battery charger for golf cart batteries in series/parallel

[Norton]

I bought a boat with two banks (two batteries in each bank) of 6v golf cart batteries in series/parallel with the typical off/1/both/2 switch in between. I have a Westerbeke w27 with a 50amp alternator. The charger is a Guest that charges 5a on one side and 10a on the other. I am currently without shore power so I rely on the motor and a portable generator for re-charging. The amp hour capacity of this system is probably overkill for my battery usage under the normal circumstance of available shore power. I tend run the generator to re-charge when I can let it run for a period of time, which can happen at odd intervals. I need to replace my batteries as one bank is shot and the other is still working but at diminished capacity. Thinking that I should keep the same set-up except for the charger, just to have reserve power between re-charges. Any suggestions for chargers?

 

[Bob V]

Solar

If you haven't got access to shore power solar would be the ticket. If you do not use all that much electricity the panels can keep your batteries topped up above 75% where they are most happy. Don't forget a charge controller though because you can fry your batteries by overcharging with solar. I have 260 Watts worth of panels mounted above the bimini but I use a lot of electricity on board. You could get by with less than half of that.It's hard to get your batteries close to 100% with a generator because the juice goes in slower as the batteries get close to the top. Solar will just keep trickling in with no moving parts, maintenence, or fuel. High initial investment with excellent long-term returns. When you trade in your boat, you can take the panels with you.Bob V

 

[GuyT]

Charger suggestions

You already have a generator that you are OK with running once in a while so solar may be nice but in your case you may want to consider a better charger.If you get a 3 rate charger - (bulk, absorbtion, float), it will charge up the batteries up much quicker than a CV/CC style. Chargers tend to be less expensive than solar. If you have at least a 2 KVA generator, you should be able to charge up your bank with a good charger in a few hours. Consider at least a 50 amp charger to work with your generator. It will minimize the amount of time you need to run it.You also need to ask the mfg. of the charger if it is compatible with generators - some are not!Always keep your batteries topped off to provide the maximum life.If you do decide to go solar, you may want to consider a small panel to keep them topped off(10-20W) and the new charger to get them charged up quicker.

 

[Landsend]

try splitting the banks...

two golf cart batteries hooked in series in two separate banks connected to the battery switch. This will be a better set up, with the added advantage that you can charge or discharge one bank or the other as needed while still maintaining the capacity to do both banks if required.

 

[Norton]

path of least resistance

Landsend, GuyT, Bob V thanks for the replies,I think I have two separate series (split) banks connected across the negative on one battery from each bank (paralleled) for when the switch is set to "both", combining banks one and two, so they remain 12v. I am probably not going to try a full blown solar charging system as I have many other boat projects which require the time/investment that setting up a large solar array would require and I already have two portable generators. I am not averse to a small panel to float though. I was interested in the battery bank - charger - alternator - sizing for good compatibility. As I have been researching on the Internet it seems like my 50a alternator is under-sized for this big of a battery bank (450ah). The 5/10 charger is probably not proper for two equally sized golf cart banks as well. To make the least amount of change/expense I may just replace two 6v golf carts and get a starting battery for the second bank even though the extra capacity is nice in lieu of shore power. Can one small solar panel float the house and starting banks? Do you connect the solar panel directly to the batteries?

 

[Bob V]

Small is good for trickle charge

You can hook directly to batteries but your solar should include a charge controller to avoid over-charging. I know that a large array is not what you need. I should have said a lot less than half of what I use.The problem with using a genset to charge batteries is that as you approach 100% the rate of charge is reduced to the point that you probably would stop at about 80% charge instead of going all the way. To get from 50% to 80% your genset hooked up to the right charge would be ideal, but with no access to shore power how do you get those expensive batteries up to near 100% where they will be happier and live longer?By the way, your voltage meter lies to you if you ask it the question too early. Back in the days when I would go for a motorboat ride when I needed to charge my batteries after a night on the hook, I would come back to the anchorage and shut everything off to check the voltage in the batteries. If it was down to about 12.1 when I left I could get it back up to about 12.7 in a couple hours of motoring (full load). I felt I had a pretty good charge. If you go back in two hours and check again, even with no electrical use in the interim, you would find it was down significantly (say 12.5). Six hours later it was slightly lower still. An amp-hour gauge like the link 10 would give accurate information but most boats only have a voltmeter.Not a solar panel salesman, just know that generators have their limits just like charging your batteries by motorboating has its limits. Now if you had access to shore power your AC charger would slow down to a trickle and keep charging until your batteries got a complete charge but are you going to run that genset for 6 or 8 hours? I doubt it.Bob V

 

[Norton]

thanks

I will run the genset for 6-8 hrs. I just have not on a day that I can't get back to the boat to check the charge, shut the generator down before it runs out of gas, and cover or put the generator away. If I go out in the boat, when I get back, it is likely that I will not want to come back to the boat later to deal with the generator. And even though I live fairly close to the boat I may not charge before I want to go out again. It would be nice to be able to supplement charging with a small solar so they are under charged as little as possible, and reducing the amount of run time necessary for the generator.

 

[Stu Jackson]

Similar discussion here last week

See: http://www.sailboatowners.com/forums/pviewall.tpl?fno=21&uid=73200280089&sku=2008023092910.49

 

[Peter]

electrical needs

Rob, what are your electrical needs? You say that you think the current set-up is overkill, or would be given batteries in better condition. I don't think you have items that require substantial power running continuously (like a fridge) because your system would not be able to accommodate them, having one usable bank with "diminished capacity." Unless you plan on adding these items, you can downsize your battery bank to something more economical. I have used two Group 27 deep-cycles for nearly five years, and they have proven adequate. This includes at least 10 weeklong cruises, a few weekenders and countless overnighters. Maybe 5 nights of all that has been spent dockside. Only twice was shorepower available. I recharged by running the engine for about half-hour each morning (more or less depending on battery use). At home, I usually keep the charger plugged in; it is no doubt a similar Guest charger with 5A and 10A outputs. I also know one battery ran the bilge pump at least once everyday over a winter in which I didn't have the ability to plug in with a dripping packing gland. One of these batteries will provide enough cranking current to start your engine.

 

[Norton]

Thanks again

I do have a frig that I am not currently using, pressurized water, instruments, lights, three bildge pumps, fans, radio. Extra power is always good to keep bildge pumps running in case of an emergency. I have to get new batteries, but I guess I am trying to get the most ah system I can without having to change all the components. Originally I was going to just swap out the batteries, but after some research it seems like the PO setup was inadequate for this big of a battery bank. Even though it has survived for a number of years, the alternator and charger are probably inadequate for four golf cart batteries. Changing the wiring of the banks, switch and alternator/starter to charge house bank and a combiner for the start bank seems to make sense as well. I guess a single output charger would work with that wiring setup as well.

 

[Peter]

Right idea

Sounds like you got the right idea. I'm a minimalist, so I guess that skews my opinion of sailing electronics. With a refrigerator, the high output alternator is a necessary. Preferably, it will also be a large-frame model, as hard as they are to find it seems because everyone seems to prefer small-frame units and they fit better, so it runs cooler at capacity. I like how Les' diagram includes all the house batteries in series and paralleled. The batteries will cycle less deeply, but you retain the ability to disconnect half the bank if you lose a cell on one side. Also, with the battery charger, I would go without the solar panel, or I would disconnect it from the circuit when its not in use. The amount of kWh consumed with the charger in float mode is miniscule compared to burning a lightbulb in your house all day every day. It's great if you're away from the dock in usable daylight. If they are not providing a charge, a solar panel may actually discharge the batteries, and the energy ends up radiating heat back through the panel. You could install a diode to prevent this, but you suffer a voltage drop in the 'proper' direction of current.

 

[Stu Jackson]

Rob, you got it except for

the combiner. Either get an echo charger which is better for your proposed configuration, or plan to switch the combiner off if you motor for long periods of time to avoid overcharging the start bank.I disagree with the small frame discussion. Many small frame alternators are made in the 100 A range which are about as much as anyone should put on a small diesel engine.

 

[Bay Sailor]

One Solar Panel, 2 Diodes

You don't want the 2 banks connected in parallel all the time. The terminal voltages won't be equal and one will discharge the other; and then they will switch roles. If you use a solar panel use a Schottky diode in series with each battery from the solar panel. Schottky diodes have a low (.35 V) voltage drop and will keep the batteries from discharging each other while connected to the solar panel. The 1N5825 (a part number) is rated at 5 A and will block 40 V. This only works for low power solar panels. If you substitute the solar panel for a fast charger the current rating of the diodes will be exceeded and they will go open circuit. If you need to connect the batteries in parallel you can use the battery switch.

 

[r.w.landau]

Bay Sailor, technically one battery does not discharge

the other, One battery charges the other thus ending up with discharged batteries.Just a thought...r.w.landau

 

[Dennis W.]

Basic Requirements

I have used the following basic guidelines in setting up my battery/recharging systems. 1. I have 3 group 27 deep cycle batteries for the house and an isolated group 24 dedicated starting battery. House has ~285 Ah. The start battery must crank a Yanmar 2GM20F. 2. My engne cranks a stock 55amp alternator dedicated to the house bank. The start battery is connected via auto charging relay set a 13.2 volts. 3. I have a Guest 40Amp 2 Bank 3 stage smart charger with seperate bank voltage sensors. 4. I run Adler/Barbour refigeration (small air cooled unit) VHF, GPS, Speed, Depth, lights and Stereo. Living aboard on a mooring for 6 months required running Honda Gen 1K two hours per day. Day sailig and harbor hopping required 1 hour of engine or compensate with the gen to keep batteries up daily. Batteries are 3.5 years old and in excellent condition as of this date. I do expect to replace within 12-18 months. The vessel is a Hunter 310.  For efficient charging of batteries the charging source should be at least 20-25% of battery bank!Dennis W.S/V FullSailed

 

[Chuck Creel]

batterie charger / banks

Rob,I run almost the same powr needs that you describe on my hunter 30.I installed a solar system that chafrges at 7.4 amps during the day replacing what i used running my refridgeration, lights etc.I have 2 banks of bateries. starting battery and 2 each grp 27 house batteries of 210 AH total. I run anchor lights, cabin lights , and norcold ice box kit all night on the hook without problems.The solar system is 1 KC-130 panel at 130 watts with charge controller.theses people were excelent on providing solar info and customer service is great both before and after the sale.www.wholesalesolar.com

 

[Norton]

can of worms segue

Thanks again for the responses.  When browsing the internet on this suject I read a couple of articles/threads on the suitable types of batteries and better brands etc. Some of these articles suggested that short of cutting open a battery it would be hard to determine the plate size/construction etc. They would go on to say buy from a respected manufacturer or that weight (for a high ah battery)and warranty could help weed out quality issues. So far I called to see about golf carts and found t105s for $89 at a golf cart place and also looked at Sam's club and found Eveready golf carts for $67, grp27 Eveready auto starting for $78, grp27 marine/rv deep cycle $73.  The normal auto starting batteries at Sam's had the longest warranty: 1 year free, 8 years pro-rated. Deep cycle 1 year free, 3 year extended. Trojan 1 year.  Don Casey thinks flooded golf carts are one of the best deals for marine deep cycle because of longevety, and the price makes for lower intial investment and replacement cost in they event that they get ruined.  I was surprised that the auto battery had a longer warranty than deep cycle, although its probably a marketing ploy, makes them cheap to replace every couple years. Wondering other's thought process on type, brand, price and warranty of batteries.

 

[Don S/V ILLusion]

comparing batteries

Robbe careful how you compare them in terms of weight and warranty claims. For example, the Sam's Club Eveready 6V battieries are rated for 120amp/hrs while the T125s are 225 amp/hr so any cost comparison is not a good indicator of which to choose.

 

[Maine Sail]

Umm Don..

I was just at Sam's last week and they're Energizers (at the Scarborough Maine club) rated at 220ah not 120ah... Still 5ah short of a T105 but also less than half the cost at 66.87ea.Don't sell these batteries short I know more than a few that have used them very successfully and they are actually made by Exide.