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Issue with bms and active balancer not reading correct voltage

Brandon8792

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Nov 20, 2019
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Hello! I have a unique situation that I don’t think has been posted about.

Let me start out by saying I accidentally shorted the pack out when screwing a terminal down, and a bms lead was under it… burnt the lead in two because my ass ran because I knew chaos was potentially about to happen, but in the end just burnt the bms wire in two, no biggie.

So my pack will read 53v at the main terminals…

Cell 2, 3, and 4 will all read their voltages out (having issues with cell two reading out the voltage to the bms and active balancer leads).

All other cells read out correctly as well, which makes sense since the main terminals read 53v.

When I read the outputs on the pins for bms and active balancer, cell 1 reads 3.3, cell 2 doesn’t read, cell 3 turns to -3.3 cell 4 -6.6 and so on.

What’s weird to me is the polarity is changing, when all the cells are hooked up correct, no reverse polarity happening. So one, I can’t figure out why cell 2 reads correctly on the terminals and the threaded screws, and even the bus bars, but will not read on the bms leads or active balancer leads
But two I can’t figure out why the polarity is changing but not causing issues anywhere else except on the bms and active balancer leads.

All bus bars, terminals, and terminal ends have been sanded, alcohol wiped down, and then rewiped down. Super clean connections, not to tight but definitely tight enough, much more it would strip. 20-25 in lbs.

Also swapped out the bms leads and connectors, and active balancer connectors and leads with new ones, just in case maybe that was causing the issue… still nothing.

I learned there was an issue about this when I hooked up my active balancer and it fried it, I was like bullshit there’s no way… well guess what, there is, because something is off and for the life of me I cannot figure it out.

Please god someone help me figure out wtf is going on here… no cells swelled or anything, everything is normal!!!

I have two other packs hooked up same way, no issues, and on 3rd pack bout to be done same way… I know I’m doing it right but something is just weird on this one.
 

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Your battery is wired wrong. Are you trying for 16S?

In the upper left, you have cell 1 with the main negative lead. Cell 2 looks good but cell 3 is reversed!! That is positive from 2 to positive on 3.

All connections for 16S need to be positive to negative.
 
MisterSandals spotted it. You likely have damaged this BMS as well, they are so sensitive that goofs 99% of the time = cooked.
The momentary Short would not have done much to the cell itself and had it, you'd know it.

Personal Exp as I run both QNBBM & Heltec Capacitive Balancers, using two ring terminals is a Bad Idea. SO I switched up the wire to 14AWG Fine Copper Wire which goes to a MOLEX Block. Then both the BMS & Balancer are routed to the other side of the Molex block. This is more than sufficient for the Active Balancer and the BMS as well without causing any stress.

16S Battery Pack will require a 17 Port Molex Eurostyle Two-Screw Terminal Strips, have to include the negative... LOL.
Link directly to Molex: https://www.molex.com/molex/search/partSearch?query=39100&pQuery=
Available from any electronics supply place NB: Places specializing in Raspberry Pi and similar computing bits/bobs have these and CHEAP !

Below is a 12 circuit model. NOTE it has feet, they come with or without, you will want without.
The ones without feet, have small screw holes for attachment. They can also be split / cut down very easily, so you could break it up as well.
OPTIONAL: Use can use a Ferule to insert the BMS & Equalizer wires into and then into the Molex hole. Otherwise you have to be careful to get both wires in and secure.

Good Luck, Hope it helps.
0391001812_hires.jpg
 
I would of thought it was reversed as well if going by the QR code, but look at the black around the terminal itself and then the tan/grey/white on the other terminal. I also confirmed this with the multi meter, and it is showing correctly.

Luckily I didn’t hook the bms up after the active balancer went up in smoke. And I refuse to hook anything else back up until I can confirm it with the multimeter.

I would swap to the molex had I known beforehand, I guess I should of researched just a little more. However I am lucky the ring terminals are working on the other 2 packs.

I am doing 16s though yes.
 
Okay, I think you are right.

Next question:
Why is the vent blue on cell#3 and not the rest? (Not that the color matters, but is clearly not the same as the others). Just grasping…

It was a replacement cell, 272ah Lishen compared to the 280ah eve. Since they test close in capacity I used them together.

But yeah this is really stumping me
 
This is the worst question (so I hope) that I will ask all day:

What are the individual cell voltages measured at each cell?
 
This is the worst question (so I hope) that I will ask all day:

What are the individual cell voltages measured at each cell?
Lol you’re fine.

They are all measuring between 3.287-3.328 I think. I was going to let the active balancer and bms balance them all back out at high voltage end over the course of a week. Or worse case throw some resistors in discharge some that are over charged or, charge up individual ones that aren’t.

Just can’t figure out why it’s not giving the reading at cell two on the bms n active balancer leads, but showing full pack voltage at the main terminals…

And then cell 3 and up reads negative voltages. With the correct polarity being touched on the bms n active balancer leads.
 
I am sure tou already quadruple checked the balance wires and also measured their voltage without the balancer connected...
 
I can't trace all the wires in a picture .... but isn't the negative wire connected in the wrong place? Looks like there is nothing connected to the main negative and the black wire is connected to cells 16 negative?
 
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I can't trace all the wires in a picture .... but isn't the negative wire connected in the wrong place? Looks like there is nothing connected to the main negative and the black wire is connected to cells 16 negative?
Hmm, yea something is up. Cell 1, the main negative is in upper right. THAT is where the pin 1 negative needs to go, with pin 2 going to the positive (black terminal base) on cell 1 in the very upper right.

Is this wired in reverse from cell 16 and not starting at cell 1 in upper right?
 
Upper left side cell with blue ring around vent port looks reversed. Question is terminal colors assembled wrong by manufacturer or bar code put on reversed side. Check with voltmeter.

I would not put much hope for survival of capacitor pump active balancer. They are 6.3v electrolytic caps so with the momentary shorting and reversed cell I would not be surprised if it is toast. I also would not leave one of the capacitor pump active balancers permanently connected.
 
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Hmm, yea something is up. Cell 1, the main negative is in upper right. THAT is where the pin 1 negative needs to go, with pin 2 going to the positive (black terminal base) on cell 1 in the very upper right.

Is this wired in reverse from cell 16 and not starting at cell 1 in upper right?

Yeah I have it wired in reverse cell on in the top left instead of top right, probably where all my cells are flipped around.

I’m confused on how this may cause an issue as I have another pack I built like this one, no issues.

And I’m still getting 53v on the main negative and main positive. Unlessssss you’re saying that the bms wires need to be moved around, to the other side and that is what is causing the issue, which means my balancer leads all need move around as well…

I bet this might be the issue I think I’m seeing it as I’m typing but I’m still going to post just to confirm *facepalm*

Edit: ^^^^ which also therefore means I did NOT built the other packs this way… and looking at them… that is the issue. Man everything really has to be JUST right on these or you go kaboom lol.
 
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MisterSandals spotted it. You likely have damaged this BMS as well, they are so sensitive that goofs 99% of the time = cooked.
The momentary Short would not have done much to the cell itself and had it, you'd know it.

Personal Exp as I run both QNBBM & Heltec Capacitive Balancers, using two ring terminals is a Bad Idea. SO I switched up the wire to 14AWG Fine Copper Wire which goes to a MOLEX Block. Then both the BMS & Balancer are routed to the other side of the Molex block. This is more than sufficient for the Active Balancer and the BMS as well without causing any stress.

16S Battery Pack will require a 17 Port Molex Eurostyle Two-Screw Terminal Strips, have to include the negative... LOL.
Link directly to Molex: https://www.molex.com/molex/search/partSearch?query=39100&pQuery=
Available from any electronics supply place NB: Places specializing in Raspberry Pi and similar computing bits/bobs have these and CHEAP !

Below is a 12 circuit model. NOTE it has feet, they come with or without, you will want without.
The ones without feet, have small screw holes for attachment. They can also be split / cut down very easily, so you could break it up as well.
OPTIONAL: Use can use a Ferule to insert the BMS & Equalizer wires into and then into the Molex hole. Otherwise you have to be careful to get both wires in and secure.

Good Luck, Hope it helps.
0391001812_hires.jpg
Here's another block option to work with when using a BMS with an active balancer to avoid using two ring terminals at a battery terminal (can cut down for 24v battery bank)
https://www.amazon.com/gp/product/B08VND5XDN/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
 
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