Kerrie-Ann Mason said:

Further guidance on fire safety and the location of batteries within an installation

On recent trends, it will be that anything bigger than an AA NiMH cell needs to be stored in a concrete bunker at least 500 metres from any dwelling.

broadgage said:

What about my lead acid battery of about 150 AH at 24 volts ? reinforced concrete bunker at least 1000M away. !

In a plastic rentacrate under my bed at present.

We are talking a range of 5-20 times that energy in the storage systems that are going into dwellings in general. However, these batteries are also permanently wired and charging/discharging constantly (which is even different to UPS operation where for long periods they are topped up with charge and monitored for voltage etc.).

With a single monobloc like that, as you'll be aware there is significant short-circuit current, and a risk of explosion on charging if there is no ventilation provision. Luckily hydrogen is heaver lighter than air - not always the case with toxic and explosive vapours from all battery chemistries.

Yes, lead-acid batteries have been around for well over 100 years - they are well understood, as are safe working practices around them. However, concentrations of them (in fact, batteries in general) are usually NOT found where ordinary persons have access - they are usually found where a duty holder is responsible. Similarly, DC protection, switching etc. is well understood by those who use them in various (usually workplace or transportation applications) but not domestic electricians in general.

You might have a different opinion if you'd seen a number of domestic installs out there.

And then there's the whole issue of battery chemistries being used.

LiFePO4 batteries, which, whilst safer than other lithium chemistries, do have their own problems, according to some UK battery fire safety experts ... but that is outside my area of expertise.

Luckily hydrogen is heaver than air

Er, are you sure? I'm sure the Hindenburg floated OK (up until ignition at least...).

   - Andy.

AJJewsbury said:

Er, are you sure? I'm sure the Hindenburg floated OK (up until ignition at least...).

   - Andy.

Nope ... thank you ... edited in earlier post. Brain thinking something different than fingers typing I think.

key though - if the fumes or vapour are heavier than air, where the battery is situated and where you place detectors, if needed, are very important.

gkenyon said:

We are talking a range of 5-20 times that energy in the storage systems that are going into dwellings in general. However, these batteries are also permanently wired and charging/discharging constantly (which is even different to UPS operation where for long periods they are topped up with charge and monitored for voltage etc.).

I have a car battery (which lives directly beneath bottom of the RH rear passenger) with a capacity of 110 Ah at 12 V, so 1.32 kWh so I take the point. However, they are constantly being charged and discharged, especially with vehicles which stop the engine at traffic lights, etc.

There is indeed the risk of a significant short circuit current: 920 A CCA is comparable with the Ze at home.

For the amount of energy in batteries in a given space, it would be hard to beat an old diesel boat.

Chris Pearson said:

However, they are constantly being charged and discharged, especially with vehicles which stop the engine at traffic lights, etc.

Quite different ... the main use is to start the engine, After that, they are charged at constant voltage ...

But then again, maybe ... or not ...

• most of it is outdoors
• away from buildings (at least when the charge/discharge is happening)
• Explosive gases are lighter than air (as above)
• electrolyte is dangerous ... but worst-case leaks on the floor outside
• Arc-fault dealt with (in modern cars ... although not always older cars) by fuse at or very near the battery
• etc
• etc.

Quite different ... the main use is to start the engine, After that, they are charged at constant voltage ...

Not in my other half's car (so called mild hybrid) - there's an extra battery that's charged by regenerative breaking when slowing down, and discharged not only on autostart but when accelerating (to aid the IC engine). And again it's under one of the passenger seats.

   - Andy.

AH, I see what you mean. We have a stop-start battery in one of our vehicles. I'm actually surprised at the length of time it has lasted without showing degradation, compared to a more traditional lead-acid.

Having said, that, on most journeys it acts just like a traditional starter battery, only needing to start the vehicle once, then recharge. The stop-start doesn't get used much at all.

Every hybrid I've encountered has an auxillary lead acid battery - I think the main battery tends to be on a contactor so it's isolated when the engine is off.

My old Honda Insight had a tiny aux battery. I often would pull over to take a call, switch off the engine but leave my electrics on. Then 30 minutes later I'd be getting the jump leads out.

Of course infuriating as it is, there's a good safety reason why manufacturers segregate things like this. Should note that nearly every petrol or diesel car has the fuel tank underneath the seats too - often the fuel pump is right underneath the back seat where the children are.

gkenyon said:

I'm actually surprised at the length of time it has lasted without showing degradation, compared to a more traditional lead-acid.

Many hybrids seem to only use their starter motor for cold starting. Once oil pressure is acheived and at operating temperature they can usually start the engine with torque from the electric drive. This is far less wear and tear - drive motors are nearly always brushless - AC, Switch reluctance or BLDC etc.

A 12V DC starter motor will always be a service part - it's remarkable that the commutators last as long as they do. Hence for recharging the battery most cars use an alternator which only need a small commutator for the field coils.

gkenyon said:

I'm actually surprised at the length of time it has lasted without showing degradation, compared to a more traditional lead-acid.

Many hybrids seem to only use their starter motor for cold starting. Once oil pressure is acheived and at operating temperature they can usually start the engine with torque from the electric drive. This is far less wear and tear - drive motors are nearly always brushless - AC, Switch reluctance or BLDC etc.

A 12V DC starter motor will always be a service part - it's remarkable that the commutators last as long as they do. Hence for recharging the battery most cars use an alternator which only need a small commutator for the field coils.