Acceptability of NCA/NMC-chemistry Lithium Battery Packs

[WithoutaRudder]

You can get reclaimed Tesla modules for ~$750 and the packs are ~22V 5.3kWh and they are pretty small and light 50-60lbs. For an 18kW 72 V propulsion system you could get pretty decent capacity with a 4s configuration and come in under the weight of an inboard diesel (240lbs vs 350-450lbs dry). For an equivalent bank using LiFePo4 you’d need a 24s configuration of 240Ah cells the weight is closer to 275-300lbs and the costs seem to be marginally higher than Tesla modules.

Seems like they’d be good candidates for a sailboat electric propulsion system, they are used frequently by other DIY-EV conversion groups. But there are some pretty serious thermal runaway risks with these chemistry modules. I guess I’m really interested in the design trade offs, can these be used on a boat safely?

The original engine in my boat was an Atomic 4 and a lot of smug diesel sailors will say a gasoline inboard is a bad day waiting to happen. And while I don’t disagree necessarily, boat manufacturers put those engines in boats for decades and they did it safely by carefully mitigating risks through system design.

I’m mostly wondering if it’s possible to mitigate thermal runaway risks with a careful, conscious design effort.

If it is do the details of that design eat away at the price/weight benefits of using the Tesla modules to begin with. I am mainly wondering if any one else has done this kind of analysis, and what the thoughts of the wider community are.

I’ve poked around the forums and looked online there doesn’t seem to be specific laws/regulations that say don’t do use NCA/NMC and people colloquially seem split on it. A lot of what I’ve looked at online is a little bit old but it could be I’m looking in the wrong places (seems like even 3-5 years is old for battery/BMS technology)

Anyway I’m looking forward to hearing what people think. I am exploring the possibility of repowering my sailboat with electric propulsion and came across this and I thought I’d ask on here

[AndyOz]

Tesla spent gazillions of $ and thousands of engineering hours to develop their battery management system to prevent most thermal runaways.

I suspect you'd have to replicate a large amount of that for a boat system.

[shrspeedblade]

AndyOz put it really well....Tesla modules are very safe, with a superb battery management system.

FWIW, I have an electric auxiliary (my sailboat is mostly wind powered, imagine that) and love it and also have over 200k miles driving Teslas and love them too!

I have and at this point would only use LiFePO4 batteries in my sailboat, for what it's worth.

Edit: Now that I think about it, there are some versions of the Model 3 out there now that use LiFePO4 packs, FYI. Still gets you into providing your own BMS though, just with a chemistry at this point better suited to boats.

[Adelie]

Atomic-4s are not as safe as diesel. That doesn’t make them dangerous per se, just less safe.

Atomic-4 safety is greatly improved by the spark arrester they all have and which is required by the USCG in the US. This is passive safety, something you need to do or think about, just don’t screw with it when doing maintenance on the engine.

A blower somewhat improves this safety. This is an active safety measure you need to remember to run for a period prior to cranking the engine.

LiFePo batteries are passive safety, they are not subject to thermal runaway except in extreme cases.

Use of other chemistries requires better thermal management by a BMS. This is active electronic safety.

Can you get away with it? Sure. I’d rather take the slight cost & weight penalty and not worry about it. Personal preference.

If you do go with a different chemistry, consider waterproofing the battery compartment so that if the do go off they might burn thru the bottom of the boat and fall away without sinking the boat. Probably a bit extreme

[CharlieJ]

OP:
I wouldn’t use a repurposed Tesla NMC battery in my boat or house.

These applications are not what the battery was designed for and there is absolutely no way that the Tesla battery can be modified to comply with the applicable ABYC/ISO Standards.

[WithoutaRudder]

I appreciate the responses and yeah, trying to evaluate the risk of any new system on a boat based on severity and likelihood of known risks, even though the incident rate of thermal runaway in NMC-chemistry batteries is relatively low in the EV world the severity is astonishing and as has been pointed out that is when the batteries are used exactly as intended.

I had a feeling that be the case, it is a bummer to find a low cost low weight solution that is fatally flawed in this way.

I am curious if LiFePo4 prismatic cells are “less” risky and if there is a specific value that “less” means in this case

[wholybee]

Originally Posted by WithoutaRudder

I appreciate the responses and yeah, trying to evaluate the risk of any new system on a boat based on severity and likelihood of known risks, even though the incident rate of thermal runaway in NMC-chemistry batteries is relatively low in the EV world the severity is astonishing and as has been pointed out that is when the batteries are used exactly as intended.

I had a feeling that be the case, it is a bummer to find a low cost low weight solution that is fatally flawed in this way.

I am curious if LiFePo4 prismatic cells are “less” risky and if there is a specific value that “less” means in this case

There is a lot of engineering that goes into an EV. It is not only the battery, but the charger, the mounting, the internal cooling of the battery. It is very unlikely you could do all of that well in a DIY installation. Plus, what is the history of the reclaimed battery? You are starting with something that is already not perfect.
Several boat manufacturers and vendors use NMC. It isn't completely unusable on a boat, but IMHO, it is a dangerous choice for a DIY or a reclaimed battery.

LiFePO4 cells are an order of magnitude safer than NMC. Most likely safer than Lead Acid. Putting a value on it is hard. But there are tables that show the temperature and conditions required for either chemistry to combust or enter thermal runaway. LiFePO4 when in thermal runaway is much cooler than NMC, and quite possibly not hot enough to catch adjacent wood on fire. I have seen an RV with LFP that melted to nothing and didn't catch the wood box they were in on fire. The RV was totaled due to smoke damage, but didn't burn down.

And it is really difficult to get an LFP to even do that.

[Drobert]

I would read this report before attempting to put a repurposed vehicle battery into a sailboat:

https://www.cbc.ca/news/canada/nova-...%2C%20Portugal.

https://www.tsb.gc.ca/eng/enquetes-i.../m24a0262.html

[s/v Jedi]

About LFP thermal runaway only in extreme circumstances: it helps to describe what is needed: the boat must be burning down from other causes with extreme heat like from burning fuel. Only after being exposed to such heat and being burned, they can be brought to a thermal runaway.

If crew is still aboard at that time, they are already dead and cremated.

A thousand items aboard have more to worry about. With propane being removed from boats, the biggest risk becomes wiring. Unfortunately many diy’ers have dangerous wiring.

[Colin Stone]

What does your insurance company say?? Haven Knox-Johnston has some clear Li pointers - https://www.havenkj.com/guides-and-t...tery-guidance/

[Nicholson58]

Originally Posted by AndyOz

Tesla spent gazillions of $ and thousands of engineering hours to develop their battery management system to prevent most thermal runaways.

I suspect you'd have to replicate a large amount of that for a boat system.

I contacted Tesla several years ago regarding using their batteries for marine applications. Their answer was a resounding NO.

Their BMS may be super duper but the number of their batteries self igniting including houses destroyed is not small. You can run out of a house. You will more likely die in a lithium boat fire. If it happens at a marina you will wind up liable.

ABYC has recognized LFP as an acceptable non hazardous battery. To my knowledge, no other chemistry has approval. You will be uninsurable and possibly not permitted in marinas or gas docks with other chemistry. Even with LFP, buy good top stuff with individual cell BMS monitoring.