14S 5P Battery build - Unexpected BMS voltage output

[gogreenpower]

Hi guys,

Just built my first battery and during some final checks before heat shrinking I've noticed a difference in voltages when measuring the actual battery cells and the XT90-S connector at the end of the discharge/charge wires.

I would have expected that the voltages would have been the same, unless there is some BMS trickery going on I'm not aware of.

I've not charged the cells yet and they all came at 3.4v.

It's a 14S 5P battery and currently the voltage is 47.6 when measured off the actual parallel groups which works out to be 3.4v per parallel group. All good.

When I measure at the discharge/charge plug the voltage is only 43.5v. Does the BMS take a bit off as part of its designed protection systems or have I totally messed something up?

Here is a pic of the schematic marked with where I am measuring said voltages.

https://www.dropbox.com/s/4t7b8j73v36mjm3/BMS.jpg?dl=0

Plus a few of the build in case anyone is interested.

https://www.dropbox.com/sc/27vyj0f6nvdrapb/AADvPLxu9DNmMLuHUkRike-Ca

 

[gogreenpower]

I have swapped BMS's and that didn't change anything, and I've also noticed that its doesn't charge. I get charge voltage to the BMS but that's it.

Then I disconnected the sense wires from the BMS, still no change in the output voltage but it does allow me to charge it.

 

[gogreenpower]

Ok so during charging, currently up to 3.65v per group I've found one parallel group that reads 3.55v, I know it's just dumb/bulk charging at the moment but interesting none the less.

All brand new cells, all started the same voltage, maybe some type of short when I soldered on the sense wires, maybe damaged a cell when spot welding them in series...

I'll wait until it's charged then connect the sense wires again and see if it will balance. If not then I guess I'll be taking it back apart to see what's going on.

Still don't have any leads on why no charging with sense wires attached and less voltage at the discharge plug.

 

[muzza.au]

G'day mate,

The only thing I can see that might be wrong, if I'm seeing it correctly, is that on pictures 27,28 & 29, there is a red wire connected to left of the board (as viewed on pictures 28 & 29) that should be a black -ve wire that goes to the -ve terminal of the battery according to the schematic of the BMS.

ps. I'm thinking of building my own battery, where did you aquire your cells?

Muzza.au

 

[gogreenpower]

G'day mate,

The only thing I can see that might be wrong, if I'm seeing it correctly, is that on pictures 27,28 & 29, there is a red wire connected to left of the board (as viewed on pictures 28 & 29) that should be a black -ve wire that goes to the -ve terminal of the battery according to the schematic of the BMS.

ps. I'm thinking of building my own battery, where did you aquire your cells?

Muzza.au

Hi muzza,

Nice pickup on the wire but its just that i didnt have enough black left, so red it was, it goes to the right spot.

I figured it out, the problem was the first 2 BMS's i tried were not working properly. I've asked for the schematics from bestech, will see if they come through and see what's going on with them.

Anyway, after ripping the pack apart, which is far more dangerous than I thought... I replaced two cells that I thought were the problem, put it all back together and still nothing. I was ready to spit the dummy and just go without a BMS, but then I thought I'd try the third BMS I ordered and it work as expected.

I got the cells from https://ru.nkon.nl, 3 euros a pop for 140 of them. Great service, would buy again from them.

Now I'm off to fit that BBSHD I have a power pack for. Here's the link if you want to have a look. https://endless-sphere.com/forums/viewtopic.php?f=28&t=82576

 

[muzza.au]

I got the cells from https://ru.nkon.nl, 3 euros a pop for 140 of them. Great service, would buy again from them.

From overseas I assume. They would have to be shipped wouldn't they, so how long does it take to get them?

Muzza.au

 

[999zip999]

So 2 bad out of 3 bms ? Now all working ? Good luck.

 

[gogreenpower]

I got the cells from https://ru.nkon.nl, 3 euros a pop for 140 of them. Great service, would buy again from them.

From overseas I assume. They would have to be shipped wouldn't they, so how long does it take to get them?

Muzza.au

It was with FedEx, took maybe one week to get to Perth. About 60 euros shipping.

 

[gogreenpower]

So 2 bad out of 3 bms ? Now all working ? Good luck.

Yeah 2 out of 3, the second one to be fair I didn't solder, just alligator clips and fancy wire knots.... I just wanted to check output voltage and it was 4v less than the battery.

I don't like my chances of this third one lasting so I'm on the hunt for something else, I just can't wait any longer, need to ride this beast