diy solar

diy solar

Connecting battery in parallel

ArranP

New Member
Joined
Nov 5, 2020
Messages
69
I've 2 5kw inverters and 2 batteries ( 48v 200ah each )

The inverter manuafacturer says the inverters can run in parallel mode with either one battery each or a single battery ( linking the batteries in parallel )

My preference is to run the batteries in parallel to ensure each battery is used equally.

Each battery has a 100amp BMS, leads rated for over 100 amps with m8 lugs, can I just join the lug nuts together with a bolt & nut, or do I need to goto the trouble of using a 200amp busbar.
 
I would use covered busbars and attach them to something.
Each battery needs a fuse near the positive terminal.
You need to verify that it ok if you plan to connect both inverters to the busbars.
 
Each battery needs a fuse near the positive terminal.
Is fusing each battery something unique to lithium batteries?

I fuse only once before the bus bar. Part of this is just like making parallel wiring the same length for resistance, I would think there’d be toptions much potential for one bank of batteries to have more resistance than the other. Similar to why NEC code only fuses once for Two smaller wires put together to equal a big one in a high current draw.

I’ve included this link that explains parallel wiring. http://www.smartgauge.co.uk/batt_con.html.

For busbars, I could not think of a reason not to use one. I only have a 2S2P so I did not need to use a busbar to configure the batteries for the link above, but I certainly used a busbar to join the charging SCCs to the Battery bank to the DC trailer loads. If I had 3 batteries in parallel, I would have used additional busbars to make the parrallel connection like method 3 in the link.
 
Each battery needs a fuse near the positive terminal.
as each battery already has its own BMS a fuse is unlikely to be usefull. 1) its sized under the current that the BMS disconnects in which case you can't get full output of the battery, or 2) its sized higher than what the BMS will disconnect and then the BMS disconnects anyway and the fuse does nothing.

A bussbar allows you to add or remove connections without disconnecting everything else. IF you think this is a common use case for you then a bussbar makes sense. Otherwise putting both battery-lead ring terminals on a single stud/bolt is sufficient.
 
As far as fuses, I was just passing along what was suggested to me. But I am willing to learn.
And I realize bolting together will work just as well as a busbar. I just thought it sounded sloppy and careless.
 
as each battery already has its own BMS a fuse is unlikely to be usefull.
This is an oversimplification at best. The fuse is to protect the wire.
If you have a 300a BMS and have wire that will not support 300a, the BMS offers no protection for the wire.
 
as each battery already has its own BMS a fuse is unlikely to be usefull. 1) its sized under the current that the BMS disconnects in which case you can't get full output of the battery, or 2) its sized higher than what the BMS will disconnect and then the BMS disconnects anyway and the fuse does nothing.

A bussbar allows you to add or remove connections without disconnecting everything else. IF you think this is a common use case for you then a bussbar makes sense. Otherwise putting both battery-lead ring terminals on a single stud/bolt is sufficient.

Thank you.

Each inverter draws upto 100 amp and each battery supplies 100amp, the cables and m8 lugs are are sized for 100 amp. When each inverter is working off its own battery this is fine, my thoughts then moved to connecting the batteries in parallel then connecting the 2 inverters to them. To keep everything balanced I believe the cables should be the same length and then I thought at the junction where the cables from the 2 inverters meet this could possibly transferring drawing 200amp when/if both inverters are draw 100amp each. hence my question if a 200amp junction busbar was needed or would the bolt suffice...

BTW I have also a 2-pole 125amp circuit breaker for each battery.
 
Last edited:
Back
Top