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PAS 63100 vs BS 7671 A721

AJJewsbury

I've been pondering battery systems at home and noticed an apparent discrepancy between PAS 63100 and BS 7671. I know the two are for (slightly) different situations (a home on wheels vs a home on solid ground) but I'm presuming the underlying physics is similar - they're both (usually) ELV rechargeable battery systems in domestic type situations (indeed the differences between the two are getting more and more blurred, as traditional "off grid" system are finding their way into traditional houses as battery storage systems).

A case in point is the position of the main battery fuse (or CB) - traditional caravan rules prohibit this entirely from the battery locker - presumably on the assumption that lead acid batteries are liable to liberate hydrogen gas and a fuse (especially the open automotive types) or a circuit breaker is very likely to create an arc when opening the circuit - and arcs and explosive hydrogen aren't a good mix. Maybe there's also a worry of acidic vapours from the battery corroding contacts. BS 7671 A721 agrees with that (A721.533.1.8). PAS 63100 on the other hand seems to take the opposite approach "6.1.1 Batteries shall comprise non-combustible enclosures containing the overcurrent protection
with the cells/monoblocs." - backed up by Figure 1. While I can see both pros and cons to both approaches - it does seem somewhat inconsistent.

Perhaps differing battery chemistries are an influence? I presume A721 was written with only lead-acid in mind - whereas the world has moved on and the majority of EESS these days use lithium (or Sodium) which have a much lower chance of evolving hydrogen (or acidic fumes) ... but as I understand it they can still emit hydrogen in some fault conditions - quite possibly the very conditions you'd want the fuse to open under.

Or are there any other reasons for the difference?

   - Andy.

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  • AJJewsbury said:
    A case in point is the position of the main battery fuse (or CB) - traditional caravan rules prohibit this entirely from the battery locker - presumably on the assumption that lead acid batteries are liable to liberate hydrogen gas and a fuse (especially the open automotive types) or a circuit breaker is very likely to create an arc when opening the circuit - and arcs and explosive hydrogen aren't a good mix. Maybe there's also a worry of acidic vapours from the battery corroding contacts. BS 7671 A721 agrees with that (A721.533.1.8). PAS 63100 on the other hand seems to take the opposite approach

    Some good points made in the discussion, but one topic has been missed so far.

    PAS63100 does not include systems using open vented lead-acid batteries within the scope of the document, Section 6.4 stipulates the applicable standards for cells/monoblocks which for lead-acid they have to be compliant with BS EN 61056-1; and BS EN 61056-2, which are standards for valve regulated lead acid cells (VRLA).

    So open vented automotive lead-acid batteries which are releasing moisture and hydrogen during normal operation wouldn't be permitted under PAS63100. 

    But strangely, they do include vented NICAD batteries (BS EN 60623) within scope. Which seems a rather bizarre choice.

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  • AJJewsbury said:
    A case in point is the position of the main battery fuse (or CB) - traditional caravan rules prohibit this entirely from the battery locker - presumably on the assumption that lead acid batteries are liable to liberate hydrogen gas and a fuse (especially the open automotive types) or a circuit breaker is very likely to create an arc when opening the circuit - and arcs and explosive hydrogen aren't a good mix. Maybe there's also a worry of acidic vapours from the battery corroding contacts. BS 7671 A721 agrees with that (A721.533.1.8). PAS 63100 on the other hand seems to take the opposite approach

    Some good points made in the discussion, but one topic has been missed so far.

    PAS63100 does not include systems using open vented lead-acid batteries within the scope of the document, Section 6.4 stipulates the applicable standards for cells/monoblocks which for lead-acid they have to be compliant with BS EN 61056-1; and BS EN 61056-2, which are standards for valve regulated lead acid cells (VRLA).

    So open vented automotive lead-acid batteries which are releasing moisture and hydrogen during normal operation wouldn't be permitted under PAS63100. 

    But strangely, they do include vented NICAD batteries (BS EN 60623) within scope. Which seems a rather bizarre choice.

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  • in reply to TurboGen

    For lead acid cells at least .the charging regime has to be more tightly controlled for the VRLA as there is no easy means to replace the lost water - and actually drying out is often a failure mode of smaller sealed cells in alarms and some emergency lihts.where they spend a long time on 'float' charge.

    Circuits for vented cells at least historically have tended to approach full charge at a higher current for rapid cycling, and not bother too much about a degree of overcharging and a bit of gas.

    The VRLA circuits ensure  that the charging current falls away to almost nothing as full charge is approached and far less gas is produced, unless the charging circuit is faulty or te battery overheats (the voltage per cell falls with temp so if the cell is hot, the charger behaves as if it is flatter than it is, and tends to overcook it.)


    NiCd cells and the more modern but related Ni/MHs have the ability to catalitically  recombine the O2 and 2H2 back to water if they are constructed correctly, and can safely be constant-current over charged slowly, say 10-20 hour rate, almost for ever, and only gassing if badly abused by huge over current or voltage.

    I suspect the apparent anomaly relates to the way the different cells are typically charged, and how much gas they then produce.

    Mike

    PS the humble car battery is more or less sealed for life these days, because of the improved all electronic regulation inside  the modern alternator - anyone old enough to have suffered a mechanically regulated dynamo will recall topping up the battery and checking the acid density was a regular fortnightly ritual. folding beck the current as full charge is reached avoids that conversion of water to gas then having to replenish it, 

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