# MiniBMS - open source project



## dimitri (May 16, 2008)

All,

as I have been toying with the idea of simple and cheap BMS I realize that it would be best to make it an open source project. I'm pretty good at reading schematics and making electronics, but certainly not as smart and/or experienced as some folks on this board. I'd like this to be super technical thread with input from anyone who can contribute specific details, we can keep general discussion at the other threads.

I have researched various BMS types and designs for many months, I have contributed a little to Brian's Volt Blochers project, I made my own version of VBs, which is currently installed in my EV and works great, I have a couple of satisfied customers using my modules as well. Since VBs aren't available anymore and there seems to be a market for cheap, simple and reliable BMS ( see poll results in the New BMS poll thread ), I figured why not take the best ideas and try to implement it all in one universal product.

I especially liked the idea of simple BMS proposed by Johnny on Australian forum, so I have taken his schematic and applied few changes based on input from other BMS discussions. I also done some research on key components and their prices at Digikey, to make sure we keep total parts cost around $5 per cell.

In past few days I prototyped this schematic on a bread board using basic Radio Shack parts and it appears to work great. I really like how comparators allow precise and fast switching when voltage gets to trigger levels. It switched from on to off with 0.01V precision and very little hysteresis.

I'd like some input from pros out there, my goal is to minimize number of parts, improve anything that may need improvement, pick best resistor values and minimize different values so there is less different resistors to buy. For example, I think we can collapse R6 and R7 if we find LED with similar voltage drop as in optorelay, so they can share same current.

I'd like to use Clare CPC1014 optorelay for NC signal loop, since its the only suitable low on-resistance relay I found which can be purchased for 80 cents in reasonable quantity.

http://www.clare.com/home/pdfs.nsf/www/CPC1014N_R01.pdf/$file/CPC1014N_R01.pdf

Using 4 comparators may seem complicated at first, but they are all integrated in one IC chip which only costs 22 cents in quantities 

I'd like to use these trimpots, which can be bought for 85 cents, yet very reliable for automotive environment.

Since there are so many needs for various HLVC levels, I think trimpots are pretty much a necessity, and they reduce number of resistors a little. 

http://www.bourns.com/data/global/PDFs/3361.pdf

Later in this thread I will post initial schemaitic for head end controller, where I will also need some input from the pros.

According to the poll, many people still want shunting function in their BMS, despite recent ideas against top balancing. I'd like to keep this as an option on the PCB and simply skip these components if one doesn't want them. I'd like to keep shunting current low, like 0.5A, to avoid heat sink on the transistor and use 5 Watt resistor, which is reasonably small to fit on PCB.

I will be designing a modular PCB for this, which will allow a number of modules on one PCB, yet be able to cut it in pieces if one wants per cell installation. This will reduce PCB cost and assembly labor. However, for this and other reasons I abandon an idea of PCB under terminal bolt, so I will just have holes for either wires or rigid bars as in my current BMS modules.

I am planning on SMD components to minimize PCB size and further reduce costs.

Once we have working design I can produce them for DIY community at best price possible. This will probably take some time, so if someone needs BMS today, you might want to explore other options.

So, please, look at the schematic and question every component, every connection, everything...


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## dimitri (May 16, 2008)

I think I found the answer for relay capabilities at low output voltage.

This is from Clare datasheet.

Seems that it can pass 200 mA at 0.12V , which would happen if 100 units in series are driving 12V head end controller.

Did I get it right?


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## Tesseract (Sep 27, 2008)

A few quick observations for now: 

* restrict the range over which the LVC and HVC can be adjustable with additional resistors. We know about where each should be so make the adjustment window maybe 0.4V or so.

* Bypass the pot wipers to both + and - so they are always at AC ground - important to prevent switching ripple from the controller tripping the circuit.

* Add hysteresis (small amount of positive feedback) to the comparators so they don't oscillate. Oscillating comparators are really annoying.

* it might be more costly in parts, but much cheaper in labor, to use multiple SMT transistors in parallel with thermal vias to a copper heatsink/ground plane. Try to avoid going 4-layer if at all possible.

I did not really look at the circuit, just giving a few quick suggestions before jetting off to the anodizing shop to find out if we will once again be able to offer colors.


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## Dave Koller (Nov 15, 2008)

Tesseract said:


> A few quick observations for now:
> 
> * restrict the range over which the LVC and HVC can be adjustable with additional resistors. We know about where each should be so make the adjustment window maybe 0.4V or so.
> 
> ...


All great comments - I will put in my schematic that has built in time delays for low and high and pulses the normal on led in the opto.. But Dimitri has a simple circuit... I just put in the delay and pulses so there was a delay under load times to prevent false open of the NC and which way things were going ..


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## Russco (Dec 23, 2008)

dimitri said:


> All,
> 
> So, please, look at the schematic and question every component, every connection, everything...
> 
> View attachment 4947


I have done considerable work on a lithium LV HV shunting BMS.

I feel using 1960 comparators with a series zener reference can be accomplished much more precisely with the common 431 precision IC. Two 431's would provide LV and HV monitoring. If the HV monitor is set higher than the shunting voltage, such at 4.2 volts and 3.70 volts, a third 431 would be required for the shunting monitor. The five ohm shunt resistor is a little high, only providing about 0.8 amps. Usually a 1-2 ohm shunt at 10 watts are used with the larger AH cells.

User adjustable pots are questionable. Can the user connect his pot across one or two cells for a reference voltage and make the pot adjustments? Many users can't. SMT eliminates easy bias resistor changes by the user or you to recalibrate users BMS units.

I have found in testing that each NPN opto output has a drop of around .15 volts. Fifty cells would work fine from the 12 volt accessory battery, but 100 cells won't.

Good work Dimitri, keep it up. You're a real go-getter. 

Russ from Russco Charger. Currently testing 600 amp IGBT modular controller priced well below $1K.


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## Dave Koller (Nov 15, 2008)

Russco said:


> I have done considerable work on a lithium LV HV shunting BMS.
> 
> I feel using 1960 comparators with a series zener reference can be accomplished much more precisely with the common 431 precision IC. Two 431's would provide LV and HV monitoring. If the HV monitor is set higher than the shunting voltage, such at 4.2 volts and 3.70 volts, a third 431 would be required for the shunting monitor. The five ohm shunt resistor is a little high, only providing about 0.8 amps. Usually a 1-2 ohm shunt at 10 watts are used with the larger AH cells.
> 
> ...


See my above schematic (uses 431's) - Dimitri plans on setting up the pots for all the various conditions - I think a person needs a reference supply to set them so that is something to think about on a DIY board. but a simple multi-meter may work.. He will be using FET optos - no drop to speak of.
BUT I will let him comment on that..


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## Tesseract (Sep 27, 2008)

Russco said:


> I feel using 1960 comparators with a series zener reference can be accomplished much more precisely with the common 431 precision IC.


Soooo.... you see some merit in using the 1970's era TL431 over the 1960's era '339, huh? 




Russco said:


> Two 431's would provide LV and HV monitoring. If the HV monitor is set higher than the shunting voltage, such at 4.2 volts and 3.70 volts, a third 431 would be required for the shunting monitor.


I really can't see how using 3 separate TL431's is any better than a single bandgap reference feeding voltage dividers/comparators. Especially since it's easy to give comparators hysteresis so the switching action can be snappy, rather than fuzzy (the TL431? not so much).



Russco said:


> The five ohm shunt resistor is a little high, only providing about 0.8 amps. Usually a 1-2 ohm shunt at 10 watts are used with the larger AH cells.


I definitely agree with this, though. If you are going to top balance 160Ah cells then you need to be able to shunt up to 2A. Whether you SHOULD top balance seems to be a matter of considerable debate, but that's for another thread...




Russco said:


> User adjustable pots are questionable.


Yep... I hate trim pots, but it still might be good/necessary to have a limited adjustment range... Dunno. I'm also concerned about the temperature coefficient of the cell voltage. 




Russco said:


> SMT eliminates easy bias resistor changes by the user or you to recalibrate users BMS units.


Maybe, but I can tell you for certain that unless these boards are totally SMT technology and machine-assembled it simply won't be worth anyone's while to sell them at the price DIY'ers, etc., are willing to pay. I mean, you can maybe charge $20 per cell of which you'll have a good $7-$9 in parts and pc board cost. If it takes more than 10 minutes to assemble, test and calibrate each one then it's simply not profitable. If your labor cost is $10 per hour or less, and still fast and accurate, then sticking with PTH technology might still be okay, but even then why bother?

Really - this product begs to be machine-assembled: it is simple, but must be totally reliable. All of the problems people had with the Volt Blochers appears to be from poor soldering or mechanical injury (ie - the heatsink getting bumped so it shorts out an adjacent resistor). SMT vastly reduces the chances of such happening and with clever design you can make the pc board the heatsink (at least for a couple of watts). 



Russco said:


> Russ from Russco Charger. Currently testing 600 amp IGBT modular controller priced well below $1K.


Heh. You know how to make a small fortune in the controller business? Start with a large fortune and spend it developing and making something that undersells Kelly, who will then come back and undersell you because their parts costs, labor costs and even the Yuan/Dollar exchange rate are all in their overwhelming favor. But hey, good luck anyway!


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## tomofreno (Mar 3, 2009)

> Dimitri plans on setting up the pots for all the various conditions - I think a person needs a reference supply to set them...


 The pot for adjustment of HVC on VBs is set using a simple resistive voltage divider, battery, and dvm. Same should work here. 

Dimitri, I believe you said you want to preset everything to eliminate user adjustments/errors. If so, is it more difficult to just give several fixed resistive divider options in place of the adjusting the pots? 

Please mount the quad comparator chip in a dip socket rather than soldering the legs directly on the board as the LTV826 chip on VBs.

Regarding mounting on the cell, the VB approach of one rigid contact bolted to the board and one wire seems to work well. The fixed contact supports/holds the board in place, and the wire gives flexibility in routing around any rod for cell hold-downs. A fully rigid mount between terminals has to clear the vent in between them.

I like it! Simple, low current draw, resistor limiting of current in event of a component failure. I agree that hysteresis is desirable. I think it should be smt, ready-to-install, nothing for a user to screw up. The more user intervention, the more headaches for you.


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## dimitri (May 16, 2008)

Everyone, thanks for great comments! 
Obviously there are many ways to skin a cat and I tested variety of designs. Russ, I tried your design and it works the same way, but has more components. Main reason for this design is minimum number of discrete components on PCB, which is my main goal, I am minimalist 

I don't see a need for more precision, I have 0.01V precision with this circuit, does anyone need more? I observe very little hysteresis, I tried adding feedback and IMHO improvement wasn't worth adding more resistors ( did I mention that I am minimalist ? ). 

Dave, your circuit is cool, but I feel that any time / pulse manipulations belong on the head end, cells should report every pulse and be simple. You have way too many components to be on each board, its not practical for mass production. Did I mention that I am minimalist? 

I tried to stay away from trimpots, but there are just too many variations of HLVC levels that different people might need, after much consideration I reluctantly came to conclusion to use trimpots to make a product that fits everyone. Calibration can be done by the vendor when customer picks specific values, or by customer, using a simple calibration board which can be sold along with BMS and cost perhaps $10-$15.

As for trimpot adjustment range, LVC trimpot has a good range since reference voltage is right in the middle of typical 2.5V LVC, and HVC and shunt trimpots have their range improved by R3 shifting voltage divison down, I tested it this way and its quite manageable with single turn trimpot, so I don't want to add anymore resistors. Values of R3 vs. trimpots can be selected carefully to further improve the adjustment range, but I feel that 50/50 split should be good enough.

More details in next post, need to step away.....


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## Dave Koller (Nov 15, 2008)

dimitri said:


> Dave, your circuit is cool, but I feel that any time / pulse manipulations belong on the head end, cells should report every pulse and be simple. You have way too many components to be on each board, its not practical for mass production. Did I mention that I am minimalist?
> 
> .


KISS principal  you are right.. Keep going!


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## Dave Koller (Nov 15, 2008)

One thought: did you find a need for_Decoupling capacitors, Bypass ?
I know it is a few more parts - but maybe a noise suppression help.. 


_


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## dimitri (May 16, 2008)

I've assembled over a hundred modules with 2 amp shunting, which requires 10W resistor and a heat sink on transistor. From my observations, if we shut off charger at HVC, we don't need to shunt so much current, especially since top balancing is becoming so controversial lately. I want to avoid heat sink and use 5 Watt ceramic resistor to make it compact and low profile, which means less than 1 Amp shunting. I tested with 4.7 Ohm and I had 0.75 Amp going thru and transistor was barely warm, so I think this is optimal based on my requirements. BMS should not be used alone for initial balancing, but for ongoing daily balancing less than 1 Amp is quite sufficient even for 200Ah cells.

Heatsink on BMS modules is one of my biggest headaches, so I will not make same mistake again 

What does the 1960 era have to do with the choice of comparators? It costs 22 cents and Digikey has gazillion in stock, is there anything wrong with it? Do you have specific alternatives which would be better?

Tom, why would you want IC in the socket??? I don't get it...


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## dimitri (May 16, 2008)

> * restrict the range over which the LVC and HVC can be adjustable with additional resistors. We know about where each should be so make the adjustment window maybe 0.4V or so.


I thought about it, but I cringe at adding more parts, while I was able to dial voltages with single turn trimpot just fine, so even though this would make it easier to calibrate, I just don't find it critical. I used R3 to make HVC range more useful, I think this should be sufficient.




> * Bypass the pot wipers to both + and - so they are always at AC ground - important to prevent switching ripple from the controller tripping the circuit.


Sorry, I don't get it. You mean bypass with capacitors on both sides? That would be 6 more parts.... . Maybe I just miss your point? I don't always get your pro slang, sorry about that 

My current modules don't have any caps and I don't see any false tripping, so perhaps this falls into "nice to have" category? Once I drive around with prototype modules in my car, I will pay attention to this.



> * Add hysteresis (small amount of positive feedback) to the comparators so they don't oscillate. Oscillating comparators are really annoying.


I thought about this a lot and even tried on the test board, don't see a need for it in real life because HVC will just trip the charger and latch on, but LVC will oscillate anyway since it will cut controller current and driver will let go of the pedal, so there is no point reducing these oscillations. Again, I tested this with my current modules, didn't see any need to reduce hysterisis.



> * it might be more costly in parts, but much cheaper in labor, to use multiple SMT transistors in parallel with thermal vias to a copper heatsink/ground plane. Try to avoid going 4-layer if at all possible.


I will definitely stay with 2 layer PCB, but I again missed your other point. You mean transistors INSTEAD of comparators? How is that cheaper in labor than one 14 pin SOP?


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## dimitri (May 16, 2008)

Here is the parts breakdown, comes to $4.69 in parts per cell. My guesstimate for PCB cost is $1.50 per cell, so $6.19 in hardware per cell.
Anyone has any ideas to reduce cost? Maybe there are cheaper alternatives on Digikey?

Looks like $10 per cell assembled is not going to happen, perhaps $15 per cell? Any ideas?









Can't paste from Excel and keep formatting....


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## Tesseract (Sep 27, 2008)

dimitri said:


> I thought about it, but I cringe at adding more parts, while I was able to dial voltages with single turn trimpot just fine, so even though this would make it easier to calibrate, I just don't find it critical. I used R3 to make HVC range more useful, I think this should be sufficient.


Okay. After messing around the TS160 cells in the New Beetle Rebirth is converting it seems that you could simply set LVC to 2.65V and HVC to 3.85V and start shunting at around 3.65V. Why make them adjustable at all? You may cringed at adding a few more resistors that cost less than $0.02 each but I cringe at putting a trimpot on a board that has to survive moderate to high vibration without failure.



dimitri said:


> Sorry, I don't get it. You mean bypass with capacitors on both sides? That would be 6 more parts.
> ...
> My current modules don't have any caps and I don't see any false tripping, so perhaps this falls into "nice to have" category?


I bet Ken Hall said the same thing when he designed the PakTrakR... 

Bypassing is just good engineering practice; ignore at your risk 



dimitri said:


> I thought about this a lot and even tried on the test board, don't see a need for it in real life because HVC will just trip the charger and latch on, but LVC will oscillate anyway since it will cut controller current and driver will let go of the pedal, so there is no point reducing these oscillations.


Yes there is - an oscillating comparator will not necessarily trip at the correct voltage anymore. Once again, it only costs 1 resistor to add hysteresis to a comparator circuit while the end user may or may not notice a functional difference, it makes for a more reliable circuit. Anyway, go for the minimalist approach and see what happens (easy to suggest because that's what you're probably going to do anyway  )



dimitri said:


> I will definitely stay with 2 layer PCB, but I again missed your other point. You mean transistors INSTEAD of comparators? How is that cheaper in labor than one 14 pin SOP?


Nope. I mean using several SMT power transistors (DPAK or SOT-223 packages) in parallel along with individual shunt resistors in, perhaps, the 2512 package instead of a single power transistor and single resistor, both PTH (that's Plated Through Hole, aka, parts with leads on them). All with extra vias to a ground plane on the underside of the board to act as a noise shield and heatsink. Usually good for 1W per sq. in. of board area.


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## dimitri (May 16, 2008)

> Okay. After messing around the TS160 cells in the New Beetle Rebirth is converting it seems that you could simply set LVC to 2.65V and HVC to 3.85V and start shunting at around 3.65V. Why make them adjustable at all? You may cringed at adding a few more resistors that cost less than $0.02 each but I cringe at putting a trimpot on a board that has to survive moderate to high vibration without failure.


Sure, this would work for people with TS160 cells, in fact I have those same voltage levels on my car and I am quite happy, however, think about people with SE cells and people up north where LVC can be significantly off and people who climb hills at 4C, etc etc, there isn't even agreement on LVC between 2 people using same exact cells. Same goes for HVC, people may need to dial it up or down depending on their specific needs and/or charger specs, etc etc.

Trust me, I hate adding trimpots, but more I think about it more I get convinced that we can't get away without them if we were to satisfy many demands.

Also, have you looked at the datasheet for these trimpots? They appear to be made for volatile environments.


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## dimitri (May 16, 2008)

> Nope. I mean using several SMT power transistors (DPAK or SOT-223 packages) in parallel along with individual shunt resistors in, perhaps, the 2512 package instead of a single power transistor and single resistor, both PTH (that's Plated Through Hole, aka, parts with leads on them). All with extra vias to a ground plane on the underside of the board to act as a noise shield and heatsink. Usually good for 1W per sq. in. of board area.


Funny, I realized what you meant few moments after I posted my reply 
There is no room for multiple parallel components. I plan to use DPAK package KSH127, so only resistor will be PTH (5W SMT resistors are too damn expensive), not too bad, just 2 leads. I also planned to use extra vias as a heatsink for DPAK module.

I really appreciate your feedback even if it appears that I am ignoring it  , every piece of advise is registered and will be tested, but as you can see I am really trying to minimize cost and components.

Actually, let me ask this question, since dealing with noise is my biggest weakness . If you were to add 1 or 2 capacitors to this circuit and get biggest bang for the buck, where would you place them and what values?

Please note that during charging noise is minimal, so shielding HVC is not as important as shielding LVC.

Thanks


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## moreati (Sep 19, 2009)

dimitri said:


> Trust me, I hate adding trimpots, but more I think about it more I get convinced that we can't get away without them if we were to satisfy many demands.


Just a thought from a naive interloper. Could you place pads on the pcb to give the option of either a trim pot or fixed resistors. Same board different configurations...


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## Russco (Dec 23, 2008)

Tesseract said:


> Soooo.... you see some merit in using the 1970's era TL431 over the 1960's era '339, huh?


I guess you're right. The quad 14 pin plastic case 339 is very futuristic next to the single 311 comparator in a metal TO5 case I used in 1972. 



Tesseract said:


> I really can't see how using 3 separate TL431's is any better than a single bandgap reference feeding voltage dividers/comparators. Especially since it's easy to give comparators hysteresis so the switching action can be snappy, rather than fuzzy (the TL431? not so much).


To each his own. 



Tesseract said:


> I definitely agree with this, though. If you are going to top balance 160Ah cells then you need to be able to shunt up to 2A. Whether you SHOULD top balance seems to be a matter of considerable debate, but that's for another thread...
> 
> Yep... I hate trim pots, but it still might be good/necessary to have a limited adjustment range... Dunno. I'm also concerned about the temperature coefficient of the cell voltage.


Six of one, half a .... 



Tesseract said:


> Maybe, but I can tell you for certain that unless these boards are totally SMT technology and machine-assembled it simply won't be worth anyone's while to sell them at the price DIY'ers, etc., are willing to pay. I mean, you can maybe charge $20 per cell of which you'll have a good $7-$9 in parts and pc board cost. If it takes more than 10 minutes to assemble, test and calibrate each one then it's simply not profitable. If your labor cost is $10 per hour or less, and still fast and accurate, then sticking with PTH technology might still be okay, but even then why bother?


You don't see me manufacturing BMS boards now, do you? Mine interfaced with the Russco Charger, providing a cell by cell voltage regulation loop, which PWM'd the charger to reduce the amps out.



Tesseract said:


> Heh. You know how to make a small fortune in the controller business? Start with a large fortune and spend it developing and making something that undersells Kelly, who will then come back and undersell you because their parts costs, labor costs and even the Yuan/Dollar exchange rate are all in their overwhelming favor. But hey, good luck anyway!


That's OK. You need not worry, Tesseract. You make Cadillac controllers. I'll deal with the Pinto controllers. The Pinto controllers on the market today don't even have active precharge. Duh! 

Russco went into the EV market 25 years ago manufacturing controllers and I'll probably go out manufacturing controllers. That's what I do!


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## dimitri (May 16, 2008)

Guys, I really appreciate your feedback, but please, let's not turn this into "who's got bigger d...." discussion 

I've analyzed and tested both "single shunt" and "multiple shunts" designs, they both work equally well, but I think single shunt can be done with fewer components and I personally like how comparators make it a clean, almost digital setup.

If you can please help me with minimum capacitors placement for noise reduction, I'd really appreciate it.


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## dimitri (May 16, 2008)

moreati said:


> Just a thought from a naive interloper. Could you place pads on the pcb to give the option of either a trim pot or fixed resistors. Same board different configurations...


Yes, I thought about it, each trimpot will have to be replaced by 2 resistors, but I will try to fit it on PCB somehow if possible. Thanks for your feedback.


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## Russco (Dec 23, 2008)

dimitri said:


> Funny, I realized what you meant few moments after I posted my reply
> There is no room for multiple parallel components. I plan to use DPAK package KSH127, so only resistor will be PTH (5W SMT resistors are too damn expensive), not too bad, just 2 leads. I also planned to use extra vias as a heatsink for DPAK module.
> 
> I really appreciate your feedback even if it appears that I am ignoring it  , every piece of advise is registered and will be tested, but as you can see I am really trying to minimize cost and components.
> ...


It's common to place a 0.1 mfd. capacitor from Vcc to common at each IC. You would require one capacitor per board. 

Where's the @**%# fuse? And crowbar the input with a 1N5402 diode to blow the fuse if some idiot connects the power backwards. 

Have you considered mounting the shunt resistor on a copper baseplate which connects to the battery post? This would resolve the heat problem. Of course, one board required per cell. 

Russco


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## dimitri (May 16, 2008)

Russco said:


> It's common to place a 0.1 mfd. capacitor from Vcc to common at each IC. You would require one capacitor per board.
> 
> Where's the @**%# fuse? And crowbar the input with a 1N5402 diode to blow the fuse if some idiot connects the power backwards.
> 
> ...


Yes, I am planning the fuse, just didn't put it in the schematic yet, sorry. I didn't think reverse polarity at 3.2V would hurt anything here, would it?
I can add the diode as you suggested.

I abandoned the idea of PCB over the terminal, it conflicts with many other ideas. 5W ceramic wirewound resistor will be fine with less than 1Amp shunting current.


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## tomofreno (Mar 3, 2009)

> Tom, why would you want IC in the socket???


 So it is easily replaced. But if you go with smt that's not an option, and I think you should go smt.


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## JRP3 (Mar 7, 2008)

dimitri said:


> Sure, this would work for people with TS160 cells, in fact I have those same voltage levels on my car and I am quite happy, however, think about people with SE cells


Just thought I'd point out that Jack has used both the TS and SE cells and feels the low end is the same on both cells, even though SE claims to go lower.


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## Tesseract (Sep 27, 2008)

JRP3 said:


> Just thought I'd point out that Jack has used both the TS and SE cells and feels the low end is the same on both cells, even though SE claims to go lower.


I suspect the only differences between TS and SE cells are whatever the idiots in their marketing departments have concocted. TS says they can do 3C so SE says they can do 4C... whutevuh.


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## Tesseract (Sep 27, 2008)

dimitri said:


> ...Actually, let me ask this question, since dealing with noise is my biggest weakness . If you were to add 1 or 2 capacitors to this circuit and get biggest bang for the buck, where would you place them and what values?...


Well, one possible idea that is really simple and elegant is to insert the RC filter before EVERYTHING else (except the shunt transistor). For example, instead of connecting directly to the + and - terminals of the cell, insert a 100 ohm resistor in series with the + terminal then bypass with a 10uF 0805 or 1206 SMT ceramic capacitor to the negative terminal. Everything besides the (optional) shunt PNP's emitter connects to the junction of this RC filter. Don't forget to factor in the effect of the additional series resistance on your voltage dividers, but as long as you do that this is a perfectly valid way to clean up an entire circuit with just one capacitor. You still need to use a ground plane on the underside of the board, though.

As for your existing circuit working properly, I ask - in all seriousness - how do you know for sure? Any decent comparator can flip states within a few dozen nanoseconds of the inputs passing the comparison threshold, which means noise on the inputs can cause all sorts of problems that you might never see unless you actually look for them with a fast and properly triggered scope. For example, LVC could be tripping for a few microseconds at every trough in the ripple waveform. If we were to add a function to the Soliton1 to reduce allowed motor power upon receiving a signal that one (or more) cells has reached LVC it would be helpful to not receive that signal 8,000 (or 14,000 in quiet mode) times per second... 

Hysteresis is necessary whenever you use a comparator to monitor a slowly changing signal (and by "slow" I mean any analog signal, even up into the MHz range) because otherwise the slight negative feedback effect from the change in input offset voltage when the comparator flips will cause the output to oscillate, and that oscillation can sometimes be up in the MHz range. That said, it is difficult to add hysteresis to the traditional window comparator circuit, as you have employed here, because the positive feedback resistor affects both thresholds dynamically, so you never really know what the threshold is. There are window comparator circuits that can accommodate hysteresis but if you are balking at adding one resistor to your circuit then you certainly aren't going to like these other designs... e.g.: http://electronicdesign.com/Articles/ArticleID/6327/6327.html

At any rate, I'm not trying to make this overly complicated for you, just throwing some suggestions out there that I have mostly learned the hard way from designing switchmode power supplies and high power RF stuff over the years. One design method is to make the circuit as simple as possible and then add parts to it to make it function as expected. This usually works best when you have a good understanding of what problems your omissions/simplifications are likely to cause in the first place. Another method, and one that is often more amenable to rapid prototyping, is to add pads for bypass capacitors all over the place - literally at every junction, both to "ground" and "V+" - and see which ones help the most and which ones don't seem to do anything but add to the cost of the board


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## dimitri (May 16, 2008)

JRP3 said:


> Just thought I'd point out that Jack has used both the TS and SE cells and feels the low end is the same on both cells, even though SE claims to go lower.


And yet when I asked him point blank what LVC level he would choose, he couldn't answer it  and said he would prefer adjustable option.

Perhaps there is some common LVC between TS and SE, but no one knows what it is, and it certainly depends on how conservative one is with the pack. I would take 2.6V , but someone else would want 2.5V or 2.7V.

On the HVC end, same thing, I want to charge TS to 3.8V , but SE claims 3.6V and some people with regen who live on top of the hill would want 3.55V or 3.5V.

Too many options and variables, although I am not giving up on the PCB option with resistors instead of trimpots, so maybe we can hit both goals.


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## tomofreno (Mar 3, 2009)

> Just thought I'd point out that Jack has used both the TS and SE cells and feels the low end is the same on both cells, even though SE claims to go lower.


 I think all Jack has done is record voltage versus Ah discharged/charged showing this curve is similar for the TS and SE cells on the low voltage end, with fast fall off in voltage with Ah discharged below around 3V for both. He has not shown that both TS and SE cells can be discharged to the same lower limit resting voltage and recover the same with same remaining cycle life. My impression is that the spec indicates the lowest rest voltage to which you can discharge without severely impacting remaining cycle life.


> I suspect the only differences between TS and SE cells are whatever the idiots in their marketing departments have concocted.


 I suspected "specmanship" also, but some time back evcomponents posted here (or maybe yahoo thundersky site) that SE had sent them information showing the cells do have real differences but they couldn't divulge in what way. Don't think evcomp would have any vested interest in promoting one over the other. I expect we won't know the definitive answer to this for years. Not until we have large enough sample sizes of both cell types, run under similar enough conditions until they start seriously degrading in performance to see if the mean difference between samples is larger than the standard error of the samples.


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## JRP3 (Mar 7, 2008)

tomofreno said:


> I think all Jack has done is record voltage versus Ah discharged/charged showing this curve is similar for the TS and SE cells on the low voltage end, with fast fall off in voltage with Ah discharged below around 3V for both. He has not shown that both TS and SE cells can be discharged to the same lower limit resting voltage and recover the same with same remaining cycle life.


True, but in both cases nothing good happens below 3 volts and there is very little capacity, so I see no benefit in setting the LVC lower for one but not the other. 2.8 ish seems safe enough for both.


> I suspected "specmanship" also, but some time back evcomponents posted here (or maybe yahoo thundersky site) that SE had sent them information showing the cells do have real differences but they couldn't divulge in what way.


Supposedly SE uses the Aleees powder where TS has added yittrium. The TS cells do seem to have a much higher HVC than the SE cells, and I think the SE cells have a flatter discharge curve, so there must be something other than just "specmanship" going on, though I'm sure that's part of it.


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## Travdude (May 11, 2009)

EVComponents said:


> And ThunderSky is also using aleees now.


Sounds like the newer cells will be very close.


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## dimitri (May 16, 2008)

So, what's the authorative answer on reversed polarity? Do I need to worry about it? I don't want to add more parts if I don't have to.

Can this circuit be damaged by 3.2V in reversed polarity?

Thanks.

I am changing schematic based on feedback, will post updated version soon.


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## dimitri (May 16, 2008)

Here is updated version.

I need help determining best value of R13 to minimize impact on input voltage , yet provide meaningful hysteresis. I think it should be somewhere between 10k and 100k , but I'd love someone to confirm.

Also, please see if any resistor values don't make sense or if any resistors can be collapsed. I was hoping to collapse R6 and R7 , but Optorelay has 1.2V forward voltage and Green LED has 1.8V , so I think they need each own resistor, right?

Thanks


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## Tesseract (Sep 27, 2008)

dimitri said:


> Can this circuit be damaged by 3.2V in reversed polarity?


Not with the 100 ohm + 10uF RC filter I suggested... that will limit the maximum current that can flow through the normally reverse-biased substrate diodes to ~35mA.

Also, consider using a PTC resettable fuse.

As I mentioned previously, it's tricky to add hysteresis to a window comparator circuit. The actual amount added will depend on the setting of the trip points for both the upper and lower comparators. Just to be safe I'd change that 10k to 100k.

Finally, doesn't the cell voltage drop quite a bit with temperature? Might be worth putting in some rough compensation for that with a thermistor or diode?

EDIT: The datasheet for TS cells says that at -35C the minimum discharge voltage is 1.5V (compared to 2.5V at 30C). No graph is given and while it seems reasonable to assume the decrease in voltage is caused solely by increased internal resistance, and is therefore self-correcting, I would be wary of relying on that. Still, even if Dimitri and me live in a semi-tropical climate, we have to consider our Canadian (and Swedish!) friends.

Might be worth puting a single cell in a freezer then see how the open circuit and under load voltages change.


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## tomofreno (Mar 3, 2009)

> Might be worth puting a single cell in a freezer then see how the open circuit and under load voltages change.


 The open circuit voltages of my cells have remained the same as temperature has varied in my metal garage from 108F to 24F. No data on under load, but others seem to be seeing a decrease under load at lower temperatures.


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## dimitri (May 16, 2008)

I already thought about temp compensation for LVC, I just need to find a cheap and effective way to do it. I will search Digikey for appropriate thermistor.

From my research I think its reasonable to assume that battery will not be operated below freezing, since that just kills discharge rates. Anyone living in below freezing zones should insulate the pack to keep it above freezing. Having said that, I need to compensate LVC by reducing LVC point about 0.3V-0.5V at freezing point, linearly from 0V compensation at approx 25C. I'll try to figure out how to do that, but if anyone has ideas, please chime in. I don't think HVC needs temp compensation since charging will warm the pack by the time HVC hits.

As for resettable fuse, I suspect it will cost more than regular fuse I found for 24 cents. Blowing the fuse in this version is virtually impossible, only if pack voltage is applied to one module or 5W resistor is shortened while shunting, so I think regular fuse is still appropriate.


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## dimitri (May 16, 2008)

Turns out that PTC fuse costs the same as regular fuse, so I will use this one MF-NSMF075-2CT-ND ( Digikey part number ).

It has hold current of 0.75A and trip current of 1.5A , but what happens in between? What if shunting current creeps to say 0.85A, what happens with the fuse? Is it just a matter of increasing resistance, which would counteract shunting current and stabilize it a little? Would it help to place fuse close to shunt resistor which would provide additional thermal protection if resistor gets too hot and causes fuse to trip sooner? Am I on the right track here? Maybe I need to get next fuse, with 1A hold current at 25C, I need to look at datasheet some more....


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## dimitri (May 16, 2008)

Found even better PTC fuse, 507-1481-1-ND ( Digikey part ) , only 20 cents 

0.75A hold and 1.5A trip at 25C, but at 80C this cuts in half. So, if I place the fuse next to the 5W resistor we will kill 2 birds with one stone. Provide protection from shorting the pack and thermal protection during shunting. If fuse gets to 80C it will trip on shunting current and stop the charger 

Any objections, issues?

Thanks


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## dimitri (May 16, 2008)

Looks like I can use 14 cents thermistor in parallel with lower arm of LVC voltage divider to shift LVC in a given temp range. With that in mind I am starting to lean back to non-trimpot version of BMS again 

What would be a good temp range? Is 0C - 50C wide enough for calculations? For example, given LVC=2.5V at 25C , would LVC=2.0V at 0C and LVC=2.7V at 50C be reasonable?

I need to do some basic calculations to determine best value of thermistor/resistor pair in parallel, so then I can figure out a common set of resistor values for the other side of voltage divider, and try to minimize number of different values I need to order to satisfy all needs.

Any feedback from people up north?


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## Dave Koller (Nov 15, 2008)

dimitri said:


> Looks like I can use 14 cents thermistor in parallel with lower arm of LVC voltage divider to shift LVC in a given temp range. With that in mind I am starting to lean back to non-trimpot version of BMS again
> 
> What would be a good temp range? Is 0C - 50C wide enough for calculations? For example, given LVC=2.5V at 25C , would LVC=2.0V at 0C and LVC=2.7V at 50C be reasonable?
> 
> ...


I believe most up here go to extremes to keep the batteries from cold (or freeze) with insulation, battery warmers, inside garages... So I wonder if the batteries get way down that cold. -30 degree days would be a day to keep the electric at home especially if it had to sit outside! I know I can't start my snowplow (ICE truck) easy without keeping a trickle charge on the starter battery.. common sense says (at this point in time) keeping batteries warm or sitting the coldest days out are the order in the far north..

As a quick side note what you have looks great.. and covering every situation might become more trouble... ( as you said KEEP IT SIMPLE!) I WOULD like to know what you used to draw your schematics.. if you please!


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## Dave Koller (Nov 15, 2008)

Tesseract said:


> As I mentioned previously, it's tricky to add hysteresis to a window comparator circuit. The actual amount added will depend on the setting of the trip points for both the upper and lower comparators. Just to be safe I'd change that 10k to 100k.
> 
> Might be worth puting a single cell in a freezer then see how the open circuit and under load voltages change.


Agree -100k makes more sense.

And putting the cell in a freezer and tracking the curve sounds like it would work - 
Then with the thermistor - fully charged - nearly discharged.. read the voltages and temps if you can (thru the curve)...


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## dimitri (May 16, 2008)

Dave Koller said:


> I believe most up here go to extremes to keep the batteries from cold (or freeze) with insulation, battery warmers, inside garages...
> 
> As a quick side note what you have looks great.. and covering every situation might become more trouble... ( as you said KEEP IT SIMPLE!) I WOULD like to know what you used to draw your schematics.. if you please!


I use free program from ExpressPCB , it has 2 parts ( both are part of single install ) , one does PCB layout and the other does schematics. I find this suitable for relatively simple stuff I am working with. I'm sure pros will laugh at it, but it works for me so far 

As for temp extremes, I hear ya, that is why I only want to cover 0C-50C, assuming temp inside the insulated battery box doesn't go below 0C and battery without the box doesn't get over 50C ( I think mine gets pretty close under the hood in July in Tampa  ). These numbers are just base points for calculations, it will still work outside of these ranges. I just need to find the best match for LVC to follow LFP temp curve.


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## dimitri (May 16, 2008)

Dave Koller said:


> Agree -100k makes more sense.
> 
> And putting the cell in a freezer and tracking the curve sounds like it would work -
> Then with the thermistor - fully charged - nearly discharged.. read the voltages and temps if you can (thru the curve)...


LVC has to be determined at 3C discharge, resting voltage is useless. I don't have tools and extra cells to measure voltage drop at 3C at extreme temps, I really hope someone can help with this.


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## Dave Koller (Nov 15, 2008)

dimitri said:


> I use free program from ExpressPCB , it has 2 parts ( both are part of single install ) , one does PCB layout and the other does schematics. I find this suitable for relatively simple stuff I am working with. I'm sure pros will laugh at it, but it works for me so far
> 
> A


LOL I use that program for small prototypes BUT never use the schematic part ! I scribble circuits on a legal pad then throw down parts and connect them in ExpressPCB it is a great little program for quick turn-around proto's...
No laughs here!


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## tomofreno (Mar 3, 2009)

The thermistor can provide only some rough indication of cell temperature at best since: 
1) Most vehicles do not have all cells in one box. Some are in the heated passenger area, others out in the engine compartment with air flow around the box when the vehicle is moving.
2) The combination of low thermal conductivity of the cell case, and significant heat capacity of a cell will result in a large lag in internal cell temperature relative to external temperature in a heated box. Especially if the heat source is just warm air rather than a heat pad in contact with each of the cells. In this case sensor temperature will rise much more rapidly than cell internal temperature.
3) Variation of cell temperature inside the same box as has been mentioned.

For example, I have heater pads under all cells, approximately 35W per pad, one pad contacting about 4 cells, and 1/2" insulation on the inside of all box walls and bottom. My temperature sensor for the heater controller is bolted to a clamp on one set of 4 cells. After two hours of heating at 34F ambient, the sensor read 38F, but the lower side of the cells by the pads felt warm.

So I am not sure what the thermistor really tells you, but it will prevent the LVC from coming on at higher soc at lower temperatures.


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## dimitri (May 16, 2008)

tomofreno said:


> So I am not sure what the thermistor really tells you, but it will prevent the LVC from coming on at higher soc at lower temperatures.


I'm not sure cell casings are low thermal conductivity, I think its the opposite, they are designed to remove the heat from the cell. When my cells get warm due to discharge current, I can feel the casing being just as warm as terminals.

Since thermistor will be on each module, it will be located near terminal posts, so I believe it will reflect cell temp somewhat accurate. If some cells are in different location and have different temp, then modules on those cells will report LVC accordingly, so there is no issue here.

I will figure out conservative compensation levels, but I believe having this feature is quite important. I drove yesterday at 55F and I could definitely feel higher sag than driving at 85F, so I think people will appreciate some level of LVC compensation, we just need to determine how much.


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## tomofreno (Mar 3, 2009)

> Since thermistor will be on each module, it will be located near terminal posts, so I believe it will reflect cell temp somewhat accurate.


 Agreed. I didn't realize there would be one on each module near the terminal. So then each LVC voltage is adjusted by the thermistor changing the resistive voltage division. I see, very nice! It seems you may be able to just offer a few options for resistive divider then and eliminate the pot as you said. I would vote for HVC being 3 to 5% below the highest permissible cell voltage, like 3.45V for SE cells, since there isn't that much energy above that level and I expect it avoids stressing cells.


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## dimitri (May 16, 2008)

Here is updated version, reindexed all resistors, added thermistor, swapped 2 comparators to ease PCB design ( adjacent pins connected to each other ), removed trimpots, removed R values to be determined.

Any suggestions? I hope not to add any more parts, its getting crowded, maybe something can be reduced?

I'm getting ready to order parts for prototyping and PCB design. Just need to figure out some base resistor values.


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## tomofreno (Mar 3, 2009)

> Any suggestions?


 Is there a reason the 100 Ohm R is in series with the other resistors, rather than in the shunt path with C1?

Tom


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## Tesseract (Sep 27, 2008)

tomofreno said:


> Is there a reason the 100 Ohm R is in series with the other resistors, rather than in the shunt path with C1?


I suggested it as one way to filter out switching ripple that might otherwise cause a lot of false LVC tripping. It's not necessarily the way I would do it - too many other interdependencies - but dimitri wanted effective filtering with the fewest parts possible and, well, it's hard to argue with a total of two (especially since it automatically provides reverse polarity protection... well, for the comparator, anyway).


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## dimitri (May 16, 2008)

tomofreno said:


> Is there a reason the 100 Ohm R is in series with the other resistors, rather than in the shunt path with C1?
> 
> Tom


Yes, it creates RC filter to reduce noise and also limits total current across comparators, but shunt has to bypass the filter since it can't carry so much current.


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## Bentzon (Sep 5, 2009)

Would it be too much trouble to have the option of two relays. One for lvc and one for hvc.


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## dimitri (May 16, 2008)

Bentzon said:


> Would it be too much trouble to have the option of two relays. One for lvc and one for hvc.


There will be two relays on the head end unit, one for throttle control ( LVC ) and one for charger control ( HVC ), but the main idea here is to control both events with a single wire NC loop from the cells. HVC control on the head end must have a latching relay, so charger can stay off once HVC is triggered, and a reset button ( or ignition key ) to reset the relay so you can charge next time. I am currently prototyping few ideas for the head end unit, I will post schematics once done.


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## Bentzon (Sep 5, 2009)

Ah okay must have missed that part.


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## Bentzon (Sep 5, 2009)

A micro plc or smart relay would be very easy to use for this and could be used for alot of other things in the car. Program it for whatever you like.

They cost 100$ around here for a 12 I/O module probably even cheaper in the states


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## dimitri (May 16, 2008)

As I am prototyping some ideas for head end controller, I have a question for the Pros 

Since the main idea of NC loop is to improve reliability of an alert, we have to also decide how to handle it on the head end. 

Option 1: NC loop will hold open a transistor gate, which will hold a signal relay energized ( very low power relays, Axicom telecom signal relay with 12mA current and DPDT contacts controlling throttle reduction and charger shutoff ). In this option entire system is energized at all times, even at night when charging, using B+ from 12V aux battery. When NC loop opens, relay drops and stops the charger or reduces the throttle.
Pros of option 1: even if 12V battery fails or head end wiring or fuse fails, battery is protected.
Cons of option 1: constant, albeit very low power drain from 12V system. Potential issues with lifetime of components which are energized 24/7.

Option 2: opposite of option 1. Relay and the gate are closed when NC loop is closed. Open NC loop will close the relay and signal charger and/or controller.
Cons of option 2: Failure of some head end components may fail to act on the HVC/LVC signal and ruin the pack.

Any feedback? Ideas? I want to make head end as simple and reliable as each module, no complex processing or mechanisms. I will use Ignition signal to distinguish between LVC and HVC actions ( i.e. when Ignition is on, process LVC, when Ignition is off, process HVC )

Thanks


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## Bentzon (Sep 5, 2009)

Why not add a NO AC mains relay to power the head board when the charger is plugged in? Add two in parallel to avoid failure if one fails. Key switch power the board other wise. 

Not that I think it matter much but I prefer to have the car "off" when you leave it parked and not plugged in.


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## dimitri (May 16, 2008)

Bentzon said:


> Why not add a NO AC mains relay to power the head board when the charger is plugged in? Add two in parallel to avoid failure if one fails. Key switch power the board other wise.
> 
> Not that I think it matter much but I prefer to have the car "off" when you leave it parked and not plugged in.


Of course there will be a NO AC relay to control the power, but BMS head end will have to control that relay. If I use NC pair to power the AC relay, then failure of a BMS head end may cause an overcharge and cell damage. If I use NO pair, its more robust, but a flipside is that control relay must be always energized when there is no BMS alert, which is 99.999% of the time.

You can't use keyswitch power to control the charger since AC relay and BMS head end must be powered while the car is charging.


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## Bentzon (Sep 5, 2009)

What I meant was to use a AC coil relay with the DC + through the contacts to power the board while charging.


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## dimitri (May 16, 2008)

Bentzon said:


> What I meant was to use a AC coil relay with the DC + through the contacts to power the board while charging.


Ahh, now I get it  , sorry. This could work, I have to think about it some more. B+ power to a small BMS board is not an issue though, its no different than clock power on the radio, that is the least of my concern.


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## Bentzon (Sep 5, 2009)

Yeah probably nothing to worry when you think about how much stuff you got going 24/7 in your house.

Cell boards looks good to me btw. Would take 50 pcs. right now


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## dimitri (May 16, 2008)

Bentzon said:


> Cell boards looks good to me btw. Would take 50 pcs. right now


Thanks, I just placed an order with Digikey for all the SMT parts, so I can start PCB design and PCB prototyping soon. Meanwhile I am playing with head end control ideas on the breadboard 

Since I just spent $300 on parts I guess there is no going back now, I need to have something to show for it


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## JimK (Mar 21, 2009)

Dimitri,

I thought of two "nice to have" features for those who also use supplementary cell monitoring (like PakTrakr) as well as those who store their EV for several weeks or more and need to disconnect the units to eliminate unnecessary draw. 

1. Having a way to connect the PakTrakr or other remote monitoring wires directly to the board rather than use the PakTrakr ring terminals can be useful especially if space is crammed and you need to disconnect things.

2. Having a way to switch off the miniBMS without removing ring terminals (ex. one of the power leads could pass through a jumper. When the jumper is removed, unit would be powered off. Obviously this could be done with a switch but my guess is it would take up more space.


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## dimitri (May 16, 2008)

Jim,

thanks for feedback. Great idea on additional connections, it fits nicely with my other ideas of adding QD tabs on PCBs, so people can use same PCBs for remote BMS, similar to TPPacks design, with multiple cells managed by single board. Those tabs can be used to connect remote cells or to connect Paktrakr type of device when PCB is on the cell. Its probably not making sense the way I describe it, but you will see it once I have PCBs done, its all in my head right now 

As for jumpers, sorry, extra risk of poor connections in a harsh environment. Plus, these BMS modules will draw less current than self discharge, so no harm in leaving them on all the time. I estimate less than 10 mA draw per cell, nothing to worry about, unless you plan on leaving a pack unattended for several months, which is a bad idea anyway.


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## tomofreno (Mar 3, 2009)

> Since the main idea of NC loop is to improve reliability of an alert, we have to also decide how to handle it on the head end.


 I like option1 due to inherent safety. If I understand correctly, in either option the opto relays on each board (D3) are always on unless an HVC or LVC signal is active (U1 or U3 output high), so I am concerned about lifetime of these. It would be a pain if these had to be replaced very often since there is one per cell. I would guess they should have long lifetime though, and so would still like this configuration due to inherent safety, and warning that something is wrong. Seems to me components on the main board are less an issue since there is only one relay for HVC and one for LVC (correct?), and these could be made easily replaceable (socket mount). I would much rather have to replace them once in a while than have no warning when something fails.


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## dimitri (May 16, 2008)

tomofreno said:


> I like option1 due to inherent safety. If I understand correctly, in either option the opto relays on each board (D3) are always on unless an HVC or LVC signal is active (U1 or U3 output high), so I am concerned about lifetime of these. It would be a pain if these had to be replaced very often since there is one per cell. I would guess they should have long lifetime though, and so would still like this configuration due to inherent safety, and warning that something is wrong. Seems to me components on the main board are less an issue since there is only one relay for HVC and one for LVC (correct?), and these could be made easily replaceable (socket mount). I would much rather have to replace them once in a while than have no warning when something fails.


These optos are made for aerospace, security, medical and industrial controls. Although datasheet does not specify the lifetime, I seriously doubt there would be any issues with optos being on all the time. In fact my only concern was for Axicom relays, but according to their datasheet, those are tough little suckers too, I don't think I need to worry about them. Since safety is number one concern of BMS, I will go with option 1.

Thanks for your feedback.


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## dimitri (May 16, 2008)

Another reason I will go with option 1 is that many DIY conversions make tons of mistakes in wiring, many DIY folks are better mechanics than electricians  , I don't mean to sound jerky, but its true. So, I'd rather offer a system which will not allow charger to come on unless its wired correctly, than give someone false sense of security if they messed up the head end wiring and blew their cells.

Option 1 it is folks, if you don't like it, don't buy it


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## Dave Koller (Nov 15, 2008)

dimitri said:


> These optos are made for aerospace, security, medical and industrial controls. Although datasheet does not specify the lifetime, I seriously doubt there would be any issues with optos being on all the time.


I have had some running for 20 + years - so you know they were made from the "old days" -- I always made sure I used a resistor that held it at it's lower current value for turn on.. In other words, I did not push the current on the LED as I thought that would be the first to fail (at high current) .. The "new" generation is extremely robust - I think the circuit you have is well thought out and should not have any problems. SO keep it up Dimitri!


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## dimitri (May 16, 2008)

Dave Koller said:


> I have had some running for 20 + years - so you know they were made from the "old days" -- I always made sure I used a resistor that held it at it's lower current value for turn on.. In other words, I did not push the current on the LED as I thought that would be the first to fail (at high current) .. The "new" generation is extremely robust - I think the circuit you have is well thought out and should not have any problems. SO keep it up Dimitri!


Thanks Dave,

I revised every resistor value to minimize current, yet stay within safe operating range for all semiconductors. It took several hours to cross reference all voltage divider values against standard decade table and Digikey stock of popular resistors. I also found best thermistor value to provide reasonable LVC compensation in a given temp range. All resistors are 1% tolerance, all parts have been ordered and should be here soon.

I should have a working prototype pretty soon.


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## tomofreno (Mar 3, 2009)

Dimitri, are you familar with the TC54 chip? Apparently people are using them for LVC - several have said so on the yahoo thundersky site. Sounds similar to what you are doing - it has a comparator with precision voltage reference and goes logic low when the input voltage drops below a predetermined value (2% accuracy). Draws 1 microAmp. Link to pdf:

http://ww1.microchip.com/downloads/en/DeviceDoc/21434g.pdf


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## dimitri (May 16, 2008)

tomofreno said:


> Dimitri, are you familar with the TC54 chip? Apparently people are using them for LVC - several have said so on the yahoo thundersky site. Sounds similar to what you are doing - it has a comparator with precision voltage reference and goes logic low when the input voltage drops below a predetermined value (2% accuracy). Draws 1 microAmp. Link to pdf:
> 
> http://ww1.microchip.com/downloads/en/DeviceDoc/21434g.pdf


Yes, very familiar, I have 40 of them in my EV and another 50 or so in the parts drawer  , those are the parts which bled your cells, although not the part's fault, but design and assembly flaw.

This part doesn't fit my strategy, since it's expensive due to builtin voltage reference, yet only serves LVC, which means I would need another one or two voltage references, which adds up parts count and costs. My new design has one voltage reference for everything.

Thanks for keeping up though  , all comments are welcome!


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## dimitri (May 16, 2008)

Here is the schematic for the head end, I modeled it on the breadboard today, works great. Looks similar to the BMS module, using single LM239 IC, few resistors , capacitor and 2 relays. Relays have 12mA coils, so I can drive them directly from IC, eliminating additional transistors. I could have used 555 timer IC for this, but decided that single LM239 is sufficient.

I tried to use same parts as in cell modules since its easier to purchase in bulk, kept it as simple as I could.

C1 provides about 2 second delay to eliminate some false LVC alarms, this can be increased or decreased by the user if I put a trimpot for R2.

Charger control part is a classic flip-flop, it's reset by Ignition key, since you don't charge when you drive and vice versa, so on first HVC alert from the cells charger relay will release and stop the charger. When driver unplugs the charger cord and starts the car, it resets back for the next time.

This also solves a potential issue with single wire NC loop, since you can't distinguish LVC from HVC from the cells. If you get home with the pack so low that LVC is set solid, then you wouldn't be able to start the charger, however, with ignition key still on you can start the charger and then once all cells climb over LVC level (should only take few minutes) you can turn ignition off and charger relay will remain active until it gets to HVC. This situation should be extremely rare and I didn't want to complicate things too much, I think this solution is appropriate.

Charger and throttle controls are basic NO/NC pairs capable of 2 Amps control current, so these can be attached to pretty much any EV design. I will supply few common examples for popular chargers and controllers. Some chargers come with low voltage BMS control, so those can be directly managed, others will need high amp AC solid state relay which will be driven by these NO/NC pairs.

Any feedback regarding this design?


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## Russco (Dec 23, 2008)

dimitri said:


> Any feedback regarding this design?
> 
> View attachment 5062



Hmmm...how about a little RC network on the raw 12 volt input and also the IGN input. This would filter out noise coming in the 12 volt inputs. This will help prevent false comparator trips.

A fuse should be included. And a crowbar diode.

A freewheeling diode across the buzzer would be nice. 

If the two relays have coils, they would require freewheeling diodes also.

Keep up the good work.


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## dimitri (May 16, 2008)

Russco said:


> Hmmm...how about a little RC network on the raw 12 volt input and also the IGN input. This would filter out noise coming in the 12 volt inputs. This will help prevent false comparator trips.
> 
> A fuse should be included. And a crowbar diode.
> 
> ...


Of course, I always forget those things  , I forgot to add diodes across coils, but I didn't know that you need one for piezo buzzers, really?

I will add these changes, thanks.


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## jackbauer (Jan 12, 2008)

Looks great. Could this setup be used for lead acid?


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## dimitri (May 16, 2008)

jackbauer said:


> Looks great. Could this setup be used for lead acid?


Theoretically, LVC and HVC can be set to Lead Acid voltage levels, but shunting would require much larger wattage resistor and there is no room for it on my mini PCBs, so I can't support balancing, but you can still use HVC to prevent overcharge of individual SLA or AGM batts, as long as you balance them manually when needed.

Personally, I see LA as such last century technology, that I don't even want to spend time on it, no offense to those still using it


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## Dave Koller (Nov 15, 2008)

LM239 ? Did I miss something or did you change the BMS boards to it also? They are pin for pin but the 239 is a better choice for us in the cold country!
( err last time I remember - I should look again as do remember the temp range is lower... ) I thought the newer piezo has built-in filter.. oh well, keep it up!

P.S. I usually put a .1 bypass cap next to the chip and on pins 3 and 12 - to help with any spikes..


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## dimitri (May 16, 2008)

Yes, 239 is rated at -40C , and 339 at 0C, but I don't think its critical since cells should be above freezing anyway. Head end control board will be outside of battery boxes most likely, so its more important to work in lower temps.

Digikey had low stock on 239, but it costs only few cents more than 339, so I might just get 239 for cell boards later on as well.

Spent a day on PCB design, prototype PCBs have been ordered, should be here in a few days.


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## dimitri (May 16, 2008)

Prototype PCBs arrived today and I already assembled one for testing. I also designed universal terminal connection, which can be used for 2 most popular cell dimensions. Use smaller hole at the end of the terminals for cells 160AH, 180AH, 200AH, or cut off one hole and use the one closer to the ring for cells 90AH, 100AH. This way I can order mass quantity of these terminals from a metal stamper and supply them with BMS modules.

Prototype module is working as expected, I need to do some LVC testing at various temps. Then I will assemble a few of them and try them in my car once I get PCBs for the head end control board, which should be in a couple of days.

I am talking to a local PCB assembly shop to get a deal on mass production, hopefully there will be enough orders to make it worthwhile.

Each cell module is 30mm x 48mm and distance between terminal holes is 40mm. That's as small as it gets


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## JRP3 (Mar 7, 2008)

Cool, looks good. If I'm ever in a BMS state of mind I'll get some


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## Dave Koller (Nov 15, 2008)

Really nice job on everything!! The boards are clean and straight forward... Tell me you didn't solder them without a special tip! Surface mount takes a lot of patience !


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## tomofreno (Mar 3, 2009)

Nice work Dimitri!


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## dimitri (May 16, 2008)

Dave Koller said:


> Really nice job on everything!! The boards are clean and straight forward... Tell me you didn't solder them without a special tip! Surface mount takes a lot of patience !


I used hot air station and solder/flux paste, it makes a beautiful end result. However, there is no way to mass produce these by hand, so I am talking to a local PCB assembly shop to automate production. Hopefully the cost of production won't be too high and leave the final price still in the affordable zone. I will know final numbers next week.

I tested LVC temp compensation, it works just as planned, 2.5V at 0C , 2.6V at 25C and 2.7V at 50C. I also tested PTC fuse, once heated to 80C it breaks the circuit, which would be interpreted as HVC event and stop the charger in case shunt resistor got too hot, which is not likely since it doesn't get over 65C in my testing, passing 0.6 Amp.

Its really exciting to hold something in your hand which only existed on paper few days ago 

I can't wait to get PCBs for head end board and put it all together in the car.


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## etischer (Jun 16, 2008)

dimitri said:


> Its really exciting to hold something in your hand which only existed on paper few days ago
> 
> I can't wait to get PCBs for head end board and put it all together in the car.


Wow, you work fast! Nice work


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## TheSGC (Nov 15, 2007)

Those are really nice boards.

Yeah, the more I think about it, the more I can't get another lead acid pack for my EV. I already have my piggy bank out and saving up for a pack and the MiniBMS would be great!


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## dimitri (May 16, 2008)

Thanks everyone for your kind words!

By the end of next week I should have this BMS ready to run in the car. Since I ordered a handful of prototype PCBs I will have a few test kits which I would like to send to people for review.

The test kit will have one head end board and two cell boards, so you can connect everything just like the final product. 

I am looking for 3-4 volunteers to test and provide independent review of my BMS. These boards are exactly the same as they will be in production, so if you need this BMS you can set it all up and later just get more cell boards to add in series.

I need people who are ready to put BMS in the car or on some bench test with real batteries and charger, and provide meaningful review on the forum within a week or two.

Please send me a Private Message via forum and provide some details of your battery pack, charger and controller, so I can provide schematics how to connect it all together. Also provide your ZIP code and contact Email, so I can figure out shipping costs and get in touch with you.


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## dimitri (May 16, 2008)

While I am waiting for more parts, I have been working on documentation.
Here is wiring diagram, please review and comment.

Please note that I only show 2 wire potbox controller connections, which is common for Curtis and few other controllers which take 0-5K resistive input. I will have additional diagrams later for 3 wire throttles, which take 0-5V input, such as Soliton1 and others.

I will also post a PDF doc later which includes features description and installation steps.


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## dimitri (May 16, 2008)

Here is the first draft of the user manual. I will add more throttle control diagrams and couple more pictures later on.

View attachment MiniBMS User Manual.pdf


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## JimK (Mar 21, 2009)

I read the manual and it is very thorough. Great job Dimitri.


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## Dave Koller (Nov 15, 2008)

Yep ! Really good - Few more pics like you said -- But nice and straightforward ...


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## dimitri (May 16, 2008)

Bad news, just got a quote for ring terminals, they want $1.50 EACH  , thats $3 for a pair for each cell module, more than all electronic parts.

There is no way I can pay this much for stupid terminals.

Any ideas on how to make it cheaper? Anyone knows a shop willing to do small jobs for less money? I was hoping a pair of terminals would be less than a buck, is that crazy of me to expect? I can't order 100,000 for this project, I can't swallow more than 2000 at a time. I don't even know how many BMS kits I can sell in this market.


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## JRP3 (Mar 7, 2008)

How much would it cost to set it up like the VB's? Those ring terminals have to be much cheaper.


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## dimitri (May 16, 2008)

JRP3 said:


> How much would it cost to set it up like the VB's? Those ring terminals have to be much cheaper.


 
They are not much cheaper according to Brian and I really want a design without any wires on terminals.


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## racunniff (Jan 14, 2009)

dimitri said:


> Bad news, just got a quote for ring terminals, they want $1.50 EACH  , thats $3 for a pair for each cell module, more than all electronic parts.


That seems way excessive. What are the dimensions of your ring terminal? I bet most of that is tooling setup. I wonder if you search for existing rings already in mass production if you will find significantly cheaper options.

Also - what is the cross-sectional area of the thin part of your terminal? It's not yet clear to me that a short 10 Gauge or 8 Gauge wire would result in enough of a resistive loss to worry about.


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## tomofreno (Mar 3, 2009)

Hi Dimitri,

You might add a comment that it is up to the user to ensure that the charging current is less than or equal to the shunt current before or when a shunt turns on, and shunts should not be used if the user's charger has no facility to ensure this. 

How do the terminal connections attach to the cell level boards? Could it be that is what is adding cost, ie assembly, not part cost? 

If a cell should swell slightly is there some way for the cell connections to accommodate this without damaging the board?

Impressive work!


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## tomofreno (Mar 3, 2009)

Dimitri,

One other thing, you mention in the user's manual that a user will be able to identify the LVC cell by looking for the board with green LED off. But that will only be possible if the cell level board is where the user can see it during driving, or if they have discharged the cell so far that it remains at or below LVC when the car is stopped, and not just during larger current draws.


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## dimitri (May 16, 2008)

racunniff said:


> That seems way excessive. What are the dimensions of your ring terminal? I bet most of that is tooling setup. I wonder if you search for existing rings already in mass production if you will find significantly cheaper options.
> 
> Also - what is the cross-sectional area of the thin part of your terminal? It's not yet clear to me that a short 10 Gauge or 8 Gauge wire would result in enough of a resistive loss to worry about.


Its not about resistance at all, these terminals are passing less than 1 Amp when shunting. I want these terminals for easy installation and mounting of the PCB. I have done my first BMS modules with wires and velcro tape to attach PCB to the cell, but I hate how ugly and messy it looks and how many wires you need to solder to PCBs. These terminals would hold the PCB and provide simple and universal install for most common cell sizes. I have done this kind of setup with my current BMS modules installed in my EV and I really like how it turned out, so I want to use the same approach in MiniBMS, but I can't make 1000s of terminals by hand, so I need to find a place to make them. 

If I can find them at about $1 per pair, it would be worth it. I will keep looking.


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## dimitri (May 16, 2008)

tomofreno said:


> Hi Dimitri,
> 
> You might add a comment that it is up to the user to ensure that the charging current is less than or equal to the shunt current before or when a shunt turns on, and shunts should not be used if the user's charger has no facility to ensure this.
> 
> ...


Actually charging current is not an issue with this BMS since shunting and HVC are 2 different triggers. Charger can and will overrun shunting current, which is expected, and once cell reaches HVC, charger shuts off. Shunting is there just to slow down first cells a little bit every cycle, to allow other cells to catch up. This was one of my main design points, to stop worrying about shunting and charging currents, just attach any dumb charger and it will still work safely every time. I can sleep much better knowing that charger will be forced off no matter what happens during shunting phase.

As for terminals cost, there is no assembly, I will just supply a bag of terminals, screws, lock washers and nuts, and QD terminals to each customer. I want everything included in the price except the wire, so people don't have to scramble at Home Depot or AutoZone to get it all done.

Swelling should not change the distance between cell terminals, only outside dimensions, so there should be no issues with BMS holding up. In case of an unimaginable stress, the terminal will tear up and cause BMS alert due to loss of power to the board, so we are still good


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## dimitri (May 16, 2008)

tomofreno said:


> Dimitri,
> 
> One other thing, you mention in the user's manual that a user will be able to identify the LVC cell by looking for the board with green LED off. But that will only be possible if the cell level board is where the user can see it during driving, or if they have discharged the cell so far that it remains at or below LVC when the car is stopped, and not just during larger current draws.


True, but in normal LVC situations you don't care which cell was the first to trigger the alert, all you care about is to get to the charging station ASAP. You only need to know which cell is down in unusual situations, like a dead cell, in which case it will remain dead while you are looking at LEDs


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## pm_dawn (Sep 14, 2009)

Hi !

I just read the manual, and have a question:
Will it be enough to go linear on the temerature correction for the LVC.
As it is setup now the LVC at -25 degC would become 2,4V ?

The TS manual says something about LVC 1.5V at -35degC

Regards
/Per Eklund


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## _GonZo_ (Mar 23, 2009)

dimitri said:


> Bad news, just got a quote for ring terminals, they want $1.50 EACH  , thats $3 for a pair for each cell module, more than all electronic parts.
> 
> There is no way I can pay this much for stupid terminals.
> 
> Any ideas on how to make it cheaper? Anyone knows a shop willing to do small jobs for less money? I was hoping a pair of terminals would be less than a buck, is that crazy of me to expect? I can't order 100,000 for this project, I can't swallow more than 2000 at a time. I don't even know how many BMS kits I can sell in this market.


Hi Dimitri, can you show me a picture of those terminals?
May be I can help.


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## dimitri (May 16, 2008)

pm_dawn said:


> Hi !
> 
> I just read the manual, and have a question:
> Will it be enough to go linear on the temerature correction for the LVC.
> ...


You are correct, if you want to run your pack at -25C then linear LVC correction is not enough, however, the real world data shows that you can't get decent discharge current from these cells at below freezing temps, so the question becomes irrelevant, why bother with LVC if you can't drive the car?

In my LVC calculations I am assuming that people will not let their cells to freeze much below 0C.

Of course we are talking actuall cell temp, not ambient temp outside the car, so you just need to insulate your pack as many have done very successfully over the years working with Lead Acid conversions.

Hope this helps.


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## JRP3 (Mar 7, 2008)

_GonZo_ said:


> Hi Dimitri, can you show me a picture of those terminals?
> May be I can help.


I think he's looking for something like the bottom picture in this post, though two different single size terminals would work if you can't incorporate both into one.

http://www.diyelectriccar.com/forums/showpost.php?p=155476&postcount=79


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## dimitri (May 16, 2008)

Here is what I want. I am embarassed to post the pic of these ugly terminals I made by hand for testing, but I wanted to show everyone the idea.

People with larger cells would use holes at the end, and people with smaller cells would cut off the hole at the end and use the one closer to the ring. This way single terminal design covers most popular cell sizes.

I may need to abandon this idea if I cant find a cheap source for these terminals.


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## tomofreno (Mar 3, 2009)

> Swelling should not change the distance between cell terminals, only outside dimensions, so there should be no issues with BMS holding up.


 The coefficient of thermal expansion of the cell case would have to be zero for no expansion between terminals. It certainly isn't for the metal lugs. It is always a bad idea to have rigid connection between two or more points of two materials with quite different coefficients of thermal expansion when the unit will see large thermal cycling - like 40F to 110F. The lugs will be fixed at the ends due to the large force on them at the terminals (>1000lb at 15 lb-ft torque), so if expansion is different by a few thousandths of an inch, it will be taken up by the ends bolted to the boards or the boards themselves. The former will scrub and loosen the connection over time. That is why I thought the one wire lug on the VB's was a good idea. The lug length is small, so maybe the difference in expansion won't be enough to cause problems and I'm just nitpicking. A member permitting some flexture would ensure there wouldn't be an issue.


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## dimitri (May 16, 2008)

So, here is another idea. What if I take this kind of terminal, flatten it with a hammer, then drill 1 or 2 holes in the flattened part and attach it to PCB with #4 screws? This would be done on one end and use the wire on the other end, a la VB style. Would that be acceptable?

Would one hole do the job or do we really need 2 to prevent it from turning around the mounting hole like on VBs? 2 holes require more room on PCB and more drilling, I'd like to avoid it. Cell module has virtually no mass and lock washer will be used on the screw, so I don't think it will be moving anywhere, right?


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## racunniff (Jan 14, 2009)

dimitri said:


> So, here is another idea. What if I take this kind of terminal, flatten it with a hammer, then drill 1 or 2 holes in the flattened part and attach it to PCB with #4 screws? This would be done on one end and use the wire on the other end, a la VB style. Would that be acceptable?
> 
> Would one hole do the job or do we really need 2 to prevent it from turning around the mounting hole like on VBs? 2 holes require more room on PCB and more drilling, I'd like to avoid it. Cell module has virtually no mass and lock washer will be used on the screw, so I don't think it will be moving anywhere, right?


I was thinking something similar - hard connection on one side, wire on the other. If you're going to be drilling holes, I would say "skip the flattening step" and just start with copper bar stock. Like this picture:









Although I think you are right - two screws on the BMS end would significantly reduce rotations and increase stiffness.


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## dimitri (May 16, 2008)

racunniff said:


> I was thinking something similar - hard connection on one side, wire on the other. If you're going to be drilling holes, I would say "skip the flattening step" and just start with copper bar stock. Like this picture:
> 
> View attachment 5210
> 
> ...


Nice drawing, what tool did you use to make it?

Drilling large 3/8" hole in thin soft metal is a bitch, I'm sure you know 

I'd rather take a standard 3/8" terminal and drill one small hole.

Unless someone comes back with compelling argument for 2 holes to prevent PCB movement against the terminal itself, I don't see a need for it. Afterall, the ring terminal itself can rotate around the cell post, so what's the point in making it rigid to the PCB?


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## dimitri (May 16, 2008)

BTW, in this design the screw will only be on one side, the other side will have a wire soldered into the PCB with a crimp ring terminal on the other end of the wire, basically the same as VBs v2 had. I just need to decide on 1 screw vs. 2 screws on the rigid side.


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## racunniff (Jan 14, 2009)

dimitri said:


> Nice drawing, what tool did you use to make it?
> 
> Drilling large 3/8" hole in thin soft metal is a bitch, I'm sure you know
> 
> ...


Google Sketchup is my friend. And free, too.

Yes, drilling holes in thin metal can be a pain. I'm sure you can find hole punches to use instead of drills... or you can stack several layers together and drill all at once.

The reason to go with two screws into the PCB is that vibrations will likely unscrew your terminal over time with only one screw. Two screws will prevent the lateral rotation that cause the screw-loosening motion.


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## dimitri (May 16, 2008)

racunniff said:


> The reason to go with two screws into the PCB is that vibrations will likely unscrew your terminal over time with only one screw. Two screws will prevent the lateral rotation that cause the screw-loosening motion.


Good link, thanks a lot!

Since I am clearly not a mechanical engineer  , I will ask potentially stupid question, still trying to defend my position of a single hole in the PCB.

Can I use a simple rivet instead of the screw to attach ring terminal to the PCB? Is there data for rivets coming loose in mobile applications?

Thanks


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## racunniff (Jan 14, 2009)

dimitri said:


> Good link, thanks a lot!
> 
> Since I am clearly not a mechanical engineer  , I will ask potentially stupid question, still trying to defend my position of a single hole in the PCB.
> 
> ...


Rivets will not have the same vibrational loosening problems as screws. They are subject to thermal stress - especially aluminum rivets (aluminum has a very low duty cycle before it cracks). I think there are copper rivets available.

I also am not an ME, but I'll ask around.


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## ellweber (Jun 3, 2009)

*attach lugs to PCB*

Have you considered providing two short slots in the PCB, then sliding the cylindrical part of the lug over the tab formed between the slots and soldering the lug to pads alongside the slots?


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## dimitri (May 16, 2008)

*Re: attach lugs to PCB*



ellweber said:


> Have you considered providing two short slots in the PCB, then sliding the cylindrical part of the lug over the tab formed between the slots and soldering the lug to pads alongside the slots?


He he, you are referring to Elithion design, of course 

Yes, I considered it, but I don't like it for a few reasons. Ring terminal would have to be large enough to slide over the PCB, and those ring terminals are relatively expensive. I would need large soldering iron to solder those with potential issues of damaging PCBs. And the main reason is that I think this design is held in place largely by the glue between copper and PCB fiberglass, which can easily come loose, especially with vibrations. I suppose there can be a hole in PCB inside the terminal, which will be filled with solder and provide additional strengh, but I still can't imagine melting so much solder to get the whole thing in place. I also think that PCB tab holding the terminal can break off somewhat easily if pressure is applied.

I don't want to bash Elithion design, I'm sure they have done homework before accepting this method, but I just don't like it.


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## JRP3 (Mar 7, 2008)

I can't see any problem with the single screw. Put a drop of locktight if you're really worried.


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## _GonZo_ (Mar 23, 2009)

I just sent inquiere for terminals like the picture









Please let me know sizes.


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## dimitri (May 16, 2008)

JRP3 said:


> I can't see any problem with the single screw. Put a drop of locktight if you're really worried.


Thanks JRP3, I don't see any issues with single screw or single rivet, I'm going to test how tight the rivet holds the terminal in place.

Theoretically the screw can come lose due to vibrations, but considering the module weighs about one gram I just can't imagine it moving around in a car environment, it simply doesn't have inertia to do that and it has absolutely no mechanical load on it.

But again, I am open to compelling arguments


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## dimitri (May 16, 2008)

_GonZo_ said:


> I just sent inquiere for terminals like the picture
> 
> Please let me know sizes.


Thanks GonZo, but it looks like I am being pursuaded to drop this idea for a couple of good reasons.


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## Dave Koller (Nov 15, 2008)

dimitri said:


> Good link, thanks a lot!
> 
> Since I am clearly not a mechanical engineer  , I will ask potentially stupid question, still trying to defend my position of a single hole in the PCB.
> 
> ...


Lee Hart Quote:
The TO-220 part up against the two big electrolytics is U1 (an LM317T 3-terminal adjustable voltage regulator). Pop rivets are a terrible way to mount a transistor to a heatsink! They can be so tight that they warp and crack the case, or so loose that they hardly do any good. In this case, it was too loose. I replaced it with a clip-on heatsink, and epoxied it to the capacitors for support.
Found in MODS for Iota as DC/DC

Don't know if that helps: 

The regular terminal you showed might work if you soldered two ring terminals - one small for the screw(bolt) on the PCB one large that it slips into for battery should be snug as one for small gauge fits INTO one for large gauge wire... Ill see if I can send you a picture of what I mean... Can solder the two together or solder dip in solder pot..


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## dimitri (May 16, 2008)

Dave Koller said:


> The regular terminal you showed might work if you soldered two ring terminals - one small for the screw(bolt) on the PCB one large that it slips into for battery should be snug as one for small gauge fits INTO one for large gauge wire... Ill see if I can send you a picture of what I mean... Can solder the two together or solder dip in solder pot..


Dave, no need for the pic, I get the idea  , sounds doable, but soldering part is a PITA.

I just took 10-12 AWG 3/8" stud terminal, hammered it flat and it fits perfectly over my PCB and gives enough clearance from the battery post. I will post a picture of complete assembled unit of this design later today for everyone's review and comments.

Thanks for all the info.


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## Dave Koller (Nov 15, 2008)

Took me a bit to find some in my junk box but you get the idea...

Might get you to thinking


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## Dave Koller (Nov 15, 2008)

dimitri said:


> Dave, no need for the pic, I get the idea  , sounds doable, but soldering part is a PITA.
> 
> I just took 10-12 AWG 3/8" stud terminal, hammered it flat and it fits perfectly over my PCB and gives enough clearance from the battery post. I will post a picture of complete assembled unit of this design later today for everyone's review and comments.
> 
> Thanks for all the info.


Lol I sent it at the same time ! Anyway you got it that way !


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## dimitri (May 16, 2008)

OK, how about this design?

I actually really like it, all parts off the shelf, I can even offer DIY kits for people to save few bucks on final assembly. Just take standard 10-12 AWG 3/8" stud terminal, hammer and drill for #4 bolt, add 18-22 AWG 3/8" terminal with a piece of wire and voila, all done.

I will of course offer fully assembled units as well for the lazy bones 

As far as bolt getting loose, no way Jose , both PCB pad and the terminal are tinned and there is plenty of friction between the two, and lock washer helps as well. It ain't going anywhere...


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## Dave Koller (Nov 15, 2008)

dimitri said:


> OK, how about this design?
> 
> I actually really like it, all parts off the shelf, I can even offer DIY kits for people to save few bucks on final assembly. Just take standard 10-12 AWG 3/8" stud terminal, hammer and drill for #4 bolt, add 18-22 AWG 3/8" terminal with a piece of wire and voila, all done.
> 
> ...


Yep -


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## JRP3 (Mar 7, 2008)

Looks good.


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## JRP3 (Mar 7, 2008)

Dave Koller said:


> Took me a bit to find some in my junk box but you get the idea...
> 
> Might get you to thinking


That's a good idea for a quick double ring terminal, as long as the dimensions worked out.


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## dimitri (May 16, 2008)

Here is the head end board. Bench tested OK. Still waiting for a couple of parts from Digikey to finish all prototype modules and then put it all in the car, hopefully this weekend.


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## dimitri (May 16, 2008)

Guys, I need some help. Here is the diagram to cut 50% throttle on controllers which use 0-5V input. This works well for 5K resistive 3 wire pot boxes. I know it works because I have this setup in my EV.

The question is, will this also work with Hall Effect throttle assembly? I never had a chance to play with those yet. I don't know if hall effect sensor is actually powered by 5V and produces 0-5V output, or is it basically a resistive component and can be put in series with 5K resistor. Any ideas?

Thanks


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## Amberwolf (May 29, 2009)

The actual hall effect sensors are typically powered by 5V and have an output that varies from 0V to 5V or 5V to 0V (depending on magnet polarity used at start point). How the output of a hall based throttle works may be different, as it may have electronics buffering the output to simulate a resistive output.

Alternately, you can always *make* it simulate a resistive output, using an adaptation of the circuit in this Maxim application note:
http://www.maxim-ic.com/app-notes/index.mvp/id/3284
________
Park Royal 3 Condos Pattaya


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## _GonZo_ (Mar 23, 2009)

Hi Dimitri,

I just received repied from provider, they can make that "contacts" in any shape for a question of cents (depends on size)
The MOC is 10,000 units. But may be worth if your actual prices is over $1
you will get 10,000 units for similar price of getting 1,000 units with the benefit to be as you exactily want.

Let me know.


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## Dave Koller (Nov 15, 2008)

dimitri said:


> Guys, I need some help. Here is the diagram to cut 50% throttle on controllers which use 0-5V input. This works well for 5K resistive 3 wire pot boxes. I know it works because I have this setup in my EV.
> 
> The question is, will this also work with Hall Effect throttle assembly? I never had a chance to play with those yet. I don't know if hall effect sensor is actually powered by 5V and produces 0-5V output, or is it basically a resistive component and can be put in series with 5K resistor. Any ideas?


Side note: 

Curtis two wire pots - 5 k either side should signal shutdown (Shows like a high resistance to internal similar to broken wire).. But I see you have use of NO or NC so not a problem and can shunt to slow down across a 2 wire pot... Do you want to think about E override if for some reason a person is passing in a boxed position say on a freeway and needs a way to get over ( as he has just killed his engine)?


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## dimitri (May 16, 2008)

Dave Koller said:


> Side note:
> 
> Curtis two wire pots - 5 k either side should signal shutdown (Shows like a high resistance to internal similar to broken wire).. But I see you have use of NO or NC so not a problem and can shunt to slow down across a 2 wire pot... Do you want to think about E override if for some reason a person is passing in a boxed position say on a freeway and needs a way to get over ( as he has just killed his engine)?


Sorry Dave, your message is a bit cryptic to me  , are you asking for an override to LVC? LVC is here to protect the pack, you shouldn't be passing on freeway with an empty pack, its no different than running out gas in ICE car in the middle of freeway. This BMS is a last resort to preserve the cells from early grave, if someone wants to deliberately override it, then my best advise is to skip the BMS all together and drive bare back, or maybe just wire the buzzer to annoy you while you are murdering your battery.

I am simply providing examples of wiring diagrams, not pushing anyone to follow them if they choose not to.

Hope this makes sense.


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## Dave Koller (Nov 15, 2008)

dimitri said:


> Sorry Dave, your message is a bit cryptic to me  , are you asking for an override to LVC? LVC is here to protect the pack, you shouldn't be passing on freeway with an empty pack, its no different than running out gas in ICE car in the middle of freeway. This BMS is a last resort to preserve the cells from early grave, if someone wants to deliberately override it, then my best advise is to skip the BMS all together and drive bare back, or maybe just wire the buzzer to annoy you while you are murdering your battery.
> 
> I am simply providing examples of wiring diagrams, not pushing anyone to follow them if they choose not to.
> 
> Hope this makes sense.


In a true sense - yes you are right - I was just thinking if it limited the engine and not completely shut it down ( which careful thought on the part of the user could be wired as such) - but as you say they should have plenty of warning NOT to get themselves into this situation -- The lawyer in me says make plenty of disclaimers ... It is a great BMS and those nasty thoughts just creep up on me..


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## dimitri (May 16, 2008)

Dave Koller said:


> In a true sense - yes you are right - I was just thinking if it limited the engine and not completely shut it down ( which careful thought on the part of the user could be wired as such) - but as you say they should have plenty of warning NOT to get themselves into this situation -- The lawyer in me says make plenty of disclaimers ... It is a great BMS and those nasty thoughts just creep up on me..


I never proposed to shut off the motor on LVC, in fact I actively argue against it ( I think its in the doc, if not I will add it ). The diagrams I posted will cut max throttle 50%, one diagram for 2 wire pot puts 5K resistor across the pot, effectively limiting it to 2.5K max. Second diagram adds 5K to top arm of voltage divider, effectively limiting max voltage to 2.5V , none of these diagrams produce "open circuit" as you seem to suggest. Diagrams use NC or NO pairs depending on the version, I'm pretty sure I have them drawn correctly.


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## Dave Koller (Nov 15, 2008)

dimitri said:


> I never proposed to shut off the motor on LVC, in fact I actively argue against it ( I think its in the doc, if not I will add it ). The diagrams I posted will cut max throttle 50%, one diagram for 2 wire pot puts 5K resistor across the pot, effectively limiting it to 2.5K max. Second diagram adds 5K to top arm of voltage divider, effectively limiting max voltage to 2.5V , none of these diagrams produce "open circuit" as you seem to suggest. Diagrams use NC or NO pairs depending on the version, I'm pretty sure I have them drawn correctly.


 Yes, you have them right.. I guess I was being sure the USER knew there is a difference in Pots as in a Curtis HIGHER resistance In SERIES will shut down the controller... But you have it correct in your other drawing.. Working with the public I tend to have to explain things over and over as some will get it wrong - but I think you have made it clear in the PDF now with all the pics and diagrams it should be foolproof... Thanks for your patience!


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## dimitri (May 16, 2008)

Here is the diagram for Hall Effect throttle reduction. Looks a little kludgy , but I wanted consistent look with other diagrams. Controller input is normally connected directly to throttle output, but when LVC flips NO/NC pair, controller will get signal from 50/50 voltage divider, effectively reducing throttle in half.

Hope this makes sense.

I am finishing 2nd revision of the doc, will post shorty.


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## hardym (Apr 2, 2008)

Dimitri,
Very nice design. I've been watching this evolve, and think this is probably the best overall EV BMS solution. Having worked several BMS designs, here are a couple of thoughts. 
( Sorry these comments are so late in the design process. )

The 4.7 ohm power resistor is wirewound, and has a large inductive capacity. When the transistor turns off, there will be a significant reverse voltage from the inductive resistor that will reach across the transistor CE junction, that could easily reach the 40V peak of the TIP42. Rather than go to a TIP42C, suggest a diode across the resistor to shunt the reverse voltage. Diode doesn't need to be especially fast. If you start seeing the TIP42 or LM339 failures, this is probably why.

(This may have been suggested before) The current across the resistor could easily be switched by a n-ch FET usign a SOT package. The gate driver would need a pullup resistor, but you could save money (.20) and real-estate. 

From most of the installation photos, it looks like you've installed in conjunction with a PakTraker. Suggest packaging mini-bms, control board, packtraker and EV Dashboard by john barton. This is a super nice display that integrates well with Paktraker. The SW could be enhanced by integrate the serial data stream with the BMS status bits.

Mark


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## dimitri (May 16, 2008)

Mark,

I appreciate your feedback and thanks for your kind words 

Unfortunately your suggestions are a little late, MiniBMS has been in production for over 2 months and several hundred units have been sold already without any issues reported. I have several conversion shops as returning customers already and I have been using it happily in my own EV since day one.

As you noted I am using Paktrakr because I used it in my first EV and got comfortable with it. However, I had so many issues with Paktrakr by now that I cannot possibly recommend it to anyone anymore and will never use it again in my future projects. It has serious limitations on number of cells, but most importantly it very unreliable and succeptible to EMI. I put a huge effort to get my Paktrakr working by completely isolating its power from the pack and adding noise suppression in multiple places, and still it sometimes decides to garble the data for no apparent reason.


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## JRP3 (Mar 7, 2008)

Anyone look at the Cycle Analyst? I think it counts amp hours.


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## isaac_alaska (Mar 18, 2011)

we actually have quite a few of these boards already, as we're building (designing/building) an electric snowmobile conversion. i just finished reading through all of the development pages here, and it's pretty cool. my question is, is there any reason that the boards can't all be produced on a single large pcb, and then interface to the cells through a ribbon cable? we're currently using 300V, 60 conductor ribbon cable, and i think it's rated for at least an amp. The reason to go to a single large pcb is so that the entire bms would be visible, rather than having to see the individual batteries. also, i think quite a bit of space could be saved by combining the entire bms onto a large board. as it is, the bms boards are nearly as big as each of our cells. (we're using radio control helicopter li-po batteries from turnigy, for minimum weight. so far the seem to work extremely well, but we need a bms that can handle as many as a hundred individual cells)

i have the tools and software to lay out the board design, and could probably have it fabricated for quite a bit cheaper than 100 individual boards would cost.


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## JRP3 (Mar 7, 2008)

Dimitri also offers a centralized BMS option for the MiniBMS. Click the ad on the side for MiniBMS.


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## EV2012 (Oct 13, 2012)

@dimitri

I just take a look on your schematic of the mini BMS. Do you really use the R1 100Ohm resitor? With this resistor you will get a wrong cell voltage measurement.

If your circuit uses for example a current of 5mA, you will get a voltage of 0,5V at this resistor. Or did I misunderstand anything?


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## dimitri (May 16, 2008)

EV2012 said:


> @dimitri
> 
> I just take a look on your schematic of the mini BMS. Do you really use the R1 100Ohm resitor? With this resistor you will get a wrong cell voltage measurement.
> 
> If your circuit uses for example a current of 5mA, you will get a voltage of 0,5V at this resistor. Or did I misunderstand anything?


You are correct, I am not using 100 Ohm resistor. Final product has been fine tuned over time with resistors values carefully picked to produce desired voltage sensing results.


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## EV2012 (Oct 13, 2012)

@dimitri

I am interested in the BMS control board and I just found the schematic in this thread. So I am wondering if the first relay is all time closed when the loop is closed.
What would be the current consumption of the board? Isn´t it to high, because it is connected directly to 12V battery?


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## dimitri (May 16, 2008)

EV2012 said:


> @dimitri
> 
> I am interested in the BMS control board and I just found the schematic in this thread. So I am wondering if the first relay is all time closed when the loop is closed.
> What would be the current consumption of the board? Isn´t it to high, because it is connected directly to 12V battery?


Yes, both LVC and HVC relays are normally energized. This is a safety feature and additional drain its causing is the cost paid for it. I use smallest relays with only 12mA coils, so 2 relays add up to 24mA drain. I think this is a fair price to pay for ability to shut off the charger if head board lost power and unable to preform its monitoring duty.


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## dubelt (Sep 27, 2011)

Hi. 
Could you please post or link to final schematics of BMS module and master board...?


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## bwjunkie (Jul 31, 2013)

I didn't realize this is open source, nice. I'm a happier customer still.

Dimitri I'm not able to picture how this warning in the user manual can take place:

"Make sure your battery pack is physically disconnected from the rest of your EV when attaching BMS modules to your cells. Failure to do so may result in last BMS module completing the high voltage circuit before it gets attached to the last cell terminal."

How does the last module complete a circuit? Or is this assuming the module interconnects are being installed along with the modules one by one?

Josh


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## racunniff (Jan 14, 2009)

bwjunkie said:


> I didn't realize this is open source, nice. I'm a happier customer still.
> 
> Dimitri I'm not able to picture how this warning in the user manual can take place:
> 
> ...


This is independent of the module interconnects. When you are hooking the modules up to the cells, you remove the bolts from each terminal and then stack the module on top of the battery interconnects, then replace the bolts. If, for some reason, one of the cell interconnects is not touching the cell terminal (for example, if it is a stiff copper strap), then the current path will go through the BMS module, not through the cell, when you touch the module terminal to the cell interconnect in preparation for putting the bolt back in place. If there is any significant current flowing (e.g., a DC-DC converter) then it likely will overwhelm the BMS components' watt rating.


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## Russco (Dec 23, 2008)

racunniff said:


> This is independent of the module interconnects. When you are hooking the modules up to the cells, you remove the bolts from each terminal and then stack the module on top of the battery interconnects, then replace the bolts. If, for some reason, one of the cell interconnects is not touching the cell terminal (for example, if it is a stiff copper strap), then the current path will go through the BMS module, not through the cell, when you touch the module terminal to the cell interconnect in preparation for putting the bolt back in place. If there is any significant current flowing (e.g., a DC-DC converter) then it likely will overwhelm the BMS components' watt rating.


Connecting both the copper cell interconnect AND the BMS wire under ONE nut can lead to an evaporated BMS module if the cell is not making contact and the BMS lead is making contact.

Best way is not to use a cap screw but an 8 mm SS stud about 1-1/2" long. Hand thread the stud in the cell, add the copper strap, then a SS washer and finally tighten with a SS hex nut to 15 ft. lbs. Repeat for all cells. Then connect the BMS leads to the cell connections and secure with an 8 mm jam nut. This will insure the cells are connected BEFORE the BMS. Also much less chance of stripping out the cell connection aluminum threads since the stud does not turn in the female cell threads. And assures full thread contact without the problem of a cap screw bottoming out resulting in a loose connection.

The Mini BMS design was a joint effort of the DIY List Members and Dimitri some time ago. As the years have gone by Clean Power has updated the design several times and keep their present design to themselves, as far as I can determine. The schematic of several years ago using the 339 comparator should work well, but that's where the open source stops.


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## dimitri (May 16, 2008)

Wow, I can't believe you dug up this old thread  



racunniff said:


> This is independent of the module interconnects. When you are hooking the modules up to the cells, you remove the bolts from each terminal and then stack the module on top of the battery interconnects, then replace the bolts. If, for some reason, one of the cell interconnects is not touching the cell terminal (for example, if it is a stiff copper strap), then the current path will go through the BMS module, not through the cell, when you touch the module terminal to the cell interconnect in preparation for putting the bolt back in place. If there is any significant current flowing (e.g., a DC-DC converter) then it likely will overwhelm the BMS components' watt rating.


While this explanation is logical, it's not entirely accurate. The issue is not with current flowing thru BMS, but with full pack voltage being present across the gap between cell terminal being worked on and adjacent cell, causing instant death to BMS module which is not designed to handle more than 5V. Pack voltage is present because a load completes the circuit. Even a charger not plugged into AC still acts as a load because it has large filter capacitors in its output stage.

Davide Andrea explained it pretty well in this video


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## bwjunkie (Jul 31, 2013)

ah, makes sense now. The video is good! Also, helps you pointed out that the Bms module isn't supposed to conduct current but it does because the HV is beyond it's rating.

josh


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## polodiy (Oct 25, 2015)

Guys does MiniBMS do cell balancing and low voltage protection?

On the Lithiumate Lite comparisons page http://elithion.com/lithiumate_lite_comparison.php it says MiniBMS does only overcharge protection.


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## dimitri (May 16, 2008)

polodiy said:


> Guys does MiniBMS do cell balancing and low voltage protection?
> 
> On the Lithiumate Lite comparisons page http://elithion.com/lithiumate_lite_comparison.php it says MiniBMS does only overcharge protection.


Elithion page is wrong. MiniBMS signals when cell is out of range, either above HVC or below LVC, so there is coverage on both sides. 
Balancing is also present, as an independent function from HVC/LVC.
Current release of MiniBMS has gone thru several design updates since this ancient thread was started, so I would suggest to check out current user guide here at the Web store

Since this is a DIY system, what it does depends entirely on how you wire it to your components. System provides relay contacts for HVC and LVC, as well as Alarm output. In some cases LVC can be difficult to wire to your motor controller and/or throttle, in which case people skip LVC wiring and just rely on Alarm to know when to stop loading the battery. This works if the driver knows how to react to alarms, so its up to the driver to kill or save the battery.


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## polodiy (Oct 25, 2015)

dimitri said:


> Elithion page is wrong. MiniBMS signals when cell is out of range, either above HVC or below LVC, so there is coverage on both sides.
> Balancing is also present, as an independent function from HVC/LVC.
> Current release of MiniBMS has gone thru several design updates since this ancient thread was started, so I would suggest to check out current user guide here at the Web store
> 
> Since this is a DIY system, what it does depends entirely on how you wire it to your components. System provides relay contacts for HVC and LVC, as well as Alarm output. In some cases LVC can be difficult to wire to your motor controller and/or throttle, in which case people skip LVC wiring and just rely on Alarm to know when to stop loading the battery. This works if the driver knows how to react to alarms, so its up to the driver to kill or save the battery.


Dimitri, does your system provide some type of logging on cell level?


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## dimitri (May 16, 2008)

polodiy said:


> Dimitri, does your system provide some type of logging on cell level?


Depends on your definition of logging. There is no data interface, so no data logging from BMS to an external computer.
However, in current release of cell boards there is LED function which indicates an alarm was triggered within past 30 minutes. If you are driving and get LVC alarm, you can stop and look at cell boards within 30 minutes of the alarm and see which cell triggered it. If you are charging and HVC tripped the charge, within 30 minutes you can tell which cell tripped HVC.
So, this is sort of logging, if you stretch the definition wide enough


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## Yukon_Shane (Jul 15, 2010)

That's a great additional feature. I have the older version of the mini-bms and I sometimes get an alarm sounding when I'm climbing a big hill which makes me wonder which cell(s) are hitting LVC first.


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## polodiy (Oct 25, 2015)

Dimitri, what voltage per cell your recommend to set on the charger to charge CALB 100ah cells?

MiniBMS shunting starts at 3.5V, i am thinking setting 3.55V/cell on charger.
So it will give some time for balancing, but still will be more favorable towards battery life comparing to 3.65V/cell.


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## dimitri (May 16, 2008)

polodiy said:


> MiniBMS shunting starts at 3.5V, i am thinking setting 3.55V/cell on charger.
> So it will give some time for balancing, but still will be more favorable towards battery life comparing to 3.65V/cell.


Yes, if you have ability to program your charger, then 3.55V per cell is very reasonable end charge voltage.


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## polodiy (Oct 25, 2015)

dimitri said:


> Yes, if you have ability to program your charger, then 3.55V per cell is very reasonable end charge voltage.


About LVC.
Is there a way to change LVC level?
The manual says: "LVC is set to 2.5V at 0C temp, 2.6V at 25C temp and 2.7V at 50C temp."

But this LVC will mean different DOD depending on load.
For example 2.7 LVC at 0.3C will be 100 DOD, and at 3C will be 85 DOD.
(attaching sample picture)

That means that LVC that are perfect for high C applications, can be destructive for low C applications.


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## dimitri (May 16, 2008)

Generally EVs are high C rate applications, with pronounced voltage sag during acceleration. LVC on MiniBMS was carefully picked to avoid premature alarms, while still allowing safe voltage range at the discharge curve. Its not destructive if you don't stay below 2.5V at no load. You can dip well below 2.0V under load, but as long as it bounces back above 2.5V then you are fine.

I imagine even a light EV like scooter gets above 1C during acceleration, no?

P.S. There is no way to change LVC level.


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## polodiy (Oct 25, 2015)

It's commuter type scooter with 50 amp rated motor.
I don't think it will reach even 1c of 100ah pack. (will need to do some testing though)

2 questions:
1. Is it possible to place custom order for higher LVC? (if yes, what's the minimum Cell Module Quantity)
2. If 1st not possible, the HousePower BMS has protective LVC = 2.9V per cell, is it measured per cell level or per pack level?


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## dimitri (May 16, 2008)

polodiy said:


> 2 questions:
> 1. Is it possible to place custom order for higher LVC? (if yes, what's the minimum Cell Module Quantity)
> 2. If 1st not possible, the HousePower BMS has protective LVC = 2.9V per cell, is it measured per cell level or per pack level?


1. No
2. Pack Level.

Why are you trying so hard to change LVC level? Default LVC is good for cell protection, what makes you think you even have a problem to solve? If you want to be sure you have enough capacity to avoid 100% DOD, then use Coulomb counting SOC gauge like our EV Display.


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## dcb (Dec 5, 2009)

Not sure why so much pushback on the hvc/lvc issue, plenty of good reason not to want to push your battery to the stock minibms levels. Plenty of good reason to expect a cell level bms to handle it.



dimitri said:


> Sorry, this is no longer an open source product.


maybe this thread should be closed since it was/is a bait and switch, and users directed to the other thread.


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## polodiy (Oct 25, 2015)

dimitri said:


> Why are you trying so hard to change LVC level? Default LVC is good for cell protection, what makes you think you even have a problem to solve? If you want to be sure you have enough capacity to avoid 100% DOD, then use Coulomb counting SOC gauge like our EV Display.


It's good for cell protecting for high C rating. Lower C rate applications will benefit from higher LVC value.

You stated it yourself when designing MiniBMS in 2009.


dimitri said:


> In case of LVC, head end controller will interpret LVC signal against discharge current and decide whether to trip soft or hard alert, for example *LVC event at 3C-5C can be a soft alert, but same LVC event at 1C will be a hard alert.* Both situations can be compensated against temp reading. All parameters can adjusted by user depending on pack size, temp limits, etc.


By adding custom LVC option your BMS solution will be more valuable for lower C rate applications which can bring you more business/customers.


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## Zmazo (May 4, 2015)

From the circuit you posted at the beginning of this thread, the shunt circuit is always active if the voltage is above the threshold. Your circuit might be balancing while the pack is charging, but it is also discharging until all cell drop below the threshold.. 
This design is wasting a lot of energy


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## AntronX (Feb 23, 2009)

Zmazo said:


> This design is wasting a lot of energy


It does not. This is literally how everyone else does it (Tesla, Volt, etc).


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## bwjunkie (Jul 31, 2013)

Zmazo said:


> Your circuit might be balancing while the pack is charging,


This is an "almost never" scenario. For most of the life of your battery pack the balancers will never turn on because they will not need to. The cells in the pack will rise to the top together and your charger will shut off under it's own authority, which is why it's possible to run without a BMS. the HVC/LVC conditions are primarily a safety mechanism for rare circumstances.

josh


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