battery maintainer.

zozomike

So my giant 24 volt 510 AH 1080 pound GB traction battery is over 7 years old and not holding a charge. Our host was having a 10% sale on the Battle Borns I lusted for, so I pulled the money and ordered, only to find out they were backordered. ( I also upped my pv from 3500 watts to 6ooo, and put in 2 FM 100s). In desperation I ordered a bottle of CHARGE IT, and poured it in. Being skeptical, I was surprised to find the old battery seemed to respond. She is not in the good yet, but fair, ( barely) I now have the 6 Battle Borns installed and do not really know what to do with the old batt. I am wondering if there is an easy/cheap way to keep it charging every day and see if it ever becomes useable again? Any Ideas?  ( at less than the $200. for a 24 volt charger) 

zozomike

So I guess what I am asking is, what is a clever way to keep an unused 510 AH 24 volt battery charged off of an existing 24 volt off grid system? 

BB.

Some suggestions (as always, I am NOT a battery engineer).

Plan on at least 1% to 2% rate of charge for an old/just about ready to recycle/ battery bank. Newer/batteries in good condition will have a float charge less than that.

If your float is 2% or greater--Time to recycle the battery. Lots of wasted energy, and the battery runs the risk of "interesting" self destructive events (overheating, etc.). The higher the float current (>2%, the more chance of a "bad" event).

The other thing to look at is how much electricity is this costing (either off grid charging, or from your utilty)... A 2% rate of charge:

• 27.0 Volts float * 510 AH * 0.02 rate of charge (worst case) = ~275 Watt (DC) load to float (worst case assumptions)
• 275 Watts * 24 hours per day = 6,600 WH per day (6.6 kWH per day)

Obviously, at 2% float charging current (assuming battery near failing), that is a lot of extra power to keep the battery around for "Just in Case" usage.

Anyway--My suggestion is to measure the steady state charging current (and voltage) and/or put a kill-a-watt meter on the AC float charger and see how much it really draws... If it is "significant (approaching 1% or higher float current)--Probably not worth keeping around.

Another way is to charge to "Full", then let it sit and check the SG (say once per week). And when it gets down to 75% SoC--Recharge. A "good battery FLA bank" should go 1 month between charges... That amount of energy would be:

• 14.5 volts charging * 510 AH * 25% depth of discharge = 1,849 WH = 1.85 kWH (per month?)

Again, assuming bank goes "1 month between charges", and you are willing to put ~2+ kWH (including losses) into keeping the bank in standby.

Anyway, some "math" to try and get data to make your decision.

-Bill

mike95490

Hook it up to the solar once a week ?

zozomike

Thank you gentlemen. BB, that is a very helpful thought process.