Thermal Runaway on AGM battery.

[Ephraim]

For the curious, this is what thermal runaway looks like in an AGM battery.

The battery is a LifeLine 8DL AGM (250AH). The charger is a Morningstar 15A MPPT charger, but it is not run off of solar panels. There is a 48V power supply feeding the Solar input instead. I kept losing batteries at this location so I replaced the current battery backup system with this solar charger because I can remotely monitor what is going on.

In the current heat wave, the battery temp has been floating between 90 and 100 degrees. On Friday, there was a power outage so the system was running off of the batter for about an hour (about 1800). When the power came back on the solar charger went into bulk mode. Its a 15A charger and the system draws 5 to 6 amps continuously, so it was putting roughly 10A into the battery for charge.

After about 30 minutes, the battery had recovered Fromm the outage, but the charger went into absorption mode which it will stay in for about an hour or two depending on the voltage in the battery. but the battery was already hot from the air and couldn't shed anymore heat. This caused it to enter a thermal runaway condition. Even though at the time it was only getting about 1.5A of charge, it couldn't shed the heat. This starts a process where oxygen bubbles start forming on the plates which further exacerbates the problem. The only way to stop it is to remove the charge from the battery completely and let the battery cool down. The solar charger couldn't tell this though. It just saw the battery voltage start dropping and requiring more current.

About 1100 on Saturday, the controller maxed out feeding about 9 amps to the battery. Since it couldn't put any more juice in, the battery voltage began to drop from the target of 14.2V till we caught it 2300 on Saturday. the battery voltage had pulled the charger all the way down to 13.5V @ 9A and was in bulk MPPT mode. The battery temp had risen to 130 degrees at that point.

this battery was large enough that continuing until it caught fire was a real possibility.

[uncle_bob]

Hi

Welcome to "why you don't set your charger(s) to put > 14V into lead acid (AGM or flooded) battery". Doubly so if you don't have a temperature probe to compensate the chargers.

Bob

[Ephraim]

Originally Posted by uncle_bob

Hi

Welcome to "why you don't set your charger(s) to put > 14V into lead acid (AGM or flooded) battery". Doubly so if you don't have a temperature probe to compensate the chargers.

Bob

So, the funny thing is that the charger specs were program to the exact specs from the battery manufacturer. Concorde Battery (Maker of LifeLine) specifies the following:

(Lifeline Technical Manual pp. 19) These numbers are at 77 degrees
bulk: What the battery will take in current.
absorption: 14.3V +/- .1V
float: 13.3V +/- .1V

When the thermal runaway started, the temperature of the battery was at 90 degrees and the charger appropriately cut back the voltages due to the existence of the temp probe on the battery.

The issue appears to be one where the ambient temperature was above the temp of the battery and the battery wasn't able to shed heat. The temp probe was also attached to the + battery lead per the manufacturers specification.

The system was obviously sitting on the verge of collapse and the added internal heat of the bulk charge started the runaway condition.

The solution is to get the battery out of the ambient heat of the system. Since this is in a non-air conditioned shed, it means either getting a fan on the batteries or moving them to a possible buried location. We have other systems where the batteries are buried and the temp never goes above 80 degrees.

It could have also been a bad battery, but since this location has a history of killing batteries, I suspect not.

It does make me wonder about Airstream installs where the batteries are in direct sunlight or even inside the coach where the temp soars and they have a solar charger on them. Reason enough to ensure the charger an/or converter are not active when the coach is not being used?

By the way, I've often heard that Thermal Runaway is a prime reason why people don't upgrade to lithium. This is proof that AGM can experience thermal runaway just like lithium can.

[uncle_bob]

Hi

With lithiums ( at least the major brands ) you have a BMS to take care of this sort of thing. Indeed back in the day before folks even used a BMS, lithiums had all sorts of problems. It did take a while for everybody to work out just what really needed to be in a BMS to get it to cover all the bases. One of the concerns about this or that "new kid" making packaged lithiums ( even today ) is how good the BMS they are using actually is ...

On any battery the "magic voltages" are temperature dependent. Lead acids change more than a bit over temperature. AGM's and flooded cells both change the same way. A setting on a charger of 13.3V at 70 degrees is going to be something like 12.6V at 120 degrees. Same thing with all the other settings.

Do battery manufacturers spell this out in big bold letters? Probably not. Not to surprisingly the folks that sell battery chargers with temperature probes *do* talk about it. They would like you to buy their expensive gizmo .

The flip side of this is also a bit of a problem. When it gets cold, the voltages all go up by kinda sorta a half volt. Now your 12.6V "charged" voltage is actually 13.2V. The "stop using" voltage is now 12.6V .... yikes ....

Are all these numbers exact? Unfortunately not. You can put various other "stuff" into the lead pot when making the plates for a battery. This can impact the delta at cold or at hot ( but not both ). When they make batteries to sell in Florida they do it one way. When they target the Yukon, the go with a different mix. Working out just what you got from a mail order outfit ... good luck.

The same this alloy / that alloy changes more than just the temperature stuff. If you look at data sheets, there are some that seem to be off by a tenth or two tenth's of a volt. Yes, it could be sloppy math. It's more likely to be yet another variation on the stuff put in with the lead in the melting pot.

Fun !!!

Bob

[franklyfrank]

Originally Posted by uncle_bob

Hi

Welcome to "why you don't set your charger(s) to put > 14V into lead acid (AGM or flooded) battery". Doubly so if you don't have a temperature probe to compensate the chargers.

Bob

Uncle Bob,
Why is my Inverter Fan Running continuously since yesterday afternoon.
I have nothing plugged into any of the Inverter outlets and we don't use the TV.
It kept me up half the night.
Tried to shut it off at the panel but the fan keeps on running even in the off position.
This is in a 2017 Classic, all original accept for AGMs last year.

[SSquared]

Very interesting. If all it takes is a period of bulk charge at around 100 degrees, a lot of us are at risk. Though I haven't heard of any Lifeline or other batteries going 'boom' in the heat.

And it shows a reason to keep the batteries on the tongue, not inside the cabin the way many of the electrical upgrades seen on Airforums are built.

[dznf0g]

Originally Posted by SSquared

Very interesting. If all it takes is a period of bulk charge at around 100 degrees, a lot of us are at risk. Though I haven't heard of any Lifeline or other batteries going 'boom' in the heat.

And it shows a reason to keep the batteries on the tongue, not inside the cabin the way many of the electrical upgrades seen on Airforums are built.

Not with a quality charger, with accurate temp sensing and proper temp compensation programming. ...assuming the battery itself isn't defective.

[uncle_bob]

Originally Posted by franklyfrank

Uncle Bob,
Why is my Inverter Fan Running continuously since yesterday afternoon.
I have nothing plugged into any of the Inverter outlets and we don't use the TV.
It kept me up half the night.
Tried to shut it off at the panel but the fan keeps on running even in the off position.
This is in a 2017 Classic, all original accept for AGMs last year.

Hi

Guess one: It's broke

Guess two: the cable from the switch has come loose ... except I think when that happens the inverter shuts off.

Sort of leaves guess one .... sorry about that.

Bob

[uncle_bob]

Originally Posted by dznf0g

Not with a quality charger, with accurate temp sensing and proper temp compensation programming. ...assuming the battery itself isn't defective.

.... or with a lower voltage setting on an uncompensated charger ....

[dznf0g]

Originally Posted by uncle_bob

.... or with a lower voltage setting on an uncompensated charger ....

Right, I am not following some of the data given, if the charger is healthy and set correctly.

[Ephraim]

Originally Posted by dznf0g

Not with a quality charger, with accurate temp sensing and proper temp compensation programming. ...assuming the battery itself isn't defective.

Hard to say in this case. this time around, the charger is a quality charger fully programmable including temperature compensation. Granted, not quite used in the way it was intended (being fed by a 48VDC power supply rather than a solar panel) but the manufacturer's FAQ on their website specifically states that that is an allowable configuration with all of their MPPT chargers (but NOT their PWM chargers) The only downside is that the internal logging capability times out at 1440 minutes. Not a big deal since I am sampling the data every 5 min via SNMP and storing it in a database.

I would suspect that the battery is defective (especially since this battery is not new, but one retired from another site which was upgraded to lithium). However, this site is known for killing batteries. We usually don't get any indication that the battery is dead until there is a power outage and the system dies when it shouldn't.

The first charging system was a 48V power supply run off of a 120V APC UPS. The UPS battery was replaced every year due to failure.

The second charging system was a Ubiquity EP-54-72W which integrated the charger and power supply. While this system could be monitored remotely, there was no temperature probe (either internally or externally) so it obviously wan't temperature controlled. additionally, every 30 days, it let the system run off the battery and timed how long it lasted to give us a report of the battery condition before recharging it. Nice in that we always new the state of the battery's condition, but hard on the battery. This system also killed the battery regularly.

The third system was using the EP-54-72W as the power supply but with the charger turned off. Instead we attached a Noco 10A charger that is supposed to be really good at managing battery charger. Again, it regularly killed batteries and now we had no idea of what the battery state was until the system failed.

This time, I used a high quality industrial solar charger that is completely programmable and manages all aspects appropriately. That is what enabled us to catch the data and the failure.

The location is obviously death to batteries because of the elevated temps in the shed during the summer. There isn't enough air movement and it is a dirty environment (lost of dust, spiders, critters, etc.. have access). At least with this data, we know that the batteries inability to shed the heat even at low levels of charge is the issue. Fans are bad because of the environment.

Observations that I've taken away from this grand experiment:

1) Once thermal runaway is initiated, a charge current of as little as 1.5A is enough to sustain the runaway event.

2) Thermal runaway can initiate at temperatures as low as 90 degrees.

3) With an elevated battery temp, thermal runaway can be initiated with as little as 10A charge on a 250AH AGM battery.

The only solution that we can come up with that will address the issue is to get the battery out of the heat zone (probably by burying it and leaving it in direct physical contact with the earth while in the hole. This should thermally couple it to a ~60 degree thermal buffer that is capable of sinking the heat from a 10A recovery charge after a power outage.)

A fan would probably do the same thing, but would be prone to failure due to the dirty environment. This site needs to run unattended for long periods of time. We will also probably leave the power system as it is so that we can accurately monitor the performance.

while this isn't on an airstream, the conditions that the thermal runaway occurred could easily be replicated on a newer Airstream that is left in a sunny environment and powered up while on shore power. Especially in the SW.

[uncle_bob]

Hi

A temperature compensated charger needs a couple things if it's going to work:

1) There needs to be a temperature sensor attached directly to the battery. It's the battery temperature that matters, not the ambient temp.

2) The sensor needs to go to the charger. If there are multiple chargers, they each need a sensor attached.

3) The sensor needs to be "turned on" in the charger.

4) The charger needs to be set up for the temperature slope of the batteries involved.

At least one of those things was not done. The data shows the voltage hanging in there above 14V. That would not happen with a properly set up compensation scheme.

Bob

[dznf0g]

Originally Posted by uncle_bob

Hi

A temperature compensated charger needs a couple things if it's going to work:

1) There needs to be a temperature sensor attached directly to the battery. It's the battery temperature that matters, not the ambient temp.

2) The sensor needs to go to the charger. If there are multiple chargers, they each need a sensor attached.

3) The sensor needs to be "turned on" in the charger.

4) The charger needs to be set up for the temperature slope of the batteries involved.

At least one of those things was not done. The data shows the voltage hanging in there above 14V. That would not happen with a properly set up compensation scheme.

Bob

^ my thoughts exactly.

[Ephraim]

Originally Posted by uncle_bob

Hi

A temperature compensated charger needs a couple things if it's going to work:

1) There needs to be a temperature sensor attached directly to the battery. It's the battery temperature that matters, not the ambient temp.

2) The sensor needs to go to the charger. If there are multiple chargers, they each need a sensor attached.

3) The sensor needs to be "turned on" in the charger.

4) The charger needs to be set up for the temperature slope of the batteries involved.

At least one of those things was not done. The data shows the voltage hanging in there above 14V. That would not happen with a properly set up compensation scheme.

Bob

Sorry, uncle_bob, but you would be wrong in stating that all these criteria were not met. The charger was doing exactly like it was supposed to do. It did lower the target voltage per the programing. while the chart is difficult to read due to data compression in displaying, the raw data shows the exact temperature of the battery and the target voltage the charger was putting out. both track EXACTLY the criteria put forward in the lifeline manual. Both manufactures (Morningstar and Concorde) have looked at the data and both state that the charger did what it was supposed to do and was programmed appropriately. It would appear that the battery's response was an anomaly from the expected performance. It is interesting that the data can be reliably repeated with the exact same response and the only conclusion that BOTH manufactures have come to is that the conditions are not letting the battery get rid of the heat. Again, the solution is to put a fan on the battery or place it on a surface that will conduct the heat away from it better. The only part that bothers me is that the storage conditions match the storage conditions often seen when the batteries are in a standard battery box and the charger is connected continuously.

FYI, here is the Lifeline tech manual specification that are matched by the data