BMS issue, not charging?

[iovaykind]

Figured it'd be much quicker to ask the question here and get a response than through email with the supplier who can barely speak english.

I got this BMS:
http://item.taobao.com/item.htm?id=15894708275

Anyway, the connections seemed simple enough, the negative of the battery goes to B- and the P- goes to the negative of the charger. All balance wires are hooked up correctly and I can read each individual cell voltage through the legs on the BMS. However, when I plug in the charger, it doesn't start charging. Charger charges fine when I connect straight to the pack, just not through the BMS, so I know its not an issue with the charger.

I use a bulk charger, similar to the BMS battery ones.

Here are some symptoms..
Plugging in charger + to battery + and then charger - to P- nothing happens. I think check the voltage of the charger, and it drops from 66v (16s lipo) to 30v and stays there unless I unplug the charger from the wall and wait a little bit and plug it back in.
There is no continuity between P- and B- on the BMS itself, and all cells are within 3.7-3.9v each.

Anyone have a similar BMS and could give me ideas as to what's going on?

 

[heathyoung]

That seems pretty strange - I would expect that the charger voltage would only sag as far as the current terminal voltage of the cells if it was properly limiting.

What happens when you just have the charger connected to the positive terminal of the BMS and the P- terminal (with no battery attached)? Does anything get hot? Sounds like there is a short somewhere, the voltage between B+ and the charge port should be the cells terminal voltage (it will be going through the body diodes of the mosfets).

 

[iovaykind]

It's not the charger voltage sagging.. something about the BMS caused the charger to "Switch" to 30v and it doesn't switch back to 66v unless I unplug it from the wall and let it sit a few seconds.

The BMS doesn't have a positive terminal. Looks to be a "bleeding" type BMS.. but its so weird that there is no continuity between B- and P-

The first three fets near B- have continuity and the last three fets have continuity with P- but nothing between the two sets of fets.

 

[agniusm]

Figured it'd be much quicker to ask the question here and get a response than through email with the supplier who can barely speak english.

I got this BMS:
http://item.taobao.com/item.htm?id=15894708275

Anyway, the connections seemed simple enough, the negative of the battery goes to B- and the P- goes to the negative of the charger. All balance wires are hooked up correctly and I can read each individual cell voltage through the legs on the BMS. However, when I plug in the charger, it doesn't start charging. Charger charges fine when I connect straight to the pack, just not through the BMS, so I know its not an issue with the charger.

I use a bulk charger, similar to the BMS battery ones.

Here are some symptoms..
Plugging in charger + to battery + and then charger - to P- nothing happens. I think check the voltage of the charger, and it drops from 66v (16s lipo) to 30v and stays there unless I unplug the charger from the wall and wait a little bit and plug it back in.
There is no continuity between P- and B- on the BMS itself, and all cells are within 3.7-3.9v each.

Anyone have a similar BMS and could give me ideas as to what's going on?

I don't know how you guy's but i would expect to connect P- to controller and not the charger. Charger - has to be marked as C-, there is your problem i think if you not burned your BMS yet. Get some high res pics of both sides of the board.
EDIT:
On a link BMS has 2 places to solder your wires, i found similar with three:

Now that i read about few BMS looks like some of the are connected to controller and charger on the same P-. Which way do you connect to the BMS in steps? First balance, than charger + than battery to BMS and then charger - to P-?
I think sometimes it matters.

 

[iovaykind]

This BMS board only has 2 ports, B- and P- There are no ports in the back if that's what you're wondering.

The way I have it set up is that battery positive is connected to positive of charger, and then negative side of the battery goes to B- on the BMS, while P- comes out to the negative wire of the charger.

P- doesn't work for connecting to controller either, I tried that already.

 

[agniusm]

What i meant was the sequence of connecting stuff. I heard somewhere that on some BMS it matters in which order you connect balance wires, negatives and positives. Don't know if that is reliable info.
I had a 13S smartBMS from BMSbattery and it would not output to controller nor charge. I went disconnecting battery and charger and reconnecting and it would work, then for some reason when battery would fully charge, BMS wouldn't let output to controlled, strangely enough after couple of hours everything was working again. i could not be bothered with that, bought BMS from cell man and had no problems with charging since. Try connecting in the fashion i described above. Another thing is to check all 16 cell voltages. Perhaps it balances them and switches off the charger. Try connecting balancing port and leaving it for a day, than connecting your charger again.
I, myself done buying cheap BMS, not worth the hassle and time and in the end you buy a better product.

 

[iovaykind]

I had much higher hopes for this BMS. I tried leaving it for the whole day, but it doesn't balance the cells unless a cell reaches 4.18v, then it starts bleeding. I'm hoping that by charging the battery itself, when the first cell reaches 4.18v, things will start kicking in and it will work. For now, I'll have to keep testing.. I tried the connection method you mentioned with no avail. I appreciate your help though.. does cell_man provide lipo BMSes?

What makes me think this BMS works well is because I know it is used in a bunch of vehicles.. this BMS is exported in bulk all the time, and I'm sure there's just a "rule" i'm not following which causes it to not work. Was hoping someone went through this already and figured out the right method.

 

[dnmun]

you only posted a link to the website. post a picture of your BMS.

what is the gate voltage on the mosfets? measure the voltage on the transistor side of the optos from the top to the bottom to see if one is bad.

 

[iovaykind]

How do I measure the voltage on the fets? A quick how to would be good here.. I always had issues with fets and how they work (in theory I do but when it comes to using a multimeter on these things I'm at a loss)

Uploading pics of front and back, but they look exactly like the BMS in the link.. gimme a sec.

Front

Back

 

[999zip999]

All I see is a black wire and a thumb.

 

[iovaykind]

sorry, always forget to resize the photos (i forgot where i read on this forum, to pick a theme and you can see pictures even if they are large.. cause i see them just fine)..

anyways, resizing now (tethering my phone cause internet's down due to sandy).. any help?

Edit:
I turned them into urls.. so click on them and you'll see the pics.

 

[iovaykind]

I'm wondering if maybe these BMSes have a built in "safety" feature? One cell is at 4.2v while another is at 3.9v.. perhaps it knows this and doesn't allow further functioning? I'm pretty much out of ideas here

 

[dnmun]

so this is a new battery you are building? did you short all the cells together before you assembled the pack?

the BMS functions to turn off the charging mosfet when the voltage reaches 3.9V on any cell. how that one cell got to 4.2V is a mystery. but nobody has ever seen this BMS before either.

just sounds like you never balanced the cells together before you built the pack up.

 

[Gregory]

Could your charger be putting out too many amps causing the bms to shut down from over current?

 

[iovaykind]

Its lipo, not lifepo4. Balances at 4.2v/cell and shouldn't be an issue with amps because it isn't outputting either..

 

[iovaykind]

Still no luck :/ manually balancing the cells now, hoping the BMS doesn't work unless the cells are within x amount of voltage for protection of sorts. Once manually balanced to within .02 or .03v, if it still doesn't work, I'm SOL. Anyone ever use a BMS like this?

 

[iovaykind]

I think I'm onto something if anyone can help me figure out if my hunch is right. I think I was sent a lifepo4 BMS and not a lipo BMS.

http://item.taobao.com/item.htm?id=15894708275
http://item.taobao.com/item.htm?spm=2013.1.w6079399.43.Vs8qgY&id=12444766446

So these both look the same, but ones for li-ion the other for lifepo4. I am basing my hunch off the fact that I can't get this BMS working for the life of me, and the dimensions (110mm vs 102mm for length) of my BMS match the lifepo4 one, not lipo.

Anyway, if the BMS is registering all the cells to be overvoltage (4v/cell right now) then it'll obviously cut off any ability to charge. I want to check if its a lifepo4 BMS

One way I'm thinking about doing it is riding it to school and back tomorrow, and then some more.. to bring the cells below the 3.75v overcharge cutoff function of the supposedly lifepo4 BMS. just worried that when i dip below 3.75v/cell, the BMS will keep discharging the cells.. and obviously I dont want to run any cells below 3.6v if at all possible.

so another way... i want to ask if there's a way of checking mosfet voltages on each leg, and if so, what the procedure is, to check if they are detecting overcharged cells. please let me know if you have an idea of how to check for overvoltage cells.