24 to 48 volt upgrade

[openplanet]

I've had four Rolls S530 6 volt batteries in series for about 2.5 years, and am planning to upgrade to a 48 volt system.  Some seem to think I can add four new S530s to the string without impacting their health or lifespan, while others think it's a mistake, meaning I'd need to purchcase (gulp) eight new batteries.  Thoughts?  Thanks.

[Westbranch]

It will work until one of cells fails, probably sooner than later...  due to the variances in  the old 1/2 and the new 1/2 the old ones will drag down the newer ones so they are all ~ even...  more so since they will all be in series vs 2 parallel 24V strings...

[Vic]

Hi open ..,

The best situation is to use batteries that are identical in design,  construction,  are the same age,  have experienced the same environment together,  and so on.

Batteries that have been in the same bank together and are the same age will still not all be identical,   and their characteristics will diverge somewhat as they age.   But  the above is still the ideal.

A 2.5 year age-difference is significant,   and would seem to border on being a bad investment to try adding four more batteries into the existing string,  to make a 48 V battery.

It is often said that a battery string is no better than its weakest battery.

Furthermore,  Surrette S-530s are no longer made  --  S-550s have replaced the 530s in the product line.   This small difference would probably increase the divergence that one would expect to see with your proposed configuration.

IMO,  adding the new 550s in parallel with the 530s would be even more problematic.

Just my opinions,   FWIW,   Vic

[russ_drinkwater]

Try to sell the old 24 volt bank surrettes and if successful buy a new bank for the 48 volt system.
Will cost a bit more but will be a good investment in the future.
Not an easy or cheap fix when changing system voltages!

[ralph day]

I've always wondered what the "drag down" means when one talks of mixing cells or batteries of different ages.  I had 2 of 24cells replaced by Surrette under warranty, and their SG readings are always in the 1.280-1.290 range while the older (22 of them) cells are full at 1.265. 

The replacements were put in when the bank was 6 years old, now 13 years old.  The variation seen is still the same since the replacement.  Would you only see the new cells being dragged down by a load test or something?

Any comments welcome.

Ralph

[russ_drinkwater]

The degradation of the plates would be more in the older batteries than the newer ones.
Newer cells will last longer as there is less "wear and tear".
It may take a lot more time before the sg levels alter enough for you to notice.
A battery can be just about buggered and will still show sg of 1275. But it will not take as long to deplete that battery if compared to a new one. Explained to me as seeing two equal sized dams both full of water, one holds 10 megaliters and the other 3 megaliters. The
difference is that the one with the less volume is full of mud!
They still look the same and appear to be full, but pumping them out shows the true holding capacity!