's a dead easy mistake to make. I've always thought it crazy to use different pin out designations for the same package. The one that got me years ago was the BC182 - the damn thing is available in two different pin outs in the same package, with similar part numbers (the BC182L is BCE, the BC182A is CBE). When the smoke cleared it was an easy fix for me though, just go and buy the other version...................

Jeremy
Last edited by Jeremy Harris on Jul 25 2008 3:16pm, edited 1 time in total.
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Re: Even Newer 16-cell Battery Management System (BMS)

Post by fechter » Jul 25 2008 10:25am

JB_EB wrote:
I have a low-tech question. I will be charging an 8s5p string so need ~ 30VDC.
I have a 240VAC to 24VAC 3A secondary transformer (240V, 50Hz mains here in Australia) and I was wondering if I added a bridge rectifier and a few thousand uF of capacitance, if I could use this unregulated linear power supply to drive the BMS? The output would be ~34V unregulated DC with some 100Hz ripple.
Or should we only use a regulated supply.
I would be happy to take 4-5 hours to charge overnight, so don't really need a high current power supply.
(Forgive me - it is my Scottish ancestry coming to the fore and looking at alternative cheap solutions. :roll: )

JohnB
Yes, I think you should be able to get away with that as long as the voltage stays in a good range.
One problem will be limiting the current. With a low pack, the thing may try to draw big amps, so you may need a big honkin resistor or just long charger wires to limit the max current.
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Re: Even Newer 16-cell Battery Management System (BMS)

Post by deVries » Jul 26 2008 8:17pm

deVries wrote:4) It's my understanding that one circuit board will work with several identical parallel packs of x# up to 16 cell packs in x# of parallel packs. As I think Gary put it simply, the bucket (each parallel pack) simply overflows from charging one parallel pack to the next until the entire parallel set is fully charged. Correct?
GGoodrum wrote:Not quite. You need to connect cells in parallel first, and then to the board. You don't connect multiple series packs in parallel.
-- Thanks Gary & everyone else for helping out too. This is my first build, and I'm not even an electronics hobbyist, yet! But I'm trying. I can see upon further reflection my thinking was/is confused to begin with. So, I will rephrase, hoping this will be ontrack???...

I'm going to make 16 4p cell-packs that I need to eventually connect in series. With your board I should connect each 4cell p-pack to each of your 16 LVC/Balancing connections. With my set-up I would use all 16 of your slots/ports in 4p-4cell configuration x 16 times. Assuming this is correct, then how should I connect the 4cell p-packs in series keeping that "separated" or "isolated" from the 4cellp connections? Won't that change all the voltages getting to each 16 port slot too once everything is connected in series? Sorry, I know I'm just talking newbie... maybe nonsense...

I'm confused about how the circuit can just isolate and deal with the 16 4cell p-packs each connected to the 16 slot/port connections, when these 4cell p-packs also have to be in series too. (Sorry I'm such a rank newbie in understanding all this!)

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Re: Even Newer 16-cell Battery Management System (BMS)

Post by Pete » Jul 26 2008 11:34pm

Hmm, Once you have connected the 4 individual cells into a parallel group you now need to think of this 4parallel group as a single cell. You then connect 16 of these 4parallel groups in series.

When you measure the voltage from end to end on the 16 cells in series you will get a nominal 48v (closer to 60v hot off the charger)

The BMS has a connection to each junction between adjacent 4p blocks. If you were to measure the voltage from one side of a 4p block to the other you will see a nominal 3.2v. It does not matter which 4p battery you measure in the series string, it will still be 3.2v nominal. Remember that you are measuring the voltage with respect to whatever reference point you happen to place your negative voltmeter lead on, not the combined series voltage.

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Re: Even Newer 16-cell Battery Management System (BMS)

Post by deVries » Jul 27 2008 4:22pm

GGoodrum wrote:
deVries wrote: 1) Anyone have links to the best ideas for chargers or dc converters for this?

For example: I want to use a total of 56 a123 DeWalt cells in a 4 parallel configuration. So it's a 14s4p set-up at the theoretical voltage of 14x3.65 = 51.1v So, I guess I would need at least a 50v DC converter that should work fine. Correct? Best Buy Suggestions are: ?
Since you are going for a "non-standard" configuration (i.e. -- not a multiple of 4 cells in series...), you are cutting out the possibility of using an existing CC/CV-type charger, so I would look on ebay for a variable supply. Awhile back, I picked up an HP 0-60V/0-15A supply on ebay for $125.
Ok, seems I needed to modify my configuration anyway for packaging and mounting purposes. :wink: :lol:

Now, I'm going with 4p packs connected to the 16 slot/ports on the board. When these 16 4p packs are connected in series it will top off at a fraction over 59v.

For set-up to use existing CC/CV-type charger what batt-series configuration should I use? What chargers would you recommend to match your best ideas and suggestions?

Anyone?

TIA.

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Re: Even Newer 16-cell Battery Management System (BMS)

Post by slayer » Jul 27 2008 4:33pm

Soneil are good for 16 series
http://soneil.com/48_volt.html

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Re: Even Newer 16-cell Battery Management System (BMS)

Post by deVries » Jul 28 2008 3:05pm

fechter wrote:
Johnbear wrote:Assuming the batteries can handle it, what is the maximum charging current this BMS can handle? What is the limiting factor?
Thanks!
I was designing for 20 amps, but I don't have a test setup that can go that high yet.
The limiting factor will be heating on the FET. If the FET runs too hot, it would just be a matter of adding a heatsink. The FET can handle up to 70 amps with a big heatsink.
From my point of view I want to charge as fast as possible without risking any damage to the cycle lifespan or reducing capacity... Is there an ideal AMP charge range to stay within?

Also, the battery specs I have A123racing suggest overcharging the batteries slightly to 3.9v will help keep the batteries balanced and not really affect the lifespan of the batts. Will it be easy to mod your BMS to cut-off at this higher voltage instead? Cost to do it? Also, I'm told the batts can be discharged down to 2.4 volts without problems. Again, will it be easy to mod your LVC to cut-off at this lower voltage instead? Cost to do it?

TIA. :)

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Re: Even Newer 16-cell Battery Management System (BMS)

Post by fechter » Jul 28 2008 3:11pm

The cutoff voltage is a function of the resistors installed on the voltage divider for each channel. With the values we're using presently, I'm getting 3.68 volts. To change the voltage would require changing the resistors. You could pick resistor values to get any cutoff voltage you want (within reason).

3.9v sounds too high, but they're in the business of selling batteries...
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Re: Even Newer 16-cell Battery Management System (BMS)

Post by deVries » Jul 28 2008 5:58pm

Three more questions :D for you (please&thankyou)...
fechter wrote:3.9v sounds too high, but they're in the business of selling batteries...
... :P
deVries wrote:From my point of view I want to charge as fast as possible without risking any damage to the cycle lifespan or reducing capacity... Is there an ideal AMP charge range to stay within?
1) Any thoughts about this? ...Is there an ideal AMP charge range to stay within for max. lifespan & cycles? (I will have 4p packs connected to all 16 slots/ports on your BMS.) Example: if I had a 20ah charger it will fill each 4p-cell pack at 5ah per cell? 20ah/4cells=5ah juice going into each cell in the 4pcell pack? Correct?

2) Also, I'm told the batts can be discharged down to 2.4 volts without problems. (This is the Racing RC version of the batt.) Again, will it be easy to mod your LVC to cut-off at this lower voltage instead? Just another 16 resistor change-out to go from 2.7 to 2.4 or ?

3) Will the corrected board be 'final tested' this week if all goes according to soldering plans? :wink: (Sorry Gary had that set-back... bummer.)

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Re: Even Newer 16-cell Battery Management System (BMS)

Post by GGoodrum » Jul 28 2008 7:56pm

a123 cells are good for 20A charge rates, and with 4 cells in parallel, each would only see 5A. In anycase, with a 20A charger, you can recharge a 4p/9.2Ah in about a half-hour.

You can discharge a123 cells to about 2V, and not damage them. However, once the capacity is used, the voltage drops very quickly. If you do't catch this, the voltage can go all the way to zero, permanently killing the cell. What the LVC portion of the BMS does is to monitor each cell's voltage, and if any one cell, or block of paralleled cells, has its voltage drop below 2.1V, under load, it will trip a signal that can be connected into a controller's brake input, which will cause it to cut the throttle, removing the load. The voltage will recover to something above 3V, which reenables the the throttle. If the throttle is still full-on, the voltage will drop again, cutting the throttle again. Usually, if you back off the throttle about halfway, you can go another mile, or two, before it cuts out for good.

Richard's found a few things, and has been tweaking some resistor values. He's also testing adding a small cap on the gate driver input, in order to make the regulation a bit more uniform. As soon as he's done, I'll see whether or not we can move forward with the existing boards, or if a new run is required.

-- Gary

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Re: Even Newer 16-cell Battery Management System (BMS)

Post by fechter » Jul 28 2008 9:47pm

I'm getting really close. I have a few more values to tweak.
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