LiFePO4 and fear of failure

[nmeyrick]

Thanks all, really appreciate the feedback and lively discussion. So far I've heard from multiple people with all lithium banks, none of whom have told me they suffered from catastrophic issues due to shutdown of the entire bank (possibly survivorship bias but hey!) I've also learn that Amel now supplies boats from factory with an all lithium bank and dont see the need for a backup, which given their relatively conservative nature and tendency to build redundancies into their design seems to say a lot.

So I'm pretty comfortable now that battery shutdown is a risk of course, and one that will be managed as any other - but that it does not seem to be significantly larger than the risk of failure from lead batteries to the point of justifying additional backups.

 

[gregcope]

No I completely agree! The argument that has been put to me is that lead batteries are dumb and don’t tend to fail without good cause, while lifepo4 depends on electronics in the BMS that could either cut it off, or fail altogether.

I do not yet fully understand how much this is a real risk, and how much simply fear of the unknown / new technology hence hoping others who have made a similar decision can shed some light

I hear / read that argument allot. However I have never seen data on this.

LifePo4 batteries BMS will shutdown under certain circumstances or fail. The former is more likely in systems that have not designed for that. Where you can access the BMS data it is possible to monitor that.

My experience is of four Lead Acid batteries failing. On two occasions this took the house boat battery bank with it. In those scenarios there was a seperate statt battery that could be used in extremis.

My point being FLAs fail.

In any design i would suggest either accepting the risk or designing to know about it and mitigate which i think is the source of your (@nmeyrick) question.

There are lots of people sailing around the work or using LifePo4 eg @geem of this parish as the OP points out. Stories of failures in well designed systems are rare - i cannot recall reading any.

 

[Refueler]

I hear / read that argument allot. However I have never seen data on this.

LifePo4 batteries BMS will shutdown under certain circumstances or fail. The former is more likely in systems that have not designed for that. Where you can access the BMS data it is possible to monitor that.

My experience is of four Lead Acid batteries failing. On two occasions this took the house boat battery bank with it. In those scenarios there was a seperate statt battery that could be used in extremis.

My point being FLAs fail.

In any design i would suggest either accepting the risk or designing to know about it and mitigate which i think is the source of your (@nmeyrick) question.

There are lots of people sailing around the work or using LifePo4 eg @geem of this parish as the OP points out. Stories of failures in well designed systems are rare - i cannot recall reading any.

Trying to compare number of LA vs LiFe failures is a waste of time as LA still outnumbers LiFe by significant margin ...

Plus forguive me for saying it - but many of us are guilty of not exactly being best managers of LA ... so we have 'events' !! If LiFe - people tend to be more serious about their use and management of .. courtesy of BMS as well of course.

 

[PaulRainbow]

Lead acid batteries can fail, but it would be extremely rare for a whole bank to fail at the same time. Not much else to fail that would leave you without power, except maybe the main isolator. Lithium can fail just the same, but does have a few additional components that could fail and cause total loss of power. There are also some circumstances that cause cause the BMS to shut the system down.

Of course, with a well designed and installed system, using good quality components, the risk is relatively small. However, Sods law says that if something does go wrong it will do so at the most inconvenient time. Building in an emergency solution isn't difficult or costly and in my opinion it's essential.

With LA systems i fit separate isolators for engine and domestic systems, with an emergency parallel switch wired between the load sides of the main isolators. If a battery/bank fails, just isolate that system and close the emergency switch.

No reason a similar arrangement could not be used with a LA/Lithium setup. The same system could be used in most systems. Another option could be to have essential systems connected to a changeover switch, switching between the LA starter battery and the Lithium system.

 

[geem]

Lead acid batteries can fail, but it would be extremely rare for a whole bank to fail at the same time. Not much else to fail that would leave you without power, except maybe the main isolator. Lithium can fail just the same, but does have a few additional components that could fail and cause total loss of power. There are also some circumstances that cause cause the BMS to shut the system down.

Of course, with a well designed and installed system, using good quality components, the risk is relatively small. However, Sods law says that if something does go wrong it will do so at the most inconvenient time. Building in an emergency solution isn't difficult or costly and in my opinion it's essential.

With LA systems i fit separate isolators for engine and domestic systems, with an emergency parallel switch wired between the load sides of the main isolators. If a battery/bank fails, just isolate that system and close the emergency switch.

No reason a similar arrangement could not be used with a LA/Lithium setup. The same system could be used in most systems. Another option could be to have essential systems connected to a changeover switch, switching between the LA starter battery and the Lithium system.

Agreed. I have isolators on each lithium battery as well as the engine batteries. There is a link from engine to lithium batteries via an emergency isolator in a steel cabinet in the engine room. With both lithium batteries isolated, I can power the domestic loads from the engine batteries. The link cable goes to the positive busbar.

 

[GHA]

There are lots of people sailing around the work or using LifePo4 eg @geem of this parish as the OP points out. Stories of failures in well designed systems are rare - i cannot recall reading any.

With a smartshunt connected which you actually look at it seems very unlikely. Add a raspberry pi which will get the data off victron kit over bluetooth you can have it in a dashboard in opencpn.

 

[PaulRainbow]

With a smartshunt connected which you actually look at it seems very unlikely. Add a raspberry pi which will get the data off victron kit over bluetooth you can have it in a dashboard in opencpn.

Neither a Smartshunt or a Pi will stop a battery failure, BMS failure etc etc

 

[PaulRainbow]

Thanks Mattonthesea, yes this is something I’m considering. It wouldn’t be automatic and not ideal but it’s at least an opportunity to jury rig. I may settle on this as it seems the simplest way to have some degree of redundancy - unless someone can tell me a reason that it’s not a good idea

You could fit a second battery, wired in series with a changeover switch between the LA and Lithium batteries. Crudely, you could take the engine supply from one battery or better, fit a DC-DC converter.

You could fit a DC-DC converter to the existing battery and use it to power the domestics (using a changeover switch). If the domestic loads are too great, just use it to power essential services.

Your statement "I'm deliberately not going into the details of our set up at the moment as I'd prefer to focus on the general question." doesn't help.

 

[GHA]

Neither a Smartshunt or a Pi will stop a battery failure, BMS failure etc etc

It will stop the bms switching off due to low battery voltage, which can and does happen and is a real concern, rather than monsters from the Id.

 

[geem]

It will stop the bms switching off due to low battery voltage, which can and does happen and is a real concern, rather than monsters from the Id.

It really hard to get to low battery with a big enough lithium bank and a smart shunt. I can just bang on the generator and throw in 115A at 24v but never needed to do that for my lithium yet. They always seem to have so much capacity available

 

[GHA]

It really hard to get to low battery with a big enough lithium bank and a smart shunt. I can just bang on the generator and throw in 115A at 24v but never needed to do that for my lithium yet. They always seem to have so much capacity available

Yep, unlikely if you look but it can happen if you don't....

 

[PaulRainbow]

It will stop the bms switching off due to low battery voltage, which can and does happen and is a real concern, rather than monsters from the Id.

Indeed, and it's a good idea to monitor the batteries, whatever the type of installation. But, there are plenty of other things that could go wrong and leave you with no power, so as far as i'm concerned, backups need to be in place.

 

[GHA]

. But, there are plenty of other things that could go wrong and leave you with no power,

with any battery chemistry

 

[Sea Change]

It really hard to get to low battery with a big enough lithium bank and a smart shunt. I can just bang on the generator and throw in 115A at 24v but never needed to do that for my lithium yet. They always seem to have so much capacity available

A mate installed a 'drop in' lithium, but didn't realise that the BMS was not set to have charge enabled. Ended up down at 6% before we'd figured it out. So it can happen, but generally only as the result of some type of failure.

 

[geem]

A mate installed a 'drop in' lithium, but didn't realise that the BMS was not set to have charge enabled. Ended up down at 6% before we'd figured it out. So it can happen, but generally only as the result of some type of failure

Ah yes, the wonderful "drop in battery"

 

[PaulRainbow]

with any battery chemistry

That's what i said in post #24

 

[ckris]

It will stop the bms switching off due to low battery voltage, which can and does happen and is a real concern, rather than monsters from the Id.

Low pack voltage disconnect and the idea the boat would go dark with no warning was the remaining worry I had when installing Lithium. Thought we might need to have a low soc alarm which is not straightforward to do.

In practice I found lithium behaves very much like LA at low voltage and if you are attuned to knowing when to charge an LA bank you get the same subtle prompts with Lithium.

What I mean is that with my LA bank, when on passage, I knew that when the voltmeter by the chart table got close to 12v it was time to start the engine. If I missed that then a few of our nav systems start to sound low voltage alarms and eventually some of the displays on deck switch themselves off (we deduced that 12v with normal on passage loads was around 12.2 -12.3v rested voltage or approx 50% SOC for a la bank).

The drop off in voltage with a lithium bank is steep between 20% to 10% SOC so exactly the same things happen as the voltage (with load) gets to 12v - at the point lithium soc is still in the teens and you have plenty of warning to start the engine.

This was a regular occurrence with the LA bank, happens very rarely with lithium because the usable capacity is so much more. Still, I am confident now that I would notice and start charging well before a low pack voltage disconnect.