Different size batteries in new bank?

[fallingeggs]

My new house bank is going to be 6 105s (each 6 volt, 225 amp hours). Realized that I have the space for two L16Hs (each 6 volts, 435 amp hours), which could replace 4 of the 105s.

There any problems with running the house bank with 2 105s and 2 L16Hs? Space wise it would be more efficient for pretty much the same capacity, but obviously would not do it if it creates problems.


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[rwidman]

Most experts recommend that all batteries in a bank be the same brand, model and age. This is so they share the load and charging current evenly.

They don't have to be the same but they will work better if they are.

[Capt Hugh Wilde]

Originally Posted by fallingeggs

My new house bank is going to be 6 105s (each 6 volt, 225 amp hours). Realized that I have the space for two L16Hs (each 6 volts, 435 amp hours), which could replace 4 of the 105s.

There any problems with running the house bank with 2 105s and 2 L16Hs? Space wise it would be more efficient for pretty much the same capacity, but obviously would not do it if it creates problems.


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Why not use 4 - L16H units and end up with 870 amp hrs vs 675 amp hrs for 6 - 6 105s?

Or 6 Fullriver 902-J350 and end up with 1005 amp hrs. Almost the same footprint as the 6 105s .

But 4 of the L16's would be the sweet way to do it if you have the height.
I would not build a bank with 2 different ratings, just asking for trouble.

[Terra Nova]

Never mix battery sizes, brands, types or ages in the same bank.

Four L16's make up TN's house bank.

[fallingeggs]

Thanks all. Knew about type and age for sure. Now that I am thinking more about it, I can see several issues with charging and reading the state of charge with a bank with batteries that different in size.

Would like to put 4 L16s, but I don't think I have the room. Will have to take better measurements.


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[Andina Marie]

Originally Posted by rwidman

Most experts recommend that all batteries in a bank be the same brand, model and age. This is so they share the load and charging current evenly.

They don't have to be the same but they will work better if they are.

There is no benefit to be gained by "sharing the load and charging current evenly" and in fact since every battery is different it never happens. Each battery will supply or receive current in proportion to its capacity so stronger batteries do their share and weaker batteries are not overloaded. There is no practical or theoretical justification for thinking they will work better if matched.

The misconception comes from two sources, the first is that batteries should be matched as closely as possible when in SERIES (as a chain is as strong as its weakest line) but it does not apply to PARALLEL. The second source is the common assumption that the current will split evenly between the batteries in parallel which has no basis.

[rwidman]

Well as we can see not all experts agree.

Now lets talk about how to connect them together.

[Andina Marie]

Oooo don't get me started there, symmetrical wiring is male bovine excrement.

The differential voltages that are going to be eliminated by symmetrical wiring are less than 10% of the normal manufacturing differences between batteries over which you have no control. You are putting lipstick on a Walrus .

Any inequality introduced during heavy loads gets equalized by battery to battery current within seconds of removing the load. Differential voltages during charging are typically less than 10 millivolts and as the current tapers to zero at full charge those disappear too.

Pick the shortest route with a minimum of connections.

[rwidman]

Originally Posted by Andina Marie

Oooo don't get me started there, symmetrical wiring is male bovine excrement.

The differential voltages that are going to be eliminated by symmetrical wiring are less than 10% of the normal manufacturing differences between batteries over which you have no control. You are putting lipstick on a Walrus .

Any inequality introduced during heavy loads gets equalized by battery to battery current within seconds of removing the load. Differential voltages during charging are typically less than 10 millivolts and as the current tapers to zero at full charge those disappear too.

Pick the shortest route with a minimum of connections.

OK I'm with you on this one but a lot of folks would argue and post diagrams of various ways of wiring multiple batteries.

[wiekeith]

"The second source is the common assumption that the current will split evenly between the batteries in parallel which has no basis"

So, if a 100ah battery was in parallel with a 200ah battery, for example, the current draw would be roughly in the ration of 1:2 between them? And I do emphasize roughly.

[Derek Lumb]

Originally Posted by Andina Marie

Oooo don't get me started there, symmetrical wiring is male bovine excrement.

The differential voltages that are going to be eliminated by symmetrical wiring are less than 10% of the normal manufacturing differences between batteries over which you have no control. You are putting lipstick on a Walrus .

Any inequality introduced during heavy loads gets equalized by battery to battery current within seconds of removing the load. Differential voltages during charging are typically less than 10 millivolts and as the current tapers to zero at full charge those disappear too.

Pick the shortest route with a minimum of connections.

I am with you on both points.

[TeddyDiver]

Remember you got to load up your batteries once a while and that doesn't work with mixed banks so well..