Catastrophic failure 200ah 12v battery

[Just John]

I think the same happened to me!
i attached two 12v/100 amp batteries in pararel and thet swell in 4 days.

what could be wrong?

thanks

The cells got above 3.65v per cell. They don't swell just sitting there, voltage is involved in this. What else was connected?

 

[Gazoo]

The cells got above 3.65v per cell. They don't swell just sitting there, voltage is involved in this. What else was connected?

He started another thread and has gel batteries.

 

[electric]

PWM pulses in 18v, cell gets over 3.65v, BMS disconnects, active balancer eventually gets ALL cells to 3.65v, BMS disconnects. BMS waits specified interval, reconnects, disconnects after first 18v pulse. Repeat every minute for 3 days.

Are you telling me that PWM type SCCs don't have a charge voltage setting beyond which it cannot keep charging?
Your statement sounds like BMS is the only stopping gate for SCC to stop charging. This is not true for a normal SCC, even if it's PWM type.
I feel like design type (PWM) is being conflated with features, such as stopping a charge at certain voltage and resuming at a different voltage, which all good SCCs should have.
To be clear, PWM type SCC simply means that it cannot charge to a higher voltage than solar panel produces at any given time, i.e. it can only step down, but not step up in voltage.
MPPT is also using PWM principle, but has additional boosting circuits which allow both stepping down and stepping up.
These terms have nothing to do with charging a battery, which is done the same way in all SCCs, regardless of type.
All inverter/chargers and all grid chargers use PWM to step down and regulate voltage/current, so we can't use those either?
This is all just nonsense.

 

[mrzed001]

A PWM is a term describing a principle of operation and all modern power conversion devices work by this principle, so to say that PWM is bad is just nonsense. What people call a particular product and efficacy of that product can be analyzed and debated, but a generic statement is nonsense.
Every system has inductance and capacitance, it comes from all cables and components. LFP cells alone have very high capacitance and inductance.
PWM cannot hurt a battery unless we are talking some ridiculous low frequency like 1 Hz. Only average current/voltage matters, peaks don't matter.

Please watch this video to understand the basic of the PWM:

PWM from the panel side (the battery side is exactly the inverse of it)

So yeah battery gets a full 19V then nothing. Again, there is no capacitor or inductor in the PWM SCC to flatten the curve.
Also when in bulk charge some PWMs put all the solar like 19V directly to the battery (without pulsating). Not very LFP friendly.

And now check the first video I linked where you can see the PWM, then the Buck converter which is the base of the MPPT and gives out a (not perfect flat but) not so heavily pulsating current with low V pulses

And now you understand, how wrong this line is:

To be clear, PWM type SCC simply means that it cannot charge to a higher voltage than solar panel produces at any given time, i.e. it can only step down, but not step up in voltage.

PWM DOES NOT STEP DOWN VOLT ! PWM lets the same volt pass through for a time, or not ... and so the average volt is lover.

MPPT is also using PWM principle, but has additional boosting circuits which allow both stepping down and stepping up.

Nope.
Some MPPTs are Buck converters alias step down converter.
Some MPPTs are Boost converters alias step up converter.
Some MPPTs are Buck-Boost converters alias step up-step down converter.
And they output is really the needed volt (with a small Vdiff).
Like if you have a 450Voc MPPT then it puts out the needed 48-52V ... and not 0 to 450V in a PWM pulsating way (like 10ms 450V then 90ms 0V).

 

[electric]

Please watch this video to understand the basic of the PWM:

Thank you, but Electrical Engineering college courses and 12 years working in this industry taught me better that some YouTube videos.
It's been a while since I checked this forum, but clearly FUD is still king around here.
Here is an example of reputable SCC https://www.victronenergy.com/upload/documents/Datasheet-BlueSolar-PWM-Pro-Charge-Controllers-EN.pdf

According to your logic this SCC is not good for Lithium. If so, then we have nothing else to talk about.

Voltage is not passing from point A to point B, only current can pass thru circuit. Voltage difference only means current can flow if allowed.
When gate is open current flows into battery, raising it's voltage ONLY based on it's internal state of charge, regardless of what voltage is at the panel. SCC senses voltage at the output and should not allow it to go above preset value regardless of voltage at the panel. During the short time when PWM gate is open voltage at SCC drops instantly due to current flowing, drop is allowed by a lenght of cable between panel and SCC.
When PWM gate is open and current is flowing, voltages are different at all points in a circuit. Even saying that panel voltage goes to battery is a nonsense statement. Voltage doesn't go anywhere and it's different everywhere in a circuit at any moment of time.

 

[Just John]

Thank you, but Electrical Engineering college courses and 12 years working in this industry taught me better that some YouTube videos.
It's been a while since I checked this forum, but clearly FUD is still king around here.
Here is an example of reputable SCC https://www.victronenergy.com/upload/documents/Datasheet-BlueSolar-PWM-Pro-Charge-Controllers-EN.pdf

According to your logic this SCC is not good for Lithium. If so, then we have nothing else to talk about.

Voltage is not passing from point A to point B, only current can pass thru circuit. Voltage difference only means current can flow if allowed.
When gate is open current flows into battery, raising it's voltage ONLY based on it's internal state of charge, regardless of what voltage is at the panel. SCC senses voltage at the output and should not allow it to go above preset value regardless of voltage at the panel. During the short time when PWM gate is open voltage at SCC drops instantly due to current flowing, drop is allowed by a lenght of cable between panel and SCC.
When PWM gate is open and current is flowing, voltages are different at all points in a circuit. Even saying that panel voltage goes to battery is a nonsense statement. Voltage doesn't go anywhere and it's different everywhere in a circuit at any moment of time.

$40 for a 30 amp controller. The first thing I see on the spec sheet is 16v high voltage disconnect. Working temperature -20 to 113. Sounds perfect for the 120 degree shed.

Sure sounds great for lithium to me, they must use state of the art components and design at that price. Because everyone buys PWM for their known durability and compatibility with lithium.

 

[mrzed001]

Thank you, but Electrical Engineering college courses and 12 years working in this industry taught me better that some YouTube videos.

This forum is because of Will's "some YouTube videos".
Did you even look at the videos I showed you? Or never saw an oscilloscope ?

Voltage is not passing from point A to point B, only current can pass thru circuit. Voltage difference only means current can flow if allowed.
When gate is open current flows into battery, raising it's voltage ONLY based on it's internal state of charge, regardless of what voltage is at the panel. SCC senses voltage at the output and should not allow it to go above preset value regardless of voltage at the panel. During the short time when PWM gate is open voltage at SCC drops instantly due to current flowing, drop is allowed by a lenght of cable between panel and SCC.
When PWM gate is open and current is flowing, voltages are different at all points in a circuit. Even saying that panel voltage goes to battery is a nonsense statement. Voltage doesn't go anywhere and it's different everywhere in a circuit at any moment of time.

Nope. Volt is potential difference. This difference causes the current to flow.
Higher V defeats more easily the resistance and raises current higher. I = U / R (A = V / Ohm)
That is why you need a CC-CV battery charger. On the bulk charge (CC) part you have to limit the V (like 3V per cell for empty LFP) to limit the charging current (like 20A).

So when you use a PWM charge controller (example 24V solar) to have 20A to flow and reduce the average volt to 12V (half the solar) you have to close the circuit half the time. Like 10ms open, 10ms closed. So 20ms period. P = U x I ( W = V x A) , W = U x I x s ( Wh = V x A x h)
Only every second part will current flow so :
- 0V 0A (circuit open 10ms), then next
- 24V 40A (circuit closed 10ms) ... hammer time ? ? (or square root 2 * 12V and 20A ?)
to have an average of 12V 20A.

On the absorption part (CV) you have to limit the V to the max allowed (like 3,5 per cell = 14V)
- 0V 0A (circuit open 10ms), then next
- 24V 40A (circuit closed 14ms)
and the current will go down as the battery gets full and the resistance rises.

On the other hand the same CC part with an MPPT:
- 12V 20A constant. (+- some V and A)

The V and A values only examples, not exact values (and it is 4am).

 

[stienman]

I don't think it's worth generalizing.

Pick a PWM unit where you have the schematic and control logic, and then do a technical analysis. Make sure you account for the lithium cell's properties, so you'll need to specify that, and you should probably specify the solar panels involved as well, since their impedance will figure into the overall system.

Otherwise you're all just talking about different assumed PWM units, and will go around in circles with no resolution. I expect I could pick a PWM unit, tie it with a specific cell and solar panel, and have it destroy the cell, and I'm certain I could create a different PWM setup that would work perfectly fine for a decade or more.

If you're going to generalize and say "ALL PWM are BAD" or "NOT ALL PWM are BAD" or "ALL PWM are FINE" you'll probably find someone poking holes in your extreme statement.

All that said, this is a topic for another thread, so consider starting one and continuing the discussion there if necessary.

Besides which, nearly all DC to DC converters used in MPPT units are just complicated PWM circuits anyway. /troll :D

 

[Just John]

My take:

PWM charge controller is like a bridge rectified A/C old school transformer charger without enough filter caps..
MPPT is more like a switch mode power supply.

One is simply better than the other for this purpose. The batteries were overcharged in a hot environment by something, the PWM charge controller is it. The balancer did a good job balancing an overcharge.

What did the BMS do? Seems it allowed it.

 

[wholybee]

Yes you are correct it is connected directly to the cells. But I am still having a difficult time comprehending how it could cause a cell to overcharge. I think we need to know what the default setting is for this particular Heltec active balancer. We know it's not for LTO. So it has to be either Li-ion of LFE or the same setting works for both.

I will explain why I don't use them. Simple...I keep my cells between the knees which keeps the delta low enough to satisfy me

I don't think a balancer is set for a particular cell type. It's job is just to equalize the voltage, and it really doesn't matter what cell type. The charger and BMS would keep the cells within the required range, and a balancer could never charge any cells to a higher voltage than the highest cell.

Now consider, 4 cells all charged to 3.4V. A balancer is connected incorrectly, so that it sees 2 cells in series, at 6.8 Volts. It then happily uses that 6.8 volts to charge the other 2 cells. I don't know for sure this could happen, but it seems very reasonable that it could.

If you keep your cells between the knees, they could drift out of balance and you would never know. You would lose capacity however. Nothing would be damaged, and you could get that capacity back by doing another top balance. Bringing them into the knee, even just a little, to 3.45 or so, would allow the cells to passively balance, and tip you off if they go out. You don't need to do that every charge, but once in a while would be a good idea.

 

[mrzed001]

@Will Prowse can you put this thread to the new Up in smoke topic please

 

[BatteryNut]

This forum is because of Will's "some YouTube videos".
Did you even look at the videos I showed you? Or never saw an oscilloscope ?




Nope. Volt is potential difference. This difference causes the current to flow.
Higher V defeats more easily the resistance and raises current higher. I = U / R (A = V / Ohm)
That is why you need a CC-CV battery charger. On the bulk charge (CC) part you have to limit the V (like 3V per cell for empty LFP) to limit the charging current (like 20A).

So when you use a PWM charge controller (example 24V solar) to have 20A to flow and reduce the average volt to 12V (half the solar) you have to close the circuit half the time. Like 10ms open, 10ms closed. So 20ms period. P = U x I ( W = V x A) , W = U x I x s ( Wh = V x A x h)
Only every second part will current flow so :
- 0V 0A (circuit open 10ms), then next
- 24V 40A (circuit closed 10ms) ... hammer time ? ? (or square root 2 * 12V and 20A ?)
to have an average of 12V 20A.

On the absorption part (CV) you have to limit the V to the max allowed (like 3,5 per cell = 14V)
- 0V 0A (circuit open 10ms), then next
- 24V 40A (circuit closed 14ms)
and the current will go down as the battery gets full and the resistance rises.

On the other hand the same CC part with an MPPT:
- 12V 20A constant. (+- some V and A)

The V and A values only examples, not exact values (and it is 4am).

You have a very poor understanding of transients and I suggest you peruse some actual literature instead of continuing with your misconstrued notions of the application of Ohm's Law under dynamic conditions.

 

[mrzed001]

You have a very poor understanding of transients and I suggest you peruse some actual literature instead of continuing with your misconstrued notions of the application of Ohm's Law under dynamic conditions.

It is possible. But that you argue without real explanation ... that is a fact.