Mixing batteries

vince

I'm selecting a 48V battery bank and just discovered that batteries are a seasonal item at Costco and Sam's and they are out of stock or ranging in age from 3-9 months old. My bank is 8 batteries in series and I was planning on getting the Duracell 6v,  215AH but they also have 6V 235AH batteries that are fresher.  Several 8V 175AH were also in stock, with last month sticker. How important is it to get all the same batteries of same date, not older than 1-2 months? Can I mix and match and even throw in 3x 8V batteries and 4x 6V ?

jcheil

Never mix batteries. Especially different brands/capacities!

They will not charge equally and in some cases (I have seen this personally), they can overcharge the weaker ones and start on fire/explode.

If your original batteries are less than a year old (6 months preferred) then you can add the same exact brand/capacity to the bank but you will effectively bring the new batteries down to the age of the old ones very quickly.

Also, you will have charge inbalances between the old and new batteries for a few months until they both "age" properly.
If the original bank is older than a year, you are better off replacing the entire bank.

vince

Thanks, I thought that a series chain was more tolerant for variations among the batteries. Good to know.

zoneblue

Series batterys have their own form of balance problems. The lowest cell easily gets reverse charged, and easily gets overcharged. The latter is sort of workable, if you keep the water up, the latter kills cells rapidly.

WaterWheel

Ok,    I've got a battery bank question...     Currently running 8 crown 6v batteries that are only 2 months old and am considering adding a 2nd string of the same batteries to double my battery bank.

Assuming I wire the 2nd battery bank the same way can I..?

negative connector to the 1st string hooks to a amp shunt and then to inverter so can I hook the new ground from the 2nd string to the same shunt connector on the amp shunt?     Shunt is rated for 500 amps.

connect the pos wire from the new string to the first string's spare pos post to inverter battery post?       I'm running 0/4 ga wire from this post to the inverter so it can easily handle the amperage.       I just want to make sure it won't harm my first string batteries by connecting these two 48v pos wires.

Current setup is 48v 395 amp/hr battery bank but well pump keeps tripping the low voltage warning when I take my pre-sunrise shower ect. so I want to enlarge the battery bank.       Currently 4500 watts in panels but may increase to 5600w in near future since that would about max out my PT-100 charge controller for best bang for the buck and winter use.

I realize it shouldn't be a problem but just trying to be super safe with this set up.

Conext XW+ 4868 inv

vtmaps

foolami said:

Current setup is 48v 395 amp/hr battery bank but well pump keeps tripping the low voltage warning when I take my pre-sunrise shower ect. so I want to enlarge the battery bank.    

What is your SOC when you start your shower?  How much power does your pump draw?  What voltage do you have your LVD (low volt disconnect) set to?   Other than the voltage sag from the pump, do the batteries have adequate capacity for your needs?  There may be other ways (than buying more battery) to deal with this.

--vtMaps

WaterWheel

SOC is rarely below 80%.      Context battery meter shows that pump draws about 2050 watts which seems high for a 1 hp new pump.       Low battery disconnect at 47.2v.      Grid Supply set at 49.2v although I set it at 48.5 v for a few days working on this problem.       Recharge set at 48.4v.

Load shave is on but at 0 amps.     Sell is disables and also set at 0.

WaterWheel

All wire connections are tight, I double checked them.

jcheil

I would verify the SOC with a hydrometer first. 

Also, IMO, there is no way even a load of 3000w should drag your battery voltage down that low.

I would make sure that you have the proper sized wires going from the batteries to the inverter, that all connections are tight and maybe even do a load test on the batteries individually (old school clamp on load tester). PI am thinking you have a bad battery in that string or one of them is not being charged properly and that is what is causing the voltage to sag so much.

Dave Angelini

You have your LBCO incorrectly set BTW. Use the default on the XW. As the previous post, if you are not charged the load will be high on a 1HP pump. The inversion loss will go up because the battery is not charged.  This is a prime example of why battery based grid tie often ends in battery failure.