lithium battery BMS... are any of the Chinese BMS offerings good above 100 Amps?

KenMorgan

so in the process of building my new lithium battery bank I have already had a BMS fail (or possibly bricked by its own program).  It had about three or fours hours of charging on it.   After tp balancing the batteries and building the bank with the BMS wiring etc.  I was using the bank to power my prototype battery heater setup to see how hot, (or not hot) the aluminum panel that I am using as a base plate/ heat sink for the batteries would get at the current ambient temperature of 18°C.  

heater specs:  8 x 25 watt 12 volt pads attached to the bottom of the 6mm (smidgen less than 1/4") plate with the heat pads taped to the aluminum with kapton tape for testing purposes.  this is controlled by a temp controller that is adjustable in .1°c increments  the pads are wired 4s x 2 and I was testing temp rise/final temp between the two heater packs wired in parallel vice series  (48 volts vice 96 volts) and current draw/Watt hours used via a hall effect cell.

when done testing on the draw side I decided to recharge the pack using a magnum 4448 that I just got back from repair.  I set the magnum at CC/CV and set the voltage for the recommended voltage (thanks McIvor) and it and the BMS proceeded to charge the pack to about 76% at which time the BMS stopped charging for some reason.  end voltage was still to low to trip the BMS into shutting off.  thinking my BMS parameters were off I started investigating and regardless of what I did it would not start charging again (monitored via Bluetooth interface)   I tried varying the end voltage settings, tried adjusting the inverter to a higher voltage charge regime, trust me over 5 hours went through all the options.  in the end I unhooked the BMS in accordance with the makers plug in/unplug requirements (at its sense wires plug into the BMS, and then the actual batter minus connection.)  From that point forward it would not restart for any reason nor would the Bluetooth dongle turn on, so now I cannot even monitor the cells.

I am studying this BMS maker on another forum that is primarily a lithium battery/BMS specialty forum and a lot of issues have cropped up it seems in the last three years since this maker came out.  and after searching many many threads it seems to me that no matter what BMS you go with...American designed/made, European designed/made, Chinese designed/made (over 50% of them are made their regardless of design location),   they all have trade offs and it seems that any BMS that is touted as being for a 48Volt system and over 100 amps charge or dischage all have major issues.  the most expensive I have researched is over 1000 USD  from the states and anything that is similiar is the same but none of the "high end ones deal with over 100 amps unless theya re a contactor design.  (IE huge freaking magnetic relays)  any that are mossfet based and considered high end seem to top off at 100 amps.

now my max draw has to date been about 60 amps, so quite a bit below 100 amps but I chose to buy a 200 amp unit so that I could "derate it " for safety sakes....

any body got any ideas on lithium BMS's or insight? 

Cheers

Ken

KenMorgan

another issue that crops up is with the contactor designed ones is that the abrupt shutoff of the charge circuit can destroy solar controllers and the way to navigate this is a complex equation involving actual coding and hardwiring the inverter, and solar controllers together via one of half a dozen communication protocols that it seems nobody agrees on.  one makers CANBUS or UART or serial or one of several others....everything from the inverter to the solar controllers to the BMS themselves nothing shares common gournd, yet they all have interfaces that are supposedly set up to talk to each other...(bullshit marketing hype for sale sit seems to me).  They are all totally different from one another even though neither of the makers makes the others products... you would think that they would embrace the ability to work together to make their products more desirable to the buying public.  the only guys that get this to truly work are breadboarding circuit cards and hand writing their own protocols... they are almost required to use a rasberry pi, an ardunio (spelling might be off)  just a bit beyond what I am willing to read up on at this point in life.

mike95490

And you (sadly) have "discovered" one of my major beefs about Li batteries, the BMS is generally a P.O.S.  Dozens of little wires with lame terminations, PCB's that may or may not have gone through any QA after being manufactured, and sketchy engineering that may or may not account for 5 years of ageing in the field.
 I'm unable to offer a solution, other than manual measurements of the pack monthly and going with a top or bottom balance scheme and hoping that you don't have a fault that needs a BMS to protect the battery. 
 I'm sure others will chime in with some suggestions.

Dave Angelini

The problem is also the battery has to safely take high charge and discharge currents. Either by using multiple battery banks or limiting the I/O current if you are using something like a Schneider XW or larger. It will surge and load 12KW for a minute. It has a charger that has 140 ADC. I saw first hand, the LG RESU 10KWH battery destroyed by one XW in testing with Schneider 4 years back.

I do not have time for DIY batteries as there are high quality LFP "battery systems" that solved these problems and are simple for my clients and have 10 year warranties. It does cost alot of money compared to LA and may be worth it over a decade or more. That is the metric you have to use for LFP.  If you are a hobbiest, go for it with eyes wide open!

jtdiesel65

I would not use the cheap Chinese BMS units. The soldering jobs on those are ridiculous. On high amp units, many have multiple leads all crimped into one wire lug. Complete hack jobs. 

One option to avoid contactors is to use a shunt trip breaker. Look for some youtubes for examples of how they can be set up.  This guy has one https://www.youtube.com/c/LithiumSolar/videos

The Batrium bms has some published integration with a variety of controllers/inverters. IIRC Rec bms does as well.

What I found was a decent BMS costs money. But why use crappy $79.99 bms to protect a $5000 battery?

KenMorgan

jtdiesel65 said:

I would not use the cheap Chinese BMS units. The soldering jobs on those are ridiculous. On high amp units, many have multiple leads all crimped into one wire lug. Complete hack jobs. 

One option to avoid contactors is to use a shunt trip breaker. Look for some youtubes for examples of how they can be set up.  This guy has one https://www.youtube.com/c/LithiumSolar/videos

The Batrium bms has some published integration with a variety of controllers/inverters. IIRC Rec bms does as well.

What I found was a decent BMS costs money. But why use crappy $79.99 bms to protect a $5000 battery?

not looking at the cheep cheep units, the ones I am playing with are middle of the pack cost wise and I am not adverse to spending more, its just that the larger ones are contactor based and they have their issues as I outlined above.  I will look into this "shunt trip breaker"  you mentioned.  this is wexactly what I was hoping for.  Some information that I had not looked into.  thanks!

Marc Kurth

Dave Angelini said:

...............................................................................................................................................................................................................................................
I do not have time for DIY batteries as there are high quality LFP "battery systems" that solved these problems and are simple for my clients and have 10 year warranties. It does cost alot of money compared to LA and may be worth it over a decade or more. That is the metric you have to use for LFP.  If you are a hobbiest, go for it with eyes wide open!

The mindset difference of a professional vs. a hobbyist perspective is not always recognized.

KenMorgan

Dave Angelini said:

The problem is also the battery has to safely take high charge and discharge currents. Either by using multiple battery banks or limiting the I/O current if you are using something like a Schneider XW or larger. It will surge and load 12KW for a minute. It has a charger that has 140 ADC. I saw first hand, the LG RESU 10KWH battery destroyed by one XW in testing with Schneider 4 years back.

I do not have time for DIY batteries as there are high quality LFP "battery systems" that solved these problems and are simple for my clients and have 10 year warranties. It does cost alot of money compared to LA and may be worth it over a decade or more. That is the metric you have to use for LFP.  If you are a hobbiest, go for it with eyes wide open!

Dave,

you are doing what you do as a business I would not expect you to put something that's not 100% guaranteed into a customers system.  even if the customer agreed to you would open yourself to all kinds of headaches. 

I originally considered buying one of the premade 48 volt battery banks that are available heck they were only a couple of grand more than what i spent to build my own bank, though mine has almost 2x the capacity.  but like any good business that sells something (heavy sarcasm here folks) they immediately get real shy when you ask them to ship them to you in Japan....   

Trust me in the electrical realm I prefer tested and warrantied items over making or assembling them myself.  Now you turn to metalworking and fabrication and I am your man... electrical I know just enough to burn the house down properly    

KenMorgan

So as before I ordered two more of the BMS's along with the "battery monitor" dongle and BT dongle.  Originally I did not order the battery monitor dongle as I thought that I should not need it. I plugged it in pressed the "on" button and the BMS immediately fired up discharge OK, charge not OK, checked the Magnum inverter and it still reads zero amps out.  it turns on and inverts fine, but refuses to charge.  I will setup the batteries on the solar charge controller tomorrow and see what happens.  but I think that I damaged the inverter trying to get the BMS to turn on.  Mind you this inverter just came back from repair whre it was damaged by a lightening strike.  (main board swap)  so it is suspect at this point.   once again with the "battery monitor" dongle,  discharge and BT dongle all work.

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