Watching various youtuber building 18650 powerwalls there seems to be two very different approaches. Those who build multi paralleled 1S "Super cell" packs, then series them together to get the desired voltage for their system,
and those who build a pack (or packs ) direct to their Voltage spec. For example 7S-xP (and then parallel more packs together to get the desired system capacity if using multiple packs)
Say i wanted a "24v" system
my understanding is as follows
7S packs ( of whatever parallel configuration)
Pros:
I could add new packs of any capacity in parallel at any time to increase the system capacity ( couldn't i ? Though i can see it would be desirable to keep them all roughly the same capacity and also to ensure that any additional pack was brought up to the existing system voltage level before introducing it
I could remove a pack for maintenance without bringing the system down, just reducing its capacity.
Bus bars and connecting leads for individual packs need not be so hefty. Only the main bus they all plug into.
Cons
Voltage is fixed and cannot be altered without an entire pack rebuild
positive and negative cell ends are mixed on each face of the pack meaning more care has to be taken over accidentally shorting them while being worked on
Monitoring/balancing needs 7S cables run to every pack
1S packs
pros:
The loss of a few cells in a pack won't unbalance the system voltage
monitoring/Balancing is easier with only 7 wires plus common to be run to the packs
You can reconfigure the system voltage easily by adding or removing more 1S packs (though I'm not sure why you would want to)
Each pack is positive on side and negative the other providing good separation and minimiszing danger of accidental shorting
Cons:
(there can be) a massive amount of current in each pack. If it did short out things could get out of hand quickly
Busbars for each pack need to be substantial
If you pull a pack for maintenance your entire system goes down as you are breaking the series. unless you have another to replace it your system will be out of action for the duration of the maintenance
Harder to add extra current capacity. You would have to add another seven 1S packs, instead of just one in a parallel system
Are the any other factors to take into account I may have missed or anything I've misunderstood?
Apologies if these questions are addressed elsewhere i wasn't sure of if the two different approaches have a naming convention i could do a search on.
and those who build a pack (or packs ) direct to their Voltage spec. For example 7S-xP (and then parallel more packs together to get the desired system capacity if using multiple packs)
Say i wanted a "24v" system
my understanding is as follows
7S packs ( of whatever parallel configuration)
Pros:
I could add new packs of any capacity in parallel at any time to increase the system capacity ( couldn't i ? Though i can see it would be desirable to keep them all roughly the same capacity and also to ensure that any additional pack was brought up to the existing system voltage level before introducing it
I could remove a pack for maintenance without bringing the system down, just reducing its capacity.
Bus bars and connecting leads for individual packs need not be so hefty. Only the main bus they all plug into.
Cons
Voltage is fixed and cannot be altered without an entire pack rebuild
positive and negative cell ends are mixed on each face of the pack meaning more care has to be taken over accidentally shorting them while being worked on
Monitoring/balancing needs 7S cables run to every pack
1S packs
pros:
The loss of a few cells in a pack won't unbalance the system voltage
monitoring/Balancing is easier with only 7 wires plus common to be run to the packs
You can reconfigure the system voltage easily by adding or removing more 1S packs (though I'm not sure why you would want to)
Each pack is positive on side and negative the other providing good separation and minimiszing danger of accidental shorting
Cons:
(there can be) a massive amount of current in each pack. If it did short out things could get out of hand quickly
Busbars for each pack need to be substantial
If you pull a pack for maintenance your entire system goes down as you are breaking the series. unless you have another to replace it your system will be out of action for the duration of the maintenance
Harder to add extra current capacity. You would have to add another seven 1S packs, instead of just one in a parallel system
Are the any other factors to take into account I may have missed or anything I've misunderstood?
Apologies if these questions are addressed elsewhere i wasn't sure of if the two different approaches have a naming convention i could do a search on.
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