Issues with lithiums in very cold weather?

[ditchcrawler]

6 minutes ago, MtB said:

 

 

Dare I suggest, I think it might be an eye deer to, like, loosen up ever so slightly :D 

 

Things change, rules get updated, personal circumstances shift and stuff that seemed important at the time turns out not to have bin. 

 

Wait until them rules actually change, then stress about it. Who nose, buy then you might have changed botes, or ANYTHINK mite of happened! This is the way of them canals, and of lief. 

 

Nice wine this. Can u tell? 

 

 

I am drinking the same stuff

[MtB]

Just now, ditchcrawler said:

I am drinking the same stuff

 

Cheese! 

 

 

 

[PeterF]

I was not really sure where to post this as the issue of lithium iron phosphate battery safety and flammability keeps coming up in many threads with reports of lack of fires. The attached came up on the Victron Community forum is not a full incident report and does not report what was the actual cause of the incident but I thought it worth adding to the discussion. I find it interesting that whatever caused the incident (e.g. BMS failure allowing overcharging) did result in overheating / localised burning of one battery, the extent of the fire was limited and burnt out / self-extinguished or was extinguished without escalation. A similar event where combustion initiated with the more reactive lithium chemistries would not have self extinguished and would have more likely escalated. I know that this is not new news to many here, but it is one of the first incidents I have seen that illustrates the safer nature of LiFePO4.

 

https://community.victronenergy.com/questions/225008/battery-fire-manufacturer-says-caused-by-smart-sol.html

 

 

Quote

 

We experienced a battery fire last week. I am curious of others thoughts on this situation.

 

We installed 4x LiFePo4 batteries in parallel in February 2023. We also added 2000 watts of solar run to a Victron 150/70 (2s3p) and a Victron 100/50 (2s2p). The system has been performing well since installation.

 

For sake of detail the panels are Rich Solar 200 watt panels, specs:

20.4 VMP

9.8 IMP

24.3 VOC

10.2 ISC

 

It is very clear that the fire was coming from one of the four batteries. This battery is now very swollen and has significant damage to the case from the fire. It was hot enough that the battery was stuck to the battery next to it and had to be pried apart.

 

 

 

[rusty69]

Interesting take on series connected panels here:

 

https://www.proboat.com/2022/07/solar-charge-controller-failures/

[IanD]

1 minute ago, rusty69 said:

Interesting take on series connected panels here:

 

https://www.proboat.com/2022/07/solar-charge-controller-failures/

But mainly that with bad installation and care things can go wrong, just like with parallel connected panels... 😉

 

(yes there's a small risk of shocks in this case with >100V DC around, but none of this is likely to be an issue anyway on a canal boat with no folding cover to trap wires)

[Tony1]

24 minutes ago, PeterF said:

I was not really sure where to post this as the issue of lithium iron phosphate battery safety and flammability keeps coming up in many threads with reports of lack of fires. The attached came up on the Victron Community forum is not a full incident report and does not report what was the actual cause of the incident but I thought it worth adding to the discussion. I find it interesting that whatever caused the incident (e.g. BMS failure allowing overcharging) did result in overheating / localised burning of one battery, the extent of the fire was limited and burnt out / self-extinguished or was extinguished without escalation. A similar event where combustion initiated with the more reactive lithium chemistries would not have self extinguished and would have more likely escalated. I know that this is not new news to many here, but it is one of the first incidents I have seen that illustrates the safer nature of LiFePO4.

 

https://community.victronenergy.com/questions/225008/battery-fire-manufacturer-says-caused-by-smart-sol.html

 

 

 

 

 

Thanks Peter, thats very interesting. 

This is a further extract from that post:

 

 "The very first response from them was the Victron mppt caused this issue. They also immediately offered to replace the battery. They went on say the Victron mppt’s should be swapped for Epever mppt’s. Their explanation is that the mppt sent pv voltage to the battery damaging the bms and causing it to start fire. He stated that the 100/50 in particular is "poorly" designed and not recommended."

 

I have two of the Victron 100/50 MPPTs that the battery manufacturer is slagging off, so it is of particular interest to ascertain whether there is even a tiny grain of truth in the accusations.  Certainly I've had no problems in the 2 years I've used mine (daily), and I'm sure the same is true for many thousands of users. 

 

Whatever the truth of it, you have to consider that even if the MPPT did have a freak malfunction and sent too high a voltage to the battery, the battery's internal BMS should still have been able to disconnect it, right? 

 

The thing is, nobody is going to test this out (and thereby wreck their own expensive batteries), but it seems like something to keep an eye on, both for MPPT 100/50 users, and lithium battery users with built in BMS's. 

 

 

 

Edited August 14, 2023 by Tony1

[rusty69]

1 minute ago, IanD said:

But mainly that with bad installation and care things can go wrong, just like with parallel connected panels... 😉

 

(yes there's a small risk of shocks in this case with >100V DC around, but none of this is likely to be an issue anyway on a canal boat with no folding cover to trap wires)

Wow, you must be a speed reader.

[IanD]

Just now, rusty69 said:

Wow, you must be a speed reader.

Indeed, about 180 pages an hour -- going on holiday before ebooks used to be a nightmare... 😉

[PeterF]

2 minutes ago, Tony1 said:

 

Thanks Peter, thats very interesting. 

This is a further extract from that post:

 

 "The very first response from them was the Victron mppt caused this issue. They also immediately offered to replace the battery. They went on say the Victron mppt’s should be swapped for Epever mppt’s. Their explanation is that the mppt sent pv voltage to the battery damaging the bms and causing it to start fire. He stated that the 100/50 in particular is "poorly" designed and not recommended."

 

I have two of the Victron 100/50 MPPTs that the battery manufacturer is slagging off, so it is of particular interest to ascertain whether there is even a tiny grain of truth in the accusations.  Certainly I've had no problems in the 2 years I've used mine (daily), and I'm sure the same is true for many thousands of users. 

 

Whatever the truth of it, you have to consider that even if the MPPT did have a freak malfunction and sent too high a voltage to the battery, the battery's internal BMS should still have been able to disconnect it, right? 

 

The thing is, nobody is going to test this out (and thereby wreck their own expensive batteries), but it seems like to something to keep an eye on, both for MPPT 100/50 users, and lithium battery users with built in BMS's. 

 

 

 

The link that @rusty69 gave above also listed MPPT failure and the link said that MPPT failure could allow large voltages to pass to the batteries that would exceed the rating of the BMS FETs.

[rusty69]

5 minutes ago, IanD said:

But mainly that with bad installation and care things can go wrong, just like with parallel connected panels... 😉

 

(yes there's a small risk of shocks in this case with >100V DC around, but none of this is likely to be an issue anyway on a canal boat with no folding cover to trap wires)

Quote

 It’s worth noting that high-quality components from manufacturers such as Morningstar, Victron, MidNite, OutBack, etc. all rely on magnetic decoupling, which should prevent a failure like this. However, the MPPT unit in question was not equipped with that safety feature.

It was really the above comment that stood out for me. Though I am a slow reader.

[MtB]

It's an interesting point. I only have a loose grasp on how an MPPT controller works but it never occured to me it would routinely put panel voltage through to charge the battery, in the way a PWM controller does. I.E. not under fault conditions. 

 

Which leads onto thinking about using a PWM solar controller with a hybrid LA/LFP installation. Probably a very bad idea.

 

 

 

 

[IanD]

2 minutes ago, Tony1 said:

 

Thanks Peter, thats very interesting. 

This is a further extract from that post:

 

 "The very first response from them was the Victron mppt caused this issue. They also immediately offered to replace the battery. They went on say the Victron mppt’s should be swapped for Epever mppt’s. Their explanation is that the mppt sent pv voltage to the battery damaging the bms and causing it to start fire. He stated that the 100/50 in particular is "poorly" designed and not recommended."

 

I have two of the Victron 100/50 MPPTs that the battery manufacturer is slagging off, so it is of particular interest to ascertain whether there is even a tiny grain of truth in the accusations.  Certainly I've had no problems in the 2 years I've used mine (daily), and I'm sure the same is true for many thousands of users. 

 

Whatever the truth of it, you have to consider that even if the MPPT did have a freak malfunction and sent too high a voltage to the battery, the battery's internal BMS should still have been able to disconnect it, right? 

 

The thing is, nobody is going to test this out (and thereby wreck their own expensive batteries), but it seems like something to keep an eye on, both for MPPT 100/50 users, and lithium battery users with built in BMS's. 

 

 

 

I also noted the quote from Victron:

 

"To be straight up with the potential, it is possible for the Victron MPPTs (excluding RS models which are galvanically isolated) to connect PV voltage directly to battery voltage in the unlikely event of a particular type of fault.

It is rare, but it can happen. It is not a transitory failure, if this fault has occurred the unit would now permanently be in that state.

 

There are 100,000's of Victron 100/50 MPPTs in the field, they are a workhorse model and there is no specific variation in their design, or statistical failure rate compared to the rest of the range. To give the claim the benefit of the doubt, because there are so many of them, anecdotally they might see more of them and presume there is some problem with that model."

 

The first paragraph is going to be true for almost all MPPT controllers from all suppliers, internally they're basically a buck SMPS with a switching transistor (and an inductor) between the panels (higher voltage) and battery (lower voltage), and if this fails short-circuit (or is turned on instead of switching) the panels will be connected directly to the battery.

 

The second one is simply saying that there are vast numbers of them out there, so there are bound to be some failures because nothing is 100% reliable. I'd also expect that if there was any failure mode which happened more often than expected Victron would have changed the design to fix it, they presumably don't want unreliable gear out there which could damage their reputation as a high-quality supplier.

[rusty69]

2 minutes ago, MtB said:

It's an interesting point. I only have a loose grasp on how an MPPT controller works but it never occured to me it would routinely put panel voltage through to charge the battery, in the way a PWM controller does. I.E. not under fault conditions. 

 

Which leads onto thinking about using a PWM solar controller with a hybrid LA/LFP installation. Probably a very bad idea.

 

 

 

 

Or perhaps another good reason not to soley rely on a BMS to disconnect the Lithium cells in a hybrid setup. 

 

 

[IanD]

3 minutes ago, rusty69 said:

It was really the above comment that stood out for me. Though I am a slow reader.

There are both isolated and non-isolated MPPT controllers. The smaller lower-power lower-voltage ones (e.g. Victron MPPT) tend to be non-isolated, because adding isolation increases cost for little benefit. The bigger high-power high-voltage ones intended for domestic installation (lots of series panels running at several hundred V e.g. Victron RS series) tend to be isolated, partly for safety reasons.

[rusty69]

I was looking into this earlier, with the intention of removing my LA from the hybrid setup, but was concerned about what effect it would have on the MPPT should a BMS disconnect occur. 

[IanD]

8 minutes ago, MtB said:

It's an interesting point. I only have a loose grasp on how an MPPT controller works but it never occured to me it would routinely put panel voltage through to charge the battery, in the way a PWM controller does. I.E. not under fault conditions. 

 

Which leads onto thinking about using a PWM solar controller with a hybrid LA/LFP installation. Probably a very bad idea.

 

 

They don't -- a non-isolated MPPT controller is basically a PWM controller with more intelligent control to find the maximum power point for the panel. The output consists of two switching transistors -- one between panel and switching node, one between switching node and GND -- driven by a PWM signal, followed by an inductor to remove the AC signal and convert this to DC.

 

For example, if the panel is at 100V and the battery at 50V the PWM signal will be about 50% duty cycle -- small changes in this duty cycle are made by the MPPT controller to allow the panel voltage to track up and down to maximise power output.

7 minutes ago, rusty69 said:

Or perhaps another good reason not to soley rely on a BMS to disconnect the Lithium cells in a hybrid setup. 

 

 

Having a relay between the MPPT output and the battery bank is a good idea, together with a BMS which can disconnect the MPPT if things go pear-shaped...

Edited August 14, 2023 by IanD

[rusty69]

5 minutes ago, IanD said:

 

Having a relay between the MPPT output and the battery bank is a good idea, together with a BMS which can disconnect the MPPT if things go pear-shaped...

Yes, it does seem like another good level of protection.I don't think my curent BMS is smart enough to have that function, but suspect the next one will be.

 

[Tony1]

8 minutes ago, IanD said:

 

Having a relay between the MPPT output and the battery bank is a good idea, together with a BMS which can disconnect the MPPT if things go pear-shaped...

 

This does seem like a very rare malfunction, and I'm not personally convinced (yet) that its something I need to take action on. 

 

But if I did want to build in a layer of protection against high voltages coming from the MPPT, what sort of relay would do the job? 

The BMV712 can be used to control a motorised switch and physically disconnect the charging cable in the event of a high voltage event, right?

But the BMV units act upon battery voltage, NOT the raw voltage coming from the MPPT.

So in my case, the charging disconnect would not activate until the battery voltage (on all three batteries collectively)  went above the 'safe' cut-off limit (currently 14.8v I think). 

 

In an ideal world, it would seem preferable to have a disconnect that acted at the MPPT end, right? Before that high voltage event even hits the battery? Is that a feasible thing? 

I'm asking more out of interest btw, this seems such a rare thing that I dont see myself spend hundreds on preventive gear. 

 

[Francis Herne]

56 minutes ago, Tony1 said:

In an ideal world, it would seem preferable to have a disconnect that acted at the MPPT end, right? Before that high voltage event even hits the battery? Is that a feasible thing?

No. Changes in voltage propagate through a plain wire almost instantaneously, at a significant fraction of the speed of light. At the speed of operation of any high-current DC disconnect, where you place it is totally irrelevant for that purpose.

 

[quick edit: if it's triggered by voltage at its location, a gradual rise in voltage would trigger the MPPT end first due to voltage drop, but with a sudden large increase that won't matter]

 

Many EVs use a 'pyro fuse' - containing a small explosive charge that severs the connection about 100μs after being activated; much quicker than a relay or motorized switch and with no possibility of contact welding or arcing. We'll probably see them in propulsion battery banks for electric boats, but the cost:benefit isn't there for house banks.

Edited August 14, 2023 by Francis Herne

[IanD]

1 hour ago, Tony1 said:

 

This does seem like a very rare malfunction, and I'm not personally convinced (yet) that its something I need to take action on. 

 

But if I did want to build in a layer of protection against high voltages coming from the MPPT, what sort of relay would do the job? 

The BMV712 can be used to control a motorised switch and physically disconnect the charging cable in the event of a high voltage event, right?

But the BMV units act upon battery voltage, NOT the raw voltage coming from the MPPT.

So in my case, the charging disconnect would not activate until the battery voltage (on all three batteries collectively)  went above the 'safe' cut-off limit (currently 14.8v I think). 

 

In an ideal world, it would seem preferable to have a disconnect that acted at the MPPT end, right? Before that high voltage event even hits the battery? Is that a feasible thing? 

I'm asking more out of interest btw, this seems such a rare thing that I dont see myself spend hundreds on preventive gear. 

 

The "failure" would be that the MPPT carries on supplying current when the battery voltage has reached the upper limit, if you use something like a Cerbo as the master controller it knows both these measurements.

 

However you could also say that the reliability of the BMS controller is probably not that much different to the MPPT, so what happens if that goes wrong? Quis custodiet ipsos custodes? 🙂

[Francis Herne]

Poking through the docs, I've just discovered that the Victron 250|100 protects against this in a way I find slightly peculiar - if the battery voltage goes above a threshold, it uses an integrated relay to short-circuit its own PV input terminals: https://www.victronenergy.com/live/mppt_pv_short_relay_reset

[rusty69]

20 minutes ago, IanD said:

Quis custodiet ipsos custodes? 🙂

Which loosely translates to: “Better drowned than duffers, if not duffers won't drown.”