One of battery banks serve as secondary backup?

[solitarysecluded]

Hey guys. I have 3 lifepo4 48v battery banks, two at 280ah and last one at 100ah.

I'm thinking to put two 280ah through diagonal connection then to busbar and third battery directly to same busbar.

Third battery will switch off usually and turn on once a week when there is a peak consumption etc, sort of act as "backup".

My question, any implication or feasible way to do this? Attach third battery on while the other two is at low capacity may cause problem when voltage varies? Thanks!

 

[sunshine_eggo]

Hey guys. I have 3 lifepo4 48v battery banks, two at 280ah and last one at 100ah.

I'm thinking to put two 280ah through diagonal connection then to busbar and third battery directly to same busbar.

Third battery will switch off usually and turn on once a week when there is a peak consumption etc, sort of act as "backup".

My question, any implication or feasible way to do this? Attach third battery on while the other two is at low capacity may cause problem when voltage varies? Thanks!

Why not just leave it connected?

 

[solitarysecluded]

Why not just leave it connected?

Well I might just do that if it's not ideal to plug in/out anytime from other battery banks.

Was planning to make it portable for other usage purpose.

 

[sunshine_eggo]

Well I might just do that if it's not ideal to plug in/out anytime from other battery banks.

Was planning to make it portable for other usage purpose.

IMHO...

When you want to take it somewhere, unplug and go.

When you come back, wait until the voltages are within 0.2V of each other and then connect them. Leave it connected until you need to take it somewhere again.

 

[solitarysecluded]

When you come back, wait until the voltages are within 0.2V of each other and then connect them. Leave it connected until you need to take it somewhere again.

Got it. Thanks man.

 

[solitarysecluded]

When you want to take it somewhere, unplug and go.

Hmm how about a transfer switch between 280ah battery banks and 100ah battery bank? workable?

Not sure how to prolong the battery life as two different capacity and age VS putting them together less recycle charging.

If put them together in diagonal connection, 280ah + 100ah + 280ah ? 100ah at center (less stress).

In parallel busbar, there is a risk of feeding back each other when there is a slight variation/error?

 

[sunshine_eggo]

Hmm how about a transfer switch between 280ah battery banks and 100ah battery bank? workable?

If you completely disconnect both, then connect one or the other, sure.

Not sure how to prolong the battery life as two different capacity and age VS putting them together less recycle charging.

Generally not a concern as the lower capacity battery can't support the same load with the same voltage drop, thus they typically share a proportional amount of current. You can confirm this with a clamp DC ammeter.

If put them together in diagonal connection, 280ah + 100ah + 280ah ? 100ah at center (less stress).

Should help a little.

In parallel busbar, there is a risk of feeding back each other when there is a slight variation/error?

Yes, but that's normal. As one drops in voltage during discharge, the parallel unit picks up more of the current.

Whatever you end up with simply use a DC clamp ammeter to confirm each battery is operating within specification during heavy discharges and charges.

 

[Shimmy]

Avoid the transfer switch; add redundant monitoring to make sure you know battery state.

 

[solitarysecluded]

Yes, but that's normal. As one drops in voltage during discharge, the parallel unit picks up more of the current.

Ok looks like diagonal is safer than parallel on busbar. Thanks again.

 

[solitarysecluded]

Avoid the transfer switch; add redundant monitoring to make sure you know battery state.

Something like Victron smart shunt? Viewing from JK Display..

 

[Shimmy]

Something like Victron smart shunt? Viewing from JK Display..

Sure, either would work. Goal is just to make sure you understand what is going on with your system and have multiple sources for the data to compare and validate.

 

[solitarysecluded]

Sure, either would work. Goal is just to make sure you understand what is going on with your system and have multiple sources for the data to compare and validate.

Right got it thanks. Trying safe route while minimizing lots time to monitor it every hours.
Wonder how often people check their solar data...?