Making up 48v

olebrass

Newbie here. Great site!
I live in The Bahamas and I'm wanting to build an off grid system. I've done a lot of research online, and I've arrived at a 240/48v system. I know that making up the 48v battery bank with 2v batteries is preferred to 6v batteries, but my question is how big a difference in performance will I likely see by making up the 48v bank with 24/2v batteries or 8/6v batteries? Also, will AGM batts give me the same basic length of service as lead acid?
Thank you.

Cariboocoot

Re: Making up 48v

Welcome to the forum.

Actually the reason you'd use 2 Volt cells over 6 Volt ones is a matter of how much Amp hour capacity you need: the more stored power, the easier it is to get in a larger size but less Voltage battery. For example a Crown 2 Volt cell may be 500 Amp hours or it may be 2350 Amp hours. At the low end you could run a couple of strings of 6 Volt 320 Amp hour batteries in parallel. At the high end you would need far too many parallel strings of 6 Volts to be practical.

AGM batteries generally do not last as long as FLA's. Another consideration for when you start out is that the flooded cells are more tolerant of mistakes and easier to keep an accurate eye on. They are also cheaper per stored Watt hour. AGM's have their own advantages such as being spill-proof, not gassing, more efficient, and can take/give higher current. But you should really only spend the extra $ if you need those advantages.

olebrass

Re: Making up 48v

Thank you for such a quick reply cariboocoot. The info was valuable.

westbranch

Re: Making up 48v

IIRC there is a board member close to you, Dapdan, who might be of assistance, try sending a personal message to Dapdan. He has used several brands of AGM batteries.

hth

olebrass

Re: Making up 48v

Will do,thanks westbranch.

DaveB

Re: Making up 48v

Cariboocoot wrote: »

AGM's have their own advantages such as being spill-proof, not gassing, more efficient, and can take/give higher current. But you should really only spend the extra $ if you need those advantages.

You forgot one of the biggest advantages, they require no maintenance!

Cariboocoot

Re: Making up 48v

DaveB wrote: »

You forgot one of the biggest advantages, they require no maintenance!

Which is also one of the big disadvantages: you can't do any maintenance!

westbranch

Re: Making up 48v

Well as Dapdan has posted, you can do a water replacement, but the issue is you don't know how much water to replace as all losses have/can not be observed as in a FLA. Of course any 'playing' with an AGM will void the warranty, so the unit would have to be post warranty. Your mileage may vary....

vtmaps

Re: Making up 48v

Cariboocoot wrote: »

AGM batteries generally do not last as long as FLA's. Another consideration for when you start out is that the flooded cells are more tolerant of mistakes and easier to keep an accurate eye on. They are also cheaper per stored Watt hour. AGM's have their own advantages such as being spill-proof, not gassing, more efficient, and can take/give higher current. But you should really only spend the extra $ if you need those advantages.

olebrass, its good that you are going to have a single string of batteries. For others reading this thread who are attracted to AGM's advantages, let me add to what Cariboocoot wrote about their disadvantages:

They don't parallel as well as flooded batteries. Because they have lower internal resistance than flooded batteries they are more sensitive to the resistances that exist in wiring and connectors, in other words: it is more difficult to get the charging current to divide equally among the parallel strings. Of course, parallel battery strings are problematic for all lead acid batteries, but even more so for AGMs.

As for "not-gassing", they don't gas until something goes wrong. Therefore they must be in a vented box, just like any other lead acid battery.

--vtMaps