Emergency start trips BMS

[Rucker]

I suppose it wasn't clear. I was responding to the general message I saw, which was 'hey sometimes people here are waaaay too casual on the safety thing'.

What should we do better? Location? Protection? Fire prevention? Limits to usage? BMS/Fusing?

I watched a few videos on LiFePo and am satisfied that as long as you don't short-circuit the thing, or draw more than say .5C, they are basically bulletproof. What am I missing?

[Bert06840]

Originally Posted by Rucker

Good conversation, and for all the right reasons. Is there a layman's version of this?

Originally Posted by Rucker

What should we do better? Location? Protection? Fire prevention? Limits to usage? BMS/Fusing?

I watched a few videos on LiFePo and am satisfied that as long as you don't short-circuit the thing, or draw more than say .5C, they are basically bulletproof. What am I missing?

For house battery use in an RV context, LFPs are totally fine, safe, reliable, provided a few basic rules are observed:

- get them from a reputable source, avoid B-grade cells and cells of unknown origin because manufacturing cleanliness is the #1 requirement for longevity and safety
- don't abuse them

That's it...! In technical terms, that means:

• Get a BMS that does all the required things, over/undervoltage, overcurrent, cell balancing, and so on. John explained this in detail.
• set the limits (e.g. cell voltage) conservatively - losing 2% of capacity to triple the longevity is a good trade-off
• charge and discharge them at reasonable rates. 0.5C is usually fine.
• Fuse them correctly
• Make sure the temperature sensors are where they should be
• Make absolutely sure they aren't charged below freezing
• Use reputable charging sources (solar charge controllers, DC-DC converters, etc. that don't produce a nasty voltage with a lot of high frequency ripples)
• Make sure that your smoke alarm works

And that's it. Use good batteries with a good BMS and don't do crazy stuff, and you're fine.

Originally Posted by John

but since single-use cells are 100% irrelevant to this use case I am flabbergasted you actually meant it that way.

Using primary Lithium batteries without a BMS is fine. So there is some general truth to it.

Originally Posted by John

Most non-USians in the forums use the term as a synonym for "leisure" aka House bank, using Primary for engine or Starter batt.

So best to use "rechargeable" or House to avoid ambiguity.

I'm clearly unfamiliar with pervasive misuse of industry standard terms... perhaps I don't hang out here enough to have come across that, or perhaps I have forgotten. And you're right, saying "rechargeable" instead of "secondary" would have avoided some misunderstandings.

Originally Posted by John

The extreme danger of using 3.6-3.7V nominal LI chemistries in a House bank cannot be emphasized enough, even with a knowledgeable and diligent user.

However mentioning LFP and LTO in the same breath is alarmist scaremongering.

Not quite. One last time my position:

- A house battery made with good LFP cells is a great, safe, cost effective, reliable solution provided the battery is not abused
- Abusing them EVEN ONCE - such as using them without a BMS and, for example, overvolting them once, turns LFP batteries from a great, safe, cost effective, reliable solution into a potential time bomb.

I agree with you that LFP is much safer than LMC, even intrinsically so. But... A well managed LMC pack is way safer than an abused LFP pack.

[john61ct]

Originally Posted by Bert06840

saying "rechargeable" instead of "secondary" would have avoided some misunderstandings.

So then why use

> Using primary Lithium batteries without a BMS is fine.



Do you **really** mean "single use disposable" for this context?





> Abusing them EVEN ONCE - such as using them without a BMS

Poppycock - reread #13 above. The safety functions are important, but a monolithic BMS is just one way to get those and often are the **cause** of catastrophic failures if the owner trusts them too much.


> for example, overvolting them once, turns LFP batteries from a great, safe, cost effective, reliable solution into a potential time bomb.

That is scaremongering. Obviously quality charge sources paired with failsafe HVC simply does not allow that scenario, but even then


> well managed LMC pack is way safer than an abused LFP pack

first off, if you mean lithium manganese cobalt oxide chemistries, the canonical TLA is NMC

NCM, CMN, CNM, MNC and MCN all designate similar formulations, but "LMC" and LCM are not widely used.

Other different chemistries like NCA, NMC, LCO, LMO

are all included in that "higher voltage, higher density, short lifespan & high thermal risk" category at nominal 3.6-3.7V

And NONE are suitable for House use anywhere near human living spaces, much less small mobile ones.

No matter the skill set of the original owner, as the pack reaches EoL, say 75-80% SoH, the risks are too great, attention moves on, other people are involved...

[Rucker]

Originally Posted by john61ct

So then why use

> Using primary Lithium batteries without a BMS is fine.



Do you **really** mean "single use disposable" for this context?





> Abusing them EVEN ONCE - such as using them without a BMS

Poppycock - reread #13 above. The safety functions are important, but a monolithic BMS is just one way to get those and often are the **cause** of catastrophic failures if the owner trusts them too much.


> for example, overvolting them once, turns LFP batteries from a great, safe, cost effective, reliable solution into a potential time bomb.

That is scaremongering. Obviously quality charge sources paired with failsafe HVC simply does not allow that scenario, but even then


> well managed LMC pack is way safer than an abused LFP pack

first off, if you mean lithium manganese cobalt oxide chemistries, the canonical TLA is NMC

NCM, CMN, CNM, MNC and MCN all designate similar formulations, but "LMC" and LCM are not widely used.

Other different chemistries like NCA, NMC, LCO, LMO

are all included in that "higher voltage, higher density, short lifespan & high thermal risk" category at nominal 3.6-3.7V

And NONE are suitable for House use anywhere near human living spaces, much less small mobile ones.

No matter the skill set of the original owner, as the pack reaches EoL, say 75-80% SoH, the risks are too great, attention moves on, other people are involved...

I just quote everything you said and ask, 'how am I to understand all this'?

If you want dialogue sometimes it's better to keep each post to one point. I'm seriously having trouble understanding your (potentially important) comments because of the jargon, acronyms and poor formatting.

And I try. Others may just blow on by.

[Salty Walty]

Bert06840, Thank you for good and thorough information from someone who knows what they’re talking about.

[john61ct]

Originally Posted by Rucker

I just quote everything you said and ask, 'how am I to understand all this'?



If you want dialogue sometimes it's better to keep each post to one point. I'm seriously having trouble understanding your (potentially important) comments because of the jargon, acronyms and poor formatting.



And I try. Others may just blow on by.

Post as I like I will.

Feel free to ask specific questions after doing some googling. Also can be a good idea to start fresh threads if you like rather than hijacking ones focused on a specific topic.

I find using a note taking app with full text search and tagging very helpful, reco Simplenote and/or Dynalist if you prefer collapsible outlining.

I'm generous with my time, so long as you are putting in most of the required learning effort, and say thanks occasionally.

http://www.catb.org/~esr/faqs/smart-questions.html

[Rucker]

Originally Posted by john61ct

Post as I like I will.

Feel free to ask specific questions after doing some googling. Also can be a good idea to start fresh threads if you like rather than hijacking ones focused on a specific topic.

I find using a note taking app with full text search and tagging very helpful, reco Simplenote and/or Dynalist if you prefer collapsible outlining.

I'm generous with my time, so long as you are putting in most of the required learning effort, and say thanks occasionally.

How To Ask Questions The Smart Way

Thanks John. Block as I like I will.