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DC LV Battery Power Supply for Motorhome

TrigPoint
Hi everyone!


I've been asked to install some wiring in a van conversion and I need a bit of advice. The plan is a 110Ah 12V leisure battery, a SELV system and TT earthing (earth electrode from the body of the van.) 


I'm trying to work out the PSCC and PFC so I can choose the overcurrent and fault protection.


So,


a) Is measuring the impedance of the battery and using Uo Cmax / Zs 2R1 (with the measured battery impedance as Zs) acceptable to calculate PSCC


and,


b) Is Uo/Ze (with measured the battery impedance as Ze) acceptable to calculate PFC?


Many thanks in advance for your answers.


Trig


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  • 0

    just thought MCB's would be safer and easier to reset



    Be very careful about using equipment designed for a.c. on d.c. systems. Anything that switches or breaks a fault current will have a much harder job to do on d.c. as there isn't the luxury of the arc being automatically extinguished for you 50 times a second as the supply current alternates. Generally d.c. switches/MCBs need larger contact gaps and or have a much lower breaking capacity than their a.c. equivalents.  Being 12V doesn't really help on that count either - if anything the currents tend to be larger rather than smaller.


    Beware of voltage drop - it's surprising how little cable you can use at 12V before exceeding recommended limits (3% from memory).


    If you ever have to work on (towed) caravans, rather than motor caravans, be aware that 'chassis return' is only used for the road lights (if at all) - all the habitation circuits (both Fridge, and from the leisure battery) are strictly isolated from the chassis (it's all to keep the 'neutrals' separate and so prevent overheating in the tow connectors especially should one contact have slightly increased resistance). Also there's a requirement that all leisure circuits other than the fridge are disconnected when the caravan is being towed.


       - Andy.
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  • 0

    just thought MCB's would be safer and easier to reset



    Be very careful about using equipment designed for a.c. on d.c. systems. Anything that switches or breaks a fault current will have a much harder job to do on d.c. as there isn't the luxury of the arc being automatically extinguished for you 50 times a second as the supply current alternates. Generally d.c. switches/MCBs need larger contact gaps and or have a much lower breaking capacity than their a.c. equivalents.  Being 12V doesn't really help on that count either - if anything the currents tend to be larger rather than smaller.


    Beware of voltage drop - it's surprising how little cable you can use at 12V before exceeding recommended limits (3% from memory).


    If you ever have to work on (towed) caravans, rather than motor caravans, be aware that 'chassis return' is only used for the road lights (if at all) - all the habitation circuits (both Fridge, and from the leisure battery) are strictly isolated from the chassis (it's all to keep the 'neutrals' separate and so prevent overheating in the tow connectors especially should one contact have slightly increased resistance). Also there's a requirement that all leisure circuits other than the fridge are disconnected when the caravan is being towed.


       - Andy.
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