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

[fechter]

Hi all!

Can I put a IDL2 in parallell with the 2-color diod? So that one colour of the diod will pull one of the optos, and the other colour will pull the other opto.
This way I can easily put a small relay on each of the optos. Any ideas on if it would work ?

Regards
/Per

I'm not really clear on what you are asking. The red/green LED is configured so that when one is on, the other is off. When the first cell reaches the target voltage, the red/green LED will switch at a high frequency to throttle the current, so driving a mechanical relay won't work.

What do you want the relay to do?

 

[pm_dawn]

Hi !

Well I was thinking in terms of using the latched green at end of charging as a way of turning of the charger on the line input.
But as you say I would start flicker on/off as soon as the first cell gets full.

But I was also thinking about using an arduino to read the green led, and then have the arduino to control a relay or contactor.
In this case I could set up the arduino to sens the first green pulse and make sure that the charger goes from Bulk to balance charge.
Then when the green has been latched (is there a way to know that ? maybe when green led has been on for 5 seconds?), turn of input power to charger.

The reason I would like to use an IDL2 is to achive isolation between the BMS and the arduino.

Best Regards
/Per Eklund

 

[fechter]

I see. It may be possible to get a signal off the SCR which latches the LED green. This won't affect the ability to throttle the charging current, but would allow you to kill the charger when the auto shutoff trips. Let me think about that.

 

[julesa]

Damn, out of stock again... guess I've gotta stay on top of these when they come in.

Fechter,
My battery pack has an 'on' switch I would rather use than my controller's e-brake line for LVC. It carries full pack voltage, but the current it sees is limited by a resistor. I was thinking of putting a pnp transistor in series with the on switch, hooking the base to one side of the BMS' LVC switch, and hooking the other side of the BMS' LVC straight to BMS vcc . What do you think?

 

[fechter]

You'd be limited to a pack voltage of 60v or less. You'd also need a resistor from the base to ground to pull the transistor on. I'm pretty sure the opto output can pull the base up enough to turn the transistor off. If you need a higher voltage, you'd need to protect the opto with more circuitry.

 

[ELETTRONICABERTINI]

Good morning everyone, I'm new and I'm using an automatic translator I apologize for mistakes.

I am in possession of an electric scooter 4000w with 20 cells TS 55Ah, I changed the charger of TS which works badly with a charger bought the "EV Components" from 60V-15A built very well, with the charger of TS I ruined two cells in only 400 kilometers.
I would like to install the BMS with minimum voltage to 2.1 V and 1000mA as shunt.

What do you think you have advice?

Excuse me for English Incorrect

MB

 

[julesa]

You'd be limited to a pack voltage of 60v or less. You'd also need a resistor from the base to ground to pull the transistor on. I'm pretty sure the opto output can pull the base up enough to turn the transistor off. If you need a higher voltage, you'd need to protect the opto with more circuitry.

Perfect. Thank you!!!

 

[fechter]

I am in possession of an electric scooter 4000w with 20 cells TS 55Ah, I changed the charger of TS which works badly with a charger bought the "EV Components" from 60V-15A built very well, with the charger of TS I ruined two cells in only 400 kilometers.
I would like to install the BMS with minimum voltage to 2.1 V and 1000mA as shunt.

What do you think you have advice?

Excuse me for English Incorrect

MB

The BMS circuit should work fine for your application. Right now, it is only available as a bare board and you have to build it yourself. If you are good at soldering, you should be OK. Otherwise, Andy might be able to supply you with a fully built one. For large TS cells, the 2.7v minimum may be better.

 

[ELETTRONICABERTINI]

The BMS circuit should work fine for your application. Right now, it is only available as a bare board and you have to build it yourself. If you are good at soldering, you should be OK. Otherwise, Andy might be able to supply you with a fully built one. For large TS cells, the 2.7v minimum may be better.

Thanks, ok I will use 2.7 V as the minimum voltage.
How to set the charger ( "EV Components" from 60V-15A) to run properly with the BMS?
The BMS will try to assembling myself, albeit a little later with the age I have yet to be hospitalized, at least I hope so.

Where and how best to order all the materials?

Thanks to all

and sorry for my horrible english
Maurizio B.

 

[fechter]

The board is available here:
http://www.tppacks.com/products.asp?cat=26
Below the item description, you'll see something called 20 Channel BOM, which is a list of parts needed for 20 cells.
This list is for Mouser catalog numbers and you can import it into their BOM import tool to generate a detailed parts list. If you are outside the US, you may want to find the equivalent parts from a local supplier.

It is a farily challenging task to build the board and it is easy to make mistakes. It may be a good idea to get a few extra parts.

 

[boostjuice]

Dear Fechter/Gary,

I currently own and run two of the V2.2 BMS boards (16S config). I am looking to update my V2.2 boards to V2.6 in the sections that will improve performance. I am happy to flywire and/or otherwise 'hack' the current PCB to accept additional components that may be needed.

-I have already replaced the 75k/182k voltage dividers feeding the LM431 Adjustable Zener Shunt Regulators with the updated 120k/330k combo so as to lower the per-cell max charge voltage from ~3.69V to a more friendly/life conserving ~3.55V.


To save me reading through a ridiculous amount of posts could you please explain;

-The purpose/reasoning behind the updated inclusion of Q2, D3 and R12 as pictured on the V2.6 schematic?

-The removal of the 10uF capacitor [C2] from V2.2>V2.6?

-The purpose/reasoning behind the addition/removal of components and the resulting voltage divider interaction between R6, R7, R8 and C2 (V2.6) in comparison with the setup in V2.2?

-Anything else i may have missed that is worth updating.

Which parts are worth changing/updating?
I remember reading a post months ago about the newer BMS revisions having reduced/increased duty cycle or frequency of the charger control fet so as to reduce component heating or something. That sounds like something worth updating. If you could explain it again that would be great

The areas of change that i need enlightening about are circled below;

Cheers!

 

[fechter]

Those changes were supposed to keep the frequency from going too high, but if your present charger is 'happy' with the 2.2 arrangement, I wouldn't bother changing it. Also note that R3 was later changed to 4.7k to make the auto shutoff more sensitive. Q2 and D3 make a voltage regulator to protect U1. This won't change performance but was added as a safety feature. As long as the voltage difference between the pack and the charger output stays below about 25v, it shouldn't be a problem.

 

[boostjuice]

Thankyou Fechter for your ever continuing technical support!

 

[Klaus]

I have a question that I can't seem to find the answer to. If you considering a series string of 40AH LiFePO4 cells, the charging current for such a pack is going to be in the 10A to 20A range. The BMS being discussed here will only shunt 1/2A, leaving the rest of the charging current to go through the shunted battery. Is this BMS for a fixed voltage charger where the charger voltage is set very close to the fully charged pack voltage? Is the assumption that as the batteries get close to fully charged that the current drops to the point where the 500mA shunt is adequate to keep cells that fill early from over charging? Thanks for answering my neophyte question. I've spent several hours going through this thread to find answers.

 

[julesa]

I have a question that I can't seem to find the answer to. If you considering a series string of 40AH LiFePO4 cells, the charging current for such a pack is going to be in the 10A to 20A range. The BMS being discussed here will only shunt 1/2A, leaving the rest of the charging current to go through the shunted battery. Is this BMS for a fixed voltage charger where the charger voltage is set very close to the fully charged pack voltage? Is the assumption that as the batteries get close to fully charged that the current drops to the point where the 500mA shunt is adequate to keep cells that fill early from over charging? Thanks for answering my neophyte question. I've spent several hours going through this thread to find answers.

My understanding is that this BMS passes full charger output current through all cells until one of the cell groups' voltage hits 3.7V (?) and one of the shunts becomes active, at which time the FET starts switching and limits total pack charge current to about 500ma. Then the rest of the cells continue charging at 500ma until they reach their shunt turn-on voltage.

http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=5416&p=125384&hilit=PWM#p125384

The build instructions on tppacks.com explain the process in much finer detail.

Not sure why I'm seeing pics of some with smaller resistors lately... I guess maybe some have been modified to shunt less than 500mA?

 

[Roy Von Rogers]

In case someone needs a version 2.3 of this board go to "Items For Sale".

Roy

 

[Klaus]

Thanks, julesa! I had missed that the BMS also controls the charging source. D-oh! I just looked at the schematic again and it's making sense now. The return side (-) of the charger has to pass through a power FET which is switched according to the charge level of the pack.

 

[shinyballs]

A few questions to the "even newer..." gurus:
My balancing wires are 22awg of uneven length – between 12 to 38 inches with 1A inline resettable fuses(http://www.allelectronics.com/make-a-store/item/RXE-065/RESETTABLE-CIRCUIT-PROTECTOR-0.65-1.3-AMP/-/1.html). Shunt to use is 1A.
How does this setup affect balancing? Will it still be able to fully bypass all the channels, ensuring that each cell reach a full 100% charge level?
I’m concerned about the shunt current being close to the fuse rating that it will trip the fuse. If that happens, I will just lower the current from my Power supply charger, right?

p.s. Not sure if this is relevant… I’ll be only using the bms for charging/balancing(Not for lvc) but will still completely populate the board. It will be cooled by force-air and/or heatsink plus adequate ventilation.

 

[fechter]

The resistance of the wires should not be a big deal, but the polyfuses look like they might be rated a bit low to carry a full amp. You might look on DigiKey or Mouser for a 1.5a rated version. With resistance in the tap wires, the voltage drop in the wire may add or subtract from the cell voltage, so the cell could go slightly higher than normal but it shouldn't be a problem. If the cells are well matched, there is almost no current in the tap wires. The two end wires (pack + and pack -) should be heavier, since they carry the full charging current.

If a polyfuse trips, it disconnects that line, so a cell could go over the set point voltage. It will not shut off the charge current.

The LVC doesn't affect any of this.

 

[baerfoot]

I am a newbie here and tried to find some answers, but did not seem to find what I was looking for. I am looking at using this BMS system for my 72V 100 AH Hipower pack.
What is the best voltage setting for the charger, for a 10 amp constant current constant voltage charger like this one from Quick Charge:
http://02a27d4.netsolstores.com/onboardchargerslarge253540amp.aspx?variation=142
to use with the BMS system.

 

[fechter]

I am a newbie here and tried to find some answers, but did not seem to find what I was looking for. I am looking at using this BMS system for my 72V 100 AH Hipower pack.
What is the best voltage setting for the charger, for a 10 amp constant current constant voltage charger like this one from Quick Charge:
http://02a27d4.netsolstores.com/onboardchargerslarge253540amp.aspx?variation=142
to use with the BMS system.

For 24series, you need something over 92v. I'm not sure what the actual output of those chargers will be, but I would guess you need one of the "gas" cycles to get high enough. Most lead acid chargers will be just a bit low. You might find a voltage adjusting pot inside the unit.

 

[Ypedal]

In the process of hooking up my 24 channel BMS for it's final resting spot and plan to box it inside a lexan enclosure, assuming a 5 amp charge rate, how much air flow will the resistors need to prevent this thing from meltdown ?

Would a row of 1/2" holes all along the top do ? or will this require forced air ? :lol:

Will be bolted to this :
http://www.endless-sphere.com/forums/viewtopic.php?f=6&t=11410&start=75

I have tested almost every charger in my collection in series with each other and have found a combination of a 48v power supply and a 36v ebk 2amp charger that goes high voltage enough to get the pack to ballance.. the rest of the time i will be using 3 x 24v soneil 5 amp units for a 95% charge..

 

[fechter]

It's not the charge rate as much as the shunt current. If you have the 500ma shunts, it will get really toasty without a fan.
I've seen somebody do it before with just a row of holes, but there were signs of heat stress. With the 250ma shunts the heat is much less. The board really only throws off heat when the cells are balancing. If you have well matched cells, the balancing time may be pretty short.

On the "to do" list is to make a fan interface on the board. I think even a very small CPU fan will be good.

Another possible approach might be to use some silicone glue to attach an aluminum bar to the resistors, then add some heat sink to the bar. The idea here is you might be able to completely seal the board inside a box, but have one side of the box include the aluminum bar to carry the heat out (untested theory).

EDIT: I see you have the smaller shunt resistors. I think you'll be fine with a row of holes. Just keep an eye on the temperature when you run it the first time.

 

[Doctorbass]

Right Now i'm assembling a 40s Version using one 24s and one 16s xtra board. the charge current will be 148Vdc with a zivan.

It will balance 40 x thundersky 100A cells in a Mazda 3 EV conversion.

I heard a bit about High EMI generated bu the controller and Dc wound motor that may cause spikes in the balance wires for some digital BMS.. I just wonder if that Analogue BMS may have similar problem...

The 40s version will be in an aluminum case and the balance wire will be shilded and grounded to the BMS box.

I used DB44 connector ( same as DB25 but with 3 row of pins and 44 pins total for the 41 balance wires I think that to carry 0.5A it will be just enough. I also have 22 gauge between the connector and the BMS board for around 1 feet. I measured around 10mV loss at 0.5A that seem ok, and will use 18 gauge from the cells to the bms connector.

For sure, i'll use heavier wire for the negative and +148V charging lead.. probably 10 gauge since that charger will handle 10-20A constant.

I like the idea of resettable fuse, I’ll put one close to every cells balances taps before linking every balance wires.

I’ll try to document that 40s project.. I guess it may interest many EV converter


I also got some FDP2532 mosfet from digikey. I'll put 3 in parallel on the BMS pwm control . will the gate driver be able to hold 3 gates?

Doc

 

[fechter]

I also got some FDP2532 mosfet from digikey. I'll put 3 in parallel on the BMS pwm control . will the gate driver be able to hold 3 gates?

Doc

No problem. The gate driver should have plenty of juice.

I'll be interested to hear how that works out.