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docbob5707 03-27-2008 06:37 PM

Figuring Battery Capacity
Hi Guys, Need the battery experts to help me. I aquired 6 - 6v golf cart battries for a great price (free). They are NAPA brand. They measure 10 1/4 x 7 x 9 and the label states 115 mins. @ 75 amps. How many amp/hrs might I expect from these? They are brand new. Searching the archives and looking at various formulas I come up with 413.25 total amp/hrs - 215.63 usable @ 50%. 3 banks/2 batteries wired for 12 Volts. Any help is greatly appreciated.
Thanks in advance
"Doc" Bob

camaraderie 03-27-2008 11:41 PM

They are almost the size of T-105's so I would guess 200ah's at 6V t the 20 hour rate for each. This translates into 600 a/H's at 12V...which is quite a nice sized bank.
Without the actual NAPA spec # and detail sheet it is tough to be accurate but between 180 and 200ah's should be in the ballpark for you. One rule of thumb is that if they weigh in the ballpark of estimate should be accurate.

erps 03-28-2008 09:54 AM

When I saw the batteries were free, I wondered if their amp capacity had diminished some how. If they're in great shape, then I envy your good luck.

docbob5707 03-28-2008 04:26 PM

Hi Ray;
Ya their in great shape a friend of mine bought them for his father's golf cart then his father sold the cart. So he had these stored in his basement and his wife wanted them out of the way. He figured I might want them and offered them to me. All I had to do was haul them away. And yes they weigh in around 60 Lbs. or more. I had to hoist them abord the boat by myself (Whew!!!)
"Doc" Bob

hellosailor 03-28-2008 04:51 PM

"So he had these stored in his basement " When wet lead batteries are stored without being on a trickle charger, they self-discharge and form insoluble sulphate compounds. After 30 days of this, there is some permanent capacity loss which gets worse the longer they are stored.
So depending on how long they were stored--they may be badly crippled in as little as six months.

If you serach on doing an "equalization charge" or equalization cycle, that's about all you can do to try bringing back whatever capacity they have. Wet cells need this type of "over"charge routinely to keep them at their best, so if it means buying a new charger to do it--you'll use that regardless of whether you keep the batteries.

A good hydrometer (foot long kind, not the six inch pocket job) and a $25 digital multimeter will also be invaluable in assessing their condition--either before or after you equalize them.

docbob5707 03-29-2008 08:39 PM

Thanks Hellosailor, I'll try that (equalization charge). My buddy works at a golf course and had kept a trickle charge on them, they were stored for about 3 mos.
"Doc" Bob

camaraderie 03-29-2008 10:02 PM

With the trickle charge, I'm sure you'll have decent batteries but perhaps a bit of sulfation so the EQ cycle is an excellent idea anyway. You will want to first fully charge the batteries and then...being sure they are topped off properly with distilled water...charge them for 8 hours at 15.5 volts. (Caps off and good ventilation!) Max Current should not exceed 30 amps for the whole group or 10 amps per 12V pair.

docbob5707 03-30-2008 05:55 PM

Thanks Camaraderie, I'll do that this weekend.
"Doc" Bob

sailingdog 04-01-2008 02:04 PM

Don't forget to check the water levels in the cells and top them off with DISTILLED water. :)

docbob5707 04-01-2008 09:33 PM

Oh for sure. I keep 2 gals stored in the barn just for that purpose. My well water is full of iron.
"Doc" Bob

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