Electrical Question

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Paul Bednarzyk

Well, the 4d house battery died do to a bad cell and will need to be replaced. While I am at it, will finally proceed to upgrade the entire system. Ideally I would like to have approximately 400 amp-hours, with plans to add a larger alternator with an external 3 stage regulator. As my fellow 376/380 owners know, space is the issue. Don Alexander had a good idea a while back, but may not entirely solve my dilemma. Has anyone else dealt with this issue? If so how did you solve it (ie where and what size batteries). Because of $$$ I will probably need to use wet cell batteries, possibly 6V golf Cart batteries. Your thoughts will greatly appreciated. Paul Bednarzyk S/V Knot Again
 
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Jim Ferretti

Electrical Questio

In my new 340 I use 2-#27 wet cells in parallel for 210 amp hours for the house bank. You can use larger capacity batteries if you need more power. I have a third #27 wet cell battery connected with a 70 amp battery combiner. Wire the house bank to bank #1 on the battery selector switch and the single #27 to bank #2. The combiner will isolate the single battery from the house bank. If the house bank discharges to a point where it will not crank the engine flip the battery selector switch to bank #2 and you have a completely charged battery for starting. Hope this helps.
 
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JFun

We have the same problem on our 376 with battery capacity and are in the process of adding more batteries. We are moving the charger to the forward hanging locker and adding 2 27 batteries in the space left vacant by moving the charger. The 27's will be parallel wired to the existing 4D, which will give us a total of about 370 AH. Wiring in parallel is not like wiring in series where all batteries must be the same size. 6V batteries are too tall for the 376.
 
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Chuck Wolfe

Golf Carters

I just took a four night electrical class and there is no question but that golf cart batteries will give you the most bang for your buck. Get the good Trojan 6 volters and you'll get 440 amps. 2 Group 27's in parallel is not a good way to go economically and otherwise. The cost per amp using golf cart batteries is lower than any other solution excluding the use of Rolls Batteries or the Heavy Duty 6 Volt Trojans which weight 140 lbs. and are so tall, that they are a space problem. You should get at least 5 years providing you have a modern battery charger. chuckwolfe@innocent.com
 
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Jim Ewing

In the midst...

I have a 37.5 that came with a group 30 as the starting bank and 4 group 27s as the house bank. It also came with a shore power charger that was about to expire. The reason that the charger packed up was that the wire supplied with the boat was inadequate for the charger's amperage over the distance between the charger and the batteries. I'm moving my new charger closer to the batteries to prevent this from happening again. The new charger is a smart charger that can handle all three battery types and can provide different charge schedules depending on the type. Golf cart batteries like to be charged differently than "normal" deep-cycle. One thing to consider is to keep all your batteries as physically close together as possible and to make your terminal connections with equal lengths of the thickest wire you can use. I'm using 2ga but am thinking of moving the batteries around and may up that to 0ga. This will make all the batteries function as one. You can check this by measuring voltage drops between the banks positive terminals. Any voltage drop is not good. Also, my boat came with "maintenance free" flooded deep cycles. I wouldn't use them again. There's no way to check them (other than the idiot light)and you can't do a cell equalization charge because you can't replace the water. If I wanted maintenance free and money were no object I'd get AGM, if I stay with flooded batteries next time I'll just get normal, check the fluid and top up batteries. According to West the difference is only about $.04/amp over the life of the battery. Jim "Prospect"
 
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Paul Akers

Jim...a question

Jim, You wrote the following and I'm quite interested. "One thing to consider is to keep all your batteries as physically close together as possible and to make your terminal connections with equal lengths of the thickest wire you can use. I'm using 2ga but am thinking of moving the batteries around and may up that to 0ga. This will make all the batteries function as one. You can check this by measuring voltage drops between the banks positive terminals. Any voltage drop is not good." What do you mean by measuring the "positive" terminals. How does this differ measuring positive AND negative terminals simutaneously? And why the same length, thickest guage cable? I've never heard of this type recommendation before. Thanks.
 
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Jim Ewing

Same as sprinkler system...

Electricity flowing in wires can be compared to water flowing in pipes. The "pressure" of the electricity is the voltage and the "volume" of the electricity is the amperage. In wires and pipes the longer they are the more the pressure/voltage drops as it flows. The bigger the carrier (pipe or wire) the lower the pressure/voltage loss per distance travelled. This is why the pipe leading into your house is bigger than the pipes within your house and why the long cable runs in the boat are larger than short ones. The idea is to deliver the maximum volume/amperage at a given distance most efficiently. If your starter were cabled with 12 gauge wire it would probably work but eventually the ends would fail from thermal breakdown trying to pump all that juice through a very small conduit. That's basically the theory. The reason for the big equal length (short as possible) cables between batteries is to minimize the effect of the voltage drop along the cable. Assume your charger applies a bulk stage voltage of 14 volts to your battery bank. If you have a very long cable between the batteries in your bank there could be an appreciable voltage drop along that length of cable. Now because the difference between a fully charged and an 80% charged battery is something like .3(I think) volts even voltage drops in the hundredths range can have an impact. First, the battery charger will sense a full bank before the bank is really full. Ok so you lose a few amphours. BUT batteries that don't get completely charged from time to time end up with sulfated plates, reduced capacity and shortened life. Second, when discharging and recharging one or two batteies will be electrically closer to the load (will be showing a higher effective voltage) due to the voltage loss along the battery connector cables. That means these batteries will work harder, be more discharged during extended use and cycled more frequently during light use. This will also have an impact on life expectancy. By using large equal length cables you can minimize the voltage drop between the batteies and make them look electrically more equal. I think the equal length part is to make sure that there is no voltage drop between any batteries that is greater or less than that between any other. The measurement between like terminals will give you an idea of the voltage drop along the battery connectors. For batteries close together it should be 0 for batteries far apart it will be measurable and dependent on the distance and size of the connecting wire. This test should be done with some kind of small current flowing, like maybe a cabin light or two. Sorry for the long winded explanation hope it makes sense. Jim "Prospect"
 
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Paul Akers

Thanks, Jim

Good (and understandable) explanation. Thanks. When you say measure between "like" terminals, does that mean to place the black and red multi-meter leads to the positive poles of connected batteries?
 
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Jim Ewing

Yes

Paul You can measure the voltage drop between individual batteries or from one end of the bank to the other. (I suppose it would be interesting to do the same with positive and negative that may identify any potentially (no pun intended) bad cables) There's also a series starting in Sail Mag. this month of battery issues. I haven't had a chance to read it yet but Nigel Calder wrote it so it will probably have some good info. Now it's off to find a place for my new battery charger! Jim "Prospect"
 
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