DIY battery BMS issues

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DaTree   1 mW

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DIY battery BMS issues

Post by DaTree » Oct 24 2019 4:35pm

uhh, i think its all wired correctly but obviously its not because my power connector only reads 16 volts, also the charge connecter reads the same 16v. its wierd because when i first get the reading it can be as high as 36v then i watch as it degrades down to 16v.
i dont know if maybe i need to do some programing with this thing before it will give me my full voltage or what ive done. the balance leads start with the positive lead which is soldered to the positive end of the battery, then each next balance lead is soldered to the negative side on the bus bar for each group then there is a negate balance lead that goes on the negative side of the battery. i followed this diagram, and included pictures with as much detail as i can get. Please haaalp
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amberwolf   100 GW

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Re: DIY battery BMS issues

Post by amberwolf » Oct 25 2019 12:31am

DaTree wrote:
Oct 24 2019 4:35pm
uhh, i think its all wired correctly but obviously its not because my power connector only reads 16 volts, also the charge connecter reads the same 16v. its wierd because when i first get the reading it can be as high as 36v then i watch as it degrades down to 16v.
That means the BMS has shut off it's input and output ports, to protect the cells, as it thinks they are either too high or too low a voltage.

The cells could actually be out of range, or there could be a wiring problem (broken wire, connected to wrong point, etc), or a defective BMS.

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Re: DIY battery BMS issues

Post by john61ct » Oct 25 2019 9:24am

Test the BMS on a known-good pack created with brand new cells

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Re: DIY battery BMS issues

Post by Jonno » Oct 25 2019 11:09am

Unplug the connector and using a multimeter put neg probe on black wire of plug and use the pos probe on each of the white leads. as you move across the white pins towards the red lead the volts should add 4.2v to the total on the meter (total 36v. black and red) If it doesn't then you have a wiring problem or bad cells. If it does then the bms is could be duff.
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Re: DIY battery BMS issues

Post by DaTree » Oct 25 2019 11:51am

The charge connector or the main power connector?

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Re: DIY battery BMS issues

Post by thundercamel » Oct 25 2019 2:17pm

Jonno wrote:
Oct 25 2019 11:09am
Unplug the connector and using a multimeter put neg probe on black wire of plug and use the pos probe on each of the white leads. as you move across the white pins towards the red lead the volts should add 4.2v to the total on the meter (total 36v. black and red) If it doesn't then you have a wiring problem or bad cells. If it does then the bms is could be duff.
Jonno
Agree with this, except we don't know the state of charge of each cell group, and the total will be 48 volts since it's a 13s pack.

Also that JBD style of BMS you have recommends not using the P- port, and just use C- for both charging and discharging. I've wired three of them that way, and they all work fine. Website diagram here.

P.S.
You may want to double up on the number of series connections you have, since that's where all the amperage will be flowing through during discharge. Positive and negative terminals as well. Here's a couple examples I've built:

Image

Image
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Re: DIY battery BMS issues

Post by DaTree » Oct 25 2019 3:37pm

ive check all my cell groups voltages they're all 3.7 - 3.9, im affraid to start charging this thing if ive miss wired it. also when i do what you suggested. negative side of the main power connector and testing each white balance lead. i get 0v for the first three groups then i get 1v on the fourht and 2.2 on the next then like 4 or 5v on the next group ending with 14.3 on the last cell group.

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Re: DIY battery BMS issues

Post by DaTree » Oct 25 2019 3:53pm

ive just swapped the connection points on the bms. from the p- to the second spot on the c-. im still getting the same readings. do i need to charge it? all of my connections look solid.

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Re: DIY battery BMS issues

Post by DaTree » Oct 25 2019 3:54pm

also what are those spacers your using?

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Re: DIY battery BMS issues

Post by thundercamel » Oct 25 2019 3:56pm

Put the negative meter probe on the black balance wire instead of the negative main power connection. Then put the positive meter probe on the first white wire, and work your way up one at a time looking at the voltages.

Do you have a bluetooth or PC interface for that smart BMS?

The spacers and all other parts are in my signature link.
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Re: DIY battery BMS issues

Post by DaTree » Oct 25 2019 4:28pm

i have a bluetooth chip that i havent yet installed. i did what you said and all my cell groups are showing correct volatges. im thinking maybe the under voltage thingy is triggered, that might be why its not working. do i need a pc interface to program this thing? or can i just do everything over an app? my total voltage right now is 51.2v

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Re: DIY battery BMS issues

Post by docw009 » Oct 25 2019 11:22pm

I believe that I bought two BMS from that guy. First one had leaky MOSFET's. Bzttery put out 18V when turned off. COuld sink about 30 ma too. I didn't want that. Bought a second one and it died the first time I put 10A thru it. He promised to do replace it, but he didn't and the paypay window expired. Using an ANnpower BMS now.

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Re: DIY battery BMS issues

Post by amberwolf » Oct 26 2019 1:16am

DaTree wrote:
Oct 25 2019 3:37pm
ive check all my cell groups voltages they're all 3.7 - 3.9, im affraid to start charging this thing if ive miss wired it. also when i do what you suggested. negative side of the main power connector and testing each white balance lead. i get 0v for the first three groups then i get 1v on the fourht and 2.2 on the next then like 4 or 5v on the next group ending with 14.3 on the last cell group.
If you don't read the same voltage at the BMS wires that you do at the cells, then the wires are broken somewhere between the measurement point and the cells.

If you measure the same low voltages on the cells themselves while connected to the BMS, then either they're wired in the wrong order and the BMS is shorting htem out, or the cells aren't "really" charged, just holding a "false" surface charge, and are defective, old, or damaged, so that any load at all on them causes that voltage to "disappear" (or drop much lower).


Alternately, with the BMS shutdown, measureing off the main wire from the BMS gives a false reading because the FETs prevent an actual negative connection from happening, so all the readings are wrong.

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Re: DIY battery BMS issues

Post by DaTree » Oct 26 2019 11:05am

when when i got those weird readding i was messuring from the negative side of the charge connect coming off the bms. but when i test off the black balance lead, and check each white lead after that i get good voltages. the problem comes when i test the charge and power connectors themselves. they only read 16v. i think im just gunna try and charge this thing and see what happens.

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Re: DIY battery BMS issues

Post by DaTree » Oct 26 2019 11:16am

what chargers do you guys use? ive got this thing hooked up to my charger. says its a 54.6v 4a charger. and when i do hook it up i can test the main power lead, which now actually tests at the correct voltage while the battery charger is plugged in. its sittin at 53.8 volts and wont go any higher. then when i unplug the charger it goes back down to 16v. im guessing i have a bad bms or something? unless these some kind of programming i need to do

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Re: DIY battery BMS issues

Post by john61ct » Oct 26 2019 11:32am

Of you are looking for handholding guidance here, you need to get a lot more precise with describing what's going on.

Have you got a known good DMM / volt meter? Ammeter, ideally clamp type?

At exactly which measurement point are you getting the reading?

Exactly what hardware do you have? Why ask what chargers a bunch of random members might have, when what is relevant, is yours, and you don't tell us that?

Link to the specific model listing for each, ideally datasheets, manuals.

And if you are using secondhand cells, it is very likely more than one aspect is faulty at a time, makes things impossible to isolate for diagnosis.

Get at least one 1P string of known good brand new cells put together with tested robust connections, in order to then be able to focus on the BMS issues.


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Re: DIY battery BMS issues

Post by docw009 » Oct 26 2019 11:41am

If the cell voltages are in range, and wiring is correctm you got a bad BMS, which wouldn't surprise me, You can bypass it and charge fully, but it's already half charged and doesn't work,

You can pull the balance connector and reset it just in case the circuit got locked up somehow,

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Re: DIY battery BMS issues

Post by amberwolf » Oct 26 2019 10:29pm

DaTree wrote:
Oct 26 2019 11:16am
ive got this thing hooked up to my charger. says its a 54.6v 4a charger. and when i do hook it up i can test the main power lead, which now actually tests at the correct voltage while the battery charger is plugged in. its sittin at 53.8 volts and wont go any higher. then when i unplug the charger it goes back down to 16v. im guessing i have a bad bms or something? unless these some kind of programming i need to do
You can't charge it thru the BMS if the BMS has the input and output shut off; that's the whole point of the BMS being able to do this, so it can protect the cells against overcharge and overdischarge.

If you measure from the main thick battery negative wire that goes to the BMS, *at the BMS*, and get wrong voltages, then you have a problem with that wire, that it's not connected to the battery itself. Bad connection, wire broken inside, etc. Or it is simply not wired to the battery. Any of those will cause the BMS to believe the cells are wrong voltages and unsafe to use or charge.

If everything is wired correctly, and you get correct voltages *at the BMS itself* on each wire, referenced from the actual main thick battery negative wire that goes to the BMS, then the BMS itself is probably bad.

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Re: DIY battery BMS issues

Post by DaTree » Oct 27 2019 2:33pm

john61ct wrote:
Oct 26 2019 11:32am
Of you are looking for handholding guidance here, you need to get a lot more precise with describing what's going on.

Have you got a known good DMM / volt meter? Ammeter, ideally clamp type?

At exactly which measurement point are you getting the reading?

Exactly what hardware do you have? Why ask what chargers a bunch of random members might have, when what is relevant, is yours, and you don't tell us that?

Link to the specific model listing for each, ideally datasheets, manuals.

And if you are using secondhand cells, it is very likely more than one aspect is faulty at a time, makes things impossible to isolate for diagnosis.

Get at least one 1P string of known good brand new cells put together with tested robust connections, in order to then be able to focus on the BMS issues.
whats a dmm? i have a volt meter and a amp meter (though i dont know how to use it)

my power connector reads 16v.

my charger is a chino special yzpower-42 https://www.ebay.com/itm/283494884759

yea im just not sure what im doing and was hoping to get some guidance from people who might have had issues like this before.
its weird cause i plugged in the bluetooth chip and it produces a signal but when i try to connect to that, it fails. why can things just work for me? i believe i am cursed

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Re: DIY battery BMS issues

Post by DaTree » Oct 27 2019 2:35pm

amberwolf wrote:
Oct 26 2019 10:29pm
DaTree wrote:
Oct 26 2019 11:16am
ive got this thing hooked up to my charger. says its a 54.6v 4a charger. and when i do hook it up i can test the main power lead, which now actually tests at the correct voltage while the battery charger is plugged in. its sittin at 53.8 volts and wont go any higher. then when i unplug the charger it goes back down to 16v. im guessing i have a bad bms or something? unless these some kind of programming i need to do
You can't charge it thru the BMS if the BMS has the input and output shut off; that's the whole point of the BMS being able to do this, so it can protect the cells against overcharge and overdischarge.

If you measure from the main thick battery negative wire that goes to the BMS, *at the BMS*, and get wrong voltages, then you have a problem with that wire, that it's not connected to the battery itself. Bad connection, wire broken inside, etc. Or it is simply not wired to the battery. Any of those will cause the BMS to believe the cells are wrong voltages and unsafe to use or charge.

If everything is wired correctly, and you get correct voltages *at the BMS itself* on each wire, referenced from the actual main thick battery negative wire that goes to the BMS, then the BMS itself is probably bad.
thank you i will try this

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Re: DIY battery BMS issues

Post by DaTree » Oct 27 2019 5:07pm

i have another small question.
i have a 14s bms, can i use that one and just disregard the 14th balancing wire?
also what are some good bms's for 13s systems. if anybodies got any good sources.
i just bought some more batteries so imma needem

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Re: DIY battery BMS issues

Post by thundercamel » Oct 28 2019 8:54am

DaTree wrote:
Oct 26 2019 11:05am
when when i got those weird readding i was messuring from the negative side of the charge connect coming off the bms. but when i test off the black balance lead, and check each white lead after that i get good voltages. the problem comes when i test the charge and power connectors themselves. they only read 16v. i think im just gunna try and charge this thing and see what happens.
This means your BMS is turning itself off. The 16v is leakage like another user mentioned, which hasn't been a big deal for me.
DaTree wrote:
Oct 25 2019 4:28pm
i have a bluetooth chip that i havent yet installed. i did what you said and all my cell groups are showing correct volatges. im thinking maybe the under voltage thingy is triggered, that might be why its not working. do i need a pc interface to program this thing? or can i just do everything over an app? my total voltage right now is 51.2v
Install that bluetooth interface, connect the xiaoxiang app, go to the Battery State page, and scroll down to see what reason the BMS decided to shut down. If that board had temperature probe inputs, I'd say it thinks the temperature is out of range since the thermocouples aren't plugged in, but I don't see any connection for temperature in your picture. The bluetooth app can view almost all of the parameters, but only configure most of the parameters. Temperature ranges on my model for instance are only configurable with the PC interface.
DaTree wrote:
Oct 27 2019 5:07pm
i have another small question.
i have a 14s bms, can i use that one and just disregard the 14th balancing wire?
also what are some good bms's for 13s systems. if anybodies got any good sources.
i just bought some more batteries so imma needem
If it's a smart BMS, it should have a way in the software to tell it how many cell groups you're using. This also requires physical modification, I believe shorting/bridging the top end unused balance wires, not including the red wire.
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Re: DIY battery BMS issues

Post by DaTree » Oct 28 2019 6:56pm

ITS WORKING! its working!!!
yay im getting the correct voltage reading now! i put the charge leads directly onto the battery. let it charge up a lil bit and now the bms is putting all the volts out to my connector. i am soooo happy i dont have to change anything else.
atm im watching as it charges just keeping an eye on the temp and voltage and will pull the plug and wrap this thing back up in some shrink wrap once i hit 54.6v. so theres a bit of a conclusion to this whole charade. thanks for the help everyone. goodbye for now

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Re: DIY battery BMS issues

Post by DaTree » Oct 28 2019 7:05pm

another question, how can i tell wether my charger is actually pushing 4a to this thing? i just put an amp meter on the negative side of my charge connector and only got a reading of 0.01ac whatever that means

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Re: DIY battery BMS issues

Post by thundercamel » Oct 30 2019 8:22am

Hand holding indeed... The smart BMS has shunt resistors built in, and the software can display current flow both in and out of the battery.
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