No output voltage after splitting pack

[zerogee]

The pack ( https://endless-sphere.com/forums/viewtopic.php?f=14&t=64348) is split between C9 and C10. I thought things went well until I checked voltages after the split. Need help troubleshooting...


Pack was fully charged and not used since last fall. Before the split the pack was at 53.3V and individual cells resting voltages measured on each cell.

Prior to split.
C1 3.33
C2 3.33
C3 3.33
C4 3.34
C5 3.33
C6 3.34
C7 3.34
C8 3.33
C9 3.33
C10 3.33
C11 3.33
C12 3.32
C13 3.33
C14 3.33
C15 3.33
C16 3.33
This is why I thought cells were well balanced.

After split during charging.
C1 3.48
C2 3.57
C3 3.68
C4 3.70
C5 3.47
C6 3.79
C7 3.79
C8 3.44
C9 3.59
C10 3.50
C11 3.61
C12 3.42
C13 3.64
C14 3.50
C15 3.61
C16 3.51
Charger went from red to green in like 5 minutes then repeatedly turned on and off for maybe an hour (C6 and C7 hit 3.89V, C3 and C4 hit 3.79 during this period) then stayed green. Left it on for a few hours until bedtime. Not as well balanced as it first appeared.

After charging for a few hour.
C1 3.52
C2 3.57
C3 3.68
C4 3.70
C5 3.47
C6 3.79
C7 3.79
C8 3.44
C9 3.59
C10 3.50
C11 3.61
C12 3.42
C13 3.64
C14 3.50
C15 3.61
C16 3.51

Next day resting.
C1 3.51
C2 3.61
C3 3.68
C4 3.70
C5 3.51
C6 3.74
C7 3.74
C8 3.47
C9 3.61
C10 3.53
C11 3.64
C12 3.44
C13 3.66
C14 3.54
C15 3.65
C16 3.55

After the split I can't measure total pack voltage either on the pack or at the power port with the key on. However, individual cells resting voltage are still around 3.33V. I can measure cumulative voltages from C1 to C5 on the BMS then nothing after that. I measure cumulative voltage on the main pack from C1 to C5 then nothing between C6 to C9. I can also measure the cumulative pack voltage on the minor pack from C10 to C14 and nothing on C15 to C16. I can't measure voltage between the two packs on C9 to C10.

To make the split, I cut the battery tab in half after removing that sense wire then soldered my C9 to C10 wire to the tabs. I have continuity on the added wire between C9 and C10. I also have continuity on the sense wire between the sense wire extension and the splice on the center of the C9 to C10 wire.

I had power OFF. I covered all terminals with tape and only worked one wire at a time to prevent shorting. I unplugged the BMS prior to starting.

Any assistance is appreciated. Thanks

 

[Hwy89]

I went back and read your original thread and it sounds like you did everything right. It should have worked.
It seems like the BMS is keeping everything shut down. You said that you unplugged the BMS while you were making the changes. Is it possible that you didn't get the BMS plug seated correctly? Go back to that plug and check for pins that may not be making contact.

 

[zerogee]

All pins are present and straight. Wondering if its possible that those high cells hit HVC and cut current??

 

[Hwy89]

It wouldn't do any harm to do a manual balance with some test leads and a resistive load to draw down the high cells. Then put it back on the charger and see what happens.

 

[amberwolf]

All pins are present and straight.

When you measure those cell voltages, are you measuring them at the solder pads on the BMS itself? If not, I would recommend doing that, so you can see if the BMS is actually seeing the correct cell voltages. If it is not, then it might explain why it is cutting off discharge.

Wondering if its possible that those high cells hit HVC and cut current??

If there is a separate charge and discharge port, then HVC will only cut off charge port, and discharge port will still have voltage.

Discharge port would then only be cutoff with LVC on a cell.

Since you can still charge it, it means the port is not being cut off for HVC, except for when you see the green light on the charger (meaning current on it's output has dropped below whatever threshold is set in it for that).

Since you can't discharge it, it means the output port is being cut off for LVC (meaning the BMS isn't seeing a high enough voltage on one or more of the cell inputs).


Do you have full pack voltage at the battery-side input port to the BMS? (I assume so, since that is shared for both charge and discharge, and it wouldn't charge if you didn't).

 

[zerogee]

I wasn't sure if I could open the BMS or if things would fall apart on the inside with some of those screws.


I can't see the other side. The heatsink is bonded to the FETs.

When you measure those cell voltages, are you measuring them at the solder pads on the BMS itself? If not, I would recommend doing that, so you can see if the BMS is actually seeing the correct cell voltages. If it is not, then it might explain why it is cutting off discharge.

D'OH! That makes sense. I was measuring off the pins on the back of the connector. When checking these voltages on the board it should be on the charger correct?

Do you have full pack voltage at the battery-side input port to the BMS? (I assume so, since that is shared for both charge and discharge, and it wouldn't charge if you didn't).

I measure pack voltage between B- and B+ on the board?
To measure this voltage... charging or not? With the key ON or OFF?

 

[zerogee]

Turns out that my work went well with this split afterall. The problem was with my cheap DVM. The high scale on the voltage is fried. The meter can't read past 20V. I borrowed a calibrated Fluke meter from work (used for certifying welding procedures) it has no scale and adjusts accordingly but only accurate to one decimal place. There was an eureka! moment. :sighs relief:

Thanks for the assistance guys.

I will attempt to balance the pack prior to mounting it.

 

[dogman dan]

And there you have the reason I try to get another of those cheap free DVM's on the coupon, every time I go buy some solder or welding wire at Harbor Freight.

Backups for those things are mighty handy, whenever one of them reads funny. Usually it's just a battery gone down with them, but older ones will start reading wonky even with a new batt.