Securing a leisure battery / power bank in rear

[middle-englander]

Hi all,

Although I've run a couple of cables in advance, I'm nearing the point in my build where I need to start thinking more seriously about the electrics.

I had always intended on using a Clayton LPS 2 under the RIB, but recently saw a post on here about the safety of having such a weight in the back. It would essentially be under the bottom of one of my children and directly behind me in th driver seat.

Presuming that there are others on here that have a similar setup, what have you done to secure your power bank / leisure battery?

 

[T6ChrisO]

The mounting bracket secured to the floor?

Mounting Bracket for LPS II power supply

www.claytonpower.com

 

[middle-englander]

I saw this yesterday but it didn't look substantial enough to stop it from flying around in a crash.
I saw somebody mention that a 20kg lump coming to a stop from 60mph had the equivalent weight of 500 odd kg!
Perhaps I'll give Clayton a shout and ask them about this

 

[ShooglyStu]

I saw somebody mention that a 20kg lump coming to a stop from 60mph had the equivalent weight of 500 odd kg!

The "equivalent weight" of your 20kg lump depends not only on the change in speed, but also the time taken for the change in speed, in other words the accel/deceleration.
Suppose you crash into a brick wall and you go from 60mph (27m/s) to zero in 1 second, then the deceleration is 27m/s2 (about 3g)
The force on the 20kg lump will be F = ma = 20 x 27 = 536 Newtons, this being an "equivalent weight" of approx. 55kg

My battery is well secured, but I worry about my fridge, which is not

 

[middle-englander]

Hadn't even thought about the fridge!
Thanks for clearing up the physics, perhaps I was thinking of 600mph

 

[denz1968]

I have a Clayton. Currently stowed on the floor to a board using the supplied clamp.
The convertors are storing it in a cupboard at the back of the van above the wheel arch.

 

[EAN]

The "equivalent weight" of your 20kg lump depends not only on the change in speed, but also the time taken for the change in speed, in other words the accel/deceleration.
Suppose you crash into a brick wall and you go from 60mph (27m/s) to zero in 1 second, then the deceleration is 27m/s2 (about 3g)
The force on the 20kg lump will be F = ma = 20 x 27 = 536 Newtons, this being an "equivalent weight" of approx. 55kg

My battery is well secured, but I worry about my fridge, which is not

If a 60mph crash only caused a 3g deceleration it wouldn‘t cause the devastating injuries that a crash at that speed does.
Its actually much, much higher (albeit for a very short duration).

Decelerating at 27m/s^2 over 1 sec and the vehicle would have travelled quite a distance, so not really a crash into an immovable object. You would have travelled:

s=ut + 1/2at^2

= (27m/s / 1s) + (1/2 x -27m/s^2)

=13.5m

If you crash into an immovable object such as a brick wall then the distance travelled during the crash is actually just the crumple zone of the vehicle, so probably less than a metre, causing a much higher deceleration

a = v^2 - u^2 / 2d

= 0 - 27m/s^2 / 2 x 1m

= 364.5 m/s^2 or 37.2g

F=ma
= 20kg x 364.5m/s^2
= 7290N

Equivalent mass = 7290N / 9.81 = 743kg

Of course its a lot more complicated than that because a brick wall isn’t really immovable, but it gives a reasonable ballpark.
Watching a proper 60mph crash test and you’d be lucky (or unlucky, depending on your injuries) to survive

 

[ShooglyStu]

If a 60mph crash only caused a 3g deceleration it wouldn‘t cause the devastating injuries that a crash at that speed does.
Its actually much, much higher (albeit for a very short duration).

Decelerating at 27m/s^2 over 1 sec and the vehicle would have travelled quite a distance, so not really a crash into an immovable object. You would have travelled:

s=ut + 1/2at^2

= (27m/s / 1s) + (1/2 x -27m/s^2)

=13.5m

If you crash into an immovable object such as a brick wall then the distance travelled during the crash is actually just the crumple zone of the vehicle, so probably less than a metre, causing a much higher deceleration

a = v^2 - u^2 / 2d

= 0 - 27m/s^2 / 2 x 1m

= 364.5 m/s^2 or 37.2g

F=ma
= 20kg x 364.5m/s^2
= 7290N

Equivalent mass = 7290N / 9.81 = 743kg

Of course its a lot more complicated than that because a brick wall isn’t really immovable, but it gives a reasonable ballpark.
Watching a proper 60mph crash test and you’d be lucky (or unlucky, depending on your injuries) to survive

Thanks for pointing out my error, you are absolutely right 1s is not really representative of crashing into anything solid.
Incidentally, the same applies to the manikin head in the crash videos - it decelerates over a very short distance. Those airbags are not soft at all, despite looking like a pillow. An automotive engineer once told me that they were effectively as "soft" as a car tyre.