Multiple batteries and isolators

[Isetech]

When you install more than one battery with one or more inverters, how many DC disconnects or isolators should be installed.

Taking into consideration that there is more than one method of connecting batteries, series parallel, cascade parallel, there seems to be a little confusion.

If you have one battery and one inverter, simple 100 amp/hr battery, 160 amp fuse disconnect and 125 amp fuse and everyone is happy.

Now you put 2 batteries and 1 inverter, things start getting a little more confusing.

Now look at a rack of batteries and all logic just seems to go out the window, it's not that bad.

If you connect 2 batteries in parallel then you need to consider a few things, the C rating of the battery, which is very important.

A C0.5 100 amp/hr battery connected in parallel, shouldn't charge/discharge each above 50 amp if you want the battery to last a long time.

A C1 100 amp/hr battery on the other hand could charge/discharge at 100 amp each.

IF you are designing a sytem, do you take the C rating into consideration or do you take the inverter max charge discharge rate into consideration.

I suppose it depends on the customer budget. If you install an inverter with a 200 amp max charge/discharge, then you should install 2 x C1 rated 100 amp hr batteries. So a 250 amp fuse disconnect is reuired using at least 50 sqmm battery cable suitable for the voltage rating. If you use a busbar, it must be rated at least 200 amps.

[Isetech]

To really confuse people then you introduce a parallel casacde method, where you have 4 batteries linked together.

If you have 4 x 100 amp/hr batteries linking in parallel cascade, would you need a 400 amp or would a 250 amp be good enough, the C rating of the battery could determine the fuse size.

If you only have 0.5 C rated batteries, then a 250 amp should be fine, provided the sytem is setup for that application.

This is why these system settings should be locked and a code (specific to the person and recorded in the inverter) required to access and adjust.

This is why, if the customer requests manager access or someone else permission to access the system, I not take resposiblity for the system. I hear there is talk of user access monitoring, this is good idea. Like the alarm system we work with, anyone arm/disarms the sytem it is recoded in the event log. If I access as the installer, a notification is sent to the customer.

[Isetech]

So how many switch disconnectors are required when installing multiple batteries?

Lets say you connect 4 X 100 amp C1 rated batteries to a common busbar (parallel), then 4 x 100 amp switch disconnectors (these seem to be missing on the installations) connected to a central busbar with a 400 amp switch disconnector from the busbar to the inverter.

If you connect the batteries in the same method they do in the battery cabinets (parallel cacade), then only one 400 amp switch disconnect is required. You need to make sure the cables from the top and bottom of the battery stack is rated for 400 amp.

Can you cascade parallel connect batteries mounted on a wall, I dont see why not. Provided the correct dip switches are selected and the comms cables are installed and the wire size is correct.

[GCE]

When connecting multiply batteries in stacks let the manufacturers instructions guide you as there are software factors , balancing of batteries etc to take into account.

The setting of charge currents etc is going to be very dependent on inverter size and battery capacity - Each installation will be different and there will be no one rule fits all
There are other variables like ,not watching base load and incoming circuit breaker size , Time and size of Peak after grid reconnection vs incoming breaker size
Just because a battery can be charged at 1C does not mean that it will suit the installation to charge at 1C nor do the majority of manufactures recommend constant charge at 1C

You come back to the start point , what are you/client wanting to achieve with the install , vs practicalities vs budget.

[Isetech]

What do you think about switch disconnectors for batteries when there are more than one, should you install 1 per battery and one at the inverter or just wire to a busbar and fit 1 big switch disconnector.