bluetooth BMS?

[lionman]

They should design the BMS with fewer, but more powerful discharge lanes.

Balancing performance would be a lot better in most situations if they had say 1/3 the number of lanes with 3x the discharge rating.

Just need some circuitry that ensures that 2 groups never connected to the same discharge lane, which some clever engineer could come up with.

Except that lots of people don't want an 8S BMS. 16S is pushing the lower limit for me. Most of my builds are 20S and I'm moving (slowly) forward on a 32S build.

What I wish is that BMS balancing had something to do with the current handling. 50mA balancing is pretty common despite the BMS being capable of 20 amps or 160 amps.

Balancing a 64 Ah pack at 50mA will take forever. It's fine for like 10 Ah, but for larger packs, it's just not enough balancing current. My band-aide is setting the balance start voltage low so that balancing gets a chance to do something on larger packs. The other option is to use multiple BMS's...which I also do.

If you had a 32S BMS that instead of 32 50mA discharge lanes, it had 10 500mA discharge lanes that could be switched between groups as needed then it would balance a lot faster, even if some of the groups had to wait for a chance to discharge.

Another option could be to use the high groups to charge a capacitor and then discharge the capacitor into the low groups. The could cycle very quickly between low and high groups bringing them to balance faster than just burning off energy from the high groups as heat.

[ElectricGod]

I like that idea! Tap into the control lines for each cell and then pass those signals over to a parallel running board that can handle some significant amperage. There would need to be a custom made board for this that uses large resistors and larger SMT transistors, but it would not be hard to design. I think 2 resistors and a mosfet are all you need per channel on the add-on board. Snag the control signal from the gates for each mosfet on the BMS and send that over to the add-on board. The BMS should be none the wiser that it is balancing at 50mA or 5 amps.

Not cheap and not quite what you are talking about but I just happend across these:

https://www.ebay.com/itm/323194962541

I have run across active balancers before...found a couple on aliexpress...can't remember where now. What I remember is they are a good bit cheaper than this auction.

[themelon]

I like that idea! Tap into the control lines for each cell and then pass those signals over to a parallel running board that can handle some significant amperage. There would need to be a custom made board for this that uses large resistors and larger SMT transistors, but it would not be hard to design. I think 2 resistors and a mosfet are all you need per channel on the add-on board. Snag the control signal from the gates for each mosfet on the BMS and send that over to the add-on board. The BMS should be none the wiser that it is balancing at 50mA or 5 amps.

Not cheap and not quite what you are talking about but I just happend across these:

https://www.ebay.com/itm/323194962541

I have run across active balancers before...found a couple on aliexpress...can't remember where now. What I remember is they are a good bit cheaper than this auction.

Not surprising as those do look way over priced.

[izeman]

Yes
No, Yes
Yes
Yes

How do you re-calibrate the BMS?

imho this should be the value for the shunts (got the pics from another guy posted a screenshot on FB)

Capture.JPG (68.44 KiB) Viewed 2748 times

[flippy]

best thing tou can do is use a suitable meter and measure the resistance of the shunt in place. in my experience they are off by 5% easy.

or just hook up a separate DMM amp meter and tune the number until it matches the known good number on the DMM.

[eee291]

or just hook up a separate DMM amp meter and tune the number until it matches the known good number on the DMM.

Exactly what I am planning, that's why I asked.

I bought two of the 24S 40A version and will be replacing the Mosfets to hopefully get 150A through it.

[ElectricGod]

imho this should be the value for the shunts (got the pics from another guy posted a screenshot on FB)

Capture.JPG

I can measure down to 1mOhm with my 4 wire meter. It's not the best meter there is. Zeroing it is a bit hard with the trim control it has from the factory, but doable. I've checked a variety of shunts that I have and they all measure very close to their rated specs. Finding the actual Resistance of my shunts and busses won't be hard to do. So far, I haven't bothered since I assumed I was close to what was already there.

https://www.ebay.com/itm/VC480-Precisio ... meter.TRS0

Cheap watt meters, these BMS and other inexpensive current measuring deoivices are not going to be very accurate. It's very probable they are a few hundred milliamps off or more. An amp meter is only going to give good results if it's accurate. Since the atmel328 (CPU on the BMS) has 12 bit ADC's, superb accuracy will not happen. Expect to always see some variance from what the BMS reads for current and what anything else reads. If I were to get .1 amps accuracy...that would be good enough. I bet if you measured the actual shunts in the BMS and put that value in the BMS settings that you would NOT get accurate current measuring. It's all about the accuracy of the ADC in the ATM328 and that can be all over the place. On may read .1 volts as actualkly .1 volts and another 328 would measure it as .3 volts.

To calibrate your BMS, you can depend on my values to be relevant to your BMS. I can't even depend on the shunt resistance from one of my BMS to be relevant to another of the exact same BMS with the exact same shunts. It could be close, but who knows what the Atmel 328 ADC reads from one BMS to the next.

To get the best results possible: (Do this for each BMS)
1. Get a milliohm meter.
2. Get a decent DMM.
3. Get a shunt with sufficient amperage for your EV.
4. Measure the actual resistance of the shunt with the mOhm meter.
5. Put the shunt inline with your EV.
6. Using your DMM, measure the voltage across the shunt.
7. V/R=I...now you know the real current with some decent accuracy.
8. You will need the USB adapter and a windows PC.
9. Adjust the value in the BMS up or down until you get close to the real results.

If you have a watt meter on your EV already, I bet the real amperage and what the watt meter reads are off a fair bit. Same for these BMS. It would be shear luck that you got one that was dead on.

[ElectricGod]

or just hook up a separate DMM amp meter and tune the number until it matches the known good number on the DMM.

Exactly what I am planning, that's why I asked.

I bought two of the 24S 40A version and will be replacing the Mosfets to hopefully get 150A through it.

Fix the copper busses and use larger shunts too.

[rio9210]

Does anybody has an idea about the password of Android app ? It's not 1234, like someone stated few posts ago. Tried every dumb-style passwords (like 1111,2222, 9999, 0000, etc) but no chance.
I have the english version, I'm clicking (in the menu) the option to change the password, but the old one isn't mentioned anywhere.
BTW, it's a number sequence, no letters.

[Dui, ni shuo de dui]

I see in this thread that some people change the mosfets and shunt resistors on their smart BMS. I kinda wonder why.
I could understand if those things were actually heating, but given my tests this has never been the case.
So unless you are pushing some really, really insane currents through it, I don't really see the point.

Myself, I'm running it at 210Amps continuous and not problem whatsoever, even in hardcore super hot chinese weather it only gets 3-4 degree C above ambiant temperature while riding at full blast for an hour.
A friend of mine pushes more than 500 Amps through the poor 300A rated BMS and we didn't notice any heat building.

So I really wonder if this is actually something useful and not just a silly precaution. I can understand that beefing up the bus bars could be a nice idea given how poorly they are done, but I really see no point in changing the Fets or the shunts. Fets won't heat much if at all if they are not doing high frequency switching (which is the case in a BMS, they mostly act as a big relay to cutoff power), and there are 10 shunts so any current will be divided between those, which, given their individual low resistance, won't generate much heat at all. Those resistor's are designed to actually allow voltage readings while heating as less as possible. They should not heat much, especially since they are 10 of them.

Also, the 10 shunts seems to have been replaced by only 8 shunts on the pictures I saw. Aside from the fact that each shunt will see their individual current levels rising a bit (hence, more heat generated), I wonder if the value has been calculated correctly to take the resistance difference into account (10 shunts to 8 in parallel, not the same total resistance). I guess yes, but I ask the question just in case it hasn't.

As for the accuracy of the power meter readings, they are indeed not super accurate. My smart BMS seem to miss about 5-6% of the total power draw on a full charge. I thought it could be the refresh rate being a bit too low, missing current spikes, but the ADC accuracy also seems like a valid possibility. Just be aware that if you're riding hard you should be careful when the battery meter indicates less than 10% remaining, it can cut off at any moment passed this point since it might not have counted all the power drawn.

[izeman]

I kinda wonder why.

Because we can
But tbh you may be right. It may not be needed but for me personally I feel better with a high quality product and some safety margin. I also can operate the BMS which is rated for 30A in a closed cabinet at 60A constant w/o getting even warm.

[usertogo]

Sorry for not having read every post in this thread, I wonder how is the communication to the developers (this is not open source, right?) is, can proposals for improvements be forwarded? I really like all the things that are being attempted, and think that the possibility to use GPS data to get to distance and speed traveled should be used to also display current and graph of average mobility efficiency in Wh/km .

This would be so convenient in order to attempt tuning and some day maybe integrate an interface to some GPS solutions, and map of charge points to eventually get to some kind of Open Source Volks Tesla Standard Interface (OS-VTSI ?

By the way I have not figured out yet how to set up the smart BMS with some kind of Security that not just anybody with the right APP could simply 'weaponize', make inoperable or destroy my battery?

[izeman]

not open source - no active community - no communication with the (chinese) developers
there is no special security. if someone has the app and is near your bike he can modify all parameters - but how likely would that be ???

[ElectricGod]

Sorry for not having read every post in this thread, I wonder how is the communication to the developers (this is not open source, right?) is, can proposals for improvements be forwarded? I really like all the things that are being attempted, and think that the possibility to use GPS data to get to distance and speed traveled should be used to also display current and graph of average mobility efficiency in Wh/km .

This would be so convenient in order to attempt tuning and some day maybe integrate an interface to some GPS solutions, and map of charge points to eventually get to some kind of Open Source Volks Tesla Standard Interface (OS-VTSI ?

By the way I have not figured out yet how to set up the smart BMS with some kind of Security that not just anybody with the right APP could simply 'weaponize', make inoperable or destroy my battery?

There is a VERY small community (3 people) working on integrating this BMS into an app. The protocols and commands are known and making that data work elsewhere is actually something that is being worked on. I can't say more than this for now, but assume it is being "worked on" and will see the light of day sometime soon.

As for security, the Chinese app has no place for a PIN. The BT module however could take a PIN. I'm currently looking into connecting with the manufacturer to get changes made such as adding a PIN. We'll see what happens...maybe nothing, maybe a lot.

[ElectricGod]

I see in this thread that some people change the mosfets and shunt resistors on their smart BMS. I kinda wonder why.
I could understand if those things were actually heating, but given my tests this has never been the case.
So unless you are pushing some really, really insane currents through it, I don't really see the point.

Myself, I'm running it at 210Amps continuous and not problem whatsoever, even in hardcore super hot chinese weather it only gets 3-4 degree C above ambiant temperature while riding at full blast for an hour.
A friend of mine pushes more than 500 Amps through the poor 300A rated BMS and we didn't notice any heat building.

So far, I have done no modding to these BMS. They seem pretty good as is. I have no complaints about the P- mosfets on them or the copper busses.

https://www.aliexpress.com/store/produc ... 3de22JQESO

or

https://www.aliexpress.com/store/produc ... 3de22JQESO


However these BMS have poor mosfets and the copper busses are too short and NOT soldered down on all 7 of them I have. They need fixing IMHO. While I'm in there doing things the factory should have done, might as well make them as strong as possible!

This is upgraded on pages 18 and 24.

https://www.aliexpress.com/store/produc ... 3de2mMrlYO

or this bigger version on page 25...

https://www.aliexpress.com/store/produc ... 3de2mMrlYO

I've posted previously of what I have found so feel free to reread my posts about the copper not being bonded properly, mosfets not being bonded properly, very low grade mosfets, etc.

If you are getting 210 amps out of a 50 amp BMS that has horrible copper bonding and even worse mosfets AND there are a mere 8 of them rated for 10 amps each, well you are doing something magical. My suspicion is you are confusing the various BMS models presented in this thread. Some don't need modding, others really benefit from it.

[rio9210]

where did you buy the bms from i wouldnt mind getting my hands on one!

https://www.greenbikekit.com/bms-pcm/sm ... ation.html

[rolf_w]

charge balancing is only enabled if the charging FETs are turned on, whereas static is always on...

The manual which came with the JBDTools 1.1 reads:

Balance: turn on balance function.
Chg balance: turn on the balance function during charge. If disabel Chg balance, then static balance, eg: the difference of battery more then 0.4V, then balance work.
Enable is charge balance.
Disable is static balance.

Static balance open condition
1. No charge and discharge current. Just battery and BMS.
( charge current is 0A, discharge current is 0A)
2. Battery voltage more then the balance voltage.
( eg: battery 1 is 3.65V, balance voltage (start voltage) is 3.6V )
3. The difference of battery voltage more then the setting windows value
(eg: windows is 30mV, battery 1 is 3.65V, balance voltage is 3.6V, so 3.65-3.6=50mV more then 30mV, so balance led turn on )


Charge balance open condition
1. In charge stage, have charge current.
( eg: charge current is 0.5A)
2. Battery voltage more then the balance voltage
( eg: battery 1 is 3.65V, balance voltage (start voltage) is 3.6V )
3. The difference voltage of battery and balance voltage more then the setting windows value.
( eg: windows is 30mV, battery 1 is 3.7V, battery 2 is 3.6V, 3.7-3.6=100mV 100mV > 30mV, so balance led turn on)

I'm not ableto make much sens out of this description. It seems neither correct nor complete. Has anyone been ableto figure out the complete balancing algorithm?

r

[Dui, ni shuo de dui]

If you are getting 210 amps out of a 50 amp BMS that has horrible copper bonding and even worse mosfets AND there are a mere 8 of them rated for 10 amps each, well you are doing something magical.

I'm using the 300A BMS, so no magic here.

My suspicion is you are confusing the various BMS models presented in this thread. Some don't need modding, others really benefit from it.

Indeed I did!
I don't know why, I thought it was the same as mine. But looking at the pictures again I see that I was totally wrong. And that you did put 2 other shunts at the back of the PCB for a total of 10, same as the original.
Sorry for this confusion

[izeman]

Has anyone been ableto figure out the complete balancing algorithm?

As simple as i wrote. What else do you need to know?

[Bison_69]

Hi guys,

I would need some help please; I purchased lately a smart BMS 16 - 32S / 200A with the LCD display from AliExpress...
https://www.aliexpress.com/item/Smart-D ... 4c4dKyuqda

In spite of the lack of technical information, I succeeded to install the BMS, the LCD display and link the Bluetooth (which is unstable even using VBMS or Xiaoxiang Android apps) I will probably use the PC version instead with a USB to RS-232 adapter…
https://www.lithiumbatterypcb.com/smart ... -download/

Or the Android to PC soft called “Remix OS’’ (with Bluetooth and etc...)
http://www.jide.com/remixos-for-pc

Now I need to know more about the BMS:
1_ if the BMS is connected such as explained on the seller’s website, will it drain the batteries?...

2_ should I use an Anderson power connector (to disconnect after use)?...

3_ will the BMS detect the charger when applied or do I have to use the Android apps to tell the BMS to go in charging mode?… (which would be ridiculous since it is called a smart BMS)

4_ will the BMS keeps its last programming memory when disconnected from the battery pack?...

5_ In the kit there is a small switch to turn on the BMS… but how do you turn it off?... (unexplained)

Special thanks to Inwo and thundercamel which helped me a lot…

The seller was stating that the LCD display was working with 6 to 20Vdc which did not worked for me… the right voltage is 24 to 100Vdc meaning it can be connected to your battery pack.

My battery pack configuration is 21S10P / VCT4 18650

Here are some pictures of my project:

I took the idea from Tesla... I fused all the cells individually in 10P groups with 0.6mm fuse wire found in England (insulator is FR4) https://wires.co.uk/acatalog/cu_tinned.html and use copper to bridge to mount the pack.
Tinned copper fuse wire amp chart... https://seshusophy.wordpress.com/2016/1 ... fuse-wire/

I also design on CAD a LCD display case to mount on the handle bar… it can be 3D printed (PLA).

LCD DISPLAY CASE - BMS.7z

(113.74 KiB) Downloaded 71 times

Thank you very much for your help.

[Dui, ni shuo de dui]

1_ if the BMS if connected such as explained on the seller’s website, will it drain the batteries?...

Nope.
I've let mine on, with the screen active too, for a whole 2 weeks. I took a picture of cells voltages before and compared with when I came back. The difference was unnoticeable. It would litterally take years to discharge the battery.

2_ should I use an Anderson power connector (to disconnect after use)?...

Yeah, put one between your BMS and the controller.

3_ will the BMS detect the charger when applied or do I have to use the Android apps to tell the BMS to go in charging mode?… (which would be ridiculous since it is called a smart BMS)

It detects automatically. Otherwise you wouldn't even be able to use the regen.

4_ will the BMS keeps its last programming memory when disconnected from the battery pack?...

Yes

5_ In the kit there is a small switch to turn on the BMS… but how do you turn it off?... (unexplained)

Press it for 6 secs. You should hear a long beep.

[ElectricGod]

All my BMS modding stuff is found spread across this thread. I figured people might want to know what I did in one concise place so I made another thread for it.

viewtopic.php?f=14&t=95853&p=1403576#p1403576

[Bison_69]

Hi Dui, ni shuo de dui ,

Thanks you so much for you help!... awesome...

[eee291]

So i just received my 40A BMS from Lithiumbatterypcb.com and this is what it looks like on the inside.
https://imgur.com/a/SYshbIc

Looks like the copper issue was fixed a long time ago. it's just that most Aliexpress sellers still sell the older versions.


I am planning on replacing the Mosfets on the B- side and discharge through the P- port, since the C- Mosfets should withstand up to 40A.

[rio9210]

Sorry for not having read every post in this thread, I wonder how is the communication to the developers (this is not open source, right?) is, can proposals for improvements be forwarded? I really like all the things that are being attempted, and think that the possibility to use GPS data to get to distance and speed traveled should be used to also display current and graph of average mobility efficiency in Wh/km .

This would be so convenient in order to attempt tuning and some day maybe integrate an interface to some GPS solutions, and map of charge points to eventually get to some kind of Open Source Volks Tesla Standard Interface (OS-VTSI ?

By the way I have not figured out yet how to set up the smart BMS with some kind of Security that not just anybody with the right APP could simply 'weaponize', make inoperable or destroy my battery?

There is a VERY small community (3 people) working on integrating this BMS into an app. The protocols and commands are known and making that data work elsewhere is actually something that is being worked on. I can't say more than this for now, but assume it is being "worked on" and will see the light of day sometime soon.

As for security, the Chinese app has no place for a PIN. The BT module however could take a PIN. I'm currently looking into connecting with the manufacturer to get changes made such as adding a PIN. We'll see what happens...maybe nothing, maybe a lot.

So, can we use another bluetooth module (like HC-05) which is more widely supported, which can be programmed with a password ?