Possible?

[Juliet 15]

Hi all. I wonder if some of the electrical smart guys can comment on something I'm considering... Thanks in advance for your input.


I currently have 4 x 6v, 230ah batteries serving as 12v house bank. Two pairs of 6v are run in series, and each pair is joined in parallel to provide 12v and 460ah to the house.


I want more capacity (don't we always?). I'm looking at adding 4 more 6v L-16 batteries, which have 420ah each. I would wire the L-16s the same way I wired the current smaller capacity batteries (4 batts, 2 pairs in series to get 12v, for a total of 840ah; then tie both pairs in to the existing bank to provide 1300ah total between the 2 banks (8 batteries).



QUESTION: Can I mix different capacity but same voltage batteries without negative outcomes?


Let me know if I'm not being clear enough, and thanks again for your input.

 

[SteveK]

Hi all. I wonder if some of the electrical smart guys can comment on something I'm considering... Thanks in advance for your input.


I currently have 4 x 6v, 230ah batteries serving as 12v house bank. Two pairs of 6v are run in series, and each pair is joined in parallel to provide 12v and 460ah to the house.


I want more capacity (don't we always?). I'm looking at adding 4 more 6v L-16 batteries, which have 420ah each. I would wire the L-16s the same way I wired the current smaller capacity batteries (4 batts, 2 pairs in series to get 12v, for a total of 840ah; then tie both pairs in to the existing bank to provide 1300ah total between the 2 banks (8 batteries).



QUESTION: Can I mix different capacity but same voltage batteries without negative outcomes?


Let me know if I'm not being clear enough, and thanks again for your input.

No, you cannot mix different batteries. You cannot mix new same batteries with old batteries. It has to do with charge/discharge.

If adding is a must, you could do a separate bank and have a manual switch to choose which bank you want to use. Needs to have separate chargers or a charger that is also switched to each bank.

 

[High Wire]

QUESTION: Can I mix different capacity but same voltage batteries without negative outcomes?

Possible yes. Desirable, no. What you described is one giant permanently connected 12 volt bank, right?
The problem is the large bank will have different internal resistance than the small bank with one always trying to charge the other. Resulting one group overcharged and the other undercharged. Next is the charger needed to drive all this would not be practical. Suggest keeping the two banks of like kind cells separate with separate chargers. For example the larger bank feeds refrigeration loads while the other feeds lights, electronics and such. Both having separate inverter/chargers fed from shore power or gen set. This would be a complex install ie not a DYI project.

 

[tiltrider1]

Mixing the different batteries will shorten the life of the battery bank. It will initially appear to work but you will experience individual cell failures very quickly.

Also be aware, increasing the size of the bank could require upgrades in safety fuses and cutoff switches. As banks get larger they have the power to arc across lower class fuses rendering them ineffective.

 

[Juliet 15]

Okay, well, I guess it's back to the drawing board. Seemed like a good idea at the time.... :^)


Thank you, everyone.

 

[O C Diver]

Okay, well, I guess it's back to the drawing board. Seemed like a good idea at the time.... :^)


Thank you, everyone.

There is another option. If you want the capacity, you can have 2 seperate banks and use a DC to DC charger. In essence, you charge one bank as you normally do and it charges the other bank through the DC to DC charger. So you get the capacity of the two banks and the charger will shut down charging the 2nd back when the 1st drops below a set voltage. Energy wise it's not as efficient as one bank, but you gain capacity.

Ted

 

[twistedtree]

Although I think the advice you have received is the correct textbook answer, I think it’s much less of an issue that it’s made out to be.

If both banks are flooded or AGM or whatever - what matters is that they have the same charge parameters, bulk, absorb, and float in particular - I think it will work just fine. Maybe not the most optimal, but close enough to not matter. I have replaced single batteries in a 7 year old bank and everything worked just fine.

I think the ideal would be to replace the existing batteries with the same
L16s, but I’m guessing that’s not practical?

 

[fryedaze]

Why not just add the same size 6v batteries. Maybe stop swinging for the fence.[emoji16][emoji23][emoji33]

 

[kchace]

Why not just add the same size 6v batteries. Maybe stop swinging for the fence.[emoji16][emoji23][emoji33]

 

[Flatswing]

As others said, not optimal but will work albeit risking earlier battery failure. I actually have this exact set up with 4 L16’s and 4 GC15’s. The L16 batteries were 10 mos older, when I added the GC batteries. I believe it is vital that the batteries have identical charging parameters. Mine were all East Penn FLA. So far 3 yrs and counting so too early to tell. My theory is that with the larger bank, I don’t go below 65% SOC, which may offset the suboptimal battery size mismatch.

 

[Shrew]

Having just upgraded from a single 8D to 2 8D for the house, I think I would have opted for 2 1 x 8D house banks controlled with a battery switch.

Right now, the charging to get to true full takes too long. I think of it like trying to fill a tub that inch as compared to filling a swimming pool the last inch.

I'd rather alternate days, so I'm effectively discharging bank #1 while charging bank #2, then simply alternate days. The draw is the same. The charge is significantly less time, even though I draw down deeper into each battery.

 

[catalinajack]

Having just upgraded from a single 8D to 2 8D for the house, I think I would have opted for 2 1 x 8D house banks controlled with a battery switch.

Right now, the charging to get to true full takes too long. I think of it like trying to fill a tub that inch as compared to filling a swimming pool the last inch.

I'd rather alternate days, so I'm effectively discharging bank #1 while charging bank #2, then simply alternate days. The draw is the same. The charge is significantly less time, even though I draw down deeper into each battery.

I would not consider using more 8Ds an upgrade, an increase in capacity, yes, but not an upgrade. In the space occupied by two 8Ds, you could have had six golf car batteries.

 

[Pete Meisinger]

Any chain is only as strong as it's weakest link. Five new, strong batteries connected to one "dud" all become "duds"

Don't do it.

pete

 

[mike66]

Get rid of the lead batteries, one and done. More money up front, but you can fill them faster and get twice as much capacity. If your current batteries were LiFePO4 you wouldn't be looking for more capacity right now.

 

[Comodave]

Just a minor point, when starting a thread it is a good idea to put a bit more information in the title than Possible. It will help entice others to click on the thread if you include better information.

 

[guy with a boat]

I would not consider using more 8Ds an upgrade, an increase in capacity, yes, but not an upgrade. In the space occupied by two 8Ds, you could have had six golf car batteries.

That is a lot of additional cable and connections for similar capacity.

 

[Ken Ongemach]

Connecting Extra Capacity ro Feed Existing or Additional Load

Hi all. I wonder if some of the electrical smart guys can comment on something I'm considering... Thanks in advance for your input.


I currently have 4 x 6v, 230ah batteries serving as 12v house bank. Two pairs of 6v are run in series, and each pair is joined in parallel to provide 12v and 460ah to the house.


I want more capacity (don't we always?). I'm looking at adding 4 more 6v L-16 batteries, which have 420ah each. I would wire the L-16s the same way I wired the current smaller capacity batteries (4 batts, 2 pairs in series to get 12v, for a total of 840ah; then tie both pairs in to the existing bank to provide 1300ah total between the 2 banks (8 batteries).



QUESTION: Can I mix different capacity but same voltage batteries without negative outcomes?


Hi, This is a common Question with serious possible effects... yes, there is No problem increasing Capacity, BUT when reaching a certain load point or type of load . you can Exceed the Fault Carrying Capacity of the system, which ,in the case of a Fault, can cause an Explosion, with blast Effect & Dispersion of Battery Acid.

To avoid this situation,a simple fix is required.. Add a Pair of Properly sizes Fuses between the battery feed & the Main Bus. The Ampacity & Time Curve is dependent of the Battery & Load configuration. A local Marine Electrician should be consulted foor the proper Fuses.


Please take this effect seriously. Some years ago, a yacht, in a marina had an explosion & fire, traced by the Insurance Investigator to a Fault Current Situation, and as the Owner had increased the Battery Capacity to cover increased load, without consulting a Marine Engineer, Refused the Claim...


Be Advised, Ken Ongemach BSEE

 

[Juliet 15]

Just a minor point, when starting a thread it is a good idea to put a bit more information in the title than Possible. It will help entice others to click on the thread if you include better information.

Yep, great point. Ill do that in the future. Thanks, ComoDave.

 

[ranger58sb]

I currently have 4 x 6v, 230ah batteries serving as 12v house bank. Two pairs of 6v are run in series, and each pair is joined in parallel to provide 12v and 460ah to the house.

I want more capacity (don't we always?). I'm looking at adding 4 more 6v L-16 batteries, which have 420ah each. I would wire the L-16s the same way I wired the current smaller capacity batteries (4 batts, 2 pairs in series to get 12v, for a total of 840ah; then tie both pairs in to the existing bank to provide 1300ah total between the 2 banks (8 batteries).

You've seen the "possible but not optimal" answers...

Why not just replace your original 4x 230Ah 6V batts with 3 pairs of L16s? If each pair is 420Ah, that'd give you 1260Ah total...

-Chris