Overcharging Golf Cart house bank batteries?

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CalebD

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Jun 27, 2006
1,479
Tartan 27' 1967 Nyack, NY
I checked the archives on this subject but I am not quite sure that I got all the subtleties so I am posting this rather long winded question. I was helping a friend with a new to him Endeavor 32' and one of the tasks I did was to replace the two 6V golf cart batteries. I got GC 15s to replace the old GC 2s (that is what they had on hand, saying only that the GC 15 has more plates which sounded good to me except the $120 price per battery). The battery store guy also said the old GC 2s looked like they had been overcharged or perhaps were frozen at one point as the cases were bulging a bit. The GC 2s were only from 2005 according to their dating label and would only show about 10V (at best) on the on board battery tester/meter and we had some trouble starting the engine off the ALL battery switch which included a new deep cycle marine 12V battery. The alternator was also shot which was contributing to the problem and was taken off and rebuilt and re-installed by me. My questions are these: Could the charge produced by the newly re-built alternator possibly overcharge the GC 2 or 15 batteries? Some of the info I found in the archives indicated that certain batteries do not like to be recharged with a voltage higher than 14.1 volts (would this apply to GC 2 or 15s?) whereas deep cycle batteries like to get the higher 14.4V charge? Could the alternator be giving too much charge for golf cart batteries? If so is there any way I can introduce some resistance to the charging circuit for the GC 15 bank to bring the voltage down to something more like what they would prefer? The alternator produces around 50 amps which is roughly 1/4 the amp hour total of the entire bank which is in the ball park for reasonability, Any help from anyone who has been down this road before will be greatly appreciated. In over my head but still learning and swimming.
 
Jan 5, 2007
101
- - NY
IF ...

you have a standard alternator that came with the engine and no special regulator hookup...changes are you are putting about 14.2V into the batteries. If the batteries are wet cells (i.e. you have caps to put water into them)...then the likelihood of overcharging is small. Put a voltage meter on your battery terminals when you are running the engine and check. 50 amps is just about ideal for a 200amp bank. Never take more than about 100 amps out of the bank before re-charging and the batteries will last a lot longer. Your setup sounds fine for weekending but inadequate for cruising. Batteries should ALL be the same type construction and preferably the same size. ONLY GEL CELL construction need voltage of 14.1 or less. WET and AGM types are fine with 14.4 and sometimes slightly more. Also ...if you are at a dock...suggest you get a THREE STAGE battery charger that will properly and fully charge your batteries better than a standard alternator and prevent sulfation and allow for occasional equalizing charges.
 
Feb 26, 2004
22,759
Catalina 34 224 Maple Bay, BC, Canada
Most internal regulators put out only

13.8V, too little to adequately charge, and chronically undercharge. You can write long questions like this, which are fine, or you can buy (get from a library) a BOOK and read what you'll need to learn. Try Nigel Calder's Boatowner's Manual or Don Casey's Sailboat Electrics. Or save some $$ and start by reading the Ample Power Primer, downloaded from www.amplepower.com. West Marine Advisors, electric section, is also free: what batteries need is a good start, then read the alternator and charging sections. A Google search on boat batteries, boat electrical systems and others would most likely keep you busy and also answer your questions. Golf cart batteries are not different as far as charging goes than any other wet cell battery. An internal regulator on an OEM alternator would usually not put out more than 13.8V, don't know where your 14.1 came from unless you did something to the regulator.
 
B

Bill

Shedding

If the battery is bulging its a good indication that the plates have started shedding and the reason your only showing 10v is that some cells have shorted out. Trying to start on "all" would most likely be difficult because your bad battery is drawing down any good battery. I can't imagin that a 50 amp alt would cook the batteries. However you did say the alt needed to be rebuilt, why? There is probably a good chance that the batteries were not getting fully recharged and spent a large amount of time in a discharged state, thats a killer. It will probably take a 50amp alt about 3-4 hours of solid running to put 95% of the charge back in if you pulled 100 amp hrs out. My alt reads 14.7 at the battery which is at the top of the charging range. Question to answer and pay attention to: How many amp hrs are being used (220amp hrs in battery 100 amp hrs used =50% discharge, a little high.) Are the batteries being fully recharged after use Is the water level being checked (I speak from experience) How often is water being added (good indicator of overcharging)
 

GuyT

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May 8, 2007
406
Hunter 34 South Amboy, NJ
Wet batteries = Golf Cart batteries

Your golf cart batteries are wet batteries. As far as float voltages, it does not matter if it was a deep cycle or high cranking capacity. The difference between the two is the plate thickness. Float voltages should be the same. Batteries like the AGM or the Gel do not like to be charged high - maybe this is what you are confused about. If you got new batteries with more plates and it has the same amp hour, you got more cranking amps. If you measure 10V on the batteries, one of the batteries probably had a shorted plate - so if you continued to charge the batteries up to 14 volts and had only 5 good cells, the result is you way overcharged the 5 good cells. There may be a good chance your alternator and charging system is good - you just had a bad cell in one of your batteries which caused you to overcharge the rest of the good cells. Batteries are made up of 2V cells - a 6V GC battery has 3 cells. Two batteries in series gives you 6 cells - capish? I would be looking at the warranty for the old batteries because if there was a shorted cell, this should be covered. It may be pro-rated but you still may be able to get some cash back.
 

CalebD

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Jun 27, 2006
1,479
Tartan 27' 1967 Nyack, NY
Thanks for all your knowledgeable reponses

and yes Stu, I do own the Nigel Calder book and have read much of the section on alternators but obviously I need to read more of it. I plead guilty to asking the experts a question I could have looked up myself. I was looking for the quick short answers to my questions and I got them. To answer one embarrasing question, the alternator got blown out when we put in the 12V battery in reverse polarity and blew out several diodes. The alt. came back looking and behaving like new and now seems to work beautifully. I capish the blown out cell theory though. Thanks for all your help and I will continue to read the Calder book.
 
B

Bill

Cells

If you were only getting a 10v reading I don't know that I would pu pu the bad cell possibility so quickly. 12v - 2v is 10v. If the batteries were fully charged they couldn't freeze, at least not outside of the artic. If they in fact froze they weren't charged, that would be a reason for death. Your atlernator should either be self exciting (controls its output by reading the batteries) or run through a regulator which controls the voltage and amps by reading the batteries. Either way you should get a reading somewhere between 14.4 - 14.7 at the battery terminals. Floods will put up with higher voltage charging then Gel's or AGM's. AGM's like to peak at 14.5 except Universal AGM's will take a 14.7 charge according to their tec department. Gel's are real sensitive and like a much lower voltage. The floods build a resistance as the become charged which slows down the charging process as they become charged (ramping down). AGM's of the other hand will take a full amp charge until the batteries are just about full which means your alternator needs to be up to the task and won't over heat. If you find yourself adding water often then you may have to start looking into how the batteries are charging ie amps & voltage & time or you could try using the Hydrocaps or WaterMiser caps. If the batteries are not being fully recharged no battery will last.
 
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