Self build battery - precautions…..

[Lincs Robert]

Hi,

Whilst I’m pondering if/how to proceed with this, a thought entered my mind about safety issues surrounding such a build. Whilst an off the shelf battery, eg Pylon etc, will cost more £, it does come with a number of safety related attributes such as CE marking etc, which a self build can’t. This isn’t a criticism, but a statement of fact.

That accepted, there are on things that can be done to minimise the risk of self build - such as fuses, insulation of busbars and tools and perhaps a cover on top of the finished article. Is there anything else? My own installation would be inside my roof space, where I have all my other kit located. I have a smoke detector up there - but little else. Should I be thinking of perhaps investing in a C02 fire extinguisher should I proceed, or even now for that matter? Would such a device even extinguish a battery fire?

Comments please …..

Rob

[Oldgreybeard]

I'd be inclined to try and fireproof the installation as best you can, not so much because there is a real risk of fire, as such, but there is a very small risk of things overheating, which could possibly damage flammable materials. Mounting the inverter on fire resistant board and perhaps creating some sort of semi-enclosure of the same stuff for the batteries and all the ancillary stuff might be a good idea, especially inside the house, and even more so in a loft space.

A heat alarm may be more useful than a smoke alarm, perhaps, and I think I'd consider a belt and braces approach to electrical enclosure fire safety by fitting an Enviroburst tube inside to suppress any fire before it gets going: https://envirograf.com/product/envirobu ... ion-system

Hardiebacker board is readily available and is fire resistant, so would be a reasonable choice for mounting stuff.

[Caesium]

Hi,

Whilst an off the shelf battery, eg Pylon etc, will cost more £, it does come with a number of safety related attributes such as CE marking etc, which a self build can’t. This isn’t a criticism, but a statement of fact.

It's my personal view that such a marking, from manufacturers like these (ie from distant lands not subject to our laws), are worth about as much as if I wrote CE on a piece of paper and stuck it on myself.

LiFePO4 are a lot safer than Li-ion though, generally speaking. There's a good video on Youtube where some chap drills through both types of battery, literally drills right through it. One of the videos he wears a lot more protective equipment and jumps back a hell of a lot faster than the second video, if I remember correctly The LiFePO4 version of the video produces a bit of steam/venting of some sort, and little else.

Seeing videos like that makes me feel quite a lot safer about DIYing my packs. The biggest danger is myself, really; shorting these things out can still lead to some brown pants situations. And as you very rightly state, fuses, breakers/disconnects and covering as much exposed metal as possible are all very sensible precautions.

However, I think if you did have a Li-ion fire in your house from a pack of the sizes we're talking about here, no fire extinguisher is going to help; get out, and stay out. You're not going to put that out, period.

[Tinbum]

Mounting the inverter on fire resistant board

When my inverter was reinstalled the installer insisted on mounting it on a fire resistant board despite it being mounted on a bare brick wall.

[Oldgreybeard]

Mounting the inverter on fire resistant board

When my inverter was reinstalled the installer insisted on mounting it on a fire resistant board despite it being mounted on a bare brick wall.

Sometimes common sense is notable by being relatively uncommon . . .

[Stinsy]

LiFePO4 batteries are pretty safe as these things go.

There is no acid (as in lead acid batteries) and they cannot burn (as in other lithium batteries). They do contain a huge amount of energy and can release it very quickly with dramatic results if a short-circuit occurs. This is the main problem you need to mitigate. You also need to ensure none of your cables or joints overheat.

A few tips:

• Location of the batteries is key. On the floor of a garage or shed is a terrible place because it is very easy for something to fall down across the terminals. An attic of other place up high reduces this risk considerably.

• The batteries should have a robust, non-conductive cover (such as 19mm OSB).

• When working on the batteries you should take your time and take great care. Wiring something incorrectly or dropping a metal tool across the terminals will have spectacular results. Insulated tools are a VERY good idea. Wrapping your tools in insulation tape is a bodge to achieve the same thing. However you're spending a few grand on batteries buy one of these: https://amzn.eu/d/9NPnlfS.

• Ensure all joints are tight and size cables correctly. Going up a cable size on what your calculations say is always a good idea. Use a IR thermometer to monitor temperatures of joints/cables.

Just to repeat: LiFePO4 batteries are pretty safe, they cannot burn. Almost all domestic batteries use this chemistry for that reason. A notable exception is the Tesla Powerwall which uses the same NMC (Nickel-Manganese-Cobalt) batteries as used in phones/laptops/EVs. Now those are prone to thermal-runaway and catching fire in a way that is exceptionally difficult to extinguish (the chemical reaction brings its own oxygen so CO2 or other traditional fire extinguishing methods are useless).

[Joeboy]

If you are competent working on electrical systems and know what you are doing and the risks involved then no reason not to. If you come to this with more hope than skill then it can still be done but think and plan through every step before moving on in the build. Personally I see the biggest risk being slack connections allowing that connection to heat up through micro arcs. Good airflow is also essential.

Diagrams and lists are very handy focus aids.

[nowty]

Correct and conservative inverter/charger settings, suitable fusing, isolators, fireproof as much as you can, mechanically protect bare bus terminals, fit smoke alarm as close as possible. When building check, double check and treble check for loose connections.

Fire extinguisher ?, I don't have one, thought about it a lot but its unlikely to help a full on lithium fire and probably endanger myself trying. Biggest risk is a loose connection, hence a smoke alarm more useful.

I recall a fire reported on St Elsewhere several years ago but it was caused by a loose connection and all the electrical stuff was screwed to a wood board rather than a fireproof one.

I recall several other incidents, no actual fires, but strange faults which all turned out to be loose connections and burnt out semi melted masses of an export meter, an isolator and several Immersun internal connectors (including my own).

[marshman]

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[nowty]

Any one got any suggestion or sources of "lower" cost fuses for DIY batteries? Specifically for mounting very close to the battery terminals to provide protection in case of a short circuit somewhere "up stream". Didn't really want to install a large KETO style NH fuse holder/isolator as I have one of those up stream nearer the inverter and they are quite pricy and big and I am getting a bit tight on space.

The smaller - and lower cost - "Mega" fuses as listed by the likes of Victron which look ideal, don't have a very high interrupt current, only 1000A. A big LiFePO4 battery could easily provide in excess of 10kA into a dead short. Probably over thinking things but if there was a neater solution it would be good.

You probably want a bolt down DC rated HRC fuse.

I recall my industrial training manager saying, "nothing stops a short circuit faster than a HRC fuse". But not all of them are DC rated !

Something like,
https://uk.rs-online.com/web/p/tag-fuses/1781030
https://docs.rs-online.com/c77e/0900766b8167459e.pdf

Rated at 250V DC with a breaking capacity of 80kA, is that enough for ya.

High rupture capacity (HRC) means this device works reliably with both high-voltage and low-voltage faults, and its ceramic body ensures it's thermally stable and can resist high temperatures. You can use this multipurpose fuse in a wide range of industrial applications, electrical equipment and wiring systems.