One cell undercharged
- Thread starter dodaly
- Start date
chrisski
Solar Boondocker
I don’t like how the BMS / Balancer leads are below the bus bar. I’d take it apart, top balance, and then install the leads on top of the busbar and torque the nit, or drill and tap a separate hole in the busbar for the BMS/Active balancer lead. See how it performs after that.
At the very least, I recommend removing the busbar, checking the high cells, draining those with a load, putting the BMS / Active balancer leads on top of the battery, and torquing the nuts.
What is this set up? I count 8 cells and see four listed on the BMS display, along with 12 volts listed on the display. I think this is 2P 4S, not 4P 3S.\
I don’t have an active balancer, so I don’t know if .1 volt would balance. I know with my built in BMS balancer, this would not balance that. My specs on the BMS balancer has the balancing come on at 3.40 volts and charging stops at 3.475, so very little time, perhaps minutes, is spent at that voltage. For me, not enough time to balance .1 volts. I’m not sure how your balancer is set.
At the very least, I recommend removing the busbar, checking the high cells, draining those with a load, putting the BMS / Active balancer leads on top of the battery, and torquing the nuts.
What is this set up? I count 8 cells and see four listed on the BMS display, along with 12 volts listed on the display. I think this is 2P 4S, not 4P 3S.\
I don’t have an active balancer, so I don’t know if .1 volt would balance. I know with my built in BMS balancer, this would not balance that. My specs on the BMS balancer has the balancing come on at 3.40 volts and charging stops at 3.475, so very little time, perhaps minutes, is spent at that voltage. For me, not enough time to balance .1 volts. I’m not sure how your balancer is set.
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I agree, this build is 2P 4S
I would let the bank charge up until the BMS disconnects when the first cell hits 3.65, then disassemble the pack, tie them all together in parallel, except the high cells and trickle charge the rest up to 3.65V then put the bank back together.
I would let the bank charge up until the BMS disconnects when the first cell hits 3.65, then disassemble the pack, tie them all together in parallel, except the high cells and trickle charge the rest up to 3.65V then put the bank back together.
TomC4306
Solar Obsessive
But when you reinstall the bus bars...
Do not put them on the cells sequentially.
When you do that, they don't lay flat against the terminal. They lay there like a ramp.
Connect cell 2 to 3, 4 to 5, THEN 3 to 4.
Do not put them on the cells sequentially.
When you do that, they don't lay flat against the terminal. They lay there like a ramp.
Connect cell 2 to 3, 4 to 5, THEN 3 to 4.
MrM1
I'm Here, But I'm Not All There
I
In the pic they are ramped
TomC4306
Solar Obsessive
I know. That's why I posted that.
There are a few rookie mistakes here.
I agree with TomC that the bus bars are incorrectly installed. Chrisski's point about the balance terminals under the bus bars is spot on.
Those two issues alone will likely fix the voltage issues. But there's more!
These cells are not sufficiently compressed. Whatever you have going on there, it isn't enough. There should be no space between the cells and you sure as heck shouldn't have wires running between the cells.
The way the big cables are attached to the terminals, it's possible that there is a lot of stress on the cell terminals. The cables are elevated above the level of the bus bar. When you tighten the nut holding the lug down, it's going to put upward stress on the cell terminal. You may or may not have good solid surface contact between the bus bar and the cable lug. Don't drape the cable over the edge of the battery box so close to the terminal.
As an example, the left cable (positive or negative? Who knows?) should be rotated counter clockwise so that the cable is coming through the gap between the two vertical wood slats. That solves the problem of lug contact with the terminal/bus bar. But then you probably need to provide some strain relief to the cable so it doesn't droop and put downward stress on the terminal.
I agree with TomC that the bus bars are incorrectly installed. Chrisski's point about the balance terminals under the bus bars is spot on.
Those two issues alone will likely fix the voltage issues. But there's more!
These cells are not sufficiently compressed. Whatever you have going on there, it isn't enough. There should be no space between the cells and you sure as heck shouldn't have wires running between the cells.
The way the big cables are attached to the terminals, it's possible that there is a lot of stress on the cell terminals. The cables are elevated above the level of the bus bar. When you tighten the nut holding the lug down, it's going to put upward stress on the cell terminal. You may or may not have good solid surface contact between the bus bar and the cable lug. Don't drape the cable over the edge of the battery box so close to the terminal.
As an example, the left cable (positive or negative? Who knows?) should be rotated counter clockwise so that the cable is coming through the gap between the two vertical wood slats. That solves the problem of lug contact with the terminal/bus bar. But then you probably need to provide some strain relief to the cable so it doesn't droop and put downward stress on the terminal.
Your also doing this but make sure you maintain the staggered connections of banked cells. Such that no one cell has both positive and negative terminals making series connections.
cell 1 and cell 2 are paralleled making CELL 1B (banked)
cell 1 positive terminal makes series connections
cell 2 negative terminal makes series connections
This will allow both cell 1 and cell 2 charged evenly.
Just change the order of how the bus bars are installed.
cell 1 and cell 2 are paralleled making CELL 1B (banked)
cell 1 positive terminal makes series connections
cell 2 negative terminal makes series connections
This will allow both cell 1 and cell 2 charged evenly.
Just change the order of how the bus bars are installed.
Thanks for all the responses guys, im going to make some changes to the pack now starting with the balance cables and also trying to compress them together more to avoid terminal stress. I fixed the voltage issue yesterday by moving one of the overcharged cells and swaping it with one of the undercharged. The pack is within good balance condition now, however after installing a breaker between my main bus bar pos and the battery my inverter now only beeps a fault when its turned on, I tried to remove the fuse to see if it would go back to working but it seems like whatever ive done has caused a problem. Pictures have been done just after reading responses so I havent made any changes yet.
Symbioquine
Solar Enthusiast
- Joined
- Jul 6, 2021
- Messages
- 460
It's somewhat minor compared with the other issues that have been pointed out, but you also should reconsider the mounting orientation of your charge controller (likely the DC-DC charger, and inverter as well).
If you're ever going to use them close to their rated power outputs for any length of time you probably want them oriented so that the cooling fins on the back are vertical. That allows convection to draw fresh cooler air over the fins as a function of the heat generated.
Placing them horizontally (without adding extra fans) means air can stagnate and even insulate hot spots in the electronics.
If you're ever going to use them close to their rated power outputs for any length of time you probably want them oriented so that the cooling fins on the back are vertical. That allows convection to draw fresh cooler air over the fins as a function of the heat generated.
Placing them horizontally (without adding extra fans) means air can stagnate and even insulate hot spots in the electronics.
MisterSandals
Participation Medalist
Lots of great advice so far!
I noticed what looks like a cheap audio breaker which NEEDS to be replaced. Wondering what the other breakers are given that installing them coincides with other issues? (link or pic?)
I noticed what looks like a cheap audio breaker which NEEDS to be replaced. Wondering what the other breakers are given that installing them coincides with other issues? (link or pic?)
chrisski
Solar Boondocker
What you say makes sense, but my fan cooled Samalex inverter in the manual says to not mount vertically like you say. My passively cooled by fin Victron Charge controllers do say to mount vertically.
Can you give anymore data? To me sounds like the BMS needs reset. Does negative Inop mean there’s 0 volts on A multimeter, no continuity with ground, or what?
I have overcharged a BMS before and to reset it, I simply disconnected the charge device. An undervoltage shutoff might mean starting with a good voltage source. Unsure about a over discharge reset.
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On a separate note, I hope you have the terminals convered on the battery. I’m assuming the cover is off for pictures.
Symbioquine
Solar Enthusiast
- Joined
- Jul 6, 2021
- Messages
- 460
Yeah, definitely prioritize following what the manual says ahead of what I said...
Even within Samlex inverters it looks like the guidance is different for different models;
They are standard breakers similar to this one
Attachments
chrisski
Solar Boondocker
Plenty of threads of breakers like that failing by popping too early or popping too late.
If it had a company name like Bussman or Blue Sea it would inspire confidence. Lack of a company name makes it more likely its not the quality needed for solar.
It could be the circuit breaker. To test that, temporarily bypass the breaker and see if the inverter will fire up.
That last battery screen shot shows that you have a problem. One cell went to low voltage and the BMS likely disconnected.
Went to pull off the pavk after charging from dc to dc and after pulling 1000w the pack went down to 10.5 v the inv crashed and so did the bms, anyone know whats going on?View attachment 120658View attachment 120659
You either have a bad cell, or a bad connection to that cell. Many times we see voltage issues here on the forum that are due to poor connections. Check the connection. Take it apart if you have to.
Otherwise, you may have a bad cell.
Otherwise, you may have a bad cell.
MisterSandals
Participation Medalist
With a 2P4S pack it’s a little more complicated and fortunately flexible.
Wondering if you might have inadvertently moved the 2 worst cells together in a 2P pair. How did you determine the weakest and strongest cells?
At low battery Soc, the lowest voltage is likely the weakest. At high battery Soc, the lowest voltage cell is likely the strongest.
I’ve spent a LOT of time arranging cells. FWIW, I could have save a lot of time doing capacity test rather than 4S ranking and swapping…
MisterSandals
Participation Medalist
Let me expand on my previous post as I think it’s important if not obvious.
With multiple cell in parallel first battery, like 2P4S or even 3P4S (and many others), it’s vital that the capacity of the pairs or triplets are as close as possible to the other pairs or triplets.
So for 2P4S, pairing strongest cell with weakest cell,
Second strongest cell with second weakest
Third strongest with third weakest
Fourth strongest with fourth weakest.
And strongest means highest capacity. Weakest is lowest capacity.
With multiple cell in parallel first battery, like 2P4S or even 3P4S (and many others), it’s vital that the capacity of the pairs or triplets are as close as possible to the other pairs or triplets.
So for 2P4S, pairing strongest cell with weakest cell,
Second strongest cell with second weakest
Third strongest with third weakest
Fourth strongest with fourth weakest.
And strongest means highest capacity. Weakest is lowest capacity.
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