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Guidelines for adding a second battery in parallel?

Featured Replies

Howzit,

potentially a stupid question be warned.

Let's say you have a system all setup and running off of 1x 12V 100AH battery

You run it for a few months, then decide, jirr, a second battery in parallel sounds lovely.

Since battery A has already been used for a while, would there be a problem adding battery B because its at "100%" factory new while A may have declined ~90% for example?

 

I'm struggling to understand under what scenario battery balancers / battery equalizers come into play 

 

EDIT: talking LifePO4 batteries with built in BMS

Edited by jeddles

1 hour ago, jeddles said:

Howzit,

potentially a stupid question be warned.

Let's say you have a system all setup and running off of 1x 12V 100AH battery

You run it for a few months, then decide, jirr, a second battery in parallel sounds lovely.

Since battery A has already been used for a while, would there be a problem adding battery B because its at "100%" factory new while A may have declined ~90% for example?

 

I'm struggling to understand under what scenario battery balancers / battery equalizers come into play 

 

EDIT: talking LifePO4 batteries with built in BMS

Generally with LifePO4 it isn't an issue - the BMS should then balance both to ensure they are both working at the same rate. Most installers would have the newer battery as the master

Edited by mzezman

2 hours ago, jeddles said:

You run it for a few months, then decide, jirr, a second battery in parallel sounds lovely.

Since battery A has already been used for a while, would there be a problem adding battery B because its at "100%" factory new while A may have declined ~90% for example?

Have been adding Pylons one by one as I went along. Oldest 664 cycles, newest 114. As long as the BMS are connected (with newest as Master) this is absolutely no problem

2 hours ago, jeddles said:

I'm struggling to understand under what scenario battery balancers / battery equalizers come into play 

Am not an expert, but to my understanding this is more for lead acid batteries

  • Author
1 hour ago, wolfandy said:

Have been adding Pylons one by one as I went along. Oldest 664 cycles, newest 114. As long as the BMS are connected (with newest as Master) this is absolutely no problem

Am not an expert, but to my understanding this is more for lead acid batteries

 

What would be meant by BMS' being "connected"? are we talking about some kind of direct ethernet/CANBUS communication? 

as far as I am aware, each battery has its own internal BMS

  • Author
1 hour ago, mzezman said:

Generally with LifePO4 it isn't an issue - the BMS should then balance both to ensure they are both working at the same rate. Most installers would have the newer battery as the master

 

If two batteries are connected in parallel, what would make one the "master"? 

5 minutes ago, jeddles said:

 

If two batteries are connected in parallel, what would make one the "master"? 

do your batteries have dip switches on them? if they do then the position of said switches will tell the inverter and the other batteries which one is the master

8 hours ago, jeddles said:

What would be meant by BMS' being "connected"? are we talking about some kind of direct ethernet/CANBUS communication? 

Correct. You connect the BMS's of your different batteries together (assuming that the batteries are same brand). Should be explained in the manual of your battery

See here for the comms connections between my Pylons (the top one is the Master):

Pylon1.thumb.jpg.326da61248b103a10b23b55eecd5200d.jpg

8 hours ago, jeddles said:

as far as I am aware, each battery has its own internal BMS

Correct. But you get all the individual BMS to talk to each other. The BMS of the 'Master' controls the BMS of the other batteries

8 hours ago, mzezman said:

do your batteries have dip switches on them? if they do then the position of said switches will tell the inverter and the other batteries which one is the master

I believe that depends on the battery. On the Pylons, you do not need to change any of the dip switches unless you need to get a hub involved (I think if you have more than 8 batteries). I have not changed any of the dip switches on my 5 Pylons

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