Reliable BMS

[macgyver0815]

Hi,

I am currently planning two 1000Wh 48V battery packs with 18650 cells
with safe chemistry like LiMnO or LiNiMnCoO.

I read about cheap BMS malfunctions, damaging cells or even catching fire.
Using safe chemistry cells together with an "unsafe" china BMS does not make much sense, right?
The goal would be "no worries" battery packs which could sit unattended for weeks
and be used daily without having to disconnect the BMS or connect external balancing charger
everytime... (not-so-easy-to-open water resistant case)

Do you have any recommendations for a reliable good quality 13 - 24S BMS (only 13S used)?
Discharge current 40A continuous, max. 60A for a few seconds (but higher is better 8) ).
Size of the board is not critical, but it should be rather thin (<30mm).
Bonus would be a digital interface for readout (RS232/485 or so), but this is not too important.

Does not have to be cheap, I'd say max. $300.

Would be great if I could avoid creating my own board...
(which I could, but is lots of work for just two boards and there are so many other things to do )

Thanks!

 

[friendly1uk]

The $25 smart bms from bmsb is worth a look. http://www.bmsbattery.com/smart/330-lifepo4lithium-ion-smart-bms-for-513-cells-in-series.html
For $100 more, they will sell you the pc software so you can make adjustments yourself. The cpu has it's own thread here http://endless-sphere.com/forums/viewtopic.php?f=14&t=48461&hilit=oz890
We have a european forum member who is happy to supply and program these, and has run them to 60A I believe. Capable chap who would likely upgrade it any how you choose. Crossbreak.
I also did a battery build thread with one, though I think I may need to edit my over voltage protection. http://endless-sphere.com/forums/viewtopic.php?f=14&t=56886&p=876585&hilit=yginrut#p876585

 

[macgyver0815]

I am not sure if I can trust a $25 BMS, this seems to be too good to be true :?

IRFB4410 in TO220 is 8 to 10mOhm RDSon, 3 parallel, plus losses in the small traces - this is roundabout 10 - 12W power dissipation at 60A (which is a lot without heatsink)
The "smart" part seems kind of OK at first sight, but the power part looks wimpy and there seems to be no good way to mount a proper heatsink (that small 2 layer board itself is not sufficient )...

I should mention that the battery will be inside of a water resistant case, there is ZERO airflow for cooling and in summer it will easily get to 40°C ambient inside that case (which raises RDSon)...

Thanks for the suggestion, but let's see if there is something better than that

 

[ohzee]

http://endless-sphere.com/forums/viewtopic.php?f=14&t=40774&p=954231#p954231

http://www.ecat.si/

The latest version of the founding power BMS is pretty solid. 2-24s, 100V max, ability to use any cell type and set values you desire.

I like this BMS because I can use my pc , bluetooth or display to see what's going on with each cell. It's under 300 and has a few different
options. Probably the best thing is mucek here on the board provides exceptional support just check out the top link to see it or the link
to his web page for pricing and options.

edit - may be a bit over 300$ us depending on what options you get but in that range and a good value IMO.

 

[dnmun]

foundingpower is also made in china so this guy would not use it. amazed he knows so much about them and does not realize there is no BMS that is not made in china.

maybe he will make one too like the other guys who decided the chinese are not capable of manufacturing things.

 

[macgyver0815]

@ohzee:

The latest version of the founding power BMS is pretty solid. 2-24s, 100V max, ability to use any cell type and set values you desire.

Thanks, this looks pretty good.
Adding external power switch may be possible, but gets a little expensive in total.

This variant with integrated power switch may be suitable and costs $225 (which is fine!):
http://www.foundingpower.com/en/Products/Smart_BMS/2012042353.html
http://www.aliexpress.com/store/product/Programmable-BMS-LTC6803-3-for-48V-batttery-packs-with-12fets/113995_982224234.html

There seem to be many different versions and lots of changes over the last two years... does anyone have experience with this particular one?


@dnmun:

maybe he will make one too like the other guys who decided the chinese are not capable of manufacturing things.

I think you misunderstood me here - I will buy a BMS made in china (or any other country) as long as it is good quality.

There are three things: software, circuit design and assembly.
Each of these is important. If assembly quality is stellar, but for example the balancer can go crazy any time and drain cells due
to bad circuit design or buggy software then it is not reliable :wink:
The technology itself is very simple - but there are lots of details that can go wrong.

does not realize there is no BMS that is not made in china.

An example of a BMS that is at least not designed in china (and potentially not made there either):
http://tritium.com.au/products/iq-battery-management-system/
Looks very solid. But for 16S this costs $840, it is rather large and still needs external power switch.
Or the EMUS BMS - in the same price range, distributed type and way too large for this application.

EDIT:
And of course:
http://www.orionbms.com/products/orion-bms-jr/
but also needs external power switch and is over my price limit...

There are several other distributed ones that are not designed / made in china as well.
Maybe someone in the forum knows something like that, but non-distributed and for medium/small size battery packs.

 

[dnmun]

nope. a BMS doesn't just suddenly fail and destroy the battery. people damage the BMS and destroy the battery. all of the BMS failures i have seen are from human causes. always from shorting or miswiring the sense wires.

there is no need for the BMS to be capable of adjusting the balancing voltage or to provide the cell voltage. there are other ways to track cell voltage. there is never a need to change the balancing voltage.

if you can find a BMS made in the US it would be interesting to see it. it is not really possible to manufacture such items in the US imo.

but i am not a racist about the gains the chinese have made to create a manufacturing economy and drag 400 million people out of poverty.

i have known and worked with many chinese who were engineers and physicists and they were all far more capable than any of the americans we worked with so this idea that the chinese are not capable of manufacturing electronics is just a racist view that is not grounded in fact.

 

[macgyver0815]

@dnmun:

if you can find a BMS made in the US it would be interesting to see it. it is not really possible to manufacture such items in the US imo.

Well take a look at the Orion BMS that I mentioned for $460, the "Made in U.S.A." flag on their website is a clear sign.
The Tritium could be made in Australia (not sure).
There are thousands of good PCB assembly companies in US and Europe and some of these can offer competitive pricing,
I know it as I have worked with some of them in the past.
Completely different example: some well known super low cost boards like the Beaglebone are made in the US and the Raspberry Pi is
made in England (a part of the production). These are mulit-layer + BGA boards, not such simple components like used in a typical BMS.

Many industrial companies have stopped off-shoring and came back (or never off-shored at all)... due to quality and IP theft issues.

all of the BMS failures i have seen are from human causes. always from shorting or miswiring the sense wires.

mmmh OK, maybe you are right.
While browsing various forums, I just got the impression that those cheap "analog" BMS (all those similar to the ones from Besttechpower) that are typically included
with e-bike batteries can fail for no obvious reason while in use or just sitting in storage.
Or for example on the $25 smart BMS there are no protection diodes on the balancer channels - like with the founding power one.
Some bad spikes coming back from the motor - or ESD while handling the battery pack - and they may get damaged. I don't say it has happened already
with this BMS, but is possible.